379 8 Land Treatment Systems Land treatment systems include slow rate (SR), overland flow (OF), and soil aquifer treatment (SAT) or rapid infiltration (RI). In addition, the on-site soil absorption systems discussed in Chapter 10 utilize soil treatment mechanisms. 8.1 TYPES OF LAND TREATMENT SYSTEMS The process of land treatment is the controlled application of wastewater to soil to achieve treatment of constituents in the wastewater. All three processes use the natural physical, chemical, and biological mechanisms within the soil–plant–water matrix. The SR and SAT processes use the soil matrix for treatment after infiltration of the wastewater, the major difference between the processes being the rate at which the wastewater is loaded onto the site. The OF process uses the soil surface and vegetation for treatment, with limited percola- tion, and the treated effluent is collected as surface runoff at the bottom of the slope. The characteristics of these systems are compared in Table 8.1 and the treatment performance expectations were summarized in Table 1.3 in Chapter 1. 8.1.1 S LOW -R ATE S YSTEMS The slow rate process is the oldest and most widely used land treatment technol- ogy. The process evolved from “sewage farming” in Europe in the sixteenth century to a recognized wastewater treatment system in England in the 1860s (Jewell and Seabrook, 1979). By the 1880s, the United States had a number of slow-rate systems. In a survey of 143 wastewater facilities in 1899, slow rate land treatments systems were the most frequently used form of treatment (Rafter, 1899). Slow rate land treatment was rediscovered at Penn State in the mid-1960s (Sopper and Kardos, 1973). By the 1970s, both the U.S. Environmental Protection Agency (USEPA) and the U.S. Corps of Engineers had invested in land treatment research and development (Pound and Crites, 1973; Reed, 1972). By the late 1970s, a number of long-term effects studies on slow-rate systems had been conducted (Reed and Crites, 1984). A list of selected municipal slow-rate systems is presented in Table 8.2. A large SR system at Dalton, Georgia, occupies 4605 acres of sprinkler irrigated forest, as shown in Figure 8.1 (Crites et al., 2001). 8.1.2 O VERLAND F LOW S YSTEMS The overland flow process was developed to take advantage of slowly permeable soils such as clays. Treatment occurs in OF systems as wastewater flows down vegetated, graded-smooth, gentle slopes that range from 2 to 8% in grade. A DK804X_C008.fm Page 379 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 380 Natural Wastewater Treatment Systems schematic showing both surface application and sprinkler application is pre- sented in Figure 8.2. The treated runoff is collected at the bottom of the slope. The process was pioneered in the United States by the Campbell Soup Company, first at Napoleon, Ohio, in 1954 and subsequently at Paris, Texas (Gilde et al., 1971). Research was conducted on the OF process using municipal wastewater at Ada, Oklahoma (Thomas et al., 1974) and at Utica, Mississippi (Carlson et al., 1974). As a result of this and other research (Martel, 1982; Smith and Schroeder, 1985), over 50 municipal OF systems have been constructed for municipal wastewater treatment. A list of selected municipal overland flow systems is presented in Table 8.3. TABLE 8.1 Characteristics of Land Treatment Systems Characteristic Slow Rate (SR) Overland Flow (OF) Soil Aquifer Treatment (RI) Application method Sprinkler or surface Sprinkler or surface Usually surface Preapplication treatment Ponds or secondary Fine screening or primary Ponds or secondary Annual loading (ft/yr) 2–18 10–70 18–360 Field area (ac/mgd) 60–560 16–112 3–60 Use of vegetation Nutrient uptake and crop revenue Erosion control and habitat for microorganisms Usually not used Disposition of applied wastewater Evapotranspiration and percolation Surface runoff, evapotranspiration, some percolation Percolation, some evaporation TABLE 8.2 Selected Municipal Slow-Rate Land Treatment Systems Location Flow (mgd) System Area (ac) Application Method Bakersfield, California 19.4 5088 Surface irrigation Clayton County, Georgia 20.0 2370 Solid-set sprinklers Dalton, Georgia 33.0 4605 Solid-set sprinklers Lubbock, Texas 16.5 4940 Center-pivot sprinklers Mitchell, South Dakota 2.45 1284 Center-pivot sprinklers Muskegon County, Michigan 29.2 5335 Center-pivot sprinklers Petaluma, California 5.3 555 Hand-move, solid-set sprinklers Santa Rosa, California 20.0 6362 Solid-set sprinklers DK804X_C008.fm Page 380 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC