ZnO纳米颗粒暴露下EPS对污泥细胞的保护作用

ZnO纳米颗粒(ZnO NPs)对膜生物反应器(MBR)中的活性污泥具有一定的毒害作用,而胞外聚合物(EPS)在这一过程中的保护作用机理尚不明晰,为此进行了相关研究。试验结果显示,暴露在ZnO NPs条件下,含有EPS的污泥的活性氧清除酶活性高于去除了 EPS的污泥,这表明EPS具有保护污泥活性、减少活性氧产生的作用。分析原因可能是EPS使ZnO NPs的Zeta电位由正值变为负值,从而减少了 ZnO NPs与污泥细胞的接触。将EPS分为大分子和小分子组分,发现小分子EPS与ZnO NPs混合后Zeta电位更低,石英晶体微天平(QCMD)试验中ZnO NPs在污泥细胞表面的吸附量更少,说明小分子EPS对污泥细胞的保护作用强于大分子EPS。

Protective Mechanism of EPS for Activated Sludge in MBR under Exposure of ZnO Nanoparticles

It is known that ZnO nanopartices (ZnO NPs) are toxic to the sludge in the membrane bioreactor ( MBR). However, the protective mechanism of extracellular polymeric substances ( EPS ) during this process is not clear. Therefore, the protective mechanism of EPS with different molecular weight under exposure of ZnO NPs was investigated. The results showed that the activity of enzymes capable of eliminating the reactive oxygen in the sludge containing EPS was higher than that of sludge containing no EPS, which indicated that EPS had the function of protecting sludge and reducing the production of reactive oxygen. It might be concluded that EPS changed the Zeta potential of ZnO NPs from positive to negative, which reduced the contact between ZnO NPs and sludge cells. EPS was divided into two groups, namely high molecular weight EPS and low molecular weight EPS. Further study showed that the Zeta potential of ZnO NPs mixed with low molecular weight EPS was lower than that of ZnO NPs mixed with high molecular weight EPS. Correspondingly, the adsoiption capacity of the former mixture on cells was lower than that of the later mixture according to quartz crystal microbalance with dissipation (QCMD) test, which indicated that the protection effect of low molecular weight EPS was higher than that of high molecular weight EPS.