Combined microbial electrolysis cell–iron-air battery system for hydrogen production and swine wastewater treatment

Swine wastewater is a typical high-strength animal wastewater. For treatment, it often requires combined processes (i.e., integrated units), such as multiple anaerobic reactors and advanced treatments. Microbial electrolysis cells (MECs) are a promising technology for wastewater treatment and simultaneous hydrogen harvesting. In this study, we constructed a MEC powered by an iron-air battery to treat swine wastewater and produce hydrogen efficiently. The performance of iron-air batteries with different electrolyte concentrations was compared in terms of coagulant production and power generation. The highest coagulation performance was obtained with coagulants generated using a battery with 35 g/L NaCl, which achieved 54 % ± 3%, 27 % ± 2%, 49 % ± 1%, and 34 % ± 3% removal of ammonia, chemical oxygen demand (COD), suspended solids (SS) and turbidity, respectively. Powered by the iron-air battery with 35 g/L NaCl, the hydrogen generation rate of MEC reached approximately 6 L/m3·d using raw swine wastewater and 57 L/m3·d using coagulated swine wastewater. The reduction of organics by coagulating helped improve hydrogen production. The total COD removal by the coagulation process integrated with MEC reached 98 % ± 0.2 %. The iron-air battery–MEC system is a promising method for simultaneous hydrogen production and wastewater treatment without any additional energy input.