nutrient and pesticide removal from laboratory ... - PubAg - USDA

NUTRIENT AND PESTICIDE REMOVAL FROM LABORATORY‐SIMULATED TILE DRAINAGE DISCHARGE K. W. King, J. McDonald, J. F. Moore, S. G. Agrawal, E. N. Fischer, J. C. Balogh

ABSTRACT. Excess nutrient and pesticide transport through subsurface tile drainage is well documented. One approach being considered to reduce the amount of these contaminants in subsurface drainage waters is the use of end‐of‐tile filters. Materials used in such filters are often comprised of natural minerals and industrial wastes or by‐products that have a significant capacity for binding or sorbing nutrients and pesticides (e.g., activated carbon, fly ash). In this laboratory study, the feasibility and efficacy of an activated carbon, zeolite (clinoptilolite), and activated alumina filter to reduce nitrate‐nitrogen (NO3 ‐N), dissolved reactive phosphorus (DRP), metalaxyl, and chlorothalonil concentrations in simulated drainage waters was determined. Hydrographs having peak flow rates of 0.63, 1.26, and 1.89 L s‐1 were simulated in a laboratory environment and replicated three times. Across all flow rates, the cartridge‐type filter system produced average load reductions of 4.7% for NO3 ‐N, 51.6% for DRP, 58.2% for chlorothalonil, and 28.8% for metalaxyl. The filter effectiveness was dependent on flow rate and position on the hydrograph. The findings from this study suggest that the end‐of‐tile filter approach could be adapted as a best management practice to reduce nutrient and pesticide transport in subsurface tile drainage where the contributing area and flow rates are relatively small. Additionally, the findings support further investigation into alternative sorbent materials and delivery designs that permit larger drainage areas and greater flow rates to be filtered. Keywords. Agriculture, Filter, Nitrogen, Pesticides, Phosphorus, Turf, Water quality.

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ubsurface tile drainage is critical for crop production agriculture and the playability of managed, recre‐ ational turfgrass (i.e., golf courses and athletic play‐ ing fields). Tile drainage is primarily designed to rapidly convey water from a site, especially in the case of a storm event. Drainage networks rapidly, efficiently, and eco‐ nomically remove excess water from a site, thus permitting traffic for planting, harvest, and recreation. However, the en‐ vironmental impacts attributed to subsurface drainage may outweigh the economic benefits. Identifying, testing, and im‐ plementing practices or strategies that reduce the environ‐ mental impacts of subsurface drainage are required to maintain a balance of productivity and environmental ser‐ vices. Discharge from subsurface tile drains is known to carry elevated levels of dissolved pollutants such as phosphorus (Algoazany et al., 2007; Kinley et al., 2007; King et al., 2006), nitrogen (Jaynes et al., 2008; Randall and Vetsch, 2005; Kladivko et al., 1999), and pesticides (Kalita et al., 2006; Kjaer et al., 2005; Buhler et al., 1993). Moreover, sub‐

Submitted for review in January 2001 as manuscript number SW 8390; approved for publication by the Soil & Water Division of ASABE in June 2010. The authors are Kevin W. King, ASABE Member Engineer, Agricultural Engineer, USDA‐ARS Soil Drainage Research Unit, Columbus, Ohio; Jon McDonald, Engineering Services Manager, Kristar Enterprises, Inc., Santa Rosa, California; James F. Moore, Director of Construction Education, U.S. Golf Association, McGregor, Texas; Sheela G. Agrawal, Research Chemist, and Eric N. Fischer, Analytical Chemist, USDA‐ARS Soil Drainage Research Unit, Columbus, Ohio; and James C. Balogh, Soil Scientist, Spectrum Research, Inc., Duluth, Minnesota. Corresponding author: Kevin W. King, USDA‐ARS, 590 Woody Hayes Drive, Columbus, OH 43210; phone: 614‐292‐9806; fax: 614‐292‐9448; e‐mail: [email protected].

