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1 CHARACTERIZATION OF WATER TREATMENT TECHNOLOGIES IN IRRIGATION By ROSA E RAUDALES A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2014
2 201 4 Rosa E Raudales
3 To my niece Karla Mar a who is my inspiration for strength
4 ACKNOWLEDGMENTS I thank first and foremost my Ph.D. committee chair, Dr. Paul Fisher, for giving me the opportunity to achieve this goal, for making the process an enjoyable and rich journey, and for being supportive in moments when I needed it most. Paul, it is one of m y greatest prides to be one of your graduate students. I thank my outstanding Ph.D. committee members Dr. Charlie Guy, Dr. Tracy Irani, Dr. Charlie Hall and Dr. Jennifer Parke for their positive feedback and collaboration in this research. I specially thank the Floriculture Research Alliance growers, industry, and researchers for providing funding, data, and outreach opportunities and for making me believe that if you all together were to rule the world this would be a better and more colorf ul place. I am also grateful to the Water Education Alliance for Horticulture sponsors for their funding and collaboration. I thank the Floriculture and Nursery Research Ini tia tive for partially funding this program. I thank present and past members of th e Fisher Lab including Jinsheng Huang, Javier Lpez, Dale Haskell, Ryan Dickson, Victor Cruz, Dustin Meador, Connie Johnson, and Steven Montalvo for their technical and personal support. I thank my fellow ZamoGators and graduate students for sharing great conversations and experiences which taught me some of the greatest lessons I am taking from this experience. I particularly thank Javier and Helen Lpez for opening the doors of their home and making me feel like it was my own. I thank Francisco Loayza, Venancio Fernndez, and Joel Mendez for their constant caring I profoundly thank Eugenio and Magdalena Velsquez for keeping me warm from day one of this journey.
5 I wholehearted thank those who despite the distance are always here. I thank Zoe, Carlos, A lejandro, Sara, Karla Mara and Sofia Raudales for constantly reminding me that the joy is on the journey and that we are blessed on every step. I thank you Mom for all you do and have done, but above all for being an inspiration of loving care, strength and perseverance. I thank my Dad for a lifetime of lessons and happiness.
6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 9 LIST OF FIGURES ................................ ................................ ................................ ........ 11 ABSTRACT ................................ ................................ ................................ ................... 12 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 14 2 LITERATURE REVIEW ................................ ................................ .......................... 18 Efficacy of Water Treatment Technologies for Control of Waterborne Plant Pathogens ................................ ................................ ................................ ........... 18 Review of Water Treatment Efficacy ................................ ................................ ....... 22 Chemical Water Treatment Alternatives ................................ ........................... 22 Chlorine ................................ ................................ ................................ ...... 22 Chlorine dioxide ................................ ................................ ......................... 25 Ozone ................................ ................................ ................................ ........ 27 Hydrogen peroxide and activated peroxygens ................................ ........... 29 Copper ................................ ................................ ................................ ....... 31 Silver ................................ ................................ ................................ .......... 32 Bromine ................................ ................................ ................................ ...... 33 Physical Water Treatment Technologies ................................ .......................... 34 Filtration ................................ ................................ ................................ ..... 34 Ultraviolet radiation ................................ ................................ .................... 36 Heat treatment ................................ ................................ ........................... 37 Ecological Water Treatment Alternatives ................................ ......................... 38 Slow filtration ................................ ................................ .............................. 38 Biosurfactants ................................ ................................ ............................ 39 Constructed wetlands ................................ ................................ ................ 40 Synopsis of Current Knowledge and Gaps in Research ................................ ......... 41 3 MODI FIED DELPHI SURVEY ON ATTRIBUTES AND SELECTION OF WATER TREATMENT TECHNOLOGIES FOR HORTICULTURE ................................ ....... 66 Overview of the Research Problem ................................ ................................ ........ 66 Materials and Methods ................................ ................................ ............................ 70 Round 1 ................................ ................................ ................................ ............ 71 Round 2 ................................ ................................ ................................ ............ 72 Results and Discussion ................................ ................................ ........................... 74 Demographics ................................ ................................ ................................ .. 74
7 Objective 1 Att ributes for selection of water treatment technologies ............... 75 Attributes ................................ ................................ ................................ .... 75 Expert types and experience ................................ ................................ ...... 75 Objective 2 Comparison of attributes between technologies ............................ 76 Cost ................................ ................................ ................................ ........... 77 System size ................................ ................................ ................................ 78 Control of microorganisms ................................ ................................ ......... 79 Effect on nutrient or inorganic molecules ................................ ................... 82 Sensitivity to water quality parameters ................................ ....................... 83 Residual effect ................................ ................................ ........................... 84 Ease of use ................................ ................................ ................................ 85 Regulation ................................ ................................ ................................ .. 86 Implications of the Research ................................ ................................ ................... 86 4 EFFICACY OF CHLORINE TO CONTROL PHYTOPHTHORA NICOTIANAE IN SOLUTIONS CONTAINING PEAT PARTICLES OR NITROGEN FERTILIZER ..... 92 Overvi ew of the Research Problem ................................ ................................ ........ 92 Materials and Methods ................................ ................................ ............................ 96 Pathogen Inoculum ................................ ................................ .......................... 96 Chlorinate d Water ................................ ................................ ............................ 97 Peat Experiment ................................ ................................ ............................... 97 Nitrogen Experiment ................................ ................................ ......................... 98 Contact Time ................................ ................................ ................................ .... 99 Measurements ................................ ................................ ................................ .. 99 Statistics ................................ ................................ ................................ ......... 100 Results ................................ ................................ ................................ .................. 100 Chlorine Demand Exerted by P. nicotianae ................................ .................... 100 Peat Experiment ................................ ................................ ............................. 101 Nitrogen Experiment ................................ ................................ ....................... 102 Implications of the Research ................................ ................................ ................. 104 5 COST ANALYSIS OF IRRIGATION WATER TREATMENT ................................ 117 Overview of the Research Problem ................................ ................................ ...... 117 Methodology ................................ ................................ ................................ ......... 1 20 Cost of Filtration Systems ................................ ................................ ............... 120 Cost of Water Treatment in a Hypothetical 20 Million gal per Year Operation 121 Actual Cost of Water Treatment Technologies in 11 Greenhouse Operations ................................ ................................ ................................ ... 124 Cost of Water, Fertilizer and Nutrient Solution ................................ ............... 125 Results and Discussion ................................ ................................ ......................... 125 Cost of Filtration ................................ ................................ ............................. 125 Cost of Water Treatment in a Hypothetical 20 Million gal per Year Operation 127 Actual Cost of Water Treatment Technologies in 11 Greenhouse Operations ................................ ................................ ................................ ... 128 Cost o f Water, Fertilizer and Nutrient Solution ................................ ............... 130
8 Implications of the research ................................ ................................ .................. 131 6 SUMMARY AND CONCLUSIONS ................................ ................................ ........ 138 LI ST OF REFERENCES ................................ ................................ ............................. 142 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 164
9 LIST OF TABLES Table page 2 1 Efficacy of chlorine (hypochlorous acid) for control of waterborne microorganisms. ................................ ................................ ................................ 45 2 2 Efficacy of chlorine dioxide for control of waterborne microorganisms. .............. 48 2 3 Efficacy of ozone for control of waterborne plant pathogens. ............................. 50 2 4 Efficacy of activated peroxygens, hydrogen peroxide and peracetic acid for control of waterborne plant pathogens. ................................ .............................. 51 2 5 Efficacy of copper for control of waterborne plant pathogens. ............................ 53 2 6 Efficacy of silver for control of waterborne plant pathogens. .............................. 56 2 7 Efficacy of bromine for co ntrol of waterborne plant pathogens. .......................... 57 2 8 Efficacy of membrane filtration for removal of waterborne microorganisms. ...... 59 2 9 Efficacy of ultraviolet radiation for control of waterborne microorganisms. ......... 60 2 10 Efficacy of heat treatment for control of waterborne microorganisms. ................ 61 2 11 Efficacy of slow filtration for control of waterborne microorganisms. .................. 62 2 12 Efficacy of biosurfactants for control of waterborne microorganisms. ................. 64 3 1 Perceptions of an Expert Panel solicited via Delphi survey that each Attribute is important when selecting between water treatment technologies. ............... 88 3 2 Comparison between technologies of Attributes associated with cost, system siz e and control of microorganisms .. ................................ ................................ .. 89 3 3 Comparison between technologies of Attributes associated with sensitivity to water quality parameters, effects on nutrients or inorganic molecules, and residual effect.. ................................ ................................ ................................ ... 90 3 4 Comparison between technologies of Attributes associated with ease of use and regulation.. ................................ ................................ ................................ ... 91 4 1 Peat experiment. Analysis of variance summary of response variables for the experiment in which solutions with Phytophthora nicotianae were treated with c hlorine and peat.. ................................ ................................ ............................ 107 4 2 Peat experiment. Effect of three chlorine concentrations on solutions containing peat and inoculated w ith Phytophthora nicotianae. ........................ 108
10 4 3 Nitrogen experiment: Analysis of variance for the experiment in which solutions containing Phytophthora nicotianae were treated with chlorine and nitrogen salts with two contact times.. ................................ .............................. 109 5 1 Cost of filtration systems from greenhouse operations of ornamental crops recirculating nu trient solution from sub irrigation.. ................................ ............ 134 5 2 Cost of sanitizing water treatment alternatives based on a hypothetical operation wi th annual water use of 20 million gal.. ................................ ........... 135 5 3 Cost of water treatment greenhouse operations of ornamental crops based on actual operation water use. ................................ ................................ .......... 136 5 4 Cost of water, fertilizer and nutrient solution from greenhouse operations of ornamental crops based on actual operation use.. ................................ ........... 137
11 LIST OF FIGURES Figure page 1 1 Innovation decision process model proposed by Everett Rogers. ...................... 17 4 1 Residual chlorine and ORP after inoculating 10,000 zoosporesmL 1 of P hyotphthora nicotian ae in sterile distilled water (in the absence of peat or nitrogen salts ) after 10 minutes contact time ................................ .................... 110 4 2 Peat experiment: Residual chlorine after exposure to peat in sterile distilled water at 0, 2, or 4 mg.L 1 Cl (in the absence of Phytophthora or nitrogen salts) after 10 minutes contact time ................................ ................................ .. 111 4 3 Peat experiment: Infection of tomato leaves with Phytophthora nicotianae in response to chlorine and peat concentrations ................................ ................. 112 4 4 Nitrogen experiment: Residual chlorine (in the absence of Phytophthora nicotianae or peat) after exposure to nitrogen salts with 10 minutes contact time. ................................ ................................ ................................ .................. 113 4 5 Nitrogen experiment: Effects of chlorine dose, nitrogen source and contact time on recovery of viable zoospores of P hytophthora nicotianae ................... 114 4 6 Nitrogen experiment: Disease incidence (percent of leaves with lesions) after dipping leaves in a solution with chlorine,nitrogen and P hytophthora nicotianae ................................ ................................ ................................ ......... 115 4 7 Nitrogen experiment: Effect of applied chlorine concentration, nitrogen source and contact time in solutions inoculated with P hytophthora nicotianae. 116
12 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy CHARACTERIZATION OF WATER TREATMENT TECHNOLOGIES IN IRRIGATION By Rosa E Raudales May 201 4 Chair: Paul R. Fisher Major: Horticultural Sciences Water treatment technologies are used to reduce the risk of plant disease and clogging of emitters caused by microb ial load carried in the water. The general obje ctive of this research was to characterize water treatment technologies used in irrigation for control of waterborne microbes to provide science based information to assist growers in the selection of technologies The specific objectives were to synthesiz e literature on efficacy of water treatment technologies for control of plant pathogens and algae to identify the perceived key attributes of water treatment technologies that should be considered by growers when selecting a technology and to characterize 14 available water treatment technologi es in terms of these attributes, to evaluate the efficacy of chlorine to control Phytophthora nicotianae in the presence of N based salts and peat and to carry out a cost analysis of water treatments. The literature available on water treatment technologies indicated that there is variable kn owledge among the technologies. C hlorine was the technology with most references (20) and number of pathog ens studied at the genus (16) and species (27) level An expert panel o f 43 ornamental growers, 29 water treatment industry suppliers, and 34 research ers indicated through a Delphi survey that selection of water treatment technologies require s consideration of technical, socio economic and regulatory related attributes
13 and te chnologies were characterized d ifferently for each attribute. The efficacy of chlorine to control P nicotianae in the presence of ammonium sulfate and potassium nitrate in laboratory conditions indicated that the efficacy of chlorine was not affected by t he presence of nitrogen salts or peat in the water. The marginal total cost per 1000 gal to treat water with particle filtration ( $0.02 to $2.83) or sanitation with chemical or membrane filtration ( $0.07 to $1.67) was lower than the marginal cost of the w ater supply and water soluble fertilizer in the nutrient solution ( $1.47 to $11.04) R esults provide science based information to overcome barriers of adoption such as uncertainty of efficacy and costs, of water treatment technologies by growers.
14 CHAPTER 1 INTRODUCTION Plant health management is a moving target, which I discuss metaphorically like an American football game, where one team is science and technology and the other is nature, where the S & T team is only rules written to, respectively, satisfy the laws of economics, protect the environment, and gain so cial acceptance R. James Cook, 2000 Advances in plant health management in the twentieth century Irrigation water can be an inoculum source or dispersal mechanism for diverse biological problems including pathogens (Hong and Moorman, 2005), algae (Cambe rato and Lopez, 2010; Dehghanisanij et al., 2005; Juanico et al., 1995) and biofilms (Adin and Sacks, 1991; Yan et al., 2009). A range of water treatment alternatives are available for management of microbial water quality problems. Technologies availabl e include chemicals (chlorine, bromine, chlorine dioxide, copper ionization, copper salts, silver ionization, ozone, hydrogen peroxide, peroxyacetic acid and surfactants), non chemical or physical treatments (filtration, heat, and ultraviolet radiation) an d ecological alternatives (biosurfactants, constructed wetla nds and slow sand filtration). The decision process of a doption of innovations, such as water treatments, is a stepwise process in which decision making units evolve from knowledge to confirmation of use (Rogers, 2003) (Fig. 1 1) Knowledge is the stage in which decision making units are exposed to the innovation and create awareness of how the innovation can be used to solve a problem. Persuasion is the stage in which decision making units develop an attitude toward the innovations. Attitude to an innovation is developed based on analys i s of relative advantages compatibility, complexity, triability and observability of the innovations. Decision is the stage of adopting or rej ecting the innovation. Positive
15 attitude towards the innovation tend to result in ad option of the innovation and negative attitudes tend to result in rejection of the innovation If the innovation is adopted, the next step is implementation in which the innovation is used. Finally, confirmation is the stage in which decisions about continued or discontinoued use are made. Plant disease management is a human decision making process that would benefit from interdisciplinary research that combines social and natural sciences (McRoberts et al., 2011; Gent et al., 2011). Uncertainty about risks, efficacy and economic benefits represent barrier s to adop t technologies in horticulture ( Breukers et al., 2012; McRoberts et al., 2012 ; Uva et al., 1998 ). Building on the knowledge and persuasion stages of the adoption of innovations process is needed to reduce uncertainties and risk aversion to adoption of water treatment technologies Growers are currently lacking a science based information resource that as sists the decision process of selecting a technology and minimize the risk and aversion of adoption of water treatment technologies To approach this problem the current research was carried out with the general objective of characterizing water treatment technologies used in irrigation for control of plant pathogens, algae and biofilm. The specific objectives were to 1) do a literature review on the efficacy of water treatment technologies for control of plant pathogens and algae (Chapter 2); 2) identify the perceived key attributes of water treatment technologies that should be considered by growers when selecting a technology for their operation and to characterize 14 available water treatment technologies in terms of these attributes (Chapter 3); 3) ev aluate the efficacy of chlorine to control Phytophthora nicotianae in the presence of peat and nitrogen salts and (Chapter 4) and 4) make a cost analysis of water treatment
16 technologies and estimate benefits of water recirculation in terms of water and fe rtilizer savings.
17 Figure 1 1. Innovation decision p rocess model proposed by Everett Rogers (2003)
18 CHAPTER 2 LITERATURE REVIEW Efficacy of Water Treatment Technologies for Control of Waterborne Plant Pathogens The biological, physical, and chemical characteristics of water sources impact its suitability for irrigation ( Cook, 2000; FAO, 1994 ). Irrigation water in plant production operations can be an inoculum source or dispersal mechanism for diverse biological problems including pathogens (Hong and Moorman, 2005; Ristaino and Gumpertz, 2000 ), algae (Camberato and Lopez, 2010; Dehghanisanij et al., 2005; Juanico et al., 1995) and biofilm organisms and/or their extracellular matrices (Adin and Sacks, 1991; Yan et al., 2009). Diverse plant pathogens have been identified in irrigation water including 17 species of Phytophthora 26 species of Pythium, 27 genera of true fungi, 8 species of bacteria, 10 viruses, and 13 species of plant parasitic nematodes (Hong and Moor man, 2005). Motile microorganisms such as Phytophthora spp. and Pythium and may be freely present in water, whereas plant pathogens that do not produce swimming structures (for example, Rhizoctonia solani Thielaviopsis basicola, and nematodes) are more l ikely to be carried along by bulk flow with the soil debris in the water (Baker and Matkin, 1978). Algae growth can also result from poor biological water quality, and is a costly nuisance in agricultural systems (Camberato and Lopez, 2010; Shwarz and Krie nitz, 2005). Algae can clog emitters, resulting in uneven irrigation distribution (Dehghanisanij et al., 2005; Juanico et al., 1994), reduce plant growth through the production of toxic substances (Shwarz and Krienitz, 2005; Schwarz and Gross, 2004), and provide food
19 and habitat for shore flies ( Scatella stagnalis ), which are vectors of plant pathogens (El Hamalawi, 2007; Goldberg and Stanghellini, 1990; Hyder et al., 2009). An impermeable algae layer can form on the surface of the media reducing water pe rmeability (Peterson, 2001). Algae can also create a worker hazard when covering walk ways, and reduce aesthetic quality of ornamental potted plants. Biofilms are a complex matrix of polymers and assorted microorganisms which can include p athogenic and no n pathogenic microorganisms (Costerton et al., 1995; Maier et al., 2009). Organic compounds on the inside surface of pipes (Maier et al., 2009), and soluble fertilizers provide nutrients for microorganisms and biofilm formation in irrigation pipes. Emitt ers are clogged directly when biofilm forms a physical barrier, or indirectly by the formation of precipitates with minerals such as iron, manganese and sulfur dissolved in water (Gilbert et al., 1981; Yan et al., 2009). Biofilms are resistant to sanitizi ng treatment because of their complexity and variability in structure and composition (Berry et al., 2006; Costerton et al., 1995; Tachikawa et al., 2009; Viera et al., 1993). A range of water treatment technologies are available for management of microbia l water quality problems. Technologies available include chemicals (chlorine, bromine, chlorine dioxide, copper ionization, copper salts, silver ionization, ozone, hydrogen peroxide, peroxyacetic acid and biosurfactants), non chemical or physical treatmen ts (filtration, heat, and ultraviolet (UV) radiation) and ecological alternatives (constructed wetlands and slow sand filtration). Control efficacy depends on the target organisms, and the dose with respect to concentration or intensity and contact time ( Ehret et al., 2001; Lane, 2004; Runia, 1995; Stewart Wade, 2011; Van Os, 2010).
20 Experimental efficacy trial results provide only one aspect in the selection of water treatment technologies and dosage levels. In contrast with scientific research conducted under controlled conditions, irrigation management is impacted by factors such as the water source, temperature, organic and inorganic contaminants, pH, irrigation system component materials, relative susceptibility of crop phytotoxicity, and varied regula tory requirements. Surface water sources tend to have higher microbial concentrations than well and municipal water (Cappaert et al., 1988; Pottorff and Panter, 1997). Effective water treatment for irrigation must adapt to varying conditions in water tem perature, water chemistry (such as pH and oxidation reduction potential), and sanitizing agent demand (from suspended solids and microbial density), which fluctuate seasonally and diurnally in irrigation ponds (Hong et al., 2009). At lower water temperatu res, survival of Phytophthora spores is prolonged (Porter and Johnson, 2004), but the overall concentration of pathogens is typically lower (Bates and Stanghellini, 1984; Bush et al., 2003; Gevens et al., 2007). Water temperature can also affect pathogen species composition. For example, a dominance of Pythium aphanidermatum was observed above 23 o C in a hydroponic spinach operation, versus Pythium dissotocum at cooler temperature (Bates and Stanghellini, 1984). The persistence of Phytophthora spp. can in crease in the presence of suspended soil in irrigation water (Porter and Johnson, 2004). For example, sanitizing power of chlorine is greatly reduced at high levels of pH and organic suspended solids (Huang et al., 2011b). The materials of water distribu tion pipes also affect the microbial composition (Costernon et al., 1995; LeChevallier et al., 1988). With resistant pathogens, the required water treatment concentration may exceed either the regulatory permitted concentration or the
21 threshold for crop p hytotoxicity. For example, doses above 4 mgL 1 chlorine were required to control several pathogens in water (Cayanan et al., 2009; Chase and Conover, 1993; Hong et al., 2003; Poncet et al., 2001; Rav Acha et al., 1995; Rosner et onnell, 1994) while the identified phytotoxicity threshold is 2.4 mgL 1 (Cayanan et al., 2009b). The growing substrate, soil, pots and plants can also be sources of pathogen inoculum, in addition to irrigation water (Parke and Grnwald, 2012). Given all these variables, experimental efficacy results should be considered a management resource rather than a specific recommendation. Furthermore, water treatments should be considered to be only one aspect of a holistic approach to pathogen management. Liter ature reviews have been conducted on the presence of plant pathogens in irrigation water (Hong and Moorman, 2005) and alternative water treatment technologies to control microbial growth in irrigation (Ehret et al., 2001; Lane, 2004; Newman, 2004; Runia, 1 995; Stewart Wade, 2011; Van Os 2009). A comprehensive review of technologies to control plant pathogens, algae, and biofilm in irrigation is needed for irrigation specialists designing water treatment options, in addition to plant pathologists and agrono mists. The objective was to summarize the concentration or intensity and contact times required for different treatment technologies for control of microorganisms in irrigation water.
22 Review of Water Treatment Efficacy Chemical Water Treatment Alternativ es Chlorine (Table 2 1) Mode of action : As an oxidizer, chlorine removes electrons from a reactant (such as a pathogen cell membrane), and in the process chlorine becomes reduced to chloride (Cl ). Chlorine can be applied to irrigation water as a gas (Cl 2 ); as a liquid, mainly as sodium hypochlorite (NaOCl) or purified hypochlorous acid (HOCl); or as a solid, most commonly calcium hypochlorite (Ca(ClO) 2 ). The mode of action of chlorine for control of microorganisms is through both oxidation and chlorinat ion (Deborde and Gunten, 2008). The two main pH dependent forms of free chlorine in water are hypochlorous acid (HOCl, a strong oxidizer that predominates below pH 7.5), and hypochlorite (OCl a weak sanitizer that predominates at higher pH) (Cherney, 20 06; Deborde and Gunten, 2008). Dose response : High mortality of oomycete zoospores has been observed with 2 mgL 1 of free chlorine (Hong et al., 2003; Lang et al., 2008), and up to 2 mgL 1 is a typical dosage rate used in irrigation (Fisher et al., 2008 ; Fisher et al., 2008b). In contrast, mortality of mycelia and sporangia of oomycetes required 4 mgL 1 with 0.5 and 8 minutes contact time, respectively (Hong et al., 2003). Fusarium oxysporum and Rhizoctonia solani required 8 mgL 1 with 5 minutes co ntact time and 10 mgL 1 with 10 minutes contact time to achieve greater than 90% mortality, respectively (Cayanan et al., 2009). The concentration required to control bacterial pathogens ranged from 0.1 to 4 mgL 1 (Poncet et al., 2001; Robbs et al., 19 95; Roberts and Muchovej 2009; Thompson, 1965). Between 5 to 30 mgL 1 were required to control algae in studies by Chase and Conover (1993) and Rav Acha et al. (1995). Commercial greenhouse
23 recycled irrigation water treated with 4 mgL 1 of chlorine (ap plied as sodium hypochlorite) with 30 minutes contact time completely eliminated Cucumber Leaf Spot Virus (CLSV) inoculum, but 3 mgL 1 had no effect on virus viability (Rosner et al., 2006). Nematodes are highly resistant to chlorination (Grech and Rijk enberg, 1991; contact times for pathogen control, and conversely the efficacy of a low chlorine dose may be increased with a longer contact time (Cayanan et al., 2009; Hong e t al., 2003; Although few published studies on the efficacy of chlorine to prevent or destroy biofilm in irrigation can be found in the literature, it appears that bacteria attached to biofilm surfaces are m any times more resistant to chlorination than free bacteria (Bois et al., 1997; LeChevallier et al., 1988). Treatment with 1 or 3 mgL 1 of chlorine resulted in 99.7% or 99% survival of bacteria within biofilm, respectively (Bois et al., 1997). Phytotoxi city : Detrimental effects of chlorine on plant health have been reported. Free chlorine at 2.4 mgL 1 applied with overhead irrigation resulted in foliar phytotoxicity was observed in container grown deciduous shrubs (Cayanan et al., 2009b). This dosage level is lower than reported chlorine concentrations required to control some pathogens in Table 2 1. Sensitivity to water contaminants and chemistry : Chlorine efficacy decreases rapidly at high pH, or in the presence of organic and nitrogen contaminant s. The peak efficacy of chlorine against pathogens is observed around pH 6 because of the predominance of the hypochlorous acid form (Cherney et al., 2006; Deborde and Gunten, 2008; Lang et al., 2008). Oxidation reduction potential (ORP, or REDOX
24 potenti al) measures the ability of oxidizing agents to remove electrons from microbial cell membranes and prompt microbial mortality (McPherson, 1993; Suslow, 2004; Taiz and Zeiger, 2006). Pathogen mortality increases as pH drops and ORP increases in a chlorinat ed solution (Lang et al.; 2008; Robbs et al., 1995). Chlorine can interact with compounds containing ammonium or organic nitrogen to form chloramines (Degrmont, 1979; Qiang and Adams, 2004; Weil and Morris, 1949). Chloramine is also a sanitizing agent (Degrmont, 1979). Chloramines have a longer residual effect and greater stability at higher temperatures (>25 C) compared with hypochlorous acid, and do not form carcinogenic trihalomethanes (Degrmont, 1979; Faust and Aly, 1983.). The disadvantages of c hloramine are reduced efficacy to control pathogens, particularly in terms of longer required contact time (Degrmont, 1979). Phytotoxicity has been observed from chloramine application, with root necrosis 1 combined with 9.4 mg NH 4 + 1 (Date et al., 2004). However, a 3:1 ratio of ammonium chloride to sodium hypochlorite was significantly more effective in reducing bacteria attached to surfaces than hypochlorous acid alone, presumably because of greater pe netration of the biofilm layers by the more stable chloramines (LeChevallier et al., 1988). More research is required to evaluate how nitrogen fertilizers commonly used in the agriculture can affect the efficacy of chlorine to control plant pathogens. Ch lorine demand, which represents the reduction in residual active ingredient concentration from contaminants in a water source, is observed in the presence of both organic matter and microorganisms (Helbling and VanBriesen, 2007). Peat at 50 mgL 1 in solu tion exerted a chlorine demand of 24% and 55% after 2 and 60 minutes,
25 respectively (Fisher et al., 2013). Biofilm in irrigation lines can greatly reduce the residual free chlorine measured at the most distant irrigation emitter compared with the applied d ose (LeChevallier et al., 1988; Meador, 2012; Thompson, 1965). Regulatory : Chlorination of organic compounds can result in toxic byproducts such as trihalomethanes and haloacetic acids, which EPA has identified as hazardous for human health (Deborde and Gu nten, 2008; Bull et al., 1990). Inhalation of chlorine at 1 mgL 1 affects pulmonary function on human populations with high sensitivity to regulated. The EPA establish ed maximum contaminant level goal (MCLG) for disinfectant and disinfectant byproducts, which represents the maximum level of contaminant in drinking water at which there is not known expected risk, is 4 mg Cl 2 L 1 (US EPA, 2013). Chlorine dioxide (Table 2 2) Mode of action : Chlorine dioxide is also an oxidizer use to treat water, but has important technical differences from hypochlorous acid, hypochlorite, and chloramines. Chlorine dioxide, unlike chlorine gas, does not hydrolyze in water and remains in gas form in water (Amy et al., 2000; US EPA, 1999). The mode of action of chlorine dioxide is exclusively oxidation, and it does not chlorinate compounds like other chlorine forms (Amy et al., 2000). Chlorine dioxide has an oxidation potential of 0.95V f or a 1 M solution at 25C, which is lower than chlorine (1.36V) and ozone (2.07V) which indicates slower reaction time than ozone and chlorine (Degrmont, 1979). Chlorine dioxide has a stronger oxidation capacity compared with chlorine and ozone because c hlorine dioxide is the only sanitizer that is a free radical in water which is capable of accepting 5 electrons per molecule (Degrmont, 1979).
