Electro-cultivation of hydrogen-oxidizing bacteria to accumulate ammonium and carbon dioxide into protein-rich biomass

Abstract

Hydrogen-oxidizing bacteria (HOBs) are prime candidates for the sustainable production of microbial protein because of their high nutritional value and simple metabolic requirements, which could allow a simple resource recycling of NH4+ and CO2 into a valuable product. The modality of hydrogen production/supply to HOBs represents a challenge. In this work, bioelectrochemical hydrogen and oxygen productions were coupled with HOBs cultivation in the same reactor. Using this approach, the protein content was 59 ± 8% with Hydrogenophaga and Xanthobacter as the most abundant HOBs. Biomass concentration was found to be dependent of the current density with bulk liquid biomass increasing between 101 and 124 mg TSS·L−1 for an increase of 0.1 mA·cm−2. Electrodes directly immersed in the bioreactor promoted biofilm formation on the electrode surface, which could become an attractive alternative for biomass harvesting. The results of this work establish a novel proof-of-concept for bio-electro production of microbial protein.