AWWA ACE63061

Population-growth-driven increased water demands and prolonged drought conditions along with source water contamination by upstream wastewater treatment plants (WWTPs) is prompting many water purveyors to rethink current and future water management practices. Water purveyors are now, more than ever, faced with the challenges of a dwindling water supply, and a greater fraction of treated wastewater is now finding its way to drinking water supplies. Many wastewater facilities are now practicing or exploring various technologies (e.g., advanced biological treatment, membranes, soil aquifer treatment) as part of reclamation, recharge, recycling, and reuse (i.e., direct use) programs. Attention has focused on pharmaceuticals and endocrine disruptors, but WWTPs are also sources of disinfection byproducts (DBPs), if chlorine disinfection is practiced, and DBP precursors. Operational conditions, treated wastewater quality, fate-and-transport phenomenon in the receiving body, and the relative flow of the WWTP discharge to that of the receiving stream will determine the overall impact of wastewater-derived DBPs on drinking water supplies. Moreover, very little is known about how best to invest public money between WWTPs and DWTPs in order to maximize societal benefits while minimizing the health risks posed by wastewater-derived DBPs. To understand these important issues, a comprehensive study was undertaken. More than 20 WWTPs and DWTPs from various geographical locations in the U.S. participated in a study sponsored by the Awwa Research Foundation (AwwaRF) and U.S. Environmental Protection Agency (USEPA). A cost benefit analyses (CBA) was performed as part of this study. This paper discusses, step by step, the approach to CBA in predicting finished water DBPs level at DWTPs whose source water is impacted by treated wastewater. The approach included a detailed characterization of the wastewater effluent by treatment type, followed by fate-and-transport (and dilution) in the receiving body prior to its treatment at the DWTP, and ultimately assessing the amount of DBPs to form at the DWTP and in the distribution system. To predict DBP precursor levels in receiving bodies after wastewater treatment, several fate-and-transport models were developed and used. These models predicted the impact of biodegradation on DBP precursor levels in a river. The predicted influent water quality to the DWTP was then used with the USEPA's Water Treatment Plant (WTP) model to predict finished water concentrations for regulated DBPs (i.e., trihalomethanes [THMs] and haloacetic acids [HAAs]) in the plant effluent and in the distribution system. Cost curves were also developed for both DWTPs and WWTPs in ascribing the costs associated with different treatment types. The cost of improved treatment at the WWTP versus at the DWTP or a combination of the two in order to ensure compliance at the DWTP with the drinking water maximum contaminant levels (MCLs) with various upstream WWTP scenarios was evaluated. A CBA was performed that included the control of both halogenated DBPs (i.e., THMs, HAAs) as well a nonhalogenated DBP (i.e., N-nitrosodimethylamine [NDMA]). The CBA model was developed to address the following issues: level of wastewater treatment and its impact on the effluent water quality (i.e., effluent organic matter [EfOM]) of the WWTP; conveyance of DBP precursors from the WWTP to the DWTP (i.e., discharge into a receiving body and its dilution factor) and the impact of fate and transport (e.g., biodegradation) on the DBP precursors; type of treatment used at the DWTP (e.g., conventional or advanced treatment) and its effectiveness in removing DBP precursor (i.e., total organic carbon [TOC], ultraviolet absorbance [UVA], dissolved organic nitrogen [DON]) prior to disinfection at the DWTP; and, disinfection practices at the DWTP (i.e., chlorine and/or alternative disinfectants) and its impact on the type and quantity of DBPs formed at the DWTP and in th