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Chemical characterization of tomato industry wastewater, Florida, United States
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 Material Information
Title: Chemical characterization of tomato industry wastewater, Florida, United States
Series Title: Journal of Water Resource and Protection
Physical Description: Journal Article
Creator: Singh, Gurpal
Chahal, Maninder K.
Santos, Bielinski M.
Publisher: Scientific Research
Place of Publication: US
Publication Date: March 2012
 Subjects
Subjects / Keywords: Tomatoes
Wastewater
Packinghouse
Nutrients
Trace Metals
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Spatial Coverage:
 Notes
Abstract: Tomato packers often struggle to find ways to reuse the large volumes of wastewater generated during the tomato cleaning and sanitizing processes due to high transportation costs for off-site disposal and strict surface water discharge regulations in Florida. Information about the composition of tomato packinghouse wastewater and the likely sources of major wastewater constituents might provide insights to develop environmentally sustainable practices for wastewater reuse. The objective of this study was to characterize the chemical composition of wastewater generated in tomato packinghouses. The wastewater samples were collected for 6 to 8 hours from dump tanks of two representative pack-inghouses at 30 minute intervals after start-up of packing operations during May-June 2009. Results showed that wastewater had high electrical conductivity (1.3 - 2.8 dS·m–1) and chloride (255 - 1125 mg·L–1) due to the use of chlo-rine as a sanitizer in the packinghouses. Concentrations of total phosphorus (P, 2.8 - 5.7 mg·L–1) and copper (Cu, 1.9 - 2.2 mg·L–1) in wastewater were elevated due to tomato cleaning and sanitizing. To reduce P and Cu concentrations, treatment or blending of wastewater may be needed before discharging wastewater to surface waters. Concentrations of P, potassium, calcium, magnesium, zinc, iron, and manganese were much higher in packinghouse 1 as compared to packinghouse 2 wastewater, probably due to the greater contact time of tomatoes with the dump tank water. Whereas concentrations of Cu were similar in both packinghouses wastewater. Greater concentrations of chemical constituents in the wastewater suggest that residues of pesticides, insecticides, and/or foliar-applied micronutrients on tomatoes may be the likely external sources of most constituents (especially P, Cu, and Zn) in wastewater.
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Gurpal Singh.
Publication Status: Published
Original Location: PDF available at: http://gcrec.ifas.ufl.edu/Toor/Pubs/Research/45_Chahal%20et%20al_JWARP_2012.pdf
Funding: Funding for this research was provided by U.S. Environmental Protection Agency (X9-95400608-0). We thank the Florida Tomato Committee and tomato packinghouse personnel for their cooperation and support.
 Record Information
Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
Resource Identifier: doi - 10.4236/jwarp.2012.43013
System ID: IR00001293:00001

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Journal of Water Re source and Protection 2012, 4, 107-114 doi:10.4236/jwarp.2012.43013 Publishe d Online March 2012 (http://www.SciRP.org/journal/jwarp) Chemical Characterization of Tomato Industry Wastewater, Florida, United States Maninder K. Chahal, Gurpal S. Toor, Bielinski M. Santos Soil and Water Quality Laboratory, Gulf Coast Research and Education Center, University of Florida, Wimauma, Florida, USA Email: gstoor@ufl.edu Received January11, revised February 1, 2011; accepted March 3, 2012 ABSTRACT Tomato packers often struggle to find ways to reuse the large volumes of wastewater generated during the tomato cleaning and sanitizing processes due to high transportation cost s for off-site disposal and strict surface water discharge regulations in Florida. Information about the composition of tomato packinghouse wastewat er and the likely sources of major wastewater constituents might provide insights