Recovery of volatile ethanol gas via microalgal-bacterial consortium: Ethanol-to-acetate conversion pathway boosts lipid production

Abstract

The pharmaceutical industry, an essential sector of the global economy, heavily relies on ethanol solvents, which leads to significant volatile organic compounds (VOCs) emissions. As a sustainable treatment method aligning with carbon reduction goals, this study proposed and demonstrated a synergistic approach of using microalgae (Chlorella sorokiniana FACHB-24) and acetic acid bacteria (Acetobacter pasteurianus CICC 20056) to recover ethanol into value-added products (algal lipids). In the innovative co-culture, A. pasteurianus oxidizes ethanol to acetic acid, which is fed to algae for lipid production. This method increased biomass and lipid yield by 21.29% and 150.16% (p < 0.05), respectively, compared to microalgae directly using ethanol. Some operational parameters including ethanol concentration, bacterial-algal biomass ratio, pH value, and light intensity made influence on lipid production. Under the optimal conditions (1.0% v/v ethanol concentration, 1:10 bacterial-algal biomass ratio, pH 6.5, and 5000 lux light intensity), the maximal biomass and lipid yields were 572.5 mg L⁻¹ and 161.1 mg L⁻¹ (26.7% lipid content), respectively. In the harvested lipid from microalgae, C16 - C18 fatty acids made up 98.22% of the total fatty acid methyl esters content. In proteomic comparison of the single culture and co-culture, the conversion of ethanol to acetate by A. pasteurianus provides C. sorokiniana with a more efficient acetyl-CoA source by bypassing energy-intensive glycolysis and directly enhancing lipid synthesis. This study provides a solution to increasing the lipid production from ethanol gas as a sustainable VOCs management of pharmaceutical industry.