surface drainage that conveys discharge directly into streams and ponds bypasses natural and managed filter processes, in‐ cluding upland and riparian buffer zones (King et al., 2006). As a consequence, excess NO3‐N discharged into the Missis‐ sippi River has led to a growing hypoxic area downstream in the Gulf of Mexico (Goolsby and Battaglin, 2001). Similarly, phosphorus originating from upper Midwest tile‐drained lands is a significant driver of eutrophication and hypoxia in the Great Lakes (Rockwell et al., 2005). Additionally, excess phosphorus levels detected in water features in or surround‐ ing managed turf sites have led to eutrophic conditions in those water bodies (Winter and Dillon, 2005; Mallin and Wheeler, 2000). Furthermore, pesticides such as atrazine and metalaxyl have been detected in tile drainage waters and have been implicated in the decline of amphibian populations (Rohr et al., 2006). Agronomic practices alone such as application timing, placement, and rate have not appreciably reduced the pollu‐ tant transport from tile‐drained watersheds (Jaynes et al., 2008). Thus, remediation efforts have shifted more towards in situ physical and structural modification, including water table management (Zucker and Brown, 1998) and/or treat‐ ment of discharge waters before and after entry into drainage tiles (Jaynes et al., 2008), streams, and waterways (Robertson and Merkley, 2009). In particular, natural minerals and industrial by‐products (e.g., zeolite, fly ash) have exhibited a range of success in the removal of nitrogen, phosphorus, and pesticides. For exam‐ ple, industrial by‐products high in aluminum, iron, and cal‐ cium, such as fly ash, blast furnace slag, and water treatment residual are ideal phosphorus‐sorbing materials (Agyei et al., 2002; Torbert et al., 2005). Novak and Watts (2004, 2005) used water treatment residual (WTR) rich in aluminum ox‐ ides, which tie up soluble phosphorus via adsorption and pre‐

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2010 American Society of Agricultural and Biological Engineers ISSN 2151-0032

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cipitation. Their results encourage the use of WTRs as a best management practice for reducing phosphorus loadings to streams and leachate. Similarly, Agyei et al. (2002), observed a 40% reduction in soluble phosphorus using fly ash and a 70% decrease using blast furnace slag as sorbents. Dao et al. (2001) showed that mixing manure with aluminum based by‐ products can reduce soluble phosphorus by 39%. Clinoptilolite, a naturally occurring, inexpensive zeolite, has been shown to effectively remove ammonium‐nitrogen (NH4‐N) from aqueous solutions through ion exchange (Hed‐ strom and Amofah, 2008; Rozic et al., 2000; Nguyen and Tanner, 1998). However, clinoptilolite is generally ineffec‐ tive at removing NO3‐N (Lin and Wu, 1996). Instead, NO3‐N removal is most efficiently accomplished through denitri‐ fication and/or sorption to activated carbon. Denitrification is a microbially mediated process requiring energy from cel‐ lulosic materials to reduce nitrate‐nitrogen (NO3‐N) to N2O and N2 gases (Robertson et al., 2000). Activated carbon, on the other hand, removes NO3‐N via physical adsorption. With respect to pesticides and other organic contaminants, adsorption to activated carbon is the preferred method for their removal from source waters (Gupta and Ali, 2006). In‐ expensive, activated carbons developed from coal, lignin (paper industry), and coconut byproducts have exhibited high contaminant removal efficiencies. For example, Namasivay‐ am and Sangeetha (2004) observed >95% removal of various dyes and organic and inorganic contaminants using ZnCl 2‐activated carbon derived from coconut coir pith wastes. As mentioned, activated carbon use is not limited to organic contaminants but can also be used to remove NO3‐N, as well as excess dissolved reactive phosphorus (DRP) via adsorption and occlusion (Namasivayam and Sangeetha, 2004). Given the availability of zeolites and industrial by‐ products and their efficacy in inorganic and organic contami‐ nant removal, investigation into these materials' combined contaminant removal capabilities in field‐scale drainage is warranted. It is important to note that many of the aforemen‐ tioned studies were conducted at the laboratory scale and thus dealt with flow volumes significantly less than what would be observed in a tile‐drained system, especially during a storm event. Since discharge volume is proportional to pre‐ cipitation, the mass of contaminants discharged during a storm event would presumably increase. In fact, King et al. (2007a, 2007b) showed that approximately 75% of the DRP exiting a golf course in Texas was a result of storm event run‐ off (baseflow transported the remaining 25%). However, in the King et al. (2007a, 2007b) studies, baseflow at an average of 1.9 L s‐1 accounted for approximately 60% of the total annual discharge and was significantly greater than flow rates typically examined in laboratory bench‐scale studies. Thus, the goal of this research was to determine the feasibility and efficiency of a mixed clinoptilolite, activated alumina, and activated carbon end‐of‐tile cartridge‐type filter to remove NO3‐N, DRP, and two pesticides (chlorothalonil and meta‐ laxyl) from laboratory‐simulated, tile drainage discharge wa‐ ters. Metalaxyl and chlorothalonil are fungicides commonly used in turfgrass environments. Based upon previous batch and bench‐scale studies conducted by others, we expected to see significant reductions in each pollutant.

