Municipal wastewaters receive discharges from homes, commercial establishments, industry and hospitals. Combined sewer systems carry waste from all the above sources as well as storm water. Within such mixtures are the microorganisms which reside in virtually all parts of the serviced
community. These include beneficial, commensal and pathogenic strains of microbes. Ultimately, particle associated microbes which survive their journey to a wastewater treatment plant will most likely be collected as sludge, and be processed to produce a biosolid. Current U.S. regulations
(40 CFR part 503) specify quantitative microbial limits for two classes of treatments. These are: Class A ≤ 1,000MPN fecal coliform/gram of total solids, or ≤ 3 MPN salmonellae/4grams of total solids; and under alternative 1 for Class B ≤ 2 × 106 MPN or CFU/gram
of total solids. However, the analytical techniques used for quantification of these microbes can produce highly variable results. The regulatory approach to compensate for the inherent variability of the analytical techniques used for these microbial assays is to require producers to assay
a minimum of seven samples (Class B biosolids) and report the geometric mean. The number of samples to be assayed to demonstrate compliance with Class A biosolids limits is not specified. Assessment of microbial risk is based upon exposure to pathogenic strains of microbes. Therefore risk
management techniques should be evaluated on their ability to demonstrate reduction of risks. In the case of land application of Class B biosolids, risk management includes treatment to reduce biodegradable components and land use restrictions. For Class A biosolids, risk management relies
on treatment to reduce biodegradable components and pathogens. Variation of analytical results reduces the certainty that risk reduction processes and management techniques have achieved their objectives. Moreover, compliance monitoring requirements may be achieved, but public health concerns
may remain. The objective of this presentation is to discuss pathogens of concern in biosolids, the analytical techniques used to evaluate microorganisms in biosolids, and to discuss the relationship between risk management and measurement of fecal coliforms and pathogens in biosolids.
A qualitative approach to monitoring will be explored for evaluation of risk management options and regulatory compliance.
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