Mutual benefits of acetate and mixed tungsten and molybdenum for their efficient removal in 40 L microbial electrolysis cells

Practical application of metallurgical microbial electrolysis cells (MECs) requires efficient removal of metals and organics in larger reactors. A 40 L cylindrical single-chamber MEC fed acetate was used to achieve high removals of W(VI) and Mo(VI). In the presence of both metals, there were nearly complete removals of W (97 ‒ 98%), Mo (98 ‒ 99%), and acetate (95 ‒ 96%), along with a low level of hydrogen production (0.0037–0.0039 L/L/d) at a hydraulic residence time (HRT) of 2 d (influent ratios of W:Mo:acetate of 0.5:1.0:24 mM). The final concentrations of these conditions were sufficient to meet national wastewater discharge standards. In the controls with individual metals or acetate, lower contaminant removals were obtained (W, 2 ‒ 4%; Mo, 3 ‒ 5%, acetate, 36 ‒ 39%). Metals removal in all cases was primarily due to the biocathodes rather than the bioanodes. The presence of metals decreased microbial diversity on the anodes and increased diversity on the cathodes, based on analysis at the phylum, class and genus levels, as a function of HRT and influent concentration. This study demonstrated the feasibility of larger-scale single-chamber MECs for efficient treatment of W and Mo, moving metallurgical MECs closer to commercialization for wastewater treatment of these two metals.