Abstract: Due to the large-scale production and wide applications,many nanoparticles (NPs) enter wastewater treatment plants and accumulate in activated sludge. It is reported that titaniumdioxide (TiO₂) NPs showsevere damage to many model microbes. However, it is still unknown whether the long-term (e.g., 100 d) presence of TiO₂ NPs would affect the performance of sludge fermentation. In this study, long-term exposure experiments (105 d) were conducted to investigate the potential risk of TiO₂ NPs to sludge fermentation system. It is found that the presence of environmentally relevant [6 mg·(g TSS)^-1] and higher [150 mg·(g TSS)^-1] concentrations of TiO₂ NPs does not affect methane production fromsludge fermentation. The analysis of fluorescence in situ hybridization indicates that these concentrations of TiO₂ NPs present marginal influences on abundances of bacteria and methanogenic archaea in sludge fermentation system. The viability of sludge microorganisms and activities of key enzymes related tomethane production such as protease, acetate kinase, and coenzyme F₄₂₀ are unchanged by the long-term presence of 6 and 150 mg·(g TSS)^-1 of TiO₂ NPs. Further investigations reveal that the insolubility of NPs and the protection role of sludge extracellular polymeric substances are the main reasons for the marginal influence of TiO₂ NPs on sludge fermentation.

Key words: Titanium dioxide nanoparticles, Waste activated sludge, Fermentation, Long-term effect, Mechanism

摘要： Due to the large-scale production and wide applications,many nanoparticles (NPs) enter wastewater treatment plants and accumulate in activated sludge. It is reported that titaniumdioxide (TiO₂) NPs showsevere damage to many model microbes. However, it is still unknown whether the long-term (e.g., 100 d) presence of TiO₂ NPs would affect the performance of sludge fermentation. In this study, long-term exposure experiments (105 d) were conducted to investigate the potential risk of TiO₂ NPs to sludge fermentation system. It is found that the presence of environmentally relevant [6 mg·(g TSS)^-1] and higher [150 mg·(g TSS)^-1] concentrations of TiO₂ NPs does not affect methane production fromsludge fermentation. The analysis of fluorescence in situ hybridization indicates that these concentrations of TiO₂ NPs present marginal influences on abundances of bacteria and methanogenic archaea in sludge fermentation system. The viability of sludge microorganisms and activities of key enzymes related tomethane production such as protease, acetate kinase, and coenzyme F₄₂₀ are unchanged by the long-term presence of 6 and 150 mg·(g TSS)^-1 of TiO₂ NPs. Further investigations reveal that the insolubility of NPs and the protection role of sludge extracellular polymeric substances are the main reasons for the marginal influence of TiO₂ NPs on sludge fermentation.

关键词: Titanium dioxide nanoparticles, Waste activated sludge, Fermentation, Long-term effect, Mechanism