POTENTIAL USE OF BY-PRODUCT CO -TREATMENTS WITH CONSTRUCTED WETLANDS FOR REMOVING PHOSPHORUS FROM WASTEWATER By JOHN WILLIAM LEADER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2005
Copyright 2005 by John William Leader
To my parents Joan R. and Richard C. Lead er, my grandparents Essie H. and William G. Reynolds and Madge C. and W.E. Leader, our earlier ancestors, and to all those whose work made this world a better pl ace for my generation to inherit. I will strive to do the same for the next generation and all those that may follow mine.
iv ACKNOWLEDGMENTS I would like to express my gratitude to Dr . K.R. Reddy for first admitting me to the graduate program in the University of Flor ida Soil and Water Science Department and specifically to his Wetland Biogeochemistry Laboratory. He is al so responsible for helping to fund my education and research af ter my teaching assistan tships and external funding had ended. His patience with my ve ry long project and dissertation completion is appreciated. I am also indebted to Dr . Ann C. Wilkie of my supervisory committee who provided encouragement and support for my research and graduate program. She followed my research and graduate school progress very closely and provided sage advice. Her very careful edit ing of my first publications wa s particularly helpful and is much appreciated. I thank my other comm ittee members, Dr. W.G. Harris, Dr. Ben Koopman, and Dr. Mike Annable, whose clas ses I truly enjoyed and whose research recommendations I greatly benefited from. I am grateful for the financial support for the wetland mesocosm research component of this study provided by The Florida Department of Agriculture and Cons umer Services (Contract No. 006969). There are numerous students, staff, and professors in the Soil and Water Science Department and elsewhere at the university th at enriched my educat ion, my research, and my life during my long stay here. It would be impossible to list them all and that would risk unintentional but unforgivable exclusi on. I must name a few persons though who very directly assisted in th e completion of my research. Dr. Hari Pant, Dr. John White, Dr. Mark Clark, and Dr. James Bonczek were ea ch very helpful in my research and in
v expanding my professional competency. De partment staff including Yu Wang, Gavin Wilson, Ron Elliot, Scott Brinton, Keith Holl ein, and Larry Schwandes all generously shared their expertise in the laboratory and either analyzed by themselves, or helped me to analyze, what seemed like an endless number of samples. Students including Carrie Miner, Todd Osborne, Jeff Higby, Chip Appel, Ed Dunne, Lance R iley (Fisheries and Aquatic Sciences), and Johnny Davis (Microbi ology and Cell Science) also directly helped me with my research. Both of my wetland mesocosm research sites were off campus and I thank my hosts Jamie Hope at Gainesville Regional Utilities and David Armstrong at the universityâ€™s Dairy Research Unit. During my graduate program I encountered personal obstacles that affected both my health and the progress of my gradua te program. During these challenges I was helped tremendously at the universityâ€™s Stude nt Health Care and Counseling Centers. Specifically, Dr. Michael Murphy and Dr. Be ree Darby were both very supportive and taught me skills that I will use for the rest of my life. Finally, there is no person in the world that I am more indebted to for my graduate education than my wife, Lesley Anita Smith Leader. Her initial promotion of the idea and her continued love, patience, and sacrifices made my gr aduate education possible. She has enriched my life immeasurably, and most recently, with our first child Benjamin. Their love further compels me to live a full a nd meaningful life. One of the most deeply held beliefs I have developed is that most, if not all, of the worldâ€™s problems are caused by anger and ignorance, and thus all solutions must come from education and love. I hope that all of my future teaching, resear ch and other endeavors will encompass this philosophy.
vi TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................ix LIST OF FIGURES...........................................................................................................xi ABSTRACT.....................................................................................................................xi v CHAPTER 1 INTRODUCTION........................................................................................................1 Background...................................................................................................................1 Statement of Problem...................................................................................................5 Need for Research.........................................................................................................9 Objectives...................................................................................................................11 Research Approach.....................................................................................................12 Dissertation Format....................................................................................................13 2 SCREENING POTENTIAL CO-TREATMENT SUBSTRATES FOR PHOSPHORUS REMOVAL AND PERF ORMANCE CHARACTERISTICS........15 Introduction.................................................................................................................15 Materials and Methods...............................................................................................16 Substrate Collection.............................................................................................16 Phosphorus Sorption Properties..........................................................................19 Physico-chemical Properties of Substrates..........................................................21 Results........................................................................................................................ .23 Phosphorus Sorption Properties..........................................................................23 Physico-chemical Properties of Substrates..........................................................29 Discussion...................................................................................................................35 Phosphorus Sorption Properties..........................................................................35 Physico-chemical Properties of Substrates..........................................................37 Conclusions.................................................................................................................39
vii 3 REMOVAL OF PHOSPHORUS FR OM AGRICULTURAL AND MUNICIPAL WASTEWATERS WITH CO-TREATMENTS AND SAND COLUMNS..............41 Introduction.................................................................................................................41 Materials and Methods...............................................................................................43 Co-Treatment and Column Construction and Operation.....................................43 Analysis of Phosphorus Removal Performance..................................................46 Other Analyses of Substrates and Sand...............................................................48 Results........................................................................................................................ .49 Co-Treatment and Column System Performance................................................49 Phosphorus Removal Performance......................................................................50 Substrate and Sand Characteristics......................................................................56 Discussion...................................................................................................................63 Co-Treatment and Column Sy stem Design and Operation.................................63 Phosphorus Removal Performance......................................................................64 Implications of Substrate and Sand Characteristics............................................66 Conclusions.................................................................................................................68 4 REMOVAL OF PHOSPHORUS FR OM AGRICULTURAL AND MUNICIPAL WASTEWATERS WITH CO-TREATMENTS AND WETLAND MESOCOSMS............................................................................................................70 Introduction.................................................................................................................70 Materials and Methods...............................................................................................74 Preparation of Sites, Equipment and Materials...................................................74 Experimental Set-Up...........................................................................................77 Analytical Methods.............................................................................................80 Results........................................................................................................................ .82 Characteristics of Wastewaters............................................................................82 Phosphorus Removal with Pre-Wetland Co-Treatment......................................87 Phosphorus Removal with Post-Wetland Co-Treatment.....................................89 Phosphorus in Co-Treatment Substrates and Mesocosm Sands..........................91 Metal Contents of Co-Treatment Substrates and Mesocosm Sands....................99 Wetland Macrophytes and Redox Cond itions in Mesocosm Sands..................108 Discussion.................................................................................................................110 Characteristics of Wast ewaters and Effluents...................................................110 Phosphorus Removal with Pre-Wetland Co-Treatment....................................112 Phosphorus Removal with Post-Wetland Co-Treatment...................................112 Phosphorus in CTR Substr ates and CWM Sands..............................................113 Metals Contents of CTR Substrates and CWM Sands......................................114 Wetland Macrophytes........................................................................................115 Conclusions...............................................................................................................116
viii 5 PHOSPHORUS REMOVAL FROM AGRICULTURAL AND MUNICIPAL WASTEWATER WITH BY-PRODUCT CO-TREATMENTS AND CONSTRUCTED WETLANDS: Ov erview of Research........................................119 A Synthesis of Laboratory, Gree nhouse and Mesocosm Results.............................119 Overall Conclusions..................................................................................................123 Recommendations for Future Research....................................................................124 APPENDIX A CO-TREATMENT REACTOR AND CONSTRUCTED WETLAND MESOCOSM............................................................................................................126 B CONCEPTUAL DESIGN FOR MUNI CIPAL WASTEWATER TREATMENT SYSTEM USING CO-TREATMENTS WITH CONSTRUCTED WETLANDS..128 C CONCEPTUAL DESIGN FOR AGRICULTURAL WASTEWATER TREATMENT SYSTEM USING CO-TREATMENTS WITH CONSTRUCTED WETLANDS............................................................................................................130 D PHOSPHORUS FACT SHEET................................................................................132 LIST OF REFERENCES.................................................................................................134 BIOGRAPHICAL SKETCH...........................................................................................141
ix LIST OF TABLES Table page 2-1 Description of substrates initia lly considered for co-treatments..............................17 2-2 The sorption and de-sorption (Â± one standard deviation) of P by several substrates..................................................................................................................24 2-3 The linear sorption coefficients (kd), equilibrium P concentrations (EPC0) (with associated r2), P sorption maximums (Smax), and kb values......................................27 2-4 Regression equations and r2 values of the regression curves, shown above in Figure 2-2, for seven substrates................................................................................29 2-5 Inorganic P fractionation analysis was done to further characterize the potential substrates..................................................................................................................30 2-6 Extractable metals (Â± one standard de viation) important to P sorption measured in several potential substrates...................................................................................33 2-7 Particle size distribution of substrates as determined by the standard soil method. Phosphorus sorption data is presented for comparison............................................34 3-1 Oxalate-extractable P (Â± one standard deviation) was determined in co-treatment substrates before and after loading with the two different wastewaters...................54 3-2 HCl-extractable P (Â± one standard devi ation) was determined in co-treatment substrates before and after loading with the two different wastewaters...................55 3-3 Oxalate-extractable iron (Â± one standard deviation) was determined in cotreatment substrates before and after load ing with the two different wastewaters..56 3-4 Oxalate-extractable aluminum (Â± one st andard deviation) was determined in cotreatment substrates before and after load ing with the two different wastewaters..57 3-5 HCl-extractable Ca (Â± one standard de viation) was determined in co-treatment substrates before and after loading with the two different wastewaters...................59 3-6 HCl-extractable Mg was determined in co-treatment substrat es before and after loading with the two different wastewaters..............................................................60
x 3-7 HCl-extractable Fe was determined in co-treatment substrates before and after loading with the two different wastewaters..............................................................61 3-8 HCl-extractable Al (Â± on e standard deviation) was de termined in co-treatment substrates before and after loading with the two different wastewaters...................62 4-1 Characteristics of wastewaters loaded to the experimental systems at each site.....83 4-2 Average metals contents were measured of filtered and acidified samples of the municipal and dairy wastewater s used in this research............................................84 4-3 Phosphorus fractionation analysis was done for co-treatment substrates before and after loading with each wastewater...................................................................97 4-4 Phosphorus fractionation analysis wa s done for mesocosm sands before and after loading with each wastewater..........................................................................98
xi LIST OF FIGURES Figure page 1-1 Diagram of the research sequence for e xploring the applicatio n potential of this technology................................................................................................................12 2-1 Multi-point phosphorus sorption isotherms (Â± one standard deviation) for eight substrates showing log trend lines and their associated r2 values............................26 2-2 Phosphorus remaining in solution (Â± one standard deviation) after various equilibration periods with seven substrates..............................................................28 2-3 The relative proportions of P fractions in seven substrates were determined..........32 3-1 This is a schematic diagram of one of the 42 experimental units used in the column study............................................................................................................44 3-2 Turbidity measured as absorbance by pa rticles in solution above substrates after pouring water on them from a height of 3 feet (0.91 m)..........................................49 3-3 Column study wastewater and effluent soluble reactive phos phorus (SRP) means for the fourth treatment cycle with municipal wastewater.......................................50 3-4 Column study wastewater and effluent soluble reactive phos phorus (SRP) means for the fourth treatment cycle with dairy wastewater...............................................51 3-5 Total phosphorus was determined in all co-treatment substrates before and after loading with either municipal (A) or dairy (B) wastewater.....................................52 3-6 Total phosphorus (Â± one standard deviat ion) was determined in all column sands before and after loading w ith either municipal (A) or dairy (B) wastewater...........53 4-1 Schematic diagram of the 18 experime ntal units used in the mesocosm study......76 4-2 Mean total suspended solids (TSS) (Â± 1 st andard deviation) in effluents at dairy site. Means include all replicates of controls and treatments..................................85 4-3 Dissolved organic carbon was determ ined for the municipal wastewater, and associated co-treatment and wetland e ffluents for two treatment cycles.................86 4-4 Dissolved organic carbon (Â± one sta ndard deviation) was determined for the dairy wastewater, and associated e ffluents for two treatment cycles.......................86
xii 4-5 Effluent total phosphorus (TP) (Â± 1 st andard deviation) 52-week means for the municipal wastewater...............................................................................................88 4-6 Effluent total phosphorus (TP) (Â± 1 st andard deviation) 52-week means for the dairy wastewater.......................................................................................................88 4-7 Total phosphorus (TP) (Â± 1 standard de viation) in pre-wetl and CTR effluents for first cycle only of the 52-week study with dairy wastewater...................................90 4-8 Total phosphorus (TP) (Â± 1 standard deviation) in post-we tland CTR effluents for the 1-week experiment with dairy wastewater...................................................90 4-9 Total phosphorus (Â± one standard devi ation) was measured in the lime (Ca) DWTR co-treatment substrate before and after loading with wastewater...............91 4-10 Total phosphorus (Â± one standard devi ation) was measured in the iron (Fe) DWTR co-treatment substrate before and after loading with wastewater...............92 4-11 One molar HCl-extractable P in Ca-DWTR (Ca) and Fe-DWTR (Fe) cotreatment substrates before and af ter loading with each wastewater.......................93 4-12 The relative proportions of P fractions in the Ca and Fe DWTR co-treatment substrates determined before and af ter loading with each wastewater....................95 4-13 The relative proportions of P fractions were determined in the mesocosm sands preand post-loading with municipal or dairy wastewater for one year..................96 4-14 Oxalate-extractable Fe in mesocosm sands was measured before and after loading with each wastewater................................................................................101 4-15 Oxalate-extractable Al in mesocosm sands was measured before and after loading with each wastewater................................................................................101 4-16 One-molar HCl-extractable Ca was de termined in the Ca-DWTR (Ca) and FeDWTR (Fe) co-treatment substrates before and after loading...............................102 4-17 One-molar HCl-extractable Ca (Â± one standard deviation) was determined in wetland mesocosm sands before and after loading with each wastewater.............103 4-18 One-molar HCl-extractable magnesium (Mg) was determined in the Ca-DWTR (Ca) and Fe-DWTR (Fe) co-treatment s ubstrates before and after loading...........104 4-19 One-molar HCl-extractable Fe was de termined in the Ca-DWTR (Ca) and FeDWTR (Fe) co-treatment substrates before and after loading...............................105 4-20 One-molar HCl-extractable Fe was determined in wetland mesocosm sands before and after loading with each wastewater......................................................106
xiii 4-21 One-molar HCl extractable aluminum was determined in the Ca-DWTR (Ca) and Fe-DWTR (Fe) co-treatment subs trates before and after loading...................107 4-22 One molar HCl-extractable aluminum was determined in wetland mesocosm sands before and after loadi ng with each wastewater............................................108 4-23 Mean bulrush green stem counts by wa stewater, treatment and counting date.....109 4-24 Mean (Â± 1 standard deviation) live bulrush stem phosphorus concentrations at the beginning and end of the one-year study..........................................................110 A-1 This is a detailed schematic diagram of the co-treatment r eactor and constructed wetland mesocosm experimental units. The drawing is not to scale......................127 B-1 This is a conceptual layout show ing incorporation of co-treatments and constructed wetlands into a municipa l wastewater treatment system....................129 C-1 This is a conceptual layout show ing incorporation of co-treatments and constructed wetlands into an agricult ural wastewater treatment system................131
xiv Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy POTENTIAL USE OF BY-PRODUCT CO -TREATMENTS WITH CONSTRUCTED WETLANDS FOR REMOVING PHOSPHORUS FROM WASTEWATER By John William Leader August 2005 Chair: Konda Ramesh Reddy Major Department: Soil and Water Science Co-treatment basins filled with inex pensive non-toxic by-products containing phosphorus (P) binding components such as ir on (Fe), aluminum (Al), calcium (Ca), magnesium (Mg), organic matter or clay might increase the sustainability of P removal from wastewater by constructe d wetland (CW) systems. The objective of this research was to optimize a co-treatment and CW system for P removal. Twelve by-product materials were selected for initial evaluatio n with laboratory experiments. The coated-sand, Ca drinki ng water treatment residual (DWTR), Al, Mg, Fe-DWTR, and the humate materials exhibite d the highest P removal. A column study included six substrates in co-t reatment bottles paired with sand columns that were batchfed municipal or dairy wastewater for one month. The Ca, Fe, Al and humate materials were most effective. The Al material was not locally available nor a useful plant nutrient. The dried humate product had limited availabi lity. The two optimal materials selected for further evaluation were the Caand Fe-DWTR.
xv An outdoor mesocosm study combined batch-fed 208-L co-treatment reactors (CTR) containing Caor Fe-DWTR (or no subs trate for controls) with 567-L verticalflow CW mesocosms (CWM), each w ith a 7-day HRT, planted with Schoenoplectus tabernaemontani and operated for one year. For m unicipal wastewater the total P (TP) concentrations (52-week means) were reduced from 1.00 to 0.72 (28%) and 0.40 mg L-1 (60%) by the Ca and Fe CTR alone compared to 0.96 mg L-1 (4%) by control CTR. These TP concentrations were reduced by the combined CTR and CWM systems from 1.00 to 0.07 and 0.05 mg L-1 (93 and 95%) by systems with Ca and Fe (compared to 0.16 mg L-1 or 84% by control systems). For dairy wastewater, TP was reduced from 48.5 to 22.5 (53%) and 22.7 (53%) mg L-1 by calcium and iron CTR and CWM systems (compared to 24.1 mg L-1 or 50% by controls). Dairy wa stewater pre-treated with CW was placed in nine CTR. The post-wetland Ca and Fe CTR reduced TP concentration (57 and 71%) more than the control CTR (14%). The overall results sugge st the potential for using by-product co-treatments to enhan ce P removal by constructed wetland systems.
1 CHAPTER 1 INTRODUCTION Background Constructed wetlands (CW) are an accep ted low-cost technology for removing P from wastewater (United States Environmen tal Protection Agency [US EPA], 1993 [a]). They effectively remove or transform many contaminants and have numerous ancillary benefits similar to natural wetlands. Howeve r, questions of mechanisms, predictability and sustainability persist (Richardson, 1999) an d there is a need to optimize P removal by these systems (Kadlec and Knight, 1996). Th ere is also a need for finding ways to capture P from wastewater and return it to ag riculture as a nutrient source in order to balance inputs and outputs of P in agricult ural systems (Sharpley, 1999). By sequestering the P with non-toxic materials it could possi bly be re-used by agriculture (MÃ¦hlum and Roseth, 2000; de-Bashan and Bashan, 2004; KvarnstrÃ¶m et al., 2004). The use of municipal or industrial by-products in co-tr eatments could be a low-cost way to improve the performance and sustainability of CW (Arias et al., 2003). Soil and non-toxic byproducts containing iron, aluminum, calcium, magnesium, organic matter or clay were selected for initial evaluation due to the in fluence of these factors on P removal (Khalid et al., 1977; Richardson, 1985; Ka dlec, 1997; Gale et al., 1994; Bridgham et al., 1998). These by-products might be effectively us ed to optimize P removal. However, interactive effects of indivi dual factors need further evaluation (Ann et al., 2000; GrÃ¼neberg and Kern, 2001). This knowledge wi ll contribute to both the characterization and optimization of P removal.
2 Several authors have noted that spatiall y, or temporally adjacent, aerobic and anaerobic conditions optimize nutrient removal from wastewater by the aquatic plant, microbe and sediment communities in wetlands (Khalid et al., 1977; Sah and Mikkelsen 1989; Toerien et al., 1990). It has been s uggested that an oxygenated microzone forms below the sediment-water interface preventing diffusion of P back into the water column after adsorption. Continuing re actions seem to cause a shift from loosely bound to tightly bound P in the sediment (Reddy et al., 1998 [a]; Syers and Iskandar, 1981). Although use of both aerobic and anaerobic tanks is comm on in the literature, few system designs employ a single basin under both conditions. Sequencing batch reactors do use four cyclic anaerobic and aerobic phases in a si ngle treatment basin. Usually, however, the aerobic and anaerobic treatment cells are placed in series (Toerien et al., 1990). In this study, individual treatment cells were floode d and drained resulting in aerobic and anaerobic conditions. Hydrologic manipulations are a practical full-scale management tool and could be optimized for P rem oval (Kadlec and Knight, 1996). Many other factors influence P dynamics in constructed we tlands. Plant type, qua ntity and ability to oxygenate the rhizosphere can all have an impact (Barko and Smart, 1980; Emery and Perry, 1996). Temperature and microbes can in fluence P indirectly by influencing pH, dissolved oxygen, and Eh. Each of these fact ors contributes to the overall P dynamics of wetlands (Gachter and Meyer, 1993; Reddy et al ., 1999 [b]) and was considered in this study. Constructed wetlands (CW) are increasingl y being used for economically treating agricultural and municipal wastewater (WW) while providing anci llary environmental benefits. In addition to the improved optim ization and characterization of phosphorus (P)
3 removal by this emerging technology, this rese arch also incorporated the recycling of non-toxic by-products or wastes for increas ing the P removal, P retention and CW sustainability. There is also interest in reusing these by-produc ts locally, once they become saturated with P, as soil amendments an d fertilizers. In Florida, for example, the by-products may be useful as soil amendments to reduce P mobility in the sandy native soils of the agricultural area above Lake Okeech obee. There is a potential to develop a more sustainable, as well as more envir onmentally sound, use of P in agriculture. The combined benefits of low-cost by-product use, wastewater treatment, and nutrient re-use could favor the economic feasibility of this type of system for wa ter quality protection. Enhanced P removal is a common goal when downstream systems are biologically P-limited (as most freshwater systems are). Since P levels in living biomass plateau as seasonal die back returns P to the water colu mn, sustainable removal by CW is limited to soil sorption and sediment burial of precip itated forms, and of organic matter. The central hypothesis of this research was that by opti mizing hydrology and co-treatments, the removal and retention of P by CW coul d be enhanced. The use of non-toxic byproducts as substrates in r echargeable pre-treatment tank s may increase the effective longevity of P removal by CW while maintaini ng the advantage of low cost treatment. In summary, the potential bene fits of the wastewater tr eatment system designed and studied as part of this research include in creased longevity of c onstructed wetlands used for wastewater treatment, decreased Â“footprintÂ” of c onstructed wetlands used for wastewater treatment, lower cost of wastewater treatment to high standards, re-use of byproducts that might otherwise be wasted, re turn of P to a more sustainable cycle,
4 enhancement of crop production with P-sa turated DWTR, and lower P levels being released to valuable ecosystems. This research began with lab and greenhous e experiments to di rect the research toward the most promising P removal design f eatures (especially co-treatment materials and hydrology). Outdoor wetland mesocosm systems with co-treatment tanks were employed for additional "proof of concept" and to verify prel iminary results at a larger, more realistic, scale. The final synthesis of these results will improve insight into the cycling of P in constructed wetland and co-tr eatment wastewater treatment systems, and the results of this study will be beneficial to CW designers and operators and the agricultural and municipa l clients they serve. This research pursued the optimization and characterization of phosphorus removal from wastewater using constructed wetlands and industrial by-produc t co-treatments. This work thus seeks to apply wetland science to the technology of wa stewater treatment. This could lead to increased environmen tal protection. The use of sequential lab, greenhouse and mesocosm studies will have more universal application to wetland science than stand-alone lab st udies or observational field st udies. The study and use of municipal and industrial by-product co-tr eatments in conjunction with wetland mesocosms will provide insight into a potenti ally powerful tool for improving wastewater treatment and increasing the sustainability of phosphorus removal. The mesocosm technology used could be transferred to econom ically evaluate wast ewater-specific and site-specific wetland treatment system designs before the costly scale-up to large working systems.
