State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China.
Water Res. 2020 Mar 15;171:115437. doi: 10.1016/j.watres.2019.115437. Epub 2019 Dec 23.
Despite plenty of literatures focused on the application of pre-ozonation prior to membrane, it was still unclear about the role of divalent cations (Ca and Mg) in reverse osmosis (RO) membrane fouling mitigation. In this study, ozone pre-treatment (0.10, 0.25 and 0.50 mg O/mg DOC (dissolved organic carbon)) was employed to oxidize model biopolymer, which was represented by bovine serum albumin (BSA) and sodium alginate (SA) in the presence of Ca and Mg (0.5, 1.0 and 2.0 mM). Cross-flow filtration was conducted to investigate RO membrane fouling by concentration mode. The results showed that at appropriate ozone dose there were measurable changes in physicochemical properties of BSA and SA, including increases in particle size, hydrophilicity, density of negative charge and carboxylic groups. Pre-ozonation markedly alleviated RO fouling by BSA at ozone dose of 0.25 mg O/mg DOC when Ca and Mg concentrations raised from 0.5 to 2.0 mM since the increase in electrostatic (EL) repulsion and decrease in hydrophobic (HP) interaction compensated the increase in divalent cation bridging. Similar results were obtained for SA fouling in the presence of Mg. In contrast, the effect of pre-ozonation on SA fouling strongly depended on the concentration of Ca. In brief, it mitigated SA fouling at 0.5 mM Ca, whereas accelerated irreversible fouling at higher Ca concentration (1.0 and 2.0 mM) due to the overwhelming effect of divalent cation bridging compared to EL and HP interactions, as revealed by adsorption experiments (in-situ streaming potential measurement). Pre-ozonation shifted the fouling layer from compact to porous and weakened the adhesion forces between foulants and membrane (foulants) except for SA containing 1.0 and 2.0 mM Ca. This study may provide the guidance for the application of pre-ozonation prior to RO filtration.
尽管有大量文献专注于膜前预臭氧化在膜过程中的应用，但二价阳离子（Ca 和 Mg）在反渗透（RO）膜污染缓解中的作用仍不清楚。在本研究中，采用臭氧预处理（0.10、0.25 和 0.50mg O/mg DOC（溶解有机碳））氧化模型生物聚合物，该生物聚合物由牛血清白蛋白（BSA）和海藻酸钠（SA）组成，同时存在 Ca 和 Mg（0.5、1.0 和 2.0mM）。采用错流过滤法以浓度模式研究 RO 膜污染。结果表明，在适当的臭氧剂量下，BSA 和 SA 的物理化学性质会发生可测量的变化，包括粒径、亲水性、负电荷密度和羧酸基团增加。当 Ca 和 Mg 浓度从 0.5 增加到 2.0mM 时，在 0.25mg O/mg DOC 的臭氧剂量下，预臭氧化显著缓解了 BSA 对 RO 的污染，这是由于静电（EL）排斥的增加和疏水性（HP）相互作用的减少补偿了二价阳离子桥接的增加。在存在 Mg 的情况下，SA 污染也得到了类似的结果。相比之下，预臭氧化对 SA 污染的影响强烈依赖于 Ca 的浓度。简而言之，在 0.5mM Ca 时，它减轻了 SA 污染，而在较高 Ca 浓度（1.0 和 2.0mM）时，由于二价阳离子桥接相对于 EL 和 HP 相互作用的压倒性影响，加速了不可逆污染，如吸附实验（原位流动电位测量）所示。预臭氧化将污染层从致密变为多孔，并削弱了污染物和膜之间的粘附力（污染物），除了含有 1.0 和 2.0mM Ca 的 SA 外。本研究可为 RO 过滤前预臭氧化的应用提供指导。