to de velop environmentally sustainable practices for wastewater reuse. The objective of this study was to characterize th e chemical composition of wastewater generated in tomato packinghouses. The wastewater samples were collected for 6 to 8 hours from dump tanks of two representative packinghouses at 30 minute intervals after start-up of packing operations during May-June 2009. Results showed that wastewater had high electrical conductivity (1.3 2.8 dSm) and chloride (255 1125 mgL) due to the use of chlorine as a sanitizer in the packinghouses. Concentrations of total phosphorus (P, 2.8 5.7 mgL) and copper (Cu, 1.9 2.2 mgL) in wastewater were elevated due to tomato cleanin g and sanitizing. To reduce P and Cu concentrations, treatment or blending of wastewater ma y be needed before discharging wastewat er to surface waters. Concentrations of P, potassium, calcium, magnesium, zinc, iron, and manganese were much higher in packinghouse 1 as compared to packinghouse 2 wastewater, prob ably due to the greater contact time of tomatoes with the dump tank water. Whereas concentrations of Cu were similar in both packinghouses wastewater. Greater concentrations of chemical constituents in the wastewater suggest that residues of pesticides, insectic ides, and/or foliar-applied micronutrients on tomatoes may be the likely external sources of most constituents (especially P, Cu, and Zn) in wastewater. Keywords: Tomatoes; Wastewater; Packingh ouse; Nutrients; Trace Metals 1. Introduction Population growth and limited water resources have led to the practice of reusing domestic wastewater to meet irrigation needs of urban, agricultural, and industrial sectors in many US states, es pecially in Florida, California, Texas, and Arizona. Flor ida is recognized as a national leader in domestic wastewater reuse, boasting more than 3400 Florida Department of Environmental Protection (FDEP) permitted wastewater facilities (61% domestic, 39% industrial). These facilities reclaim wastewater for a wide range of beneficial purposes such as landscape and agricultural irrigation, groundwater recharge, and industrial uses [1]. However, reuse of wastewater presents a number of environmental and technical challenges. For instance, high biological oxygen demand, high total soluble solids, and toxic chemical residues present in industrial wastewat er require specialized treatments [2]. Wastewater generated by 640 food processing plants (e.g. tomato canning, meat packing, wine production, dairy processing) in Californias Central Valley is typically high in organic carbon, nitrogen (N), iron (Fe) and manganese (Mn) sulfates [3] requiring treatment before reuse. Similarly, wastewater from swine lagoon facilities has high levels of nu trients, particularly N (472 mgL) and P (61 mgL), which require biological and chemical treatments [4]. The sources of contaminants in wastewater vary greatly among industries, and are the result of a combination of external and intern al factors. For example, commonly reported sources of copper (Cu) and zinc (Zn) in the domestic wastewater are pesticide residues, pipe corrosion, wood preservatives, anti-fouling paints, and cosmetics [5]. However, info rmation about the chemical composition and the likely sources of chemical constituents in many food processing wastewaters, especially in tomato packinghouse wastewater is not available in scientific literature. There are approximately 70 tomato packinghouses in Florida that pack fresh-mark et tomatoes [6]. However, recent informal surveys among growers indicated that C opyright 2012 SciRes. JWARP

