AWWA WQTC69443

This paper presents results from the final phase of an on-going study exploring chemical treatment of high-pressure membrane concentrate, specifically the removal of arsenic by adsorption to iron solids followed by solid-liquid separation. Concentrate received from two brackish water reverse osmosis plants located in California and Florida, respectively, were spiked with arsenate to approximately 500 ppb as As. Arsenic removal was determined experimentally using small volume jar test procedures. After iron addition (as ferric chloride), the test solutions were rapidly mixed for a short time followed by a longer period of mixing at a slower rate. After mixing, solids formed during treatment were separated from solution using a 0.22 mm pore size filter. Levels of arsenic, natural organic matter (as dissolved organic carbon), UV254 absorbance, and iron in the raw and treated waters are reported as a function of iron dose and final pH. The effect of pH on arsenic removal by adsorption to in situ precipitated iron hydroxide is discussed. Arsenic removal from the full-scale residuals is also compared with removal from simpler model concentrates made in the laboratory. Includes 2 references, tables, figures.