环境水质学国家重点实验室知识库

      水资源短缺是人类社会在发展过程中面临的全球性问题，水质净化回用是缓解该问题的重要手段。 膜分离 技术因其具有 工艺简洁、自动化程度高、出水水质优良 等 优点 在水处理中的 应用日益广泛 。膜污染问题严重制约了膜技术的推广应用，因此如何控制膜孔堵塞造成的不可逆污染是膜法水处理 研究的 核心问题 。 电化学 水处理技术由于其产生 的 絮凝、 氧化 、曝气 以及 电场作用 均可 不同程度的控制膜污染 通常作为预处理 单元与 膜技术组合。 此外 将 滤膜同时作为电极，利用膜电极的静电排斥以及电极反应，有望提高膜分离选择性 同时 获得更高水通量打破 trade-off”效应 。
      通过将超滤膜组件置于电化学 系统的电场区域，开发了 电絮凝 -膜分离一体式反应器（ Electrocoagulation membrane reactor ECMR），利用 絮凝和电场的协同作用 既减缓 膜污染， 又提升 出水水质。 研究 发现， 电场作用提高了滤饼层孔隙率和亲水性，增加了出水通量 ，同时 较高的电流密度和弱酸性 pH条件 有利于更快地 形成 大的絮体进而有效地减少膜孔堵塞 ，控制不可逆污染 。在 ECMR反 应器的 基础上，通过 配置 形稳电极 功能 ，形成电絮凝 /氧化 -膜分离反应器（ Electro-coagulation/oxidation membrane reactor ECOMR），利用 电场下氧化和絮凝的 联合作用 进一步改善了滤饼层的亲水性和孔隙率 ，更加 有效 地控制了 膜污染。 在ECOMR中， 电氧化过程破坏了腐殖酸的羧基官能团和芳 香 族结构，形成更疏松多孔的滤饼层 。与未进行预处理的超滤过程相比， ECOMR滤饼层的水接触角降低至 55.07°，通量提高 29.12%。 同时， 水解 絮体参与滤饼层生成降低了滤饼层与膜表面之间的亲和力， 因此膜污染更容易通过 物理清洗 脱除 。与传统 分体式的 电化学 -超滤 反应器 相比， 一体化的电控膜分离反应器系统的膜通量更高、 占地面积更小 、 更节能。
      开发了石墨烯导电膜，研究 了 石墨烯基 滤膜 的 水通道构建 与 选择性 截留 调控方法， 并 阐明了导电膜 的电场膜分离 选择性 机制。 通过在石墨烯膜表面修饰 含 氧基团 改善了膜表面亲水性，提高了水分子孔道尺寸及孔道周围的电荷密度， 使其兼顾 了高水通量 和 良好 截留性能。 通过 热还原及 MoS2片层材料插层手段 调控氧化石墨烯膜（ graphene oxide membrane GOM）的 尺寸筛分效应和离子 -纳米通道相互作用， 对铜离子的选择性最大提高了约 25.5倍 。  在 电场作用下， GOM脱盐过程中 具有明显 的 电场响应 规律：在 GOM上施加与过滤方向相同的电场时，截留率降低；施加与过滤方向相反的电场时，截留率下降，且截留率与电场强度成正相关 。 电场的调控过程受到膜的层间距及膜表面电荷密度的 影响 ，层间距越小，电荷密度越大，对电场的响应越显著。分析发现 阳离子对电场的响应行为控制了 GOM整体 离子 的 渗透 行为。
      合成了更加稳定的 石墨烯水凝胶膜， 开发了 相应的 导电膜组件，将其同时作为滤膜和电极 （即膜电极 应用于 电控膜分离反应器。 研究表明，导电膜作为膜 阳极时 ，会因静电吸附作用导致 膜污染 加剧； 作为膜阴极时， 强化 的 静电排斥和原位氧化反应 减小了导电膜 表面 有机物分子量分布和含量 ，通量较不加电时最高可提高 9.83%。 静电排斥 作用是控制 膜污染 减缓的最主要机制，在膜污染控制贡献中占比为 83.01%。 可以 利用膜电极发生 的 原位氧化作用 清除膜污染、 恢复水通量 ，达到膜污染电清洗的目的。 通量恢复率 与电解质浓度、电清洗时间成 正比，优化条件下 电清洗的通量恢复率 可达 98%。 将导电膜应用于电控 膜分离反应器，达到了膜污染控制与原位电清洗的目的，为电控膜分离反应器的发展 与 应用提供了重要的科学依据 。

         Water shortage is a global problem faced by human society throughout development process. Water purification and reuse are the key methods important means to alleviate this problem. Membrane separation technology has been widely applied in water treatment industry in recent years due to its simple technology, high automation and high effluent quality. However, the application of membrane technology in water treatment is limited by membrane fouling. To control the irreversible pore blockage fouling is the core issue in membrane water treatment. Electrochemical methods are usually employed as pretreatments prior to membrane filtration to control membrane fouling due to the coagulation, oxidation and aeration effects, together with electric field. In addition, employing the membrane as electrode, and taking advantage of the electrorepulsion and reaction on membrane electrode would be promising to improve the ion selectivity and enhance water permeability, breaking the “trade-off” effect.