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M. K. CHAHAL ET AL 108 f ewer than ten of those packinghouses process about 90% of the total tomato volume produced in Florida. Packinghouses use freshwater from a municipal supply and add chlorine sanitizers in dump tanks to rinse, wash, and sanitize field-harvested tomatoes before packing each day. The amount of water required depends on the type of tomato packed. For in stance, the amount of water used for cleaning round tomatoes typically ranges from 3000 to 22,000 galday while roma and grape tomatoes require 70 to 25,000 galday [6]. This water is continuously recirculated in the dump tanks and drained at end of the day (hereafter, referr ed to as wastewater). The quantity of wastewater generated by Florida tomato packinghouses is approximately 31.3 million gal per season [6], which needs to be handled in an environmentally sustainable way. Wastewater produced in tomato packinghouses may contain nutrients and metals washed from tomatoes as well as metals leached from dump tanks. Elevated concentrations of elements, especi ally P and Cu, may restrict wastewater use in the environm ent due to strict discharge regulations in Florida [7,8]. It has been suggested that water kept stagnant for long periods (24 48 h) in a tank may leach metals such as Cu and Zn from pipes [9]. Similarly, at low pH, halogens such as chloride (Cl) can penetrate the chromium (Cr) oxide rust-protective coating of stainless steel tanks, commonly used in packinghouses, which contains 10 to 12% Cr and <2% nickel (Ni) thereby causing corrosion and re lease of Cr and Ni in the water [10-12]. However, tomato packinghouses in Florida maintain pH in the neutral range, which can effectively reduce the potential for Cr and Ni leaching from stainless steel to wastewater. Knowledge of the chemical composition of wastewater produced in tomato packinghouses and the sources of chemical constituents in the dump tanks can help develop solutions to sustainably manage wastewater in Florid a. Therefore, the objective of this study was to charact erize the potential accumulation of chemical constituents in tomato packinghouse wastewater. 2. Materials and Methods 2.1. Tomato Packing Operations in Packinghouses In west-central Florida, there are two major tomato growing seasons: July-Dec and Jan-Apr [13]. During each season, tomatoes are picked in two harvests, usually 10 12 weeks after planting; packing of tomatoes continues for about 4 8 weeks after the start of harvesting. Field-harvested tomatoes are transported to the packinghouses, where the tomatoes are washed and sanitized before packing. The tomatoes are first dumped into a water flume system (hereafter, referred to as dump tanks). The rate at which tomatoes are added to the dump tanks drives the flow of tomatoes through the packing line. Each day, the dumping rate is adjusted to accommodate the degree of sorting and grading required at the packing counter. To avoid cross-contamination with pathogens during washing in the recirculated dump tank water, sanitizers such as chlorine gas, are constantly added to the water to maintain free chlorine levels in the dump tank at 150 200 mgL in water at a pH of 6.5 to 7.5 [14]. The daily packing operation typically lasts for 6 to 8 hours. 2.2. Wastewater Sample Collection Wastewater samples were collected from two representative tomato packinghouses (hereafter, referred to PKG 1 and PKG 2) during May-June 2009; the packing season for tomatoes grown in Jan-Apr 2009. PKG 1 used chlorine gas (Cl2) and PKG 2 used chlorine dioxide (ClO2, Selectrocide 12 G, 500 ppm) as a sanitizer in the dump tanks. In both packinghouses, typical operational time of tomato packing lines varied from 6 (PKG 2) to 8 (PKG 1) hours. Daily operational hours in packinghouses varied due to the amount of tomatoes packed. In addition, variation in the size and quality of different lots of tomatoes from different growers also altered the flow time. For each of the two packinghouses, four sampling events were conducted at weekly intervals during MayJune 2009. During each sampling ev ent, water samples were collected from the dump tanks in 250 mL plastic bottles before the beginning of packing operation. After the start of packing operation, wastewater samples were collected from the dump tanks at 30 minute intervals throughout daily operation (6 to 8 h). The collected samples were chilled on ice, brought to the laboratory, and analyzed for pH, EC, Cl, P, and trace metals. The amount of tomatoes washed in 30 minute intervals was calculated based on the rate of dumping i.e. time taken to wash a given amount of tomatoes, say 1000 kg. Amount of tomatoes washed (kg) = Time interval (30 minutes)/Rate of dumping (minutes per 1000 kg of tomatoes). 