长期暴露下纳米TiO_2对厌氧颗粒污泥体系稳定性的影响

Long-term Impacts of TiO_2 Nanoparticles on the Stability of an Anaerobic Granular Sludge Bioreactor

以厌氧颗粒污泥为研究对象,通过静态试验和连续流厌氧反应器,重点研究了长期暴露下纳米TiO_2在对厌氧产甲烷体系的影响及其在颗粒污泥中的归趋.结果表明,短期急性暴露于150 mg·g-1(以VSS计)的纳米TiO_2尽管会暂时减缓产甲烷速率,但产酸阶段及产甲烷阶段代谢产物总量不会明显受到影响,纳米TiO_2对厌氧颗粒污泥具有较低的急性毒性.反应器运行结果表明,纳米TiO_2的长期暴露可导致挥发性脂肪酸(VFAs)积累及生物气产量降低,产酸菌比产甲烷菌对纳米TiO_2的累积效应更加敏感,纳米TiO_2抑制机制可归因于"物理遮蔽"作用.出水中TiO_2的平均含量只有0.632 mg·L^(-1),绝大多数纳米TiO_2都被截留在了反应器中.FISH检测表明,厌氧颗粒污泥微生物的菌群结构有所变化,纳米TiO_2在反应器内的积累使得甲烷八叠球菌的丰度大幅增加了115.6%,其优势地位明显增强.长短期暴露试验的结果对比也说明,用短期暴露试验来说明纳米颗粒对厌氧体系的长期累积效应具有一定局限性,纳米TiO_2对厌氧颗粒污泥中微生物的负面影响需要较长时间的积累才会显现.本研究结果可为厌氧污水处理体系中纳米颗粒的潜在生态风险评价提供理论支持和参考依据.

In the present study, the fate and long-term effect of TiO2 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 TiO2 NPs was greater than 150 mg·g - 1 . However, no significant difference in the products of acidification and methanation between the control and 150 mg·g - 1 （as VSS） of TiO2 NPs assays was observed, indicating low bacteria cytotoxicity of TiO2 NPs on AGS in dark anaerobic digestion. The operation data of the AGS bioreactor showed that acidogens was more sensitive to prolonged exposure to TiO2 NPs with the accumulation of VFAs and a decrease of biogas production in the TiO2 NPs containing reactor. The inhibiting effect of TiO2 NPs on the AGS might be attributed to the physical restraints. The average TiO2 concentration escaping with the effluent was 0. 632 mg·L - 1 , suggesting most of the NPs were retained inside the reactor. The long-term presence of TiO2 NPs could alter the composition of the microbial communities in the AGS, since the amount of Methanosarcina increased by 115. 6% . The results also indicated that the treatment of short-term sudden exposure to TiO2 NPs using batch tests might not be appropriate for interpreting their cumulative effects on the AGS, since a long time was need for the TiO2 NPs to show negative effects on the microbial populations in the AGS. Our study could supply useful proof for assessments of potential risks for TiO2 NPs on anaerobic activated sludge.