5 A great deal of research has been done on constructed wetlands, phosphorus removal, chemical amendments, hydrology, and the ecological engineering of wastewater treatment. This work will contribute to these research areas by testing the biogeochemistry of novel combinations and se ttings for these fact ors. Studying the biological and chemical processes in the so il substrates and by -product co-treatments focused the research on the key components of phosphorus removal and retention. By testing the underlying mechanisms for effici ent and cost-effective phosphorus removal, the design of wetland wastewater tr eatment systems may be improved. Much of the research that has been done on P removal in constructed wetlands has been in the form of observational studies of existing systems and, thus, cause-and-effect relationships cannot be inferred from the results. This study involved replicated, controlled and randomized experiments so that inferences can be made based on treatment differences and the results will have more universal application. Mass balance of P can be obtained to avoid the common "black box" approach that includes just inflow and outflow measurements. The literature suggests the importance of nitrogen and carbon, dissolved oxygen, metals, pH, redox (Eh), mineralogy, temperature, microbiology, and hydrology. Each of these f actors was considered as the research progressed. The applicability of the result s depended on the detec tion of statistically significant differences between treatments and c ontrols. The results wi ll further elucidate the mechanisms for P removal and suggest th e optimal design for improving wastewater treatment with constructed wetlands. Statement of Problem Phosphorus is an essential nutrient for all lif e forms. It is a critical resource for both the natural environment and human indus try and agriculture (Appendix D). Its
6 sustainable management is thus crucial to both environmental protection and human economies. It cycles through the environment pr imarily in solid and dissolved forms. It is taken up by plants, which are then consumed by animals, and is eventually returned to the soil. In the soil it can be sequestered by organic or inorganic compounds, remain in the soil solution or on exchange complexes, or be returned to the cycle (Burgoa et al., 1991; Lookman et al., 1995). By mining burie d phosphate and using it in detergents, fertilizers and other products an imbalan ce in the natural cycl e occurs. Phosphorus becomes a common component of municipal an d agricultural wastewaters. When not removed from the wastewater it can cause eu trophication of the surf ace waters to which it is discharged. Eutrophication occurs as exces s nutrients enter an aquatic ecosystem and cause an imbalance in the grow th of aquatic plants. Excess P is linked to algal blooms in fresh surface waters, such as Lake Okeec hobee in Florida and tributaries of the Chesapeake Bay in Maryland, and other lakes and rivers worldwide, when it is the limiting nutrient. Blooms result from the accelerated growth of surface algae that shades out the submerged vegetation and thus redu ces aquatic habitat a nd oxygen production. Upon senescence the algae decompose, cons uming dissolved oxygen and acidifying the water. This cascade of events can cause fish kills and damage aquatic ecosystems (Wetzel, 1983). In Florida, for example, the eutrophication of Lake Okeechobee has increased due to the high levels of P in agricultural runoff (Nair et al., 1998). More recently it has been suggested that P from ag ricultural sources, discharged to surface waters elsewhere along the Atlantic coast, has stimulated blooms of a virulent form of the aquatic microorganism Pfiesteria . This organism represents a threat to human and ecosystem health as well as to the tour ism and seafood industries (Burkholder, 1999).
7 Elevated levels of P have also been a ssociated with increased geosmin production by cyanobacteria (Saadoun et al., 2001). Geosmin causes bad odors and tastes in drinking water supplies and fish and subsequent econom ic damages (Dionigi et al., 1991; Blevins et al., 1995). Maintaining low P and nitrogen levels in aquatic habi tats is recommended as one way to limit this problem (Saadoun et al., 2001). Many improvements have been made to municipal wastewater treatment plants to increase P removal but even lower levels are desired (Water E nvironment Federation, 1998). The US EPA has also identified agricultu re as a source of the excess P that is damaging surface waters. However, management of excess P can be cost-prohibitive to farmers (Sharpley, 1999). The need for inexpensive and sustainable removal of phosphorus (P) from municipal and agricultural wastewater is well documented in the literature (Kadlec and Knight, 1996). High leve ls of P discharged to surface waters can cause serious environmental and economic problems. This study provides further insight into the enhancement of P removal from wastew ater using co-treatments with constructed wetlands. The effects of soils, co-treatment substrates, plants and cyclic flooding of treatment cells were measured to determin e optimal conditions for P removal and the controlling mechanisms. Contents of the by-pr oducts were expected to affect P sorption not only in the co-treatment cells but also in the wetland mesocosm cells downstream in the treatment sequence. The use of co-t reatments with inexpensive and non-toxic industrial by-products has potential for incr easing the sustainability of P removal by constructed wetland (CW) systems. Conventional wastewater tr eatment systems and wetlands usually include aerobic and anaerobic stages or zones for the remova l of nitrogen (Reddy et al., 1989; Toerien et
8 al., 1990). Under aerobic conditio ns nitrogenous wastes are c onverted to nitrates by the process of nitrification. Unde r anaerobic conditions nitrates are converted to nitrogen gas that escapes to the atmosphere. This allows for treatment systems to theoretically be sustainable, since the atmosphere provides an essentially unlimited sink for nitrogen. Phosphorus, however, is not significantly convert ed to gaseous form and thus a treatment system cannot be completely sustainable unl ess P is removed in some other form. Natural wetlands buffer the impact of excess P, in effluent and runoff, on downstream waters (Reddy and Gale, 1994; Richardson, 1999). Constructed wetlands have been widely used in recent years to remove P fr om wastewater. Current CW treatment systems rely on the sequestration and burial of P in organic and inorganic sediments (Kadlec, 1997) and are thus unsustainable as the wetland fills in. Although CW may be managed to act as sink for P, their functional longev ity and cost effectiveness are limited by their size. In addition to the inherent sustainability problem of P removal by wetlands, the dynamics are not fully understood and thus not always accura tely predictable (Richardson, 1999). The literature of CW wastewater trea tment contains many inconsistencies concerning the major factors affecting the removal of P. Depending on many factors, specific to each system studied, the removal of P has been reported to be mainly dependent on aluminum, iron, or calcium in the soil; aquatic plants; microbes; pH; oxygen; redox, Eh; and/or th e temporal or spatial re lationship of aerobic and anaerobic sites in wetland treatment system s (Khalid et al., 1977; Richardson, 1985; Gale et al., 1994). Each of these factors may be the main controlling factor in respective wetland systems, but the universality of these findings appears to be limited. The use of
9 CW for wastewater treatment is expanding as the desire for protecting surface waters increases and awareness of the ancillary bene fits of wetlands grows. With this expanding use there is a need for con tinued research into the dyna mics of wetland systems. Although CW have been used extensively for wastewater treatment due to economic and environmental advantages over conventional tr eatment, efficiency of P removal can be improved. Need for Research It is costly and difficult to conduct experi mental research with controlled conditions and adequate replication on full-scale CW. In situ mesocosms within natural wetlands are also problematic due to the heteroge neity of soils, plants, and other confounding variables. The disadvantage of field research with full-scale systems in general is the inability to control many confounding variables that might bias an experiment. Without being able to systematically vary the majo r controlling factors it is difficult to make general conclusions regarding causality or treatment effects. The laboratory and greenhouse studies completed provided eviden ce for mechanistic explanations of treatment performance as well as valuable insight regarding scal e-up feasibility. The outdoor constructed wetland mesocosm studies bridged the gap between the Â“bench-topÂ” laboratory and greenhouse resear ch done and observational studi es of full-scale systems found in the literature. A c ontrolled experimental design with replicated mesocosms improves the validity of the causal explan ations derived and, ultimately, wider transferability of the knowle dge gained. The need exists for constructed wetland mesocosm studies where confounding factors can be controlled (Kadlec, 1997). There is also a need to bridge the gap between lab studies and field studie s (Kadlec and Knight, 1996; Richardson, 1999). Constructed wetland mesocosms are considered to be a
10 practical and useful tool in testing wetla nd design features. The wetland mesocosms constructed were very similar to others used in wetland research (Ahn et al., 2001). Based on reviews of the published litera ture on wastewater treatment with constructed wetlands, and the laboratory and greenhouse experiments, the following unique combination of features was invest igated to optimize phosphorus removal and system sustainability. The system was desi gned to improve both removal and retention of phosphorus. This design concept has the po tential to increase the functional lifespan of treatment wetlands for phosphorus remova l and to decrease the required area or Â“footprintÂ” of the constructed wetlands. Th e potential to reuse the phosphorus-saturated co-treatment materials for agriculture increase s the sustainability of phosphorus fertilizer use and could result in additional cost-sav ings for both crop production and wastewater treatment. The key features of the system investigated in this research were the following: 1. Free or inexpensive drinki ng water treatment residuals, and other non-toxic byproducts available locally, with phosphorus binding potential are used in cotreatments with constructed wetlands. 2. When they have ceased to efficiently remove phosphorus, the co-treatments are materials that could be safely land applied for agriculture. 3. Co-treatments are in cells separate from the wetlands and thus can be emptied (when saturated) and refilled with Â“f reshÂ” material wit hout disturbing the established wetland. 4. Passive mixing of wastewater with co-treatment materials minimizes mechanization and energy costs for wastewater treatment. 5. Separate co-treatment cells allow for flexib ility in future to modify co-treatments based on availability and performance of various co-treatment materials (used singly or in combination). 6. Phosphorus-removing materials used in se parate co-treatment cells increases control of the materials in th e event that treatment conditi ons or priorities change in the future.
11 7. A fraction of co-treatment material will be carried with the wastewater into the constructed wetland and thus may increas e the stability of phosphorus in the wetland itself. 8. The system is designed with both vertical and horizontal flow of wastewater in wetland to maximize contact with wetland root-bed. 9. Alternating flood and drain cycles in each cell will encourage anaerobic and aerobic conditions to optimize phosphorus removal and retention. 10. Cells are batch-fed allowing for operator-c ontrolled hydraulic retention time (HRT) and hydraulic loading rate (HLR). Objectives My central hypothesis was that optimizi ng hydrology and co-treatments could be a low-cost way to enhance P removal by c onstructed wetland systems. The overall objective of the research was to develop and optimize a wastew ater treatment system that employed by-product co-treatments with c onstructed wetlands to enhance phosphorus removal performance and sustainability. The specific objectives were to 1.) scr een potential by-pr oduct co-treatment substrates in the lab for P removal/retention from solution, and other parameters relevant to wastewater treatment; 2.) test sy stem hydrology (flood/drain cycle) and P removal/retention from real wastewater in a greenhouse co-treatment bottle and sand column experiment; 3.) test the substrates , hydrology, and aquatic plants in an outdoor co-treatment and wetland mesocosm syst em for P removal from wastewater; 4.) synthesize the combined data from lab, gr eenhouse and outdoor mesocosm experiments to determine optimization plan for P remova l/retention by the co-treatment and wetland system.
12 Research Approach In order to complete the specific objectiv es, research questions were pursued using a sequence of lab, greenhouse, and ou tdoor mesocosm studies (Figure1). MESOCOSM STUDIES OUTDOORS: 50gal. Co-trt. tanks 150gal. Wtl. Mesocosm tanks WASTEWATER TREATMENT APPLICATIONS: Agricultural (basin scale) Agricultural. (on farm) Municipal Storm-water Lake/Stream Restoration BENCH-TOP STUDIES IN THE LABORATORY: 50mL test tubes COLUMN STUDIES IN THE GREENHOUSE: 1000mL Co-trt. substrate bottles 3"diam. x 2' long sand columns Figure 1-1. Diagram of the research sequence for exploring the application potential of this technology.
13 This sequence progressively leads to ward a better understanding of the biogeochemical and practical f actors of P removal by co-treatment and wetland systems. Forms and amounts of P were measured in al l major components of the systems before and after loading. A mass balance of P in th e mesocosm systems could thus be acquired. Sequential extraction and fracti onation procedures were used to identify the levels and forms of P. Numerous parameters relevant to P removal and retention were measured at each stage of the research. The goal was to measure the biogeochemical variables most closely associated with P removal performan ce and to use this information to optimize and better understand removal. Random assignment and replication of treat ments reinforce the statistical validity and interpretation of the results. The entire research project was divided up into four major tasks: 1-lab studies; 2-greenhouse co lumn studies; 3outdoor mesocosm studies, and 4-synthesis of combined results. Each ta sk helped direct and focus the following task as insight and experience were gained with the system design features. Results at each stage informed the system design process for P removal from municipal and agricultural wastewater. Dissertation Format This dissertation includes fi ve chapters. Chapter 1 presents a brief introduction including statement of problem, need for re search, and objectives. The lab experiments in Chapter 2 include data collection to determine effectiveness of potential co-treatment substrates for removal of phosphorus from solu tion. Results of this study formed a basis to develop subsequent greenhouse column expe riments. Chapter 3 describes the use of greenhouse experiments to determine the e ffectiveness of substrates to remove phosphorus from agricultural and municipal wast ewater in batch-fed bottles. The effluent
14 from the substrate bottles was drained into vertical-flow sand columns to simulate, and test the impacts of, the substrates as co-t reatments with a vertical-flow constructed wetland. The results and experience of this study were then used to design, construct and test a larger scale outdoor system using the substrates in conjunc tion with constructed wetland mesocosms as described in Chapter 4. The overall conclu sions and significance of the combined results and experience of the laboratory, greenhouse, and outdoor mesocosm studies are then presented in Ch apter 5. This final chapter also makes recommendations for applications and de sign details of the technology as well as suggested directions for future research.
15 CHAPTER 2 SCREENING POTENTIAL CO-TREATMENT SUBSTRATES FOR PHOSPHORUS REMOVAL AND PERFORMANCE CHARACTERISTICS Introduction The first task in testing my central hypothesis regarding the enhancement of phosphorus (P) removal from wastewater with co-treatments was to gather several potential substrates and perform relevant tests on them in th e laboratory. As discussed in Chapter 1, by-product co-treatment basins filled with inexpensive and non-toxic byproducts containing P binding components such as iron, aluminum, calcium, magnesium, organic matter or clay, might enhance P removal by constructed wetland (CW) systems (Arias et al., 2003). Ideal materials woul d be free, non-toxic, industrial by-products, generated locally, widely available, and usef ul as soil amendments once saturated with P (MÃ¦hlum and Roseth, 2000; de-Bashan and Bash an, 2004; KvarnstrÃ¶m et al., 2004). Byproducts with the potential to be safely used as agricultural soil amendments, once saturated with P, could increase both the envi ronmental and economic feasibility of this treatment concept (Zhu et al., 2003). Conven tional wastewater trea tment chemicals for P removal are costly and may result in the pr oduction of additional solid waste once they are used in wastewater treatment. Several potential by-product materi als were sought out for initial evaluation with labor atory batch experiments. Two main hypotheses were tested in the la boratory studies. The first was that materials would differ in their abilities to re move and retain P from solution. The second was that certain physico-chemical characterist ics, as suggested by the literature, of the
16 materials would relate to their P removal pe rformance. The objective of the laboratory studies was to determine the P removal and retention capacities of a wide-range of byproduct materials. These experiments were also used to screen out undesirable materials, which were not expected to perform well in a full-scale system, and to choose materials worthy of further investig ation in a greenhouse colu mn study. The laboratory experiments would reveal any handling char acteristics or performance behaviors that might affect performance in a full-scale co-t reatment and constructed wetland treatment system. Information from the suppliers of th e materials and the literature was also used to assess the practical use of the materials as co-treatments and their ultimate disposal or recycling once used for P removal. Materials and Methods Substrate Collection Potential substrate materials were gathered from a variety of sources. One source was the Southern Waste Exchange (SWIX) website. Waste and by-product materials from regional industries and organizations ar e listed with SWIX in an effort to find potential users and thereby reduce the waste stream burden on regional landfills. Ultimately, twelve by-product materials were selected for initial evaluation with laboratory batch experiments and general info rmation about the materials was collected from the suppliers (Table 2-1). A calcium-based (Ca) drinking water trea tment residual (Â“Ca-DWTRÂ”) and an ironbased DWTR (Â“Fe-DWTRÂ”) were obtained fr om nearby public util ities (Gainesville Regional Utilities, Gainesville FL and Hillsborough River Water Treatment Plant, Tampa FL) in the form of wet sludge. A magnesium (Mg) by-product of fertilizer production (Â“SuperMag by-productÂ”) was acquired direc tly from the manufacturer (SuperMag,
17 Bradley FL) as a dry dust. A dried huma te by-product of titanium mining (Â“humate productÂ”) was acquired directly from the pr ocessing research company (SIGARCA, Inc., Gainesville FL). Table 2-1. Description of substrates initially considered for co-treatments. SUBSTRATE COMPOSITION ORIGINAL SOURCE SUPPLIER LOCATION COMMENTS Fe-DWTR Fe humate & hydroxides Ferric sulfate for water treatment Water treatment plant in FL Useful soil amendment Ca-DWTR Calcium oxide (CaO) CaO used to treat water Water treatment plant in FL Useful soil amendment SuperMag by-product Mg, S Mg fertilizer production Fertilizer facility in FL Fertilizer material Humate product Humate, Al, Fe, Ca, Mg, Titanium mining by-product By-product processor in FL Processing costs Sand Â– coated Sand, Fe, Al, clay Sand mine byproduct Sand mine in FL Native material Sand Â– concrete Sand, Fe, Al Sand mining Sand mi ne in FL Market value Sand Â– masonry Sand, Fe, Al Sand mining Sand mi ne in FL Market value Organic soil Histosol with peat and Ca Wetland restoration Wetlands in south FL High value for wetlands Aluminum #1 Al-oxide (Al2O3) Al ore processing Al company Missouri Market value Aluminum #2 Ca, Al, Fe Alcoke mix Al ore processing Al company Missouri Currently land-filled Dehydrated Fe-sludge Fe Vortex dehydrator (processed waste) Waste processor in Kansas Not locally available Sandblast grit Fe; other metals Ship repair (sandblasting paint) Ship repair facilities Toxicity concerns
18 Three sands were obtained from a local mi ne in Grandin, Florida (Florida Rock, Inc., Jacksonville FL). Two of the sands are mined and separated for use in the production of concrete (Â“sand concreteÂ”) or masonry (Â“sand masonryÂ”) products. The third sand had iron coatings (Â“sand coatedÂ”) and was not suitable for those products so it had less value. An organic soil sample (Â“ organic soilÂ”) was obt ained from a wetland restoration project. It ha s high value for use in wetland restoration and not a true byproduct. However, it was analyzed in this study since it is freque ntly a component of natural wetland restoration and phosphorus is so metimes an issue in those projects. Two aluminum materials were obtained from the SWIX waste exchange. The first aluminum material (Â“Al #1Â”) was mostly alumina or Al-oxide (Al2O3). It was later determined that it had been submitted to the waste exchange in error and in fact was not a by-product but a material with high market value for alum inum production. The second Al material (Al #2) was an alumina-coke mixture that wa s a by-product and was currently being land filled according to the supplier. A dried Fe-sludge processed in a vortex dehydrator (Â“dehydrated Fe-sludgeÂ”) was obtained direc tly from the processor (SOS Technologies, Inc., Mission KS) after contacting SWIX. Fina lly, a by-product of ship repair operations (Â“sandblast gritÂ”) listed with SWIX was obtained for P sorp tion studies (Compliance and Remediation, L.L.C., Mango FL). Although some of the materials did not meet all of the criteria for an ideal cotreatment substrate they were chosen for pur poses of comparison. Some of the materials might also have potential to be used in diffe rent types of wastewat er treatment systems and thus their analysis would contribute useful information to the literature. It was also necessary to use materials that were currently available for research purposes, could be
19 obtained free of charge, and would be pere nnially available for follow-up research studies. Phosphorus Sorption Properties Sorption and de-sorption isotherms. The most important property to test of potential co-treatment substrates was their ab ility to remove P from solution (sorption) and to not readily release that P (de-sorption). Sorption of phosphorus was defined here as removing P from solution by association with the solid phase (substr ate material). Desorption was defined as releasing some or all of that P from the solid phase back into solution when equilibrated with P-free solu tion. Substrate sample s were equilibrated with phosphorus solutions in order to determine their potential for removing P from solution and then for retaining that P when equilibrated with P-free solution. For the single-point sorption isotherms, two grams (d ry weight equivalent) of substrate were placed in a centrifuge tube with 20mL of 100 mg L-1 P (as potassium phosphate) solution prepared in a 0.01 molar (M) potassium chlori de (KCl) matrix. Tubes were then placed on an end-to-end shaker for 24 hours. Afte r 24 hours the samples were centrifuged at 6,000 rpm for 10 minutes. The supernatant from each tube was vacuum filtered through a 0.45Âµm membrane filter into a scintillation vial , acidified with one drop of concentrated sulfuric acid (H2SO4) and refrigerated at 4Â°C until an alyzed for P (within 24 hours). All sample solutions were analyzed using the co mmon molybdate colorimetric test (Murphy and Riley, 1962) and a spectrophotometer calibrated with P solutions of known concentration (in the same matr ix) and validated with an ex ternal quality control (QC) sample. The difference between the amount of P left in solution and the amount of P in the original solution was described as the P that was sorbed to the solid phase of the substrate.
20 For the de-sorption isotherms, 20mL of P-free 0.01M-KCl solution was added to the substrate and wet residue left in the t ube after centrif ugation. Tubes were then put back on the shaker for 24 hours after which th ey were centrifuged and vacuum filtered as above. The filtered de-sorption supernatant was then analyzed for P by the same method described above. Taking into account the P content of the wet residue, the mass of P desorbed per kilogram of substrate was calculate d based on the P content of this de-sorption supernatant. Multipoint isotherms. Multipoint P sorption isotherms were completed in order to derive theoretical sorption maximum (Smax) and equilibrium P concentration (EPC0) values for potential co-treatment substrates . These P retention parameters give some indication of the potential P removal performa nce of substrates under various P loading and solution concentration conditions. The me thod is the same as described above for the P sorption isotherms however, groups of sample replicates were equilibrated with several different concentrations of P (0, 0.5, 1, 2, 5, 10, 20, 50, and 100 mg P L-1). Samples were also analyzed similarly but with semi-automated colorimetry according to US EPA Method 365.1 (US EPA, 1993 [b]). The P retentio n parameters of interest were derived using the Langmuir equation as described in previous research (Reddy et al., 1998 [a]). The desired parameters and coefficients are derived using two different graphs of the multipoint isotherm data. First, the mg of P adsorbed per kg of material (SÂ’) versus P left in solution after 24 hours of equilibration (C24) were plotted. The linear portion (linear regression yields r2 > 0.94) of this curve is described by equation one below. SÂ’ = kdC24-S0 (1)
21 The slope of that line (kd) is the linear sorption coefficient. The y-intercept of the line (S0) represents the amount of P or iginally sorbed to the mate rial. The total amount of P sorbed to the solid phase (S) is equal to SÂ’ plus S0. The x-intercept of the line represents the point at which adsorption a nd de-sorption are equal and is called the equilibrium P concentration (EPC0). The second graph plots C24/S versus C24 and the linear portion of this curve is the linear form of the Langmuir equati on and is written as equation two below. The theoretical maxi mum amount of P the material can adsorb (Smax) is the inverse of the slope. Calculating Smax allows for the calculation of the constant (kb) related to bonding energy. (C24/S) = (1/Smax) C24 + (1/kb Smax) (2) Kinetic study. Substrate samples were equilibrated with phosphorus solutions for different lengths of time in order to dete rmine relative rates of removal of P from solution. This data could provide insight into the theoretical hydrau lic retention times for wastewaters in P co-treatment basins. The me thod is the same as described above for the P sorption isotherms; however, groups of sa mple replicates were equilibrated for 0.5, 1, 2, 4, or 12 hours. Phosphorus remaining in solution was plotted against equilibration time and regression analysis was done to descri be the rate of P removal and to provide insight into the type of P re moval process for each material. Physico-chemical Properties of Substrates Inorganic phosphorus fractionation analysis. Substrates were analyzed for their inherent inorganic P forms. This info rmation could not only describe how P was currently retained in these materials but also where additional P may potentially be stored. It will also provide insi ght into the stability of P in these materials before they are exposed to additional P loading. Substrate samples (0.5 grams dry weight equivalent)
22 were subjected to an inorganic P sequential fr actionation scheme as de scribed in previous research (Reddy et al., 1998 [b]) but using an initial substrat e to solution ratio of 1:50 on a weight to volume basis. Sequential extr actants used included 1-M KCl, 0.1-M NaOH, and 0.5-M HCl. The NaOH extracts were analy zed for both soluble reactive P (SRP) and total P (TP). The residue from the final HCl extraction was combusted at 550Â°C for 4 hours and dissolved in 6-M HCl before anal ysis. All solutions were analyzed as described in the P isotherm methods sections above. Metals analysis. Substrate extracts were analyzed for content of the main metals that are known to be significant to P so rption, namely Ca, Mg, Fe, and Al. Sample replicates (0.5 grams dry weight equivalent s each) were subjected to acid ammonium oxalate extractions for Fe and Al (Sheldric k, 1984), and 1-M HCl (3 hour equilibration on shaker) extractions for Ca and Mg, as these ar e thought to be the forms most relevant to P sorption. Filtered (0.45Âµm) extr acts were analyzed for Fe, Al, Ca, and Mg by atomic absorption spectrophotometry (AAS) using US EPA Methods 236.1, 202.1, 215.1, and 242.1 respectively (US EPA, 1993 [b]). Particle-size distribution analysis. Nine of the materials were analyzed for particle-size distribution. The method was adapted from a standard method for analyzing the particle-size distribution of the mineral fraction of so il samples (USDA NRCS, 1992). This method yields the relative percentage of the three soil size fractions: sand, silt and clay, based on their theoretical particle-size di ameter. In actual soil samples, the claysized particles are known to be involved in P sorption and particle-size was suspected to be relevant in the potential co -treatment substrates as well. It should be noted that when using this analytical method soluble salts can be counted as clay particles and thus
23 introduce some error in the interpretation of the results. The theoretical specific surface area of the materials was determined by assu ming that sand particles have a specific surface area of 30, silt 1,500, and clay 3,000,000 cm g-1. Particle-size distribution, and the theoretical specific surface area that can be calculated from it, is also relevant to the ultimate cropland application of potential co-treatment substrates as discussed earlier. The humate product could not be analyzed in this way due to the high organic content and the internal porosity of the hardened aggregates. Results Phosphorus Sorption Properties Sorption and de-sorption. Substrate P sorption poten tials ranged from a low of 66 mg kg-1 to a high of 990 mg kg-1 (Table 2-2). The maximum possible amount of P available for sorption in this experiment was 1000 mg kg-1 and several samples adsorbed almost 100% of this P. De-sorption of the P by substrates ranged from a low of less than 10 mg kg-1 (the detection limit of the method used) to a high of 178 mg kg-1 (Table 2-2). The two sands and the sandblast grit desorbed less than 5 to 10% of adsorbed P. The Kansas iron, SuperMag by-product, Fe-DWTR, and humate product released approximately 1% or less of adsorbed P. The organic soil released th e greatest amount of adsorbed P. It released over 25% of adsorbed P. Overall, the aluminum (Al #1), magn esium (SuperMag by-product), iron (FeDWTR), calcium (Ca-DWTR), and dried humate materials exhibited the highest P removal and retention capacities. The concrete -grade coarse sand removed very little P from solution compared to the other materials.
