Pathogenic organisms may be present in both wastewaters and sludges, and their control is one of the fundamental reasons for waste management. Many regulatory agencies specify bacterial limits on discharges to surface waters. Other potential risks are impacts on groundwaters from both aquatic and land treatment systems, the contamination of crops or infection of grazing animals on land treatment sites, and the off-site loss of aerosolized organisms from pond aerators or land treatment sprinklers. Investigations have shown that the natural aquatic, wetland, and land treatment concepts provide very effective control of pathogens (Reed et al., 1979).

3.4.1 Aquatic Systems

The removal of pathogens in pond-type systems is due to natural die-off, predation, sedimentation, and adsorption. Helminths, Ascaris, and other parasitic cysts and eggs settle to the bottom in the quiescent zone of ponds. Facultative ponds with three cells and about 20 days' detention time and aerated ponds with a separate settling cell prior to discharge provide more than adequate helminth and protozoa removal. As a result, there is little risk of parasitic infection from pond effluents or from use of such effluents in agriculture. Some risk may arise when sludges are removed for disposal. These sludges can be treated, or temporary restrictions on public access and agricultural use can be placed on the disposal site.

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