Autoheating biosolids Application of biosolids from municipal wastewater treatment processes on agricultural, forest, or other land sites is an appealing option, but the biosolids ideally must meet EPA Class A standards that allow unrestricted use. Traditional methods of reducing potential pathogens to meet these standards involve aerobic or anaerobic digestion, composting, heat treatment, and irradiation. A. U. Ahmed and D. L. Sorenson investigated the effectiveness of autoheating for pathogen destruction. Biosolid columns seeded with pathogens and were nonmixed mixed month or mixed twice a month Biosolids mixed once a month and twice a month were autoheated °C and 57 °C respectively Pathogen levels were reduced to below detectable levels within one year independent of the mixing or attainment of SDecified temperature This study demonstrates an alternative mprhod for meeting Class A hin solids r e r m i r e m e n t s {Water Pf>t 1 9 9 7 fiQ ft 1-94)
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Sludge pretreatment Anaerobic digestion of municipal sludge results in a digested sludge that does not meet new regulations on pathogens and vector attraction. It also involves operational problems of digester foaming caused by Nocardia bacteria. K. R. Pagilla and co-workers evaluated aerobic thermophilic pretreatment (ATP) to solve these problems. Class A pathogen regulations limit total coliform and Salmonella spp. density. Because these organisms and Nocardia cannot tolerate high temperatures the authors theorize that ATP would be effective ATP stage sludge heated to >55 °C and cooled for subsequent anaerobic digestion Results indicate a reduction in all Class A parameters to below required levels The system also provided higher volatile solids reduction higher methane content in sludge gas and lower sludse suDern a t a n t COD {Water Envirnn 199B RH 1093-98)
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UV disinfection UV light is being investigated as a potential substitute for chlorination to kill bacteria and viruses in wastewater. Unlike chlorine, UV light does not form toxic compounds such as trihalomethanes (THMs). However,
there has been much concern about the effectiveness of UV treatment. J. A. Oppenheimer and colleagues compared the effectiveness of UV and chlorine disinfection in producing wastewater that meets California Wastewater Reclamation criteria. UV and chlorine disinfection were studied in parallel using nitrified and partially denitrified tertiary treated wastewater effluent. Results of the study demonstrated that UV levels could be adjusted to reduce microbial contaminants to comply with the criterici The use of UV light at these levels prevented the formation of THMs and aldehydes and eliminated chronic toxicity in the effluent {Water Environ Res 1997 69 14-24)
Heavy-metal removal Despite many laboratory studies, there have been few trials of new biotechnological methods for removal of heavy metals from actual metal-processing wastes. L. E. Macaskie and colleagues evaluated a biomineralization system that can function at the low pH values typical of many industrial wastewater streams. It involved the biologically mediated formation of metal phosphates by immobilized cells of a Citrobacter strain. Heavy metals (M) were precipitated as cell-bound MHPO using an enzym3.tically liberated phosphate ligand. Immobilized cells of Citrobacter in flowthrough columns removed uranyl ions with >70% efficiency The liberated phosphate ligand (HU0 PO ) precipitated and crystallized continuously on the cell surface providing a steady-state removal of the heawmetal ions {Biotechnol Bioene 1997 „ 1no_o9)
Contributors: Michael Brauer, University of British Columbia, Vancouver, Canada; Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven, Conn.; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, Pa.; Vincent Hand, Miami University, Institute oo Environmental Sciences, Oxford, Ohio; Louis Kovach, Ecolife Associates, Wilmington, Del; Geoffrey Nobes, McGiil University, Montreal; Raewyn Town, Queen'' University of Belfast, Northern Ireland; and Margaret Whittaker, NSF International, Ann Arbor, Mich.
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