2.3. Laboratory Analysis Approximately 100 mL of each collected wastewater sample was preserved with concentrated H2SO4 (~1 ml) at pH < 2 and stored at 4 C before analysis for total P and trace metals. Another 150 mL of unpreserved sample was shelved and allowed to acclimate to room temperature before measuring pH and electrical conductivity (EC) using a digital meter (Accumet XL 60, dual channel pH/ion/conductivity/dissolved oxygen meter, Fisher Scientific, Pandan Crescent, Singapore). Chloride in unpreserved samples was determined using a discrete analyzer Copyright 2012 SciRes. JWARP

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M. K. CHAHAL ET AL 109 (AQ2+, Seal Analytical Inc, Mequon, WI). Preserved wastewater samples were analyzed for total P and 18 metals including aluminum (Al), arsenic (As), boron (B), calcium (Ca), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na), nickel (Ni), lead (Pb), selenium (Se), and zinc (Zn) on an inductively coupled plasma-optical emission spectrometer (ICP-OES; PerkinElmer Optima 2100 DV; PerkinElmer, Shelton, CT) using an EPA approved method [15]. Among these trace metals, 11 were not detected (Al, As, B, Cd, Co, Cr, Mo, Mn, Ni, Pb, and Se) in any wastewater sample and therefore are not reported. For trace metals such as Cr and Ni, the detection limits were 0.02 and 0.1 mgL, respectively. 2.4. Statistical Analysis Mean, standard deviation, and range for the concentration of different parameters in wastewater samples were calculated in Microsoft Excel 2007. A correlation matrix was used to evaluate the significance of relationships between the different constituents at 0.05 probability level using the DATA analysis program in Microsoft Excel. Simple and stepwise linear regression was performed using Statistix (Statistix Analytical Software, version 8, Tallahassee, FL) with LINEAR MODELS procedures. 3. Results and Discussion 3.1. Amount of Tomatoes Washed in the Packinghouses During four sampling events, approximately 305 tons (103 kg) of tomatoes were washed in 8 h in PKG 1, while 287 tons of tomatoes were washed in 6 h in PKG 2 ( Figure 1 ). In PKG 1, most of the tomatoes washed during the first 6 h of operation were roma tomatoes (range of weight: 102 121 g), followed by 1 2 h washing of round tomatoes (range of weight: 170 252 g) [16,17]. In PKG 2, only round tomatoes were packed all day. The variability in tomato types (and sizes) resulted in different flow times in dump tanks. For example, approximately 454 kg of tomatoes moved through the dump tanks every 55 72 seconds in PKG 1 (roma) and 29 40 seconds in PKG 2 (round). This resulted in greater contact time of roma tomatoes that had more surface area due to small size with dump tank water in PKG 1 as compared to PKG 2 that p acked round tomatoes with larger size and lower surface area. 3.2. Chemical Characteristics of Municipal Water Used in Packinghouses Municipal water was used in the dump tanks of both Time (hours) 02468 1 0 Amount of tomatoes washed (tons) 0 50 100 150 200 250 300 350 Packinghouse 1 Packinghouse 2 Y = -2.58 + 47.69X R 2 = 0.9995, P <0.0001 Y = -1.66 + 34.16X R 2 = 0.9996, P <0.0001 Y = -150.5 + 56.75X R 2 = 0.9982, P <0.0001 Figure 1. Mean (n = 4 for ea ch packinghouse) cumulative amount of washed tomatoes with time during May-June 2009. Error bars indicate standa rd deviation. Packinghouse 1 packed roma tomatoes for 6 hours followed by round tomatoes for 2 hours. Packinghouse 2 only packed round tomatoes. packinghouses to wash and sa nitize tomatoes. Both packinghouses were located in cl ose proximity to each other and shared a municipal water source. As a result, the pH (7.1 7.2), EC (0.38 0.43 dSm), and concentration of all chemical constituents, including Cl, P, Ca, Mg, K, Cu, Fe, and Zn were similar in both packinghouses municipal water. 