24 Table 2-2. The sorption and de-sorption (Â± one standard deviation) of P by several substrates. SUBSTRATE Phosphorus Sorption Phosphorus De-sorption Â…Â….Â… mg kg -1 Â…Â…Â…. Sand concrete 66.2 Â± 18.3 < 10 Sand masonry 96.8 Â± 8.8 < 10 Sandblast grit 243.6 Â± 29.4 < 10 Sand coated 515.4 Â± 13.4 14.1 Â± 4.7 Organic soil 657.1 Â± 9.2 178.5 Â± 16.2 Al #2 804.9 Â± 26.7 47.2 Â± 3.2 Ca-DWTR 893.5 Â± 20.3 33.7 Â± 7.1 Al #1 911.7 Â± 5.8 34.4 Â± 2.5 Dehydrated Fe sludge 920.2 Â± 38.9 < 10 SuperMag byproduct 944.1 Â± 8.6 < 10 Fe-DWTR 952.1 Â± 15.9 < 10 Humate product 990.1 Â± 5.0 < 10 Multipoint isotherms. For each substrate the mass of P adsorbed to the substrate (SÂ’) was plotted against the concentration of P left in solution after the 24-hour equilibration period (C24). The graphs of SÂ’ versus C24 from the multipoint P isotherms are presented in three separate graphs (Figure 2-1) due to the wide variation in P sorption results for the eight substrates. The Langm uir isotherms assume a finite number of adsorption sites for P and thus have an implied maximum sorption value (Smax). Log
25 regression curves are shown for each substrate and the r2 values suggest a good fit to this model of P sorption. The curves for the conc rete and masonry sands plateau at less than 70 mg kg-1. The sandblast grit, organic soil, and coated sand curves plateau between 100 and 400 mg kg-1. The curves of the two aluminum ma terials, and of the humate product appear to level out between 500 and 1300 mg kg-1. The results of the multi-point P isotherm data allowed for the calculation of linear sorption coefficients (kd), equilibrium P concentrations (EPC0), theoretical P sorption maximums (Smax), and constants rela ted to bonding energy (kb) as presented in Table 2-3, using the linear portion of the adsorption isothe rm curves. This method of utilizing the data has been described in detail in prev ious research (Reddy et al., 1998 [a]; Reddy et al., 1999 [a]; Pant et al., 2001). The kd values presented in Table 2-3 are know n as linear sorption coefficients and represent the slopes of the linear portion of the adsorption isotherm curves. The aluminum (#1) and coated sand materials had the highest kd values. The organic soil had the lowest kd value. The EPC0 values are taken as the point at which the curve crosses the C24 axis. This is the point at which sorpti on is equal to de-sor ption and thus it is referred to as the equilibrium P concentration. Theoretical EPC0 values ranged from 0.364 (organic soil) down to 0.003 mg L-1 (aluminum materials) as shown in Table 23. Using the results from the adsorption isotherm curves and then plotting C24 S-1 vs. C24 one can obtain Smax and kb values using the linear form of the Langmuir equation.
26 r2 = 0.83 r2 = 0.980 10 20 30 40 50 60 70 80 01020304050 Sand-concrete Sand-masonry r2 = 0.98 r2 = 0.96 r2 = 0.860 100 200 300 400 500 051015202530 Coated Sand Organic Soil Sandblast Grit r2 = 0.73 r2 = 0.83 r2 = 0.860 400 800 1200 1600 2000 020406080 Aluminum #1 Aluminum #2 Humate Product Figure 2-1. Multi-point phosphorus sorption isotherms (Â± one standard deviation) for eight substrates showing log tre nd lines and their associated r2 values. SÂ’ (mg kg-1) C24 (mg L-1)
27 Theoretical Smax values ranged from 46 (coarse sand) up to 2000 mg-P kg-1 (dried humate product). The kb values presented are the constant s that are thought to be related to P bonding energy. The orga nic soil had the lowest kb value and the masonry sand, coated sand and aluminum materi al (#1) had relatively high kb values. Table 2-3. The linear sorption coefficients (kd), equilibrium P concentrations (EPC0) (with associated r2), P sorption maximums (Smax), and constants related to bonding energy (kb) (with associated r2) calculated for several substrates from the multi-point sorption isotherm data ranked from lowest to highest Smax. SUBSTRATE kd (L kg-1) EPC0 (mg L-1) r2 Smax (mg kg-1) kb (L mg-1) r2 Sand concrete 297 0.011 0.98 46 0.46 0.96 Sand masonry 442 0.006 0.99 54 4.72 0.99 Sandblast Grit 347 0.020 0.98 233 0.46 0.99 Sand coated 1466 0.017 0.98 417 4.00 0.99 Aluminum #2 362 0.003 0.99 476 1.00 0.99 Aluminum #1 1755 0.003 0.96 500 3.33 0.98 Organic soil 32 0.364 0.98 625 0.05 0.92 Humate product 461 0.050 0.98 2000 0.25 0.99 Kinetic study. The graphs of the results of th e P sorption kinetic study also had to be presented in three separate graphs (Figure 2-2) due to th e wide variation in rates of removal of P from solution. The Fe-DWTR ma terial removed P so rapidly from solution that an adequate regression curve co uld not be calculated for the graph. The equations for the regression curves s hown in Figure 2-2 are presented in Table 2-4. The r2 values indicate a good fit with all of the regression curves derived except for the concrete sand. This is expected since th is sand performed poorly at removing P from
28 0 10 20 30 40 50 60 70 80 90 100 110 120 024681012141618202224 Sand-concrete Sand-coated Humate Product 0 5 10 15 20 25 30 024681012141618202224 Lime-DWTR Aluminum #1 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 024681012141618202224 Fe-DWTR SuperMag Figure 2-2. Phosphorus remaining in solution (Â± one standard deviat ion) after various equilibration periods with seven substrates. Phosphorus Remaining in Solution (mg L-1) Equilibration Time (hours)
29 solution, irrespective of the e quilibration time. The fact that the equations are all negative log, power or exponential, suggest s that P may be rem oved from solution by precipitation reactions. Table 2-4. Regression equations and r2 values of the regression curves, shown above in Figure 2-2, for seven substrates. In th e equations, y represents concentration of phosphorus remaining in solution, and x represents equilibration time. SUBSTRATE REGRESSION EQUATION r2 Sand-concrete y = 0.02 x2 + 0.34 x + 96.79 0.70 Sand-coated y = 73.6 e-0.02x 0.99 Humate product y = -22.3 ln(x) + 82.6 0.95 Ca-DWTR y = -4.9 ln(x) + 20.7 0.92 Aluminum #1 y = -4.4 ln(x) + 20.6 0.95 SuperMag by-product y = 1.8 x-0.4 0.90 Physico-chemical Properties of Substrates Inorganic Phosphorus fractions. The seven substrates analyzed, displayed a wide range of initial P amounts and forms. The am ounts of each operationally defined form of P are provided in Table 2-5 below. The KCl fraction is considered to be labile or readily available P. There was very little of this form in the substrates analy zed and it was below detection limits in many materials. Most of these materials had been exposed to weathering in their previous uses so would not be expected to retain labile P.
30Table 2-5. Inorganic P fractionati on analysis was done to further characterize th e potential substrates. Values represent mass of that P fraction (if above detection limit) per kg of substrate (Â± one standard deviation). Phosphorus Fractions KCl NaOH-Pi NaOH-Po HCl Residual Sum Substrate Â…Â…Â…Â….Â…Â…Â…Â…Â…Â…Â….Â…Â…Â…Â….. mg kg-1 Â…Â…Â…Â…Â….Â…Â…Â…Â…Â…Â…Â…Â…Â…Â…Â… Sand concrete < 0.10 13.53 Â± 0.86 < 1.50 10.57 Â± 3.33 8.02 Â± 0.65 32.22 Â± 3.35 Sand coated < 0.10 430.11 Â± 37.53 < 1.50 < 1.00 333.09 Â± 16.69 763.20 Â± 51.36 Aluminum #1 < 0.10 < 0.50 2.06 Â± 0.02 0.24 Â± 0.05 2.45 Â± 0.03 4.95 Â± 0.06 SuperMag by-product 0.12 Â± .02 < 0.50 2.04 Â± 0.07 60.42 Â± 4.70 8.58 Â± 1.15 71.25 Â± 5.75 Ca-DWTR < 0.10 < 0.50 1.95 Â± 0.14 0.77 Â± 0.09 25.79 Â± 1.36 28.77 Â± 1.46 Fe-DWTR 0.99 Â± 1.5 11.30 Â± 3.35 214.74 Â± 33.92 1.56 Â± 0.97 142.55 Â± 62.41 371.14 Â± 51.24 Humate product 0.14 Â± 0.03 66.44 Â± 7.06 < 1.50 397.34 Â± 5.40 185.29 Â± 8.92 649.21 Â± 15.18
31 The NaOH-Pi fraction is believed to represen t Feand Al-bound P since these metals tend to release P at elevated pH leve ls. The coated sand ha d the highest level of this fraction. The Fe-DWTR did not have a high level of this fraction in comparison. The difference between the NaOH-TP of the sample extracts and the NaOH-Pi is assumed to be the organic P associated with fulvic and humic acids (NaOH-Po). The NaOH-Po fraction was highest in the Fe-DWTR. The HCl fraction is assumed to represen t Caand Mg-bound P since these metals tend to release P under low pH conditions. Th e humate product had the highest level of this fraction and the SuperMag material also had a relatively high level. The Ca-DWTR did not have a comparatively high level of this fraction. The residual P fraction is normally regarded as representing relatively unavailable organic P forms but may also include tightly bound inorganic P forms. The coated sand, Fe-DWTR, and humate product each had relativel y high levels of this fraction. The sum of each of these fractions is also provided in Table 2-5 and is comparable to the TP levels found in these materials. The relative proportions of each P fraction ar e provided for the seven substrates in Figure 2-3. The P in the concrete sand wa s almost evenly divided between the NaOH-Pi, NaOH-Po and residual fractions but overall held comparatively little P. The P in the coated sand was almost evenly divided between the NaOH-Pi and residual fractions. Most of the P in the aluminum material was in the NaOH-Po and residual fractions but there was about 5% in each of the NaOH-Pi and HCl fractions. The P in the SuperMag material was primarily in the HCl fraction th at is thought to repr esent Caand Mg-bound P. The Ca-DWTR on the other hand had P pr imarily residing in the residual fraction.
32 The P in the Fe-DWTR was mostly in the NaOH-Po and residual fractions. Finally, the humate material was dominated by the HCl fraction with lesser proportions in the residual and KCl fractions. 0% 20% 40% 60% 80% 100%Sand concrete S a n d -c o ate d Alu min u m # 1 SuperMag Ca-DWTR F e -DWTR H u ma te Residual HCl NaOH-Po NaOH-Pi KCl Figure 2-3. The relative proportions of P fractions in seven su bstrates were determined. The total masses (mg) of P per mass (kg) of substrate are provided above each column. Extractable metals in substrates. A wide range extractab le metal concentration was found in the materials analyzed and are pr esented in Table 2-6. The concrete sand had relatively high oxalate-extract able Al. The masonry sand had low levels of all metals extracted. The coated sand had relatively high oxalate-extractabl e Fe and Al. The sandblast grit had relatively high levels of all metals extracted. The organic soil had very high HCl-extractable Ca and high Mg as we ll as high oxalate-extractable Fe. The aluminum material #1 had high leve ls of oxalate-extractable Al. 32 763 5 71 29 371 649
33 Table 2-6. Extractable metals (Â± one sta ndard deviation) important to P sorption measured in several potential substrates. Substrate Oxalate Extracted Metal (mg kg-1) HCl Extracted Metal (mg kg-1) Iron Aluminum Calcium Magnesium Sand concrete 45 Â±23 314 Â±510 6 Â±0 2 Â±3 Sand masonry 32 Â±4 32 Â±9 8 Â±3 20 Â±9 Sand Coated 875 Â±25 548 Â±19 41 Â±3 21 Â±6 Sandblast Grit 12129 Â±1868 5173 Â±355 10267 Â±318 1467 Â±318 Organic Soil 2135 Â±199 550 Â±44 79596 Â±13584 1790 Â±844 Aluminum #1 < 2 8330 Â±409 128 Â±32 < 5 Aluminum #2 2361 Â±826 14918 Â±1549 51883 Â±1145 121 Â±105 Humate Product 3114 Â±443 14180 Â±2165 1100 Â±550 162 Â±35 SuperMag By-product 653 Â±10 276 Â±10 1998 Â±18 167838 Â±972 Ca-DWTR 608 Â±197 684 Â±62 343750 Â±4911 19599 Â±163 Fe-DWTR 174685 Â±2292502 Â±13 7924 Â±66 < 5 The aluminum material #2 had the highest level of oxalate-extractable Al but also had relatively high levels of Fe and HCl-extractable Ca. Th e humate product contained a high concentration of oxalate-extractable Al but also considerable am ounts of Fe and Ca.
34 The SuperMag material contained the highest level of HCl-extractable Mg but also contained considerable Ca. The Ca-DWT R contained the highest levels of HClextractable Ca but also had ve ry high levels of Mg. The Fe-DWTR contained the highest levels of oxalate-extractable Fe and also large amounts of Ca. Particle-size distribution. The results of the particle-size distribution analysis are presented as proportions of theoretical size fractions in Table 2-7 below. Table 2-7. Particle size distri bution of substrates as dete rmined by the standard soil method. Phosphorus sorption data is presented for comparison. Substrate Theoretical Particle Diameters (0.05 to 2.0 mm) (%) (>0.002 and <0.05 mm) (%) (< 0.002 mm) (%) Theoretical Specific Surface Area (cm2 g-1) Phosphorus Sorption By Substrate (mg-P kg-1) Aluminum #1 96.5 3.5 0.0 81 912 Aluminum #2 80.2 19.8 0.0 322 805 Sandblast Grit 95.7 4.0 0.3 9689 244 Sand concrete 99.1 0.1 0.8 24031 66 Sand masonry 96.3 2.8 0.9 26471 97 Sand coated 80.8 2.2 17.0 508857 515 Fe DWTR 82.6 15.6 1.8 55458 952 Ca DWTR 0.7 95.1 4.2 126227 893 SuperMag By-product 36.0 41.5 22.5 675034 944
35 In soil samples the three size fractions are operationally described, based on their particle size diameters, as sand (0.05 to 2.0 mm), silt (< 0.05 and >0.002 mm) and clay (< 0.002 mm). Several substrates, though not soils, were analyz ed for their proportions of these theoretical particle sizes. The al uminum, sand, and Fe-DWTR materials were composed primarily of sand-sized particles. The Ca-DWTR was do minated by silt-sized particles. The SuperMag by-product was fair ly evenly divided between sand, silt, and clay-sized particles. Discussion Phosphorus Sorption Properties Sorption and de-sorption. The single point P sorption and de-sorption isotherms conducted give some indication of the potential for the candidate materials to adsorb, and to not readily release, P in solution (Brix et al., 2001; Zhu et al., 2003; Seo et al., 2005). The aluminum, iron, calcium, magnesium and hu mate materials all removed substantial amounts of P from solution and re leased relatively little P upon equilibration with P-free solution. The organic soil desorbed the hi ghest amount of adsorbed P making it a poor candidate for use in a co-treatme nt system. It also has a ve ry high value as either upland or wetland soil so it would not be widely av ailable for use in a wastewater treatment system. The coarse sand (c oncrete-grade) removed relativel y little P from solution. It would not be a good material to use as a co-tre atment substrate. However, this feature would make it a useful material for further studies requiring a rela tively inert substrate with respect to P removal. In these laboratory batch experiments of s hort duration the P sorption is expected to be primarily inorganic. The four main inor ganic P reactions are 1.) precipitation with Al, Fe, Manganese (Mn), Ca or Mg; 2.) anion exch ange; 3.) reaction with hydrous oxides; 4.)
36 fixation by silicate clays. Precipitation is expected to be the primary mechanism with these materials. Multipoint isotherms. Reduction and analysis of the multi-point phosphorus isotherm data provided insight into the potential for these materials to be effectively used for removal of P from wastewater. A high Smax indicates the material has the potential to adsorb more total P mass than lower ranked materials. A low EPC0 is an indication that the material will continue to adsorb P even when the overlying water column has a low orthophosphate concentration. The humate pr oduct had the highest Smax but the two aluminum materials had the lowest EPC0. The organic soil had a high Smax but it had the highest EPC0 making a poor candidate for low P wastewater treatment. The organic soil also had the lowest kb value. This coincided with the highest P de-s orption, supporting the premise that the kb value is related to bonding ener gy, and that the wetland organic soil itself is not inherently effective at removing and retaining P from solution. Conversely, the masonry sand had the highest kb value and one of th e lower de-sorption concentrations of these substrates. Th is further supports th e description of kb values but this sand also had a very low Smax and thus would not be a good co-treatment substrate in spite of the exhibited te nacity of P adsorption. Kinetic study. The kinetic study results indicate that the Ca-DWTR, aluminum #1, Fe-DWTR and SuperMag materials all remove P from solution very quickly to relatively low levels. The Humate product and the Fe-D WTR brought P to the lowest levels in 24 hours. The Fe-DWTR removed most of th e P applied within 0.5 hours, which would make it a good candidate for a co-treatment syst em with a short hydrau lic retention time.
37 The regression equations for the kinetic study indicate that precipitation may be a mechanism of P remova l by these materials. Physico-chemical Properties of Substrates Inorganic phosphorus fractionation. Most materials contained little or no P in the KCl fraction. This suggest s that none of the materials would readily release P upon exposure to water in a co-treatment system . The coated sand contained the largest fraction associated with Feand Al-bound P (NaOH-Pi fraction). The Fe-DWTR did not have a large amount in this fraction and it may represent the potential of this material to adsorb more P. The Fe-DWTR did have the la rgest amount of P in the fraction thought to be alkali-extractable organic P (NaOH-Po). The Fe-DWTR is commonly referred to as Â“iron humateÂ” in the industry since it is used to remove dissolved organic material from drinking water treatment supplies that are darkly colored. The humate product and SuperMag materials had the highest levels of P assumed to be Ca and Mg-bound (HClfraction). The Ca-DWTR had relatively little P in this fraction and this may represent potential for adsorption of P. With th e exception of the Fe-DWTR and the humate product, these materials had relatively low levels of organic matter. This suggests that at least part of the residual P fractions we re composed of crystalline or tightly bound inorganic forms that were only released upon combustion. The coated sand, Fe-DWTR and humate product had the highest sums of P fractions coinci dent with thei r ability to remove P from solution. This may be count er-intuitive but not uncommon that materials already high in TP may still have great potential adsorb P from solution. Extractable metals. The concrete and masonry sands had relatively small amounts of oxalate-extracted Fe and Al, and HCl-extracted Ca and Mg, for binding P. The coated sand had higher iron and aluminum levels that may have contributed to its
38 better P removal performance since the materi als otherwise were very similar (mined from the same site and artificially separate d by color and particle size). The sandblast grit had relatively high levels of all of the metals extracted contributing to its P removal performance. However, as reported by the s upplier, it also containe d some heavy metals in small amounts. That factor might limit its potential as a suitable co-treatment substrate in a wastewater treatment system that incl uded repeated cropland application. The high Ca content of the organic soil likely contribu ted to its P removal but as mentioned earlier it is not a potential co-treatme nt substrate due to its high va lue elsewhere. The aluminum #1 material was a refined ma terial (alumina) and thus contained mostly oxalateextractable Al available for P sorption. Th e aluminum #2 material was actually an alumina-coke mixture that was a waste product of the refining process and thus had Fe, Al and Ca potentially available for P sorp tion. The humate product had very high levels of oxalate-extractable Al that were probably responsible for most of its P sorption. The SuperMag product had the highest HCl-extractab le Mg available for P sorption. The CaDWTR had the highest HCl-extractable Ca and the Fe-DWTR, not surprisingly, had the highest level of oxala te-extractable Fe. The P removal parameters of all of these materials that were compared to their extractable metals contents. Comparisons we re made between their moles of individual metals, pairs of metals and a ll metals vs. their P sorption, Smax and EPCo values. In none of these comparisons was any significant corre lation found. This is not surprising since they were such different materials with widely different metals cont ents. These types of significant correlations would be more likely among common so ils that varied only in their metals contents.
39 Particle-size distribution. In soil samples the three size fractions are operationally described as sand, silt and clay. These desi gnations would only apply to the three sand substrates. However, as noted in the Methods section above, particle size and theoretical specific surface are relevant to the suitability of co-treatment substrates. The theoretical specific surface area did correla te well (linear regression r2 of 0.99) with P sorption for the three sands (concrete, masonry, and coated). The coated sand had a large proportion of its theoretical specific surface area contributed by its relatively high clay fraction. Many type s of clay are known to contribute to P sorption in soils and perhap s some contributed to the coated sands P removal performance (and perhaps its low kb value in the multipoint isotherm data). The particle size distributions did not necessarily correspond to P sorption performance (P sorption, Smax, or EPCo) in the other materials. This is not surprising since the materials had very different metal contents that would affect P sorption more directly. The particle size distribution of the material s does have relevance to the ultimate application of these materials to cropland after they had been used to remove P from wastewater. If they contributed a dditional surface area to the soil they might increase cation exchange capacity (CEC) and water holding capacity of the soil. This would increase the desirability of the materi al by farmers and thus increase the feasibility of using the material as a renewable co-tre atment for wastewater treatment systems. Conclusions The Al #1, Fe-DWTR, Ca-DWTR, SuperM ag by-product, humate product and coated sand removed substantial amounts of P from solution. These materials also had the potential to remove P from low P wastewater s. These materials may be useful as co-
40 treatments for P removal with CW systems. Some materials were not locally available and others presented potential toxicity concerns . The Fe-DWTR, Ca and magnesium mate rials contain plant nutrients and thus may be desirable as soil amendments after be ing used as co-treatments. The coarse concrete-grade sand was found to be relatively inert with resp ect to P and thus would be useful as a substrate in late r column or mesocosm studies. Based on the results of these laborato ry studies and the several practical considerations discussed, the SuperMag byproduct, Fe-DWTR, Ca-DWTR, coated sand, Al #1, and humate product were chosen for further evaluation as co-treatments in a greenhouse column study. The concrete sand was chosen as the column substrate.