26 Dose response : The effective dose to control microorganisms with chlorine dioxide (Table 2 2) ranged from 0.5 mgL 1 with 2 minutes contact time for Fusarium oxysporum conidia in municipal water (Mebalds et al., 1995b) to an estimated dose of 57 mgL 1 for Thielaviopsis basicola conidia when the pH was 8.0 (Copes et al., 2004). Growers typically target around 0.25 mgL 1 residual concentration at the emitter for continuous injection and 20 to 50 mgL 1 for shock treatment to eliminate biofilm (Fisher et al., 2008c). Phytotoxicity : A dose of 2.5 mgL 1 chlorine dioxide in pepper plants irrigated for 4 weeks is the l owest dose reported in which reduction of plant growth was reported (Rens, 2011). Some ornamental bedding plants and woody ornamentals receiving 5 1 ) of chlorine dioxide did not show phytotoxic ity (Copes et al., 2003). Symptoms associated with phytotoxicity caused by chlorine dioxide included yellowing of the leaf margin or tip (early symptoms), necrotic leaf tips and margins, necrotic spots and blotches on leaves and flowers, plant death, and overall reduction of plant growth (Carrillo et al., 1996; Copes et al., 2003; Rens, 2011). Sensitivity to water contaminants and chemistry : Organic matter and inorganic ions in solution, for example, with surface water sources, exert a demand on chlorine dioxide (Mebalds et al., 1995). The presence of 50 mgL 1 of peat in the solution increased the demand of chlorine dioxide up to 36.3% and 52.5% after 2 and 60 minutes, respectively (Fisher et al., 2013). Chlorine dioxide is less sensitive than chlorine to solution pH (Bernarde et al., 1965; Yao et al., 2010), although a chlorine dioxide solution required higher concentrations to achieve the same level of pathogen
27 control at pH 8 than pH 5 (Copes et al., 2004). The presence of micronutrients in the solu tion also increased the required chlorine dioxide concentration to achieve pathogen mortality (Copes et al., 2004). The combination of micronutrients with water hardness (magnesium, calcium, and bicarbonate) and nitrogen increased the required concentrati on of chlorine dioxide to kill fungal pathogens in water at pH 5 and decreased the required concentration to kill pathogens at pH 8 (Copes et al., 2004). As a dissolved gas, the maximum concentration of dissolved chlorine dioxide decreases with increasi ng temperature (US EPA, 2009). Regulatory : Unlike chlorine, the reaction of chlorine dioxide with organic matter does not result in trihalomethanes (US EPA, 1999). However, direct ingestion or inhalation of chlorine dioxide or its byproducts (chlorites and chlorates) can result in irritation of the digestive tract or chronic respiratory deficiencies, skin and nasal irritations (US EPA, 2000). The maximum contaminant level goal for drinking water for chlorites and chlorates together should not exceed 1 mgL 1 (Bull et al. 1990; US EPA, 1999). The maximum residual disinfectant level (MRDL) for chlorine dioxide is 0.8 mgL 1 in drinking water (US EPA, 2013). Ozone (Table 2 3) Mode of action : Ozone (O 3 ) acts by direct oxidation or through the production of hyd roxyl free radicals (Hoign and Bader 1976; US EPA, 1999). Ozone has an oxidation reduction potential of 2.07V, which is the highest of water treatment oxidizers (Degrmont, 1979). Ozone is an unstable gas which must be generated onsite, usually via coro na discharge or ultraviolet radiation (Degrmont, 1979; US EPA, 1999). A 1 is typically suggested for greenhouse growers (Fisher, 2013).
28 Dose response : Plant pathogens varied widely in resistance to oxidation by ozone, with the required ozone dose ranging from 0.5 mgL 1 with 1 minute contact time for Pectobacterium carotovorum subsp. carotovorum (Kobayashi et al., 2011) to 100 mgL 1 with 30 minutes contact time for Tomato Mosaic Virus (Runia, 1994) (Table 2 3). The minimum reported doses to control bacteria, fungi, oomycetes and virus were 0.5, 0.7, 0.8 and 7.9 mgL 1 with contact time of 1, 16, 8, and 75 minutes, respectively (Beardell and Bakier, 1996; Kobayashi et al., 2011; Runia, 1994). Phytotoxicity : 1 at the emitter ozone applied daily as overhead irrigation for 7.5 minutes during 6 weeks caused phytotoxicity symptoms, but no negati ve effects were observed at 0.5 mgL 1 (Graham et al., 2009). Symptoms associated with ozone phytotoxicity were leaf injury, reduction of leaf area, shoot weight (fresh and dry), shoot height, and root dry weight (Graham et al., 2009). Sensitivity to wate r contaminants and chemistry : Manganese, iron, and micronutrient chelates can be oxidized by ozone, creating a demand for active ingredient (Ohashi Kaneko et al., 2009; Vanachter et al., 1988). Demand for ozone active ingredient from the nutrient solutio n reduced control of Fusarium oxysporum and Corynebacterium michiganense by ozone (Vanachter et al., 1988). Ozone efficacy was less at pH 8.0 than pH 7.2 in laboratory experiments (Domingue et al., 1988). Like other dissolved gases, the maximum concentra tion of dissolved ozone in solution decreases as temperature increases (Kobayashi et al., 2011). Residual ozone concentrations after 5 minutes contact time reduced from 1.58 mgL 1 at 15 C to 1.24 mgL 1 at 25 C and 0.82 mgL 1 at 30 C (Kobayashi et al., 2011)
29 Regulatory : Ozone is a regulated atmospheric pollutant with human health risk (US EPA, 1999), and systems must be designed to avoid off gassing of concentrated ozone into the work environment. Because of its reactive nature, ozone up to 15 mg L 1 was rapidly depleted to undetectable levels, after a single pass through a rockwool slab (Graham et al., 2011; Graham et al., 2011b; US EPA, 1999). Although ozone normally breaks down into oxygen, in some situations carcinogenic by products such as bromat e may result from ozonation (US EPA, 1999). Hydrogen peroxide and activated peroxygens (Table 2 4) Mode of action : Hydrogen peroxide can be used directly as an oxidizing water ducts where H 2 O 2 is combined with organic acids such as acetic acid to form more stable and effective sanitizing molecules including peroxyacetic acid (Hopkins et al., 2009; Nederhoff, 2000; Newman, 2004; Pettit, 2003; Van Os, 2010). Hydrogen peroxide has an oxidation potential of 1.76 V (Degrmont, 1979), however the relationship between hydrogen peroxide concentration and ORP is complex, and dosage is normally tested using colorimetric methods. Dose response : The effective dose to control microorganism s with hydrogen peroxide based products (Table 2 4) ranged from 12.3mgL 1 hydrogen peroxide combined with 8mgL 1 peroxyacetic acid for control of algae (contact time not specified) (Choppakatla, 2009) to 185 mgL 1 hydrogen peroxide plus 120 mgL 1 pero xyacetic acid with 1 minute contact time to control Phytophthora sp. (Steddom and Pruett, 2012). The required dose for water treatment varies between commercial activated peroxygen products, because there products vary in the ratio of hydrogen peroxide to peroxyacetic and other acids.
30 Phytotoxicity : Phytotoxicity thresholds for hydrogen peroxide have been observed between 8 mgL 1 applied in the nutrient solution of soilless lettuce seedlings (Nedderhoff, 2000) to 125 mgL 1 applied in the nutrient solut ion in cucumber plants on rockwool (Vnninen and Koskula, 1998). Phytotoxicity thresholds for activated peroxygens and peroxyacetic acids remain to be established. Symptoms associated with hydrogen peroxide toxicity included leaf scorching (Vnninen and Koskula, 1998), reduced plant growth (Nedderhoff, 2000) and plant mortality (Van Wyk et al., 2012). Symptoms associated with very high concentrations of activated peroxygens included necrosis and dehydration of leaf and flowers, and spots and blotches on the leaves (Copes et al., 2003). Sensitivity to water contaminants and chemistry: Hydrogen peroxide concentration is reduced by increased temperature and light levels, alkaline pH and some metals (Degrmont, 1979). Activated peroxygens exposed to 50 mg L 1 of peat in the solution did not reduce active ingredient concentration of activated peroxygens after 2 and 60 minutes (Fisher et al., 2013). However, higher concentrations (10 gL 1 ) of peat reduced the amount of hydrogen peroxide and peroxyacetic ac id from activated peroxygens by 33% and 50%, respectively, after 4 hours contact time (Huang et al., 2011). Regulatory : The reaction of hydrogen peroxide with organic matter in solution has end products of water and oxygen. Therefore, hydrogen peroxide is considered a safe alternative for workers and the environment compared with some other water treatment alternatives (Nederhoff, 2000), although a short re entry interval is required in greenhouses following application of commercial activated peroxygen pr oducts.
31 Copper (Table 2 5) Mode of action : Copper is an essential element for plant growth and other eukaryotes and prokaryotes (Evans et al., 2007; Marschner, 1995), but at high concentration copper can bind protein prosthetic groups and therefore disrup t normal cellular protein structure and reduce microbial and plant metabolism (Degrmont, 1979; Evans et al., 2007; Flemming and Trevors, 1989; Thurman et al.,2009). Copper can be delivered for water treatment in the form of copper ionization or copper sa lts. Copper salts have been used as fungicide as early as the 1880s (Agrios, 2005) and as an algaecide since the early 1900s (Flemming and Trevors, 1989; Thurman et al., 2009). Commercial copper algaecides include a number of inorganic or organic copper molecules. Copper ions are generated by electrolysis, where positively charged copper ions are displaced at the anodes (Stewart Wade, 2011). Dose response: The effective dose of copper ionization (Table 2 5) to control microorganisms ranged between 2 m gL 1 for several microorganisms (Mohammad Pour et al., 2011; Wohanka and Fehres, 2007a; Wohanka et al., 2007; Wohanka and Fehres, 2006d) to 4 mgL 1 for Agrobacterium tumefaciens (Wohanka and Fehres, 2006a). In many cases, an extended contact time of sev eral hours was required for control. Copper algaecide salts varied widely in the required dose for control of Phytophthora capsici zoospores (Granke and Hausbeck, 2010) or Erwinia carotovora subsp carotovora (Gracia Garza et al., 2002). Greenhouses and nursery growers typically apply 1 mg CuL 1 from copper ionization to prevent algae buildup and control plant pathogens (Zheng et al., 2005). Phytotoxicity : Reported phytotoxicity thresholds caused by copper applications in water ranged between 0.08 mgL 1 in taro ( Colocasia esculenta ) applied in the
32 nutrient solution of a hydroponic system (Hill et al., 2000) to 5.0 mgL 1 in woody ornamentals applied in the nutrient solution of plants grown in sand (Kuhns and Sydnor, 1976). Calla lilies ( Zantedeschia sp p.) overhead irrigated with water containing fixed copper or copper hydroxide resulted in shorter plants with fewer flowers compared with plants that were sub irrigated with the same solution (Gracia Garza et al., 2002). Sensitivity to water contaminants a nd chemistry: Peat at 50 mgL 1 reduced the applied 2 mgL 1 free copper from either copper salts or copper ionization by only 3.4% and 5.5%, respectively, after 1 hour contact time (Fisher et al., 2013). Copper ionization was less effective at controlli ng Phytophthora root rot in gerberas when the nutrient solution contained iron chelates (Fe HEEDTA) compared with iron salts (FeSO 4 ) (Toppe and Thingaard, 1998), presumably because of substitution reactions of copper with the iron chelate. Ionized copper and copper salts were less effective to control algae when the nutrient solution contained Fe EDDHA compared with Fe EDTA (Mohammad Pour et al., 2011). Regulation : Copper ionization is regulated by US EPA as a pesticide (US EPA, 1999). Based on the Safe Drinking Water Act, the maximum contaminant level goals for copper in water is 1.3 mgL 1 (US EPA, 2013). Silver (Table 2 6) Mode of action : Silver ionization is generated in the same way as copper in that an electrical charge passed through water release s ions from anodes (Stewart Wade, 2011), or silver can also be applied as a salt. Silver ions disrupt membranes of microorganisms, resulting in cell lysis (Slade and Pegg, 1993; Miller and McCallan, 1957).
33 Dose response : The efficacy to control plant pa thogens with silver nitrate ranged between 0.07 mgL 1 for conidia of Fusarium oxysporum f. sp. lycopersici to 0.5 mgL 1 for conidia of Fusarium oxysporum f. sp. dianthi (Slade and Pegg, 1993). Combined silver and copper ionization has been widely used as a water disinfection disease (Lin et al., 2011; Perez Cachafeiro et al., 2007; Rohr et al., 1999; Stout, 2003). Silver ionization was reported to be ineffective to control Alternaria Fusarium sp. and toba cco mosaic virus (TMV) (Stewart Wade, 2011). Phytotoxicity : Little is known about using silver alone or in combination with copper as water treatment in plant production (Stewart Wade, 2011). However, silver impacts plant health by inhibiting ethylene re sponses (Bradford and Dilley, 1978), reducing the number of staminate flowers (Hallidri 2004), reducing petal abscission (Cameron and Reid, 1983), and reducing plant height (Karakaya and Padem 2012). Regulation : Silver salts and ionization generators are regulated by US EPA as pesticides (US EPA, 1999). Silver is listed as a secondary contaminant which means that is not threat to health and therefore monitoring is voluntary. The suggested maximum level goal for drinking water is of 1 mgL 1 (US EPA, 2013) Bromine (Table 2 7) Mode of action : Bromine is a an oxidizer with oxidation potential of 1.33 volts or 0.70 volts in the form of hypobromous acid (HBrO) or bromide (BrO ), respectively (Degrmont, 1979). Dose response : Chase (1990 and 1991) evaluated application of bromine in overhead irrigation in diverse ornamentals and pathogens, with variable levels of control at 25 to 60 mgL 1 (Table 2 7). Weekly applications of bromine applied at 15 mgL 1 in
34 sub irrigation fo r the first 5 weeks and then 30 mgL 1 for 9 weeks did not prevent algae 1 was not effective in removing Thielaviopsis basicola from plastic, wood and metal surfaces (Copes and Hendrix, 1996) Phytotoxicity : Some plants (A eschynanthus pulcher, Dracaena marginata, Ficus benjamina, Hedera helix, Hibiscus rosa sinensis, Saintpaulia ionantha, and Schlumbergera truncate ) irrigated overhead with d oses between 50 to 60 mgL 1 presented symptoms that included distortion of immature leaves and abscission, severe necrosis, chlorosis on mature and immature leaves, stunting, and white spots on flowers (Chase, 1991). A lower concentration of 15 mgL 1 applied as sub irrigation for 5 weeks did not reduc e plant quality of Ficus benjamina, Schefflera arboricola and Dieffenbachia maculata (Chase and Conover, 1993). Regulation : The reaction of bromine with organic matter results in the formation of halogenated organics which are considered detrimental for human health (US EPA, 1999). Registered bromine products do not generate bromate ion (BrO 3 ), which is considered a possible carcinogenic agent and has a maximum concentration in drinking water of 0.010 mgL 1 (US EPA, 1999). Physical Water Treatment Tec hnologies Filtration (Table 2 8) Mode of action : The mechanisms of particle removal with filtration consist on straining, impaction, interception, adhesion, and flocculation (Levine et al., 1985). Filters suitable for removal of microorganisms from water are either membrane filtration with small pore size (<10m) or slow sand filtration, described under the Ecological Alternatives section (Ehret et al., 2001; Stewart Wade, 2011; Ufer et al., 2008; V an Os,
35 2010). Membrane filters can be classified as micro (0.1 10 m), ultra (0.1 .002 m), nano (0.0005 0.002 m) filtration, or reverse osmosis (<0.0005 m) depending on pore size (Van der Bruggen et al., 2003). Particle filters with larger pore si zes and rapid sand filters are important to reduce clogging of membrane filters, to remove soil and plant material that may contain pathogens, and to reduce demand of the irrigation water for subsequent injection of a chemical sanitizing agent. Microbial p ropagules differ in size depending on the type of organism and the life stage. For example, the length of Phytophthora s porangia ranges from 10 m ( P. katsurae ) up to 171 m ( P. erythroseptica var. erythroseptica ) (Erwin and Ribeiro, 1996). Zoospores of Phytophthora and Pythium which emerge from sporangia, are approximately 7 to 10 m in diameter (Dreschsler, 1952; Hardham, 2001). Mycelia of Phytophthora spp. have a diameter between 5 to 8 m (Erwin and Ribeiro, 1996). Fusarium sp. macroconidia are app roximately 50 m long and 7 m wide and approximately 20 m in diameter (Toussoun and Nelson, 1976). Bacteria range between 0.6 to 3.5 m in diameter (Agrios, 2005). Viruses vary in size from 0.03 m (spherical plant virus), 0.3 by 0.018 m (rigid rod sh ape), and up to 2 m long (filamentous virus) (Gergerich and Dolja, 2006). Efficiency of removal : The pore size range at which pathogens wer e effectively removed (Table 2 8) ranged between 0.003 m for Tomato Mosaic Virus (ToMV), Fusarium oxysporum f. s p. lycopersici and Verticillium spp. (Runia, 1995) up to 7 m for Pythium aphanidermatum zoospores (Goldberg et al., 1992). Membrane filtration was most effective at controlling pathogens when combined in a series of multi stage filters from larger to smaller pore size, and in combination with other technologies
36 (Goldberg et al., 1992; Macha do et al., 2013; Moens and Hendrickx, 1992; Ohtani et al., 2000; Schuerger and Hammer, 2009; Van der Bruggen et al., 2003). There is increasing resistance to water flow as filter pore size decreases, and efficacy at a given pore size decreases as flow rat e increases. Sensitivity to water contaminants and chemistry : Membrane filtration can be clogged by suspended solids (sand, silt, organic matter), chemical precipitates (Fe, Mn, carbonates, pesticides), or bacteria and algae (Moens and Hendrickx, 1992; Yi aosumi et al., 2005). Pre filtration of suspended solids is therefore necessary before membrane filtration to reduce contamination (Van der Bruggen et al., 2003). Reverse osmosis removes nutrients from the solution, which is a disadvantage if the nutrien t solution will be recirculated (Runia, 1995), but salt removal is an advantage in water with excess sodium or chloride. Regulation : There is no federal regulation on membrane filtration as a water treatment technology so disposal of liquid and solids was tes (including brine and used membrane filters) from membrane filtration are regulated at the state level (US EPA, 2005). Reverse osmosis is regulated at the state level for the maximum volumes of liquid and solid residuals that can be disposed in a speci fic location (US EPA, 2005). Ultraviolet radiation (Table 2 9) Mode of action : Ultraviolet (UV) radiation results in a photochemical reaction that damages DNA and RNA molecules, and inhibiting their replication and translation in cells (Newman, 2004). T he peak of UV absorbance by DNA is at 260 nm (Hijnen et al., 2006) which is within the UVc range of 100 280 nm (Diffey, 2002). Radiation with UV is often combined with other sanitizing technologies such as ozone or activated peroxygens, leading to increas ed pathogen control.
37 Dose response : The effective range of UVc radiation to control plant pathogens ranged between 28 mJcm 2 for Fusarium oxysporum f.sp. lycopersici (Runia, 1995) up to 850 mJcm 2 for Alternaria zinniae (Mebalds et al., 1996). The sugg ested water treatment for growers to control most pathogens is 250 mJcm 2 (Runia, 1994b; Runia, 1995). Sensitivity to water contaminants and chemistry : Water and nutrient solution treated with UVc radiation should be clear from contaminants (e.g. organic and inorganic suspensions) allowing at least 60% transmission (Yiasoumi et al., 2005 ). Therefore, filtration should precede UVc radiation to prevent interference of absorbance by suspended solids (Newman, 2004; Runia, 1995; Stanghellini et al., 1984). Higher UVc radiation doses were required to achieve the same pathogen mortality in nutrient solutions compared with clear water (Sutton et al., 2000). The iron content (specific form was not indicated) in a hydroponic nutrient solution was reduced from 4 .5 to 0.1 1 after being treated with UVc radiation at 30 mJcm 2 (Stanghellini et al., 1984), and UV light can lead to photo degradation of iron chelates (Albano and Miller, 2001). Because UVc radiation is a physical water treatment, its efficacy is not pH dependent (Stewart Wade, 2011). Regulation : Radiation with UV is a point treatment with no residual effect or toxic byproducts (Wolfe, 1990; Stewart Wade, 2011). Heat treatment (Table 2 10) Mode of action : High temperatures disrupt cell integrity and interrupt metabolic processes in sensitive microorganisms (Crisan, 1973). Water passes through a series of heat exchangers that gradually increase temperature. The last heat exchanger increases the temperature to target temperature (Steward Wade, 20 11). Heat
38 treatment is more commonly used to control microorganisms in greenhouses in Europe than in the United States (Runia, 1994; Van Os, 2010). Dose response : Efficacy to control plant pathogens with heat treatment ranged from 40C for 90 seconds t o control Phytophthora cryptogea (Runia and Amsing, 2001) to 95C for 30 seconds to control Agrobacterium tumefaciens (Poncet et al., 2001). Sensitivity to water contaminants and chemistry : Heat generally has little interaction with the nutrient solution and does not result in toxic chemicals (Runia, 1995). However, scale (salt precipitates) may form that affect clogging of irrigation equipment. Ecological Water Treatment Alternatives Slow filtration (Table 2 11) Mode of action : Slow sand filtration works as a result of biological, physical and chemical reactions. Water flows slowly through layers of fine sand at a flow rate between 100 to 300 Lm 2 h 1 (Wohanka, 1995). An upper layer containing a complex microbial community, known as a Schmutzdecke car ries out biological control in slow sand filtration by a mechanism that remains to be characterized (Ellis and Wood, 1985; Gimbel et al., 2007). Efficiency of removal : Slow sand filtration (Table 2 11) has been observed to remove a high percentage of Phy tophthora Fusarium bacteria, nematodes, and viruses from irrigation water, but may not completely eliminate them (Ufer et al., 2008; Van Os 1999; Van Os, 2010; Wohanka, 1995). The efficiency of slow media filtration will depend on the media material and the depth of the filter (Wohanka et al., 1999). A comparison of different filter media showed that rockwool media had the highest (99%) removal efficiency of Xanthomonas campestris pv. pelargonii compared with sand
39 (83%), pumice (85%) and anthracite (82% ). Rockwool filters with depths of 60 or 90 cm removed more Xanthomonas campestris pv. pelargonii than a 30 cm depth filter (Wohanka et al., 1999). Sensitivity to water contaminants and chemistry : Slow sand filtration does not alter the concentration of elements, pH or electrical conductivity of the nutrient solution (Wohanka, 1995). Since slow sand filtration is a type of biological control treatment, any factor (such as temperature or pH) that a ffects the biology of microorganisms will affect the activity in the Schmutzdecke Biosurfactants (Table 2 12) Mode of action : Rhamnolipid biosurfactant is a contact biofungicide that is produced from the aerobic fermentation of Pseudomonas aeruginosa (St anghellini and Miller, 1997; US EPA2013b). Rhamnolipids disrupt cells membranes of oomycetes, of which zoospores are most vulnerable (US EPA, 2013b). Nitrapyrin is an active ingredient of nitrification inhibitor products, which in a recirculated solution increased the populations of beneficial bacteria ( Pseudomonas putida ) while reducing oomycete survival and disease incidence (Pagliaccia et al., 2007). Dose response : Continuous application of 150 mgL 1 of rhamnolipid controlled 100% of disease caused b y Phytophthora capsici in pepper plants ( Capsicum annuum ). Nutrient solution treated with nitrapyrin resulted in 40% less mortality of cucumber plants ( Cucumis sativus ) caused by Pythium aphanidermatum than untreated control (Paggliacia et al., 2007). Nu trient solutions of pepper plants treated with rhamnolipid and nitrapyrin biosurfactant resulted in two orders of magnitude higher concentration of aerobic bacteria (Nielsen et al., 2006) and Pseudomonas putida (Paggliacia et al., 2007) than the untreated solution. Proliferation of beneficial bacteria may be a
40 secondary benefit of using biosurfactants, however high bacterial density also increases the risk of biofilm buildup and irrigation emitter clogging (Rogers et al., 2003). Phytotoxicity : Reduction i n plant biomass of pepper plants was observed when 150 mgL 1 rhamnolipid biosurfactant was applied in overhead and ebb and flow irrigation in organic or rockwool media (Nielsen et al., 2006). Nitrapyrin at 12.5 mgL 1 reduced plant growth of peppers and resulted in chlorosis (Paggliacia et al., 2007). Regulation : No adverse health effects, except eye irrigation, have been observed with the use of rhamnolipid biosurfactant (US EPA 2013b). Because of the low concentration of active ingredient and fast d egradation in the environment, minimal toxicity from the residual concentrations in runoff is expected (US EPA 2013b). Constructed wetlands Mode of action : Constructed wetlands used to treat agricultural runoff can be surface flow (free water surface) and subsurface flow (horizontal or vertical flow) or a combination of both (White et al., 2011). The exact mechanism by which constructed wetlands remove pathogens is unknown (Huett, 2002). However, like all ecological systems it is most likely that the inte ractions of diverse physicochemical and biological activities are responsible for the reduction of pathogen populations (Headley et al., 2005; Huett, 2002). Efficiency of removal : A subsurface flow constructed wetland with a surface of 4 m 2 and 0.5m deep planted with reed ( Phragmites australis ) in a gravel bed was effective in removing 100% of the inoculated Phytophthora cinnamomi in a retention time (time from inflow to outflow) of 1.3 and 4.5 days all year round (Headley et al., 2005; Huett 2002). The efficacy of constructed wetlands to control waterborne pathogens is an active and emerging area of research.
