Evaluation of low cost cathode materials for treatment of industrial and food processing wastewater using microbial electrolysis cells

Microbial electrolysis cells (MECs) can be used to treat wastewater and produce hydrogen gas, but low cost cathode catalysts are needed to make this approach economical. Molybdenum disulfide (MoS₂) and stainless steel (SS) were evaluated as alternative cathode catalysts to platinum (Pt) in terms of treatment efficiency and energy recovery using actual wastewaters. Two different types of wastewaters were examined, a methanol-rich industrial (IN) wastewater and a food processing (FP) wastewater. The use of the MoS₂ catalyst generally resulted in better performance than the SS cathodes for both wastewaters, although the use of the Pt catalyst provided the best performance in terms of biogas production, current density, and TCOD removal. Overall, the wastewater composition was more of a factor than catalyst type for accomplishing overall treatment. The IN wastewater had higher biogas production rates (0.8–1.8 m³/m³-d), and COD removal rates (1.8–2.8 kg-COD/m³-d) than the FP wastewater. The overall energy recoveries were positive for the IN wastewater (3.1–3.8 kWh/kg-COD removed), while the FP wastewater required a net energy input of −0.7–−1.2 kWh/kg-COD using MoS₂ or Pt cathodes, and −3.1 kWh/kg-COD with SS. These results suggest that MoS₂ is the most suitable alternative to Pt as a cathode catalyst for wastewater treatment using MECs, but that net energy recovery will be highly dependent on the specific wastewater.