41 CHAPTER 3 REMOVAL OF PHOSPHORUS FROM AGRICULTURAL AND MUNICIPAL WASTEWATERS WITH CO-TREATMENTS AND SAND COLUMNS Introduction Laboratory studies demonstrated that se veral by-product materials could remove phosphorus (P) from solution. The next step in evaluating the potential of by-products for use in wastewater treatment was to conduct a greenhouse study in which real wastewaters would be loaded to the materials in co-treatment bottles before flowing into sand columns. Column and greenhouse studies are considered useful tools for evaluating the performance of co-treatment and wetland su bstrates (Brix et al ., 2001; KvarnstrÃ¶m et al., 2004). Based on the initia l screening process in the lab, and several practical considerations, six substrat es were chosen for these greenhouse column studies. The sand columns in this study were used to represent the ver tical profile of a constructed wetland (CW) built on mineral soils or sands. As in a real CW any removal in the sand columns is necessarily unsustainabl e unless they are emptied and refilled with new material. Removal and refilling is im practical and cost-prohibitive with CW but may be feasible in separate co-treatment containment areas, such as represented by the substrate bottles in this st udy. The sand used in the columns was the coarse (concretegrade) sand that had relatively low P removal and retention capacities based on the earlier lab studies. This was intended to represent a wetland profile that had a low capacity to remove additional P. For experimental purpos es that should highlight the contribution of the by-product co-treatments co mpared to the control units.
42 The overall objective of this greenhouse sa nd column study was to test if combined co-treatment bottle and sand column systems would remove more P from municipal and agricultural wastewater if the co-treatme nt bottles were filled with P-adsorbing byproducts. There were several specific hypot heses being tested by the column study. First, P removal by the potential co-treatme nt materials from r eal wastewater would differ from their performance with artificial la boratory P solutions used earlier. Second, P removal in a static system such as the co -treatment bottles would be less than in the shaken tubes used in the laboratory studies . The P removal with a 3.5-day hydraulic retention time (HRT) was also expected to differ from the removal in the 24-hour laboratory experiments. Finally, it was susp ected that the P concentrations in the effluents of columns that followed by-product co-treatment bottles would be lower than those from the control columns that followed empty co-treatment bottles. There were numerous scientific and opera tional objectives pursued in the column studies. Although P removal performance was th e major point of interest, several other characteristics and behaviors of the materials, and the system design specifications, were tested more thoroughly by the greenhouse colu mn studies than could be done with laboratory studies alone. The effectiveness of non-mixed batch-fed co-treatment reactors, with a 3.5-day HRT, was being tested. The handling, containment, chemistry and hydraulic properties of the wastewaters and byproducts in this type of system would provide critical data and experience for the desi gn of a larger scale system. This column stage of the overall research plan was also intended to provide insight into hydraulic conductivity issues associated with clogging of the substrates, sand and gravel drainage
43 beds. Clogging of systems by bio-films (Wu et al., 1997) is a concern and was monitored during this part of the research. Materials and Methods Co-Treatment and Column Construction and Operation Design features and system operation. Earlier laboratory studies suggested the potential of six by-products including: aluminum material number one; the SuperMag fertilizer by-product; the drie d humate product; the coated sand; the Ca-DWTR; and the Fe-DWTR. The greenhouse column study paired these six potential substrates in cotreatment bottles with sand columns that re presented vertically drained constructed wetlands. The paired units were batch-fe d municipal (low P) or dairy (high P) wastewater for one month. The dairy effl uent had undergone anaerobic digestion for primary treatment but still had high phos phorus levels. The secondarily treated municipal wastewater had relatively low P leve ls. The effluent from a substrate bottle, representing a co-treatment ta nk or basin, flowed into a sa nd column that represented a constructed wetland profile (Figure 3-1). W ith two wastewaters, six substrates and a control, each replicated thr ee times; there were a total of 42 of these paired units randomly placed in the slots of a 48-column rack in a greenhouse. Dry weight equivalent amounts of substrates were placed in the co -treatment bottles and wastewater was poured into them from a height of three feet. Th is fall was chosen to represent a reasonable hydraulic head, due to gravity feed or pu mping, for the effluent from a primary wastewater treatment system or lagoon. Th e falling wastewater was the only mixing energy that was used for the wastewater a nd co-treatment material. After a hydraulic retention time (HRT) of 3.5-days, the wastew ater was decant-drained from the cotreatment bottles (drain outlet was above leve l of substrates in bottles) into the sand
44 columns for an additional HRT of 3.5-days. Sand had been placed in the columns at approximately the same depth as would occu r in experimental wetland mesocosms. The substrate dry mass was the same in all of the bottles and was based on a conservative design. The incoming wastewater P con centration was assumed to be 30 mg L-1 and the removal rate was assumed to be 500 mg-P kg-1 of dry substrate. A D B C Figure 3-1. This is a schematic diagram of one of the 42 experimental units used in the column study. Wastewater was added (A) to the co-treatment substrate bottle (B). Bottle effluent was drained into the sand column (C) from where it was later drained (D). Since 500mL of wastewater could be load ed to the bottles, and the column sand surface was approximately 28.3 cm2, the hydraulic loading rate (HLR) for a 3.5day
45 hydraulic retention time (HRT) was 5.1cm day-1. This HLR coincides with typical design parameters for a wastewater treatm ent wetland (Kadlec and Knight, 1996). The sides of the clear plastic columns were covered with aluminum foil to prevent algae growth below the su rface of the sand profile. Testing the turbidity of s ubstrates in the system. During laboratory studies with the substrates differences were noted in their settling times in solution. Before implementing the design of the co-treatment bo ttle there was some concern as to whether all materials would settle out of solution w ithin the 3.5-day HRT. Wastewater flowing from the co-treatment bottle to the sand column could carry substrate material. If a large portion of the material remained suspende d, the co-treatment bottle would become rapidly depleted of substrate with each treatm ent cycle. Likewise, the associated sand columns might become rapidly clogged with th ese suspended substrate materials. On the other hand, a small amount of transport of collo idal substrate material was expected from the co-treatment bottle to the sand column a nd this could be a favorable occurrence. Small amounts of substrate material might help to stabilize P in the sand columns without clogging them prematurely. To test this impor tant variable of turbidity in solution, 250 ml of distilled and de-ionized water was dropped from a height of 3 feet (0.91 m) into 450 ml cylindrical glass jars containing dry weight equivalent masses (25 g) of each substrate. There were three replicates of each material tested. This arrangement was used to represent the situation with the e xperimental unit design described above. The solutions were sampled immediately (tim e zero) and at 0.5, 1, 2, 4, and 24 hours by collecting 10 ml with a wide-bore syringe pl aced at 6 cm above the bottom of the jar. Samples were kept in 20 ml plastic scintill ation vials to be anal yzed with a Milton Roy
46 Spectronic 601 spectrophotometer with a 1 cm light path and with wavelength set at 420 nm. Before analysis, each vial was shaken vigorously, inverted to allow any bubbles to dissipate, and re-inv erted before placing into the absorption cell of the spectrophotometer. Absorbance readings were taken 15 seconds after placing sample in cell. Some samples had to be diluted with di stilled de-ionized water, especially for time zero samples. Turbidity is normally measur ed in nephelometric turbidity units (NTU) directly by a specialized turbidimeter wh en available (American Public Health Association [APHA], 1998). Ab sorbance was used here as an analog for turbidity in the absence of a turbidimeter. Absorbance values and NTU values are not necessarily linearly related. However, with these samp les, calibrating the spectrophotometer with NTU standards and then converting absorbance values to NTU produced essentially the same results. Analysis of Phosphorus Removal Performance Analysis of wastewaters, co-trea tment and sand column effluents. Phosphorus forms and levels in the wastewaters, and bottl e and column effluents, were measured for each treatment cycle. Wastewaters and efflue nts were collected and then transported to the laboratory in coolers. Samples were vacuum-filtered through 0.45 Âµ m membrane filters into plastic scintillation vials and st ored at 4Â° C until analysis. Samples were analyzed for soluble reactive P (SRP) with se mi-automated colorimetry according to USEPA Method 365.1 (US EPA, 1993 [b]). This part of the research focused on SRP because this is the only form the co-treatment substrates were expected to remove from wastewater through adsorption and precipita tion mechanisms. However when it was noted that some particulate P was also be ing removed from the wastewaters it was
47 decided to plan look more closely at total P (TP) a nd total dissolved P (TDP) concentrations in the larger scale me socosm experiments to be done later. Preand post-loading analysis of substrates and sand. Phosphorus forms and levels in the by-product substrat es from the co-treatment bo ttles, and in the sands from the columns, were tested at the beginning a nd end of the 32-day experiment to measure P removal and storage. For post-loading samples, the entire substrate present in each cotreatment reactor bottle, or the entire sand present in each column, was homogenized before sub-sampling for analysis. To tal phosphorus (TP) by the ignition method (Anderson, 1976) was measured in all substrates and sands before and after loading with wastewater for 32-days. Substrate and sand sa mples (three replicates of each sample) were oven-dried to remove most water before placing 0.5 grams of each in a beaker and then into a muffle furnace at 550Â° C for 4 hours. Samples were then digested in 6.0MHCl and filtered (Whatman #41 filter paper) for analysis by semi-automated colorimetry according to US-EPA Method 365.1 (US-EPA, 1993 [b]). Oxalate-extractable P was determined in substrate and sand sub-samples before and after loading with each of the two wastewaters. Samples were subjected to acid ammonium oxalate extractions for P (Sheldrick, 1984). The filtered (0.45 Âµ m) extracts were analyzed for P (by ICAP) at the Univ ersity of Florida Analytical Research Laboratory. HCl-extractable P was determined in substr ates and sands before and after loading with each of the two wastewaters. Samples were equilibrated for 3 hours with 1-M HCl and filtered extracts were analyzed for P (by ICAP) at the University of Florida Analytical Research Laboratory.
48 Other Analyses of Substrates and Sand Oxalate-extractable iron (Fe), and aluminum (Al) were also measured preand post-loading with in both co-treatment bottle substrates and column sands loaded with each wastewater. The samples were prepared, extracted and analyzed as described above for oxalate-extractable P. HCl-extractable calcium (Ca), magnesium (mg), Fe, and Al were measured preand post-loading with each wastewater. The samples were prepared, extracted and analyzed as described above for HCl-extractable P. Oxidation-reduction pote ntial (redox) levels were m easured in all column sands preand post-flooding with each wastewater in the manner commonly used in the study of wetland sediments and flooded soils (Faulkner et al., 1989). Probes were tested before and after use with pH 4 and pH 7 buffe r solutions saturated with quinhydrone. A platinum-tipped copper wire redox probe was in serted into each sand column to a depth of 12.5 cm (the midpoint of the sand profile). Redox readings were taken with a Corning Model #313 portable pH meter (with automatic te mperature correction) that had been set to read in milivolts (mV). An adapter (Fis her Catalog # 13-620-498) was attached to the meter that allowed for attachment of a cal omel reference probe (Accumet Catalog # 13620-258) that was placed in the water (when flooded) or wet sand (if drained) at the surface of the column sand. The other end of the adapter was attached with an alligator clip to the copper tip of the redox probe that extended above the top of each column sand profile. Readings were taken in mV and then 241 mV was added to correct for using the calomel reference electrode instead of a hydroge n electrode. There were three replicates of every treatment in the column study and thus the mean mV reading of the three
49 experimental replicates was taken. Redox measurements were taken 3.5 and 7 days postflooding and 3.5 days post-draining. Results Co-Treatment and Column System Performance Turbidity tests. The results of the turbidity test s are presented in Figure 3-2. The solutions above most of the substrates cleare d substantially within the first half hour. However the Tampa Fe-DWTR solution remained cloudy for 24 hours. 0 5 10 15 20 25 024681012141618202224 time since pouring (hours)Absorbance Aluminum#1 Sand-coated Ca-DWTR Humate product SuperMag by-product Sand-concrete Fe-DWTR Figure 3-2. Turbidity measured as absorbance (Â± one standard deviation) by particles in solution above substrates after pouring wa ter on them from a height of 3 feet (0.91 m). Evaluation of the system design. The co-treatment substrate bottle and sand column experimental units performed well in terms of hydraulic flow throughout the study. Most of the substrate material rema ined in the co-treatment bottles upon draining and the sand columns did not clog during th is one-month study. There was no apparent
50 reduction in the time required to drain the sand columns after one month of wastewater loading. Phosphorus Removal Performance Wastewaters, co-treatment bottle and sand column effluents. The wastewater, co-treatment bottle, and sand column effluent soluble reactive P (SRP ) concentrations are shown in Figure 3-3 (municipal wastewater) and Figure 3-4 (dairy wastewater). The SuperMag material performed no better than th e controls with the municipal wastewater. It clumped and hardened, upon wetting, in the unstirred co-treatment bottles. The CaDWTR, coated sand, aluminum, humate, and Fe-DWTR units all removed considerably more P than the control units. Municipal wa stewater SRP concentrations were reduced from 0.44 mg L-1 to 0.18 by the controls and 0.03 and 0.01 mg L-1 by the Caand FeDWTR respectively (Figure 3-3). 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50Municipal Wastewater Co-Treatment Effluent Sand Column EffluentSRP (mg/L) Control Magnesium Lime DWTR Coated Sand Aluminum #1 Humate Product Iron DWTR Figure 3-3. Column study wastewater and e ffluent soluble reac tive phosphorus (SRP) means for the fourth treatment cy cle with municipal wastewater.
51 The SuperMag material performed bette r than the controls with the dairy wastewater (Figure 3-4). Ho wever, as with the municipal wastewater, it clumped and hardened, upon wetting, in the unstirred co-t reatment bottles and did not perform as well as most other materials. The coated sand al so removed less P from the dairy wastewater than other materials. The Ca-DWTR, aluminum, humate, and Fe-DWTR units all removed considerably more P than the control units. Dairy wastewater SRP concentrations were reduced from 9.03 mg L-1 to 3.70 by the controls and 2.25 and 0.60 mg L-1 by the Caand Fe-DWTR respectively (Figure 3-4). With both wastewaters, the control experimental bottle and column units reduced P levels. The control co-treat ment bottles alone receiving municipal wastewater did not reduce phosphorus concentrations significantly (Figure 3-3). The c ontrol co-treatment bottles alone receiving dairy wastewat er did reduce phosphorus concentrations significantly (Figure 3-4). 0 1 2 3 4 5 6 7 8 9 10Dairy WastewaterCo-Treatment Effluent Sand Column EffluentSRP (mg/L) Control Magnesium Lime DWTR Coated Sand Aluminum #1 Humate Product Iron DWTR Figure 3-4. Column study wastewater and e ffluent soluble reac tive phosphorus (SRP) means for the fourth treatment cycle with dairy wastewater.
52 Co-treatment substrates and column sands. The total P determined in the cotreatment bottle substrates before and after lo ading with each wastewater is displayed in Figure 3-5. 0 500 1000 1500 2000 2500 3000 3500 4000A luminum Magn e sium Co ated S a nd L i m e DWTR Hu ma t e Iron DWTR Pre-Loading Post-Loading A. Municipal Wastewater 0 500 1000 1500 2000 2500 3000 3500 4000 4500A l uminum M a gn e si u m C o a ted S a n d Li me DWTR H u mate Ir o n DW TR Pre-Loading Post-Loading B. Dairy Wastewater Figure 3-5. Total phosphorus (Â± one standard deviation) was determined in all cotreatment substrates before and after loading with either municipal (A) or dairy (B) wastewater. The TP in most substrates increased after loading with either wastewater (Figure 35). The notable exception was the coated sand that had less TP after loading with either Total Phosphorus (mg-P per kg of substrate)
53 wastewater. The TP more than tripled in the Fe-DWTR receiving either municipal or dairy wastewater. The total P determined in the column sa nds before and after loading with each wastewater is displayed in Figure 3-6. 0 20 40 60 80 100 120ControlAluminumMagnesiumCoated Sand Lime DWTR HumateIron DWTR Pre-Loading Post-Loading A. Municipal Wastewater 0 50 100 150 200 250 300 350 400ControlAluminumMagnesiumCoated Sand Lime DWTR HumateIron DWTR Pre-Loading Post-Loading B. Dairy Wastewater Figure 3-6. Total phosphorus (Â± one standard deviation) was determined in all column sands before and after loading with either municipal (A) or dairy (B) wastewater. Total Phosphorus (mg-P per kg of sand) Co-Treatment Substrate Preceding the Sand Column
54 Most column sands that received municipa l wastewater had lower mean TP levels post-loading but the standard deviations we re sometimes large (Figure 3-6). The postloading means were higher in the sand columns following the Fe-DWTR and Aluminum co-treatment bottles but again the standard deviations were large. For sand columns loaded with dairy wast ewater the TP levels did not change significantly for the columns following contro l, coated sand, or humate co-treatment bottles. They did appear to increase some what in sands following the SuperMag, CaDWTR, Fe-DWTR and aluminum co-treatment s although the standard deviations were large. Oxalate-extractable P was also measured in the co-treatment substrates before and after loading with each wastewater and is displayed in Table 3-1. Table 3-1.Oxalate-extractable P (Â± one sta ndard deviation) was determined in cotreatment substrates before and af ter loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated 86 Â± 9 < 50 301 Â± 73 SuperMag 73 Â± 19 68 Â± 6 313 Â± 176 Ca-DWTR < 50 < 50 534 Â± 16 Fe-DWTR 653 Â± 15 1699 Â± 341 1701 Â± 526 Aluminum #1 < 50 < 50 255 Â± 40 Humate Product 755 Â± 26 790 Â± 86 1368 Â± 121
55 After loading with municipal wastewater for one month, most substrates showed little change in oxalate-extractable P except for the Fe-DWTR where the level more than doubled. However after loading with dairy wa stewater, the oxalate-extractable P levels increased significantly in every co-treatment s ubstrate. Both the initial and post-loading levels were highest in the Fe-DWT R and humate product materials. Oxalate-extractable P was also measured in the column sands before and after loading with each wastewater. The amount of oxalate-extractable P of the sand preloading was below the detection limit of 50 mg kg-1. The post-loading levels of this form of P were also all below that limit excep t for the sand columns following Fe-DWTR cotreatment bottles that were loaded with dairy wastewater. The post-loading oxalateextractable P level in the sand columns following Fe-DWTR co-treatment bottles averaged 73 mg kg-1 but had a standard de viation of almost 69. The levels of HCl-extractable P were determined for each of the substrates before and after loading with each wastew ater and are given in Table 3-2. Table 3-2. HCl-extractable P (Â± one standard deviation) was determined in co-treatment substrates before and after loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated < 63 < 63 214 Â± 51 SuperMag 67 Â± 16 < 63 273 Â± 159 Ca-DWTR < 63 < 63 542 Â± 38 Fe-DWTR 712 Â± 16 3227 Â± 1012 4403 Â± 91 Aluminum #1 < 63 < 63 80 Â± 26 Humate Product 697 Â± 14 712 Â± 16 1230 Â± 123
56 The content of HCl-extractable P increased in all substrates that were loaded with dairy wastewater but when loaded with muni cipal wastewater only increased in the FeDWTR. The HCl-extractable P was also measur ed in the column sands before and after loading with each wastewater. The amount of HCl-extractable P of the sand pre-loading was below the detection limit of 63 mg kg-1. The post-loading levels of this form of P were also all below that limit except for the sand columns following the Al #1 (93 mg kg1) and humate product (105 mg kg-1) co-treatments that were loaded with municipal wastewater and the control co-treatment bottles (451 mg kg-1) loaded with dairy wastewater. These may indicate small increa ses in the HCl-extractable P in the column sands but the standard deviations in each case were greater than the means. Substrate and Sand Characteristics Extractable metals. Oxalate-extractable Fe was measured in the co-treatment substrates before and after loading with each wastewater and is di splayed in Table 3-3. Table 3-3. Oxalate-extractable iron (Â± one st andard deviation) was determined in cotreatment substrates before and af ter loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated 902 Â± 26 398 Â± 53 618 Â± 46 SuperMag 653 Â± 10 739 Â± 3 935 Â± 147 Ca-DWTR 584 Â± 24 363 Â± 18 543 Â± 303 Fe-DWTR 159729 Â± 3862 147329 Â± 32760 130044 Â± 38960 Aluminum #1 11 Â± 2 40 Â± 45 27 Â± 3 Humate Product 8259 Â± 372 7373 Â± 1164 7522 Â± 424
57 The mean oxalate-extractable Fe decreas ed in the coated sand, Ca-DWTR, FeDWTR, and humate product post-loading with bo th wastewaters (Table 3-3). It increased in the SuperMag and aluminum with both wast ewaters. The standard deviations were large for the Fe-DWTR material and the aluminum material receiving municipal wastewater. Oxalate-extractable Fe was also measured in the column sands before and after loading with each wastewater. The amount of oxalate-extractable Fe in the sand preloading averaged 23Â± 4 mg kg-1. The post-loading levels of this Fe were approximately the same as pre-loading levels in all sands with both wastewaters except for the sand columns following Fe-DWTR co-treatment bottl es. The post-loading oxalate-extractable Fe level in the sand columns following Fe-D WTR co-treatment bottles averaged 710 Â± 641 mg kg-1 with municipal wastewater and 1467 Â± 1458 mg kg-1 with dairy wastewater. Table 3-4. Oxalate-extractable aluminum (Â± one standard deviation) was determined in co-treatment substrates before and after loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated 1324 Â± 117 519 Â± 61 701 Â± 147 SuperMag 276 Â± 10 442 Â± 19 603 Â± 156 Ca-DWTR 641 Â± 21 506 Â± 8 476 Â± 12 Fe-DWTR 482 Â± 16 550 Â± 111 484 Â± 160 Aluminum #1 8027 Â± 286 8216 Â± 185 10394 Â± 266 Humate Product 31807 Â± 394 27746 Â± 1884 28240 Â± 686
58 Oxalate-extractable Al was measured in the co-treatment substrates before and after loading with each wastewater and is disp layed in Table 3-4. The mean oxalateextractable Al levels were lower in the coated sand, Ca-DWTR, and humate product postloading with both wastewaters. The mean oxa late-extractable Al le vels were higher in the SuperMag, Fe-DWTR, and aluminum postloading with both wastewaters. The standard deviations were re latively large for the Fe-DWTR and aluminum substrates. Oxalate-extractable Al was also measured in the column sands before and after loading with each wastewater. The amount of oxalate-extractable Al in the sand preloading averaged 45Â± 15 mg kg-1. The post-loading levels of this Al were approximately the same as pre-loading levels in all sands with both wastewaters except for the sand columns following Aluminum #1 co-treatment bot tles loaded with dairy wastewater. The average post-loading level in those sands was 69Â± 58 mg kg-1. HCl-extractable Ca, Mg, Fe and Al were al so measured in the co-treatment bottle substrates and column sands before and af ter loading with each wastewater and are displayed in Tables 3-5, 3-6, 3-7, and 3-8. Tables are only provided for the substrate materials since in most cases the sands did not have dramatic increases in these metal forms at the end of the one-month column st udy. The results for the sand analyses are provided in the text following the tables below, corresponding to each of the metals measured. The mean HCl-extractable Ca increased in the coated sand and aluminum material post-loading with both wastewaters (Table 3-5) . It also increased in the SuperMag, FeDWTR, and humate product post-loading with dairy wastewater. The levels did not
59 change significantly in the SuperMag, Fe -DWTR, or humate product post-loading with the municipal wastewater nor in the Ca-D WTR post-loading with either wastewater. Table 3-5. HCl-extractable Ca (Â± one standard deviation) was determined in co-treatment substrates before and after loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated 60 Â± 29 210 Â± 61 863 Â± 360 SuperMag 1998 Â± 18 1878 Â± 90 4153 Â± 615 Ca-DWTR 349268 Â± 2329 345951 Â± 13580 348527 Â± 16225 Fe-DWTR 6676 Â± 119 6537 Â± 1575 13315 Â± 472 Aluminum #1 428 Â± 566 1574 Â± 568 4699 Â± 575 Humate Product 2596 Â± 45 2254 Â± 588 7728 Â± 889 The amount of HCl-extractable Ca in the sand pre-loading was 64 mg kg-1. The post-loading levels of this form of Ca were somewhat higher in the column sands following most co-treatment bottles loaded with either municipal or dairy wastewater. However, the standard deviations were genera lly as large or larger than the means and thus no significant changes were detected. The HCl-extractable Mg levels were meas ured in both substrates preand postloading with municipal and dairy wastewater s (Table 3-6). The mean HCl-extractable Mg levels increased substant ially in the coated sand, Fe-D WTR and aluminum material post-loading with both wastewaters. They d ecreased in the SuperMag post-loading with both wastewaters. They did not change significantly in Ca-DWTR post-loading with
60 either wastewater. In the humate product, the HCl-extractable Mg decreased postloading with municipal wastewater and in creased with dairy wastewater loading. Table 3-6. HCl-extractable Mg (Â± one sta ndard deviation) was determined in cotreatment substrates before and af ter loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated < 5 178 Â± 234 344 Â± 271 SuperMag 167838 Â± 972 138835 Â± 2142 145451 Â± 1614 Ca-DWTR 18252 Â± 120 18445 Â± 678 17295 Â± 637 Fe-DWTR < 5 70 Â± 120 2364 Â± 503 Aluminum #1 < 5 546 Â± 207 1345 Â± 130 Humate Product 2525 Â± 250 465 Â± 62 3565 Â± 786 The amount of HCl-extractable Mg of th e column sand pre-loading was below the detection limit of 5 mg kg-1. The post-loading levels of this form of Mg in all the column sands were also below this detection limit with the exception of the columns following the SuperMag co-treatment substrate bo ttles. These sands had measurable HClextractable Mg levels (16-60 mg kg-1 for the municipal and dairy wastewaters respectively) however the standard devi ations were larger than the means. The HCl-extractable Fe levels were meas ured in both substrates preand postloading with municipal and dairy wastewaters (Table 3-7). The HCl-extractable Fe was lower in the coated sand post-loading with both wastewaters. The levels increased in the Fe-DWTR and aluminum post-loading with both wastewaters, although the standard deviation was very large in the aluminum material post-loading with the municipal
61 wastewater. The levels in the SuperMag a nd humate product substrates did not change significantly post-loading with either wastewat er. The HCl-extractable Fe decreased in the Ca-DWTR post-loading with municipal wastewater and increased with dairy wastewater loading. Table 3-7. HCl-extractable Fe (Â± one standard deviation) was determined in co-treatment substrates before and after loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated 649 Â± 175 260 Â± 80 322 Â± 100 SuperMag 649 Â± 46 679 Â± 111 773 Â± 148 Ca-DWTR 512 Â± 22 342 Â± 35 643 Â± 483 Fe-DWTR 135990 Â± 3237 312976 Â± 97586 375353 Â± 5479 Aluminum #1 8 Â± 4 219 Â± 338 44 Â± 12 Humate Product 7694 Â± 200 6924 Â± 1617 6795 Â± 774 The amount of HCl-extractable Fe of th e column sand pre-loading was 38Â± 46 mg kg-1 with the large standard deviation repres enting the heterogeneity of the sand with respect to Fe content. The post-loading levels of this Fe were generally less than preloading levels in all sands with both wast ewaters except for the sand columns following Fe-DWTR co-treatment bottles. The post-load ing HCl-extractable Fe level in the sand columns following Fe-DWTR co-treatment bottles averaged 505 Â± 502 mg kg-1 with municipal wastewater and 1906 Â± 2144 mg kg-1 with dairy wastewater. The HCl-extractable Al levels were meas ured in both substrates preand postloading with municipal and dairy wastewaters (Table 3-8). The mean HCl-extractable Al
62 decreased in the coated sand, Ca-DWTR, and humate product post-loading with both wastewaters. The mean levels in the S uperMag and Fe-DWTR increased post-loading with both wastewaters. The m ean HCl-extractable Al did not change substantially in the aluminum co-treatment bottle substrate. Table 3-8. HCl-extractable Al (Â± one standard deviation) was determined in co-treatment substrates before and after loading with the two different wastewaters. Pre-Loading Post-Loading with Post-Loading with Municipal Wastewater Dairy Wastewater Substrate Â…Â…Â….Â…Â…Â…. (mg kg -1) Â…Â…Â…Â…Â…Â….. Sand-coated 1655 Â± 84 679 Â± 102 792 Â± 321 SuperMag 479 Â± 19 552 Â± 22 692 Â± 172 Ca-DWTR 772 Â± 3 603 Â± 28 564 Â± 27 Fe-DWTR 568 Â± 5 1135 Â± 303 1354 Â± 54 Aluminum #1 7512 Â± 884 6515 Â± 396 7848 Â± 156 Humate Product 28801 Â± 980 24725 Â± 2150 24324 Â± 887 The amount of HCl-extractable Al of th e column sand pre-loading was 99Â± 5 mg kg-1. The post-loading levels of this Al we re approximately the same as pre-loading levels in most sands with both wastewat ers except for the sand columns following Aluminum #1 and Humate Product co-treatment bottles. The average post-loading levels in those sands were 106Â± 43 mg kg-1 and 140Â± 34 mg kg-1 respectively with municipal wastewater and 121Â± 40 mg kg-1 and 158Â± 39 mg kg-1 respectively with dairy wastewater. Oxidation-reduction potential. The redox values in the sand columns receiving municipal wastewater remained above +350 mV after 3.5-days of flooding. In all of the
63 columns receiving dairy wastewater, except th e ones following Fe co-treatments (+290 mV), redox levels were less than +200 mV after 3.5-days of flooding. After being drained for 3.5-days, the redox of all of the sand columns, that had been loaded with either wastewater, were great er than +300 mV except for SuperMag systems flooded with dairy wastewater (164 mV). Discussion Co-Treatment and Column System Design and Operation In general, the co-treatment bottle and sa nd column system demonstrated that the basic design was functional and effective fo r handling both types of wastewater loading for one month of operation. Since the lengt h of time required draining the sand columns did not change noticeably, afte r one month of wastewater lo ading, there was no apparent clogging of the sand columns. However, ve rtical flow could eventually present functional problems with hydrau lic conductivity in larger sc ale systems and should be considered carefully in the system design process. Turbidity in a disturbed solution was a rele vant factor primarily for the Fe-DWTR. If the suspended solids in the Fe-DWTR c ontained P binding materi als it could be a favorable factor. Depending on the hydrauli c retention time those suspended solids from a co-treatment basin might flow with a wast ewater into the CW and improve P stability there. However, if too much material flow ed with the wastewater it might hasten the clogging of the systems porosity. Also, if settli ng or filtration in the CW or elsewhere did not remove the suspended solids, they might exceed final discharge requirements for suspended solids.