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METHODS SOLUTION PREPARATION Contaminant concentrations in the simulated drainage water solution were achieved immediately prior to each run by combining prepared nutrient and fungicide solutions. Concentrations exceeding or comparable to those previously reported for golf course leachate or tile effluent were selected to represent a worst‐case scenario; if the filters were effective at these concentrations across a range of flow rates, then it follows that the filters should be effective at the lesser con‐ centrations expected from typical golf course management. Using typical golf course management on a plot‐sized green in California, Wu et al. (2002) documented a maximum me‐ talaxyl concentration of 7.2 mg L‐1 and chlorothalonil con‐ centrations less than 1 mg L‐1. In the Wu et al. (2002) study, leachate was collected and analyzed periodically following application for a duration of 150 days. Leaching losses of NO3‐N in managed turf are generally considered to be negli‐ gible (Branham, 2008). NO3‐N concentrations reported by Starr and DeRoo (1981) on a three‐year, plot‐scale study in Connecticut ranged from 0.3 to 10 mg L‐1, while King et al. (2006) reported maximum subsurface drainage concentra‐ tions of 3.94 mg L‐1 for NO3‐N and 0.99 mg L‐1 for DRP from a four‐year study on a golf course in Texas. Average con‐ centrations used in the immediate study for each contaminant over all runs can be found in table 1. A stock nutrient solution was prepared within 24 h of the simulation by dissolving appropriate amounts of American Chemical Society (ACS) grade KNO3 (potassium nitrate) and Na2HPO4 (sodium phosphate dibasic) (Fisher Scientific, Fair Lawn, N.J.) in approximately 2 L of deionized water. An aqueous solution of fungicides was prepared monthly as 1:250 and 1:200 dilutions of 29.6% chlorothalonil (log Kow = 2.64 to 4.38; Caux et al., 1996) as Daconil (GardenTech, Lexington, Ky.) and 22.5% metalaxyl (log Kow = 1.56; Singh and Tripathi, 1982) as Mefenoxam 2 AQ (Quali‐Pro, Raleigh, N.C.), respectively. The entire stock nutrient solution and 0.1 L of the fungicide mixture were transferred to a 7.6 m3 (2000 gal) polyethylene storage tank and brought to volume with municipal water. The resulting pH of the tank solution was assumed to be near neutral. HYDROGRAPH SIMULATION AND DATA COLLECTION A modified hydrograph generator was created to simulate tile flow discharge (Yoder et al., 1998). The hydrograph gen‐ erator was designed to produce standard hydrograph shapes based on a dimensionless unit hydrograph (SCS, 1972). De‐ sign hydrographs with equivalent discharge volumes and peak flows of 0.63, 1.26, and 1.89 L s‐1 were used for this study. The selected peak flows were consistent with unpub‐ lished peak flow rates measured from a 100% sand green lo‐ cated on a golf course in Waco, Texas. The hydrograph generator was able to accurately reproduce flow rates greater Table 1. Mean initial concentrations (standard deviation) of nutrients and fungicides in simulation drainage water solution at filter inlet (n = 9). Pollutant Initial Concentration NO3‐N (mg L‐1) PO4‐P (mg L‐1) Chlorothalonil (μg L‐1) Metalaxyl (μg L‐1)

12 (0.8) 0.9 (0.02) 34 (6) 13 (2)

TRANSACTIONS OF THE ASABE

Material Activated carbon (coconut shell) Activated alumina Zeolite (clinoptilolite)

Table 2. Media component properties. Grain Size (mm × mm) Chemical Composition

Surface Area (m2 g‐1)

Bulk Density (g cm‐3)