41 Sensitivity to water contaminants and chemistry : Constructed wetlands are highly effective in removing contaminants from runoff and sewage (Vymaz al, 2009; White et al., 2011). In agriculture, constructed wetlands are known for their high et al., 2011). Adequate timing in the harvesting and replacement of the pl ants is crucial for proper absorption of nutrients (Headley et al., 2005). Synopsis of Current Knowledge and Gaps in Research Irrigation water treatment is a risk management strategy to reduce crop losses associated with plant pathogens, biofilm, and algae and to reduce contamination of fresh produce by human pathogens. This summary of efficacy tests is intended to support agricultural management decisions, by indicating the effective dose for controlling target organisms under research conditions, in addition to reported phytotoxicity thresholds, and the breadth of research available for each technology. The research summaries in Tables 2 1 to 2 12 show that target microorganisms vary widely in resistance to water treatment. The effective doses for chemical water treatment technologies for control of plant pathogens were in many cases above known phytotoxicity thresholds, and for most crops and technologies the phytotoxicity thresholds remain unknown. Where required dose to control microorganisms e xceeded phytotoxicity levels, effective strategies may include increased contact time to increase efficacy at a given dose, monitoring active ingredient at the point of water application to the crop to verify that it is below the phytotoxicity threshold, r emoving active ingredient after treatment but before water is applied to crop. Combining more than one treatment technology may also increase efficacy. The concept of multi stage water treatment in drinking water has a long history, since the
42 18 th century (Galvis, 2002), and has equal importance in horticulture applications (Lewis Ivey and Miller, 2013). Multiple stages of filtration is a critical design component, which reduces the amount of inoculum that needs to be chemically treated as well as organic matter that depletes the active ingredient of sanitizing agents. There are widely varying levels of knowledge of the different water treatment technologies for irrigation (Table 2 13). Although chlorine and copper ionization have been studied by several researchers on different microorganisms, other technologies such as membrane filtration have received less research effort. Little research has been conducted on effective control methods for algae and biofilms, which are common problems in micro irrigat ion systems and result in plant loss, labor costs and worker hazard. Most of the efficacy research was carried out in vitro (Table 2 13), and additional research is needed under environments that resemble the conditions of actual operations. Efficacy to control microbes greatly differed when evaluations were done in water compared with nutrient solutions (Sutton et al., 2006; Vanachter et al., 1988) or in vitro compared with in vivo (Gracia Garza et al., 2002). Most efficacy testing has focused on patho gen mortality, but disease development is also important. Some experiments observed discrepancies between pathogen mortality and disease incidence Harwood 2005). Although the s cope of this review is limited to plant pathogens, algae, and biofilm, irrigation water can also be a source of human food safety pathogens (Alsanius et al, 2011; Gortres Moroyoqui et al., 2011; Ijabadeniyi et al., 2011; Lewis Ivey and Miller, 2013; Steel e et al., 2005). Fresh produce growers are facing the need to follow
43 food safety guidelines to minimize risk of contamination from diverse sources including irrigation water. Research by Lewis Ivey and Miller (2013) measured the effect of chlorine dioxid e simultaneously on E. coli and Phytophthora capsici and many of the design principles for control of plant pathogens apply equally to human food safety pathogens. The selection of water treatments is a difficult task for growers, particularly given the l arge selection of technologies available, the limited and variable knowledge about efficacy (Table 2 13), and the multiple social, economic, and technical factors involved in technology adoption decisions. Despite the number of review articles discussing the available water treatment technologies and their technical characteristics (Ehret et al., 2001; Newman, 2004; Raviv and Lieth, 2007; Runia, 1995; Van Os, 2010; Stewart Wade 2011; Zhou and Smith, 2001) the literature lacks clear guidelines for selectin g a technology. Growers are willing to adopt risk management strategies, like water treatments, to prevent plant disease spread in their operations (Breukers et al., 2012). With new regulations pending to reduce the risk of water borne contamination of fr esh produce by human pathogens (FDA, 2013) there will be an even greater need to provide growers with the tools they need to make informed choices. However, risk and uncertainty are major factors that prevent adoption of innovations in agriculture (Feder a nd Umali, 1993; Marra et al., 2002). Ultimately, water treatment is just one component of integrated crop management. Selection of resistant cultivars, disease free starting plant material, monitoring of microbial water quality, matching irrigation practices with plant water need, preventive applications of pesticides, are just some of the management practices
44 essential for healthy and safe crops (Jarvis, 1992). Further knowledge is needed to effectively integrate water treatment into plant health m anagement systems.
45 Table 2 1. Efficacy of chlorine (hypochlorous acid) for control of waterborne microorganisms. Chlorine form Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References NaOCl Agrobacterium tumefaciens 4 mgL 1 30 min 100% None observed Rosa sp. Poncet et al., 2001 NaOCl Algae (Species not identified) 15 to 30 mgL 1 applied in sub irrigation solution once weekly for 9 weeks Qualitative evaluation with no algae observed Not observed Ficus benjamina, Schefflera arboricola and Dieffenbachia maculata Chase and Conover, 1993 Cl 2 Chlamydomonas sp. 5 mgL 1 30 min 100% N/A In vitro Junli et al., 1997 NaOCl Ralstonia solanacearum 1.7 mgL 1 10 min 100% N/A In vitro Machado et al., 2013 NaOCl Xanthomonas axonopoid 1.7 mgL 1 10 min 100% N/A In vitro Machado et al., 2013 NaOCl Botrytis cinerea 0.6 mgL 1 10 min 100% N/A In vitro Machado et al., 2013 NaOCl Cylindrocladium candelabrum 0.5 mgL 1 10 min 100% N/A In vitro Machado et al., 2013 NaOCl Chlorella vulgaris 2 mgL 1 5 min 99% N/A In vitro Rav Acha et al.,1995 NaOCl Cucumber leaf spot virus (CLSV) 4 mgL 1 30 min 100% Not measured Cucumis sativus Rosner et al., 2006 NaOCl Erwinia carotovora f. zeae 0.1 mgL 1 1 min 100% Not observed Zea mays Thompson, 1965 NaOCl Erwinia carotovora subsp. carotovora 0.4, 0.5, and 0.75 mgL 1 at pH 6,7,and 8; respectively, 2 min 99% N/A In vitro Robbs et al., 1995 NaOCl Fusarium foetens (conidia) 2.6 mgL 1 15 min 100% N/A In vitro Elmer, 2008 NaOCl Fusarium oxysporum 8 mgL 1 1.5 min 90% N/A In vitro Cayanan et al., 2009 NaOCl Geotrichum candidum (conidia) 20, 25, and >30 mgL 1 at pH 6,7,and 8; respectively, 2 min 99% N/A In vitro Robbs et al., 1995 NaOCl Meloidogyne javanica (eggs and juveniles) 50,000 mgL 1 60 min(eggs) or 2 mgL 1 24 hours (juveniles) 75% (egg hatching), 100% (juvenile motility) N/A In vitro Cayanan et al., 2009
46 Table 2 1. Continued Chlorine form Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Cl 2 Microphorimidum sp. 5 mgL 1 30 min 81% N/A In vitro Junli et al., 1997 NaOCl Phytophthora cactorum (zoospores) 0.3 mgL 1 0.5 min 90% N/A In vitro Cayanan et al., 2009 NaOCl Phytophthora capsici (zoospores) 2 mgL 1 10 min 100% N/A In vitro Roberts and Muchovej, 2008 NaOCl Phytophthora citricola (zoospores) 1 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Phytophthora citrophthora (zoospores) 2 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Phytophthora cryptogea (zoospores) 2 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Phytophthora infestans (sporangia) 0.4 mgL 1 1.5 min 95% N/A In vitro Cayanan et al., 2009 NaOCl Phytophthora megasperma (zoospores) 2 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Phytophthora nicotianae (mycelia) 2 mgL 1 8 min 98% N/A In vitro Hong et al., 2003 NaOCl Phytophthora nicotianae (sporangia) 4 mgL 1 8 min 95% N/A In vitro Hong et al., 2003 NaOCl Phytophthora nicotianae (zoospores) 2 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Phytophthora sp. 5 mgL 1 1 min 100% N/A In vitro Steddom and Pruett, 2012 NaOCl Phytophthora sp. (chlamydospores and zoospores) 50 mgL 1 100% N/A In vitro Grech and Rijkenberg, 1991
47 Table 2 1. Continued Chlorine form Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Cl 2 Phytophthora spp. a 0.6 mgL 1 88% Not measured Container perennials Bush et al., 2003 NaOCl Phytophthora capsici (zoospores) 2 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Phytophthora capsici (zoospores) 2.42 mgL 1 10 min 100% N/A In vitro Granke and Hausbeck, 2010 NaOCl Phytophthora cinnamomi (zoospores) 1 mgL 1 2 min 100% N/A In vitro Hong et al., 2003 NaOCl Plasmodiophora brassicae 20 mgL 1 10 min 47% Stunting and intervenal chlorosis Brassica oleracea Datnoff et al., 1987 NaOCl Pythium aphanidermatum (zoospores) 0.5 mgL 1 10 min 90% N/A In vitro Cayanan et al., 2009 Not specified Pythium aphanidermatum (zoospores) 2 mgL 1 2 min 99% N/A In vitro Hong and Richardson, 2004 NaOCl Pythium aphanidermatum (zoospores) 0.5 mgL 1 at pH 6.3 0.25 min, 764 mV ORP 90% N/A In vitro Lang et al., 2008 NaOCl Pythium dissotocum (zoospores) 0.5 mgL 1 at pH 6.3, 4 min, 766 mV ORP 90% N/A In vitro Lang et al., 2008 NaOCl Pythium spp. (zoospores) 2 mgL 1 10 min 100% N/A In vitro Roberts and Muchovej, 2008 not specified Pythium sulcatum (zoospores) 2 mgL 1 2 min 100% N/A In vitro Hong and Richardson, 2004 NaOCl Rhizoctonia solani (mycelia) 10 mgL 1 10 min 90% N/A In vitro Cayanan et al., 2009 Cl 2 Ulothrix sp. 5 mgL 1 30 min 100% N/A In vitro Junli et al., 1997 NaOCl Xanthomonas campestris pv. vesicatoria 2 mgL 1 10 min 100% N/A In vitro Roberts and Muchovej, 2008 a 0.6 mg L 1 was the average free chlorine of two year sampling period
48 Table 2 2. Efficacy of chlorine dioxide for control of waterborne microorganisms. Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Alternaria zinniae (cfu) 2 mgL 1 12 min 90% N/A In vitro Beardsell and Bankier, 1996 Ankistrodesmus sp. 5 mgL 1 30 min 100% N/A In vitro Junli et al., 1997 Chlamydomonas sp. 5 mgL 1 30 min 75% N/A In vitro Junli et al., 1997 Chlorella vulgaris (green algae) 2 mgL 1 5 min 99% N/A In vitro Rav Acha et al., 1995 Colletotrichum capsici (spores) 0.5 mgL 1 2 min (municipal water) a 4 mgL 1 2 min (surface water) 100% N/A In vitro Mebalds et al., 1995 Erwinia carotovora subsp. carotovora 1.3 mgL 1 10 min 90% N/A In vitro Yao et al., 2010 Fusarium oxysporum f.sp. narcissi (macro and micro conidia) 2.2 mgL 1 0.5 min (pH 8.0) b 0.8 mgL 1 0.5 min (hard water with 100 mgL 1 N) 90% N/A In vitro Copes et al., 2004 Fusarium oxysporum (conidia) 0.5 mgL 1 2 min (municipal water) c 2 mgL 1 2 min (surface water) 99% N/A In vitro Mebalds et al., 1995 Microphorimidum sp. 5 mgL 1 30 min 100% N/A In vitro Junli et al., 1997 Phorimidium sp. 5 mgL 1 30 min 100% N/A In vitro Junli et al., 1997 Phytophthora capsici (zoospores) 3 mgL 1 1 min 7 24% N/A In vitro Lewis Ivey and Miller, 2013 Phytophthora cinnamomi (chlamydospores) 9 mgL 1 4 min 92% N/A In vitro Beardell and Bankier, 1996 Phytophthora cinnamomi (zoospores) 0.9 mgL 1 ,12 min 100% N/A In vitro James et al., 1996 Phytophthora cinnamomi (zoospores) 1 mgL 1 2 min (municipal water) d 4 mgL 1 2 min (surface water) 100% N/A In vitro Mebalds et al. 1995 Pythium ultimum (oospores) 0.5 mgL 1 2 min 99% N/A In vitro Beardsell et al.,1996 Ralstonia solanacearum 1.3 mgL 1 10 min 99% N/A In vitro Yao et al., 2010 Thielaviopsis basicola (aleuriospores) 47 mgL 1 0.5 min (pH 5.0) b 57 mgL 1 0.5 min (pH 8.0) b N/A In vitro Copes et al., 2004
49 Table 2 2. Cont inued Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Thielaviopsis basicola (conidia) 2.1 mgL 1 0.5 min (pH 5.0) b 2.0 mgL 1 0.5 min (pH 8.0) b 90% N/A In vitro Copes et al. 2004 Ulothrix sp. 5 mgL 1 30 min 100% N/A In vitro Junli et al., 1994 Xanthomonas campestris pv. campestris 3 mgL 1 daily overhead irrigation c 90% Not measured Cauliflower seedlings Krauthausen et al., 2011 a Residual concentration of 0.4 mg L 1 (municipal water), 1.8 mg L 1 (surface water) b Estimated LD90 values c Residual concentration of 0.4 mg L 1 (municipal water), 1 mg L 1 (surface water) d Residual concentration of 0.9 mg L 1 (municipal water), 2 mg L 1 (surface water) e Residual concentration of 0.21 mg L 1
50 Table 2 3. Efficacy of ozone for control of waterborne plant pathogens. Organism (Life stage) Treatment dose (mgL 1, contact time) Inactivated propagules (%) Phytotoxicity Crop References Acidovorax avenae subsp. citrulli 0.05 mg/L a Not measured Citrullus lanatus Hopkins et al., 2009 Alternaria zinniae (spores) 0.7 mgL 1 16 min b 90% N/A In vitro Beardsell and Bankier, 1996 Fusarium oxysporum (conidia) 1 mgL 1 10 min 99% N/A In vitro Igura et al., 2004 Fusarium oxysporum (conidia) 1.8 mgL 1 4 min b 99% N/A In vitro Beardell and Bankier, 1996 Fusarium oxysporum f. sp. melonis 1 mgL 1 100% N/A In vitro Kobayashi et al., 2011 Pectobacterium carotovorum subsp. carotovorum 0.5 mg L 1 1 min 100% N/A In vitro Kobayashi et al., 2011 Phytophthora cinnamomi (chlamydospores) 0.8 mgL 1 8 min b 99% N/A In vitro Beardsell and Bankier, 1996 Pythium ultimum (oospores) 1.2 mgL 1 for 2 min b 95% N/A In vitro Beardsell and Bankier, 1996 Corynebacterium michiganense 1.1 mgL 1 for 55 min c N/A In vitro Vanachter et al., 1988 Cucumber green mottle mosaic vir us (CGMMV) 7.9 mgL 1 for 75 min (ORP 673mV) 100% d Not measured Cucumis sativus Runia, 1994 Tomato mosaic v irus (ToMV) 100 mgL 1 for 30 min (ORP 517 mV) 99% d Not measured Nicotiana glutionosa Runia, 1994 a Did not decrease Fruit blotch symptoms b Residual concentration in municipal water c Residual concentration in nutrient solution containing Fe DTPA d Reduction in infectivity of the virus
51 Table 2 4. Efficacy of activated peroxygens, hydrogen peroxide and peracetic acid for control of waterborne plant pathogens. Active Ingredient Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Hydrogen peroxide Fusarium circinatum 400 mV (ORP) for 6 hours (specific H 2 O 2 dose was not specified) 100% Not observed. High mortality (>89%) was observed with higher doses (>450 mV) Pinus spp. Van Wyk et al., 2012 Hydrogen peroxide Algae 125 mgL 1 a N/A b Scorching of leaf margins, wilting, reduced number of leaves and dry weight Cucumis sativus Vnninen and Koskula, 1998 Hydrogen peroxide and peroxyacetic acid Algae: Microcystis sp., Scenedesmus sp., and Chlorococcum sp. 12.3mgL 1 hydrogen peroxide + 8mgL 1 peroxyacetic acid a 100% N/A In vitro Choppakatla, 2009 Hydrogen peroxide and peroxyacetic acid Fusarium foetens (conidia) 135 mgL 1 hydrogen peroxide + 10 mgL 1 of peroxyacetic acid, 15 min 100% N/A In vitro Elmer, 2008 Hydrogen peroxide and peroxyacetic acid Fusarium foetens (conidia) 37 mgL 1 hydrogen peroxide + 24 mgL 1 of peroxyacetic acid, 15 min 100% N/A In vitro Elmer, 2008 Hydrogen peroxide and peroxyacetic acid Fusarium oxysporum f. sp. lycopersici (conidia) 100 mgL 1 5 min 100% d d Runia, 1995
52 Table 2 4. Cont inued Active Ingredient Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Hydrogen peroxide and peroxyacetic acid Phytophthora sp. 185 mgL 1 hydrogen peroxide + 120 mgL 1 peroxyacetic acid, 1 min 100% mortality in nursery runoff and pond water 88% in greenhouse runoff N/A In vitro Steddom and Pruett, 2012 Hydrogen peroxide and peroxyacetic acid Phytophthora sp. 12.3 mgL 1 hydrogen peroxide + 8 mgL 1 peroxyacetic acid a 100% N/A In vitro Choppakatla, 2009 Hydrogen peroxide and peroxyacetic acid Pythium spp. 12.3 mgL 1 hydrogen peroxide + 8 mgL 1 peroxyacetic acid a 100% N/A In vitro Choppakatla, 2009 Hydrogen peroxide and peroxyacetic acid Tomato Mosaic Virus (ToMV) 400 mgL 1 (specific concentrations of H 2 O 2 or PAA not specified) c 99% d d Runia, 1995 Peroxyacetic acid Acidovorax avenae subsp. citrulli 80 mg L 1 a 50% e Not observed Citrullus lanatus Hopkins et al., 2009 a Contact time not specified b Algae control estimated based on a scale index c Applied daily as overhead irrigation d Not specified e Reduction in bacterial fruit blotch
53 Table 2 5. Efficacy of copper for control of waterborne plant pathogens. Copper form Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicit y Crop References Copper ionization Acidovorax avenae subsp. citrulli 1.5 mgL 1 applied daily a 97% a Not measured Citrullus lanatus Hopkins et al., 2009 Copper ionization Agrobacterium tumefaciens 2 mgL 1 24 hours or 4 mgL 1, 4 hours 99% N/A b Wohanka and Fehres, 2006a Copper ionization Agrobacterium tumefaciens 4 mgL 1, 1 hours 53% N/A b Wohanka and Fehres, 2006a Copper ionization Algae (unidentified species) 2 mgL 1 99% N/A In vitro Mohammad Pour et al., 2011 Copper ionization Clavibacter michiganensis 2 mgL 1 2 hours 91% N/A b Wohanka and Fehres, 2007a Copper ionization Clavibacter michiganensis 2 and 4 mgL 1 1 hour 54% N/A b Wohanka and Fehres, 2007a Copper ionization Erwinia carotovora subsp. carotovora 2 mgL 1 1 hour 96% N/A b Wohanka et al., 2007 Copper ionization Erwinia carotovora subsp. carotovora 2 mgL 1 and 4 mgL 1 5 min 0% N/A b Wohanka et al., 2007 Copper ionization Fusarium oxysporum f.sp. cyclaminis (conidia) 1 to 3 mgL 1 1 to 24 hours 0% N/A b Wohanka and Fehres, 2006b Copper ionization Phytophthora cinnamomi (zoospores) 0.28 mgL 1 84% Not measured Hedera helix Toppe and Thinggaard, 2000 Copper ionization Phytophthora cryptogea (zoospores) 0.28 mgL 1 69% a Not measured Gerbera jamesonii Toppe and Thinggaard, 1998 Copper ionization Pythium aphanidermatum (zoospores) 4 mgL 1 1 hour 0% N/A b Wohanka and Fehres, 2006c Copper ionization Ralstonia solanacearum Race 3 2 mgL 1 1 hour 96% N/A b Wohanka and Fehres, 2007b Copper ionization Ralstonia solanacearum Race 3 2 and 4 mgL 1 5 min <1% N/A b Wohanka and Fehres, 2007b Copper ionization Trichoderma asperellum (conidia) 4 mgL 1 24 hours 0% N/A b Wohanka et al., 2009 Copper ionization Xanthomonas hortorum pv. pelargonii 2 mgL 1 4 hours 97% N/A b Wohanka and Fehres, 2006d Copper ionization Xanthomonas hortorum pv. pelargonii 0.5 and 1 mg L 1 24 hours 41% N/A b Wohanka and Fehres, 2006d
54 Table 2 5. Continued Copper form Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Copper hydroxide Acidovorax avenae subsp. citrulli 0.43 mgL 1 ; applied weekly 50% a Not measured Citrullus lanatus Hopkins et al., 2009 Copper nitrate Algae 4 mgL 1 99% N/A In vitro Mohammad Pour et al., 2011 Copper sulfate Algae 2 mg L 1 weekly c Good and marketable plant quality d Dieffenbachia maculata, Ficus benjamina L., Schefflera arboricola Chase and Conover, 1993 Copper chloride Erwinia carotovora subsp. carotovora 32 mgL 1 a 1% a Reduction in height, fresh mass and root growth e Zantedeschia spp. Gracia Garza et al., 2002 Copper chloride Erwinia carotovora subsp. carotovora 4 mgL 1 30 min 99% N/A In vitro Gracia Garza et al., 2002 Copper hydroxide Erwinia carotovora subsp. carotovora 5.2 mgL 1* 13% Reduction in height, fresh mass and root growth e Zantedeschia spp. Gracia Garza et al., 2002 Copper hydroxide Erwinia carotovora subsp. carotovora 1 mgL 1 30 min 100% N/A In vitro Gracia Garza et al., 2002 Copper oxychloride Erwinia carotovora subsp. carotovora 8 mgL 1* 15% Reduction in height, fresh mass and root growth e Zantedeschia spp. Gracia Garza et al., 2002 Copper oxychloride Erwinia carotovora subsp. carotovora 2 mgL 1 30 min 100% N/A In vitro Gracia Garza et al., 2002 Copper sulfate Erwinia carotovora subsp. carotovora 4 mg L 1 a 3% Reduction in height, fresh mass and root growth e Zantedeschia spp. Gracia Garza et al., 2002
55 Table 2 5. Continued Copper form Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Copper sulfate Erwinia carotovora subsp. carotovora 0.5 mgL 1 30 min 100% N/A In vitro Gracia Garza et al., 2002 Copper carbonate Phytophthora capsici (zoospores) 1.6 mgL 1 2 hours 100% N/A In vitro Granke and Hausbeck, 2010 Copper citrate and copper gluconate Phytophthora capsici (zoospores) 1.7 mgL 1 2 hours 40% N/A In vitro Granke and Hausbeck, 2010 Copper ethanolamine Phytophthora capsici (zoospores) 1.6 mgL 1 2 hours 100% N/A In vitro Granke and Hausbeck, 2010 Copper sulfate pentahydrate Phytophthora capsici (zoospores) 1.6 mgL 1 2 hours 100% N/A In vitro Granke and Hausbeck, 2010 Copper sulfate pentahydrate Phytophthora capsici (zoospores) 0.5 mgL 1 2 hours > 90% N/A In vitro Granke and Hausbeck, 2010 Copper triethanolamine and copper hydroxide Phytophthora capsici (zoospores) 1.7 mgL 1, 2 hours 100% N/A In vitro Granke and Hausbeck, 2010 Copper carbonate Phytophthora citricola, P. citrophora, P. cryptogea, P. nicotianae P. palmivora, P. ramorum (chlamydospores, sporangia and zoospores ) 0.8 mgL 1 30 min 100% N/A In vitro Colburn and Jeffers, 2010 Copper triethanolamine + copper hydroxide Phytophthora citricola, P. citrophora, P. cryptogea, P. nicotianae P. palmivora, P. ramorum (chlamydospores, sporangia and zoospores ) 1 mgL 1 30 min 100% N/A In vitro Colburn and Jeffers, 2010 a Applied with irrigation, reduction in disease incidence. b Experiments carried out in greenhouse conditions without including any crops. c Qualitative assessment rating 2: slight green growth (1: None, white bench; 5: complete green surface) d Average qualitative rating 4.2 for all crops (1: dead, 5: excellent quality) e General results for copper phytotoxicity. Results varied between overhead and subirrigation and by copper source.