64 Phosphorus Removal Performance With both wastewaters the combined co-t reatment bottle and sand column units reduced SRP concentrations by at leas t 50%. There was no reduction in SRP concentration by the control co-treatment bottles alone receiving municipal wastewater but there was by those receiving dairy wastew ater. The dairy wast ewater was not only higher in initial P levels, but also had much higher levels of nitrogen and other plant nutrients and so may have supported algal or bacterial growth. With the dairy wastewater, in the first stage (co-treatment bottles), some P may have been taken up by algae or bacteria and then settled out of so lution. In the second stage (sand columns), some P, from either the m unicipal or dairy wastewaters, may have been bound to the sand. Also, floating algae or bacteria from the co-treatment bottles may have been filtered out by the sand columns and accounted for additional sequestration of P there. All the co-treatment materials, except the SuperMag, performe d much better than controls at removing P from municipal wastewater. The SuperMag material did not perform well and it was observed that it clumped and hardened upon wetting in the unstirred co-treatment bottles. Based on th e better performance of the SuperMag material in the earlier lab studies , it might however be useful as a co-treatment material if it was mixed with other non-clumping substrates or used in a stirred or mixed reactor basin. Most of the substrates contained more TP post-loading with either wastewater as expected. After being used for P removal in a system of this type these materials would contribute P to the soil when land applied. At least some of this P would be available to plants and thus has fertiliz ing potential for croplands (MÃ¦hlum and Roseth, 2000; deBashan and Bashan, 2004; KvarnstrÃ¶m et al., 2004). The coated sand apparently lost P
65 when treated with wastewater in this co-treat ment system and thus would not be a useful material for this application. The TP levels in the column sands only appeared to increase following the aluminum or Fe-DWTR co-treatments w ith both wastewaters and following the SuperMag and Ca-DWTR co-treatments with da iry wastewater. In a longer study it is suspected that the TP levels would eventually rise in the sands after repeated wastewater loadings, particularly if the wastewater was high in nutrients or organic matter. In general it should be noted that stan dard deviations for TP and the various extractable metals in the column sands were sometimes quite large. As described earlier in the methods section the en tire column sand profiles we re homogenized before subsampling for processing and analysis. The P and other metals did not likely disperse evenly throughout the depth of the sand columns. In this on e-month study much of the P and other metals content may have been concen trated in discrete aggregates in the top layers of the sand, thus cont ributing to high standard devi ations when the entire sand profiles were mixed. After just one month of muni cipal wastewater loading most co-treatment substrates showed little increase in oxalate -extractable P (considered a plant-available form). All substrates showed significant increases in this form of P after one month of loading with the dairy wastewater. If the co-treatment substrates were to be cropland-applied after being used for P removal, this P mi ght be available as a crop nutrient. In this one-month study, oxala te-extractable P levels in the column sands did not increase measurably following most of the co -treatment substrate bo ttles, including the (empty) control bottles. There only appeared to be a slight in crease in this P form in the
66 column sand following the Fe-DWTR co-treatme nt bottle that recei ved the high P dairy wastewater. As discussed earli er the column sands were sub-sampled for analysis after homogenizing each entire column sand profile. It is suspected that any P that may have been physically or chemically entrained in the column sand surface layers would have been diluted below detection limits by this sampling technique. Future experiments might benefit from analyzing discreet layers of the sand column profiles. The HCl-extractable P primarily increased in the substrates that were loaded with dairy wastewater. This P could represent Caand Mg-bound P as well as some organic forms that are not readily available under comm on field conditions if the substrates were applied to cropland. Implications of Substrate and Sand Characteristics For all of the co-treatment substrate and column sand ex tractable metals data, the many reasons for metal concentration cha nges in the sampled materials should be considered. Phosphorus and other metals coul d either be added to, or leached out of, substrates by the wastewaters. The P a nd metal forms could also change under the various biogeochemical conditions created in the co-treatment and sand column systems with different substrates. Algae and micr obes are both common in wastewater systems and these too could affect the transformati on and movement of P and other metals. Finally, small changes could be artifacts of the sampling and processing techniques. For example, if large amounts of organic solid s were added to a substrate from the wastewater, the mass of a single metal might not change but the total mass of substrate might change, thereby changing the concentrat ion of the metal per mass of substrate. Oxalate-extractable Fe decreased most pr ominently in the Fe-DWTR co-treatment substrate post-loading with both wastewaters. Consequently, this form of Fe increased
67 most in the column sands following the Fe-DWT R co-treatment bottles. If this Fe could react with P it might increase the stability of P in the column sands and thus further enhance treatment performance. Large amounts of oxalate-extractable Al did not appear to be transported from most of the co-treatment substrate bottles to the column sands. The notable exception, not surprisingly, was with the alum inum co-treatments. Aluminum is not a plant nutrient and does present toxicity concerns in some situ ations (Gensemer and Playle, 1998) so it may not favorable to have Al tran sported by the wastewater from co-treatments into treatment wetlands. The mean HCl-extractable Ca levels did not change dramatically in most substrates post-loading with either wastewater but it did increase in some. Calcium is a plant nutrient, as well as being reactive with P, a nd so its transport from co-treatment to a treatment wetland may be less problematic. The concentration of HCl-extractable Mg changed dramatically only in the SuperMag material, where it decreased. The decrease in this Mg form in the SuperMag by-product co-treatment bottles was matched with an increase in the column sands following those co-treatments. The HCl-extractable Fe changed dramatically only in the Fe-DWTR co-treatment substrate bottles, where it increased. It is suspected that this increase may have been at least partially caused by a transf ormation from another Fe form already present in the FeDWTR rather than additions from the wast ewaters themselves. Reducing (low redox) conditions in the co-treatment substrate bottle s (particularly with the dairy wastewater) may have contributed to this transformation.
68 The HCl-extractable Al concentrations did not change dramatica lly in any of the substrates post-loading with eith er wastewater. Some of this form of Al did move from the aluminum and humate product co-treatment bottles into the column sands. As has been discussed earlier, it may not be desira ble for significant levels of Al to be transported in the wastewater fr om co-treatments to wetlands. The redox data suggests that an alternati ng flooding and draining cycle of 3.5-days is adequate to promote aerobic conditions at least part of the time in sand columns receiving either municipal or dairy wastew ater. All of the sa nd columns receiving municipal wastewater remained aerobic while flooded for 3.5 days. Most sand columns receiving dairy wastewater became aerobic (> 300 mV) after being drained for 3.5 days. Conclusions In the greenhouse column study the Ca, Fe , aluminum, and humate materials were found to be effective in P removal from both wastewaters. The aluminum material was not locally available and presented potential toxicity and end-user perception concerns. The dried humate product had limited availabil ity and added processing costs. Thus the two optimal materials selected based on the laboratory and column study results, and the operational considerations combined, were th e Caand Fe-DWTR. These two materials warranted additional evaluation with outdoor experimental mesocosm systems. Post-loading with both wastewaters the co-t reatment substrates contained P in both readily available forms and in more tenaci ously bound forms. If they were to be ultimately cropland-applied after being used for P removal from wastewater, consideration would need to be given to the leaching potential and pl ant availability of the P sequestered in these substrates. Like wise the effects of different biogeochemical
69 conditions between upland and wetland sites would need to be considered for each potential co-treatment material. The coarse (concrete-grade) sand proved to have adequate hydrau lic conductivity in the columns, suggesting suitability for use as a root bed media in vertically drained constructed wetland mesocosms. The 3.5-day hydraulic retention ti me (HRT) did allow for P removal in the co-treatment stage and alternating aerobic and anaerobic conditions in the sand column stage. However, for a manually operated system it would be less labor-intensive to have a 7-day HRT. It is also suspected that, in the long-term, in a system loaded with high nutrient conten t wastewater (such as dairy wastewater) anaerobic conditions would pr evail longer after draining as the system aged. Since aerobic conditions are generally favorable fo r P sequestration and stability the longer HRT might be advisable. Th e unmixed batch-fed co-treatment and vertically drained systems did function adequately in this one -month study and demonstrated the potential for implementing this co-treatme nt strategy at a larger scale.
70 CHAPTER 4 REMOVAL OF PHOSPHORUS FROM AGRICULTURAL AND MUNICIPAL WASTEWATERS WITH CO-TREATMENTS AND WETLAND MESOCOSMS Introduction In order to more adequately test the f easibility of constructed wetland (CW) and co-treatment systems, further research was n eeded at the outdoor mesocosm level. The term mesocosm comes from Â“mesokosmosÂ” and tr anslates literally as Â“middle worldÂ” and has been described as the Â“world of interm ediate dimensionsÂ” (Mayr, 1997). Outdoor wetland mesocosm studies are used as model ecosystems to bridge the information gap between greenhouse studies and full-scale cons tructed wetlands. They include more realistic conditions than gree nhouse studies yet are small en ough to be more feasibly replicated than large in-g round wetlands. Results from the laboratory and greenhouse column experiments guided the design of th e larger scale outdoor wetland mesocosms and co-treatment tanks used in this resear ch. The mesocosms provide a more realistic test of the principles examined in the laboratory and greenhouse studies. The results provide data to support a better understandi ng of, and optimization of, P removal and retention during the design a nd operation of co-treatment CW wastewater treatment systems. Researchers have examined the use of vari ous materials as pote ntial substrates to improve P removal by wetland treatment system s (Brix et al., 2001; GrÃ¼neberg and Kern, 2001). Other researchers have investigated the addition of P-adsorbing materials in
71 separate rechargeable cells to improve the ability and sustainab ility of constructed wetlands to remove phosphorus from wastewater (Arias et al., 2003; Zhu et al., 2003). By sequestering P with non-toxic materi als, it could possibly be reused by agriculture (MÃ¦hlum and Roseth, 2000; de-Bas han and Bashan, 2004; KvarnstrÃ¶m et al., 2004). The use of by-products in co-treatment cells could be a low-cost way to improve the performance and longevity of CW or could be used to reduce the wetland area required for a given level of treatment. Laboratory and greenhouse experiments were used to test several available by-products as potential wetland co-t reatment substrates. Based on those results, a 52-w eek mesocosm study was conducte d to evaluate two of the most promising materials at a more realis tic scale with both an agricultural and a municipal wastewater. Aquatic macrophytes have frequently been shown to enhance nutrient removal by CW (Gersberg et al., 1986; Brix, 1994; Yang et al., 2001). Soft-stem bulrush, Schoenoplectus tabernaemontani (K.C. Gmel.) Palla was used in the eighteen experimental constructed wetland mesocosm systems used in this research. One objective of this research was to determin e if bulrush planted in constructed wetland mesocosms would be adversely affected when following by-product co-treatment cells. The feasibility of this wastewater treatment design depended not only on P removal performance but also on the impact of the co-treatment materials on the wetland macrophytes. Any phytotoxic impact on the plan ts would also have consequences for possible cropland application of the co-treatment materials after having been used for wastewater treatment. There were also c oncerns regarding the alternating flood-drain hydrology of the systems as well as the depth and composition of the root-bed media.
72 Finally, both low-strength muni cipal and high-strength agricultu ral wastewaters with very different compositions were to be applied to the bulrush with uncertain consequences. The earlier laboratory batch and greenhous e column studies suggested that two drinking water treatment residuals (DWTR) w ould be feasible candidates for use as cotreatments. One was calcium based and the other contained consid erable amounts of iron (Fe). Iron is a plant nutrient but exce ssive amounts under wetland conditions may be problematic. Iron plaques can form in the aerobic rhizosphere of macrophytes. Both positive and negative effects have been observed, including P sequestration and nutrient deficiency in aquatic plants (Mendelssohn et al., 1995; Zhang et al., 1999; Batty et al., 2000; Lucassen et al., 2000). Soft-stem bulrush, a widespread native pl ant in the US, is one of the plants recommended as suitable for use in wa stewater treatment by the Environmental Protection Agency, the Army Corps of Engin eers and the Department of Agriculture (US EPA 1993 [a], US ACE 2001, USDA NRCS 2002) . Consequently, it is commonly used in CW and information on its use is widely av ailable in the literatur e (Gersberg et al., 1986; Tanner, 1996; Hunter et al., 2000; Nguyen, 2000; Tanner, 2001; Clarke and Baldwin, 2002; Poach et al., 2003). The taxonomi c nomenclature has changed in recent years and it is variously listed in the literature as Schoenoplectus tabernaemontani (K.C. Gmel) Palla or Scirpus validus (Vahl), as well as other co mbinations of these names (USDA NRCS, 2004). It was desirable to us e a native wetland plant, as well as one commonly used in wastewater treatment, for th e greatest applicability of this research. The recommended root-bed media depth for bulru sh in CW varies in the literature. Higher stem production but lower root productio n has been reported with greater media
73 depth (Hunter et al., 2000). In a gravel be d system, most roots were found in the upper 10 cm with few penetrating below 30 cm (R eed and Brown, 1995; Tanner, 2001). Course sand was used as the root-bed media for the CW mesocosms in this st udy, with a depth of 20 cm. Part of the approach for optimizing P re moval by the co-treatments included an alternating 7 d hydraulic re tention time (HRT) followed by a 7 d unloaded period. During these unloaded periods, wastewater was not added but rainfall additions did occur and sometimes resulted in standing surface wa ter in the CW mesoco sms. When large rain events did not occur during these pe riods, the mesocosm root-bed media was unsaturated. Drying out of CW can be problematic for bulrush rhizomes and can reduce stem production. Root production is also greater when CW remain permanently flooded (Hunter et al., 2000). Theoretical HRT ha s been calculated for the wastewater in continuous-flow wetland systems and treatment performance has been shown to increase only slightly in those syst ems with HRT greater than 1 day (Reed and Brown, 1995). Another concern with the bulrush performance in this study was the wide variation in the characteristic s of the two different wastewat ers applied. The low-strength secondarily treated municipal wastewater might have insufficient nutrients for the bulrush plants. Alternately, the high-strength dairy wastewater could have ammonia levels in excess of their reported tolerance levels (Clarke and Baldwin, 2002). In this wetland mesocosm study, bulrush live stem counts were used as an indicator of plant health and we re expected to reflect any si gnificant impact of the design features, treatments, or wastewat ers. Bulrush tissue P concen trations were also measured as an indication of plant health and performance.
