Biomethane upgrading from dairy wastes via microbial cell-to-cell signaling molecules

Anaerobic digestion (AD) of wastewater treatment plant (WWTP) sludge is commonly practiced but often yields suboptimal methane production due to substrate limitations. This study explores a novel strategy to enhance biogas and methane production by co-digesting WWTP sewage sludge with a lipid-rich residue from cheese factory wastewater treatment plant —dairy waste greases— and stimulating microbial activity using the quorum sensing (QS) molecule N-dodecanoyl-L-homoserine lactone (12-HSL). An 80:20 ratio of sewage sludge to grease achieved high biogas volume (700 NmL CH4 /g VS ) with ∼70 % methane content. The addition of 12-HSL significantly boosted methane production, with the most pronounced effect (38 % increase in methane yield and 33 % in biogas volume) observed when applied on day 4 of digestion. Metagenomic analysis revealed that 12-HSL modulated the microbial community, enriching key hydrolytic and methanogenic populations—particularly Halobacterota —and upregulating pathways related to signal transduction, stress tolerance, and substrate degradation. These findings demonstrate that QS-based biostimulation is a promising tool to improve methane yields and microbial efficiency in anaerobic digestion of water treatment systems, offering a scalable microbiome-driven tool to improve energy recovery, reduce organic loads, and support circular resource use. • BMP of dairy wastewater treatment plant wastes reached 750–1100 NmL biogas /g VS . • Co-digestion of sewage sludge and dairy waste greases improved AD and CH 4 content. • Early 12-HSL addition further increased biogas (↑ 33 %) and biomethane (↑37. 5 %). • Supplementation with 12-HSL enhanced the methane concentration in biogas by 6 %. • 12-HSL enriched specific microbial populations boosting biogas and CH 4 production.