Development of chemical reduction and air stripping processes to remove mercury from wastewater

摘要

This study evaluates the removal of mercury from wastewater using chemical reduction and air stripping with a full-scale treatment system at the Savannah River Site. The existing water treatment system utilizes air stripping as the unit operation to remove organic compounds from groundwater that also contains mercury (C～250 ng/L). The baseline air stripping process was ineffective in removing mercury from the water that exceeded a proposed limit of 51 ng/L. To test an enhancement to the existing treatment modality a continuous dose of reducing agent was injected for 6 h at the inlet of the air stripper. This action resulted in the chemical reduction of mercury to Hg(0), a species that is removable with the existing unit operation. During the injection period a 94% decrease in concentration was observed and the effluent satisfied proposed limits. The process was optimized over a 2-day period by sequentially evaluating dose rates ranging from 0.64-297X stoichiometry. A minimum dose of 16X stoichiometry was necessary to initiate the reduction reaction that facilitated mercury removal. Competing electron acceptors likely inhibited the reaction at the lower doses, which prevented removal by air stripping. These results indicate that chemical reduction coupled with air stripping can effectively treat large volumes of water to emerging part-per-trillion regulatory standards for mercury.