Effect of Natural Organic Matter On Arsenic Removal From Drinking Water.

Arsenic contamination in water is a worldwide concern because of its toxicity and carcinogenicity. Arsenic exists in water primarily as arsenite (As(III)) and arsenate (As(V)). As(III) is more toxic and difficult to remove from water than As(V). In our previous studies we found that combined use of Fe(VI) and Al(III) salts were efficient in removing arsenite below the drinking water standard of 10 µg L^-1. Natural organic matter, a prevalent constituent of natural waters, interacts strongly with arsenic, influencing its speciation and mobility in aquatic environments. The objective of this study was to evaluate the effect of natural organic matter on arsenite removal by Fe(VI) and Al(III) salts. Six different types of NOM (Suwannee River NOM, Nordic Reservoir NOM, Suwannee River fulvic acid, Suwannee River humic acid, Pahokee Peat humic acid and Aldrich humic acid) were used in this study.  The solutions of NOM samples were prepared by dissolving them into deionized water and filtered through a 0.45 µm filter membrane.  The dissolved organic carbon concentration in the stock solutions was determined using a Shimadzu 6001 TOC Analyzer. Experiments were conducted by adding 20 µM of Fe(VI) and varied amount of AlCl₃ (20-127 µM) to the arsenite solution (6.7 µM) containing dissolved organic carbon in the range1-20 mg C L^-1. The pH of the samples was adjusted to 6.5.  After 24 h of equilibration, the samples were filtered using 0.2 µm filter membranes. Arsenic was analyzed by atomic absorption spectrometer using hydride generation technique.  The results indicated that DOC at concentration >2 mg C L^-1 had a detrimental impact on arsenic removal from water. At 4 mg C L^-1, arsenite removal decreased from 99.8% (without C) to 60%, 68%, and 74% with SWNOM, NRNOM, and HA, respectively.  Further experiments are under way and the results will be discussed during presentation.