3.3. Wastewater EC and Chloride Chloride concentrations and EC in wastewater continuously increased as more tomatoes were washed ( Figure 2 ). However, the magnitude of EC and Cl increase was much greater in PKG 1 (higher slope) than PKG 2 (lower slope). For instance, in PKG 1, mean EC and Cl in four sampling events was 0.4 dSm and 24 mgL before washing, which increased to 1.3 dSm and >400 mgL after washing 50 tons of tomatoes, respectively. In contrast, EC and Cl were 0.72 dSm and 107 mgL in PKG 2 wastewater after washing 50 tons of tomatoes. This increase in EC and Cl in both packinghouses was attributed to the use of sanitizers such as chlorine gas in PKG 1 and chlorine dioxide in PKG 2 dump tanks. Overall, EC and Cl trends showed much less variability among four sampling events in PKG 2 as compared to PKG 1 as can be seen from standard error bars in Figure 2 This finding may be due to more controlled conditions in PKG 2 than in PKG 1. Fo r instance, in PKG 1, chlorine gas was manually injected from pressurized gas cylinders based on chlorine, pH, and oxidation-reduction potential measurement in dump tanks. Copyright 2012 SciRes. JWARP

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M. K. CHAHAL ET AL 110 050100150200250300350 EC (dS m -1 ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Packinghouse 1 Packinghouse 2 Tomatoes washed (tons) 050100150200250300350 Chloride (mg L -1 ) 0 200 400 600 800 1000 1200 1400 1600 Packinghouse 1 Packinghouse 2 Y = 0.972 + 0.0068X R2 = 0.9093, P <0.0001 Y = 0.566 + 0.0031X R2 = 0.9087, P <0.0001 Y = 209.0 + 3.08X R2 = 0.8848, P <0.0001 Y = 70.0 + 0.73X R2 = 0.8603, P <0.0001 Figure 2. Effect of cumulative amounts of washed tomatoes on mean (n = 4 for each pack inghouse) wastewater EC and chloride during May-June 2009. Bi-directional error bars indicate standard error of the mean. However, in PKG 2, chlorine dioxide addition was automated in the dump tanks. Other factors that may have caused greater variability and greater concentration of EC and Cl in PKG 1 wastewater may include: 1) more breaks or stops during the packing operation due to technical problems in the dumping machine; 2) crowding of tomatoes at the packing coun ter that slowed the packing operation; and 3) shifting of tomatoes from small-sized roma to large-sized round. These factors resulted in greater flow time and more contact time of tomatoes in the dump tanks. It is important to note that the previous study [18] has shown that levels of total hetrotrophic bacteria were lower and similar in both packinghouses wastewater despite a much hi gher Cl concentration in PKG 1 than PKG 2, suggesting that these Cl levels were effective in killing microbes and that chlorine use in the packinghouse may be reduced. The regular monitoring of EC in dump tanks will aid in determining when EC approaches high values so that chlorine use can be curtailed, which, in turn, will reduce operating costs and reduce Cl and EC in the resulting wastewater. 3.4. Wastewater Chemical Constituents The primary constituents that enter into the dump tanks are those present in the freshwater source, the chlorine sanitizers used in the dump tanks, and those carried from the field with harvested tomatoes (such as residues on tomatoes). As the levels of these constituents were minimal in the freshwater source, the only thing accounting for increase in the c oncentration of P, Cu, Zn, Fe ( Figure 3 ) and Ca, Mg, K ( Figure 4 ) in wastewater is the amount of tomatoes washed. In the two packinghouses, a significant relation (R2 = 0.90 0.98, P < 0.0001) between amounts of washed tomatoes and wastewater constituents (except lower R2 of 0.55 for Zn in PKG 2) indicates that the amount of tomatoes washed (external factor) are likely the major sources of P, Cu, Zn, Fe, Ca, Mg, and K in the wastewater ( Figures 3-4 ). Similar to Cl and EC increase in wastewater, concentrations of P, Zn, Fe, Mg, and K were elevated and more variable in PKG 1 than in PKG 2; whereas the variability and magnitude (similar slope of 0.0081) of Cu increase was similar in both packinghouses. Overall, a greater contact time (55 72 seconds) of