2.38 × 0.60 1.41 × 0.61 2.38 × 0.84

1100 to 1200 380 40

0.484 0.673 0.905

C Al2O3 (Na3K4Ca)(Al8Si40O96)·2H20

than 0.012 L s‐1. For flow rates less than 0.012 L s‐1 the error was ±10%. Water samples were collected by grab sampling and by an automated sampler (model 6712, Isco, Inc., Lincoln, Neb.). Inflow samples (collected prior to interaction with the filter, but after flow from the tank) were collected at five different times throughout the simulation. An initial sample was col‐ lected from the tank following 30 min of agitation, while the five inflow samples were collected every time 1.14 m3 (300gal) of water was pumped through the filter. The auto‐ mated flow sampler was programmed to collect samples after 0.38 m3 (100 gal) of water had passed through the cartridge filter, and every 0.38 m3 (100 gal) after that, until the simula‐ tion was completed. For each simulation/replicate, 15 to 17filtered samples and 6 pre‐filter samples were collected. A power interruption in the middle of one run prevented a full complement of samples for that simulation. FILTER DESIGN The filters contained a proprietary mixture of activated alumina, activated carbon (from coconut shells), and natural‐ ly occurring zeolite (clinoptilolite) in a cartridge design (table 2). The cartridge design was chosen because of its ease in capturing discharge from tile drains. The filters were de‐ signed by Kristar Enterprises, Inc. (Santa Rosa, Cal.) in a par‐ ticularly low profile and footprint to minimize the required excavation for placement in‐line with the drain tile as well as to maximize filter surface area with low available operating head (fig. 1). The filter system (U.S. Patent No. 7,374,364) consisted of three replaceable cartridges, each approximately 600 mm long × 200 mm diameter filled with 0.015 m3 of granular me‐

dia, in a fiberglass test structure nominally 0.92 m × 0.92 m × 0.46 m (3 ft × 3 ft × 1.5 ft). A media blend of 33.2% granu‐ lar activated carbon (GAC), 34.0% zeolite (clinoptilolite), and 32.8% activated alumina (AA) by weight was used for purposes of this test. These proportions were consistent with the patent application and were selected based on limited bench‐scale screening tests (conducted by Kristar Enter‐ prises, Inc.), but not necessarily optimized for the intended application. However, the materials of interest as deployed were considered adequate to provide opportunity for ob‐ servation of functional mechanisms. Three new filter car‐ tridges and materials were introduced prior to each replicate/simulation event. Each of the three design hydro‐ graphs was replicated three times. Thus, a total of 27 car‐ tridges (3 cartridges per simulation × 3 design hydrographs× 3 replications) were used in the study. Runoff was conveyed to the system through a 10.2 cm (4in.) inflow/inlet pipe and over a flow‐spreading baffle. Water entered the cartridges radially, passing through the packed media bed to a perforated central tube. Flow leaving the system through the 10.2 cm (4 in.) outlet pipe was regu‐ lated by a control baffle, which also kept the cartridges fully submerged when in operation. CHEMICAL ANALYSIS All collected samples were handled according to U.S. EPA Method 353.3 for NO3‐N, U.S. EPA Method 365.1 for phos‐ phorus analysis, and U.S. EPA Method 525.2 for pesticide analysis (U.S. EPA, 1983, 1995). Samples were stored below 4°C and analyzed within 28 days. Prior to analysis, samples were vacuum filtered through a 0.45 mm pore diameter membrane filter for analysis of dissolved nutrients and suspended

Figure 1. Test filter apparatus.

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Table 3. Mean (standard deviation) percent reduction in total load resulting from discharge water passing through the filter, summarized by hydrograph peak flow rate and pollutant (n represents number of replicates).[a] Peak Flow (L s‐1) NO3‐N DRP Chlorothalonil Metalaxyl

[a]

0.63 (n = 3) 1.26 (n = 3) 1.89 (n = 3)

5.2 (0.43) a 4.9 (0.56) a 3.9 (0.11) b

53.5 (1.75) a 53.9 (4.71) a 47.3 (10.87) a

59.3 (1.89) a 64.4 (7.45) a 50.8 (12.05) a

31.0 (1.31) a 30.1 (5.52) a 25.5 (4.05) a

Mean across all flows (n = 9)

4.7 (0.68)

51.6 (7.17)

58.2 (9.91)

28.8 (4.58)

Means within a column followed by different letters are significantly different (p < 0.05).