56 Table 2 6. Efficacy of silver for control of waterborne plant pathogens. Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Fusarium oxysporum f. sp. dianthi (conidia) 0.5 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993 Fusarium oxysporum f. sp. lycopersici (conidia) 0.07 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993 Phytophthora cryptogea (zoospores) 0.08 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993 Phytophthora nicotianae (zoospores) 0.1 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993 Pythium aphanidermatum (zoospores) 0.08 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993 Thielaviopsis basicola 0.1 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993 Verticillium albo atrum 0.1 mgL 1 18 hours 100% N/A In vitro Slade and Pegg, 1993
57 Table 2 7. Efficacy of bromine for control of waterborne plant pathogens. Organism (Life stage) Treatment dose (mgL 1 contact time) Percentage control (%) Phytotoxicity Crop References Algae (unidentified) 15 mgL 1 (first 5 weeks) and 30 mgL 1 (final 9 weeks) 4 a Not observed Ficus benjamina, Schefflera arboricola and Dieffenbachia maculata Chase and Conover, 1993 Alternaria panax 50 60 mgL 1 daily irrigation 82% Not observed Brassaia actinophylla Chase, 1991 Alternaria panax 50 60 mgL 1 daily irrigation 90% Not observed Polyscias fruticosa Chase, 1991 Botrytis cinerea 50 60 mgL 1 daily irrigation 15% (flowers), 3% (leaves) Not observed Pelargonium hortorum Chase, 1991 Botrytis cinerea 50 60 mgL 1 daily irrigation 0% White spots on flowers Saintpaulia ionantha Chase, 1991 Corynespora cassiicola 50 60 mgL 1 daily irrigation 93% Distortion of immature leaves and abscission with severe necrosis Aeschynanthus pulcher Chase, 1991 Drechslera setariae 50 60 mgL 1 daily irrigation 71% Not observed Maranta leuconeura Chase, 1991 Erwinia chrysanthemi 55 mgL 1 daily irrigation 71 or 80% b,c Not observed Philodendron selloum Chase, 1990 Erwinia chrysanthemi 55 mgL 1 daily irrigation 100% d Not observed Philodendron selloum Chase, 1990 Fusarium moniliforme 50 60 mgL 1 daily irrigation 80% Chlorotic tip burn on older leaves Dracaena marginata Chase, 1991 Myrothecium roridum 50 60 mgL 1 daily irrigation 77% Chlorotic etching on immature leaves Ficus pumila Chase, 1991 Myrothecium roridum 50 60 mgL 1, daily irrigation 0% Not observed Syngonium podophyllum Chase, 1991 Pseudomonas andropogonis 25 mgL 1, daily irrigation 0 or 59% b Not observed Bougainvillea sp. Chase, 1990 Pseudomonas cichorri 25 mgL 1, daily irrigation 71% Not observed Chrysanthemum morifolium Chase, 1990 Pseudomonas cichorri 55 mgL 1, daily irrigation 100% Not observed Chrysanthemum morifolium Chase, 1990
58 Table 2 7. Continued Organism (Life stage) Treatment dose (mgL 1 contact time) Percentage control (%) Phytotoxicity Crop References Pseudomonas syringae 25 mgL 1 daily irrigation 60 or 70% b Not observed Impatiens wallerana Chase, 1990 Rhizoctonia solani 50 60 mgL 1 daily irrigation 88 Not observed Epipremnum aureum Chase, 1991 Rhizoctonia solani 50 60 mgL 1 daily irrigation 93% Not observed Nephrolepis exaltata Chase, 1991 Xanthomonas campestris pv. dieffenbachiae 55 mgL 1 daily irrigation 70% Not observed Syngonium podophyllum Chase, 1990 Xanthomonas campestris pv. dieffenbachiae 25 mgL 1 daily irrigation 0% Not observed Syngonium podophyllum Chase, 1990 Xanthomonas campestris pv. dieffenbachiae 55 mgL 1 daily irrigation 40% Not observed Anthurium andraeanum Chase, 1990 Xanthomonas campestris pv. dieffenbachiae 55 mgL 1 daily irrigation 12% Not observed Dieffenbachia maculata Chase, 1990 Xanthomonas campestris pv. fici 55 mgL 1 daily irrigation 55% Observed (symptoms not specified) Ficus benjamina Chase, 1990 Xanthomonas campestris pv. fici 25 mgL 1, daily irrigation 0 or 60% b Not observed Ficus benjamina Chase, 1990 Xanthomonas campestris pv. hederae 55 mgL 1, daily irrigation 46 or 88% Observed (symptoms not specified) Hedera helix Chase, 1990 Xanthomonas campestris pv. hederae 25 mgL 1, daily irrigation 87% Not observed Hedera helix Chase, 1990 Xanthomonas campestris pv. malvacearum 55 mgL 1, daily irrigation 100% Observed (symptoms not specified) Hibiscus rosa sinensis Chase, 1990 Xanthomonas campestris pv. malvacearum 25 mgL 1, daily irrigation 76% Not observed Hibiscus rosa sinensis Chase, 1990 Xanthomonas campestris pv. pelargonii 25 mgL 1, daily irrigation 67 or 70% Not observed Pelargonium hortulanum Chase, 1990 a Rated in a 5 point scale where 1= none, white bench, and 5= complete green surface. b Results from two separate experiments c Under high disease pressure d Under low disease pressure
59 Table 2 8. Efficacy of membrane filtration for removal of waterborne microorganisms. Organism (Life stage) Pore size Flow rate Material Propagules removed (%) Crop References Pythium myriotylum (zoospores) 0.5 m prefiltered with 1.0 m 20 Lmin 1 Polypropylene membrane 88% a Capsicum annuum Schuerger and Hammer, 2009 Pythium aphanidermatum (zoospores) 20 m 57 Lmin 1 20 m Cartridge filter (model CFT25 with C5624 filter) 67% a Cucumis sativus Goldberg et al., 1992 Pythium myriotylum (zoospores) 20 Lmin 1 Polypropylene membrane 44% a Capsicum annuum Schuerger and Hammer, 2009 Pythium aphanidermatum (zoospores) 7m prefiltered with 20 m 57 Lmin 1 20 m membrane cartridge 7 m membrane cartridge 100% a Cucumis sativus Goldberg et al., 1992 Cylindrocladium candelabrum 0.05 m 40 mLmin 1 Fiber polymeric ultrafiltration 100% None Machado et al., 2013 Globodera rostochiensis, Meloidoigyne incognita, Radopholus similis 1m prefiltered with 1m, 80 m and 150 m 17 Lmin 1 Polyester felt filter bags (1, 80m) Metal gauze cartridge (150m) 100% None Moens and Hendrickx, 1992 Pythium aphanidermatum (zoospores) 5 m 50 Lmin 1 Fiber membrane strands 100% In vitro Tu and Harwood, 2005 Pythium aphanidermatum (zoospores) 5 m 50 Lmin 1 Celllulose polyester 100% In vitro Tu and Harwood, 2005 Botrytis cinerea 0.05 m 40 mLmin 1 Fiber polymeric ultrafiltration 99% None Machado et al., 2013 Pseudomonas solanacearum 0.3 m prefiltered with 10 m 27 Lmin 1 Poly sulphone 99% In vitro Ohtani et al, 2000 Ralstonia solanacearum 0.05 m 40 mLmin 1 Fiber polymeric ultrafiltration 99% None Machado et al., 2013 Xanthomonas axonopoid 0.05 m 40 mLmin 1 Fiber polymeric ultrafiltration 99% None Machado et al., 2013 Globodera rostochiensis, Meloidoigyne incognita, Radopholus similis 3m prefiltered with 5m and 150 m not specified Polypropylene filter bags (3,50m) Metal gauze cartridge (150m) 97% Moens and Hendrickx, 1992 a Reduction in disease incidence
60 Table 2 9. Efficacy of ultraviolet radiation for control of waterborne microorganisms. Organism (Life stage) Treatment dose (mJcm 2 ) Inactivated propagules (%) Crop References Agrobacterium tumefaciens 71 mJcm 2 15% Rosa sp. Poncet et al., 2001 Alternaria zinniae (spores) 850 mJcm 2 100% In vitro Mebalds et al., 1996 Colletotrichum capsici (spores) 31 mJcm 2 100% In vitro Mebalds et al., 1996 Fusarium oxysporum f. sp. lycopersici (conidia) 28 mJcm 2 92% Solanum lycopersicum Runia, 1994b Fusarium oxysporum f. sp. lycopersici (conidia) 28 mJcm 2 80% Rosa sp. Runia, 1994b Fusarium oxysporum f. sp. melongenae (conidia) 50 mJcm 2 96% Solanum melongena Runia, 1994b Fusarium oxysporum (spores) 30 mJcm 2 100% In vitro Mebalds et al., 1996 Fusarium oxysporum f. sp. chrysanthemi (conidia) 300 mJcm 2 100% a Gerbera sp. Minuto et al., 2008 Fusarium oxysporum f. sp. cyclaminis (conidia) 45 mJcm 2 (Water) 45 mJcm 2 (nutrient solution) 99.4% 75% In vitro Sutton et al., 2000 Phytophthora cinnamomi (spores) 43 mJcm 2 100% In vitro Mebalds et al., 1996 Pythium aphanidermatum 30 mJcm 2 100% Spinacia oleracea Stanghellini et al., 1984 Pythium aphanidermatum 88 mJcm 2 50% In vitro Tu and Zhang 2000 Pythium aphanidermatum (zoospores) 45 mJcm 2 >99.9% (water) < 90% (nutrient solution) In vitro Sutton et al., 2000 Pythium aphanidermatum (zoospores) 17 mJcm 2 (water) 38 mJcm 2 (nutrient solution) 100% In vitro Sutton et al., 2000 Pythium aphanidermatum (zoospores) 20mJcm 2 99% In vitro Tu and Zhang 2000 Pythium ultimum (spores) 40 mJcm 2 100% In vitro Mebalds et al., 1996 Tomato mosaic virus (ToMV) 118 mJcm 2 97% b Cucumis sativus Runia, 1994b Tomato mosaic virus (ToMV) 100 mJcm 2 99% b Solanum melongena Runia, 1994b a Disease incidence b Reduction in lesions caused by virus
61 Table 2 10. Efficacy of heat treatment for control of waterborne microorganisms. Organism (Life stage) Treatment (time, contact time) Inactivated propagules (%) References Agrobacterium tumefaciens 95 C, 30 sec 100% Poncet et al., 2001 Erwinia chrysanthemi 54C,15 sec; 50C,110 sec; or 46C,300 sec 99.80% Runia and Amsing, 2001 Erwinia chrysanthemi 42C,110 sec 30% Runia and Amsing, 2001 Fusarium oxysporum f.sp. lycopersici (conidia) 54C, 15 sec; or 46C, 200 sec 100 Runia and Amsing, 2001 Phytophthora cryptogea (zoospores) 44C,15 sec; or 40C for 90 sec 100% Runia and Amsing, 2001 Pythium aphanidermatum (zoospores) 51C,15 sec; or 47C, 45 sec 100% Runia and Amsing, 2001 Radopholus similis 49C for 15 sec 100% Runia and Amsing, 2001 Tomato Mosaic Virus 95C for 10 sec 100% Runia, 1995 Tomato Mosaic Virus 85C for 3 min 100% Runia and Amsing, 2001 Verticillium dahliae 90C, 10 sec 94% Runia, 1995
62 Table 2 11. Efficacy of slow filtration for control of waterborne microorganisms. Material Organism (Life stage) Propagules removed (%) References Antracite Xanthomonas campestris pv. pelargonii Antracite, grain size 0.8 1.6 mm at a flow rate of 200 lm 2 h 1 removed 82% of Xanthomonas campestris pv. pelargonii from a nutrient solution. Wohanka et al., 1999 Lava grain Phytophthora spp. Slow sand filtration at a flow rate between 566 lm 2 h 1 completely removed Phytophthora spp. from commercial nursery runoff. Ufer et al., 2008 Pumice Xanthomonas campestris pv. pelargonii Pumice grain size 0.4 4 mm at a flow rate 200 lm 2 h 1 removed 85% of Xanthomonas campestris pv. pelargonii from nutrient solution. Wohanka et al., 1999 Rockwool Xanthomonas campestris pv. pelargonii Rockwool granulate at a density of 136 kg m 3 at a flow rate 200 lm 2 h 1 removed 99% of Xanthomonas campestris pv. pelargonii from nutrient solution. Wohanka et al., 1999 Sand Fusarium oxysporum f.sp. chrysanthemi (conidia) Slow sand filtration at a flow rate of 200 lm 2 h 1 reduced 89% of the incidence of Fusarium wilt on Gerberas. Minuto et al., 2008 Sand Fusarium oxysporum f.sp. cyclaminis Slow sand filtration with an effective surface of 279 cm 2 at a flow rate of 200 lm 2 h 1 reduced the concentration of Fusarium oxysporum f. sp. cyclaminis in > 99.9%. Wohanka, 1995 Sand Pelargonium Flower Break Virus Slow sand filtration (200 lm 2 h 1 area 279 cm 2 ) reduced around 70% of Pelargonium Flower Break Virus and viral infection in geraniums from nutrient solution. Berkelman et al., 1995 Sand Phytophthora spp. Slow sand filtration at a flow rate between 269 to 300 lm 2 h 1 completely removed Phytophthora spp. from commercial nursery runoff. Ufer et al., 2008 Sand Phytophthora capsici Slow sand filtration at a flow rate of 148 lm 2 h 1 in a two meter long filter removed 100% of Phytophthora capsici from week 2 to 5. Lee and Oki, 2013 Sand Phytophthora capsici Slow sand filtration at a flow rate of 148 lm 2 h 1 in a two meter long filter did not removed Fusarium oxysporum from week 2 to 5. Lee and Oki, 2013
63 Table 2 11. Continued Material Organism (Life stage) Propagules removed (%) References Sand Phytophthora cinnamomi Slow sand filtration (sand grain size between 0.15 0.35 mm with a diameter of 15 cm and depth of 80 cm) at a filtration rate of 100 lm 2 h 1 removed 100% of Phytophthora cinnamomi from nutrient solution. Van Os et al., 1999 Sand Phytophthora cryptogea (zoospores) After week 3 of the establishment of the slow sand filtration system, 100% removal of Phytophthora cryptogea zoospores was observed. Calvo Bado et al., 2003 Sand Radopholus similis Slow sand filtration (sand grain size between 0.2 0.8 mm with a diameter of 15 cm and depth of 80 cm) at a filtration rate of 100 lm 2 h 1 removed 96% of Radopholus similis from nutrient solution after 21 days. Van Os et al., 1999 Sand Xanthomonas campestris pv. pelargonii Slow sand filtration (grain size 0.2 2 mm, depth 80 cm) removed 93% of Xanthomonas campestris pv. pelargonii Wohanka et al., 1999
64 Table 2 12. Efficacy of biosurfactants for control of waterborne microorganisms. Active Ingredient Organism (Life stage) Treatment dose (mgL 1 contact time) Inactivated propagules (%) Phytotoxicity Crop References Rhamnolipid Phytophthora capsici (zoospores) 150 mgL 1 continous 100% Reduction in biomass Capsicum annuum Nielsen et al., 2006 Rhamnolipid Phytophthora capsici (zoospores) 60 mgL 1 ,< 10 sec 100% N/A In vitro Stanghellini and Miller, 1997 Rhamnolipid Plasmopara lactucae radicis (zoospores) 60 mgL 1 ,< 10 sec 100% N/A In vitro Stanghellini and Miller, 1997 Rhamnolipid Pythium aphanidermatum (zoospores) 60 mgL 1 ,< 10 sec 100% N/A In vitro Stanghellini and Miller, 1997 Nitrapyrin Phytophthora capsici (zoospores) 12.5 mgL 1,a 69% b N/A In vitro Paggliacia et al., 2007 Nitrapyrin Pythium aphanidermatum (mycelia) 12.5 mgL 1,a 46% b N/A In vitro Paggliacia et al., 2007 Nitrapyrin Pythium aphanidermatum (mycelia) 12.5 mgL 1,a 40% c Reduction in biomass, chlorotic Cucumis sativus Paggliacia et al., 2007 a Single application in agar media b Reduction in mycelia growth c Reduction in plant mortality
65 Table 2 13. Number of citations found for efficacy studies on control waterborne microorganisms for a range of water treatment technologies. a Water treatment Genus Species In vitro References Biosurfactants 3 3 2 3 Bromine 10 13 0 3 Chlorine 16 27 13 20 Chlorine dioxide 15 15 7 1 Copper ionization 11 12 1 12 Copper salts 4 10 4 6 Filtration 3 4 2 5 Heat 8 8 0 3 Hydrogen peroxide and peroxyacetic acid 10 10 4 7 Ozone 9 9 4 7 Silver ionization 0 0 0 0 Silver salts 5 6 1 1 Slow media filtration 5 6 0 6 Ultraviolet light 7 8 3 7 a Literature review carried up on September, 2013
66 CHAPTER 3 MODIFIED DELPHI SURVEY ON ATTRIBUTES AND SELECTION OF WATER TREATMENT TECHNOLOGIES FOR HORTICULTURE Overview of the Research Problem Commercial greenhouse and nurseries use high water volumes, reportedly averaging over 54, 530 gal of water per hectare per day (Camberato and Lopez, 2010), and compete with other industries and drinking water for high quality sources. Irrigation water in greenhouse and nursery operations can be a source or dispersal mechanism for pathogens, algae and biofilm, especially when recirculated a nd surface water sources are used. A broad spectrum of plant pathogens, including oomycetes, fungi, bacteria, viruses, and nematodes have been detected in water sources or distribution systems (Hong and Moorman, 2005). Algae and biofilm can also be prob lematic in greenhouse production by clogging emitters (Bucks et al., 1979; Dehghanisanij et al., 2005; Gilbert et al., 1981; Juanico et al., 1994), harboring plant pathogens (El Hamalawi, 2007; Goldberg and Stanghellini, 1990; Hyder et al 2009) and causing worker safety issues. R eview articles on t echnical aspects of water treatment (Ehret et al., 2001; Fisher, 2013; Newman, 2004; Raviv and Lieth, 2007; Runia, 1995; Stewart Wade 2011; Van Os 2010; Zhou and Smith, 2001) have shown there is incomplete inform ation about the technologies and their interaction s with chemical and physical characteristics of water. Considerable research has been undertaken by plant pathologists on the efficacy of water treatment technologies for controlling waterborne pathogens. However, investigation has focused largely on chlorination and control of oomycetes with less information available for other combinations of technologies and target organisms (Raudales et al., 2013) There are limited data estimating phytotoxicity
67 thres holds for chemical water disinfectants. H owever the high levels of active ingredient required to control resistant pathogens suggest that in many cases the effective dose may cause phytotoxicity. K nowledge gaps remain about the compatibility of water tr eatment technologies with the many biological, chemical, physical, social, and economic factors that characterize greenhouse and nursery operations. All these possible factors make it difficult for growers to select a technology that best fits their opera tion. Horticulture growers are willing to adopt risk management strategies to prevent disease spread in their operations (Breukers et al., 2012). However, risk and uncertainty about disease management strategies affect decision making and represent a barr ier to adoption (McRoberts et al., 2012). Horticulture growers identified uncertainties about efficacy and costs as some of the barriers for adoption of disease management strategies (Breukers et al., 2012). Growers of ornamental crops indicated that a m ajor obstacle to implement sustainable practice s was the perception that the practices were not compatible with current operation systems (Dennis et al., 2010). Uncertainties about adopt ing a practice or technology lessen with time as grower acquire of in formation by experience or knowledge (Breukers et al., 2012; Feder and Umali, 1993; Marra et al., 2003; McRoberts et al., 2011; Rogers et al., 2003). Rogers ects of innovations as the information or knowledge about the performance of the technology. Some researchers have proposed that models on adoption of innovations in agriculture should consider interrelationship s associated with the innovation, such as ch anging chemical applications and fertilization practices when
68 adopting a new plant variety (Feder, 1982; Smale and Heisey, 1993). Adoption of innovations in agriculture therefore requires consideration of additional factors other than the technology itsel f. Such factors can include operation size, adaptability to current infrastructure, perceived technical benefits, ease of use, costs, financial benefits, external incentives, and public policy among others (Adesina and Zinnah, 1993; Feder and Umali, 1993; Loo et al., 2012; Mangiafico et al., 2008; Padel, 2002; Rogers, 2003; Sunding and Zilberman, 2001). Plant disease management is a human decision making process that would benefit from interdisciplinary research that combines social and natural sciences (McRoberts et al., 2011; Gent et al., 2011). Interdisciplinary research by plant pathologists, horticulturists, chemists, engineers, environmentalists, economists, and social scientists would be required to make a thorough analysis of all the factors that characterize water treatment technologies for use in greenhouses and nurseries. However, given budget constraints on experimental research to resolve existing knowledge gaps, it is appropriate to utilize non experimental, but systematic, research designs The Delphi method involves soliciting a group of experts on an individual basis using a series of questionnaires to reach consensus about a problem for which quantitative data are not available or experimental research designs are not feasible (Brown and Helmer, 1968; Dalkey and Helmer, 1963; Murray, 1979). In other words, the Delphi method is a structured communication process used to predict outcomes based on consensus of a group of experts (Mirtroff and Turoff, 2002). The Delphi survey method is base d on the epistemology of inexact sciences which convey quasi
69 laws based on past knowledge, experience, and critical analysis of the experts for prediction of a problem (Helmer and Rescher, 1959). Quasi laws cannot be derived from simplified observations, and are instead inferred by the experience and views of the experts of complex situations (Aligica and Herritt, 2009 ; Helmer and Rescher, 1958). A major distinction between the Delphi survey and other types of survey is that the expert panel has the oppor tunity to anonymously reconsider their answers based on their reaction to the group responses (Helmer and Rescher, 1959; Mitroff and Turoff, 2002). Selection of the expert panel undeniably involves some degree of bias by researchers as random selection of the experts is not possible given the demand of specific knowledge and experience (Hasson et al., 2000). Alternatives to deal with researcher bias on selection of the expert panel are self rating of expertise (Brown and Helmer, 1964), peer nomination of experts (Murray, 1979), and selection based on indicators such as publications, research programs, or public presentations (Helmer and Rescher 1958). Dalkey and Helmer (1963) designed the method as an anonymous survey to stimulate independent thinking by each of the participants. The Delphi method is carried out under anonymous conditions to prevent influence from other bandwagon effect standard definition of consensus, and some external factors (such as budget or time frame of project) might influence how consensus is defined. Consensus among the experts is defined a priori by the researchers with the goal of matching consensus to the objective of the research question (Hasson et al., 2000; Mitroff and Turoff, 2002; Sackman, 1974).
70 Specific objectives of this research were (1) to identify the perceived key a ttributes of water treatment technologies that should be considered by growers when selecting a technology for their operation; and (2) to characterize 14 available water treatment technologies in terms of these a ttributes. The Delphi survey method was used to evaluate these objectives. Results of this survey were intended as a first step to develop a framework of selection criteria for water treatment technologies in irrigation for control of waterborne pathogens algae, and biofilm Materials and Methods sion water treatment workshops hosted by the Water Education Alliance for Horticulture, which is a university/industry education consortium. of a list of companies with products or services focused on the des ign, installation and scientists who had published articles and/or had known experience on water treatment. The names of the individuals who participated and their associatio n remained anonymous throughout the process. A list of 23 3 1 ) that were potentially important in technology selection was developed based on informal grower and industry feedback by surveying during cooperative extension works hops. Water treatment technologies included calcium hypochlorite, chlorine dioxide, chlorine gas, copper ionization, copper sulfate, filtration (excluding membrane filtration), heat treatment and pasteurization,
71 hydrogen peroxide hypochlorous acid, ozone reverse osmosis/ membrane filtration, silver ionization, sodium hypochlorite, and ultraviolet radiation. A draft survey was developed with online Qualtrics (Qualtrics Labs, Inc., Provo, Utah, USA) software. The survey was approved by the University of Florida Institutional Review Board 02 under the protocol # 2010 U 1178. In a pilot study, this version of the survey was sent for clarification and verification to a subset of the Expert Panel of 8 people from the three Expert Types. The survey was amen ded with minor changes based on the feedback received. Round 1 The revised survey was sent to Expert Panel members, who were contacted contact was via email two weeks pri or to sending the survey informing them about their selection as part of the Expert Panel and the upcoming survey. The survey was first sent via email on January 07, 201 1. Over a period of four months, four reminders were sent to the Panel including one postcard and three emails. Round 1 of the survey was closed on May 04, 2011. A booklet was sent to the Expert Panel in appreciation for completing Round 1 of the survey, with notification that a second Round was forthcoming. The first Round of the survey consisted of several sections. The demographics section requested information on their job title, organization, years of experience with water treatment technologies, and an open ended question on that experience. Growers only were also surveyed as to t heir reasons for adopting water treatment technologies, the area of crop production, and which technologies were currently in use at their operation. For objective 1, which aimed to identify important factors in
72 technology selection, all Experts were aske d to evaluate the importance of different Attributes in the selection between water treatment options. In this section, Experts rated their level of agreement (on a Likert scale f rom 1=strongly disagree, 3= neither agree or disagree, to 5 = strongly agree) that each of the 23 Attributes listed was an important selection criterion. A third section asked Experts to self rate their level of Expertise for each of 14 technologies using a Likert scale from 1= no knowledge, 2= beginner, 3= informed without direct exp erience, 4 = informed with direct working experience, to 5 = Expert. A fourth section related to objective 2, which was to identify the Attributes of each technology. The Qualtrics software dynamically presented questions only on technologies for which a pa rticipant had a self rated Expertise level of participant based on a level of agreement (with a Likert scale from 1=strongly disagree to 5= strongly agree) that each of the Attributes listed accurately des cribed a specific technology. In Round 1, open questions were also provided to allow comments about each of the Attributes and technologies. Round 2 The survey was sent to the sub group of the Expert Panel who answered the questionnaire in Round 1. The Round 2 questionnaire included only sections 3 and 4 described for Round 1, and in this Round the average Expert Panel response for each n where the participant agreed with the Round 1 response, the participants were asked to leave this value unchanged. If a participant disagreed with any Round 1 response, the participants were asked to indicate their own response on the Likert scale. Rou nd 1
73 responses left unchanged were therefore assumed to indicate agreement by the participant. Average rating and the percentage of agreement among Experts were the two charact erize water treatment technologies. An a verage rating >3.0 indicated that the Expert Panel perceived the Attribute to characterize the technology and an average rating o f 3.0 has been used as point of acceptance or rejection by other researchers (Duffield, 1993). When fewer than 30% of respondents changed the rating between Panel, whereas cha This threshold was based on the consensus level of 70% that has been previously used by other researchers (Loughlin and Moore, 1979; McKenna, 1994; Slaughter et al. 1999; V an Steenkiste et al ., 2002). Analysis of variance was used (PROC GLM ) in SAS ( version 9.2, SAS institute, Cary, NC) to analyze main and interaction effects of Expert Type and Attribute, and the main effect of years of experience in objective 1 (importance of Attributes in te chnology selection). For objective 2, to determine Attribute values for each technology, ANOVA was run by Attribute using PROC GLIMMIX (SAS 9.2, SAS institute, Cary, NC), with main and interaction effects of Expert Type and Technology, and the main effect of P 0.05 level.
