Use of Reclaimed Water and Sludge in Food Crop Production (1996) / Chapter Skim
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3 Municipal Wastewater and Sludge Treatment
3 Municipal Wastewater and Sludge Treatment
Pages 45-62
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From page 45... ...
, processes intended specifically to accommodate wastewater application to crops, and typical sludge treatment processes. QUANTITY AND QUALITY OF MUNICIPAL WASTEWATER EFFLUENT AND SLUDGE Municipal wastewater represents the spent water supply of communities.
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From page 46... ...
Sludge from wastewater treatment processes are treated and then disposed or reused in crop production or other applications. age per capita usage from public water supply systems in the United States was I84 gallons (700 liters)
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From page 47... ...
CONVENTIONAL WASTEWATER TREATMENT PROCESSES Municipal wastewater treatment typically comprises preliminary treatment, primary treatment, and secondary treatment. Secondary treatment is the United States national standard for effluent discharged to surface waters.
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From page 48... ...
Now, primary treatment is used as an economical means for removing some contaminants prior to secondary treatment. The residue from primary treatment is a concentrated suspension of particles in water called "primary sludge." Although the goal of primary wastewater treatment is to separate readily-removable suspended solids and BOD, wastewater constituents that exist as settleable solids or are sorbed to settleable wastewater solids may also be removed.
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From page 49... ...
Wastewater constituents can become associated with secondary sludge as a result of microbial assimilation, by sorption onto settleable solids, or by incorporation into agglomerate particles formed as a result of bioflocculation. Some of the wastewater constituents that are incidentally associated with the biomass from secondary treatment processes include pathogens, trace elements, and organic compounds.
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From page 50... ...
The latter two processes do not provide a residual disinfectant as required by some state regulations for applying treated wastewater to food crops (EPA, 1992~. Additionally, suspended solids are sometimes removed from conventional wastewater treatment plant effluent prior to using the effluent in agriculture.
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From page 51... ...
Volume Reduction Processes Biological sludge, as produced from secondary wastewater treatment processes, often has a suspended solids content of less than one percent by weight; that is, each kg of activated sludge solids is accompanied by more than 99 kg of water. Primary sludges are more concentrated, but marginally so; typical combined primary and secondary sludge might contain about 3 percent solids by weight.
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From page 52... ...
The solids content of mechanically dewatered sludge typically ranges from 20 to 45 percent solids by weight; most processes produce concentrations of solids at the lower end of that range. Conditioning Sludge conditioning processes do not, in and of themselves, reduce the water content of sludge.
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From page 53... ...
in the United States. Chemical Stabilization Chemical stabilization of sludges is aimed not at reducing the quantity of biodegradable organic matter, but at creating conditions that inhibit microorganisms in order to retard the degradation of organic materials and prevent odors.
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From page 54... ...
Human health concerns about pathogenic organisms and viruses in sludge are considered in more detail in Chapter 5, and regulations to control infectious disease transmission from the use of sludge in crop production are discussed in Chapter 7. Other Sludge Treatment Processes A wide variety of processes are used to treat sludges.
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From page 55... ...
Beneficial uses of treated municipal wastewater sludges on land include agriculture and silviculture uses; application to parks, golf courses, and public lands; use in reclaiming low quality or spoiled lands; and use as landfill cover or fill material. Disposal on land includes landfilling and permanent storage of dewatered sludge or sludge incinerator ash in lagoons or piles.
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From page 56... ...
Integration of sludge treatment processes for use on agricultural land also requires consideration of the effects of the treatment processes on sludge quality. For example, dewatering, comporting, or alkaline treatment can be expecter]
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From page 58... ...
Unlike heavy metals, which are concentrated in sludge, many organic priority pollutants are removed from wastewater by a variety of mechanisms: volatilization during secondary treatment aeration, sedimentation and sorption onto both primary and secondary sludges, and biodegradation (Hannah et al., 1986; Petrasek et al., 1983; Kincannon et al., 1983; Tabak et al., 19811. Seven of the organic priority pollutants were found in over 50 percent of samples of treated wastewater effluent from 40 POTWs in the United States: I,l,l-tnchloroethane (52 percent)
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From page 59... ...
establishes limits on industrial discharges of hazardous pollutants to municipal sewers in order to: · prevent the introduction of pollutants which will interfere with the performance of the POTW treatment processes for wastewater and sludge; · prevent the pass-through of toxic pollutants into surface waters receiving discharges of treated wastewater effluent; and 1993b) · enhance opportunities to recycle treated municipal wastewater and sludge (EPA, Pretreatment Implementation The pretreatment regulations identify strategies for setting numerical standards on industrial dischargers to POTWs.
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From page 60... ...
SUMMARY Conventional municipal wastewater treatment processes were developed to produce effluents suitable for discharge to surface waters. The processes are intended primarily to remove BOD and suspended solids, but wastewater constituents associated with particles are also removed.
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From page 61... ...
1980. Cyanide problems in municipal wastewater treatment plants.
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From page 62... ...
1974. The efficiency of heavy metal removals by a conventional activated sludge treatment plant.
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