74 There were three specific hypotheses to be tested in this mesocosm study. The first tested if co-treatments could reduce the P load to constructed wetlands. The second tested if the calcium (Ca-DWTR) or iron (F e-DWTR) co-treatments could reduce P better than the control (water) cells. The third hypothesis tested if e ither the Ca or Fe materials would affect wetland macrophyte (bulrush) growth. There were both scientific and operational objectives in this mesocosm stage of the research. The scientific objective was to test the earlier hy potheses regarding cotreatments at the more realistic mesocosm scale. The operational objective was to test the practical functioning and maintenance of a co-treatment and wetland wastewater treatment system under more realistic conditi ons than the laboratory or greenhouse could provide. Materials and Methods Preparation of Sites, Equipment and Materials Co-treatment substrates and wetland root-bed media. Earlier laboratory and greenhouse column experiments with several pot ential co-treatment substrates guided the design of this mesocosm study. Factors including turbidity in solution, wide availability, and current use as agricultural soil amendmen ts, non-toxicity, and overall performance in the column studies were considered in addi tion to P removal performance. Two drinking water treatment residuals (DWTR) were chosen based on all of these relevant factors. The first was a Ca sludge (primarily calci um carbonate) by-product of using calcium oxide for drinking water softening. The sec ond was an Fe sludge by-product of using ferric sulfate to remove color from drinking water supplies, which is low in sulfur and high in dissolved organic carbon. The minera l fractions of the Caand Fe-DWTR were 95% silt-sized and 83% sand-sized particles, respectively. However, the Fe material held
75 approximately twice the water content, pe rhaps due to the higher organic fraction. Coarse sand with low P sorption ability (66 mg kg-1) and high hydraulic conductivity was used as the root-bed media in the wetlands. Wastewaters. Both agricultural and municipal wa stewaters were used to test the treatment design over a range of matrix ch aracteristics. These included secondarily treated municipal wastewater from the local wastewater reclamation facility and anaerobically digested flushed dairy manur e from the University of Florida Dairy Research Unit. The flushed dairy manure underwent mechanical solids separation and settling prior to being treated in a fixed-film anaerobic digest er (Wilkie et al., 2004). Wetland macrophytes. The plant chosen for this research, for reasons stated earlier, was the aquatic macrophyte Schoenoplectus tabernaemontani (K.C. Gmel.) Palla. The plants were obtained from the nearby City of Waldo Wastewater Treatment Facility CW (Frame and Toby, 2000) by digging up rhizom es, leaving stems intact. Plants were stored in water in 19 L buckets for several m onths at each site while the mesocosms were constructed. The storage water at the dairy site was well wa ter and reclaimed wastewater was used at the municipal site. Also, the municipal site was somewhat shaded and the dairy site was in full sun. These differences may have caused initial growth differences, as described below, during plant storage prior to the experiments. Individual plants were mixed and randomly assigned to control and tr eatment CWM at each site before planting. Bulrush rhizomes were manually planted by burying them under approximately 15 cm of sand. Design of co-treatment reactors a nd constructed wetland mesocosms. A novel wastewater treatment syst em was designed and constructe d to test a combination of
76 various strategies for low-cost phosphorus rem oval. The experimental systems combined batch-fed co-treatment reactors (CTR) containi ng either Feor Ca-DWTR in series with vertical-flow constructed wetland mesocosms (CWM) containing coarse sand and planted (Figure 4-1) with the native soft-stem bulrush Schoenoplectus tabernaemontani (K.C. Gmel . ) Palla (= Scirpus validus Vahl). A B C D Figure 4-1. Schematic diagram of the 18 experi mental units used in the mesocosm study. Wastewater was loaded to the co-treat ment reactor (A) then drained to the constructed wetland mesocosm (B) before exiting the unit (D). A storm event rainfall overflow collection system (C) was employed to insure that a phosphorus mass balance could be maintained. A more detailed and labele d drawing of an experime ntal unit is provided in Appendix A (Figure A-1) of this dissertati on. The horizontal surf ace area in the CTR was 0.23 m2 and in the CWM was 0.70 m2. Eighteen of these systems were built and operated for one year to treat the two different wastewat ers, using two DWTR from Florida plus controls, with th ree replicates of each in a complete randomized design at two sites in Alachua County, Fl orida, the wastewater reclam ation facility and the Dairy Research Unit. Each CTR consisted of a 208 L plastic barrel with a side outlet drain that directed outflow into a CWM. A dry-wei ght equivalent of 10.4 kg of co-treatment
77 substrate was placed in the barrel below the side outlet drain level to allow wastewater drainage with minimal substrate loss. Both DWTR substrates were used at the water contents as obtained from the water treatment pl ant storage fields. In practice, drying of the DWTR reduces mass for transport but incr eases handling costs. The optimal water contents would be site and situation-specific so equivalent masses, rather than volumes, were used in this study. At the e quivalent mass, the Ca occupied 0.015 m3 and the Fe 0.023 m3. Each control CTR had no substrate added but was filled with water. Each treatment CTR was initially toppe d off with water, to maintain equivalent volumes. Each CWM was a 567 L plastic tank with a bottom outlet drain. Each tank had a 7.6 cm diameter plastic perforated agricultural drai nage pipe in the bottom covered by 10 cm of washed gravel, a geo-textile cloth (to preven t sand seepage), and 20 cm of course sand, and was planted with bulrush. This was a gr avity-driven system without electric mixers, aerators or valves. Pumps were only used to move wastewater from the source to the CTR at each site. Experimental Set-Up Operation of mesocosm system. A treatment cycle began by batch-feeding 132.5 L of wastewater to the CTR (Figure 4-1) , where it was held for 7 days. Then the CTR was drained into the CWM, which remain ed flooded for another 7 days for a total system hydraulic retention time (HRT) of 14 days. This cycle was repeated every 14 days for one year with CTR and CWM cells alternating between loaded and unloaded conditions. As noted earlier, rainfall additions could result in saturated conditions in the CWM even when now wastewater had been added. The hydrau lic loading rate (HLR) of wastewater to the CTR cells was 0.08 m3 m-2 day-1 and to the CWM cells was 0.03 m3 m-
78 2 day-1 (due to the larger surf ace area of the CWM). The overall HLR to the combined systems, based on total area and total HRT, was 0.01 m3 m-2 day-1. This HLR does not include rainfall additions to the CWM. The CTR were covered and not affected by rainfall but the substrates remained satura ted due to the placement of the drain valve above the wet substrate level. The CTR substrates at the dairy were re placed every four months (i.e. twice) during the 52-week study as P removal perfor mance declined. They were replaced only once at the municipal site (aft er 8 months) due to storm dama ge and not due to a decline in performance. Additional experiment: post-wetland co-treatment. The dairy wastewater had much higher TSS and DOC and it was suspecte d that this reduced the co-treatmentÂ’s efficiency of P removal from this wastewater . The co-treatments preceded the wetland cells in the 52-week experiment but, for wast ewaters with high TSS, the co-treatment may remove P more efficiently when used following an initial wetland cell in the treatment sequence. An additional shortterm experiment was conducted using dairy wastewater. Effluents were collected from the three control wetland mesocosms at the dairy. This effluent had lower TSS but had not been exposed to Ca or Fe co-treatments. Sub-samples of a composite sample of this e ffluent were added to nine smaller scale cotreatment containers (three each of control, Ca, and Fe, randomly assigned) with proportionally the same ratio of wastewater to co-treatment substrate as in the 52-week study. The wastewater was held in these containers for 7 days, just as in the larger study, and then analyzed for P concentration.
79 Sampling of system components. Numerous parameters relevant to the optimization of phosphorus removal were measured. Due to the 7-day HRT in each stage wastewater sampling for P alternated each wee k. Samples of the inflowing wastewater to the CTR and the CWM effluent were collected one week. On the alternate week the effluents of the CTR were sampled. Extr a wastewater and effluent samples were collected during some cycles for the testing of parameters other than P levels. Cotreatment substrates, the supernatant liqui d above the substrates and below the CTR drains, the CWM sands and the bulrush were al l sampled before loading with wastewater at the beginning of the experiment. The CTR substrates were sampled at each of the two change-outs at the dairy site and the one change-out at the municipal site. Final destructive sampling of substrates, sands and plants from all eighteen CTR and CWM units was done at the end of 52 weeks to obtain critical data required for a thorough analysis and critique of the design features. A sub-sample of bulrush green (live) stems, roots and rhizomes was taken at each site at the beginning of the study. Green stems, brown (dead) stems and below ground (roots a nd rhizomes) were harvested and separated at the end of the study. Monitoring measurements. Water temperature in the CTR was measured hourly by electronic temperature data l oggers in one of the three co ntrol CTR at each site. Sand temperature in the CWM was measured hourly by temperature data loggers in one of the three control CWM at each site. Air temp erature, CTR water temperature and CWM sand temperature were also manually measured w eekly at each site at the time of effluent sampling.
80 Weekly net rain accumulation was measured weekly at each site with standard rain gauges mounted on posts. Water levels in the tanks were measur ed each week with fixed calibrated depth sticks. Depth measurements could be converted to CWM water volumes based on several direct effluent volum e measurements for given water depths. The pH of all wastewaters, CTR effluent s and CWM effluents was measured with each treatment cycle. Oxidation-reduction po tential, or Â“redoxÂ”, was measured in mV with a portable meter at two depths in every CWM tank every week. Two platinum tipped redox probes were set in the sand of each CWM at dept hs of 10 and 20-cm. These probes were removed, cleaned and retested with standard quinhydrone solutions every few months. The aboveground, and above-water level, copper ends of the probes were cleaned more frequently at the dairy site as corrosion occurred there more rapidly. Dissolved oxygen, conductivity, salinity, te mperature and pH were measured onsite in the wastewaters, CTR efflue nts and CWM effluents seasonally. Bulrush stem counts, both standing gr een (live) and brown (dead), were conducted seasonally in every CWM at both sites. Drainage rates of the CWM were timed at the beginning and end of the one-year mesocosm study to quantify any detectable re ductions due to clogging of the vertically drained sands. Analytical Methods Wastewater. Samples were analyzed weekly within allowable holding times. Due to the alternate sampling each week of the 14-day to tal HRT, data was organized after analysis such that a single cohort of inflowing wastewater, CTR effluent and CWM effluent were grouped together.
81 Standard methods for wastewater analys is (APHA, 1998) were used to measure pH, total suspended solids (TSS), dissol ved oxygen, conductivity, sa linity and oxidationreduction potential (Eh) for characterization of the two wastewaters. To measure dissolved organic carbon (DOC), wastewaters and effluents were vacuum-filtered through 0.45 Âµm membrane filters and acidified to pH 2 drop-wise with concentrated sulfuric acid before analyzing for non-purgeab le organic carbon. Samples were analyzed according to standard methods (APHA, 1998) using a Shimadzu Model TOC-5050A total organic carbon analyzer. To measure the most reactive forms of seve ral relevant metals in the wastewaters, samples were vacuum filtered through 0.45 Âµm membrane filters and acidified to pH 2 drop-wise with concentrated nitric acid. They were stored at 4Â°C until analysis by ICAP by the University of Florida An alytical Research Laboratory. Soluble reactive phosphorus (SRP) samples were likewise filtered and analyzed by the standard semi-automated colorimetr ic method (US EPA, 1993 [b]) as described earlier in chapters two and three. For total phosphorus (TP), effluent samples were digested at high temperature in sulfuric acid and potassium persulfate before analysis by the same method. Mean wastewater TP concentrations were analyzed statistically using Minitab Release 14 software (Minitab Inc., State Coll ege PA). Means were compared using oneway analysis of variance and the Tukey multiple comparisons test. Statistical significance was tested at the level of p <0.05. Co-treatment reactor substrates and wetland mesocosm sands. Water contents of substrate and sand sub-samples we re measured so that sample dry-weight
82 equivalents could be analyzed without the e ffects of oven drying. Standard methods of soil analysis were used to process and an alyze CTR substrates and CWM sands at the beginning (pre-loading) and end (post-loading) of th e one-year mesocosm study. Samples were analyzed for total P (TP) by the ignition method (Anderson, 1976) and for 1-M HCl-extractable P as descri bed earlier in chapter three. Samples were subjected to inorganic P sequential fractionation as described earlier in chapter two. Substrate and sand samples were analyzed for oxalate-extractable Al and Fe (Sheldrick, 1984). Samples were also analyz ed for 1-M HCl-extractable Ca, Mg, Fe and Al as described earlier in chapter three. Wetland macrophytes. Bulrush samples were dried and ground before processing further for analysis. At the beginning and end of the one-year mesocosm experiment dried plant samples were analy zed for total P (TP) by the ignition method (Anderson, 1976) as was done with the substr ate and sand samples. The standard colorimetric method was used to analyze digestates for TP as was done with the substrates and sands. Results Characteristics of Wastewaters Phosphorus and common wastewater parameters. Phosphorus, as well as many other parameters measured, differed by orders of magnitude between the two wastewaters used in this research (Table 4-1). The pH was very similar although buffering capacity differed greatly (as determin ed by amount of acid needed to adjust pH for other analyses). The total suspended so lids (TSS) were below detection limits in the municipal wastewater but were high in the dairy wastewater. Li kewise, the dissolved organic carbon was much higher in the dairy wastewater. The municipal wastewater was
83 generally aerobic and the da iry wastewater anaerobic base d on dissolved oxygen (DO) measurements done immediately at the time of sampling. The conductivity measurements (and by extension the salinity ) were five times higher in the dairy wastewater. The dairy wastewater had been treated anaerobically so oxidation-reduction potential and dissolved oxygen were correspon dingly much lower than in the aerobic municipal wastewater. Table 4-1. Characteristics of wa stewaters loaded to the experi mental systems at each site. Parameter (units) Anaerobically Digested Flushed Dairy Manure Secondarily Treated Municipal Wastewater SRP (mg L-1) 3.8-15.6 0.44-1.80 TP (mg L-1) 33-49 0.47-2.50 pH 6.7-7.4 6.7-7.4 TSS (mg L-1) 2390 < 1 DOC (mg L-1) 453 < 7 DO (mg L-1) ~ 0.1 ~ 8 Conductivity (mS cm-1) 4.5 0.7 Salinity (ppt) 2.2 0.3 Eh (mV) -45 > +350 Metals content of wastewaters. The average metals contents of filtered (0.45 Âµm) and acidified (to pH 2 with nitric acid) wastewater samples are presented in Table 42 below. The dairy wastewater had thirty times the amount of potassium, nearly three times the calcium, over one and a half times the magnesium, over four times the Fe, and over one and a half times the aluminum. The total content of these metals in the two
84 wastewaters was not determined directly but, due to the filtration step, the assumption was made that these were inorganic form s of the metals dissolved in solution. Table 4-2. Average metals contents (Â± one standard deviation) were measured of filtered and acidified samples of the municipal and dairy wastewaters used in this research. Municipal Wastewater Dairy Wastewater Metal Â…Â…Â…..Â…Â…... (mg L-1) Â…Â…..Â…Â…Â…... Potassium 10.81 Â± 0.24 376.63 Â± 7.46 Calcium 49.15 Â± 0.66 144.10 Â± 2.07 Magnesium 48.05 Â± 0.93 81.93 Â± 1.42 Fe 0.03 Â± .002 0.13 Â± 0.05 Aluminum 0.07 Â± 0.04 0.12 Â± 0.04 Total suspended solids in wastewaters and effluents. Total suspended solids (TSS) were measured in the inflowing wast ewaters and the CTR and CWM effluents at each site. The municipal wastewater had less than 1 mg L-1 (the detection limit of the method used). The dairy wastewater had re latively high TSS, but these levels were greatly reduced (Figure 4-2) by the CTR and CWM cells. Although TSS levels were high at the dairy site, clogging did not present a problem in the vertically drained CWM sands and drainage rates were unchanged after 52-weeks of wastewater loading. Dissolved organic carbon in wastewaters and effluents. Filtered wastewater and effluent samples from the 23rd and 24th treatment cycles were analyzed for dissolved organic carbon (DOC) and the re sults are presented in Figure 4-3 and Figure 4-4 for the municipal and dairy wastewaters respectively. As is most evident with the municipal
85 wastewater data (Figure 4-3), the Fe-DWTR co-treatment material contributed significant amounts of DOC to the wastewater before it fl owed into the wetland treatment cells. It appears that the Fe-DWTR materi al added approximately 25 mg L-1 of DOC to the municipal wastewater as compared to the control and Ca-DWTR co-treatments. This amount of increase may be similar for the sy stems receiving dairy wastewater (Figure 44) although the change appears less dramatic due to the much higher DOC intrinsic to that wastewater. It is also more evident in the systems receiving municipal wastewater that a greater amount of DOC exited the treat ment wetland cells when preceded by an FeDWTR co-treatment reactor. It is not possibl e to say that this is the same DOC that was added by the Fe-DWTR co-treatment material but that seems likely. 68 229 2390 0 500 1000 1500 2000 2500 Dairy WastewaterCTR (co-treatment)CWM (wetland)TSS (mg L-1) Figure 4-2. Mean total suspended solids (TSS) (Â± 1 standard deviati on) in effluents at dairy site. Means include all replic ates of controls and treatments.
86 0 5 10 15 20 25 30 35 40Municipal Wastewater ControlCa-DWTRFe-DWTR(Control)(Ca-DWTR)(Fe-DWTR) InflowCo-Treatment EffluentWetland Effluent Dissolved Organic Carbon (mg L-1) 23rd Treatment Cycle 24th Treatment Cycle Figure 4-3. Dissolved organic carbon (Â± one st andard deviation) was determined for the municipal wastewater, and associated co -treatment and wetland effluents for two treatment cycles. The CTR pr eceding each wetland is listed in parentheses. 0 100 200 300 400 500 600 700 Dairy Wastewater ControlCa-DWTRFe-DWTR(Control)(Ca-DWTR)(Fe-DWTR) InflowCo-Treatment EffluentWetland Effluent Dissolved Organic Carbon (mg L-1) 23rd Treatment Cycle 24th Treatment Cycle Figure 4-4. Dissolved organic carbon (Â± one st andard deviation) was determined for the dairy wastewater, and associated e ffluents for two treatment cycles
87 Phosphorus Removal with Pre-Wetland Co-Treatment For municipal wastewater, soluble react ive P (SRP) concentrations (52-week means) were reduced from 0.70 to 0.03 mg L-1 (95%) or 0.01 mg L-1 (98%) by systems with the Ca or Fe co-treatments, respectively, compar ed to 0.09 mg L-1 (87%) by control systems (with no CTR substrate). Also for the municipal wastewater, TP concentrations (52-week means) were reduced from 1.00 to 0.72 mg L-1 (28%) and 0.40 mg L-1 (60%) by the Ca and Fe cotreatments alone, compared to 0.96 mg L-1 (4%) by the controls alone. The means and standard deviations are shown in Figure 4-5. The analysis of variance revealed significant differences in the means ( F =38.49, df=2, p <0.001). The Tukey multiple comparisons test confirmed that the control and treatment means were all different from each other. The municipal wastewater TP c oncentrations (Figure 4-5) were reduced by the combined CTR and CWM systems from 1.00 to 0.07 mg L-1 (93%) and 0.05 mg L-1 (95%) by systems with Ca and Fe compared to 0.16 mg L-1 (84%) by the control systems. For the dairy wastewater, average SRP was reduced from 7.68 to 6.43 mg L-1 (16%) or 5.95 mg L-1 (22%) by the systems with Ca or Fe, respectively (compared to 7.37 mg L-1 or 4% by controls). The TP (Figur e 4-6) was reduced from 48.5 to 22.5 mg L-1 (53%) and 22.7 mg L-1 (53%) by the same treatmen ts (compared to 24.1 mg L-1 or 50% by controls). The average P mass loading rates at the municipal and dairy sites were 0.01 and 0.49 g m-2 day-1, respectively. These rates were ca lculated from the 52-week mean P mass in the inflowing wastewaters, the total areas of the co-treatme nt and wetland cells, and the total HRT of 14 days.
88 1.00 (+/0.61)0.16 (+/0.08) 0.96 (+/0.44) 0.07 (+/0.03)0.72 (+/0.42) 0.05 (+/0.02)0.40 (+/0.27) 0.0 0.2 0.4 0.6 0.8 1.0 1.2Municipal WastewaterCo-Treatment Reactor Effluent Constructed Wetland Mesocosm EffluentTP (mg/L) Control Lime Iron Figure 4-5. Effluent total phosphorus (TP) (Â± 1 standard deviation) 52-week means for the municipal wastewater. 35.5 (+/8.5)24.1 (+/9.7)48.5 (+/11.0)34.3 (+/7.9) 22.5 (+/9.1)32.6 (+/8.2) 22.7 (+/8.5) 0 10 20 30 40 50 60Dairy WastewaterCo-Treatment Reactor Effluent Constructed Wetland Mesocosm EffluentTP (mg/L) Control Lime Iron Figure 4-6. Effluent total phosphorus (TP) (Â± 1 standard deviation) 52-week means for the dairy wastewater. Phosphorus mass removal rates were calculated for CTR and CWM cells separately and combined. For the dairy wa stewater, the 52-week mean combined CTR and CWM system phosphorus mass removal rates were very similar for control, Ca, and
89 Fe systems at 0.27, 0.28, and 0.29 g m-2 day-1, respectively. The P mass removal rates by the CTR cells alone were likewise very simila r for control, Ca and Fe treatments at 1.1, 1.2, and 1.3 g m-2 day-1, respectively. For the municipa l wastewater, the 52-week mean combined rates for control, Ca, and Fe systems were also similar at 0.008, 0.009, and 0.010 g m-2 day-1, respectively. However, the differen ce between treatments and controls was more evident in the P mass removal rate s by the CTR cells alone. For control, Ca, and Fe CTR cells at the municipal site, the rates were 0.003, 0.023, and 0.049 g m-2 day-1, respectively. The percent P mass reductions by the CTR cells alone also more clearly illustrate the differences between treatments and controls. For the control, Ca, and Fe CTR cells at the municipal site, the 52-week mean P mass reductions were 4%, 28%, and 60%, respectively. Phosphorus Removal with Post-Wetland Co-Treatment The co-treatment reactor performance changed dramatically with the dairy wastewater in this experiment where the wa stewater had already been through a wetland (control) system before entering the CTR. On e can compare the results of this additional short-term experiment with the CTR effluent TP levels of the first w eek of the larger 52week study. Initial TP reductions in the 52-week st udy at the dairy (Figure 4-7), with CTR preceding wetlands, were from 43.8 to 25.6 mg L-1 (41%) and 20.4 mg L-1 (53%) by the CTR with Ca or Fe, respectiv ely (compared to 24.8 mg L-1 or 43% by controls). However, for the post-wetland CTR experime nt, initial TP reductions (Figure 4-8) were from 28.4 to 12.3 mg L-1 (57%) and 8.1 mg L-1 (71%) by the CTR with Ca or Fe, respectively (compared to 24.5 mg L-1 or 14% by controls).
90 24.8 (+/0.6)43.8 (+/1.4)25.6 (+/0.4)20.4 (+/4.3) 0 5 10 15 20 25 30 35 40 45 50Dairy WastewaterCo-Treatment Reactor EffluentTP (mg/L) Control Lime Iron Figure 4-7. Total phosphorus (TP) (Â± 1 standard deviation) in prewetland CTR effluents for first cycle only of the 52-week study with dairy wastewater. 28.4 (+/0.7)24.5 (+/1.0)12.3 (+/1.0)8.1 (+/0.5) 0 5 10 15 20 25 30Control Constructed Wetland Mesocosm Effluent Co-Treatment Reactor EffluentTP (mg/L) Control Lime Iron Figure 4-8. Total phosphorus (TP) (Â± 1 standard deviation) in postwetland CTR effluents for the 1-week experiment with dairy wastewater. The SRP data also highlighted the contri bution of co-treatments with reductions from 7.3 to 3.5 mg L-1 (52%) and 0.3 mg L-1 (96%) by the CTR with Ca or Fe, respectively (compared to 3.8 mg L-1 or 48% by controls).
91 Phosphorus in Co-Treatment Substrates and Mesocosm Sands Total P levels were determined for bo th Ca-DWTR and Fe-DWTR co-treatment substrates before and after loading and at each change-out of substrates during the oneyear study (Figures 4-9 and 4-10). Before loading, the Ca-DWTR averaged 34 mg P kg-1 (Figure 4-9). When the Ca was replaced at the dairy (DRU), it averaged 244 mg P kg-1, as compared to only 59 mg kg-1 at the municipal site (GRU). 71 333333 35 35 269 337 126 470 50 100 150 200 250 300 350 400 450 500Ca at GRU Ca at DRU Ca at GRU Ca at DRU Ca at GRU Ca at DRU Apr-03Dec-02(no change-out)May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment Total Phosphorus (mg kg-1) Pre-Loading Post-Loading Figure 4-9. Total phosphorus (Â± one standard de viation) was measured in the lime (Ca) DWTR co-treatment substrate before and after loading with wastewater. The Fe-DWTR averaged 1484 mg P kg-1 pre-loading and 1715 mg kg-1 postloading with municipal (GRU) wastewater (F igure 4-10). Post-loading with dairy (DRU) wastewater, the Fe materi al averaged 2169 mg P kg-1. Based on the dairy site means, neither substrate was P-saturated at the munici pal site but the Fe ma terial may have been at the dairy.
92 Total P levels were also determined for the wetland mesocosm sands at each site before and after loading with each wastewater for one year. The average pre-loading P content of the sand was 50Â± 4 mg kg-1. The post-loading P content of mesocosm sand loaded with municipal wastewat er was nearly identical following control, Ca and Fe CTR (48Â± 0.5, 1.6 or 2.9 respectively). There was generally three times as much TP in the mesocosm sands that received dairy wastewat er. The sands following control, Ca and Fe CTR contained 151Â±28, 171Â±63 and 129Â±6 mg kg-1 of TP respectively. 0 500 1000 1500 2000 2500 3000 3500 Fe at GRU Fe at DRU Fe at GRU Fe at DRU Fe at GRU Fe at DRU Apr-03Dec-02(no change-out)May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment Total Phosphorus (mg kg-1) Pre-Loading Post-Loading Figure 4-10. Total phosphorus (Â± one standard deviation) was measur ed in the iron (Fe) DWTR co-treatment substrate before and after loading with wastewater. One molar HCl-extractable P levels were determined in the two co-treatment reactor substrates (Figure 4-11) and in the constructed wetland mesocosm sands before and after loading with each wastewater. Post -loading with both wastewaters there was an increase in the mean HCl-extractable P in the Caand Fe-DWTR co-treatment substrate materials. The one molar HCl-extractable P in the pre-loading constructed wetland mesocosm sands averaged 21.8 Â±0.5 mg kg-1. Although the standard deviation was
93 relatively small, that is still below th e quantifiable detect ion limit of 62.5 mg kg-1 for P by this method (analyzed by ICAP). 0 50 100 150 200 250 300 350 400 Ca at GRUCa at DRUCa at GRUCa at DRUCa at GRUCa at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment HCl-Extractable P (mg kg-1) Pre-Loading Post-Loading 0 200 400 600 800 1000 1200 1400 1600 Fe at GRUFe at DRUFe at GRUFe at DRUFe at GRUFe at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment HCl-Extractable P (mg kg-1) Pre-Loading Post-Loading Figure 4-11. One molar HCl-extractable P (Â± one standard deviati on) in Ca-DWTR (Ca) and Fe-DWTR (Fe) co-treatment substrates before and after loading with each wastewater.