solids. Concentrations of NO3‐N and DRP (as PO4‐P) were determined colorimetrically by flow injection analysis using a QuikChem 8000 FIA automated ion analyzer (Lachat In‐ struments, Milwaukee, Wisc.). NO3‐N was determined by copperized‐cadmium reduction, while DRP as PO4‐P was de‐ termined by the ascorbic acid reduction method (Parsons et al., 1984; U.S. EPA, 1983). Chlorothalonil and metalaxyl residues were determined using gas chromatography and a gas chromatography‐mass spectrometer (Saturn 2200 GC‐MS, Varian Instruments, Palo Alto, Cal.) (U.S. EPA, 1995). As above, samples were stored at 4°C until processing, which generally occurred within seven days. Two hundred milliliters of each of these samples was vacuum filtered (Fisherbrand 42.5 mm diameter glass fi‐ ber filter, grade G6) and stored below 4°C until extraction. Prior to pesticide extraction, each filtered sample was forti‐ fied with 1 mL methanol and terbutylazine standard at a final concentration of 500 mg L‐1. The samples were then extracted using 10 mL (500 mg) Varian Bond Elut C‐18 cartridges pre‐ conditioned with methanol. Each extract was eluted with four 0.5 mL aliquots of ethyl acetate, dried under N2 gas, and re‐ constituted with 1 mL ethyl acetate containing 100 mg L‐1 phenanthrene‐d10 as an internal standard. The extracted samples were then frozen at or below 0°C until analysis. Dur‐ ing analysis, two mL of sample were injected via splitless mode into a Varian CP‐Sil 8 CB low bleed column (30 m × 0.25 mm ID) using a Varian CP‐8400 autosampler. Helium was the carrier gas at a flow rate of 1 mL min‐1. The oven tem‐

perature program consisted of temperature ramping from 55°C to 300°C at various time intervals with an injector tem‐ perature of 280°C. Extract composition was determined with the mass spectrometer and monitoring the masses for chloro‐ thalonil (mass‐to‐charge ratio [m/z] 266) and metalaxyl (m/z 206). Matrix spikes were prepared by adding a concentrated mixture of the analytes (chlorothalonil and metalaxyl) to ul‐ trapure water for a final concentration of 500 mg L‐1. Extrac‐ tion recovery for the analytes was 100% ±5%. No pesticide residues were detected in blanks. STATISTICAL ANALYSIS Before‐after statistical analyses were conducted on sam‐ ple concentrations and loads entering and exiting the filter. All statistical analyses were conducted using SigmaStat 3.1 for Windows (Systat, 2004) with a significance level of p < 0.05. All pairwise multiple comparisons in which normality was preserved were determined by a one‐way ANOVA using the Student‐Newman‐Keuls (SNK) method. When normality was not preserved, multiple comparisons were instead made using a one‐way ANOVA and Dunn's test on ranks.

RESULTS Flow‐proportional sampling (samples based on an equal volume of discharge past a collection point) was used to automatically collect discharge samples from the outflow of the

100 80 Nitrate-Nitrogen

60 40

Chlorothalonil

% Reduction

20 0 100 80 Metalaxyl

60 40 Dissolved Reactive Phosporus

20 0 0.0

0.5

1.0

1.5

2.0 0.0

0.5

1.0

1.5

2.0

Flow Rate (L/s)

Figure 2. Relationship between flow rate and percent reduction (solid points) and mean removal across all flow rates (dashed line) for each pollutant measured in this study.

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20 Nitrate-Nitrogen

Chlorothalonil

90

a

Percent Load Reduction


15

b 10 b 5

ab

a

80 70

b

60 50 40 30 20 10

0 b

80

a

70 60

Metalaxyl

ab

80 Percent Load Reduction


0 90

Dissolved Reactive Phosphorus

90

b

50 40 30 20 10

70 60 50

a

40 b

30 20 10

0

0 Rising Limb

Peak Flow

Receding Limb

Rising Limb

Peak Flow

Receding Limb

Figure 3. Box and whiskers plot of percent load reduction as a function of position on the discharge hydrograph. Letters indicate significant differences (p < 0.05) in median values. Boxes are bound by the 25th and 75th percentile concentrations; the line in the box represents the median concentration. Whiskers represent the 10th and 90th percentile concentrations. 100

Chlorothalonil

Nitrate-Nitrogen

1.4 1.2

80

1.0 Discharge Rate % Load Reduction

60

Discharge Rate (L/s)

0.6

Discharge Rate % Load Reduction

0.4

40

20

0.2 0.0 1.4

Dissolved Reactive Phosphorus

0 100

Metalaxyl

1.2

80

Percent Reduction

0.8

1.0 60

0.8 Discharge Rate % Load Reduction

0.6

40 Discharge Rate % Load Reduction

0.4

20

0.2 0.0

0 0

50

100

150

200

250

300 0

50

100

150

200

250

300

Time (minutes)