Land Treatment Systems 381 FIGURE 8.1 Typical sprinkler irrigation system at the forested slow rate site at Dalton, Georgia. FIGURE 8.2 Overland flow process. Evapotranspiration Surface application Percolation Vegetative thatch and biological slime layer Water depth Grass Effluent Effluent collection channel Spray application Sprinkler application Surface runoff DK804X_C008.fm Page 381 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 382 Natural Wastewater Treatment Systems 8.1.3 S OIL A QUIFER T REATMENT S YSTEMS Soil aquifer treatment is a land treatment process in which wastewater is treated as it infiltrates the soil and percolates through the soil matrix. Treatment by physical, chemical, and biological means continues as the percolate passes through the vadose zone and into the groundwater. Deep permeable soils are typically used. Applications are intermittent, usually to shallow percolation basins. Continuous flooding or ponding has been practiced, but less complete treatment usually results because of the lack of alternate oxidation/reduction conditions. A typical layout of SAT basins is shown in Figure 8.3 (also see Table 8.4). Vegetation is usually not a part of an SAT systems, because loading rates are too high for nitrogen uptake to be effective. In some situations, however, vegetation can play an integral role in stabilizing surface soils and maintaining high infiltration rates (Reed et al., 1985). TABLE 8.3 Municipal and Industrial Overland Flow Systems in the United States Municipal Systems Industrial Systems Alma, Arkansas Chestertown, Maryland Alum Creek Lake, Ohio El Paso, Texas Beltsville, Maryland Middlebury, Indiana Carbondale, Illinois Napoleon, Ohio Cleveland, Michigan Paris, Texas Corsicana, Texas Rosenberg, Texas Davis, California Woodbury, Georgia Falkner, Michigan Gretna, Virginia Heavener, Oklahoma Kenbridge, Virginia Lamar, Arkansas Minden-Gardnerville, Nevada Mt. Olive, New Jersey Newman, California Norwalk, Iowa Raiford, Florida Starke, Florida Vinton, Louisiana DK804X_C008.fm Page 382 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC Land Treatment Systems 383 FIGURE 8.3 Typical layout of soil aquifer treatment basins. TABLE 8.4 Selected Soil Aquifer Treatment Systems Location Hydraulic Loading(ft/yr) Brookings, South Dakota 40 Calumet, Michigan 115 Darlington, South Carolina 92 Fresno, California 44 Hollister, California 50 Lake George, New York 190 Los Angeles County Sanitary District, California 330 Orange County, Florida 390 Tucson, Arizona 331 West Yellowstone, Montana 550 PREAPPLICATION TREATMENT EMERGENCY STORAGE INFILTRATION BASINS #6 #2 #7 #3 #5 #1 SPLASH APRONS #4 CONTAINMENT BERM DK804X_C008.fm Page 383 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 384 Natural Wastewater Treatment Systems 8.2 SLOW-RATE LAND TREATMENT Slow-rate systems can encompass a wide variety of different land treatment facilities ranging from hillside spray irrigation to agricultural irrigation, and from forest irrigation to golf course irrigation. The design objectives can include wastewater treatment, water reuse, nutrient recycling, open space preservation, and crop production. 8.2.1 D ESIGN O BJECTIVES Slow-rate systems can be classified as type 1 (slow infiltration) or type 2 (crop irrigation), depending on the design objective. When the principal objective is wastewater treatment, the system is classified as type 1. For type 1 systems, the land area is based on the limiting design factor (LDF), which can be either the soil permeability or the loading rate of a wastewater constituent such as nitrogen. Type 1 systems are designed to use the most wastewater on the least amount of land. The term slow infiltration refers to type 1 systems being similar in concept to rapid infiltration or soil aquifer treatment but having substantially lower hydrau- lic loading rates. Type 2 systems are designed to apply sufficient water to meet the crop irrigation requirement. The area required for a type 2 system depends on the crop water use, not on the soil permeability or the wastewater treatment needs. Water reuse and crop production are the principal objectives. The area needed for type 2 systems is generally larger than for a type 1 system for the same wastewater flow. For example, for 1 mgd (3785 m 3 /d) of wastewater flow, a type 1 system would typically require 60 to 150 ac (24 to 60 ha) as compared to the 200 to 500 ac (80 to 200 ha) for a type 2 system. 