School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University), Guangzhou 510275, China.
School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University), Guangzhou 510275, China.
Water Res. 2017 Jan 1;108:115-123. doi: 10.1016/j.watres.2016.10.065. Epub 2016 Nov 2.
Chemical cleaning is an essential process for the permeability recovery of fouled membranes, which is highly related to the interactions between chemicals and bio-macromolecules in fouling layers. In this study, three bio-macromolecules (i.e., effluent biopolymers (i.e., 0.45 μm-100 kDa) from a full-scale municipal wastewater treatment plant, bovine serum albumin (BSA) and dextran) were exposed to different chemicals (i.e., NaClO, HO, NaOH, and HCl) with varied concentrations to understand the changes in their properties and functional groups. The results showed that exposure to oxidants and alkali decreased the consistency index of all bio-macromolecules. With an increased oxidant dose, the molecular sizes of effluent biopolymers and dextran continuously reduced because of the oxidative cleavage of the long molecule chains. However, the molecular size of BSA sharply increased after being treated with oxidants and alkali, likely due to the cross-linkage of protein molecules. Three-dimensional fluorescence excitation-emission matrix (3D-EEM) spectra showed that the aromatic protein-like and humic substances in the effluent biopolymers were destructed readily during the treatments of oxidants and alkali. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyse further confirmed that exposures to NaClO, HO and NaOH led to the destruction of protein structures (i.e., amide I, II and III), the increase of carbonyl and carboxyl groups, and the decrease of fatty acids/lipids, all of which could make the bio-macromolecules more hydrophilic. Most importantly, the bio-macromolecules exposed to chemicals had better filterability, and their permeability through membranes also significantly increased, which could be explained well by the above analysis. The chemical cleaning mechanisms of fouled membranes are understood in depth in this study, and all of the results shed light on the implementation of on-line chemical enhanced backwashing in membrane processes.
化学清洗是恢复污染膜渗透性能的必要过程，这与化学物质与污染层中生物大分子之间的相互作用密切相关。在这项研究中，三种生物大分子（即来自大型城市污水处理厂的出水中的生物聚合物（0.45μm-100kDa）、牛血清白蛋白（BSA）和葡聚糖）与不同浓度的不同化学物质（即次氯酸钠、HO、氢氧化钠和盐酸）接触，以了解其性质和功能基团的变化。结果表明，氧化剂和碱的暴露降低了所有生物大分子的稠度指数。随着氧化剂剂量的增加，出水中生物聚合物和葡聚糖的分子尺寸不断减小，因为长分子链的氧化断裂。然而，BSA 在经过氧化剂和碱处理后，分子尺寸急剧增加，可能是由于蛋白质分子的交联。三维荧光激发-发射矩阵（3D-EEM）光谱表明，在氧化剂和碱的处理过程中，出水中的芳香蛋白样物质和腐殖质物质很容易被破坏。傅里叶变换红外（FTIR）和 X 射线光电子能谱（XPS）分析进一步证实，暴露于次氯酸钠、HO 和氢氧化钠会破坏蛋白质结构（即酰胺 I、II 和 III），增加羰基和羧基基团，减少脂肪酸/脂质，所有这些都会使生物大分子更亲水。最重要的是，暴露于化学物质的生物大分子具有更好的过滤性能，并且它们通过膜的渗透率也显著增加，这可以通过上述分析得到很好的解释。本研究深入了解了污染膜的化学清洗机制，所有结果都为膜过程中在线化学增强反冲洗的实施提供了启示。
