Chemical Treatment for Arsenic Removal from Full-Scale High-Pressure Membrane Concentrates

摘要

This paper presents results from the final phase of an on-going study exploringchemical treatment of high-pressure membrane concentrate, specifically the removal ofarsenic by adsorption to iron solids followed by solid-liquid separation. Concentratereceived from two brackish water reverse osmosis plants located in California andFlorida, respectively, were spiked with arsenate to approximately 500 ppb as As. Arsenicremoval was determined experimentally using small volume jar test procedures. Afteriron addition (as ferric chloride), the test solutions were rapidly mixed for a short timefollowed by a longer period of mixing at a slower rate. After mixing, solids formedduring treatment were separated from solution using a 0.22 μm pore size filter.Levels of arsenic, natural organic matter (as dissolved organic carbon), UV254absorbance, and iron in the raw and treated waters are reported as a function of iron doseand final pH. The effect of pH on arsenic removal by adsorption to in-situ precipitatediron hydroxide is discussed. Arsenic removal from the full-scale residuals is alsocompared with removal from simpler model concentrates made in the laboratory.