8.2.1.1 Management Alternatives Unlike SAT and overland flow, slow-rate systems can be managed in several different ways. The other two land treatment systems require that the land be purchased and the system managed by the wastewater agency. For slow-rate systems, the three major options are (1) purchase and management of the site by the wastewater agency, (2) purchase of the land and leasing it back to a farmer, and (3) contracts between the wastewater agency and farmers for use of private land for the slow rate process. The latter two options allow farmers to manage the slow rate process and harvest the crop. A representative list of small SR systems that use each of the different management alternatives is presented in Table 8.5. 8.2.2 P REAPPLICATION T REATMENT Preliminary treatment for an SR system can be provided for a variety of reasons including public health protection, nuisance control, distribution system protec- tion, or soil and crop considerations. For type 1 systems, preliminary treatment, except for solids removal, is de-emphasized because the SR process can usually DK804X_C008.fm Page 384 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC TABLE 8.5 Management Alternatives Used in Selected Slow-Rate Systems Purchase and Management by Agency Flow (mgd) Agency Purchase and Lease to Farmer Flow (mgd) Farmer Contract Flow (mgd) Dinuba, California Fremont, Michigan Kennett Square, Pennsylvania Lake of the Pines, California Oakhurst, California West Dover, Vermont Wolfeboro, New Hampshire 1.5 0.3 0.05 0.6 0.25 1.6 0.3 Coleman, Texas Kerman, California Lakeport, California Modesto, California Perris, California Winter, Texas Santa Rosa, California 0.4 0.5 0.5 20.0 0.8 0.5 15.0 Camarillo, California Dickinson, North Dakota Mitchell, South Dakota Quincy, California Petaluma, California Sonoma Valley, California Sonora, California 3.8 1.5 2.4 0.75 4.2 2.7 1.2 Source: Adapted from Crites, R.W. and Tchobanoglous, G., Small and Decentralized Wastewater Management Systems , McGraw-Hill, New York, 1998. DK804X_C008.fm Page 385 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 386 Natural Wastewater Treatment Systems achieve final water quality objectives with minimal pretreatment. Public health and nuisance control guidelines for type 1 SR systems have been issued by the EPA (USEPA, 1981) and are given in Table 8.6. Type 2 systems are designed to emphasize reuse potential and require greater flexibility in the handling of waste- water. To achieve this flexibility, preliminary treatment levels are usually higher. In many cases, type 2 systems are designed for regulatory compliance following preliminary treatment so irrigation can be accomplished by other parties such as private farmers. 8.2.2.1 Distribution System Constraints Preliminary treatment is generally required to prevent problems of capacity reduc- tion, plugging, and localized generation of odors in the distribution system. For this reason, a minimum primary treatment (or its equivalent) is recommended for all SR systems to remove settleable solids and oil and grease. For sprinkler systems, it is further recommended that the size of the largest particle in the applied wastewater be less than one third the diameter of the sprinkler nozzle to avoid plugging. 8.2.2.2 Water Quality Considerations The total dissolved solids (TDS) in the applied wastewater can affect plant growth, soil characteristics, and groundwater quality. Guidelines for interpretation of water quality for salinity and other specific constituents for SR systems are presented in Table 8.7. The term “restriction on use” does not indicate that the TABLE 8.6 Pretreatment Guidelines for Slow-Rate Systems Level of Pretreatment Acceptable Conditions Primary treatment Acceptable for isolated locations with restricted public access Biological treatment by lagoons or in-plant processes, plus control of fecal coliform count to less than 1000 MPN per 100 mL Acceptable for controlled agricultural irrigation, except for human food crops to be eaten raw Biological treatment by lagoons or in-plant processes, with additional BOD or SS control as needed for aesthetics, plus disinfection to log mean of 200 MPN per 100 mL (USEPA fecal coliform criteria for bathing waters) Acceptable for application in public access areas such as parks and golf courses Note: MPN, most probable number; BOD, biological oxygen demand; SS, suspended solids. Source: USEPA, Process Design Manual for Land Treatment of Municipal Wastewater , EPA 625/1-81-013, U.S. Environmental Protection Agency, Cincinnati, OH, 1981. DK804X_C008.fm Page 386 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC Land Treatment Systems 387 