A hybrid bioelectrochemical system coupling a zero-gap cell and a methanogenic reactor for carbon dioxide reduction using a wastewater-derived catholyte

Hybrid electrochemical and biological systems hold promise for pro-ducing valuable products from abundant feedstocks. An electro-lyzer-bioreactor assembly using wastewater streams as catholytes could bring bioelectrochemical methanogenesis closer to practical implementation. Herein, we develop a zero-gap cell with a porous transport layer in the cathode specifically conceptualized for oper-ating in line with a wastewater-fed methanogenic reactor. In-depth analysis of the electrode composition indicates an up to 4-fold vari-ation of the current density depending on the binder and carbon black contents. This electrolyzer configuration and electrode selection, along with a robust pentlandite-type cathode catalyst, Fe3Ni3Co3S8, allow for an efficient supply of hydrogen into the catholyte that recirculates through the bioreactor, which is domi-symbolscript symbolscript Methanobacterium symbolscript Methanobrevibacter symbolscript This hybrid system produces methane over 220 days with a maximal weekly average rate of 669 LN m-2cathode d-1. The corresponding average current density sustained by the entire hybrid system is 30 mA cm -2 at a 2.2 V set potential.

Automated summary

Hybrid electrochemical and biological systems using wastewater as the catholyte have the potential to bring bioelectrochemical methanogenesis closer to practical implementation. A zero-gap cell with a porous transport layer in the cathode is developed specifically for operating with a wastewater-fed methanogenic reactor. In-depth analysis of the electrode composition shows a significant variation in current density depending on the binder and carbon black contents. This hybrid system, equipped with a robust pentlandite-type cathode catalyst, Fe3Ni3Co3S8, produces methane over 220 days with a maximal weekly average rate of 669 LN m-2cathode d-1. The average current density sustained by the entire hybrid system is 30 mA cm -2 at a 2.2 V set potential.