A new strategy for greenhouse gas emission reduction in the anaerobic/anoxic/oxic biological treatment process using exogenous N-acyl-homoserine lactones, a quorum-sensing signaling molecules

In this study, the impact of exogenous N-acyl-homoserine lactones (AHLs) on greenhouse gas (GHG) emissions in anaerobic/anoxic/oxic (A/A/O) systems was analyzed by manipulating the type and dosage of AHLs. The mechanism behind AHLs' effects on GHG emissions was explored through changes in microbial community structure. Findings revealed that N-octanoyl-homoserine lactone (C8-HSL) and high-dose N-dodecanoyl-homoserine lactone (C12-HSL) increased GHG emissions, while low-dose C12-HSL decreased them. Moreover, C8-HSL and high-dose C12-HSL promoted methane (CH₄) and nitrous oxide (N₂O) production by affecting sludge particle size. Bacterial community analysis highlighted <i>Acinetobacter</i> and <i>Flavobacterium</i>'s roles in N₂O emissions and acetate methanogens in methane synthesis. Metabolic pathway analysis showed that the acetic acid (CH₃COOH) methanogenic pathway was the main methanogenic pathway; C8-HSL and C12-HSL influenced methane emission by affecting the methanogenic pathway and N₂O emission by changing nitrous oxide reductase (<i>Nos</i>) abundance. This research underscores AHL-based quorum sensing's potential in mitigating GHG emissions during activated sludge wastewater treatment, offering insights into their application and impact on key microbial activities. Limitations include the absence of methane emission reduction by signaling molecules and the need for further investigation into their effects on sludge accumulation.