The invention provides for the integration of a CO-consuming process, such as a gas fermentation process, with a CO2 electrolysis process. The invention is capable of utilizing a CO2-comprising gaseous substrate generated by an industrial process and provides for one or more removal modules to remove at least one constituent from a CO2-comprising gaseous substrate prior to passage of the gaseous substrate to a CO2 electrolysis module. The invention may further comprise one or more pressure modules, one or more CO2 concentration modules, one or more O2 separation modules, and/or an H2 electrolysis module. Carbon conversion efficiency is increased by recycling CO2 produced by a CO-consuming process to the CO2 electrolysis process.