درمان فصلی فاضلاب نوع سوم در کالیفرنیا : تجزیه و تحلیل سود و زیان بهداشت عمومی

A number of communities in the Central Valley of California have requested that seasonally based effluent limits be developed for their wastewater treatment facilities. These seasonal limits would be based on disinfected secondary treatment during the winter and disinfected tertiary treatment during the rest of the year. Such a request for seasonal limits raises a significant water quality policy question with regard to the costs and relative benefits of tertiary treatment during the winter season. A benefit–cost analysis for winter season tertiary wastewater treatment in California's Central Valley is presented here. The assumed societal benefit of winter tertiary treatment is enhanced water quality for recreational purposes, and thus reduced risk to public health. Based on the results of this analysis, between four and sixteen million recreation events would need to occur annually region-wide during the winter to justify the costs of winter tertiary treatment. A similar method and the information described herein could be used by the state water quality regulatory agency to develop a risk-based policy to consider seasonal limits.

Approximately 43 communities in the Central Valley of California (Central Valley) have permitted dry weather wastewater discharges of over 109 L/d (500 Mgal/d) to surface waters. Several communities have requested wastewater discharge permits that would allow them to discharge the disinfected secondary treated effluent during the winter season and disinfected tertiary treated effluent during the rest of the year (seasonal limits). The request for seasonal limits raises a significant water quality policy question with regard to the costs and relative benefits of tertiary wastewater treatment during the winter season. The benefit of tertiary wastewater treatment compared to secondary treatment is improved water quality of the effluent, and thus a reduction in the risk of illness when the receiving waters are used by the public. Recreation in receiving waters represents the highest potential for exposure to pathogens and was thus the focus of this investigation. Water quality has been regulated in the United States for over one hundred years. The earliest regulations were established to protect public health and to increase navigability. More recently, water quality regulations have been extended to promote other goals such as fishable and swimmable waters and to restore and maintain the “chemical, physical, and biological integrity of the nation's waters” (US Congress, 1972). Numerical water quality objectives for recreational activities are almost always met by disinfected secondary effluents. However, regulatory agencies sometimes apply more stringent criteria to wastewater effluents to provide additional public health protection. California State law requires that economic factors be considered during such a decision process (CA Water Code sections 13241, 13263(a)). Regulatory actions to address the potential risks associated with human exposure to microbiological contaminants in water are based on two distinct elements: risk assessment and risk management. In microbial risk assessment, data are used to define potential health effects associated with exposure to infectious agents. Risk management is the process of weighing different policies and selecting the most reasonable regulatory action, by integrating the results of the risk assessment with other important criteria such as engineering data and social, economic, and political concerns (National Research Council, 1983).

The analysis presented in this paper provides part of a rational basis for a careful consideration of seasonal effluent limits for wastewater treatment facilities in the Central Valley of California. A similar method and the information described herein could be used by the state water quality regulatory agency to develop a risk-based policy to consider such an approach.