Figure 4. Example relationships between discharge rate and removal efficiency for each of the pollutants studied.

filter system. This sampling method introduces less error compared to time interval sampling approaches (King and Harmel, 2003). Additionally, flow‐proportional sampling permits an evaluation of filter performance and effectiveness throughout the discharge event. Furthermore, because this sampling method was used, the reduction in concentrations was equal to the reductions in loadings. In order to standard‐ ize the data, percent reductions between inflow and outflow were calculated for each replication. For each of the three simulated hydrograph shapes, the cli‐ noptilolite/activated carbon/activated alumina cartridge fil‐ ter significantly reduced the experimental pollutant loads (table 3). Hydrograph peak flow rate had a measurable effect

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on the amount of pollutant removed from solution (table 3). In general, filter removal efficiency for all four contaminants tended to decrease as peak flow rate increased across all peak flow hydrographs (fig. 2). However, a small lag in removal efficiency was observed relative to the hydrograph peak, presumably because of tortuous flow through and adsorption processes within the filter media. Lag times (and thus contact time) were more pronounced for the low peak flow hydro‐ graphs (peak flow = 0.63 L s‐1). Removal efficiency also depended on the pollutant type. For example, an approximate 50% percent reduction in the total loads of DRP and chlorothalonil was observed as a func‐ tion of flow rates and across all peak flow hydrographs

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(table3). Similarly, metalaxyl removal was nearly 30% of its total load. In contrast, filter removal efficiencies for NO3‐N were significantly less (4% to 5%) than for DRP, chlorothalo‐ nil, and metalaxyl. However, the only statistically significant (p < 0.05) difference in total load reduction across hydro‐ graph shapes was measured for NO3‐N. Removal efficiencies for DRP, chlorothalonil, and metalaxyl did not change signif‐ icantly across the three hydrograph shapes examined (table3). Visible differences in concentrations for like flows within the same hydrograph led to an investigation of the rising limb, peak flow, and receding limb portions of each hydro‐ graph. Median percent load reduction in the discharge hydro‐ graph was significantly greater (p < 0.05) in the rising limb compared to the reduction recorded at the peak flow (fig. 3). With respect to NO3‐N and DRP, the load reduction in the ris‐ ing limb was significantly greater (p < 0.05) than that mea‐ sured in the receding limb. However, for the two pesticides measured, there was no notable difference in the median load reduction occurring between the rising and receding limbs. Additionally, there was no measurable difference (p > 0.05) between percent pollutant reduction at peak flow and the re‐ ceding limb. However, in every case, the greatest single per‐ cent contaminant reduction was measured at the end of the receding limb, when flows were lowest and contact time with the media was greatest (fig. 4). Here, removal efficiencies at the end of the receding limb approached 100% for chlorotha‐ lonil, DRP, and metalaxyl, and 20% for NO3‐N.

DISCUSSION As previously described, the clinoptilolite/alumina/acti‐ vated carbon filter cartridge's pollution removal efficiency differed depending upon the flow rate, the hydrograph shape as determined by designed peak flow, the location on the hy‐ drograph, and pollutant type. These factors considered, the filters exhibited the highest removal efficiency for DRP and chlorothalonil, intermediate removal for metalaxyl, and the lowest removal for NO3‐N. Since activated alumina has been previously identified as an ideal media for sorbing DRP, high removal efficiencies for DRP were expected. The reduction of DRP measured here was comparable to results achieved by incorporating alumi‐ num oxide materials into the soil or blending with manure prior to application (Novak and Watts, 2004; Dao et al., 2001). However, the extent of DRP removal observed in this study was not as great as that observed in previously cited batch and column type studies (i.e., >90% reported by Baker et al., 1998). The reduced efficiency was attributed to shorter contact times with the filter media, a direct consequence of greater peak flows. For example, in the Baker et al. (1998) study, the durations of batch tests were allowed to approach 10 h while the mean residence time within the column tests was 0.9 days. In contrast, the contact time in the present study was on the order of seconds. Short residence time from high flows, coupled with the initial circumneutral pH of the influent water, may have also decreased DRP removal. Activated alumina, for example, re‐ moves DRP most efficiently in an acidic pH range (Huang, 1977; Németh et al., 1998; Tanada et al., 2003). Similarly, precipitation of DRP generally occurs under acidic or alka‐ line conditions, neither of which was generated in this study.

