Selenate is a contaminant in aqueous systems such as industrial wastewater and agricultural drainage. Many studies have shown that selenate can be chemically or biologically reduced to elemental selenium, which can be further removed from the aqueous systems, but the application of this approach in water and wastewater treatment has been very limited due to its high cost. To reduce the cost, this study recovered elemental selenium and generated electricity while removing selenate from a synthetic selenate-contaminated water in a two-chamber microbial fuel cell. With acetate as the electron donor in the bioanodic chamber, selenate in the biocathodic chamber was removed from 2 to below 0.02 mg Se/L in the continuous flow reactor at a surface loading rate of 50 mg-Se/m2-day, which is comparable to the median loading rate in conventional biofilm reactors. The intermediate selenite accumulated momentarily and disappeared during steady state operation. Only extracellular elemental selenium nanoparticles were produced, which eliminated the need to separate intracellular elemental selenium nanoparticles as in the conventional biofilm reactors. 16s rRNA gene sequencing analysis showed that the microbial community on the biocathode was dominated by Comamonas sp., which is known to reduce selenate to extracellular elemental selenium nanoparticles. About 87% of the elemental selenium in the effluent was recovered by gradient centrifugation. The effects of flow rate and selenate concentration on reactor performance was also investigated. The maximum selenate removal flux achieved was 1,090 mg-Se/m2-day, which is comparable to the maximum flux reported for conventional biofilm reactors. The current density during steady state was 14 mA/m2. Replacement of cation exchange membrane after 27 days enhanced the current density by 56%. Scanning electron microscopic study of the replaced cation exchange membrane revealed biofouling that probably caused the lower power density. Thus, regular replacement or cleaning of cation exchange membrane would improve selenate reduction, elemental selenium production, and electricity generation.

Simultaneous selenate removal, elemental selenium recovery and electricity generation by a biocathode microbial fuel cell

2019 Spring National Meeting

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