Arsenic (As+3) Removal by Standard & High- Rejection RO Membranes and Oxidation to As+5 Prior to RO

Arsenic (As) is present in several of the wells that El Paso Water Utilities (EPWU) uses as part of the drinking water supply. EPWU has several wells that are equipped with reverse osmosis (RO) systems for desalting brackish groundwater. This process is referred to as Wellhead RO. At most of the wells, the RO membranes do an excellent job of rejecting As, but at one of the well sites, As rejection is less than 40%. Several techniques were investigated for removing the As, including new standard RO membranes, high-rejection (HR) RO membranes, and oxidation of As followed by standard membrane treatment. This paper presents the results obtained from pilot testing the standard and HR membranes, pilot testing of arsenic oxidation by chlorine and hydrogen peroxide, and full-scale implementation of a prechlorination/dechlorination process for arsenic oxidation prior to treatment in a reverse osmosis treatment system.