Performance and microbial community responses of anaerobic digestion of waste activated sludge to residual benzalkonium chlorides

The emerging organic pollutants, quaternary ammonium compounds, have attracted extensive attention due to their great enrichment in waste activated sludge (WAS). This study selected benzalkonium chlorides (BACs) as model to reveal its effects of levels and alkyl chain lengths (ACLs) on methane production from anaerobic digestion of WAS. Results showed that BACs caused more release of soluble polysaccharides and proteins, increased by 42.6-55.7% and 11.5-19.4%, which were positively related to the levels of BACs. In contrast, the methanogenesis was inhibited, and a higher level or a shorter ACL led to a more significant inhibition. The maximum production of methane was 171.1 mL/g VSS in control, and reduced to 97.8, 41.5 and 7.63 mL/g VSS for ACL16, ACL14 and ACL12 at the BAC level of 25 mg/g TSS, consequently, the corresponding accumulations of short-chain fatty acids were 1.57-1.84 times higher than that of control. Moreover, the presence of BACs also affected the diversities of both bacteria and archaea involved in methane production. Compared to control, BACs reduced Firmicutes, Bacteroidetes and Chlorofiexi, especially Firmicutes, with a decrease ratio of 12.6-20.2%, whereas Proteobacteria and Actinobacteria were increased. Besides, a longer ACL led to a higher enrichment of Methanomicrobia, and with the ACLs of BACs decreasing from 16 to 12, the dominant methanogens shifted from acetotrophic to mixotrophic, and further to hydrogenotrophic methanogens. The findings of this study demonstrated that both levels and ACLs of BACs could affect the performance of anaerobic digestion of WAS, as well as the microbial community.