74 Results and Discussion Demographics The response rate of the survey was 59% and 60% for Rounds 1 and 2, respectively. The sample population that responded to Round 1 included 27 Grower, 15 Industry, and 21 Researcher individual s compared with 15 Grower, 9 Industry, and 14 Researchers in Round 2. The majority (54%) of the Expert Panel self rated as having more than 10 y ears of experience, with 26% or 20% self rated as having 5 to 10 years, or less than 5 years of experience, respectively. Silver ionization was the only technology where only two of the three Expert types where represented (Industry and Researcher) (n=7 i ndividuals), with no Growers represented, and no growers in the survey group had direct experience with using silver ionization. control treatment technology. The operation si ze of the growers who participated in the survey ranged from 1 to 51 ha of covered greenhouse, 1 to 28 ha of open field production area, and 1 to 61 ha of total production area. The areas of greenhouse and open area production in the Grower group totaled 1 85 and 96 hectares, respectively. The mean value for operation areas for greenhouse and open area were 8 and 4 hectares, respectively. Growers indicated that the technologies currently used either alone or in combination with other technologies were coppe r (n=9), chlorine (n=4), activated peroxygens (n=4), chlorine dioxide (n=4), ozone (n=2), reverse osmosis (n=2) and rapid sand filtration (1).
75 Objective 1 Attributes for selection of water treatment technologies Attributes In choosing the Attributes that should be considered when selecting water treatment technologies, the perceived importance differed between Attributes ( P <0.001 ) and there was an interaction between Expert Type and Attribute ( P=0.0002 ). There was no main effect of Expert Type ( P=0.244 ) affect response ( P=0.0011 ) (Table3 1 ). treatment technologi es. An average rating of 3 was previously set as the threshold for consideration in Round 2, and all 23 Attributes were therefore conserved (Table 3 1). was not significantly different from 11 other Attributes that included aspects related to efficacy against a range of target organisms, practical aspects of worker safety and operation, and regulatory considerations. Operating and capital costs were lower ranked ranked lower than controlling plant pathogens, algae, and biofilm. Expert types and experi ence The perceived importance of Attributes associated with control of algae, biofilm, and human food safety pathogens differed between Expert Types. However, all Expert Re 0.48, mean standard deviation) was lower than the opinion of Growers (4.930.72)
76 technolog (3.920.92) and Researchers (3.940.57). L ower rating of biofilm control and control of human food safety pathogens by Growers compared with other Expert Types presumably meant that Growers perceived these problems to be of lower importance in their own production systems. The Gro wer population was primarily producing ornamental rather than edible crops, and may therefore have been less sensitive to human food safety pathogens than other Exp ert Types. dual effect through the entire ). The overall perceived importance of Attributes was greater for Experts who self rated as having either more than 10 years of experience or less than 5 years of experience (4.19 for both groups), compared with the group who self rated as having the int ermediate 5 to 10 years of experience (4.00). Despite a statistical significant effect of years of experience, there may not be a practical significance in this difference. Objective 2 Comparison of attributes between technologies In the next survey sectio n which evaluated Attributes of each technology, the rating scale indicated how strongly participants perceived that a particular Attribute characterized each individual technology. In the ANOVA that evaluated effects of Technology, Expert Type, and year s of experience on Attribute ratings, there were
77 differences between technologies ( P <0.05) for all 23 Attributes. For six Attributes, ratings differed across technologies between Expert Types. Across technologies, Industry considered that water treatment had a higher initial capital cost and was not as suitable for small operations or small volumes, compared with other Expert Types. Researchers had a higher perception that water treatment technologies were able to control plant pathogens, biofilm, human f ood safety pathogens, and removal of pesticides and herbicides compared with Growers and Industry. The highest rating for rated among Researchers, followed by Industry and then Growers. Silver ionization was removed from the analysis because of small sample size (n=7) Cost The water treatment technologies calcium hypochlorite, chlorine dioxid e, chlorine gas, copper sulfate, hydrogen per oxide, hypochlorous acid, a nd sodium hypochlorite based on an average rating above 3 .0 (Table 3 2). All of these technologie s require a fairly sim ple, low cost injection system to deliver the dosage (Parke and Fisher, 2012). Copper ionization, filtration, h eat treatment, ozone, re verse osmosis and UV radiation were not considered to have low initial capital cost, with average ratings below 3. Copper ionization was the only technology where at least 30% of Experts disagreed in ratings of initial capital cost between Rounds 1 and 2, indicating a lack of consensus on this Attribute. Calcium hypochlorite, chlorine dioxide, chlorine gas, copper ionization, copper su lfate, filtration, hypochlorous acid, and sodium hypochlorite had average ratings above 3 .0 (Table 3 2),
78 although more than 30% of Experts disagreed on ratings of ozone and hydrogen peroxide between Rounds 1 and 2. A preliminary cost analysis indicates that operation costs for the different technologies can range widely between $0.25 up to $1.00 per 1000 gal of water treated (Fisher, 2013). Considering the large volumes of water used fo r irrigation minor changes in operation costs could result in large annual costs. A cost comparison of UV radiation and chlorine dioxide for control of Phytophthora cinnamomi in nurseries in Australia indicated that the capital and operation costs of chl orine dioxide were higher than UV when the daily water use ranged between 5,000 to 100,000 L per day (Mebalds, 1996). However, the capital cost of chlorine dioxide did not change between 10,000 and 100,000 L of water per day, suggesting that chlorine diox ide may be more cost effective for treating large volumes of water. No comprehensive studies that compare the cost of other water treatment technologies for use in irrigation are available. System size All treatments other than chlorine gas were consider average rating above 3 (Table 3 2). However, there was no consensus (more than 30% of Experts disagreed between Rounds 1 and 2) regarding the sui tability of chlorine dioxide, chlorine gas, hypochlorous acid, ozone, reverse osmosis, and UV radiation for small operations. Heat treatment copper sulfate and hydrogen peroxide were not considered to be suitable for large operations (Table 3 2). M ore t han 30% of the Expert Panel disagreed on the ratings for the suitability of chlorine dioxide, hydrogen peroxide and ozone for large operations.
79 Among the technologies being used by the Grower group at the time of the survey, the only technologies used in small operations under 2 ha were chlorine dioxide in stabilized packets with single stock tanks (a 0.5 ha operation) or copper ionization (1.0 h a). Copper ionization was the water treatment technology used in the widest range of operation sizes (3.6 to 40 .5 ha), followed by chlorine dioxide generators (3.6 to 40.5 ha), and sodium hypochlorite (10.1 to 40.5 ha). Although only 13% of growers indicated they were using non membrane filtration, it is likely that screen or other filters were in use in all opera tions. Calcium hypochlorite and chlorine gas were used in individual operations of 9.3 and 4.0 ha, respectively. Hydrogen peroxide, ozone and reverse osmosis were used in operation sizes ranging between 4 to 10.1 ha, 10.1 to 20.2 ha, and 2.4 to 6.5 ha, r espectively. Control of microorganisms Filtration (excluding membrane filtration) was rated 3 for all the Attributes relat ed to control of microorganisms including plant pathogens, algae, biofilm, and human safety pathogens (Table 3 2 ). All other techno logies had mean ratings above 3 for controlling algae and plant pathogens. Both forms of copper and filtration had a There was more than 30% disagreement among the Expert Panel on two or mor e Attributes related to control of algae, plant pathogens, biofilm or human food safety organisms for the technologies chlorine gas, copper ionization, filtration, hydrogen peroxide reverse osmosis, and UV radiation. Membrane filtration with small pore si ze (<10m) or slow media filtration are the only filtration options for removal of microorganisms from water (Ehret et al., 2001; Stewart Wade, 2011; Van Os 2010). Multiple stages of membrane filtration were more
80 efficient in removing plant parasitic nematodes than a single filtration stage in experimental research ( Moens and Hendrickx, 1992; Ohtani et al, 2000 ). Disagreement among the Expert s for ratings related to filtration (excluding membrane filtration) may have arisen because slo w media filtration was not specifically included as a technology in the survey. In contrast to screen filters, slow media filters significantly decreased Fusarium oxysporum Pelargonium Flower Break Virus; Phytophthora cinnamomi, Phytophthora cryptogea, R adopholus similis and Xanthomonas campestris (Berkelma n n et al, 1995; Calvo Bado et al., 2003; Minuto et al., 2008; Wohanka, 1995; Wohanka et al., 1999; Van Os et al., 1999 ) Copper ionization was rated 3.6 for the Attribute Ho wever, 46% of Experts disagreed between rounds with this rating, indicating a lack of consensus A h igh level of disagreement may have arisen because copper ionization requires extended a typical dose of 1 to 2 mg L 1 for effective control of plant pathogens. For example, Agrobacterium tumefaciens Clavibacter michiganensis, Erwinia carotovora, Ralstonia solanacearum Xanthomonas hortorum treated with 2 mg L 1 required 24, 2, 1, 1, and 4 hours, respectively, to achiev e 90% mortality of pathogen propagules (Wohanka and Fehres, 2006a; 2006d; 2007a; 2007b; Wohanka et al., 2007). In contrast, other combinations of lower doses or contact times were ineffective in controlling these pathogens and certain pathogens ( Fusarium oxysporum, Pythium aphanidermatum, and Trichoderma asperellum ) were resistant to copper ionization treatment at 4 mg L 1 Fehres, 2006b; 2006c; Wohanka et al., 2009). Extended contact times are unlikely to
81 occur in commercial greenhouse and nursery operations, unless treatment is applied in storage tank s with long residual time. All technologies other than filtration, reverse osmosis, and UV radiation were considered to be effective at controlling biofilm. Because biofilm resides inside irrigation distribution lines, the point treatment nature of the three aforementioned technologies, and therefore the lack of residual effect, reduces their potential efficacy in controlling biofilm. Biofilms are a matrix of polymer s with a complex community of microo rganisms attached to a surface (Costerton et al., 1995; O'Toole et al., 2000; Stoodley et al., 2002). The metabolic behavior and structure of biofilms is highly dependent on the microbial composition of the biofilm (Cos terton et al., 1995; O'Toole et al., 2000; Stoodley et al., 2002). In general, microbes attached to surfaces are more resistant to control than planktonic organisms (Bois et al., 1997; LeChevallier et al., 1988). 1 chlorine reduce d the density of coliform pathogens in the biofilm, and resulted in release of biofilm particles but it did not completely control biofilm (Morin et al., 1996). All technologies except copper ionization and filtration were considered to be effective at c ontrolling human food safety pathogens (Table 3 2). Inactivation of human pathogens has been widely studied in drinking water (Maier et. al, 2009). I rrigation water has been identified as a potential source of human food safety pathogens (Alsanius et al, 2011; Gortres Moroyoqui et al., 2011; Ijabadeniyi et al., 2011; Lewis Ivey and Miller, 2013; Steele et al., 2005). Irrigation water treated with chlorine gas or chlorine dioxide ( both at residual concentrations of 1 1 ) in combination with slow sand filtration were not effective in reducing coliform bacteria levels to the US EPA
82 required levels (Lewis Ivey and Miller, 2013). Control and monitoring of food safety pathogens in irrigation will be necessary given increasing regulation to reduce the risk of water borne contamination of fresh produce by human pathogens (FDA, 2013) More research is required to determine synergistic efficacy of control of plant pathogens and human pathogens. Effect on nutrient or inorganic molecules C alcium hypochlorite, c opper ionization, copper sulfate, filtration, hypochlorous acid and UV radiation were 3 3). Ozone, which obtained the highest rating (3.6) for this attribute is commonly u sed to remove pesticides to protect natural water resources and in drinking water supplies (Chiron et al., 2000). Ozone oxidizes directly or via hydroxyl free radicals, which is the strongest oxidizer form (Hoign and Bader, 1976). Hydroxyl free radicals can result in complete mineralization of molecules (Chiron et al., 2000). Other technologies may be used alone or in combination with other technologies to reduce pesticide levels in irrigation water, including; r everse osmosis carbon filtration, chlori nation (or other oxidizers), and UV radiation (Chian et al., 1975 ; Chiron et al., 2000; Kamel et al., 2009 ; Lafi and Al Qodah, 2006 ; Legrini et al., 1993) Calcium hypochlorite, copper sulfate, h ydrogen peroxide, hypochlorous acids, ozone, reverse osmosis and sodium hypochlorite were the only technologies with the Attribute O zone can oxidize manganese, iron, and any other micronutrient chelates (Ohashi Kaneko et al., 2009; Vanachter e t al., 1988). Reverse osmosis removes most nutrients from irrigation water (Runia 1995). Calcium hypochlorite, hydrogen peroxide, hypochlorous acid and sodium hypochlorite were also rated 3.0 presumably because it is assumed
83 that they are a strong enou gh oxidizers to affect organic chelates although data are not available Sensitivity to water quality parameters Several technologies including calcium hypochlorite, chlorine dioxide, chlorine gas, copper ionization, copper sulfate, hydrogen peroxide, hyp ochlorous acid, and (Table 3 3 ). More than 30% of Experts disagreed for ratings of calcium hypochlorite, chlorine gas, copper ionization, sodium hypochlorite for this Attribute. Hypochlorous acid, which is the active ingredient of calcium hypochlorite, chlorine gas, hypochlorous acid, and sodium hypochlorite, has decreased sanitizing activity as pH increases ( White, 1992 ; Lang et al., 2008). Chlorine dioxide is e ffective at a wider pH range than other chlorine forms (Faust and Aly, 1983). Copper solubility also decreases with increasing pH (Lindsay, 1979), which could reduce efficacy of copper ionization and copper sulfate. All the technologies had ratings above Higher EC facilitates electrolysis in solutions, and therefore ionization of copper or silver (Fischer et al., 2008). Copper ionizat ion units currently used in horticulture differ in their ability to adjust to the changing EC that commonly occurs in greenhouses using water soluble fertilizers, and the authors have frequently measured doses of copper lower than the target concentrations in commercial greenhouse installations. F iltration (excluding membrane filtration), heat treatment and reverse osmosis were the only technologies rated above 3 for the Effective in water with 3 3). More than 30% of the Experts disagreed about the average rating of heat treatment and UV radiation. All the chemical
84 sanitizers are affected by the presence of organic particles in the solution because the particles exert chemical sanitizer demand ther efore reducing the residual active ingredient for sanitizing water. It is well known that UV radiation efficacy is affected by the presence of organic and inorganic particles that block the transmission of radiation to the target organism (Yiaosumi et al. 2005). One of the principle roles of filtration in water treatment is to reduce suspended solids and sanitizing agent demand (Maier et al., 2009), and survey results reinforce the importance of filtration as an essential component of any water treatment system design. In addition, the rating and the disagreement for UV radiation indicates the need to educate growers on water clarity and pre treatment when using UV radiation for sanitation. e in solutions 3 3). However, in a study where chlorine interacted with ammonium, a reduction in oxidation reduction potential (ORP) and free chlorine were observed (Meador and Fisher, 2013 ), which would be exp ected to occur because of conversion of hypochlorous acid to chloramine (Deborde and v on Gunten, 2008). It is unknown how chloramines affect the efficacy to control plant pathogens Research on human health found chloramine was more effective than chlori ne in reducing the incidence of Legionella and biofilm buildup (Lin et al., 2011), however longer contact times are required (Degr mont, 1979 ) Residual effect Filtration (excluding membrane filtration), heat treatment, ozone, reverse osmosis and UV radiat ion were not considered to have Has a residual effect 3 3) As discussed early in relation to biofilm control, most of these technologies are characterized as point treatments, in contrast
85 with c hemical s that are transported through the irrigati on system (Stewart Wade, 2011) Ozone is an unstable oxidant with fast reaction in water (Hoign and Bader, 1994) which by definition reduces its residual activity Copper ionization, f iltration (excluding membrane filtration), heat treatment, ozone, reverse osmosis and UV radiat ion were perceived to have 3 ). However, more than 30% of the Expert panel disagre ed on the ratings for chlorine dioxide, copper ionization, heat treatment, ozone, reverse osmosis, sodium hypochlorite and UV radiation for one of the Attributes related to residual effect (Table 3 3). 1 (Cayanan et al., 2009), 1 (Rens, 2011), ozone at 0.9 1 (Graham et al., 2009), and hydrogen peroxide at 8 1 (Vnninen and Koskula, 1998) have resulted in phytotoxicity of diverse crops. Ease of use Copper sulfate, hypochlorous acid, ozone, a nd UV were not considered to have the Attribute operation (Table 3 4). More than 30% of the Expert Panel disagreed with the ratings on ease of monitoring for copper ionization, heat treatment, hydrogen per oxide and ozone. I nline and handheld devices and kits are available for onsite monitoring active ingredients of sanitizing agents (Fisher, 2013). Chlorine gas and sodium hypochlorite were the only technologies perceived as not being (Table 3 4) Chlorine based products have been categorized in Toxicity Category I, which is the highest degree of acute toxicity ( US EPA 1999) Chlorine dioxide, chlorine gas, ozone, and reverse osmosis were not considered to have the Attribute imple to use and does not 3 4 ). Chlorine gas, ozone, reverse
86 osmosis, and UV radiation were not considered to have the Attribute maintenance for calibration, cleaning, or replacing parts (Table 3 4). All technologies were rated for the Attribute 3 4). Regulation Chlorine gas was the only technology not considered to have the Attribute (Table 3 4). More than 30% of the hlorine dioxide and chlorine gas (Table 3 4) US EPA under the National Primary Drinking Water Regulations (NPDWRs) created a list of disinfectants and disinfection byproduct contaminants specifying the maximum contaminant level (MCL) for various sanitiz ers and their byproducts for public water sources (Tarver, 2008; US EPA 2013). The MCL for disinfectants are 0.8 mg L 1 for chlorine dioxide and 4 mg L 1 for chlorine as annual average (Tarver, 2008; US EPA 2013). The MCL for disinfectant byproducts ar e 0.01 mg L 1 for bromate, 1.0 mg L 1 for chlorite, 0.06 mg L 1 for halo acetic acids (HAA5), 0.10 mg L 1 for total trihalomethanes (Tarver, 2008; US EPA 2013). Copper, which is listed under the inorganic chemicals contaminant, has an action level of 1.3 mg L 1 ( US EPA 2013). The action level (Tarver, 2008). Implications of the Research The results of this survey confirmed that decision making for selection of water treatment technologies is multifaceted. Hence multidisciplinary approaches are required to accurately model the selection process of water treatment technologies in
87 irrigati on. D isagreement among experts, and lack of published quantitative research data, highlight areas of needed research and outreach. For example, the Expert Panel disagreed on 11 of 24 Attributes that characterized copper ionization and in 8 of 14 technolo E fficacy of copper ionization for control of plant pathogens has received little attention and m ost of the available information comes from research reports generated in Europe by Wohanka and Fehres (2006a, 2006 b, 2007a, 2007b, 2009), two peer reviewed articles by Toppe and Thingaard (1998, 2000) and a peer reviewed article by Hopkins et al. (2009). Technologies vary widely in the number of published efficacy studies (Raudales et al., 2013) with c hlorine being the most studied technology. Aspects other than control of plant pathogens, such control of biofilm or algae, or e conomic analysis of technology options, have received little attention despite the importance of these factors as identified by the survey pa nel M ore quantitative research on this topic will ensure that growers successfully meet future regulatory requirements to capture and recirculate water and comply with food safety regulations Although the results of this survey do not substitute for qu antitative experimental data, the information surveyed current perceived attributes of each technology This analysis provided the necessary information for the development of a framework that will facilitate the decision making process for growers by pro viding selection criteria of water treatment technologies in irrigation for control of waterborne microbial problems. Growers and extension agents can identify the selection criteria that are priorities for the target operation and match the se priorities with the strengths and weaknesses of each technology
88 Table 3 1. Perceptions of an Expert Panel solicited via Delphi survey that each Attribute is important when selecting between water treatment technologies. Expert Panel was composed of growers of ornamental crops, researchers, and water treatment industry supplies. Attribute n Mean a,b If residues are present, they are not toxic to plants 54 4.7 a Controls plant pathogens 54 4.6 ab Is suitable for large operations (>5 acres or > 10,000 gal per day) 50 4.6 abc Easy to monitor active ingredient and efficient operation 53 4. 6 abc Low risk of environmental impacts if treated water runs off from property 54 4. 6 abc Is safe for workers to use 53 4. 6 abc Controls algae 54 4.4 abcd Controls biofilm 52 4.3 abcd Regulatory permission is unlikely to be an obstacle 54 4.3 abcd Requires minimal maintenance for calibration, cleaning, or replacing parts 53 4.3 abcd Is suitable for small operations (<2 acres) or small volumes (such as mist systems) 49 4.2 abcde Is effective in solutions containing water soluble fertilizers 52 4.2 abcde Has low operating cost per volume of irrigation water 54 4.2 bcde Has a residual effect through the entire irrigation system 54 4.1 bcde Fertilizers including micronutrients are not affected 51 4.1 cde Is effective in water with suspended organic or inorganic particles 52 4.0 cde Is simple to use and does not require specialist training for workers 52 4.0 cde Has a long shelf life of materials (>3mo nths) 53 3.9 def Controls human food safety pathogens 54 3.7 efg Is effective with low electrical conductivity ( EC ) water 52 3.7 efg Has a low initial capital cost 54 3.4 fg Is effective at high water pH 52 3.4 fg Removes or oxidizes pesticides or herbicides 50 3.3 g a The mean rating is based on a Likert scale from 1(strongly disagree) to 5 (strongly agree). b P< 0.0 5.
