Single-cell protein production from CO₂ and electricity with a recirculating anaerobic-aerobic bioprocess

Microbial electrosynthesis (MES) represents a promising approach for converting CO₂ into organic chemicals. However, its industrial application is hindered by low-value products, such as acetate and methane, and insufficient productivity. To address these limitations, coupling acetate production via MES with microbial upgrading to higher-value compounds offers a viable solution. Here we show an integrated reactor that recirculates a cell-free medium between an MES reactor hosting anaerobic homoacetogens (Acetobacterium) and a continuously stirred tank bioreactor hosting aerobic acetate-utilizing bacteria (Alcaligenes) for efficient single-cell protein (SCP) production from CO₂ and electricity. The reactor achieved a maximum cell dry weight (CDW) of 17.4 g L^-1, with an average production rate of 1.5 g L^-1 d^-1. The protein content of the biomass reached 74% of the dry weight. Moreover, the integrated design significantly reduced wastewater generation, mitigated product inhibition, and enhanced SCP production. These results demonstrate the potential of this integrated reactor for the efficient and sustainable production of high-value bioproducts from CO₂ and electricity using acetate as a key intermediate.