Use of Reclaimed Water and Sludge in Food Crop Production (1996) / Chapter Skim
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4 Soil, Crop, and Ground Water Effects
4 Soil, Crop, and Ground Water Effects
Pages 63-88
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From page 63... ...
SLUI) GE AS A SOURCE OF PLANT NUTRIENTS Sewage sludge contains all the elements essential for the growth of higher plants.
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From page 64... ...
In aerobically digested sludges, microbial oxidation is greater and there is less residual organic nitrogen than in anaerobically digested sludges. Ammoniacal nitrogen is about 10 percent of the total nitrogen in aerobically digested sludge and about 30 percent of the total nitrogen in anaerobically digested sludge (Linden et al., 1983~.
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From page 65... ...
Based on long-term evaluations of treated sludge use over periods ranging from 9 to 23 years, the Water Environment Research Foundation (1993) has recommended soil phosphorus levels be monitored where sludge applications are used continuously over time, and that sludge application rates may need to be determined by crop phosphorus levels rather than the nitrogen needs of the crop.
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From page 66... ...
Irrigation Water Quality Concerns The feasibility of using treated municipal wastewater as a source of irrigation water depends upon its quality. This in turn depends upon the quality of the municipal water supply, the nature of the constituents added during water use, and the kind and degree of wastewater treatment.
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From page 67... ...
EFFECTS OF SLUDGE AND WASTEWATER ON SOIL PHYSICAL PROPERTIES Organic Matter Soil organic matter enhances the structural properties of a soil by binding together soil particles into aggregates or lumps and creating large (non-capillary) pores through which air and
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From page 68... ...
Soils under continuous cultivation are very deficient in organic matter because the rate at which organic matter returns from crop residues is lower than the rate of organic matter decomposition in soils. Where organic matter is lacking, the less stable soil aggregates easily fall apart in the presence of rain or percolating water; in spite of cultivation, the larger soil pores are lost, soil air decreases, water movement is restricted, the soil becomes more closely packed, and the bulk density increases.
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From page 69... ...
Plants vary in their tolerance of soil salinity (Maas, 19901. ERECTS OF SLUDGE AND WASTEWATER ON SOIL CHEMICAL PROPERTIES Biologically stabilized sewage sludge contains an average of approximately 50 percent organic matter on a dry weight basis.
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From page 70... ...
(19901. Trace Elements Following organic matter decomposition, trace elements from wastewater and sludge are released and form sparingly soluble reaction products.
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From page 71... ...
Because repeated sewage sludge applications lead to accumulations of trace elements in soil, concern has been expressed over possible adverse effects associated with the use of sludge on soils that are acid or that may become acid (McBride, 19951. In an attempt to address this concern, Ryan and Chaney (1994)
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From page 72... ...
. Therefore, where industrial pretreatment programs are effectively enforced, it would seem reasonable to permit treated municipal wastewaters that meet irrigation water quality criteria to be used for crop irrigation.
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From page 73... ...
Actual experience at numerous sewage sludge land application sites has indicated that uptake of metals by plants has been minimal.
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From page 74... ...
The public health concerns about exposure to trace elements through the consumption of crops grown on sludge-amended soils are discussed in Chapter 6. Accumulations of Potentially Harmful Organ~cs in Soils and Crops Organic chemicals, when added to the soil may volatilize, decompose, or be adsorbed.
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From page 76... ...
They are important in the decomposition of organic matter and in the cycling of plant nutrients such as nitrogen, phosphorus, and sulfur. Metal accumulations in soils associated with the long-term applications of sewage sludge have been shown to affect microbial activity and biomass, biological nitrogen fixation, and vesicular-arbuscular mycorrhizae (Giller et al., 1989; McGrath et al., 1988; McGrath et al., 1994; Smith, 19911.
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From page 77... ...
Long term applications of sewage sludge resulting in metal accumulations in surface soils have been shown to reduce nitrogen fixation by free-living heterotrophic bacteria (Brookes et al, 1986a; Lorenz et al., 1992; Martensson and Witter, 19901. In an experiment where sludgetreated soils were compared to manure-treated soils, nitrogen-fixing activity by diazotrophs in the sludge-treated soil was decreased to 2 percent of that of the manure-treated soil.
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From page 78... ...
As described earlier in this chapter, nitrate pollution of groundwater from application of wastewater effluent and sludge can be controlled by the same nutrient management techniques used in traditional agriculture. The potential for ground water contamination by microorganisms, trace elements and toxic organic compounds from wastewater and sludge is evaluated below.
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From page 79... ...
Disinfection appears to be advisable in preventing ground water contamination by viruses from irrigation with treated municipal wastewater. In the context of food crop production, EPA guidelines recommend a minimum of secondary treatment plus disinfection (EPA, 19921.
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From page 80... ...
Toxic Organic Compounds PCBs and detergents are the only classes of synthetic organic compounds that occur in municipal wastewater sludges and effluents in concentrations higher than those in conventional agricultural irrigation water or soil additives (O'Connor et al., 1991; Brunner et al., 1988; Giger et al., 1987; Purr et al., 19761. In municipal treatment plants, both PCBs and detergents are concentrated into the sludge fraction.
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From page 81... ...
Overcash (1983) has stated that leaching of toxic organic constituents to ground water will not occur when application rates for either treated wastewater effluent or sludge to agricultural soils are controlled by crop water and nutrient demands.
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From page 82... ...
Sludge also contains all other essential plant nutrients and, when used as an nitrogen source at agronomic rates, will usually satisfy crop requirements for all essential nutrients, except possibly potassium. The salts, nitrogen, trace elements and trace organics in sludge and wastewater effluents need to be managed properly to avoid damage to the soil, crop, consumer of the crop, and ground water.
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From page 83... ...
. As long as treated municipal wastewaters meet irrigation water quality criteria and state regulations governing disease-causing organisms in the water, they should be considered safe for agricultural use.
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From page 84... ...
1992. A methodology for establishing phytotoxicity criteria for chromium, copper, nickel, and zinc in agricultural land application of municipal sewage sludge.
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From page 85... ...
Pp. 122-135 in The Influence of Sewage Sludge Application on Physical and Biological Properties of Soils.
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From page 86... ...
1990. Mycorrhizal infection of clover is delayed in soils contaminated with heavy metals from past sewage sludge applications.
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From page 87... ...
1988. Effects of potentially toxic metals in soil derived from past applications of sewage sludge on nitrogen fixation by Trifolium repens L
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From page 88... ...
1991. Effects of sewage sludge application on soil microbial processes and soil fertility.
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