94 Post-loading with municipal wastewat er the sands averaged 38.8 Â± 9.7 mg kg-1 of HCl-extractable P, which is still below the de tection limit. However, post-loading with dairy wastewater the mesocosm sands averaged 106.9 Â±18.2 mg kg-1. Inorganic P fractions for the CTR substr ates and CWM sands are presented in Figures 4-12 and 4-13 respectively. The sum of the masses of all fractions is also provided in these figures. The fractionation results are presente d in these figures in terms of relative proportions of each fraction to the sum of all fractions for that substrate or sand. In the Ca-DWTR, the KCl (readily avai lable) fraction increased in both proportion and amount post-loading with both wastewater s (Figure 4-12 and Table 4-3). The mean NaOH-Pi fraction (thought to represent Aland Fe-bound P) increased the most in this material post-loading with dairy wastewater . There were no apparent trends in the NaOH-Po fraction (considered alkali-extractable organic P) in the Ca-DWTR. Postloading with dairy wastewater there was an increase in the HCl fraction (thought to be Caand Mg-bound P) in this co-treatment subs trate. This was also the case with the residual P fraction (considered to be mostly organic P). In the Fe-DWTR, there were almost undetectable amounts of the KCl (readil y available) fraction of inorganic P preloading and post-loading with both wastew aters. There were greater amounts and proportions of both NaOH-Pi (A land Fe-bound) and NaOH-Po (alkali-extractable organic) fractions with both wastewaters but there was litt le or no change preand postloading with either wastewater. The amount of the HCl fraction of inorganic P (Caand Mg-bound) in the Fe-DWTR was below detecti on limits preand post-loading with both wastewaters. The greatest proportion was the residual fraction (mostly organic) of the FeDWTR but there was no change in amount or proportion post-loading.
95 42 50 231 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pre-Loading Lime DWTR Post-Loading with Muncipal Wastewater Post-Loading with Dairy Wastewater Residual HCl NaOH-Po NaOH-Pi KCl 1768 1724 1909 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pre-Loading Iron DWTR Post-Loading with Muncipal Wastewater Post-Loading with Dairy Wastewater Residual HCl NaOH-Po NaOH-Pi KCl Figure 4-12. The relative proporti ons of P fractions in the Ca and Fe DWTR co-treatment substrates determined before and after loading with each wastewater. Total P masses (mg kg-1) are provided above each column.
96 48 55 47 49 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pre-Loading Sand Following Control Following Ca-DWTR Following Fe-DWTR Post-Loading with Municipal Wastewater Residual HCl NaOH-Po NaOH-Pi KCl 48 123 121 139 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pre-Loading Sand Following Control Following Ca-DWTR Following Fe-DWTR Post-Loading with Dairy Wastewater Residual HCl NaOH-Po NaOH-Pi KCl Figure 4-13. The relative proporti ons of P fractions were determined in the mesocosm sands preand post-loading with municipa l or dairy wastewater for one year. Total masses (mg kg-1) are provided above each column. The masses of each P fraction before and af ter loading, in the CTR substrates and CWM sands, are presented for comparison in Tables 4-3 and 4-4 respectively.
97Table 4-3. Phosphorus fractionation analysis was done for co-treatment substrates befo re and after loading with each wastewater . Values represent mass of that P fracti on (if above detection limit) per kg of s ubstrate (Â± one standard deviation). Phosphorus Fractions Substrate KCl NaOH-Pi NaOH-Po HCl Residual Sum Â…Â…Â….Â…Â…..Â…Â…Â…Â…Â….. mg kg-1 Â…Â…Â…Â…Â…Â…..Â…Â…Â…Â…Â… Ca-DWTR Pre-Loading < 0.1 < 0.5 8.6 Â± 1.2 15.45 Â± 13.4 17.1 Â± 7.6 42.0 Â±7.4 Post-Loading Municipal Wastewater 0.4 Â± 0.2 1.8 Â± 1.4 6.1 Â± 0.9 20.54 Â± 16.5 21.6 Â± 12.0 50.4 Â± 5.8 Post-Loading Dairy Wastewater 25.7 Â± 23.7 18.6 Â± 6.6 5.7 Â± 5.0 131.5 Â± 90.2 49.9 Â± 51.6 231.3 Â± 84.1 Fe-DWTR Pre-Loading 0.6 Â± 0.4 340.9 Â± 15.4 131.2 Â± 9.9 < 1.0 1295.7 Â± 26.4 1768.4 Â± 14.6 Post-Loading Municipal Wastewater 0.5 Â± 0.1 322.5 Â± 93.7 94.3 Â± 23.4 < 1.0 1306.9 Â± 141.9 1724.2 Â± 99.1 Post-Loading Dairy Wastewater 0.8 Â± 0.6 410.8 Â± 150.6 77.6 Â± 21.4 < 1.0 1420.2 Â± 139.9 1909.5 Â± 310.4
98Table 4-4. Phosphorus fractionation analysis wa s done for mesocosm sands before and afte r loading with each wastewater. The co treatment reactor substrate that preceded each mesocosm is given in parentheses. Phosphorus Fractions Sand KCl NaOH-Pi NaOH-Po HCl Residual Sum Â…Â…Â….Â…Â…..Â…Â…Â…Â…Â….. mg kg-1 Â…Â…Â…Â…Â…Â…..Â…Â…Â…Â…Â… Sand Pre-Loading 0.5 Â± 0.1 19.8 Â± 0.4 < 1.50 10.1 Â± 5.6 17.1 Â± 0.2 47.6 Â± 6.1 Sand Post-Loading With Municipal Wastewater (Control) 1.6 Â± 0.2 19.4 Â± 1.9 < 1.50 9.6 Â± 6.1 23.2 Â± 8.4 55.1 Â± 8.1 (Ca-DWTR) 1.5 Â± 0.2 20.1 Â± 4.0 < 1.50 8.9 Â± 2.6 15.7 Â± 1.0 46.7 Â± 5.6 (Fe-DWTR) 0.5 Â± 0.1 17.3 Â± 2.9 < 1.50 15.1 Â± 16.4 15.6 Â± 4.1 49.2 Â± 23.1 Sand Post-Loading With Dairy Wastewater (Control) 46.7 Â± 11.9 32.9 Â± 4.6 4.8 Â± 0.9 10.1 Â± 3.2 28.0 Â± 3.3 122.5 Â± 16.3 (Ca-DWTR) 47.8 Â± 6.2 28.8 Â± 4.7 2.7 Â± 0.2 9.5 Â± 3.5 31.7 Â± 5.4 120.5 Â± 4.4 (Fe-DWTR) 51.1 Â± 22.5 37.4 Â± 11.0 2.5 Â± 1.9 10.9 Â± 5.2 37.2 Â± 12.4 139.0 Â± 41.5
99 The inorganic P fractionation results for the mesocosm sands are presented in Figure 4-13 (proportions) and Table 4-4 (amounts). The gr eatest change of all P fractions in the mesocosm sands was in the KCl fraction (read ily available) post-loading with the dairy wastewater (Figure 4-13). There was no appa rent difference caused by the co-treatments preceding the wetlands in this fraction. Ther e were no apparent trends in the NaOH-Pi (Aland Fe-bound) fraction with either wastewater even in the wetlands that were preceded by Fe-DWTR co-treatments. The NaOH-Po (alkali-extractable organic) fr actions increased in amount and proportion in wetland sands loaded with eith er wastewater. Ther e were no apparent trends in the HCl fraction of inorganic P (C aand Mg-bound) even in wetlands that were preceded by a Ca-DWTR co-treatment. There were also no trends apparent in the residual P fraction (mostly organic) in the wetland sands receiving either wastewater. Metal Contents of Co-Treatment Substrates and Mesocosm Sands Oxalate-extractable Fe was measured in th e co-treatment reactor substrates before and after loading with each wastewater. Th ere was little or no change in oxalateextractable Fe in either of th e two co-treatment reactor substrates before and after loading with either municipal or dairy wastewater. The pre-loading am ount of this form of Fe in the Ca-DWTR co-treatment reactor substrates was 583Â± 184 mg kg-1. After loading with municipal wastewater the am ount of oxalate-extractable Fe in the Ca-DWTR was 620Â± 248 mg kg-1. After loading with dairy wastewater the amount of oxalate-extractable Fe in the Ca-DWTR was 672Â± 218 mg kg-1. The pre-loading amount of this form of Fe in the Fe-DWTR co-treatment reactor substrates was 176664Â± 3542 mg kg-1. After loading with municipal wastewater the amount of oxalate-extractable Fe in the Fe-DWTR was
100 176675Â± 1176 mg kg-1. After loading with dairy wa stewater the amount of oxalateextractable Fe in the Fe-DWTR was 181758Â± 2250 mg kg-1. Oxalate-extractable Al was also measured in the co-treatment reactor substrates before and after loading with each wastewater . There was also little or no change in oxalate-extractable Al in either of the two co -treatment reactor substrates before and after loading with either municipal or dairy wastew ater. The pre-loading amount of this form of Al in the Ca-DWTR co-treatment reactor substrates was 613Â± 90 mg kg-1. After loading with municipal wastewater the amount of oxalate-extractable Al in the CaDWTR was 657Â± 25 mg kg-1. After loading with dair y wastewater the amount of oxalate-extractable Al in the Ca-DWTR was 647Â± 36 mg kg-1. The pre-loading amount of this form of Al in the Fe-DWTR co-tre atment reactor substrates was 452Â± 55 mg kg-1. After loading with municipal wastewater the amount of oxalate-extrac table Al in the FeDWTR was 446Â± 17 mg kg-1. After loading with dair y wastewater the amount of oxalate-extractable Al in the Fe-DWTR was 392Â± 25 mg kg-1. Oxalate-extractable Fe and Al were al so measured in the constructed wetland mesocosm sands before and after loading with each wastewater. The results are presented in Figures 4-14 and 4-15 and appear to show some increase in these metals in controls and treatments for both wastewaters. There is no apparent difference in the amounts of these forms of Fe and Al betw een wetland sands preceded by control or treatment co-treatment reactors. There does appear to be more oxalate-extractable Fe post-loading with dairy wastewater compared to post-loading with municipal wastewater. However there does not appear to be a diffe rence in the amount of oxalate-extractable aluminum post-loading with the dairy wast ewater versus the municipal wastewater.
101 0 10 20 30 40 50 60 70 80 90 100 (Control)(Ca-DWTR)(Fe-DWTR)(Control)(Ca-DWTR)(Fe-DWTR) Municipal WastewaterDairy Wastewater Oxalate-Extractable Fe (mg kg-1) Pre-Loading Post-Loading Figure 4-14. Oxalate-extractable Fe in meso cosm sands was measured before and after loading with each wastewater. The co -treatment reactor preceding each mesocosm is listed in parentheses. 0 10 20 30 40 50 60 (Control)(Ca-DWTR)(Fe-DWTR)(Control)(Ca-DWTR)(Fe-DWTR) Municipal WastewaterDairy Wastewater Oxalate-Extractable Al (mg kg-1) Pre-Loading Post-Loading Figure 4-15. Oxalate-extractable Al in meso cosm sands was measured before and after loading with each wastewater. The co -treatment reactor preceding each mesocosm is listed in parentheses.
102 0 50000 100000 150000 200000 250000 300000 350000 400000 450000 Ca at GRUCa at DRUCa at GRUCa at DRUCa at GRUCa at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of Substrates End of Experiment HCl-Extractable Ca (mg kg-1) Pre-Loading Post-Loading 0 2000 4000 6000 8000 10000 12000 14000 16000 Fe at GRUFe at DRUFe at GRUFe at DRUFe at GRUFe at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of Substrates End of Experiment HCl-Extractable Ca (mg kg-1) Pre-Loading Post-Loading Figure 4-16. One-molar HCl-extractable Ca (Â± one standard deviation) was determined in the Ca-DWTR (Ca) and Fe-DWTR (Fe) co -treatment substrates before and after loading with each wastewater (GRU and DRU).
103 One molar HCl-extractable Ca, Mg, Fe and Al were determined in co-treatment reactor substrates and wetland mesocosm sands before and after loading with municipal wastewater (GRU) and da iry wastewater (DRU). 0 200 400 600 800 1000 1200 1400 (Control)(Ca-DWTR)(Fe-DWTR)(Control)(Ca-DWTR)(Fe-DWTR) Municipal WastewaterDairy Wastewater HCl-Extractable Ca (mg kg-1) Pre-Loading Post-Loading Figure 4-17. One-molar HCl-extractable Ca (Â± one standard deviation) was determined in wetland mesocosm sands before and afte r loading with each wastewater. The co-treatment reactor prec eding each mesocosm is listed in parentheses. The HCl-extractable Ca in the Ca-DWTR (Ca) and in the Fe-DWTR (Fe) substrates is presented in Figure 4-16. The means di d not appear to increase substantially, post-loadin g with either wastewater, relative to the amount of this form of Ca in this Ca-based co-treatment material. Th is form of Ca appeared to decrease in the Fe-DWTR post-loading with municipal wastewat er and increase post-loading with dairy wastewater. The HCl-extractable Ca was measured in the wetland sands at the beginning and end of the one-year mesocosm study. There wa s an increase in the mean levels of this form of Ca in all sands post-loading with both wastewaters (Figure 4-17). There was no
104 greater increase in this form of Ca in th e sands following Ca-DWTR co-treatments than in those following controls or Fe-DWTR co-treatments. 0 5000 10000 15000 20000 25000 Ca at GRUCa at DRUCa at GRUCa at DRUCa at GRUCa at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of Substrates End of Experiment HCl-Extractable Mg (mg kg-1) Pre-Loading Post-Loading 0 100 200 300 400 500 600 700 800 900 1000 Fe at GRUFe at DRUFe at GRUFe at DRUFe at GRUFe at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment HCl-Extractable Mg (mg kg-1) Pre-Loading Post-Loading Figure 4-18. One-molar HCl-extractable magnesi um (Mg) (Â± one standard deviation) was determined in the Ca-DWTR (Ca) and Fe-DWTR (Fe) co-treatment substrates before and after loading with each wastewater (GRU and DRU).
105 There were no apparent trends in the mean levels of HCl-extractable Mg in the Ca-DWTR co-treatment material post-loadi ng with either wastewater (Figure 4-18). 0 100 200 300 400 500 600 700 800 900 1000 Ca at GRUCa at DRUCa at GRUCa at DRUCa at GRUCa at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment HCl-Extractable Fe (mg kg-1) Pre-Loading Post-Loading 0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000 Fe at GRUFe at DRUFe at GRUFe at DRUFe at GRUFe at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of Substrates End of Experiment HCl-Extractable Fe (mg kg-1) Pre-Loading Post-Loading Figure 4-19. One-molar HCl-extractable Fe (Â± one standard deviation) was determined in the Ca-DWTR (Ca) and Fe-DWTR (Fe) co -treatment substrates before and after loading with each wastewater (GRU and DRU).
106 The mean HCl-extractable Mg increase d dramatically in the Fe-DWTR postloading with both wastewaters (Figure 4-18). The mean levels we re higher post-loading with dairy wastewater. The pre-loading le vel of HCl-extractable Mg in the sand was below the methods detection limit of 5 mg kg-1. Post-loading with municipal wastewater for one year the average level of Mg in the mesocosm sands was 27Â±24 mg kg-1. Postloading with dairy wastewater the average level was 54Â±84 mg kg-1. In each case the standard deviation was as large or larger than the mean. 0 10 20 30 40 50 60 70 80 90 (Control)(Ca-DWTR)(Fe-DWTR)(Control)(Ca-DWTR)(Fe-DWTR) Municipal WastewaterDairy Wastewater HCl-Extractable Fe (mg kg-1) Pre-Loading Post-Loading Figure 4-20. One-molar HCl-extractable Fe (Â± one standard deviation) was determined in wetland mesocosm sands before and afte r loading with each wastewater. The co-treatment reactor prec eding each mesocosm is listed in parentheses. One molar HCl-extractable Fe was dete rmined in the co-treatment reactor substrates and in the wetland mesocosm sa nds before and after loading with each wastewater. There were no apparent changes in the mean levels of HCl-extractable Fe in either co-treatment substrate post-loadi ng with either wastewater (Figure 4-19).
107 0 100 200 300 400 500 600 700 800 900 1000 Ca at GRUCa at DRUCa at GRUCa at DRUCa at GRUCa at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment HCl-Extractable Al (mg kg-1) Pre-Loading Post-Loading 0 100 200 300 400 500 600 700 800 Fe at GRUFe at DRUFe at GRUFe at DRUFe at GRUFe at DRU Apr-03Dec-02(no changeout) May-03Aug-03Aug-03 1st Change-Out of Substrates2nd Change-Out of SubstratesEnd of Experiment HCl-Extractable Al (mg kg-1) Pre-Loading Post-Loading Figure 4-21. One-molar HCl extractable alum inum (Â± one standard deviation) was determined in the Ca-DWTR (Ca) and Fe-DWTR (Fe) co-treatment substrates before and after loading with each wastewater (GRU and DRU). There was an increase in HCl-extractable Fe in all of the wetland mesocosm sands post-loading with both wastewaters as seen in Figure 4-20. However, only in the case of
108 the dairy wastewater was there a greater increase in this form of Fe in the sands following Fe-DWTR co-treatments compared to thos e following control or Ca-DWTR reactors. There were no trends in the mean levels of HCl-extractable Al in either substrate post-loading with either wastewater (Figure 4-21 ). The mean levels of this form of Al may have been slightly higher in the wetla nd sands but the standard deviations were relatively large (Figure 4-22). 0 20 40 60 80 100 120 (Control)(Ca-DWTR)(Fe-DWTR)(Control)(Ca-DWTR)(Fe-DWTR) Municipal WastewaterDairy Wastewater HCl-Extractable Al (mg kg-1) Pre-Loading Post-Loading Figure 4-22. One molar HCl-extractable alum inum (Â± one standard deviation) was determined in wetland mesocosm sands before and after loading with each wastewater. The co-treatment reactor preceding each mesocosm is listed in parentheses. Wetland Macrophytes and Redox Conditions in Mesocosm Sands At both sites, bulrush plants survived one year of wastewater loading and spread considerably from initial plantings. Influent wastewater mean TP concentrations to the mesocosms ranged from less than 0.5 mg L-1 at the municipal site to greater than 30 mg
109 L-1 at the dairy site. Oxidation-reduction pot ential (ORP) in the root-bed sand ranged from +440 mV at the municipal si te to -147 mV at the dairy. Green stem counts were completed at both sites through four seasons and suggested little difference in plant growth between treatments and controls. However, after 4 months of wastewater loading the counts were significantly higher at the dairy site (Figure 4-23). The initial (pre-loading) stem counts at the dairy site were higher but this difference is small compared to the differen ce after wastewater loading when the dairy mesocosms had far greater stem densities than those at th e municipal site. 0 50 100 150 200 250 300 350 400 450 500ControlLimeIronControlLimeIron Receiving Municipal WastewaterReceiving Dairy Wastewater Number of Green Stems 06/24/02 11/16/02 3/5/03 8/28/03 Figure 4-23. Mean bulrush green stem c ounts by wastewater, treatment and counting date. Standard deviation error bars ar e not shown for the first date when an exact number of stems were planted in each mesocosm. At the dairy site, the stem count one-year totals for control, Ca and Fe systems were 904, 989 and 1008 respectively. At the munici pal site, the totals for control, Ca and Fe were 206, 246 and 211 respectively.
110 Tissue P concentrations in live (green) st ems were measured at the beginning and end of the one-year study a nd there were no large differe nces between treatments and controls (Figure 4-24). There were howev er large differences in the tissue TP concentrations between the two wastewaters. Although initial (pre -planting) tissue P concentrations were higher at the munici pal site, the mesocosms that received dairy wastewater had much higher tissue P in the live stems after one year. Post-loading TP concentrations of dead bulrush stems were also much higher at the dairy site. These concentration patterns were repeated in the bulrush roots and rhizomes. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 ControlLimeIronControlLimeIron Receiving Municipal WastewaterReceiving Dairy Wastewater Tissue P Concentration (mg kg-1) Pre-Loading Post-Loading Figure 4-24. Mean (Â± 1 standard deviation) live bulrush stem phosphorus concentrations at the beginning and end of the one-year study. Discussion Characteristics of Waste waters and Effluents The tremendous differences between the two wastewaters provided a more informative test of the co-treatment reac tor and wetland wastewater treatment system.
111 The more reducing conditions associated with th e dairy wastewater likely played a role in the performance differences but this was diffi cult to assess due to the differences in so many other parameters. The dissolved metals concentrations in th e wastewaters also di ffered greatly. This not only has implications with respect to P re moval by co-treatments but also with respect to the biological aspects of this treatment design. All of the metals tested except aluminum are necessary plant (and microbe ) nutrients and could affect plant (and microbial) growth in the systems. The nutri ent metal contents of the wastewaters after leaving the treatment system would need to be compared with the receiving waters. If the aluminum (not a plant nutrient) accumulated to toxic levels it could have negative implications for the biology of the treatment sy stem as well as the fi nal receiving waters. There were no such problems observe d in this one-year experiment. Total suspended solids were not an issue at the municipal site as the levels were below detection both entering and exiting the treatment system. The TSS in the dairy wastewater were significant to the functioni ng of the system but were greatly reduced before being discharged from the system. A full-scale wetland treatment system typically would have multiple cells and it is expected that TSS would be reduced even further unless algal growth in the system added so lids to the effluent. Even the higher TSS levels in the dairy wastewat er did not present any apparent clogging problem in the vertically drained constructed wetland mesocosms in this one -year experiment. It would be more prudent however to construct a horiz ontally drained wetland for treatment of this wastewater.
112 It is apparent from the results that the Fe-DWTR contributed DOC to the cotreatment and wetland effluents. The Fe-DWTR is the by-product of removing color from drinking water supplies so it is known to contain di ssolved organic carbon. There are two main implications of this in terms of co-treatment potential. Irrespective of its ability to remove P from wast ewater it is generally not acceptable to discharge effluent with a higher DOC than the wastewater origin ally contained. In a full-scale wetland treatment system this problem may be negligible since multipl e wetland cells after the cotreatment might remove any excess DOC. On e positive aspect of the high DOC is the potential for it as a carbon sour ce to help fuel nitrificati on and denitrification. This hypothesis would have to be test ed in further experiments. Phosphorus Removal with Pre-Wetland Co-Treatment Newly constructed wetland cells alone are fairly efficient at removing P from wastewater in the first year of operation (Kadlec and Knight, 1996). This Â“start-upÂ” effect may have masked the contribution of the co-treatments in this 52-week study since the overall system removal rates were similar for controls and treatments. However, the data from the co-treatments alone suggests th at larger differences would eventually be evident in the overall system removal rates. It should also be noted that the P removed by the co-treatments does not stay in the syst em but is removed when the co-treatment substrates are changed out. This suggests that, in the long-term, wetlands with cotreatments will become saturated with P more slowly and thus have a longer functional lifespan for P removal. Phosphorus Removal with Post-Wetland Co-Treatment The TP minus SRP equals particulate P. We observed that particulate P, not just SRP, was reduced by treatments compared to controls. This suggests some particulate P
113 was captured by the DWTR and thus, sediment ation and filtration were not the only mechanism of P removal from dairy wastewat er. This additional experiment supported the hypothesis that placing a CTR after a wetland cell was more effective for P removal from wastewaters with high TSS. Phosphorus in CTR Substrates and CWM Sands Total phosphorus levels in both co-treatment substrates were higher post-loading with both wastewaters as expected. This P would be completely removed from the wastewater stream, as the substrates were periodically changed out , thus reducing the P loading to the wetland cells as predicted. The TP levels did not appear to increase in the mesocosm sands post-loading with municipal wastewater. However, the sands receiving dairy wastewater did experi ence substantial increases in TP. There was no clear difference in post-loading me socosm sand TP caused by the co-treatments. It is suspected that differences in the sand TP levels would be detected in a longer-term experiment. The HCl-extractable P levels were higher in both substrates post-loading with both wastewaters. The increases were greate r with the dairy wastewater as expected. The same was true for the mesocosm sands and no large differences were observed between treatments and controls. The inorganic P fractionation data revealed little change in the proportions of P forms in the Fe-DWTR co-treatment material pos t-loading with either wastewater. If the Fe-DWTR material were cropland applied af ter being used as a co-treatment, the P availability would presumably differ little fr om that of the Fe-DWTR that had not been used for wastewater treatment. There was, as expected, a larger su m of P fractions postloading with dairy wastewater.