89 Table 3 2. Comparison between technologies of Attributes associated with cost, system size and control of microorganisms a, b Ratings were provided by an Expert Panel, via a Delphi survey, who was asked to rate their level of agreement that each Attribute characte rized the listed technology. On a second round, the Expert Panel was asked to express their agreement with the average rating of Round 1. Cost System size Control of microorganisms Has a low initial capital cost Has low operating cost per volume of irrigation water Is suitable for small operations (<2 acres) or small volumes (such as mist systems) Is suitable for large operations (>5 acres or > 10,000 gal per day) Controls algae Controls plant pathogens Controls biofilm Controls human food safety p athogens Calcium hypochlorite 4.1 a 3.8 abc 3.8 ab 3.6 ab 3.7 ab 4.0 a 3.4 ab 3.7 ab Chlorine dioxide 3.4 abc 3.2 abcd 3.6 abc 3.5 ab 4.1 a 4.3 a 4.2 a 4.0 a Chlorine gas 3.2 bc 3.7 abc 2.8 c 4.0 a 3.7 ab 4.2 a 3.6 ab 3.9 a Copper ionization 2.9 bcd 3.8 abc 3.9 ab 4.0 a 3.9 ab 3.6 ab 3.2 bc 2.8 c d Copper sulfate 3.7 abc 3.3 abcd 4.0 ab 3.0 ab 3.8 ab 3.4 ab 3.3 abc 3.0 bc d Filtration c 2.9 cd 4.0 a 4.1 a 4.0 a 2.7 c 3.0 b 2.5 c 2.4 d Heat treatment 2.1 de 2.5 d 3.2 abc 2.9 b 3.9 ab 4.3 a 3.1 bc 3.5 abc Hydrogen peroxide 3.8 ab 2.8 cd 3.8 ab 3.0 b 3.7 ab 3.8 ab 3.6 ab 3.6 abc Hypochlorous acid 3.4 abc 3.2 abcd 3.6 abc 3.2 ab 3.7 abc 3.6 ab 3.5 ab 3.6 abc Ozone 1.9 e 3.0 bcd 3.1 bc 3.7 ab 3.8 ab 3.9 a 3.3 abc 4.0 a Reverse osmosis 1.7 e 2.5 d 3.4 abc 3.2 ab 3.2 bc 3.5 ab 2.9 bc 3.6 abc Sodium hypochlorite 4.1 a 3.9 ab 3.8 ab 3.8 ab 4.0 ab 4.0 a 3.4 ab 3.9 a UV radiation 1.9 e 3.0 bcd 3.5 abc 3.2 ab 3.5 abc 3.8 ab 2.9 bc 3.6 abc a test at P <0.0 5 b Underlined values indicate there was more than 30% disagreement between experts from Round s 1 to 2. c The technology was l isted in the survey as
90 Table 3 3 Comparison between technologies of Attribute s associated with sensitivity to water quality parameters, effects on nutrients or inorganic molecules, and residual effect a,b Ratings were provided by an Expert Panel, provided via Delphi survey, who were asked to rate their level of agreement that each Attribute characterized the listed technology. On a second round, the Expert Panel was asked to express their agreement with the average rating of Round 1. Technologies Effects on nutrients or inorganic molecules Sensitivity to water quality parameters Residual effect Removes or oxidizes pesticides or herbicides Fertilizers including micronutrients are not affected Is effective at high water pH Is effective with low EC c water Is effective in water with suspended organic or inorganic particles Is effective in solutions containing water soluble fertilizers Has a residual effect through the entire irrigation system If res idues are present, they are not toxic to plants Calcium hypochlorite 3.0 abc 3.0 abc 2.6 d 3.7 ab 2.5 cd 3.3 b 3.3 abc 2.7 d Chlorine dioxide 3.2 ab 3.4 ab 3.0 cd 3.6 ab 2.9 b c d 3.6 ab 3.6 abc 2.8 cd Chlorine gas 3.1 ab 3.2 abc 2.5 d 3.8 ab 2.9 b c d 3.5 ab 3.7 a 2.5 d Copper ionization 2.3 cd 3.5 ab 2.9 cd 3.1 b 3.0 b c 3.7 ab 3.5 abc 3.1 abcd Copper sulfate 2.0 d 3.0 abc 3.0 bcd 3.5 ab 2.9 b c d 3.6 ab 3.5 abc 2.3 d Filtration d 2.5 bcd 3.7 a 4.1 a 4.1 a 4.1 a 4.1 a 2.7 bc 4.0 a Heat treatment 2.4 bcd 3.2 abc 3.7 abc 4.1 a 3.7 ab 3.9 ab 2.4 cd 3.7 abc Hydrogen peroxide 3.1 abc 2.8 bc 3.0 cd 3.7 ab 2.8 b c d 3.5 ab 3.2 abc 3.3 abcd Hypochlorous acid 2.9 abcd 3.0 abc 2.6 d 3.4 ab 2.6 bc d 3.5 ab 3.4 abc 2.7 cd Ozone 3.6 a 2.5 c 3.4 abcd 3.8 ab 2.5 cd 3.3 b 2.7 abc 3.0 bcd Reverse osmosis 3.2 ab 2.5 c 4.0 ab 3.9 a 3.6 ab 3.2 b 2.7 abc 3.9 ab Sodium hypochlorite 3.1 abc 3.0 abc 2.6 d 3.9 a 2.6 b c d 3.5 ab 3.7 ab 2.4 d UV radiation 2.6 bcd 3.1 abc 4.0 ab 4.1 a 2.0 d 3.4 ab 1.7 d 4.1 a a test at P<0.05. b Underlined values indicate there was more than 30% disagreement between experts from Rounds 1 to 2. c EC refers to electr ical conductivity, which is an indirect measurement of total ion concentration. d
91 Table 3 4 Comparison between technologies of Attribute s associated with ease of us e and regulation a,b Ratings were provided by an Expert Panel, via Delphi survey, who were asked to rate their level of agreement that each Attribute characterized the listed technology. On a second round, the Expert Panel was asked to express their agree ment with the average rating of Round 1. Ease of use Regulation Technologies Easy to monitor active ingredient and efficient operation Is safe for workers to use Is simple to use and does not require specialist training for workers Has a long shelf life of materials (>3months) Requires minimal maintenance for calibration, cleaning, or replacing parts Low risk of environmental impacts if treated water runs off from property Regulatory permission is unlikely to be an obstacle Calcium hypochlorite 3.5 3.4 dbc 3.5 abc 3.5 abc 3.3 ab 3.2 cd 3.6 ab Chlorine dioxide 3.3 3.1 dc 2.6 ecd 3.0 c 3.0 ab 3.5 bcd 3.6 abc Chlorine gas 3.5 2.2 e 1.9 e 3.8 abc 2.8 ab 3.2 cd 2.8 c Copper ionization 3.2 4.3 ab 3.6 ab 4.1 ab 3.6 a 3.3 bcd 3.7 ab Copper sulfate 2.6 3.3 dbc 3.6 abc 3.7 abc 3.8 a 2.8 d 3.1 bc Filtration c 3.4 4.5 a 4.0 a 4.2 a 3.4 ab 4.1 ab 4.3 a Heat treatment 3.7 3.9 abc 3.5 abc 3.6 abc 3.3 ab 4.3 ab 4.3 a Hydrogen peroxide 3.1 3.2 dc 3.5 abc 3.2 bc 3.6 a 3.9 abc 3.8 ab Hypochlorous acid 3.0 3.1 dec 3.2 abcd 2.9 c 3.2 ab 3.1 cd 3.3 abc Ozone 2.6 3.2 dc 2.3 ed 3.4 abc 2.6 ab 3.7 abcd 3.8 ab Reverse osmosis 3.5 4.2 ab 2.7 ebcd 3.7 abc 2.5 b 4.2 ab 4.2 a Sodium hypochlorite 3.5 2.8 de 3.3 abcd 3.0 c 3.2 ab 2.9 d 3.5 abc UV radiation 2.7 4.0 abc 3.2 abcd 3.7 abc 2.9 ab 4.4 a 4.2 a a test at P <0.0 5 b Underlined values indicate there was more than 30% disagreement between experts Round s 1 to 2. c Th e technology was listed in the survey as
92 CHAPTER 4 EFFICACY OF CHLORINE TO CONTROL PHYTOPHTHORA NICOTIANAE IN SOLUTIONS CONTAINING PEAT PARTICLES OR NITROGEN FERTILIZER Overview of the Research Problem Recirculated irrigation water from greenhouse and nursery operations has abundant microbial load and suspended solids which increases both the risk of plant disease development and clogging of irrigation emitters (MacDonald et al., 1994 ; Meador et al., 2012) Phytophthora species are a common plant pathogen found in greenhouses and nurseries (Leonberger et al., 2013; Olson et al., 2011; Parke and Grnwald, 2012) and have been identified in recirculated irrigation (MacDonald et al., 1994; McIntosh, 1966; Orlikowski et al., 2007; Themann et al., 2002; Werres et al., 2007) Water treatment technologies are used in irrigation for control of plant pathogens (Ehret et al., 2001; Fisher, 2013; Newman, 2004; Raviv and Lieth, 2007; Runia, 1995; Stewart Wade, 2011; Van Os, 2010; Zhou and Smith, 2001) Water treatment technologie s can be chemical (activated peroxygens, bromine, chlorine, chlorine dioxide, copper, ozone, peroxyacetic acid, and surfactants), physical (membrane filtration, ultraviolet radiation, h eat treatment), or biological (slow media filtration, constructed wetlands and biosurfactants) (Stewart Wade, 2011) A survey carried out to Australian nurseries indicated that 71% of nurseries that recirculated water used chlorine as a disinfection method (Lane, 2004) The common use of c hlorine in irrigation (Hong et al., 2003) and drinking water (Deborde and von Gunten, 2008) has been attributed to its low cost and potency as a germicide (White, 1999). Chlorine is an oxidizer which removes electrons from reactants (such as microbial cell membranes) and in the process chlorine becomes reduced to chloride (Cl ) (Deborde and von Gunten, 2008) Chlorine can be applied to water as a gas (Cl 2 ); as a
93 liquid in the form of sodium hypochlorite (NaOCl) or purified hypochlorous acid (HOCl); or as a solid in the form of calcium hypochlorite (Ca(ClO) 2 ) (Stewart Wade, 2011) The mode of action of chlorine for control of microorganisms is through oxidation and chlorination (Deborde and Gunten, 2008; White, 1999) Chlorin e in water is hydrolyzed to form hypochlorous acid (HOCl) (Eq uation 4 1) which is further dissociated to form hypochlorite ion (OCl ) (Eq uation 4 2 ) (White, 1999). Cl 2(g) + H 2 + + Cl ( 4 1) H O + H + (4 2) S odium hypochlorite (Eq uation 4 3 ) and calcium hypochlorite (Eq uation 4 4) also result in the formation of hypochlorous acid. NaOCl + H 2 ( 4 3) Ca(OCl) 2 + 2 H 2 ( OH ) 2 (4 4) The concentration of HOCl, ClO and Cl 2 in the water is known as free chlorine (Deborde and Gunten, 2008) The exact proportion of HClO and OCl in solution is pH dependent (Morris, 1966) HOCl is a stronger form of oxidizer than OCl (White, 1999) and is more abundant when the pH of the solution is 7.5 or less (Morris, 1966) As a r esult the oxidation reduction potential (ORP), the oxidative strength of a solution, of chlorine is also higher at lower pH (White, 1999). Oxidant demand, as defined by the Standard Methods of Water and Wastewater, ant dose and the residual oxidant concentration measured at a prescribed contact time and at a given pH and temperature Chlorine requirement or dose refers to the amount of chlorine to be added to water under specific conditions to obtain control of a
94 target microorganism when demand is satisfied (Faust and Aly, 1983) The e ffective dose of chlorine to control 90% of plant pathogen propagules in water ranged between 0.1 ( Erwinia carotovora ) to 50,000 mgL 1 Cl ( Melodoigyne javanic a ) with a range in contact time between 15 seconds to 24 hours respectively (Raudales et al., 2011) A pplication of 2 mgL 1 Cl effectively controls zoospores of Phytophthora spp. (Cayanan et al., 2009; Hong et al., 2003) Mortality of Pythium spp. zoospo res at a given chlorine dose between 0.25 to 4 mgL 1 was increased when the pH of the solutions were Decreased pH also resulted in increased ORP (Lang et al., 2008). A chlorine dose of 2.4 mgL 1 was a thre shold for phytotoxicity on woody ornamental varieties (Cayanan et al., 2009b) however sensitivity of crops varied Chlorine demand is increased by the presence of organic and inorganic compounds in s olution (Faust and Aly, 1983) Organic compounds in the solution are quickly oxidized by chlorine (Deborde and von Gunten, 2008) An initial chlorine concentration of 2 mgL 1 Cl combined with 200 mg L 1 of a 60% Canadian sphagnum peat substrate reduced free chlorine concentration to 0 mgL 1 and ORP decreased from 600 to under 400mV after 30 minutes contact time (Huang et al., 2011) However, it is unknown whether the oxidation of organic matte r in a solution will occur more quickly than oxidation of a target plant pathogen, thereby rendering chlorination ineff ective. Hypochlorous acid reacts with organic and inorganic ammonia to form N chloro compounds also known as chloramines (White, 1999; Deborde and von Gunten, 2008) Chlorine substitutes the hydrogen from the ammonia to result in the formation of
95 monochlo ramines (Eq uation 4 5) and subsequently dichloramines (Eq uation 4 6) and trichloramines (Eq uation 4 7) (White, 1999). NH 3 2 Cl +H 2 O ( 4 5) N 2 2 +H 2 O (4 6 ) NHCl 2 3 +H 2 O (4 7) The rate of substitution of chlorine for hydroge n in the ammonia molecule occurs very quickly. A concentration of 0.2 x 10 3 molL 1 of HOCl to 1x10 3 molL 1 of NH 3 resulted in 99% conversion of free chlorine to monochloramine in just 0.2 seconds at 25C and pH 7.0 (White, 1999) Organic and inorganic forms of chloramine are known as combined chlorine 1979; White, 1999) For example, control of E. coli in laboratory conditions with combined chlorine forms required 10 and 10 0 times more contact time than HOCl and OCl respectively (Akin et al., 1982) However, monochloramine was more effective than hypochlorous acid or chlorine dioxide in controlling bacteria attached to surfaces suggesting that chloramines were better able to penetrate biofilm (LeChevallier et al, 1988) Water soluble fertilizers containing a mmonium and nitrate are commonly used in greenhouse and nursery operations (Nelson, 2011). An initial free chlorine concentration of 2.6 mgL 1 combined with 200 mgL 1 of nitrogen from NH 4 based fertilizers reduced to 0.1 mgL 1 free chlorine after 2 minutes contact time (Meador and Fisher, 2013). It is unknown whether combining chlorine with NH 4 salts affect efficacy of chlorine to control plant pathogens in water. The objective of this research was to determine if the presence of ammonium sulfate and potassium nitrate or increased concentrations of peat in the solution affected
96 the efficacy of sodium hypochlorite to control Phytophthora nicotianae in water under laboratory conditio ns. Materials and Methods Pathogen I noculum Phytophthora nicotianae has been reported in over 250 crops (Erwin and Ribeiro, 1996; Farr and Rossman, 2013) and irrigation water sources and distribution systems (Bush et al., 2003; Feld et al., 1990; Neher an d Duniway, 1992; Strong et al., 1993; van der Gaag et al., 2001; van Voorst et al., 1987; Wills, 1964) and was chosen as the model organism to evaluate the efficacy of chlorine in the presence of contaminants. Efficacy of chlorine to control P. nicotianae under laboratory conditions was estimated to be 2 mgL 1 Cl (Hong et al., 2003). A culture of Phytophthora nicotianae was provided by Dr. Aaron Palmateer (Plant Pathology Department, Tropical Research and Education Center of the University of Florida, Home stead, FL). Zoospores were produced based on a previously published protocol (Mitchell and Kannwischer Mitchell, 1992). Briefly, P. nicotianae was grown on clarified V8 juice agar plates for 5 days, then a mycelial plug of approximately 2 cm 2 was transferred to an empty petri dish and flooded with enough V8 juice broth to reach the surface without submerging or floating the plug. The plates were incubated in the dark at 25C for 72 hours. Then the broth was discarded and the plugs were triple rinsed with sterile distilled water. The plugs were flooded with fresh sterile distilled water and incubated at 25C under constant light for 24 hours. Water was replaced with fresh sterile water, then the plates were chilled at 10C for one hour and then allowed to sit at room temperature for one hour. The resulting zoospore solution was filtered through a 35 m nylon mesh (Pentair Aquatic Ecosystems, Apopka FL). Zoospores were enumerated with a Hausser Bright Line hemacytometer (Hausser
97 Scientific, Horsha m, PA). Zoospore concentration was adjusted to obtain a final concentration of 10,000 zoospores mL 1 Chlorinated Water Water used for all the experiments was sterile distilled water adjusted to pH 6.0 ( 0.02) with H 2 SO 4 or KOH before addition of chlorin e, peat, nitrogen, or P. nicotianae inoculum. Water was treated with 5% reagent grade sodium hypochlorite (ACROS, Belgium) to reach a final concentration of 0, 2, or 4 mg L 1 Cl in a final volume of 100mL. Peat Experiment Sphagnum peat (Sun Gro Horticultu re, Sea Beach, Canada) was sieved through a 149m (100 US mesh) pore size screen. The pH of peat was adjusted to 6.0 0.1 by amending with 3.5g of calcium hydroxide (Ca(OH) 2 ) to one liter of peat. Wetting agent (PSI Matric A.I. 99% Alkoxylated polyols) was incorporated at 0.25mL per liter of peat (Huang, 2011). The peat was allowed to air dry at room temperature in an open plastic bag for 5 days. After 5 days, pH was measured by using the saturated media extract (SME) method. The pH was confirmed to be 6.0 0.1. The peat was dried at 70C for 24 hours. The bulk density of peat was 176 gL 1 Sterile distilled water was mixed with 0, 10, 20, 40 and 80 mg L 1 of peat and stir red until the peat was completely rewetted. U.S. EPA guidelines for water reuse suggest < 20 mgL 1 of total suspended solids (TSS) for 1 of TSS for non edible crops to avoid clogging of sprinklers (US EPA, 2012). A pre liminary trial quantified chlorine demand in response to peat in the absence of P. nicotianae Solutions containing peat were mixed with 0, 2 and 4 mg L 1 Cl for 10 minutes contact time in sterile water, followed by measurement of free and total
98 chlorine, ORP, and pH. The experiment was a complete randomized design with 3 replicates per treatment (N=45) per trial, and the whole trial was run twice. A second preliminary trial quantified chlorine demand of P. nicotianae inoculum at either 0 or 10,000 zoospore s mL 1 in the absence of peat, by measuring residual total chlorine, free chlorine, ORP, and pH after 10 minutes in solutions of 0, 2, or 4 mg L 1 Cl. The experiment was a complete randomized design with 4 replicates per treatment (N=24) per trial, and th e whole trial was run twice. In the main experiment, efficacy of chlorine was evaluated for control of P. nicotianae in the presence of peat. Solutions with peat were mixed with P. nicotianae and then treated with 0, 2 and 4 mg L 1 of chlorine with 10 minu tes contact time. The experiment was a randomized complete block design. Each block represented a time period, during which a single replicate combination of chlorine and peat concentration treatments were tested. There was a total of 4 blocks (N=72) per e xperiment, and the whole experiment was run twice. Nitrogen Experiment Water was treated with 50 mgL 1 nitrogen from graded salts of ammonium sulfate ((NH 4 ) 2 SO 4 ), or potassium nitrate (KNO 3 ) (Thermo Fisher Scientific, Beverly, MA), or no nitrogen. A preli minary trial quantified chlorine demand in response to nitrogen salts in the absence of P. nicotianae Solutions containing nitrogen were mixed with 0, 2 and 4 mg L 1 of chlorine with 10 minutes contact time, followed by measurement of free and total chlor ine, ORP, and pH. The trial was a complete randomized design with 3 replicates per treatment (N=27) per trial, and the trial was run twice.
99 The main experiment evaluated efficacy of chlorine to control P. nicotianae in the presence of nitrogen salts. Solut ions with the nitrogen treatments were mixed with 0, 2 or 4 mg L 1 of chlorine stirred for one minute and then P. nicotianae was added and incubated for 10 minutes or 24 hours contact time. The experiment was a randomized complete block design. Each block represented a time period, during which a single replicate combination of chlorine and nitrogen treatments were tested. There was a total of 4 blocks (N=72) per experiment, and the experiment was run twice. Contact Time Independent flasks were used for each contact time and the treated flasks were kept at 25 C for 10 min or in the dark for 24 1 hours. The flasks incubated for 24 hours were maintained in the dark for 241 h. Measurements At each contact time, the number of zoospores, pathogen infectivity, free and total chlorine, oxidation reduction potential (ORP), pH, and electroconductivity (EC) were measured. The number of zoospores in the nitrogen experiment was measured by estimating the average of 4 subsamples of 10l of the solutions on the hemacytometer under the microscope. Intact zoospores were identified as being bean shaped with int act cell membrane. The number of zoospores was not measured in the Peat experiment because particles obscured accurate counts of zoospores by microscopy. Pathogen infectivity was evaluated by dipping tomato leaves ( Solanum lycopersicum L. cv. Mountain Fresh) in the s uspension and storing them in moist chambers (plastic containers with moisten ed paper towels) for 5 to 7 days at room temperature Each moist chamber was treated as an experimental unit which contained 4 leaves per container. Disease incidence (the n umber of infected leaves ) and disease severity
100 (lesion area) were measured. Leaf area with l esion was estimated with Photoshop (Adobe Systems Inc orporated, San Jose, CA) by measuring the total green and healthy area and the necrotic area with lesions. Free and total chlorine were measured with chlorine AQUAfastTM powder packs and an Orion AQ4000 meter (Thermo Fisher Scientific, Beverly, MA). ORP wa s measured with a Dual ORP pH meter (Spectrum Technologies, Inc, Plainfield, IL). EC and pH were measured with an Orion VersaStar meter (Thermo Fisher Scientific, Beverly, MA). Statistics Analysis of variance was used (PROC GLM) in SAS (version 9.2, SAS i nstitute, Cary, NC) to analyze main and interaction effects of chlorine and the contaminants. nitrogen experiment with P. nicotianae total chlorine and number of infected leaves A). Results Chlorine Demand Exerted by P. nicotianae P. nicotianae inoculum alone at 10,000 zoospores mL 1 exerted a strong demand on chlorine (applied minus residual concentration) in the absence of peat and nitrogen (Fig. 4 1). There was a significant i nteraction of chlorine and P. nicotianae on residual free and total chlorine, ORP, and pH ( P <0.0001). The free chlorine demand of P. nicotianae was 1.7 and 3.0 mgL 1 in water treated with 2 and 4 mgL 1 Cl ( ), respectively (Fig. 4 1a). In contrast, t otal chlorine demand from P. nicotianae was 0.7 and 1.5 mgL 1 for water treated with chlorine at 2 and 4 mgL 1 respectively (Fig. 4 1 a )
101 Presence of P. nicotianae decreased ORP by 191 mV or 141 mV in solutions with 2 and 4 mgL 1 of chlorine, respectiv ely but increased ORP with no chlorine (Fig. 4 1b). The pH was 6.1 with the combination of no chlorine and no P. nicotianae the remainder combinations ranged from 7.1 to 7.7 for other chlorine and P. nicotianae Peat Experiment In the absence of P. nic otianae i ncreasing peat concentration from 0 to 80 mg L 1 decreased residual free and total chlorine particularly at the highest peat and chlorine concentrations (Fig. 4 2). There were significant main and interaction effects of peat and chlorine ( P L 1 decreased free chlorine by 1.00 mg L 1 and 0.96 mg L 1 at 2 mg and 4 mg L 1 Cl concentrations, respectively, and decreased total chlorine by 0.62 or 0.96 mg L 1 at the 2 and 4 mg L 1 Cl conc entrations, respectively. The ORP was affected by chlorine concentration, but not by peat, with the highest ORP at 4 mgL 1 Cl (660mV), followed by 2 mgL 1 Cl (654mV), and 0 mgL 1 Cl (569mV). The pH was affected by chlorine and peat, but not by their int eraction. Increasing applied chlorine increased pH, with 4 mg L 1 Cl having the highest pH (7.9), followed by 2 mg L 1 Cl (7.0) and 0 mg L 1 Cl (6.1). Solutions without peat had the highest pH (7.4) and decreased to pH 6.7 at 80 mg L 1 peat. In the presen ce of peat and P. nicotianae chlorine was the only factor that significantly affected all response variables (Table 4 1). Peat only affected pH, but pH differences were minor and ranged from 7.2 to 6.9 as peat increased from 0 to 80 mg L 1 peat. The highe st free and total chlorine, ORP and pH were observed with treatments containing 4 mg L 1 Cl (Table 4 2). Disease incidence and severity w ere only affected by chlorine concentration (Table 4 1), with no impact of peat. With no chlorine, disease incidence of
102 disease severity of were observed across all peat concentrations (Fig. 4 3). There was no difference in infection between 2 and 4 mg L 1 Cl, with diseases incidence disease severity to 1% at 2 and 4 mg L 1 Cl, regardless of peat concentration. Because peat at all measured levels did not affect the efficacy of chlorine to control infection, this suggests that P nicotianae was rapidly oxidized by chlorine before the peat consumed active ingredient Nitrogen Ex periment In the absence of P. nicotianae ammonium sulfate, and to a lesser extent potassium nitrate, created a strong demand on free chlorine at 10 minutes contact time (Fig. 4 4 a ). In contrast, no demand on total chlorine was observed for any nitrogen s ource at 10 minutes contact time (Fig. 4 4 b ). There were significant main and interaction effects of nitrogen source and chlorine dose ( P <0.001) on free chlorine, and main effects of nitrogen and chlorine ( P <0.001) on total chlorine. Ammonium sulfate decre ased free chlorine by 1.2 and 2.7 mg L 1 Cl in applied solutions of 2 and 4 mg L 1 Cl, respectively (Fig. 4 4). In comparison, potassium nitrate decreased free chlorine by only 0.4 or 0.6 mg L 1 Cl at the 2 and 4 mg L 1 applied Cl levels. The ORP varied only by chlorine dose ( P <0.001), with the highest ORP at 4 mg L 1 Cl (700 mV), followed by 2 mg L 1 Cl (643 mV), and 0 mg L 1 Cl (505 mV). In the control solution (no chlorine or nitrogen) containing P. nicotianae 5,887 or 486 viable zoospores mL 1 were recovered after 10 min or 24 h, respectively (Fig. 4 5). The percent of infected tomato leaves in the no chlorine and no nitrogen control decreased from 92% when exposed at 10 min to 81% when exposed at 24h (Fig. 4 6). The se data indicated a decrease in viability of the zoospores over time, but showed that the inoculum retained the ability to infect tomato leaves after 24 h.
103 There was a significant interaction of chlorine, nitrogen, and contact time on viable zoospore count whereby the number of viable zoospores tended to decrease with increasing chlorine, increasing contact time, and also in the presence of ammonium or nitrate N (Table 4 3, Fig. 4 5). After 10 min, the viable zoospore count was under 208 zoospores mL 1 wit h all treatments containing 2 or 4 mg L 1 Cl (Fig. 4 5). By 24h, the only viable zoospores recovered were from the no chlorine/no nitrogen control treatment. Incidence of disease decreased with both increasing chlorine concentration ( P < 0.001) and contact time ( P <0.05), whereas severtity only decreased with increasing chlorine concentration ( P < 0.001) (Table 4 3 & 4 4, Fig. 4 6). Tomato disease was not affected by nitrogen source. Disease incidence decreased from 34% to 27% across chlorine treatments with extended contact time (Table 4 4). Disease incidence 4 4). Disease severity (Table 4 4). In the presence of P. ni cotianae free residual chlorine level was very low (0.07 to 0.14 mg L 1 Cl across contact times and nitrogen), and was only affected by applied chlorine concentration ( P <0.001, Table 4 3). However, residual total chlorine and ORP were both affected by interactions between applied chlorine, nitrogen, and contact time (Table 4 3, Fig. 4 7). At 10 min, residual total chlorine tended to increase with increasing applied chlorine, and at 24 h the highest levels of residual total chlorine occurred with increased chlorine concentration for the ammonium sulfate treatment (Fig. 4 7a). The higher residual level at 24h may indicate greater stability of chloramine form
104 compared with hypochlorous aci d which would be expected to be present with no nitrogen or potassium nitrate. The ORP increased with increasing chlorine concentration at 10 min, but at 24 h ORP had decreased and there was little difference between chlorine and nitrogen treatments (Fig. 4 7b). Electrical conductivity was affected by nitrogen, and to a lesser extent applied chlorine concentration ( P <0.01, Table 4 3). For ammonium sulfate, potassium nitrate and no nitrogen solutions, EC was 514, 512 or 60 S cm 2 respectively, which woul d be expected given the higher ion concentration with the nitrogen salt treatments (Table 4 4). Applied chlorine concentration slightly increased EC, ranging from 354 to 369 S cm 2 (Table 4 4). The pH was affected by interactions between chlorine, nitroge n and contact time (Table 4 3). However, pH differences were minor between treatments. For example, pH increased with increasing applied chlorine concentration from 7.0 to 7.3 for 0 and 4 mg L 1 Cl, respectively, and from 7.1 at 10 min to 7.2 at 24 hours contact time, respectively (Table 4 4). Implications of the Research Results demonstrated that despite a reduction in residual free chlorine concentration from peat and nitrogen, as well as demand from the Phytophthora inoculum itself, there was a high l evel of control of P. nicotianae with chlorine doses applied at 2 or 4 mg L 1 Previous research has also shown that the presence of Phytophthora spp. (Hong et al., 2003), peat (Huang et al., 2011) and nitrogen (Meador and Fisher, 2013) decreased residual levels of free chlorine. Peat at all levels applied in this study did not affect the efficacy of chlorine in controlling tomato leaf infection, indicating that zoospores were rapidly oxidized by chlorine even in the presence of other organic matter. Our ex perimental peat
105 concentration was 4 times greater than the EPA recommended limit of 20 mg L 1 of total suspended solids for irrigation of non edible crops (US EPA, 2012). Poor filtration systems result in ineffective sanitization of water under field condi tions (Meador et al., 2012). Therefore, despite the encouraging results from our research, filtration is highly suggested until more research on other microorganisms is carried out. I ntegrated system designs that include filtration to reduce suspended sol ids and microbial inoculum carried out by the suspended solids prior to disinfection are highly recommended to growers (Lewis Ivey and Miller, 2013). Nitrogen in the solution did not affect tomato leaf infection by P. nicotianae nor did nitrogen affect t he efficacy of chlorine to control zoospores. Both ammonium and nitrate salts decreased the density of viable zoospores by more than 58% in a zero chlorine solution compared with the no nitrogen control (Fig. 4 5). However nitrogen salts had no effect on z oospore concentration or leaf infection at 2 or 4 mg L 1 applied Cl. Hypochlorous acid in the presence of ammonia is rapidly converted into chloramines (White, 1999). In our study, ammonium sulfate caused a greater reduction in residual free chlorine than potassium nitrate (Fig. 4 4a). At 10 min contact time, both free chlorine (hypochlorous acid or hypochlorite in the absence of N), or nitrogenated chlorine compounds (chloramines) controlled zoospores and leaf infection. This is the only controlled study w e are aware of evaluating efficacy of chlorine in the presence of nitrogen, whereas other research has focused on control of plant pathogens by hypochlorous acid alone (Cayanan et al., 2009; Hong et al., 2003). Further research is needed on the efficacy of nitrogenated chlorine forms, for example with shorter contact times and other pathogen species or life stages.