        An electro-membrane reactor (EMR) was developed, in which ultrafiltration membrane modules are placed in the electric field zone. It’s revealed that the combined effect of coagulation and electric field mitigated membrane fouling and improved the effluent water quality. Higher current densities and weakly acidic pH in the EMCR favored faster generation of large flocs and effectively reduced membrane pore blocking. The water permeability of the formed cake layers on the membrane surface was increased due to an increase in cake layer porosity and hydrophilicity, which was induced by the applied electric field. An Electro-coagulation/oxidation membrane reactor (ECOMR) was developed by altering the electrode material and arrangement based on ECMR. The hydrophilicity and porosity were further enhanced due to the synergistic effect between electrocoagulation and electrooxidation with electric field, leading to the enhancement in anti-fouling performance. Electrooxidation modulated the morphology of the cake layer by breaking up humic acid molecules (i.e., carboxylic functional groups and aromatic structures), giving a more porous cake layer, achiving higher water permeability. Electrocoagulation prevented the contaminates from attaching to membrane and increased the hydrophilicity of the cake layers, resulting in 55.07° decrease in contact angle and 29.12% increase in water permeability. Moreover, the cake layers formed in the ECOMR exhibited lower affinity for the membrane surface, which meant they were easier to clean off. Compared to traditional electrocoagulation-ultrafiltration process, ECMR has a smaller footprint and could achieve significant water permeability and energy savings.
         Utilizing the excellent conducitivity of graphene, we fabricated graphene conductive membrane, and investigated its selective separation under electric field. The structure and performance optimization of graphene-based membrane were delineated. The oxygen-containing group modification strategy improved the hydrophilicity of membrane surface, as well as enhanced the nanochannel size for water and the charge density around the nanochannel, leading to improved filtration performance and enhanced water permeability. The influence of thermal reduction and flake (MoS2) intercalation on the ion penetration process of graphene oxide membrane (GOM) has been investigated. The results indicated that thermal reduction and MoS2 intercalation could work in concert to control the size-sieving effect and ion-nanochannel interactions to achieve fine selective separation, leading to ~25.5 times improvement in Cu2+ ion selectivity over Na+. The response of its desalination performance under electric field exhibited apparant principle. When the direction of electric field was along the filtration direction, the rejection declined, and when the the direction of electric field was opposite to the filtration direction, the rejection increased. The response degree was positively correlated to the electric field strength. The results indicated that the response to electric field could be tuned by the interlayer spacing and surface charge density in concert. Narrower interlayer spacing and higher charge density would lead to obvious response to electric field. The response mechanism was controlled by cations.
      Ultizing the conductivity of graphene, a conductive graphene hydrogen membrane (GHM) was fabricated. The conducive membrane module was employed in EMR as electrode and membrane (namely membrane electrode). The results showed that when the membrane worked as an anode, the membrane fouling increased due to the electro-adsorption. When the membrane worked as a cathode, the in-situ electro-cleaning would be achived by the in-situ oxidation and electrorepulsion effect on membrane surface, which changed the molecular weight distribution and content, leading to an increase in water flux by 9.83%. Electrostatic repulsion was the primary factor (83.01%) that endowed the membrane with anti-fouling performance, which was confirmed by controlling the reactions occurred on electrodes. The irreversible fouling rate was inversely proportional to background electrolyte as well as cleaning time, leading to 98% decrease at most. The membrane fouling control and in-situ electro-cleaning were achieved by applying conductive membrane into EMR, giving important scientific support to the evolution and application of EMR system.