| Microbial electrolysis cells (MECs) is one new promising and environmental friendly method for efficient wastes and wastewaters removal with requirement of a small amount of energy input. Biocathodes, which use bacteria as biocatalysts to accept electrons from the cathode substratum, provide a different path that both avoids the use of noble catalysts and enables the use of alternative electron acceptors, and thus expands the scope of applicable MECs. Despite removal of recalcitrant substrates such as Cr(VI), nitrobenzene and chlorophenol in biocathode MECs, removal of Cd(II) in biocathode MECs has not previously been investigated.Biocathodes developed at 0.3 V exhibited a lower Cd(II) removal than those at 0.5 V,0.7 V and 1.0 V, among which less differences were observed each other. A switch from 0.5 V to 1.0 V achieved a Cd(II) removal of 93.0 ± 2.7%, an improvement of 34.4% compared to the original 0.5 V and similar to the previous 1.0 V. In addition, a switch from 0.3 V to 1.0 V reasonably improved Cd(II) removal to 75.3 ± 2.6%, an improvement of 69.4% compared to that at previous 0.3 V, but led to a diminishment of 14.8% in Cd(II) removal in comparison with that at original 1.0 V. Compared to an inorganic carbon source of NaHCO3 and at a low initial Cd(II) concentration of 20 mg/L, carbon source of acetate enhanced Cd(II) removal (a 20.0% improvement) and had less effects on hydrogen evolution. However, acetate achieved a Cd(II) removal of 59.9 ± 2.3% and hydrogen production of 0.21 ± 0.03 m3/m3/d at a high initial Cd(II) concentration of 60 mg/L, higher than 49.7 ± 1.8% and 0.01 ± 0.00 m3/m3/d with NaHCO3 at the same initial Cd(II) concentration, mainly ascribed to a higher bacterial growth in the former. These results demonstrate the preferable acetate as one carbon source for efficiently removing Cd(II) at high concentrations with simultaneous hydrogen generation in the biocathode MECs. |
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