106 Although our results are encouraging as to chlorine efficacy in the presence of peat and nitrogen fertilizer, it is recommended in commercial pr oduction to reduce chlorine demand in order to increase the concentration of active ingredient available to control target pathogens such as Phytophthora Several strategies could be considered when designing a water treatment control system, including fil tration, extended contact time, and monitoring of both active ingredient and microbial density. Research shows that increasing contact time up to 8 minutes increased the mortality rate of Phytophthora with 2 mg L 1 of free chlorine (Hong et al., 2003). Gi ven that 10 min contact time was the shortest contact time measured in our study, this would be the minimum contact time currently recommended when applying chlorine in combination with water soluble fertilizers. The complexity of chlorine reactions in the presence of nitrogen, suspended particles, and other contaminants creates a challenge for monitoring active ingredient level and efficacy when using chlorine to treat irrigation water. Monitoring is essential to successfully incorporating water treatment as a risk management strategy in IPM. Our research indicates the importance of monitoring free and total chlorine and microbial load at the point of injection and at the furthest outlet. Monitoring of active ingre dient concentration is essential to prevent phytotoxicity and to assess that an adequate dose for control is being applied. In addition, monitoring presence of target plant pathogens, as well as non specific quantitative tests of microbial load before and after treatment points, can be used to evaluate efficacy of chlorine injection (Meador et al., 2012).
107 Table 4 1. Peat experiment Analysis of variance summary of response variables for the experiment in which solutions with Phytophthora nicotianae were treated with chlorine and peat (n=8) Experimental run, and blocks (measurement over time) within each run, were not significant and were not included in the reported ANOVA model. Response variable Source DF Type III SS Mean S quare F value P value Free chlorine Chlorine 2 0.21247687 0.10623843 14.78 0 .0001 Peat 4 0.02429105 0.00607276 0.85 0.4998 Chlorine*Peat 8 0.05108805 0.00638601 0.89 0.5289 Total chlorine Chlorine 2 65.66741795 32.83370897 380.04 0 .0001 Peat 4 0.79427078 0.1985677 2.3 0.0638 Chlorine*Peat 8 0.86390097 0.10798762 1.25 0.278 ORP Chlorine 2 29272.26667 14636.13333 4.94 0.0089 Peat 4 3324.78333 831.19583 0.28 0.8899 Chlorine*Peat 8 27349.06667 3418.63333 1.15 0.334 pH Chlorine 2 1.16373494 0.58186747 68.89 0 .0001 Peat 4 1.56300745 0.39075186 46.26 0 .0001 Chlorine*Peat 8 0.0391181 0.00488976 0.58 0.7932 Disease incidence Chlorine 2 84650.06667 42325.03333 48.2 0 .0001 Peat 4 4220.13333 1055.03333 1.2 0.3147 Chlorine*Peat 8 2714.01667 339.25208 0.39 0.9258 Disease severity Chlorine 2 15781.61667 7890.80833 53.99 0 .0001 Peat 4 293.78333 73.44583 0.5 0.7339 Chlorine*Peat 8 722.96667 90.37083 0.62 0.7607
108 Table 4 2. Peat e xperiment. E ffect of three chlorine concentrations on solutions containing peat and inoculated with Phytophthora nicotianae Peat was applied at 0, 10, 20, 40 and 80 mg L 1 to these samples but had no effect on HSD test at P <0.05 (n= 24). Disease incidence was estimated by counting the number of leaves with lesions. Disease severity was estimated by measuring the surface leaf area covered with lesions. Applied chlorine (mg/L) Free chlorine (mg L 1 ) Total chlorine (mg L 1 ) ORP (mV) pH Disease incidence (%) Disease severity (%) 0 0.05 b 0.09 c 545 b 7.0 c 74 A 26 a 2 0.07 b 1.18 b 550 b 7.1 b 17 B 2 b 4 0.14 a 1.88 a 580 a 7.2 a 19 B 1 b
109 Tabl e 4 3. Nitrogen experiment: Analysis of variance for the experiment in which solutions containing Phytophthora nicotianae were treated with chlorine and nitrog en salts with two contact times. Disease incidence was estimated by counting the number of leaves with lesions. Disease severity was estimated by measuring the surface leaf area covered with lesions. Total chlorine and number of infected leaves differed by experimental run in the ANOVA model. However, equality of variances was confirmed by t at and therefore both experimental r uns were analyzed together. No difference by experimental run, and blocks (measurement times) within each run were observed for any other variable and were not included in the reported ANOVA model. Zoospore s Disease incidence Disease severity Source DF F value P value F value P value F value P value Chlorine dose (Cl) 2 64.32 0 .0001 291.67 0 .0001 107.3 0 0.0001 Nitrogen source (N) 2 14.27 0 .0001 1.04 0.3571 0.47 0.6251 Contact time (Ct) 1 62.19 0 .0001 5.55 0.0206 0.18 0.6717 Cl N 4 12.66 0 .0001 1.2 0 0.3177 1.18 0.3258 Cl Ct 2 52.44 0 .0001 0.59 0.5570 0.61 0.5442 N Ct 2 9.06 0.0002 0.8 0 0.4535 2.45 0.0916 Cl N Ct 4 7.85 0 .0001 0.95 0.4393 1.97 0.1051 Free chlorine Total chlorine ORP pH EC Source DF F value P value F value P value F value P value F value P value F value P value Chlorine dose (Cl) 2 7.47 0.0009 109.55 0 .0001 60.29 0 .0001 45.93 0 .0001 5.52 0.0053 Nitrogen source (N) 2 0.59 0.5565 17.48 0 .0001 1.91 0.1528 0.22 0.8049 6264.4 0 0 .0001 Contact time (Ct) 1 0.64 0.4264 65.73 0 .0001 183.16 0 .0001 8.25 0.005 0.37 0.5426 Cl N 4 1.75 0.144 7.85 0 .0001 1.68 0.1612 0.26 0.9029 0.4 0 0.8051 Cl Ct 2 0.64 0.5286 19.3 0 0 .0001 22.2 0 0 .0001 13.53 0 .0001 0.29 0.7511 N Ct 2 1.21 0.3013 3.54 0.0325 0.49 0.6170 5.15 0.0074 0.12 0.8851 Cl N Ct 4 1.52 0.2021 1.53 0.0501 2.83 0.0286 0.93 0.4489 0.4 0 0.8103
110 Figure 4 1 Residual chlorine and ORP after inoculating 10,000 zoosporesmL 1 of P nicotianae in sterile distilled water (in the absence of peat or nitrogen salts) after 10 minutes contact time (A) Free and total chlorine and (B) O xidation reduction potential Symbols represent the mean of 8 samples standard error. 0 1 2 3 4 0 2 4 Measured chlorine (mgL 1 ) Applied chlorine (mgL 1 ) Total chlorine Free chlorine Total chlorine + P. nicotianae Free chlorine + P. nicotianae 400 450 500 550 600 650 700 750 800 0 2 4 ORP (mV) Applied chlorine (mgL 1 ) ORP ORP + P. nicotianae A B
111 Figure 4 2 Peat experiment: Residual chlorine after exposure to peat in sterile distilled water at 0, 2, or 4 mg.L 1 Cl (in the absence of Phytophthora or nitrogen salts) after 10 minutes contact time A) Free chlorine. B) Total chlorine. Symbols represent the mean of 6 samples standard error. -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 0 10 20 40 80 Free chlorine (mg L 1 ) Peat (mgL 1 ) 4 mg/L 2mg/L 0 mg/L -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 0 10 20 40 80 Total chlorine (mg L 1 ) Peat (mgL 1 ) 4 mg/L 2mg/L 0mg/L A B
112 Figure 4 3. Peat experiment: Infection of tomato leaves with Phytophthora nicotianae in response to chlorine (P< 0.001) and peat concentrations (ns) (n=8, where each experimental unit included 4 leaves). Leaves were briefly dipped at 10 minutes after the P. nicotianae was in contact with the chlorine and peat solutions, and leaves were then incubated in a moist chamb er for 5 days. Error bars represent the standard error from the mean. A) Disease incidence was estimated by counting the n umber of leaves infected with lesions B) Disease severity was estimated measuring the s urface area of leaves with lesions. -10 10 30 50 70 90 0 10 20 40 80 Number of infected leaves (%) Peat (mgL 1 ) 0 mg/L 2mg/L 4mg/L -10 0 10 20 30 40 50 0 10 20 40 80 Surface area with lesions (%) Peat (mgL 1 ) 0 mg/L 2mg/L 4mg/L A B
113 Figure 4 4 Nitrogen experiment: Residual chlorine (in the absence of P nicotianae or peat) after exposure to nitrogen salts with 10 minutes contact time Means were compared using P < 0.0 01 (n=6). (A) Free and (B) Total chlorine. c b a c b a c b a 0 0.5 1 1.5 2 2.5 3 3.5 4 0 2 4 Total chlorine (mgL 1 ) Dosed chlorine (mgL 1 ) No nitrogen Ammonium sulfate Potassium nitrate f c a f de de f cd b 0 0.5 1 1.5 2 2.5 3 3.5 4 0 2 4 Free chlorine (mgL 1 ) Applied chlorine (mgL 1 ) No nitrogen Ammonium sulfate Potassium nitrate A B
114 Figure 4 5. Nitrogen experiment: E ffects of chlorine dose, nitrogen source and contact time on recovery of viable zoospores of P nicotianae Means were compared using P <0.05 (n=8 ) a c c c c c b c c c c c bc c c c c c 0 1000 2000 3000 4000 5000 6000 7000 8000 0 2 4 0 2 4 ZoosporesmL 1 10 min 24 h No nitrogen Ammonium sulfate Potassium nitrate Chlorine (mgL 1 ) Contact time
115 Figure 4 6. Nitrogen experiment: Disease incidence (p ercent of leaves with lesions ) after dipping leaves in a solution with chlorine nitrogen and P nicotianae after (A) 10 min or (B) 24h. Symbols represent means (n=8) standard error 0 20 40 60 80 100 0 2 4 Number of infected leaves (%) Chlorine (mg/L) No nitrogen Ammonium sulfate Potassium nitrate 0 20 40 60 80 100 0 2 4 Number of infected leavess (%) Chlorine (mg/L) No nitrogen Ammonium sulfate Potassium nitrate 24 h 10min A B
116 Figure 4 7. Nitrogen experiment: Effect of applied chlorine concentration nitrogen source and contact time in solutions inoculated with P nicotianae A) Residual t otal chlorine B) Oxidation reduction potential Means were compared using P <0.05 (n=8 ) g cdef bcd g g fg g cde a g defg abc g cdef ab g g efg 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 2 4 0 2 4 Total chlorine (mg L 1 ) 10 minutes 24 hours No nitrogen Ammonium sulfate Potassium nitrate Contact time Dosed chlorine (mgL 1 ) def bcd a fg fg efg efg abc abc g fg def fg cde ab fg fg fg 200 300 400 500 600 0 2 4 0 2 4 ORP (mV) 10 minutes 24 hours No nitrogen Ammonium sulfate Potassium nitrate Contact time Dosed chlorine (mgL 1 ) Contact time Dosed chlorine (mgL 1 ) A B
117 CHAPTER 5 COST ANALYSIS OF IRRIGATION WATER TREATMENT Overview of the Research Problem Horticultural producers face limited avail ability of high quality water for irrigation, coupled with increasing regulation in response to competition for water resources and environmental degradation. Climate change is expected to decrease available irrigation w ater quantity and modify temporal an d spatial water distribution patterns ( Ay e r s, 1994; Gleick, 2010; Schaibe and Aillery, 2012) Regulatory responses to limited resources include limited ground water permitting, restrictions on fertilizer and pesticide runoff tiered pricing of water, and establishment of water markets at local, regional, national, and international scales (Schaibe and Aillery, 2012 ; US EPA 2013) These trends are likely to increase the cost of irrigation water, use of low quality water sour ces such as surface water and captured runoff for irrigation and additional costs for remediation of water quality issues Treatment of recirculated and surface water sources is needed to minimize the risk of crop losses and increased labor from plant dis ease algae, and irrigation emitter clogging from biofilm ( Maier et al., 2009 ) Surface water sources tend to have higher concentrations of microbes than well and municipal water (Cappaert et al., 1988; Pottorff and Panter, 1997) which increases the risk of microbial clogging of irrigation emitters ( Gilbert et al., 1981; Yan et al., 2009 ) resulting in increased labor, crop losses from uneven water distribution, and shorter useful life of irrigation equipment Re circulated water can accumulate and distrib ute plant pathogens to crops thereby increasing the risk of plant disease and the cost of crop losses ( MacDonald et al., 1994; McIntosh, 1966; Orlikowski et al., 2007; Themann et al., 2002; Werres et al., 2007 ).
118 Water treatment technologies are used in i rrigation to control micro organisms in water (Ehret et al., 2001; Fisher, 2013; Newman, 2004; Raviv and Lieth, 2007; Runia, 1995; Stewart Wade 2011; Van Os, 2010; Zhou and Smith, 2001). Water treatment alternatives include chemical (activated peroxygens, bromine, chlorine, chlorine dioxide, copper, ozone, peroxyacetic acid, and surfactants), physical (membrane filtration, ultraviolet radiation, heat treatment), and biological options (slow media filtration, constructed wetla nds and biosurfact ants). Growers are more likely to adopt technologies when the y perceive economic and technical benefits of adoption, and are informed or have experienced the risk of non adoption A survey of growers who recirculated irrigation water ind icated that 84% of locations did not treat recirculated water for control of plant pathogens (Uva et al., 1998) H owever only 2% of the surveyed growers perceived they had experienced problems with waterborne pathogens. G rowers identified economic cost a nd uncertainty of efficacy as barriers to adoption of disease risk management strategies in horticulture (Breukers et al., 2012) and water and energy conservation strategies in farms (Schaibe and Aillery, 2012). Uncertaint y can be reduce d with the acquis ition of information by either direct experience or research and education (Breukers et al., 2012; Feder and Umali, 1993; Marra et al., 2003; McRoberts et al., 2011; Rogers et al., 2003). To date, we are not aware of economic analysis of water treatment technologies for irrigation which is needed to assist growers in making technology adoption decisions Investment analysis has been used for greenhouse technologies such as zero runoff subirrigation systems (Uva e t al., 200 1), soil moisture sensor based i rrigation (Belayneh et al., In Press ), transplanting equipment (Brumfield, 2005), and greenhouse
119 lighting (Fisher and Donnelly, 2002). A typical investment analysis annualizes purchase and installation cost, which is combined with operating and maintenanc e cost to calculate the total annual cost. Benefits may be quantified in terms of increased revenue (such as plant cuttings yield from lighting stock plants, Fisher and Donnelly (2002)), and/or reduced production cost (for example, reduced labor comparing automatic and manual transplanting, Brumfield (2005) or water savings from sensor based irrigation (Belayneh et al., In Press) ). Costs and benefits can be combined to estimate return on investment, net present value, or payback time. Net cost and benef it of irrigation technologies ha ve been quantified on the basis of either production time and space ($/square meter week, Uva et al., 2001) or irrigation water volume ($/1000 gal, Belayneh et al., In Press). Cost analysis of water treatment technologies requires consideration of the cost to purchase and install equipment, the cost of consumables such as sanitizing chemicals or electricity, and labor cost for maintenance. There are several potential economic benefits. If water treatment allows successful capture and re use of irrigation runoff, there is a reduction in production cost. This saving equals the economic value of recirculated water and nutrients (especially where water soluble fertilizer is used), which would otherwise need to be purchased (a n opportunity cost) The cost to treat recirculated water relative to the purchase cost of water and nutrients is therefore useful H owever a complete comparison between inefficient irrigation systems with a high level of runoff compared with a zero run off system requires consideration of cost of both water treatment and also the larger cost of the recirculation technology itself such as ebb and flood benches or floors and associated plumbing (Uva et al., 2001)
120 Potential benefits from controlling biof ilm include savings in labor required to clean clogged irrigation equipment, non uniformity of unevenly irrigated plants, and death of dried plants. Potential benefits from controlling plant pathogens include a reduction in crop losses, and savings in lab or to monitor and sort plants before shipping. However, in most cases water treatment is used as a preventative risk management technology where it is not possible to quantify actual benefit unless there is a history of a biofilm or plant pathogen issue. The overall goal was to analyze costs of water treatment technologies in greenhouse operations, in order to assist growers in selecting between alternative technologies, and as a step towards a complete investment analysis of water recirculatio n and treatm ent. Our specific objective s were to estimate the cost of (1) filtration, (2 ) sanitizing treatment and (3 ) water and fertilizer per 1000 gal To collect costing data, interviews were carried out with growers of ornamental greenhouse crops and suppliers of water treatment technologies. Methodology Cost of Filtration Systems Filtration costs were obtained from 6 ornamental plant growers, which was a subgroup of 11 surveyed greenhouse operations The greenhouse operations had previously par ticipat ed in water quality research (Meador et al., 2012]), were large operations ranging from 72,000 to 6,533,989 ft 2 of production area, and experienced with a range of water treatment technologies The c apital cost included purchase of filtration equip ment, shipment and installation costs. The ca pital cost s were linearly depreciated for 10 years for all filt ration systems The Gross Domestic Product (GDP)
121 deflator index calculated by the U S Bureau of Economic Analysis was used to convert the capital cost values from the year of purchase to 2012 values. C on sumable costs consisted of filter component replacement and e lectricity required to run the equipment during the year 2012 T hree types of screen filters were evaluated, including micro scr een drum filter where water passed through a rotating screen filter and particles and filtered water are removed in two different streams ( http://www.praqua.com ) pressurized inline filters that were automatically back flushed following a pressure drop post filter ( http://www.tekleen.com ) and a vibrating screen filter where gravity fed water passed through a screen that vibrated rapidly and separated particles to a waste stream ( http://www.kason.com ) In synthetic fiber filters, gravity fed water passes through fabric, which is indexed forward as the fabric clogs and water is backed up ( http://www.clearstream.ca ) In the media filter, pressurized water was passed through a cylinder containing crushed glass ( www.dramm.com ) Cost of Water Treatment in a Hypothetical 20 Million gal per Year Operation An analysis of chemical water treatments was carried out for a hypothetical greenhouse operation using 20 million gal of water per year. Water treatment equipment installation, and operation costs were obtained from 7 ornamental plant growers, and 6 indust ry suppliers. The capital cost of liquid sanitizers was estimated by quoting the cost of a system with two injector s in series ( http://www.dosatronusa.com ) to allow for a range of dilution levels. The capital cos t of injectors for liquid sanitizers includ ed equi pment purchase and in stallation plus an annual maintenance cost estimated by the equipment supplier. A ll capital cost s w ere linearly depreciated for 10 years. The marginal c apital cost of sanitizers per 1000 gal was estimated based on an annual water volume of 20 million gal for all technologies. The consumable costs were
122 estimated by obtaining the actual costs paid by growers during 2012 or from industry suppliers where th e technology was not used by this group of growers. C onsumable cost of sanitizing chemicals for activated peroxygen products was estimated by using the US EPA label lowest rate for continuous use in irrigation For bromine, the high US EPA label rate for continuous application was used (35 mg L 1 ) because that the low label rate was below the required level for control of various plants pathogens (Chase, 1990 and 1991) Calcium hypochlorite, chlorine gas, and sodium hypochlorite share the same active ing redient (hypochlorous acid), and a concentration of 2 mg L 1 was analyzed because the surveyed growers were applying this concentration, and this concentration of residual free chlorine has been found to be effective on a wide ran ge of plant pathogens ( Hon g et al., 2003; Cayana n et al., 2009 ). A concentration of 1 mg L 1 was used for quantifying chlorine dioxide costs, because this was a compromise between the 0.5 or 1 mg L 1 applied by the two surveyed growers using two tank systems research showing 2.6 mg L 1 required for control of oomycetes ( Mebalds et al., 1995 ), and US EPA labels for single tank chlorine dioxide products for a residual (rather than applied) concentration for cont inuous irrigation of 0.25 mg L 1 A concentration of 2 mg L 1 was analy zed for copper ionization because this was the application r ate at the surveyed grower, and 1.0 mg L 1 was not effective for control of oomycetes and higher doses have not been evaluated ( Wohanka and Fehres, 2006) Ozone was not included in the 20 million gal scenario because the only ozone system in the grower survey group had more than 10 times the capacity (250 million gal) compared with the hypothetical operation and economies of scale are likely to apply. Labor for all liquid
123 sanitizers was determine d by using the average labor cost ($0.03/1000gal) of three surveyed growers that were applying liquid sanitizers. The sanitizers evaluated for the 20 million gal scenario included activated peroxygens, bromine, chlorine based products, chlorine dioxide, an d copper ionization. Activated peroxygens, also known as peroxyacetic acid, are oxidizers formed by combining a hydrogen peroxide with an organic acid such as acetic acid (Newman, 2004). Bromine is another oxidizer which is used in the form of hypobromous acid (HBrO) or bromide (BrO ) ( Degrmont, 1979 ). Chlorine is an oxidizer that can be applied in the form of gas (Cl 2 ); as a liquid, mainly as sodium hypochlorite (NaOCl) or purified hypochlorous acid (HOCl); or as a solid in the form of calcium hypochlori te (Ca(ClO) 2 ) (Deborde and Gunten, 2008) Chlorine dioxide is an oxidizer which differs from chlorine in that it is less affected by water pH, does not hydrolyze in water but rather remains as a dissolved gas does not chlorinate compounds, and can only be generated onsite ( Degrmont, 1979). Chlorine dioxide can be generated from a package of reagents applied to a single stock tank, and three alternative products were evaluated. Two of the surveyed growers also generated chlorine dioxide from a system wit h two separate tanks of reagents. In one case, the two tank chlorine dioxide system was leased and both equipment and consumable chemical reagents were paid as a combined monthly fee and in the second operation the equipment was purchased and the consuma bles were paid separately Copper ionization, is no t an oxidizer, instead acting a s a toxic compound by replacing other ions that are essential for cell processe s ( Degrmont, 1979; Evans et al., 2007; Flem m ing and Trevors, 1989; Thurman et al., 2009).
