Michael Hardy1, Konstantinos C. Makris1, Dibyendu Sarkar1, and Rupali Datta2. (1) University of Texas at San Antonio, One UTSA Circle, Dept of Earth and Environmental Science, San Antonio, TX 78249, (2) Earth and Environmental Sciences, University of Texas at San Antonio, one utsa circle, San Antonio, TX 78256
Ecological problems associated with hexavalent chromium have been on the rise since the advent of the chromium-based industry. Chromium remediation is a significant problem in many industrial sites—especially shipyards, where chromium is used in the painting and plating processes. While there are a wide variety of remediation techniques, this study evaluates the effectiveness of using a waste by-product—drinking water treatment residuals or WTRs—as a sorbent to remove chromium(VI) from stormwater runoff in industrial sites. Drinking WTRs can be obtained free of charge from drinking-water treatment plants, and they have already been shown to have a high capacity for removing both arsenic and phosphate from water, which behave similarly to chromium. Two WTRs were used in this experiment (one Fe and one Al based) to evaluate the adsorption/desorption kinetics of chromium with WTRs. Both WTRs showed a capacity to irreversibly adsorb large amounts of chromium. In studies involving stock solutions of Cr(VI) in 0.005 M NaCl and in simulated stormwater, both WTRs were able to remove more than 90% out of an initial load of 500 mg/kg Cr(VI) after 24 hours at a ratio of 1:5 (g WTR: mL solution). When desorption was induced using phosphate as a competing ion, the Al-WTR desorbed approximately 2–7 % of previously sorbed chromium, while the Fe-WTR desorbed only negligible amounts of Cr(VI). Different factors such as pH, competing ions, reaction times, and solid:solution ratios were also evaluated to determine their effect on sorption capacity and kinetics. Overall, results for both the Fe and the Al-WTRs demonstrated the ability to irreversibly retain Cr(VI) that could lead to the possible development of a new remediation technique for chromium.