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Nanofiltration (NF) is a promising drinking water treatment technology for arsenic removal; however, most of the research on NF treatment of arsenic has used synthetic water. In this investigation, a pilot membrane system treated groundwater naturally contaminated with arsenic to test the performance of two NF membranes and one reverse osmosis (RO) membrane, both with and without oxidizing pretreatment using manganese dioxide (MnO2). The arsenic concentration in the groundwater was ~ 40 μg/L, mostly present as arsenite, a neutral species. Without the oxidizing pretreatment, the two NF membranes provided almost no removal whereas the RO membrane provided ~ 25 to 50% arsenic removal, depending on operating conditions. Following pretreatment with MnO2, the treated arsenic concentration dropped to < 4 μg/L (90% removal) for all three membranes. The substantially improved performance for these negatively charged membranes was attributed to the oxidation of the neutrally charged arsenite to negatively charged arsenate. These results indicate that where arsenite is present, facilities with RO or NF processes can dramatically enhance their arsenic removal by adding a membrane‐compatible oxidation step such as MnO2 filtration.

This article discusses problems with the pretreatment system at the Tampa Bay Seawater Desalination Facility. Currently the plant uses a two‐stage dual sand filtration pretreatment system to remove turbidity, algae, organic material, and other particulate matter from the incoming raw seawater and ensure optimum performance of the plant's reverse osmosis (RO) system. The manufacturer's recommended silt density index (SDI) for the RO membranes is typically < 4; however, the current pretreatment has not been able to consistently meet these parameters to protect the RO system. As a result, the RO membranes foul too quickly, and the plant cannot achieve peak water production. The desalination plant also faces more frequent cleaning of the RO membranes, significantly increased operating costs through higher energy consumption, increased chemical usage for cleaning, and more frequent RO membrane replacement. Moreover, the plant only operates intermittently and produces less drinking water than it is designed to deliver. The article discusses the selection of ultrafiltration (UF) membranes as the solution, specifically Veolia Water North America's bid for ZeeWeed membranes, and explains the benefits of ZeeWeed membranes in a RO system.