AWWA ACE58301

The Southern California Water Company has conducted testing to simultaneously remove arsenic and manganese from groundwater at its Centralia plant south of Los Angeles. The testing was funded in part by the AWWA Research Foundation as a Tailored Collaboration. The project included bench- and pilot-scale process testing, design and construction of full-scale improvements, and full-scale trials to investigate the potential for chlorine and ferric chloride addition followed by filtration to simultaneously remove arsenic and manganese. Many wells in Southern California have been equipped with pressurized filters for manganese removal. However, the manganese removal process (oxidation/direct filtration) is not very effective for arsenic removal especially when iron concentration in the groundwater is low. There are several known treatment technologies for arsenic removal, including both conventional processes (e.g., coagulation/filtration and softening) and emerging technologies (e.g., coagulation assisted membrane processes and proprietary adsorbents). However, most all of them are not feasible for urban groundwater wells to address the particular arsenic/ manganese concern due to larger space requirements, multiple chemical handling, and high costs. Since many well sites in Southern California are adjacent to residential areas, a small footprint and minimum chemical usage are often required. The specific goals of the research were to answer the following key questions: will chlorine and ferric chloride addition followed by filtration simultaneously remove arsenic and manganese; what is the relationship between ferric chloride dose and filtered water arsenic concentration; how effectively will bench-testing estimate the required ferric chloride dose to achieve the target filtered water arsenic concentration; how effectively will pilot-testing estimate filtration design and operating parameters including filter run time; and, what are the optimal design and operating parameters to achieve the target finished water arsenic concentration with minimum water waste and sludge production? The following major tasks were performed to investigate arsenic and manganese removal: analysis of existing conditions; bench-scale testing; pilot-scale testing; design and construction of full-scale improvements; full-scale testing; and, data management and reports. Includes tables, figures.