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Furthermore, the filter materials themselves may influence the pH of the influent water, which in turn may affect DRP removal. The overall number and quality of available DRP adsorp‐ tion sites in the selected filter materials (activated carbon and alumina) may have also contributed to the relatively low DRP removal. For example, increasing the ratio of alumina and/or activated carbon in the filter could increase the abso‐ lute number of available active sites. Furthermore, different types of activated carbon and alumina exhibit varying effica‐ cies of DRP removal. For example, surface area, polarity, hy‐ drophobicity, ash content, pore size and distribution, and density and type of surface functional groups can vary across activated carbons and can profoundly impact adsorption (Sa‐ lame and Bandosz, 2003; Li et al., 2002). In this study, only coconut‐shell based activated carbon and one proprietary ac‐ tivated alumina were used. Future testing with various other types of activated carbon and alumina is necessary to deter‐ mine the best activated carbon and alumina blend for DRP re‐ moval in transient systems. As noted in the Results section, the removal efficiency of DRP did not significantly change with respect to the gener‐ ated hydrograph shapes. That is, for hydrographs with peak flows of 0.63, 1.26, and 1.89 L s‐1, little difference in DRP removal was observed. We attributed this trend to the abun‐ dance of activated sites (table 2) found in the activated carbon and alumina as well the circumneutral pH of the influent wa‐ ter (Hano et al., 1997; Namasivayam and Sangeetha, 2004). With respect to NO3‐N removal, the results were some‐ what surprising; we expected a greater removal efficiency than was observed. Admittedly, clinoptilolite has been iden‐ tified as an ideal agent for sorbing nitrogen as NH4‐N and not NO3‐N. However, activated carbon has been shown to be an effective NO3‐N sorbent (Baes et al., 1997; Orlando et al., 2002a, 2002b). For example, Namasivayam and Sangeetha (2004) observed 95% removal of a comparable amount of NO3‐N with ZnCl2‐activated coir pith carbon. As with the pesticides, perhaps a different type of activated carbon or blend of activated carbons could more effectively overcome rapid flow rates and high NO3‐N solubility to reduce aqueous NO3‐N concentrations. Alternatively, NO3‐N removal may be most efficiently and economically achieved through microbial denitrification prior to or after water discharge through an end‐of‐tile filter. Cellulosic by‐product materials such as wood mulch, saw‐ dust, and leaf compost are well‐suited, abundant, and sources of carbon necessary for microbial denitrification. For exam‐ ple, Robertson et al. (2000), observed 58% to 80% NO3‐N re‐ duction in septic tank effluent passing through vertical and horizontal positioned permeable walls comprised of various cellulosic materials over a seven‐year period. Similarly, Tsui et al. (2007) measured a 75% reduction in NO3‐N concentra‐ tions by mixing an NO3‐N rich solution with immature yard waste compost as a carbon source. They determined retention time in the compost material to be the most critical compo‐ nent for denitrification; given the relatively high flow rates in this study, water retention time was comparatively nonex‐ istent. Furthermore, Jaynes et al. (2008) observed significant NO3‐N removal in tile drains lined with parallel trenches filled with oak pallet woodchips. NO3‐N removal in these trench‐system tiles continued to be high after five years when compared to conventional, unlined drainage tile plots. The average annual NO3‐N concentration in discharge for the


