Microbial protein production from methane via electrochemical biogas upgrading

Microbial protein (MP) can alleviate the increasing pressure of food demand on agriculture and our environment. For its sustainable production, feedstocks such as biomethane or (bio)hydrogen are needed. Here, we coupled biogas produced from agricultural waste directly with electrochemical biogas upgrading to subsequently produce MP from methane, hydrogen or a mixture thereof. Biogas was produced from co-digestion of pumpkin and pig manure at production rates of 0.73 +/- 0.24 L-biogas L-reactor(-1) day(-1) (59% CH4) and 0.59 +/- 0.29 L-biogas L-reactor(-1) day(-1) (50% CH4). The biogas was directed to the cathode of an electrochemical cell. At current densities of 20 and 40 A m(-2), CO2 removal efficiencies of 88 +/- 14% and 99 +/- 1% were achieved. Enrichments of MP (hydrogen- and methane oxidizing bacterial cultures) were cultivated on either raw biogas or gases obtained from the cathode (CH4, CO2, H-2) and anode (CO2, O-2) in batch mode with external supplementation of O-2 and H-2 when required. The best performance was obtained when the cathode off-gas was used in terms of biomass concentration (0.585 g CDW L-1), yield (0.150 g CDW g(-1) COD), efficiency of COD conversion to protein (17%) volumetric biomass productivity (0.226 g CDW L-1 day(-1)) and volumetric protein productivity (0.181 g protein L-1 day(-1)). The protein content was similar when using anode and cathode off-gases (66.3 +/- 7.3% of CDW) with raw biogas resulting in a 6% lower protein content. This proof of concept demonstrated that electrochemical biogas upgrading enables steering MP production.