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STABILITY OF ARSENIC AND SELENIUM IMMOBILIZED BY IN SITU MICROBIAL REDUCTION

A promising in situ remediation alternative for metal oxyanions such as arsenic, chromium, and selenium is microbial reduction to insoluble oxide, sulfide, or elemental phases. An important question that must be addressed before this technology can be implemented is the stability of these phases. This paper describes an investigation of the stability of reduced arsenic and sulfide precipitates produced by Desulfovibrio desulfuricans. The precipitates were first leached by the toxicity characteristic leaching procedure (TCLP), which demonstrated that the metal concentrations in the leachate are below the standards established by RCRA. A series of long-term leaching tests showed moderate release of the immobilized metals over a period of approximately 100 pore volumes, followed by very low leachability for at least 200 additional pore volumes. These results suggest that, although the metals may be slightly leachable, in an in situ immobilization process, their concentration would be below federal drinking water standards.