small-sized roma tomatoes (with higher surface area) in PKG 1 dump tank compared with lower contact time (29 40 seconds) of large-sized round to matoes (with lower surface area) in PKG 2 dump tank probably resulted in greater concentrations of all constituents (except Cu) in PKG 1 than PKG 2 wastewater. In Florida, a variety of organophosphate insecticides, containing P, with active ingredients such as dimethoate, malathion, and methamidophos are foliarly applied on the tomato crop to control aphids, mites, white flies, and fruitworms [13]. Stevens and Kilmer [19] reported that 52% of field-grown tomatoes contained residues of methamidophos, with concentrations up to 0.56 mgL. Similarly, foliar applied fungicides containing mono and di-K salts of phosphorous acid to control powdery mildew and Phytopthora species may also leave residues on the tomato fruits and foliage (leaves, stems) which may act as sources of P and K in the wastewater. The Cu based fungicides (Cu hydroxide or Cu sulfate as active ingedients) are frequently used in foliar applications in tomato production against bacterial spot, anthracnose, and early blight, and are sometimes applied 1 2 days before harvesting [13]. The foliar application of fungicides containing Zn salts (e.g. Mancozeb and Ziram) against anthracnose, early blight, and grey leaf spot may be another source of Zn residues to th e wastewater. In addition, residues of foliar-applied Cu and Zn as micronutrients may also be a likely source of wastewater Cu and Zn. Copyright 2012 SciRes. JWARP

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M. K. CHAHAL ET AL 111 050100150200250300350 P (mg L -1 ) 0 2 4 6 8 Packinghouse 1 Packinghouse 2 Tomatoes washed ( tons ) 050100150200250300350 Zn (mg L -1 ) 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 Packinghouse 1 Packinghouse 2 Y = 0.020 + 0.0211X R2 = 0.9643, P <0.0001 Y =0.333 + 0.0093X R2 = 0.9888, P <0.0001 Y = 0.123 + 0.0005X R2 = 0.9513, P <0.0001 Y = 0.092 + 0.0002X R2 = 0.5533, P <0.0036 050100150200250300350 Cu (mg L -1 ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Packinghouse 1 Packinghouse 2 050100150200250300350 Fe (mg L -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 Packinghouse 1 Packinghouse 2 Y = 0.103 + 0.0081X R2 = 0.9777, P <0.0001 Y = -0.086 + 0.0081X R2 = 0.9632, P <0.0001 Y = 0.131 + 0.0023X R2 = 0.9460, P <0.0001 Y = 0.021 + 0.0007X R2 = 0.9547, P <0.0001 Figure 3. Effect of cumulative amounts of washed tomatoes on mean (n = 4 for each pack inghouse) wastewater P, Cu, Zn, and Fe concentrations during May-June 2009. Bi-directional error bars indicate standard error of the mean. 050100150200250300350 Ca (mg L -1 ) 30 35 40 45 50 55 60 65 Packinghouse 1 Packinghouse 2 Tomatoes washed (tons) 050100150200250300350 K (mg L -1 ) 0 10 20 30 40 50 60 Packinghouse 1 Packinghouse 2 Y = 38.5 + 0.0760X R2 = 0.9062, P <0.0001 Y = 34.5 + 0.0848X R2 = 0.9646, P <0.0001 Y = 3.05 + 0.1695X R2 = 0.9684, P <0.0001 Y = 6.77 + 0.0598X R2 = 0.9827, P <0.0001 050100150200250300350 Mg (mg L -1 ) 14 16 18 20 22 24 26 28 Packinghouse 1 Packinghouse 2 Y = 15.3 + 0.0357X R2 = 0.9771, P <0.0001 Y = 15.8 + 0.0168X R2 = 0.9614, P <0.0001 Figure 4. Effect of cumulative amounts of washed tomatoes on mean (n = 4 for each packinghouse) wastewater Ca, Mg, and K concentrations during May-June 2009. Bi-directional error bars indicate standard error of the mean. 3.5. Implications of Using Packinghouse Wastewater in the Environment According to FDEP rule 62-660.805 [7], an industrial wastewater discharge permit is required if wastewater volume is between 19,000 and 190,000 Lday. Wastewater generation of less than 19,000 Lday is exempted from the requirement of perm it provided that the wastewater meets all surface water quality standards. Several Copyright 2012 SciRes. JWARP

