Vanillin as a quorum sensing inhibitor: effect on extracellular polymeric substance production and defoaming potential in anaerobic digestion system

• The addition of vanillin effectively decreased the foaming potential of digesters . • The optimal concentration for vanillin addition was determined to be 100 mg/L. • The addition of vanillin inhibited the AHLs-mediated quorum sensing (QS) effect. • The suppression of QS altered the composition of EPS and the digestate properties. To evaluate the effect of vanillin, a quorum sensing inhibitor (QSI), on the defoaming potential in food waste anaerobic digestion (AD) systems, various concentrations of vanillin were introduced into different AD reactors. The performance of these systems, along with foaming characteristics, extracellular polymeric substances (EPS) parameters, and microbial community structure and functional genes were monitored. The results show that the addition of vanillin at varying concentrations effectively reduced the foaming potential of the AD system. Specifically, vanillin at low concentrations (50 and 100 mg/L) did not inhibit methane production, whereas higher concentrations (200 and 500 mg/L) significantly inhibited methane production performance (p < 0.05). Optimal methane production and defoaming performance were observed at a vanillin concentration of 100 mg/L, where its methane production rate was not significantly different from that of the control group, but foam stability was significantly reduced by 84.69 % (p < 0.05). The incorporation of vanillin suppressed AHLs-mediated quorum sensing effects, reduced the synthesis and secretion of proteins (PN), decreased the content of PN and hydrophobic PN in EPS, lowered the viscosity of the digestate, reduced the contact angle, and ultimately diminished both foaming potential and stability, thereby achieving effective defoaming.