Unravelling the role of coumarin on anaerobic digestion of waste activated sludge: Determination of operational dynamics and microbial community structure

Anaerobic digestion, as an effective method for sludge treatment, still has excellent potential for development in energy recovery. Therefore, this study proposed a method to increase methane production by adding coumarin (a green antibacterial agent). The results indicated that coumarin can significantly improve the methane production performance of sludge, but high coumarin concentrations delay methane production. Methane generation through the acetoclastic pathway is inhibited at high concentrations of coumarin and can be restored after bacterial adaptation or degradation of coumarin. Mechanism exploration revealed that coumarin enhanced the destruction of EPS and poorly tolerant bacterial cell membranes, thereby benefiting the solubilization of sludge. It was also found that coumarin promotes sludge hydrolysis, acidification, and methane production stages. Microbial analysis revealed that the abundance of functional microorganisms in the coumarin reactor was more advantageous to methane production. These findings are expected to provide a reference for enhancing the methane production performance of sludge.