Modelling and Control of Membrane Fouling in Ultrafiltration of Water and Wastewater

以超滤为代表的膜过滤技术是一种高效节能的处理技术，已广泛应用于净水、废水处理、生物技术、水包油乳状液分离等领域。然而，料液中的溶质/颗粒对膜的污染是该行业的一大挑战，目前操作上的担忧阻碍了膜过滤的广泛应用。膜污染会导致膜通量随时间的延长而降低，从而导致过滤效率低、过滤成本高。涂料生产废水中含有多种物质，如有机/无机颜料、乳胶、溶剂和乳化剂等。超滤膜处理乳胶漆废水会产生污染，导致水力阻力显著增加，渗透通量下降，跨膜压(TMP)增大。通过我们以前的研究，我们已经开发了使用均匀和非均匀孔径的膜来预测膜污染、TMP和功率消耗的机理模型。我们还开发了创新的污染修复技术，能够控制乳胶废水的横流超滤过程中的膜污染。为了在中试规模和工业应用中进一步实现节能，仍然需要深入了解以下机理：i)颗粒滞留在孔表面(孔收缩)；ii)附着在膜表面导致部分或全部堵塞孔入口(结饼)；iii)颗粒聚集导致结饼；以及iv)颗粒从滤饼层分解并重新进入保留液，及其对污染的影响。本研究的目的是用计算流体力学和离散元方法(CFD-DEM)模拟板框膜上的颗粒沉积，包括膜孔内和膜表面的颗粒沉积与膜污染现象的关系。计算粒子到其最终捕获位置的轨迹涉及水动力和表面相互作用。将DEM与CFD相结合，研究膜污染过程中的流体-颗粒相互作用系统，其中溶质(固)相和溶液(流体)相对流动动力学和颗粒沉积都有贡献。深入了解这一现象，并通过这一研究计划开发减少膜污染的新技术和创新技术，对该行业具有重要意义。拟议的研究计划产生的主要好处是开发了一种设计分离/过滤膜的创新技术/方法。这一新方法将结合我们的机械污垢附着模型和CFD-DEM模型来实现。开发的方法将对加拿大膜制造商和膜使用者产生重大影响。针对加拿大行业的HQP培训是拟议研究计划的一个额外好处。

Membrane filtration, such as ultrafiltration (UF), is an efficient and energy saving process that has been widely used in water purification, wastewater treatment, biotechnology, and oil-in-water emulsion separation. However, membrane fouling by the solutes/particles in a feed solution is a major challenge for the industry and has operational concerns that are currently hindering widespread application of membrane filtration. Membrane fouling causes a reduction of the permeating flux with time, resulting low filtration efficiency and higher filtration cost. Wastewater from paint manufacturers contains variety of substances, such as: organic/inorganic pigments, latex, solvents and emulsifying agents. Treatment of latex-paint wastewater with UF results in fouling, which causes a significant increase in hydraulic resistance, permeate flux decline and transmembrane pressure (TMP) increase. Through our previous studies, we have developed mechanistic models to predict membrane fouling, TMP, and power consumption using uniform and non-uniform pore size membranes. We also have developed innovative fouling remediation techniques capable of controlling membrane fouling in the cross-flow UF of latex effluent. For further development towards energy saving in pilot scale and industrial applications, there remains a need for a profound understanding of the following mechanisms: i) particle retention on the pore surface (pore constriction); ii) attachment on the membrane surface causing in blocking of the pore inlet, partially or completely (cake formation); iii) particle aggregation causing cake buildup; and iv) particle break-up behavior from the cake layers and reentering into retenate, and their effects on fouling. The objective of the proposed research is to use Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) to model the particle deposition on the plate-and-frame membrane, both inside the pore and on the surface, in relation to membrane fouling phenomena. Computing the trajectory of a particle to its final capture location involves both hydrodynamic and surface interactions. DEM will be coupled with CFD to study fluid-particle interaction systems occurring during membrane fouling in which both the solute (solid) and solution (fluid) phases contribute to the flow dynamics and particle deposition. A thorough understanding of this phenomenon and development of novel and innovative techniques to reduce membrane fouling through this research plan are of great importance to the industry. Main benefit arising from the proposed research plan is development of an innovative technique/method in designing separation/filtration membranes. This novel method will be achieved by combining our mechanistic fouling attachment model and the CFD-DEM model. The developed method will have a major impact on Canadian membrane manufacturers and membrane users. Training of HQP for the Canadian industry is an added benefit of the proposed research plan.