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M. K. CHAHAL ET AL 112 o f the Florida packinghouses generate more than 19,000 L of wastewater day [6]. The chemical composition of wastewater at the end of th e packing operation showed elevated concentrations of all elements, but the magnitude of increase was much great er for some elements (Cl, EC, P, Cu). Wastewater pH wa s maintained in the neutral range (6.5 8) as recommended for Florida packinghouse dump tanks [14]; therefore the wastewater is suitable for irrigating most crops without any adverse pH effects on crop and soil properties [20]. The pH is also in the recommended range for Florida class IV agricultural water use [7]. However, the EC in final wastewater was greater in PKG 1 (2.8 dSm) than PKG 2 (1.3 dSm) due to higher Cl in PKG 1 (1125 mgL) compared with PKG 2 (255 mgL). The high EC values found in PKG 1 wastewater should be interpreted as having slight to moderate irrigation restrictions for salt sensitive crops such as strawberry, onions, and beans [20] Significant correlation of EC with Cl in this study (r = 0.95) indicated that chlorine use in packinghouses increased EC in wastewater. According to Bartz et al. [14], when chlorine gas (Cl2) is dissolved in water, it readily forms hypochlorous acid (HOCl) and hypochlorite ion (OCl). Thus, three forms of chlorine (Cl2, HOCl, and OCl) are present in aqueous chlorine solution which readily oxidizes organic compounds with different redox potentials and generate Cl ions in the solution [21]. Our previous study [18] in these two packinghouses found that microbe levels in dump tank water were lower and similar; therefore, it seems intuitive that any reduction in the use of chlorine sanitizers will substantially reduce wastewater EC. For example, EC was 2.8 dSm in PKG 1 and 1.3 dSm in PKG 2. The EC levels in wastewater can be reduced by blending wastewater with higher-quality water (groundwater, municipal water) before using as an irrigation source for the salt sensitive crops. As a comparison, EC in our wastewater was lower than dairy wastewater (3.1 dSm) and poultry lagoon wastewater (7.9dSm) [22]. All chemical constituents showed a greater magnitude of increase in PKG 1 wastewater than PKG 2 due to greater contact time of the tomatoes (with high surface area) with water, which was 55 72 seconds in PKG 1 and 29 40 seconds in PKG 2 per 454 kg of dumped tomatoes. Among all detected elements, the greatest increase was observed for Cu, whose concentrations increased from 0.01 mgL in municipal water to 1.9 2.2 mgL in the final wastewater. This concentration is greater than the threshold limit of 0.03 mg CuL for surface water discharge and 0.5 mg CuL for irrigation water use [7]. Whereas concentrations of Fe and Zn were less than the threshold limits of 1 mgL for irrigation water. Therefore, wastewater may need to be treated to remove Cu before discharging into city sewers. Alternatively wastewater can be blended with higher-quality water to reduce Cu concentrations. Concentrations of P in the wastewater (PKG 1:5.7 mgL; PKG 2:2.8 mgL) were similar to that of municipal wastewater (2.5 6.5 mgL) [23] and potato processing wastewater (3.4 mgL) [24]; but were much lower than animal wastewaters such as dairy (30 mgL) and poultry (34 mgL) lagoon wastewater [22] and swine lagoon wastewater (61 mgL) [4]. The higher concentrations of total P in the wastewater relative to the highest new surface water qual ity standard of 0.49 mgL for Florida streams [25] suggests that packinghouse wastewater needs to be treated to remove P before it can be discharged into streams. Increase in concentrations of Ca, Mg, K, Fe, and Zn wastewater (see Figures 3-4 ) do not present constraints on wastewater reuse. As a comparison, Ca concentrations in the wastewater (55 59 mgL) were similar to swine lagoon wastewater (51 mgL), but were much greater than municipal wastewater (4 mgL) [4,26]. Similarly, K concentration in packingh ouse wastewater (24 49 mgL) was lower than the swine (614 mgL), dairy (178 mgL) and poultry (1244 mgL) lagoon wastewater [4,22]. Concentrations of Zn in packinghouse wastewater (0.1 0.3 mgL) were only slightly lower than animal manure wastewater (0.4 0.6 mgL) [22]. The tremendous variability in wastewater from different sources highlights the impact of internal and external sources in elevating