Influence of Natural Organic Matter on the Arsenic Removal from Drinking Water By Ferric and Aluminum Salts.

Arsenic is a highly toxic and carcinogenic element which has been found in elevated concentrations in groundwater worldwide including USA.  The arsenic removal from drinking water is usually performed by coagulation with ferric salts or alum followed by filtration.  However, the removal efficiencies of these methods vary depending on the presence of other substances in the water.  Natural organic matter which is ubiquitous in natural waters adversely affects the removal of arsenic by ferric salts.  The present study was undertaken to evaluate the effect of natural organic matter on arsenic removal by ferric and aluminum salts under similar experimental conditions.  Suwannee River Natural Organic Matter (SRNOM) used in this study, was obtained from the International Humic Substance Society (University of Minnesota, St. Paul, MN).  The batch experiments were conducted in duplicate with a background electrolyte of 0.01 M NaCl solution containing 500 µg L^-1 arsenate (6.67 µM) and various concentrations of SRNOM (1, 2, 4, and 8 mg C L^-1) .  To this solution ferric chloride or aluminum chloride solution (72 µM Fe or Al) was added and the pH was adjusted to the desired value. The samples were equilibrated on a rotatory shaker for 24 h and filtered using 0.20 µm pore size nylon membrane filters.  The filtered samples were analyzed for Fe, Al, and As concentrations using ICP-OES, Perkin-Elmer and for dissolved organic carbon using TOC-V analyzer, Shimadzu.  The similar experiments were also conducted at various pHs ranging from 5.5 to 8.5 and at various iron and aluminum concentrations.  The results indicated that aluminum chloride was more effective than ferric chloride to remove arsenic from water in the presence of natural organic matter.  In order to understand the removal mechanism, FT-IR spectra and atomic fluorescence spectra are being obtained and the results will be presented at the meeting.