Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. Ideally, this goal is to be met without introducing other risks, such as those that could be associated with disinfection by-products. The purpose of this research was to assess the effects of wastewater disinfection on human health.
Fecal coliforms and enterococci were both critically examined in terms of their ability to function as indicator organisms. Both bacterial groups were observed to be easily inactivated by chlorine and UV, and both indicators were observed to be relatively sensitive to these disinfectants, as compared with the remaining bacterial population. These observations are even more important when it is recognized that these indicator species represent a small fraction of the total bacterial population in wastewater effluent samples. Total culturable bacteria (TCB) were suggested as a possible alternative to coliform bacteria and enterococci as bacterial indicators. TCB represents a larger fraction of the bacterial population. However, the TCB assay requires a longer incubation time than is required for either coliforms or enterococci, and provides essentially no specificity in the analysis of water samples.
Taken together, and when considered in conjunction with previously published research, the results of these experiments illustrate several important limitations of common disinfection processes as applied in the treatment of municipal wastewaters. In general, it is not clear that disinfection processes, as commonly implemented, are effective for control of the risks of disease transmission, particularly as associated with viral pathogens. Microbial and chemical quality in receiving streams may not be substantially improved by the application of these methods; under some circumstances, it could be argued that disinfection may actually yield a decrease in effluent and receiving water quality. Decisions regarding the need for effluent disinfection must account for site-specific characteristics, but it is not clear that disinfection of municipal wastewater effluents is necessary or beneficial for all facilities. When direct human contact or ingestion of municipal wastewater effluents is likely (i.e., close to an outfall or in cases of discharge to bathing areas or food production areas), disinfection appears to be necessary. Under these circumstances, the data from these experiments illustrate clear advantages of UV irradiation over chlorination in terms of microbial quality, as well as chemistry and toxicology. This advantage is more evident in effluents that contain appreciable quantities of ammonia-N or organic-N.
This title belongs to WERF Research Report Series
ISBN: 9781843396734 (Print)
ISBN: 9781780403274 (eBook)
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