Monday, November 13, 2006 - 3:00 PM

Effects of Solution Properties on Arsenic Immobilization in Drinking Water Treatment Residuals-Amended Soils: Incubation Study.

Rachana Nagar, Dibyendu Sarkar, Konstantinos Makris, and Rupali Datta. Univ of Texas, 6900 N. Loop 1604 West, San Antonio, TX 78249

Recent studies have shown that drinking water treatment residuals (WTRs) effectively immobilize arsenic (As) in soils, but detailed studies focusing on the effects of soil solution properties on As immobilization in WTR-amended soils are yet to be reported. We hypothesized that contact time, solution pH, ionic strength, complexing metals (e.g., calcium), and competing ligands (e.g., phosphate, sulfate) could influence the overall effectiveness of WTRs in immobilizing As in soils. A batch incubation study was set up with a sandy soil (from Immokalee series) that was amended with different rates (0, 2.5, 5 and 10%) of two WTRs (Al- and Fe-based) and equilibrated for 7 days. Moisture content was maintained at 70%. Arsenic adsorption was monitored as a function of pH (3 to 9). Five initial arsenic concentrations (1 ppm, 25 ppm, 375ppm, 750 ppm and 1500 ppm) from sodium arsenate were used in the presence of competing ligands and complexing metals by considering their typical concentrations encountered in the agricultural runoffs. Preliminary results indicate that solution properties significantly influence arsenic adsorption by Immokalee soil amended with both WTRs.

Key words: Drinking-water treatment residuals, arsenic, immobilization, competing ligands, complexing metals.