AWWA ACE63218

In addition to water recycling and reclamation programs, indirect potable reuse of wastewater has occurred over the past few decades, which will likely increase in the future as upstream wastewater treatment plants (WWTPs) discharge water into rivers or lakes that serve as downstream drinking water supplies. 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. Biological wastewater treatment takes one of two general forms: suspended growth (biofloc) systems (e.g., activated sludge); and, attached growth (biofilm) systems (e.g., trickling filter). Depending on operational conditions, both can operate as partial or complete nitrifying processes. Increased levels of nitrification decrease the concentrations of ammonia and organic nitrogen (amino) compounds. Nitrification transforms ammonia and organic nitrogen to nitrate. Suspended growth systems under anoxic conditions can denitrify (convert nitrate primarily to nitrogen gas). Treated wastewater has been shown to be a source of precursors for a wide range of DBPs (trihalomethanes [THMs], haloacetic acids [HAAs], haloacetonitriles [HANs], and nitrosamines). The objective of this study was to evaluate the contribution of treated wastewater to DBP formation in drinking water supplies, including an examination of seasonal impacts. Methods included a survey of approximately 20 WWTPs in the U.S. that used a range of treatment processes (oxidation ditch, aerated lagoon, trickling filters, activated sludge, nitrification/denitrification, soil aquifer treatment, membranes, or various combinations). For most of the study sites, samples were collected at the WWTPs and downstream DWTPs, effluent-impacted rivers or monitoring wells. Samples were collected during a wet/cold season and a dry/warm season in 2004, and once more in a second year (2005). The two sampling events in year 1 were based on hydrology and treatment considerations. These two seasons showed the different impacts of hydrology and treatment. In year 2, many of the utilities were re-sampled in the season that provided especially informative data for that system to ascertain temporal (year-to-year) variations. The samples were analyzed for ammonia, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and DBP precursors. Selected WWTP samples were analyzed for total Kjeldahl nitrogen (TKN), which consists of organic nitrogen in a -3 oxidation state (i.e., amino nitrogen) and ammonia. DBP precursors were measured using formation potential (FP) tests. The anti-convulsant pharmaceutical primidone was measured, as it is a conservative tracer (indicator) of wastewater influences in drinking water supplies. Includes 4 references, tables, figures.