concentrations of chemical constituents in different wastewaters. To comply with the surface water discharge standards for P and Cu, one potential option might be to treat wastewater with chemical amendments (alum, ferric chloride, lime) to remove P and Cu from the wastewater [27,28]. Another option could be to use wastewater for land irrigation in frequent but small application rates that do not promote leaching. Ou r recent study [29] found that if packinghouse wastewater is land applied at up to 1.68 cmday or 168, 000 Lhaday, the risk of P and cation (Na, Ca, Mg, K) leachi ng to groundwater is minimal. In these wastewater applied sites, a minimum unsaturated depth of 45 cm to the water table has been recommended to avoid ponding at the surface and maintain aerobic conditions in the root zone of the cover crops [30]. 4. Conclusions Results suggest that EC and Cl were elevated in the wastewater because of the use of chlorine sanitizers in the dump tanks. This may pose moderate to strict restrictions for wastewater use as irrigation water for crops such as beans, carrot, okra, onion, and strawberry [31]. The concentrations of wastewater constituents were relaCopyright 2012 SciRes. JWARP

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M. K. CHAHAL ET AL 113 tively higher in PKG 1 than PKG 2, which were mainly due to greater contact time of small-sized tomatoes (having greater surface area) with dump tank water in PKG 1. Among all elements, P was above the total P standard of 0.49 mgL for surface water discharge in Florida streams. Concentrations of Fe and Zn were less than the threshold value (1 mgL) for irrigation water suitability in agriculture [20]. In the current study, washing of tomatoes resulted in increased concentrations of all chemical constituents in the wastewater. This suggests that the P and Cu residues (from pesticides, insecticides, and/or foliar-applied micronutrients) originated from the fieldharvested tomatoes may be the likely sources of P and Cu in the wastewater. These results imply that wastewater needs to be treated for P and Cu, if directly discharged to surface water bodies as their concentrations were above the critical values. Another attractive and feasible option is blending wa stewater with higher-quality water (groundwater, municipal water) to dilute the concentrations of P and Cu, which will also reduce Cl and EC. Future research shou ld evaluate the scope of field best management practices to reduce P and Cu concentrations in the wastewater and develop a feasible and cost-effective treatment system to remove P and Cu from wastewater for economic and environmental sustainability of tomato industry in Florida. 5. Acknowledgements Funding for this research was provided by U.S. Environmental Protection Agency (X9-95400608-0). We thank the Florida Tomato Committee and tomato packinghouse personnel for their cooperation and support. REFERENCES [1] FDEP, General Facts and Statistics about Wastewater in Florida, 12 June 2011. http://www.dep.state.fl.us/wa ter/wastewater/facts.htm [2] G. A. OConnor, H. A. El liott and R.K. Bastian, Degraded Water Reuse: An Overview, Journal of Environmental Quality Vol. 37, Suppl. 5, 2008, pp. S157S168. [3] California League of Food Pr ocessing, Manual of Good Practice for Land Application of Food Processing/Rinse Water, Davis, CA, 2007. [4] A. A. Szogi and M. B. Va notti, Removal of Phosphorus from Livestock Effluents, Journal of Environmental Quality Vol. 38, No. 2, 2009, pp. 576-586. doi:10.2134/jeq2007.0641 [5] G. Firfilionis, et al. The Removal of Trace Metals at the Wastewater Treatment Plant of Psyttalia, Mediterranean Marine Science Vol. 5/1, 2004, pp. 71-81. [6] Florida Tomato Committee, Options for Utilization of Tomato Packinghouse Solid Waste and Water, In: Critical Issues in Tomato Production in FloridaA Special Research Report, Florida Tomato Committee and University of Florida/IFAS, 2007. [7] Florida Administrative Weekly, Florida Administrative Weekly and Florida Administrative Code 62-302.530, 2006. 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