From sewage sludge to microbial protein: the role of H2S- and CO- tolerant hydrogen-oxidizing bacteria in syngas aerobic fermentation

The aerobic fermentation of syngas, generated through the pyrolysis of municipal sewage sludge, for the purpose of producing value-added products like microbial protein (MP), holds the potential to open new horizons in biorefinery approaches for wastewater treatment plants. In this regard, this study aimed to investigate the capability of a mixed community of hydrogen-oxidizing bacteria (HOB) to convert a synthetic syngas with varying H2/CO2 ratios, along with increasing concentrations of H2S and CO, into MP. Remarkably, no inhibition of the enriched HOB culture within H2/CO2 ratios ranging from 2 to 10, H2S concentrations up to 0.4%, and CO concentrations up to 40%, was observed. Moreover, this process exhibited consistent performance over an extended period of 30 days and resulted in the production of MP containing as much as 65% protein content in biomass.