Synergistic effects of domestic wastewater sludge and leachate on medium-chain fatty acid production

Landfill leachate and liquid sewage sludge (LS) are two major waste steams generated from solid and liquid waste management processes. Both contain medium chain fatty acids (MCAFs), which are valuable as low-cost feedstocks for bio-based chemicals and lubricant. This study explores the potential of co-fermenting leachate and LS for enhance MCFA production. Two types of leachates (young and old) were used, alongside LS sourced from the decanter tank of a wastewater treatment plant. Leachate and LS were mixed at two ratios (50:50 and 75:25), with ethanol (E) serving as an electron donor under controlled pH and temperature conditions. The results demonstrated that MCFA production was significantly influenced by the age of the leachate and the (leachate: LS) ratio. Notably, the 50:50 mixture showed continuous increases in MCFA production over time. Principal component analysis (PCA) further revealed that young leachate (YL) was the most effective substrate for MCFA elongation, offering the highest acid production and extraction potential. These findings suggest that the co-fermentation of leachate and LS, particularly with young leachate, presents a promising method for MCFA production, supporting waste valorization and sustainable bio-based chemical production. • Producing MCFAs from sludge and leachate is an innovative carbon recovery method. • Using decanter sludge improves MCFA yield and quality with leachate co-substrate. • Leachate age and sludge mix ratios strongly affect chain elongation behavior. • COD and pH tracking give key insights into chain elongation and feedstock status. • Heavy metals and retention time effects need more study for chain elongation.