Economic co-production of cellulosic ethanol and microalgal biomass through efficient fixation of fermentation carbon dioxide

An integrated process for the co-production of cellulosic ethanol and microalgal biomass by fixing CO₂ generated from bioethanol fermentation is proposed. Specifically, over one-fifth of the fermentative carbon was converted into high-purity CO₂ during ethanol production. The optimal concentration of 4 % CO₂ was identified for the growth and metabolism of Chlorella sp. BWY-1. A multiple short-term intermittent CO₂ supply system was established to efficiently fix and recycle the waste CO₂. Using this system, economical co-production of cellulosic ethanol by Zymomonas mobilis and microalgal biomass in biogas slurry wastewater was achieved, resulting in the production of ethanol at a rate of 0.4 g/L/h and a fixed fermentation CO₂ of 3.1 g/L/d. Moreover, the amounts of algal biomass and chlorophyll a increased by over 50 % and two-fold, respectively. Through techno-economic analysis, the integrated process demonstrated its cost-effectiveness for cellulosic ethanol production. This study presents an innovative approach to a low-carbon circular bioeconomy.