124 Act ual Cost of Water Treatment Technologies in 11 Greenhouse Operations T he cost of water treatment from 11 surveyed ornamental plant growers was estimated based on their actual water use equipment (such as a range of injector types which was standardized for the 20 million gal scenario ), and reported costs Capital costs comprised purchase of equipment, shipment and installation costs. The depreciation period was determined by each operation and ranged between 5 to 10 years (in co ntrast to the standardized 10 years for the 20 million gal scenario) The GDP deflator index calculated by the US Bureau of Economic Analysis was used to convert the capital cost values from the year of purchase to 2012 values. O peration and maintenance costs included consumables costs and labor. The c onsumable cost for ionized copper consisted on replacement of copper rods and electricity use. The c onsumable cost for chlorination ( chlorine gas, calcium hypochlorite and sodium hypochlorite) and bromine consisted o f the cost of sanitizer required to treat the respective volume of water and electricity used by injectors. The c onsumable cost for chlorine dioxide generators comprised the service agreement which includes the chemical inputs for the generator and the maintenance of the equipment. Ozone is one of the more complex technologies that is only effective as an integrated system with filtration, oxygen purification, controls, and other equipment. T he capital investment cost of the ozone system there fore included filtration pumps and controls. The c onsumable cost s associated with ozone w ere the electricity of running the system. The technologies evaluated in this section were bromine tablets, chlorine based products, chlorine dioxide, copper ioniza tion, ozone, and reverse osmosis. Bromine tablets, chlorine based products, chlorine dioxide, and copper ionization were described in the section above. Ozone (O 3 ) is an unstable gas that acts as an oxidizer and can
125 only be generated onsite (Degrmont, 1979; US EPA, 1999). Reverse osmosis is a semipermeable membrane that removes ions by separating solutes from solvents and has a pore size of <0.0005 m ( Van der Bruggen et al., 2003). Cost of Water, Fertilizer and Nutrient Solution All gro wers used water soluble fertilizers as their main nutrient supply technology. The cost of water and fertilizer in the nutrient solution was estimated for 8 of the surveyed grower s based on year 2012 values for water use and co sts. Capital costs included establishment cost of wells, ponds or rainwater systems and purchase price of pumps. Capital costs were linearly depreciated for 40 years for the establishment of the system and 20 years for water pumps because this was the average expected system life r eported by the surveyed growers GDP deflator index calculated by the U S Bureau of Economic Analysis was used to convert the capital cost values from the year of purchase to 2012 values. Consumable costs consisted on the electricity cost of pumping wat er or the price of municipal water. The cost of fertilizer s was provided by 6 of the 8 growers and estimates were provided by a fertilizer supplier for the 2 growers not reporting fertilizer cost Results and Discussion Cost of Filtration The capital costs of filtration systems ranged between $9,311 to $45,000 and the annualized total cost of capital, consumables and labor ranged from $931 to $5,987 per location (Table 5 1) The marginal total cost of screen filtration systems was mainly allocated t o t he capital cost of total cost ) which ranged from $0.02 to $ 0.11 per 1000 gal of filtered water Both rotating drum and vibrating screen filters had electric
126 motors and electricity contributed the consumable cost in Table 5 1 The marginal capita l cost of synthetic fiber filtration varied widely between $0.05 to $1.99 per 1000 gal depending on the volume of water treated and size of the filtration unit C onsumable costs of synthetic fiber rolls contributed between 23 and 64% of the total margina l cost for this type of filtration Screen filtration systems had lower total costs per volume of water than synthetic fiber filtration mainly because of a lower cost of consumables (electricity versus fiber rolls) Multiple stage filtration is generally recommended for treatment, in order to allow decreasing pore size with each subsequent filtration stage (Konjoian et al. 2008). Given the higher marginal total cost of synthetic fiber filters compared with screen filters, synthetic fiber filtration may be most appropriate as a second filtration stage following an initial screen filtration in order to reduce the consumable cost of fiber rolls. Total w ater volume a nd size of the equipment greatly affect ed the marginal cost of filtration per unit of water v olume treated A greenhouse o peration with synthetic fiber filter listed in Table 5 1 had installed the highest cost installation ( $42,000 or $1.99/1000 gal ), with the most expensive fiber rolls ($0.74/1000 gal) and the largest capacity of the equipment surveyed, but filtered the lowest volume ( 2.1 million gal of water per year ) Economies of scale apply to technologies such as filtration that have a high capital cost relative to consumables, whereby the marginal cost to treat an additional volume of wat er treated is reduced when the capital cost can be allocated over a larger volume of water. Sizing equipment with excess capacity increases marginal cost, and Caswell and Zilberman (1986) emphasized that the capacity of irrigation technology must be match ed to the water volume used in order to maximize
127 profit. Information was not available on filtration efficacy, which is a key component in technology selection and further research is required to quantify benefits of each filtration option Filtration ha s potential benefits of removing infected plant material, and red ucing sanitizing agent demand ( Huang et al., 2011 ) and can therefore reduce the cost of subsequent sanitation and risk of crop losses Cost of Water Treatment in a Hypothetical 20 Million gal per Year Operation The cost of sanitizing 20 million gal of water per year ranged from $ 1,800 (for sodium and cal cium hypochlorite) to $ 390,800 (for chlorine dioxide with a single tank) (Table 5 2). All technologies except chlorine dioxide (two tank, pur chased), chlorine gas and sodium hypochlorite, allocated between 44 to 100% of the total cost in the form of consumable costs. T he cost of injectable sanitizing agents with the same active ingredient such as activated peroxygens or single tank chlorine di oxide varied by brand by more than a factor of 10 Two alternatives of chlorine dioxide with a single tank had the highest total cost mainly allocated to the high cost of consumables. The marginal total cost of chlorine based products ranged from $0.09 to $0.10 per 1000 gal Calcium hypochlorite costs were mainly allocated to consumables whereas chlorine gas costs were largely allocated to the capital cost. The l easing agreement of the two tank c hlorine dioxide generator resulted in higher cost ($0.69 per 1000 gal) than purchasing the equipment ($0.12 per 1000 gal) The c opper ionization system had the highest capital investment cost ($41,207) of all sanitizers in the 20 million gal scenario, in addition to moderate operation costs relative to other techno logies Technologies that have a high allocation of costs to consumables are more suited to operations treating a low water volume, for example in an operation that only treats water used in a mist propagation zone where high water quality is particularly important. In contrast, capital
128 intensive technologies with lower consumable cost have advantages from economies of scale in cases where large volumes of water are treated, including central treatment of all incoming water Actual Cost of Water Treatment Technologies in 11 Greenhouse Operations The m arginal total cost of water treatment based on actual water use by greenhouse operations ranged between $0.07 for chlorine gas to $1.67 per 1000 gal for reverse osmosis (Table 5 3). All the technologies, exce pt ozone and reverse osmosis, 3 per 1000 gal All chlorine based products had total marginal cost of $0.12 per 1000 gal and they differed as to how the cost was allocated The total marginal cost of chlorine gas was evenly dist ributed between capital ( 34% ), consumable ( 30%) and labor (36% ) costs. The total marginal cost of calcium hypochlorite was largely allocated to consumable cost (78%), whereas sodium hypochlorite had 47% allocation to capital cost Capital cost of copper ionization systems varied between the locations because of scale, equipment manufacturer, and ionization equipment design The copper ionization system costing $41,207 was a custom built system to be used inside a tank with customized copper plates which resulted in higher costs compared with the other inline copper ionization systems. Reverse osmosis had the highest labor cost of all technologies, where labor cost alone surpassed the total cost of technologies in half of the other operations surveyed The analysis of the 11 greenhouse operations emphasizes that most capital intensive technologies (copper ionization, ozone, and reverse osmosis) are most suited to large water volumes because of economies of scale. Bromine was the second cheapest alterna tive for treatment (Table 5 3) mainly because was used in a simple, uncontrolled dosage system that did not require capital
129 investment. Bromine tablets we re placed in a basket on the entrance of return tanks from sub irrigation systems with tablets bein g dissolved as water flowed through the basket The operation cost s for bromine were only $0.07 per 1000 gal However, the grower in this operation was dosing at 4 mg L 1 bromine based on water volume versus the amount of bromine consumed, which is under the US EPA label recommendation of 10 to 35 mg L 1 bromine. R esearch on the efficacy of bromine for control plant pathogens in water indicate s that doses between 25 to 60 mg L 1 are required for effective control of several plant pathogens (Chase, 1990 and 1991). The total marginal cost of bromine at 35 mg L 1 bromine was estimated to be $0.19 per 1000 gal (Table 5 2). Two scenarios of chlorine dioxide with two tank generators illustrate factors affecting the decision to purchase versus lease equipment (Table 5 3) The operation that purchased the chlorine dioxide equipment had a capital cost of $7,950 along with an annual service agreement of $6,000 which included all chemical inputs. The operation that leased chlo rine dioxide equipment had $0 capita l cost and an annual service agreement of $13,800 including all chemical inputs. The purchase option resulted in a total cost of $0.49 pe r 1000 gal compared with $0. 92 per 1000 gal from the lease option Both operations had total costs that we re independe nt of water volume within technical limits T herefore total cost of treatment would decrease as water volume increase d for both operations. A depreciation period of 5 years was estimated by the purchasing grower If the equipment was still functional after the five year period, the total cost of water treatment w ould decrease by $0.10 per 1000 gal compared with the initial 5 years Nonetheless, equipment leasing provides the opportunity to assess
130 efficacy of equipment and ease of use prior to making an investment and therefore reduces financial risk (Rogers 2003) Cost of Water, Fertilizer and Nutrient Solution The m arginal total cost of n utrient solution based on the actual water use by the eight surveyed greenhouse operations ranged from $ 1.47 to $ 1 1. 04 per 1000 gal (Table 5 4). The marginal cost of water alone ranged from $0.02 for pond water to $6.13 per 1000 gal for municipal water. The marginal cost of fertilizer varied from $0.8 6 to $6.58 per 1000 gal Municipal water from the surveyed locat ion s in Michigan and Colorado cost $3.75 or $6.13 per 1000 gal respectively. The cost of rainwater was mainly attributed to the high capital cost ($362,108) to retain a relatively small water volume Well and pond water were relatively inexpensive sources However, the cost of well water differed between operations mainly based on the number of wells per location and differences in the cost of pond water were mainly attributed to the water volumes pumped from each pond. The cost of water soluble fertilizers in the nutrient solution was the most expensive portion of irrigation water for all water sources, except for municipal water The cost of water treatment can be compared against the cost of water alone, or the combined cost of the water and wa ter soluble fertilizer in the nutrient solution. The cost of all water treatment options ($0.65 or less) was lower than the cost of municipal water ($3.75 or $6.13), or the cost of the complete nutrient solution ($1.47 to $11.04) in all locations. In mos t locations, the cost of water treatment at that location was lower than the cost of water alone. Although all the growers surveyed used water soluble fertilizers, some ornamental plant growers in the industry rely on solid controlled release
131 fe rtilizer a pplied directly to the soil, which would reduce the potential savings from capturing, treating, and reusing the water. Implications of the research Our research provides a n initial insight to the costs of treating irrigation water and can be used to reduce uncertainties on capital investment and operational cost of treatment High capital investment cost can be a barrier to adoption of water conservation technologies (Schaibe and Aillery, 2012) O ur analysis showed that water treatment technologies varied widely in the required capital investment costs, including sanitizing chemicals that can be supplied with low cost injectors Options also varied widely in the total marginal cost per 1000 gal (from $0.09 to $19.54), and our results can therefore assist in matching technologies with different scales of operation. The benefits associated with water treatment could be quantified in terms of the value of water. US EPA estimated that the value of water in agriculture ranged between $12 to $4500 per acre foot or an equivalent of $0.04 to $13.80 per 1000 gal (US EPA, 2012) depending on the cost to supply water and assumptions on how value is quantified. The annual total cost of irrigation water for the operations in our survey ranged from $30,789 to $505,000 (T able 5 4), resulting in a range of water cost before onsite treatment from $0.02 for pond water to $6.13 for municipal water. The cost of well water is largely determined by energy costs of pumping and pressurizing water ( Caswell and Zilberman 1986) Po nd and surface water sources are more likely to have quality issues requiring treatment, which may increase final cost compared with well water Municipal water supply was the most expensive source in our survey, but there is low risk associated with this water source because of centralized treatment. However, the true value of water is elusive because it is essential for life (Schaibe and
132 Aillery, 2012) and plant growth (Taiz and Zeiger, 200 6). The total value of the plants from the greenhouse operations surveyed in this project was $73 million per year, for the year 2010. Considering that plants could not be grown without water, the value of the crop itself could be considered the true val ue of irrigation water for these operations. Risk management in terms of both ensuring a reliable water supply and ameliorating water quality issues are relevant to economic analysis of water treatment. Several growers surveyed indicated th at capturing of rainwater and runoff was a risk management strategy whereby future regulation or climate change could result in plant loss or limited company growth as a consequence of insu fficient water for irrigation. The benefits associated with risk management strate gies tend to be underestimated in the absence of problems (Solliman et al., 2009). However, the benefits can also be estimated in terms of the risk of not treating (McRoberts et al., 2011). Potential risks of not treating water could be estimated in term s of plant loss as consequence of uneven irrigation due to clogging of emitters and plant disease and further research is needed on the cost of water quality issues The marginal cost of treatment (Table 5 1 to 5 3) relative to the high marginal cost o f nutrient solution and water (Table 5 4) suggest that water treatment of recirculated water has a strong potential to save water and fertilizer costs More financial research is needed to comprehensively estimate the cost of complete system designs that include storage tanks, establishment of sub irrigation systems and any other additional infrastructure needed in addition to water treatment The wide range in the cost of water supply and treatment in our survey population emphasize that the decisions m ade by growers in selecting and designing
133 water treatment technologies have important economic implications. For example, an o versized filtration system in one location (Table 5 1) clearly illustrated that profitability (by increasing production costs) ca n be affected when the size of the technologies is not matched to the corresponding water volume (Caswell and Zilberman, 1986) Reverse osmosis was the only technology with high labor cost ($0.47 per 1000 gal) (Table 5 3). All the remain ing technologies gal indicating that cost and availability of labor may favor technologies other than reverse osmosis. Cost is only one of the considerations when selecting water treat ment technologies (Chapter 3), with attributes relating technical, socio economic and regulatory aspects also consider ed important by growers and experts As the U.S. moves forward on assessing alternative solutions to manage fluctuation in water availa bility (U.S. EPA, 2013) increased r egulation is very likely to occur The competition for water demand is likely to force regulatory agencies to increase the marginal cost of water as a strategy to reduce water use (Schaibe and Aillery, 2012) and to estab lish more regulations of water quality to protect contamination of the limited water sources available (USDA, 2012). Many European countries (Molitor, 1990 ; Runia, 1994 ) and states in the Pacific coast of the U.S. have already put in place zero runoff cult ivation systems as part of their regulations. Therefore, growers need information to make informed decisions on the selection of water treatment technologies available to treat recirculated water or water sources with low quality.
134 Table 5 1. Cost of filtration systems from greenhouse operations of ornamental crops recirculating nutrient solution from sub irrigation. C apital cost includes the cost of equipment, shipping and installation. All capital cost values were converted to 2012 values b ased on the gross domestic product (GDP) deflator index calculated by the U S Bureau of Economic Analysis Consumables and labor cost were estimated based on 2012 values from each operation. Filter Type Reported pore size Water filtered Capital cost Annual total Cost ($/1000gal) (m) (1000 gal/year) ($) ($) Capital Consumables Labor Total Screen filter Drum screen filter 89 65,790 $31,735 $4,636 $0.05 68% $0.01 15% $0.01 17% $0.07 Pressurized inline screen 100 50,000 $9,311 $931 $0.02 100% $0.00 0% $0.00 0% $0.02 Vibrating screen filter 100 15,200 $17,000 $2,506 $0.11 68% $0.04 24% $0.01 8% $0.16 Synthetic fiber filter rolls b Nylon 88 17,600 $24,000 $5,498 $0.14 44% $0.15 49% $0.02 8% $0.31 Polyester 10 25 32,400 $13,500 $5,822 $0.04 23% $0.12 66% $0.02 11% $0.18 Polyester 40 65 32,400 $13,500 $2,660 $0.04 51% $0.02 25% $0.02 24% $0.08 Polyester (90%) cotton (10%) 70 2,115 $42,000 $5,987 $1.99 70% $0.74 26% $0.10 4% $2.83 Media filter Crushed glass media 5 50,000 $45,000 n/a $0.09 n/a n/a n/a a Commonly known in the greenhouse industry as paper filter b Proprietary data not shared with the team by the industry supplier The operation using this filtration system ha s not replaced the glass media yet
135 Table 5 2. Cost of sanitizing water treatment alternatives based on a hypothetical operation with annual water use of 20 million gal Capital cost includes the cost of equipment, shipping and installation Initial investment for liquid sanitizers was based on a quote from a supplier company. The quote included the cost of a pre injector, an injector, installation and annual maintenance. Technology Source of information Active ingredient (mg L 1 ) Capital total cost Annual total cost Marginal cost ( $/ 1000gal) (Percentage from total cost) ($) ($/year) Capital Consumables Labor Total cost Activated peroxygen Supplier H 2 O 2 : 185 PAA: 120 $4,580 $5,400 $0.03 ( 11% ) $0.21 ( 78% ) $0.03 ( 11% ) $0.27 Activated peroxygen Supplier H 2 O 2 : 33 $4,580 $36,800 $0.03 ( 2% ) $1.78 ( 97% ) $0.03 ( 2% ) $1.84 Activated peroxygen Supplier H 2 O 2 : 27.1, PAA: 2 $4,580 $55,200 $0.03 ( 1% $2.70 ( 98% ) $0.03 ( 1% ) $2.76 Bromine Grower 35 $0 $3,800 $0.00 ( 0% ) $0.16 ( 84% ) $0.03 ( 16% ) $0.19 Calcium hypochlorite Grower 2 $3,000 $1,800 $0.02 ( 22% ) $0.04 ( 44% ) $0.03 ( 33% ) $0.09 Chlorine dioxide (Single tank) Supplier 1 $4,580 $9,200 $0.03 ( 7% ) $0.40 ( 87% ) $0.03 ( 7% ) $0.46 Chlorine dioxide (Single tank) Supplier 1 $4,580 $184,000 $0.03 ( 0.3% ) $9.14 ( 99% ) $0.03 ( 0.3% ) $9.20 Chlorine dioxide (Single tank) Supplier 1 $4,580 $390,800 $0.03 ( 0.2% ) $19.48 ( 100% ) $0.03 ( 0.2% ) $19.54 Chlorine dioxide (Two tank, leased) a Grower 1 $0 $13,800 $0.00 ( 0% ) $0.69 ( 100% ) $0.00 ( 0% ) $0.69 Chlorine dioxide (Two tank, purchased) b Grower 1 $7,950 $2,400 $0.08 ( 67% ) $0.03 ( 25% ) $0.01 ( 8% ) $0.12 Chlorine gas Grower 2 $7,000 $2,000 $0.04 ( 40% ) $0.03 ( 30% ) $0.03 ( 30% ) $0.10 Copper ionization Grower 2 $41,207 $17,000 $0.21 ( 25% ) $0.63 ( 74% ) $0.01 ( 1% ) $0.85 Sodium hypochlorite Grower 2 $4,580 $1,800 $0.03 ( 33% ) $0.03 ( 33% ) $0.03 ( 33% ) $0.09 a Equipment leased and service agreement that provides all the necessary supplies, maintenance and calibration. b Equipment purchased and service agreement that provides all the necessary supplies, maintenance and calibration
136 Table 5 3. Cost of wate r treatment greenhouse operations of ornamental crops based on actual operation water use Capital cost s include the cost of equipment, shipping and installation. All capital cost values were converted to the year 2012 values based on the GDP deflator index. Water volume, consumable and labor costs were Technology Target dose Water volume (1000gal/year) Capital cost ($) Annual total cost ($ / year ) Cost ($/10 0 0gal) (percentage from total cost) Capital Consumables Labor Total Bromine tablets 4.0 28,758 $0 $2,337 $0.00 ( 0 %) $0.07 ( 86 %) $0.01 14 %) $0.08 Calcium hypochlorite 2.0 43,546 $4,580 $3,875 $0.01 ( 11 %) $0.07 ( 78 %) $0.01 11 %) $0.09 Chlorine dioxide (two tank, leased) 0.8 12,775 $0 $11,753 $0.00 ( 0 %) $0.92 ( 100 %) $0.00 0 %) $0.92 Chlorine dioxide (two tank, purchased) 1.0 15,835 $7,950 $7,750 $0.10 ( 21 %) $0.38 ( 77 %) $0.01 2 %) $0.49 Chlorine gas 2.0 36,500 $7,000 $2,669 $0.03 ( 34 %) $0.02 ( 30 %) $0.03 36 %) $0.07 Copper ionization 2.0 22,674 $41,207 $21,574 $0.39 ( 41 %) $0.56 ( 58 %) $0.01 1 %) $0.95 Copper ionization 0.5 20,945 $15,970 $5,007 $0.11 ( 46 %) $0.12 ( 49 %) $0.01 5 %) $0.24 Copper ionization 2.2 5,164 $18,035 $4,009 $0.50 ( 64 %) $0.27 ( 34 %) $0.01 1 %) $0.78 Ozone 1.5 250,000 $704,922 $162,344 $0.56 ( 87 %) $0.05 ( 7 %) $0.04 6 %) $0.65 Reverse osmosis n/a 6,618 $64,605 $11,056 $1.16 ( 70 %) $0.04 ( 2 %) $0.47 28 %) $1.67 Sodium hypochlorite 2.0 10,000 $5,600 $1,189 $0.06 ( 47 %) $0.03 ( 28 %) $0.03 25 %) $0.12 Sodium hypochlorite 2.5 8,604 $2,143 $907 $0.05 ( 47 %) $0.05 ( 45 %) $0.01 8 %) $0.11
137 Table 5 4. Cost of wate r, fertilizer and nutrient solution from greenhouse operations of ornamental crops based on actual operation use. Capital costs included establishment cost of wells, ponds or rainwater system s and purchase price of pumps. Capital costs were linearly deprec iated for 40 years for the establishment of the system and 20 years for water pumps. All capital cost values were converted to the year 2012 values based on the GDP deflator index. Consumable costs of water consisted on the electricity cost of pumping wate r or the price of municipal water. The cost of fertilizers was provided by the growers unless specified Nutrient solution cost is the sum of the cost of water and fertilizer. Water source Technology Water volume (gal/year) Annual total cost of water+ fertilizer ($/year) Cost ($/1000 gal) Water Fertilizer Water +fertilizer Water treatment Municipal Chlorination 8,603,600 $47,320 $3.75 ( 68 %) $1.75 ( 32 %) $5.50 $0.11 Municipal Calcium hypochlorite 43,546,000 $480,748 $6.13 ( 56 %) $4.92 ( 44 %) $11.04 $0.07 Well Ionized copper 5,163,610 $35,113 $0.22 ( 3 %) $6.58 ( 97 %) $6.80 $0.78 Well Ionized copper 20,945,044 $30,789 $0.61 ( 41 %) $0.86 ( 59 %) $1.47 $0.36 Well Chlorine dioxide generator 15,834,960 $45,921 $0.46 ( 16 %) $2.44 ( 84 %) $2.90 $0.15 Well Chlorine gas b 36,500,000 $182,500 $0.09 ( 2 %) $4.91 a ( 98 %) $5.00 $0.07 Rainwater Chlorination 3,802,120 $27,946 $2.44 ( 33 %) $4.91 a ( 67 %) $7.35 c Pond Ozone 250,000,000 $505,000 $0.02 ( 1 %) $2.00 ( 99 %) $2.02 $0.65 Pond Sodium hypochlorite b 10,000,000 $51,500 $0.24 ( 5 %) $4.91 a ( 95 %) $5.15 $0.19 a Fertilizer cost was not provided by the grower. Therefore the cost of fertilizer was estimated based on 100 ppm N from 17 5 17 at $1 per pound of fertilizer quoted from a fertilizer company supplier b Same location. Pond water is used to supplement irrigation 10 weeks in the summer. c New system, not treating water yet.
138 CHAPTER 6 SUMMARY AND CONCLUSIONS The published literature on efficacy testing of water treatment technologies available for control of waterborne microbes was reviewed (Chapter 2) included chemicals (chlorine, bromine, chlorine dioxide, copper ionization, copper salts, silver ionization, ozone, hydrog en peroxide, and peroxyacetic acid), non chemical or physical treatments (filtration, heat, and ultraviolet radiation) and ecological alternatives (constructed wetlands, biosurfactants, and slow sand filtration). The objective was to summarize the effecti ve dose for controlling target organisms under research conditions, in addition to reported phytotoxicity thresholds. The effective doses for chemical water treatment technologies for control of plant pathogens were in many cases above known phytotoxicity thresholds, however for most crops and technologies the phytotoxicity thresholds remain unknown. A wide variation number of publications were found between thte different water treatment technologies, with most research conducted on chlorine (20 articles ) or copper ionization (12), but only 0 to 7 articles found on other technologies currently in use. Additional research is clearly needed on control methods for algae and biofilms, in vivo pathogen studies, and disease incidence when treating irrigation w ater. An online modified Delphi survey was carried out to identify the perceived key attributes that growers should consider when selecting among water treatment technologies and to characterize a list of 14 technologies based on those same attributes (Cha pter 3) The expert panel consisted of ornamental growers (n=43), water treatment industry suppliers (n=28), and research and extension faculty (n=34). The survey was delivered to the expert panel in two rounds. In the first round, the expert
139 panel was asked to rate the level of agreement of 23 listed attributes (related to cost, system size, control of microorganisms, chemistry, ease of use, and regulation) when selecting between treatment technologies and to characterize the technologies based on those attributes. In the second round, the expert panel received the average rating of the characterized technologies from round 1 and were asked to change the attribute rating if they disagreed with the average group response. Response rate was 59% and 60% f or each round, respectively. All 23 attributes were perceived to be important when selecting between water treatment technologies. For example, injectable sanitizing chemicals such as chlorination were considered to have low capital cost, unlike technolo gies that require installation of complex equipment, such as heat treatment, hydrogen peroxide, ozone, reverse osmosis and UV radiation. Chlorine gas was perceived to be the only technology for which regulatory permission would be an obstacle. Filtration (excluding membrane filtration) was the only technology not perceived to be effective to control microorganisms. All technologies were perceived to be effective in low EC water, and in solutions containing water soluble fertilizers. This survey indicate s perceived attributes of water treatment technologies, which are particularly useful where experimental data are not yet available. Research and outreach needs were highlighted by cases where perceived attributes differed from available experimental data or where there was a lack of consensus between experts. Efficacy of chlorine to control Phytophthora nicotianae in the presence of nitrogen salts or increased concentrations of peat was evaluated under laboratory conditions (Chapter 4) Solutions with p eat at 0, 10, 20, 40, or 80 mg L 1 were inoculated with P. nicotianae at 10,000 zoospores mL 1 and were then combined with 0, 2, or 4 mg L 1 of
140 chlorine with 10 minutes contact time. In a separate experiment, ammonium sulfate ((NH 4 ) 2 SO 4 ) or potassium nitr ate (KNO 3 1 nitrogen were combined with 0, 2, or 4 mg L 1 of chlorine and inoculated with P. nicotianae with 10 minutes and 24 hours contact time. In the absence of chlorine, peat, or nitrogen, P. nicotianae infected 92% or 81% of tomato leaves and had 5,887 or 486 viable zoospores mL 1 after 10 min or 24 h, respectively. Increasing chlorine concentration decreased the number of viable posed to the Peat at all concentrations levels did not affect the efficacy of chlorine in controlling tomato leaf infection, suggesting that zoospores were rapidly oxidiz ed by chlorine. Nitrogen did not affect tomato leaf infection. Nitrogen decreased the density of viable zoospores by more than 58% in a zero chlorine solution compared with the no nitrogen control, but had no effect on zoospore density at 2 or 4 mg L 1 ap plied Cl. Ten minutes contact time was therefore adequate for both free chlorine (hypochlorous acid) and total chlorine (nitrogenated chlorine compounds chlorine) to control zoospores. Despite the positive results of chlorination under these controlled c onditions, filtration and extended contact time of chlorine are recommended to reduce chlorine demand in commercial applications. High capital investments and operation costs are considered barriers to adoption of equipment. The objecti ve of research in Ch apter 5 was to estimate the cost of filtration, sanitizing treatment, irrigation water and fertilizer per 1000 gal (Chapter 5). To collect costing data, interviews were carried out to 11 growers of ornamental greenhouse crops and 6 industry suppliers of water treatment technologies. Screen
141 In one ca se, a grower who installed a synthetic fiber filt er that was over sized for their treated water volume had a very high marginal total cost of filtration of $2.83 per 1000 gal. For most sanitizing chemicals, majority of the marginal treatment cost per 1000 gal was from the chemical reagents Chlorine gas, calcium hypochlorite and sodium hypochlorite were the least expensive alternatives with a marginal total cost of $0.09 0.10 per 1000 gal to sanitize 20 million gal of water. The marginal total cost of wa ter treatment based on the actual water use by greenhouse operations ranged between $0.07, for chlorine gas, to $1.67 per 1000 gal for reverse osmosis. The marginal total cost of the nutrient solution at nine greenhouse operations including both water s upply and fertilizer, ranged from $1.47 to $11.04 per 1000 gal The marginal total cost of nutrient solution was mainly from fertilizer cost water sources, except in locations that used municipal water. The marginal cost of water alone ranged from $0.02 for pond water to $6.13 per 1000 gal for municipal water. The result of this research can be used to assist growers in selecting between alternative technologies by evaluating the total ca pital cost and allocation of capital and operation costs to the marginal cost of treating water.
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164 BIOGRAPHICAL SKETCH Rosa E Raudales was born in 1982 in Tegucigalpa, Honduras. She received a Bachelor of Science degree in agricultural science and production from Zamorano University in Honduras. She went to The Ohio State University where s he worked in the IPM program with Dr. Joe Kovach. She earned a Master of Science degree in the department of Plant Pathology from The Ohio State University in Dr. Brian McSpadden itiated disciplinary applied research to problem to bridge the gap between science and production by continuously delivering unbiased and science based information to growers that can be implemented in their operations.