Department of Environmental Science and Engineering, School of Energy and Environment, Wuxi Engineering Research Center of Taihu Lake Water Environment, Southeast University, Nanjing, Jiangsu, 210096, China; Key Laboratory of Environmental Medicine Engineering, Ministry of Education, Southeast University, Nanjing, Jiangsu, 210009, China.
Department of Environmental Science and Engineering, School of Energy and Environment, Wuxi Engineering Research Center of Taihu Lake Water Environment, Southeast University, Nanjing, Jiangsu, 210096, China; Department of Water Supply and Drainage Science and Engineering, College of Civil Engineering, Nanjing Forestry University, Nanjing, Jiangsu, 210037, China.
Environ Res. 2021 Jan;192:110256. doi: 10.1016/j.envres.2020.110256. Epub 2020 Sep 28.
Despite the behaviors of ZnO nanoparticles (ZnO NPs) in wastewater treatment processes have been widely explored, the impacts of ZnO NPs on the activated sludge's flocculation and sedimentation performances for solid-liquid separation have rarely been involved yet. In this study, ZnO NPs were observed to exert a dose-dependent negative effect on the sludge's flocculation performance but did not significantly impact the sludge' sedimentation behaviors. Furthermore, it was NPs themselves rather than the dissolved Zn who impaired on the sludge flocculation performance because the Zn alone would not compromise the sludge's flocculation efficiency. In addition, the sludge flocculation performance was revealed to be inversely related to the extracellular polymeric substances (EPS) content in the sludge and the direct contacts between ZnO NPs and the cells in the sludge should be the prerequisite to stimulate the secretion of the sludge EPS. The poor sludge flocculation performance could also be caused by the reduced protein/polysaccharide (PN/PS) ratio and the zeta (ζ) potential in the loosely bound (LB-EPS) after the sludge exposure to ZnO NPs. Fourier transform-infrared spectra (FT-IR) and three dimensional - excitation emission fluorescence spectra (3D-EEM) analysis further revealed that the decrease of the tyrosine PN-like substance level in the LB-EPS was probably the key reason for the decreased PN/PS ratio and ζ potential in the LB-EPS, which eventually induced the decline of the sludge flocculation performance under the ZnO NP stress. These results could potentially expand the knowledge on sludge flocculation and sedimentation in the presence of ZnO NPs.
尽管氧化锌纳米粒子（ZnO NPs）在废水处理过程中的行为已被广泛研究，但 ZnO NPs 对活性污泥固液分离絮凝和沉降性能的影响尚未涉及。在本研究中，ZnO NPs 被观察到对污泥的絮凝性能表现出剂量依赖性的负面影响，但对污泥的沉降行为没有显著影响。此外，是 NPs 本身而不是溶解的 Zn 破坏了污泥的絮凝性能，因为单独的 Zn 不会影响污泥的絮凝效率。此外，污泥的絮凝性能与污泥中胞外聚合物物质（EPS）的含量呈反比关系，而 ZnO NPs 与污泥细胞的直接接触应该是刺激污泥 EPS 分泌的前提条件。此外，由于污泥暴露于 ZnO NPs 后 LB-EPS 中的蛋白质/多糖（PN/PS）比值和 ζ 电位降低，污泥的絮凝性能也会变差。傅里叶变换-红外光谱（FT-IR）和三维激发发射荧光光谱（3D-EEM）分析进一步表明，LB-EPS 中酪氨酸 PN 类似物水平的降低可能是 LB-EPS 中 PN/PS 比值和 ζ 电位降低的关键原因，这最终导致在 ZnO NP 胁迫下污泥絮凝性能下降。这些结果可能会扩展关于存在 ZnO NPs 时污泥絮凝和沉降的知识。
