AWWA ACE62969

To meet the requirements of the Stage 2 Disinfection Byproducts Rule (DBPR), removal of disinfection byproduct (DBP) precursor materials must be improved at the water treatment facilities owned and operated by the Cobb County-Marietta Water Authority (CCMWA). CDM has been working with the Authority since 2002, investigating alternative treatment technologies to reduce DBP precursors at the Hugh A. Wyckoff Water Treatment Plant (WTP). The study was conducted at this plant since it is the facility that provides water to CCMWA's most remote customers and will be most influenced by the new DBP regulations. The purpose of the granular activated carbon (GAC) filtration pilot study was to determine whether GAC adsorption is a technically and economically feasible solution to enable the Wyckoff WTP to comply with the upcoming Stage 2 DBPR. Technical suitability was determined by comparing the DBP formation potential (DBPFP) observed in the GAC treated water with the treatment goals, while economic suitability was determined by monitoring the total organic carbon (TOC) and DBPFP breakthrough during the course of the study to determine the required frequency of GAC replacement and regeneration. At the Wyckoff WTP, GAC could be utilized as an organic precursor adsorber by replacing the existing anthracite media in the filters with GAC or by constructing post-filter GAC contactors. The objectives of the filter adsorber study included the following: determine the TOC and DBPFP reduction in a 30-inch deep GAC filter bed with an empty bed contact time (EBCT) of 4.6 minutes (note that 4.6 minutes is the EBCT at the plant's average summer filtration rate of 4.5 gpm/sf); estimate the breakthrough time for TOC and DBPFP in the 30-inch filter adsorber with an EBCT of 4.6 minutes; determine the impact on manganese removal in the absence of a chlorine residual across the GAC filter beds; and, evaluate performance difference between bituminous and lignite based GAC. The objectives of the post-filter GAC contactor study included the following: determine the TOC and DBPFP reduction in post-filter GAC contactors operating at two different EBCTs; estimate the breakthrough time for TOC and DBPFP at two different EBCTs; and, estimate the capital and O&M cost associated with post-filter GAC contactors. Testing strategy, treatment goals, GAC filter adsorbers, design implications of pilot results, key process design considerations, preliminary design criteria, and cost estimate are all discussed. Includes 2 references, tables, figures.