effluent is unsuitable for use; rather, it means there may be a limitation on the choice of crop or need for special management. Sodium can adversely affect the permeability of soil by causing clay particles to disperse. The potential impact is measured by the sodium adsorption ratio (SAR) which is a ratio of sodium concentration to the combination of calcium and magnesium. The SAR is defined in Equation 8.1. (8.1) where SAR = Sodium adsorption ratio (unitless). Na = Sodium concentration (mEq/L; mg/L divided by 23). Ca = Calcium concentration (mEq/L; mg/L divided by 20). Mg = Magnesium concentration (mEq/L; mg/L divided by 12.15). TABLE 8.7 Guidelines for Interpretation of Water Quality Problem and Related Constituent No Restriction Slight to Moderate Restriction Severe Restriction Crops Affected Salinity as TDS (mg/L) <450 450–2000 >2000 Crops in arid areas affected by high TDS; impacts vary Permeability: SAR = 0–3 SAR = 3–6 SAR = 6–12 SAR = 12–20 SAR = 20–40 TDS >450 TDS >770 TDS >1200 TDS >1860 TDS >3200 130–450 200–770 320–1200 800–1860 1860–3200 <130 <200 <320 <800 <1860 All crops Specific ion toxicity: Sodium (mg/L) Chloride (mg/L) Boron (mg/L) Residual chlorine (mg/L) <70 <140 <0.7 <1.0 >70 140–350 0.7–3.0 1.0–5.0 >70 >350 >3.0 >5.0 Tree crops and woody ornamentals; fruit trees and some field crops; ornamental, only if overhead sprinklers are used Note: TDS, total dissolved solids; SAR, sodium adsorption ratio. Source: Ayers, R.S. and Westcot, D.W., Water Quality for Agriculture , FAO Irrigation and Drainage Paper 29, Revision 1, Food and Agriculture Organization of the United Nations, Rome, 1985. SAR Na Ca Mg 2 = + DK804X_C008.fm Page 387 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 388 Natural Wastewater Treatment Systems In type 2 SR systems the leaching requirement must be determined based on the salinity of the applied water and the tolerance of the crop to soil salinity. Leaching requirements range from 10 to 40% with typical values being 15 to 25%. Specific crop requirements for soil–water salinity must be used to determine the required leaching requirement (Reed and Crites, 1984; Reed et al., 1995). 8.2.2.3 Groundwater Protection Most SR systems with secondary preapplication treatment are protective of the receiving groundwater. The concern over emerging chemical constituents, such as endocrine disruptors and pharmaceutical chemicals, has led to research on the ability of the soil profile to remove these trace organic compounds (Muirhead et al., 2003). 8.2.3 D ESIGN P ROCEDURE A flowchart of the design procedure for slow-rate systems is presented in Figure 8.4. The procedure is divided into a preliminary and final design phase. Deter- minations made during the preliminary design phase include: (1) crop selection, (2) preliminary treatment, (3) distribution system, (4) hydraulic loading rate, (5) field area, (6) storage needs, and (7) total land requirement. When the preliminary design phase is completed, economic comparisons can be made with other waste- water management alternations. The text will focus on preliminary or process design with references to detailed design procedures (Hart, 1975; Pair, 1983; USDA, 1983; USEPA, 1981). 8.2.4 C ROP S ELECTION The selection of the type of crop in a slow-rate system can affect the level of preliminary treatment, the selection of the type of distribution system, and the hydraulic loading rate. The designer should consider economics, growing season, soil and slope characteristics, and wastewater characteristics in selecting the type of crop. Forage crops or tree crops are usually selected for type 1 systems, and higher value crops or landscape vegetation are often used in type 2 systems. 8.2.4.1 Type 1 System Crops In type 1 SR systems, the crop must be compatible with high hydraulic loading rates, have a high nutrient uptake capacity, a high consumptive use of water, and a high tolerance to moist soil conditions. Other characteristics of value are tolerance to wastewater constituents (such as TDS, chloride, boron) and limited requirements for crop management. The nitrogen uptake rate is a major design variable for design of a type 1 system. Typical nitrogen uptake rates for forage, field, and tree crops are presented in Table 8.8. The largest nitrogen removal can be achieved with perennial grasses and legumes. Legumes, such as alfalfa, can DK804X_C008.fm Page 388 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC [...]... 414 Friday, July 1, 2005 3:47 PM 414 Natural Wastewater Treatment Systems TABLE 8. 