114 In the Ca-DWTR the readily available P fraction did increase in amount and proportion post-loading with bot h wastewaters. If the Ca -DWTR was cropland-applied after being used as a co-treatment this could have positive implications in terms of fertilizer value. However, it could have negative implications if the amount was in excess of crop needs. Metals Contents of CTR Substrates and CWM Sands As discussed earlier in chapter three, there are many reasons why metal forms and amounts could change in these systems post-lo ading with wastewater. The implications of these changes could be positive or negative with respect to P removal or environmental impact of discharged effluent or cr opland-applied co-treatment materials. The apparent increase in oxalate-extract able Al in the mesocosm sands could become a concern if levels caused any t ype of phytotoxicity or negative impacts on receiving waters. As mentioned, no such problems were observed in this one-year experiment but the issue should be investigat ed further. It should be noted that the increases did not appear greater follow ing treatments than following controls. Increases in the HCl-extractable Ca in the wetland mesocosm sands post-loading with both wastewaters could have a positive impact on long-term P stability in the wetland cells. The HCl-extractable Mg may ha ve increased somewhat in the sands postloading and that could also have a positive impact on wetland performance. This form of Fe also increased post-loading in the wetland sands but not substantially more in those that followed treatments versus controls. There was no substantial increase in HClextractable Al in any of the sands, but due to potential toxicity con cerns that would need to be monitored.
115 Wetland Macrophytes Bulrush thrived in spite of frequent 7 d unsaturated conditions every two weeks. The bulrush plants were healthy enough to withstand an infestation of spittle bugs ( Philaenus spp. ) at the dairy site, with no long-term stem damage observed. Apparently, none of the conditions present in this one-yea r study were lethal to the bulrush plants. However, bulrush survival alone was not an adequate metric for plant performance with this experimental co-treatment and CW sy stem design. The stem counts suggested no detrimental effects of the treatments on bulrush stem production. There were, however, differences in stem growth and tissue TP concentration between wastewaters and between treatments. The differences in storage water compositi on and light conditions at the two sites may have caused the initial differences in buc ket stem counts at each site before plants were transferred to the mesoco sms. There was considerably more growth, as expected, with the high-nutrient dairy wastewater a nd this difference quickly overshadowed the initial stem count difference. A seasonal patte rn was evident at all sites and treatments but the Ca and Fe co-treatments preceding the CWM did not reduce stem counts in those cells. The total number of green stems counted at each site for the entire year indicated that the co-treatments had no negative, and perhaps a slight positive, impact on stem growth. The live (green) bulrush tissue P concentr ations are within the ranges commonly reported in the literature (A hn et al., 2001; Tanner, 2001; Kir by et al., 2002; Garbey et al., 2004). The bulrush tissue P concentration results show no large differences between treatments and controls. It should be noted th at wastewater P concen trations flowing into the CWM, where the bulrush were planted, were not all the same due to differences in P
116 removal rates by the preceding control and treat ment CTR cells. This could explain why the post-loading live tissue P concentrations a ppear to be slightly lower in the CWM that followed Ca or Fe CTR at both wastewater sites (Figure 4-24 ). The post-loading tissue P concentrations in live stems at the dairy site were considerably higher than those at the municipal site even though initial concentr ations were actually lower due to the preloading storage differences described earlier. Post-loading TP concentrations of dead bulrush stems were also much higher at the dairy site. This may have some implicat ions for eventual release of P back to the water column and, conversely, for long-term st orage of P in the plant detritus component of new soil accretion in the CW. The concentrat ion patterns were repeated in the bulrush roots and rhizomes, indicating potentially greater long-term below ground P sequestration with the more heavily loaded wetlands. The effluent, substrate, sand and plant observations and data will provide insight into the ultimate application of these de sign features to wastewater treatment. Conclusions The experimental co-treatment and wetland systems removed P from both wastewaters tested but performance varied with wastewater and treatment material. Wetlands paired with co-treatments generally removed P as well, or much better than, control wetland systems. Results from the parallel experiments run with both dairy and municipal wastewater provided Â“proof of conceptÂ” for the use of co-treatments with wetlands, and added insight for improved design for specific wastewaters. For the municipal wastewater, total phosphor us (TP) concentrations were reduced 93 to 95% by the combined CTR and CWM syst ems. For the dairy wastewater, TP was reduced by 53%. High total suspended solids (TSS) were thought to have caused the
117 lower TP reduction with the dairy wastewater and a simple design modification, tested with additional experimentati on, was shown to ameliorate this problem. As with the standard multiple cell CW systems, an initia l settling basin for solids removal would be advisable. Placing the co-treatment after a so lids removal cell is compatible with current agricultural CW system desi gn recommendations (USDA NRCS, 2002). Also, to prevent long-term clogging problems surface drained, ra ther than vertically drained, CW would be more appropriate for treat ing high TSS wastewaters. Wastewater volumes were the same in trea tment and control systems at each site and thus P mass removal rates mirrored th e TP concentration reductions. Average P mass removal rates for the combined CTR and CWM systems were 0.009 g m-2 d-1 and 0.284 g m-2 d-1 for the municipal and dairy wastewat ers respectively. Differences in P removal rates between control a nd treatment systems at both sites were greater exiting the CTR cells than after exiting the CWM cells that they flowed into. The control, Ca, and Fe CTR cells at the municipal site, where di fferences between treatments and controls were greatest, removed 0.003, 0.023, and 0.050 g-P m-2 d-1 respectively. The greater differences between treatments and controls by the CTR alone are likely due to the high first-year assimilation of P in the CWM ce lls by plant uptake and root-bed media sorption. In the long term, it is expected that this P sink would become exhausted, revealing greater differences in final CWM ef fluent TP concentrations between controls and treatments. The study supported the hypothe sis that the co-treat ments could reduce P loading to a CW. Overall the soft-stem bulrush, Schoenoplectus tabernaemontani (K.C. Gmel.) Palla, performed well under a va riety of potentially detrim ental conditions in these
118 experimental co-treatment and constructed wetland wastewater treatment systems. The plants in this study survived with both low and high nutrient loadings. The plants also performed well in spite of being drained and frequently unsaturated for up to 7 d. Cotreatment materials used to enhance P rem oval had no apparent negative, and perhaps a small positive, impact on bulrush stem growth with the greatest stem counts observed in the high-nutrient systems. The co-treatment s did not impact plant performance in terms of P uptake. At higher nutrient loadings, ti ssue TP concentrations were higher in green stems, dead stems, and rhizomes. Higher stem counts and higher tissue TP concentrations in the high-nutrient systems demonstrate the capacity of bulrush in the first year of operation to cont ribute significantly to P removal. Thus, in a one-year study, they may mask the effects of any co-treatme nts, or other design features, on overall P removal performance by the systems. Researchers attempting to enhance P removal with design modifications should be aware of this plant effect in CW studies of one year or less. The results support the suitability of Schoenoplectus tabernaemontani for use in Ca or Fe co-treatment and constructed wetland systems. The use of co-treatments with locally available inexpensive and non-toxic byproducts, such as the DWTR used in this experiment, has potential for increasing the sustainability of P removal by CW systems. The Fe and calcium-based DWTR used were chosen in part based on their potential to be used as agricultural soil amendments and fertilizers after they have been satura ted with phosphorus in this system. Both DWTR used in this mesocosm study have been applied to agricultural lands in Florida. This feature of reuse could increase both th e environmental and economical feasibility of this design.
119 CHAPTER 5 PHOSPHORUS REMOVAL FROM AGRICULTURAL AND MUNICIPAL WASTEWATER WITH BY-PRODUCT CO-TREATMENTS AND CONSTRUCTED WETLANDS: OVERVIEW OF RESEARCH A Synthesis of Laboratory, Greenhouse and Mesocosm Results By-product co-treatment basins filled w ith inexpensive and non-toxic by-products containing phosphorus (P) binding component s such as iron, aluminum, calcium, magnesium, organic matter or clay, might in crease the sustainab ility of P removal by constructed wetland (CW) systems. The centr al hypothesis being test ed was that select by-product co-treatments could be optimized to reduce the P load to a constructed wetland. Thus the main objective of this research was to optimize a by-product cotreatment and constructed wetland wastewater treatment system for P removal. Eleven by-product materials were obtained for initial evaluati on with laboratory batch experiments that tested P sorption and ot her relevant physico-chemical properties. A greenhouse column study then paired six of the optimal substrates in co-treatment bottles with sand columns that represented ve rtically drained constructed wetlands. The paired units were batch-fed municipal (low P) or dairy (high P) wastewater for one month. The laboratory and column st udy results, as well as many practical considerations, led to two optimal materials, a Caand a Fe-DWTR, being selected for further evaluation at the mesocosm scale. Finally, an outdoor mesocosm study pair ed 208-L co-treatme nt reactors (CTR) containing Caor Fe DWTR (or clean water in itially for controls) with 567-L verticalflow constructed wetland mesocosms (C WM) planted with soft-stem bulrush
120 ( Schoenoplectus tabernaemontani ). Eighteen of these CTR and CWM experimental units were loaded with either sec ondary municipal, or anaerobica lly digested dairy, wastewater for one year. Both treatments removed P from the wastewater. However, P reductions by the co-treatments receiving dairy wastewater were not more effective than the control systems. Additional experimentation was done with high P, but lower total suspended solids (TSS), dairy wastewater that had first passed through a control CTR and CWM system. Reductions in P concentration by the Ca and Fe systems were then greater than by the controls. Overall the results do suggest the potent ial for using by-product co-treatments to enhance P removal by constructed wetland system s. The combined results were used to develop two conceptual designs for the inco rporation of co-treatment basins into constructed wetland wastewater treatment system s. The two designs reflect the different types of wastewater that might be treated, as well as the co-treatment substrates that appear to have the potentia l for practical application. A conceptual diagram showing the use of co-treatment basins with constructed wetlands for municipal wastew ater treatment is provide d in Appendix B of this dissertation. This design is a modificati on of more typical layouts for constructed wetland wastewater treatment systems. Th e modification mainly incorporates the addition of co-treatment basins containing drinking water treatment residuals (DWTR) for enhanced phosphorus removal. Since this is a new technology, the recommended layout allows for bypassing these basins if needed, for adjustments or testing requirements. A certain amount of redundancy an d flexibility in the design is a prudent engineering approach prior to a new system becoming a more proven technology. One of
121 the two wastewaters used in this research wa s secondarily treated m unicipal wastewater. The recommended co-treatment material for th at wastewater situation is a Ca-DWTR. This co-treatment choice also drives the s uggestion that the second stage wetland cells be of the submerged aquatic vegetation (SAV) type (e.g., Naiad sp.). Some calcium from the Ca-DWTR co-treatment basin would be e xpected to dissolve into the wastewater solution. In the SAV wetland that followed, the elevated pH values present would be expected to encourage the prec ipitation of P from solution by the calcium. The design might need to be altered for substantially diffe rent types of wastewat er or a different cotreatment material. The exact dimensions are not provided and would need to be determined based on the wastewater volume and characteristics, treatment needs, and site factors of a particular loca tion. Variations in reuse n eeds and/or local discharge requirements would also demand site-specific design details. Chlorination basins are not shown, as their placement would depend on disc harge requirements. The initial stages, through secondary treatment, are generalized in the diagram, as they would vary by site. The individual components of the concep tual municipal system described above, and shown in Appendix B, are described below: Wastewater Source any municipal raw wastewat er collected for treatment. Initial Treatment any type of floatable debris, sand or solids removal prior to primary treatment. Primary Treatment any combination of anaerobi c, anoxic, and/or aerobic primary wastewater treatment units. Secondary Treatment any form of secondary treatment. Tertiary Treatment System combination of wetland treatment cells with cotreatment basins for enhanced P removal. Final Pond pond for collection and storage of treated wastewater for reuse needs or final discharge if permitted.
122 Recycle Line pipeline to allow for recycling of treated wastewater back to an earlier stage if needed for enhanci ng de-nitrification or other reasons. A conceptual diagram showing the use of co-treatment basins with constructed wetlands for livestock wastewater treatment is provided in Appendix B of this dissertation. This design is a modification of the Â“typical layoutÂ” presented in the USDA NRCS National Engineering Handbook Part 637 for constructed wetlands for animal waste treatment (USDA NRCS, 2002). The modification mainly incorporates the addition of co-treatment basins containing drinking water treatment residuals (DWTR) for enhanced phosphorus removal. Since this is a new technology, the recommended layout allows for bypassing these basins if needed, for adjustments or testing requirements. One of the two wastewaters used in this resear ch was anaerobically digested flushed dairy manure. The reco mmended co-treatment material for that wastewater situation is an Fe DWTR. Th is wastewater was found to have high enough total suspended solids (TSS) to inhibit the P removal effectiveness of co-treatment materials. Thus a Â“secondary treatmentÂ” (e.g., settling basin) cell prior to the wetlands and co-treatment basins is suggested. Th e design might need to be altered for substantially different types of agricultural wastewater. The exact dimensions are not provided and would need to be determin ed based on the wastewater volume and characteristics, treatment needs, and site f actors of a particular agricultural operation. Variations in irrigation and fe rtigation needs and/or local discharge requirements would also demand site-specific design details. The individual components of the con ceptual agricultural livestock system described above, and shown in A ppendix C, are described below:
123 Animal housing any confined livestock areas from which runoff or flush-water is collected for treatment. Initial Treatment any type of floatable debris, sand or solids removal prior to primary treatment. Primary Treatment anaerobic wastewater treatment lagoon or anaerobic digestion system. Secondary Treatment settling pond for clarifi cation (TSS removal) and/or winter storage. Tertiary Treatment System combination of wetland treatment cells with cotreatment basins for enhanced P removal. Final Pond pond for collection and storage of treated wastewater for irrigation needs or final discharge if permitted. Recycle Line pipeline to allow for recycling of treated wastewater back to an earlier stage if required to meet discharg e needs. This can also be useful for enhance N removal (water high in nitrat es is pumped back to earlier, more anaerobic stages for de-nitrification). Overall Conclusions The use of co-treatments with locally available inexpensive and non-toxic byproducts has potential for increas ing the sustainability of P removal by CW systems. The Feand Ca-based DWTR used in the final me socosm study were chosen in part based on their potential to be used as agricultural so il amendments and fertilizers after they have been saturated with phosphorus in this type of system. Both DWTR used in the mesocosm study have been applied to agricultura l lands in Florida. This feature of reuse could increase both the environmental a nd economical feasibility of this design. A less mechanized, less energy-intensive sy stem that utilizes non-toxic by-product co-treatments with CW, and returns P back to agriculture, could conserve valuable resources and accomplish multiple goals. The ultimate application of this wastewater treatment system design will depend on the type and quality of wastewater being treated.
124 Consideration of many local f actors would also be require d to optimize the design and operation to insure the economic feasibility a nd positive environmental impact in a given situation. Co-treatments might be incorporat ed into either existing or new wastewater treatment systems. Recommendations for Future Research Additional pilot scale experimentation w ould be recommended before a full-scale system was constructed. The non-toxicity of any co-treatment materials considered would have to be tested with standard protocols. The materi als would also have to be retested for toxicity, after bei ng used in a wastewater treatm ent system, and before being land-applied. The economics of transpor ting, handling and cropland application (as opposed to landfill disposal) of the by-products would have to be compared to the costs of other types of P removal sy stems. The net costs would vary considerably depending on many situation-specific conditions. Greenhouse pot studies would be useful to determine the agronomic value of the co-treatment materials after they had been used for P removal from wastewater. Land application rates would also need to be evaluated from both an agronomic and environmental impact perspective. Further column or mesocosm studies coul d be used to determine optimal surface area to depth ratios of the s ubstrates in co-treatment react ors or basins. The P removal performance gain and cost-eff ectiveness of incorp orating other wastewater engineering techniques, such as mechanical mixing or aeration, could be tested. Also, mesocosms planted with submerged aquatic vegetation (S AV) could be used to test the possible removal of P to very low levels following a Ca based co-treatment basin. This research
125 has suggested the potential for the beneficial use of by-product co-treatments and further research is warranted.
APPENDIX A CO-TREATMENT REACTOR AND CONSTRUCTED WETLAND MESOCOSM
127 Storm event rainfall overflow PVC pipe & 5gal. collection bucket placed before drain valve Decant after HRT (some of the substrate fines, entrained in effluent, will flow into the wetland cell) 50 gal. CoTreatment Tank with substrate in bottom V ertical Fall onto Substrate causes mixing of substrate and wastewater Wastewater Inflow Drain tiles direct water towards effluent valve >>> Gravel Open the Drain Valve after HRT Inflow deflection plate supported by PVC standpipe that serves as contingency drain Permeable geotextile between sand and gravel Coarse Sand Emergent macrophytes Wastewater flooding the wetland after it has been discharged from the cotreatment tank. Significant percolation through sand is expected during the 7-day HRT. Figure A-1. This is a detailed sche matic diagram of the co-treatment reactor and constructed wetland mesocosm experimental unit s. The drawing is not to scale.
APPENDIX B CONCEPTUAL DESIGN FOR MUNICI PAL WASTEWATER TREATMENT SYSTEM USING CO-TREATMENTS WITH CONSTRUCTED WETLANDS
129 Overhead View: Municipal Wastewater Source Initial Treatment Primary Treatment Secondary Treatment Constructed Wetlands 1st Stage Cells (Submerged) Constructed Wetlands 2nd Stage Cells (Emergent) Co-Treatment Basins (initially leave two empty) Tertiary Treatment System Final Collection Pond Side View: Recycle Line Figure B-1. This is a conceptual layout s howing incorporation of co-treatments and c onstructed wetlands into a municipal wastew ater treatment system. The drawing is not to scale.
APPENDIX C CONCEPTUAL DESIGN FOR AGRICULT URAL WASTEWATER TREATMENT SYSTEM USING CO-TREATMENTS WITH CONSTRUCTED WETLANDS
131 Overhead View: Animal Housing Initial Treatment Primary Treatment Secondary Treatment Constructed Wetlands 1st Stage Cells Constructed Wetlands 2nd Stage Cells Co-Treatment Basins (initially leave two empty) Tertiary Treatment System Final Collection Pond Side View: Recycle Line Figure C-1. This is a conceptual layout s howing incorporation of co-treatments and c onstructed wetlands into an agricultural wastewater treatment system. The drawing is not to scale.
132 APPENDIX D PHOSPHORUS FACT SHEET Â“WHATÂ’S SO SPECIAL ABOUT PHOSPHORUS?Â” Phosphorus (P) is an essential component of all living things yet less than 1% of the earthÂ’s crust. Name comes from Greek word for Â“bringer of lightÂ”. Discovered in 1669 by Hennig Brand; first isolated from urine. Most plentiful sources are phosphate ores that are mined (90% used for fertilizer). Mostly found in apatite minerals. It is mined mostly in the USA (especially Florida ), the former Soviet Union, and Morocco. Phosphate rocks weather to release P for plant uptake. P accumulates in the oceans, marine organisms, and eventually marine sediments (similarly in isolated freshwater systems); present in accreted organic matter in ponds/wetlands; soluble phosphates also bind with inorganic compounds, especially those with iron, aluminum, calcium and/or magnesium . Atomic number 15; atomic weight 30.97 g mol-1; valence +5 (as in H3PO4) , also Â±3 or +4. Pure form can be colorless, red or silvery white. Chronic poisoning of unprotected workers with white P leads to necrosis of the jaw known as Â“phossy-jawÂ”. White form catches fire spontaneously in ai r; sunlight or heating in its own vapor converts it to the less dangerous red variety. Inorganic phosphate compounds are relatively harmless. THE MANY USES OF PHOSPHORUS: Fertilizer (essential plant macronutrient ) and animal feed. Essential in nervous tissue, bones, teeth, cell protoplasm, DNA, RNA, ATP . (155 lb. Person contains about 775 g of phosphorus). Matches , pyrotechnics, tracer bullets. Special optical gla ss and light bulbs. Film; flame resistant fabric; calcium phosphate used to make chinaware and baking powder . Used in production of steel and phosphor bronze. Sodium phosphate used for cleaning, in toothpaste , and as a water softener. Sodas (check the ingredients of a cola ) and vitamins. Used in pesticides.
133 Â“THEN WHATÂ’S THE MATTER WITH PHOSPHORUS?Â” Many freshwater ecosystems (ponds, stre ams, rivers, lakes, wetlands) are Â“phosphorus-limitedÂ” which means that th eir plant/animal productivity canÂ’t increase without more P (they have mo re than enough of the other essential nutrients such as nitrogen). When they are polluted with excess phosphates (from detergents, animal/human waste, or fertilizer s) algae are often the first plants that can take advantage of the higher nu trient level. Consequently, the algae multiply or Â“ bloom Â” exponentially (much faster than ot her plants can) an d cause a damaging condition known as eutrophication . This is when the algae shade out the submerged aquatic vegetation (important invertebrate and young fish habitat) and consume oxygen from the water column when they die and decay (algae have a rapid turnover rate). Wh en the oxygen is consumed massive fish kills can result. In the long term, excess P loading to an ecosystem can cause destructive shifts in the entire native flora and fauna . Recently, excess P in surface water has been linked to blooms of the virulent form of the microorganism Pfiesteria . Pfiesteria presents a serious threat to human (rashes and nervous system damage) and ecosystem (fish kills) health, and the tourism and seafood industries. Elevated levels of P are also associated with increased geosmin production by cyanobacteria. Geosmin causes bad odors a nd tastes in drinking water supplies and fish and the subsequent economic damages. Phosphorus mined from underground ores a nd applied as fertilizer to fields everywhere has created an imbalance in the earthÂ’s phosphorus cycle . There is a need to capture P from municipal and agri cultural wastewater and runoff in order to return it to agriculture as a nutrient source. At least it needs to be intercepted, if not reused, before it can damage receiving aquatic ecosystems. Much research is being done and a great de al of effort is being applied to solving Â“the phosphorus problemÂ” . Consequently a great need exists for students and scientists to understand the proper measurement and control of phosphorus . Many soil and aquatic scientists, resource managers, and environmental engineers now specialize in the study and control of phosphorus as a key element in environmental protection . Information for Fact Sheet Compiled by John Leader from These Sources: (Blevins et al., 1995), (Burgoa et al., 1991), (Dionigi et al ., 1991), (Florida Phosphate Council, 1997), (Harben and Bates, 1990), (Lookman et al., 1995), (Saadoun et al., 2001), (Sharpley, 1999), (Water Environm ent Federation, 1998), (Wetzel, 1983), (Whitten et al., 1988), and (Winter, 2005).
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141 BIOGRAPHICAL SKETCH John Leader was born in a Wilmington, De laware, hospital but lived his entire childhood and young adulthood in Maryland, on the Chesapeake Bay, mostly on Perch Creek. After primary and secondary school in Chesapeake City, Maryland, he attended the University of Maryland at College Park. He graduated with a B.S. degree in science education and went on to get his Maryland teacher certification. His first full-time teaching job was at Walter Johnson High School in Bethesda, Maryland where he taught biology and physical and chemical Â“lab science.Â” John left to return to, and teach about, his treasured Chesapeake and rural Eastern Shore of Maryland at Echo Hill Outdoor School near Worton. However, wanting to wo rk on solutions to the BayÂ’s environmental problems he returned to the urbanized wester n shore of Maryland to begin post-graduate classes and to work at the USDA in Beltsvi lle where he met his future wife Lesley, formerly of Bangalore, India. John is proud of his informal education obtained from a wide variety of jobs since age 13, from car pentry to oyster dredging, and by remaining actively engaged in family, community, music, nature, social activities, and informal scholarship in the scientific, mechanical and liberal arts. John married Lesley Anita Smith in 1995 on a bluff overlooking the Chesapeake Bay at Echo Hill Outdoor School. The two pursued graduate school at Oregon State University where she completed an M.S. degree and John transferred to the University of Florida to study wetlands constructed for water pollution control. In 2003 their first son, Benjamin, was born in Gainesville, Fl orida, greatly enri ching their lives.