Preferable utilization of in-situ produced H2O2 rather than externally added for efficient deposition of tungsten and molybdenum in microbial fuel cells

Recent advances in the recovery of metals from waste through biological processes

Wastes containing critical metals are generated in various fields, such as energy and computer manufacturing. Metal-bearing wastes are considered as secondary sources of critical metals. The conventional physicochemical methods of metals recovery are energy-intensive and cause further pollution. Low-cost and eco-friendly technologies including biosorbents, bioelectrochemical systems (BESs), bioleaching, and biomineralization, have become alternatives in the recovery of critical metals. However, a relatively low recovery rate and selectivity severely hinder their large-scale applications. Researchers have expanded their focus to exploit novel strain resources and strategies to improve the biorecovery efficiency. The mechanisms and potential applicability of modified biological techniques for improving the recovery of critical metals need more attention. Hence, this review summarize and compare the strategies that have been developed for critical metals recovery, and provides useful insights for energy-efficient recovery of critical metals in future industrial applications.

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.

Deposition and separation of W and Mo from aqueous solutions with simultaneous hydrogen production in stacked bioelectrochemical systems (BESs): Impact of heavy metals W(VI)/Mo(VI) molar ratio, initial pH and electrode material

The deposition and separation of W and Mo from aqueous solutions with simultaneous hydrogen production was investigated in stacked bioelectrochemical systems (BESs) composed of microbial electrolysis cell (1#) serially connected with parallel connected microbial fuel cell (2#). The impact of W/Mo molar ratio (in the range 0.01 mM : 1 mM and vice-versa), initial pH (1.5 to 4.0) and cathode material (stainless steel mesh (SSM), carbon rod (CR) and titanium sheet (TS)) on the BES performance was systematically investigated. The concentration of Mo(VI) was more influential than W(VI) in determining the rate of deposition of both metals and the rate of hydrogen production. Complete metal recovery was achieved at equimolar W/Mo ratio of 0.05 mM : 0.05 mM. The rates of metal deposition and hydrogen production increased at acidic pH, with the fastest rates at pH 1.5. The morphology of the metal deposits and the valence of the Mo were correlated with W/Mo ratio and pH. CR cathodes (2#) coupled with SSM cathodes (1#) achieved a significant rate of hydrogen production (0.82 ± 0.04 m³/m³/d) with W and Mo deposition (0.049 ± 0.003 mmol/L/h and 0.140 ± 0.004 mmol/L/h (1#); 0.025 ± 0.001 mmol/L/h and 0.090 ± 0.006 mmol/L/h (2#)).