[Long-term Impacts of TiO Nanoparticles on the Stability of an Anaerobic Granular Sludge Bioreactor].

In the present study, the fate and long-term effect of TiO nanoparticles (NPs) on anaerobic granular sludge (AGS) was evaluated in an anaerobic methanogenic system. In the short-term experiment, the methane production rate decreased when the dosage of TiO NPs was greater than 150 mg·g. However, no significant difference in the products of acidification and methanation between the control and 150 mg·g(as VSS) of TiO NPs assays was observed, indicating low bacteria cytotoxicity of TiO NPs on AGS in dark anaerobic digestion. The operation data of the AGS bioreactor showed that acidogens was more sensitive to prolonged exposure to TiO NPs with the accumulation of VFAs and a decrease of biogas production in the TiO NPs containing reactor. The inhibiting effect of TiO NPs on the AGS might be attributed to the physical restraints. The average TiO concentration escaping with the effluent was 0.632 mg·L, suggesting most of the NPs were retained inside the reactor. The long-term presence of TiO NPs could alter the composition of the microbial communities in the AGS, since the amount of a increased by 115.6%. The results also indicated that the treatment of short-term sudden exposure to TiO NPs using batch tests might not be appropriate for interpreting their cumulative effects on the AGS, since a long time was need for the TiO NPs to show negative effects on the microbial populations in the AGS. Our study could supply useful proof for assessments of potential risks for TiO NPs on anaerobic activated sludge.