Two-stage valorization of glycol-based waste fluids via Yarrowia lipolytica bioconversion and biomethane production

Coolant waste containing propylene glycol (PG) and ethylene glycol (EG) is a growing environmental problem requiring innovative disposal methods. This study presents a novel approach to the biological valorization of these hazardous wastes using the yeast Yarrowia lipolytica . The growth kinetics analysis revealed that Y. lipolytica catabolizes both glycols (q_S = 0.19 g g −1 ·h −1 ; ∼6% of glycol-C recovered in biomass), achieving complete substrate depletion within 144 h of cultivation. The yeast biomass obtained was then used as a substrate in the anaerobic fermentation process, generating a high biomethane production yield of 400 mL g VS −1 after 21 days, which is 2.67 times higher than the fermentation of the coolant alone (150 mL g VS −1 ). The developed two-stage valorization strategy, involving the bioconversion of waste glycols into yeast biomass and its subsequent use for biomethane production, represents a comprehensive solution in line with the principles of the circular economy, combining hazardous waste management with renewable energy production.