15 BOD Removal for Soil Aquifer Treatment Systems Location Applied Wastewater BOD (lb/ac-da) Applied Wastewater BOD (mg/L) Percolate Concentration (mg/L) Removal (%) 131b 10b 92 Boulder, Colorado 48b Brookings, South Dakota 11 23 Calumet, Michigan 95b 228b 58b 75 77 112 12 89 156 220 8 96 Ft Devens, Massachusetts Hollister,... nitrogen balance is given in Equation 8. 5: © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 393 Friday, July 1, 2005 3:47 PM Land Treatment Systems 393 TABLE 8. 9 Denitrification Loss Factor for Slow-Rate Systems Carbon/Nitrogen Ratio Warm Climate f Factor Cold Climate f Factor High-strength wastewater >20 0 .8 0.5 Moderate-strength industrial wastewater 8 20 0.5 0.4 Primary effluent 3–5 0.4 0.25... Design Percolationc (4) Wastewater Loadingd (5) Available Wastewatere (6) Change in Storagef (7) Cumulative Storage (8) January 1.1 7.2 6.1 0.0 7.6 +7.6 8. 5 February 2.0 7.0 10.3 5.3 7.6 +2.3 10.8g March 2.7 4.5 10.3 8. 5 7.6 –0.9 9.9 April 3.9 3.0 8. 1 9.0 7.6 –1.4 8. 5 May 5.6 0.4 3.7 8. 9 7.6 –1.3 7.2 June 7.0 0.1 2.0 8. 9 7.6 –1.3 5.9 July 8. 6 0.1 0.4 8. 9 7.6 –1.3 4.6 August 7.4 0.2 1.7 8. 9 7.6 –1.3 3.3 September... Australia Primary effluent 0.32 82 0 507 12 © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 404 Friday, July 1, 2005 3:47 PM TABLE 8. 12 BOD Removal for Overland Flow Systems DK804X_C0 08. fm Page 405 Friday, July 1, 2005 3:47 PM Land Treatment Systems 405 TABLE 8. 13 Nitrogen Removal for Overland Flow Systems Ada, Oklahoma Hanover, New Hampshire Utica, Mississippi Screened raw wastewater Primary effluent... Figure 8. 5 © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 406 Friday, July 1, 2005 3:47 PM 406 Natural Wastewater Treatment Systems Ammonia Removal Percent 0 20 40 60 80 100 2 1 0.5 0.33 Wet-Dry Ratio 0.25 0.20 FIGURE 8. 5 Effect of wet/dry ratio on the removal of ammonia by overland flow (From Johnston, J and Smith, R., Operating Schedule Effects on Nitrogen Removal in Overland Flow Treatment Systems, ... Table 8. 9) © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 394 Friday, July 1, 2005 3:47 PM 394 Natural Wastewater Treatment Systems TABLE 8. 10 BOD Loading Rates at Industrial Slow-Rate Systems Location Industry BOD Loading Rate, Cycle Average (lb/ac·d) Almaden Winery; McFarland, California Winery stillage 420 Anheuser-Busch; Houston, Texas Brewery 360 Bronco Wine; Ceres, California Winery 1 28. .. the wet/dry ratio is higher than 7% 8. 2.5.2 Hydraulic Loading for Type 2 Slow-Rate Systems For crop irrigation systems, the hydraulic loading rate is based on the crop irrigation requirements The loading rate can be calculated using Equation 8. 4: © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 392 Friday, July 1, 2005 3:47 PM 392 Natural Wastewater Treatment Systems ET − Pr 100 Lw = ... Available wastewater minus the wastewater loading February is the maximum month © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 3 98 Friday, July 1, 2005 3:47 PM Month (1) DK804X_C0 08. fm Page 399 Friday, July 1, 2005 3:47 PM Land Treatment Systems 399 3 The design percolation rate (column 4 data) is 10.3 in./mo when that much rainfall or wastewater is applied From April to October, the wastewater. .. (WEF, 2001) © 2006 by Taylor & Francis Group, LLC DK804X_C0 08. fm Page 4 08 Friday, July 1, 2005 3:47 PM 4 08 Natural Wastewater Treatment Systems TABLE 8. 14 Suggested Application Rates for Overland Flow Systems Stringent Requirements (BOD = 10–15 mg/L) (gal/min·ft) Less Stringent Requirements (BOD = 30 mg/L) (gal/min·ft) Screening, septic tank, or short-term aerated cell 0.1–0.15 0.25–0.33 Sand filter,... Group, LLC DK804X_C0 08. fm Page 410 Friday, July 1, 2005 3:47 PM 410 Natural Wastewater Treatment Systems 1 Calculate the BOD load from the concentration and flow: BOD load = 8. 34QC (8. 9) where BOD load is the daily BOD load (lb/d; kg/d); 8. 34 is the conversion factor; Q is the flow (mgd; m3/d); and C is the BOD concentration (mg/L) 2 Calculate the land area from Equation 8. 10: A = (BOD load)/100 (8. 10) where . & Francis Group, LLC 384 Natural Wastewater Treatment Systems 8. 2 SLOW-RATE LAND TREATMENT Slow-rate systems can encompass a wide variety of different land treatment facilities ranging. Decentralized Wastewater Management Systems , McGraw-Hill, New York, 19 98. DK804X_C0 08. fm Page 385 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 386 Natural Wastewater Treatment. 1 985 . SAR Na Ca Mg 2 = + DK804X_C0 08. fm Page 387 Friday, July 1, 2005 3:47 PM © 2006 by Taylor & Francis Group, LLC 388 Natural Wastewater Treatment Systems In type 2 SR systems