AWWA WQTC60713

Many communities are, unknowingly, practicing indirect, unintentional reuse by relying on wastewater effluent impacted sources for drinking water. An immediate concern identified with reclaimed water as a drinking water source are the potential health impacts associated with bulk effluent organic matter (EfOM), measured as dissolved organic carbon (DOC), and trace organic compounds. The characteristics of the DOC in recycled wastewater are less understood than those in traditional drinking water sources. The main goal of this investigation was to characterize the DOC in an existing wastewater reuse system. Specifically, the investigation compared the concentrations of the three separate DOC fractions defined by size exclusion chromatography with on-line DOC detection (SEC-DOC), that included: high-molecular weight, polysaccharide or protein-like substances; humic-like substances; and, low molecular-weight acids. The wastewater reuse system investigated was a segment of the South Platte River near Denver, Colorado. The segment studied began at Chatfield Reservoir and continued downstream to the city of Thornton, Colorado. In between Chatfield Reservoir and Thornton, the largest single wastewater effluent (the Metro Wastewater Reclamation District Treatment Plant) discharges into the South Platte River. Overall, this study segment is an example of indirect, unintentional wastewater reuse, where samples from Chatfield Reservoir represent a water source unaffected by wastewater effluents and samples from the South Platte River at Thornton represent a water source affected by wastewater effluents. The resultant concentrations of each DOC fraction were significantly greater in the South Platte River at Thornton than in the Chatfield Reservoir. Between these two sampling points, the DOC concentrations increased by 59%, 59% and 34% for proteins and polysaccharides, humic substances, and low-molecular weight acids, respectively. This DOC increase suggests that drinking water treatment must be modified or optimized for removing larger quantities of each of these DOC fractions when treating effluent-affected sources similar to the South Platte River at Thornton, as opposed to sources unaffected by effluents. As examples, protein-like (nitrogenous) substances should be removed to avoid the formation of nitrogenous disinfection byproducts at a concentration that would be health hazardous, and polysaccharide-like substances should be removed before membrane treatment. In conclusion, the DOC in recycled wastewaters exhibits higher concentrations of proteins and polysaccharides, humic substance, and low-molecular weight acids than waters unaffected by wastewater effluents. Other analytical techniques including fluorescence excitation-emission matrices and DON measurements are discussed to further elucidate the SEC-DOC trends. Includes 23 references, tables, figures.