Constraints on the Efficiency of Engineered Electromicrobial Production

Electromicrobial production aims to combine electricity and microbial metabolism for solar and electrical energy storage. We have constructed molecule to reactor models of highly engineered electromicrobial production systems that use H-2 oxidation and direct electron transfer (DET). We predict electrical-to-biofuel conversion efficiency could rise to 52% with engineered in vivo CO2 fixation. H-2 diffusion at ambient pressure requires areas 20 to 2,000 times the solar photovoltaic (PV) area supplying the system. Agitation can reduce this below the PV area, and the power needed is negligible when storing >= 1.1 megawatts. DET systems can be built with areas <= 15 times the PV area and have low energy losses even with natural conductive biofilms and can be even smaller if the conductivity could be raised to match conductive artificial polymers. Schemes that use electrochemical CO2 reduction could achieve efficiencies of almost 50% with no complications of O-2 sensitivity.