AWWA ACE99418

To prevent the formation of disinfection byproducts (DBPs), the US Environmental Protection Agency has introduced a two stage Disinfectants-Disinfection Byproduct rule (D/DBPR). Stage 1, finalized in November of 1998, established the maximum contaminant level for total trihalomethanes (TTHMs) and for five haloacetic acids (HAA5). Stage 2 follows, which is anticipated to set lower contaminant levels for TTHMs and HAA5, respectively. Enhanced coagulation has been identified as the best available technology for meeting the requirements of the D/DBP Stage 1 Rule for Total Organic Carbon (TOC) reduction and the removal of disinfection byproduct precursors. With enhanced coagulation, natural organic matter (NOM), color and TOC reduction is achieved using a higher coagulant dosage than would be utilized for turbidity removal. The pH of the raw water is also commonly optimized to maximize process efficiency. The application of immersed ultrafiltration membranes using enhanced coagulation has recently been developed and applied for disinfection byproduct precursor, color and TOC removal for drinking water applications. With this process, a single tank coagulation-ultrafiltration process replaces the coagulation-flocculation-sedimentation-filtration stages of a conventional treatment plant. Powdered activated carbon (PAC) can also be used in combination with enhanced coagulation, or alone to reduce disinfectant byproduct precursors by addition to the rapid mix stage upstream of the ultrafiltration membranes. Compared to conventional treatment, this method of water treatment results in higher color and TOC removal and requires less coagulant and PAC. The use of lower chemical dosage results in significantly less treatment residuals and reduced disposal costs. The system also has a small footprint since it is designed with a shorter hydraulic retention time as it is only necessary to form a floc that exceeds the membrane pore size.