trench system tiles was 8.8 mg L‐1, while the concentration in the conventional tile system discharge was 22.1 mg L‐1. It should be noted that in each of these denitrification scenarios, flow rates into and through the medium would be much less than tested in this study. Thus, future investigation should fo‐ cus on using a combined end‐of‐tile filter cartridge and in‐ stream or in situ denitrification system for greater NO3‐N removal. Regarding chlorothalonil and metalaxyl, we assumed that adsorption to activated carbon would be their primary remov‐ al mechanism due to their generally aromatic and thus hydro‐ phobic nature. Variation in chemical structure may account for the differential removal efficiencies observed for each of these pollutants. For example, chlorothalonil is significantly less water soluble (0.6 mg L‐1) than metalaxyl (7100 mg L‐1) and thus may be more hydrophobically attracted to the acti‐ vated carbon in the filter cartridge. Indeed, its log Kow of 2.64 to 4.38 (Caux et al., 1996) is greater than that of metalaxyl (log Kow = 1.56; Singh and Tripathi, 1982), indicating greater fugacity from the aqueous phase. Additionally, molecular size of the contaminants as well as the pore sizes within the activated carbon may also account for the observed removal efficiencies. However, a detailed assessment of all of the chemical and physical variables affecting metalaxyl and chlorothalonil adsorption is beyond the scope of this study. As with DRP, total removal of metalaxyl and chlorothalo‐ nil remained relatively constant over the three studied hydro‐ graph shapes. We attribute this trend to the high surface area of activated carbon. Again, using different types of activated carbons could increase their removal efficiency. Neverthe‐ less, removal efficiency for metalaxyl and chlorothalonil was significant in this study. As previously described, the removal efficiency for all contaminants was consistently highest at the extremes of the rising and receding limbs of the hydrograph when the flow rates were lowest (and residence time high). Thus, not sur‐ prisingly, this filter design may be most effective under base‐ flow conditions rather than stormflow events. This may be especially true for NO3‐N, as annual NO3‐N concentrations in tile drainage have been reported to be greater in baseflow than in stormflow (King et al., 2007b). This effectiveness at low flows was also corroborated by McDowell et al. (2008), who used smelter slag in both a fluvarium and a field experi‐ ment and determined that the best effectiveness was mea‐ sured at low flows. However, as we have demonstrated, use of these filters can also have a significant effect under high flow, storm event conditions. Thus, these filters can be used under baseflow and stormflow conditions, although the latter may rapidly expend the filter. Overall then, further field‐scale, long‐term, studies of these filters are required to determine the longevity of these filter materials; once adsorption sites are exhausted, the filter will require replacement. Precipitation of DRP can further shorten filter longevity, especially if conditions become alka‐ line or acidic, although Baker et al. (1998) suggested that the life of an activated aluminum oxide material under field con‐ ditions may be greater than two years. After two years, great‐ er than 99% of the phosphorus in that study was still being removed.

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SUMMARY AND CONCLUSION A replicated laboratory‐scale simulation study was de‐ signed and completed to evaluate the feasibility and efficacy of a clinoptilolite/alumina/activated carbon cartridge type filter to sorb NO3‐N, DRP, chlorothalonil, and metalaxyl in a transient aqueous solution. The blended filter materials were tested over a range of generated flow rates using a hy‐ drograph generator capable of peak flow rates equivalent to 1.9 L s‐1. The results of the study can be summarized as fol‐ lows: S Substantial loading reductions were measured for dis‐ solved reactive phosphorus (51.6%) and chlorothalonil (58.2%), with intermediate reductions for metalaxyl (28.8%) and minor reductions for NO3‐N (4.7%). S For all contaminants, the discharge flow rate was in‐ versely related to percent removal and was consistent across all tested hydrographs. The single greatest re‐ moval efficiency was observed at the end of the reced‐ ing limb when flow is low, and contact time is high. S Differences in removal efficiencies by hydrograph shape were statistically significant only for NO3‐N. This was perhaps due to an excess of DRP, chlorothalo‐ nil, and metalaxyl adsorption and the circumneutral pH of the influent water. S The efficiency of the filters varied depending on the location within the hydrograph. A greater percent re‐ moval was observed during the rising limb compared to the peak and receding limbs. The particular filter material blend used in this study may not be ideal for NO3‐N removal due to greater flow rates and the high solubility of NO3‐N; however, the material blend did significantly reduce DRP, chlorothalonil, and metalaxyl. Based on the finding of this feasibility study, it is recom‐ mended to field test these type of filters on tile drainage areas where the discharge is within similar peak flows. In addition, investigation of additional byproducts, filter designs, and blending ratios is recommended to optimize filtering capabil‐ ity and longevity, especially at high flows. Further develop‐ ment of this type of system for application in agricultural and large‐scale recreation watersheds where greater flows are ex‐ pected is also recommended. ACKNOWLEDGEMENTS The authors wish to acknowledge the contributions of Ann Kemble for preparing and completing the laboratory simula‐ tions, Brian Heskett for his engineering expertise in setting up and calibrating the micro motion mass flow and density transmitter, Phil Levison for assembling and constructing the plumbing components of the hydrograph simulator, and Ginny Roberts for her analytical work. This research was funded in part by the U.S. Golf Association and through the generous material contributions from Kristar Enterprises.

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