Many treatment approaches have been developed to remove arsenic from drinking water sources around the world. However, these create arsenic-bearing wastes, which must be managed to reduce human exposure and potential re-contamination of source waters. Concrete stabilization for arsenic-bearing wastes has recently received attention, based on its potential for use in buildings and road construction. While research has shown concrete stabilization can minimize arsenic leaching as measured by the US EPA Toxicity Characteristic Leaching Procedure (TCLP), arsenic stability under environmental conditions relevant to the use of arsenic-containing concrete in roads and buildings has not been studied. This investigation focuses on two environmental factors likely to impact arsenic release from concrete stabilized waste: carbonation and microbial activity. Carbonation, in which calcium hydroxide is converted to calcium carbonate through exposure to carbon dioxide, occurs when concrete is subjected to wetting and drying cycles. During these cycles, arsenic speciation within the concrete and its leaching potential may be impacted.  Microbial activity may also impact arsenic release from concrete by changing redox and pH conditions, especially in regions where seasonal flooding occurs and there is sufficient organic carbon for microbial growth. In this study, long-term simulations of concrete containing arsenic-bearing waste are being conducted to evaluate arsenic release from simulated rainwater with varying levels of carbonation (with and without wetting and drying) and microbial activity (with and without organic carbon). Aqueous concentrations of arsenic and calcium leached over time are compared with TCLP results. X-ray diffraction is used to quantify the extent of carbonation by determining relative amounts of calcium hydroxide and calcium carbonate in the concrete. Microbial arsenic transforming genes (for arsenate reduction, arsenite oxidation, and arsenic methylation) are measured using quantitative PCR (qPCR). Results from these experiments will be useful in minimizing arsenic release during the use of concrete containing arsenic-bearing wastes.

Assessing chemical and microbial processes affecting arsenic stability in concrete containing arsenic-bearing wastes from drinking water treatment

246th National Meeting (2013)

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