Effects of urea formaldehyde resin on the characteristics and microbial community of anaerobic granular sludge

The effects of urea formaldehyde (UF) resin on the performance and characteristics of anaerobic granular sludge (AnGS), the microbial community and related inhibition mechanisms were studied. During the exposure period, a low concentration of UF resin (0.1 g/L) had no significant effect on the AnGS activity, while a high concentration of UF resin (0.2 g/L, 0.5 g/L) decreased methane production and chemical oxygen demand (COD) removal by 16.5–19.7% and 6.4–7.9%, and short-chain fatty acid (SCFA) increased by 17.1–18.9%. Meanwhile, a low concentration of UF resin could stimulate cell stress, induce the production of more EPS and realize the self-defence mechanism; however, a higher UF resin concentration will inhibit the production of EPS, the extracellular polymer in the reactor with high concentration of UF resin was only 83.1–69.3% of that in control group, it leads to the crushing of AnGS and the decline of cell viability. In addition, high concentration of UF resin reduced the relative abundance of Proteobacteria and Bacteroidota by 9.2%− 16.7% and 8.0%− 10.5% respectively, led to the decline of bacterial diversity and richness, and the metabolic performance in anaerobic system was prepared. UF resin induced oxidative stress has been proved to be the main reason for the decline of AnGS activity, this is reflected in the increase of reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release, this further explains the reason why UF resin inhibits sludge acidification and methanation.