XDLVO理论分析混合有机污染物的膜污染

通过XDLVO理论分析了混合有机污染物的膜污染状况,对腐殖酸、海藻酸钠、牛血清蛋白这3种典型的模型污染物及其不同比例的混合物及PVDF膜的界面自由能进行了定量分析,从而判断膜污染性能,并通过过滤实验对预测结果进行了验证。结果表明,混合污染物和单一污染物界面性质完全不同,但根据界面自由能判断膜污染程度与过滤实验相符;溶液pH对混合污染物的溶液性质影响较大,最终影响膜过滤实验的污染程度,当pH较大时,膜污染程度相对较轻;添加不同的金属盐会影响混合污染物的界面性质,进而影响膜污染程度,添加钙离子相对镁离子和钠离子更容易导致膜污染。     

基于分形学的膜面滤饼特性研究进展

膜污染问题限制了膜分离技术在实际工程中的广泛应用。从分形解析的角度深入探讨混凝-膜过滤过程中滤饼层的微观结构对控制膜污染情况至关重要。总结和回顾了运用分形理论表征滤饼层重要性质参数孔隙率、比阻、渗透率研究的前沿动态,对絮体特性和滤饼层特性两者内在关系进行分析评述,以期为混凝-膜过滤工艺优化提供参考。     

基于XDLVO理论分析物理化学相互作用对纳滤膜有机污染影响

基于XDLVO理论定量解析了2种商用纳滤膜(NF90和NF270)与2种典型有机物腐殖酸(HA)和海藻酸钠(SA)之间的界面相互作用能,考察了溶液条件及系统操作压力对膜污染的影响。结果表明,纳滤膜污染程度与物理化学作用密切相关。pH减小使污染物之间或者污染物与膜之间黏附自由能负值明显增大,膜污染程度增加,膜通量衰减明显。离子强度增加特别是Ca~(2+)的添加会导致同样结果。SA比HA表现出对纳滤膜更强的膜污染。过滤液预处理可以降低膜污染,而增加跨膜压差可以增加膜污染并导致膜通量的快速衰减。XDLVO理论对膜污染预测的相关结果与实验结果相对一致,表明XDLVO理论在预测及控制膜污染方面具有很大的潜力。     

膜表面孔结构对PVDF超滤膜耐污染性能的影响

本文通过改变纺丝制膜工艺得到两种不同表面结构的聚偏氟乙烯（PVDF）中空纤维超滤膜，一种中空纤维膜外表面光滑，膜孔颈在膜表面，一种中空纤维膜表面相对粗糙，膜孔颈位于膜外表面层下，它们的泡点压力和水通量相当；通过用这两种外表面结构不同的膜过滤卵清蛋白、淀粉、SiO2悬浮液、柴油4种典型体系进行实验，实验结果发现过滤卵清蛋白体系时，这两种不同表面结构的膜耐污染性能基本上相当，过滤其它3种体系时，表面粗糙的膜耐污染性能明显好于表面较光滑的膜。     

短程混凝-膜过滤工艺清洗过程中气液两相流对絮体形成的影响

基于数值模拟的方法研究了不同填充密度和不同曝气强度下短程混凝-膜过滤工艺中膜清洗过程反应器内流场特性。结合絮凝动力学理论,引入微涡旋尺度参数来判定影响絮体形成的流场状态,以评估膜清洗过程中曝气强度对絮体形成及膜清洗效果的影响,并用实时图像技术对模拟结果进行验证。研究结果表明,反应器填充密度为7.38%,气水比为15:1时,反应器内平均有效能耗适中,且形成的微涡旋尺度也适中,不会对絮体产生明显的破坏作用,有利于形成较大尺寸的絮体;同时在膜组件附近产生较强的水流剪切速度,使膜面得到有效的清洗。结合实验分析,反应器填充密度为7.38%,气水比为15:1时,反应器内形成的絮体粒径较大且与数值模拟得到的微涡旋尺度相近,上清液UV254和TOC值最低,去除效果最好。     

XDLVO理论在膜污染解析中的应用研究

膜分离过程中存在的膜污染问题严重制约了膜分离技术的大规模应用。扩展的XDLVO（Derjaguin-Landau-Verwey-Overbeek）理论可以为膜污染机理的阐述提供理论支撑,它不仅可以用来解析及预测膜污染,还可为膜污染控制提供理论指导。介绍了XDLVO理论的分析计算方法,综述了XDLVO理论在不同污染物的膜污染行为解析中的应用,讨论了膜面性质及操作条件对膜污染行为的影响以及XDLVO理论对膜污染控制的指导作用,并提出了XDLVO理论在膜污染行为研究中存在的问题以及对未来研究方向的展望。     

短程混凝-膜过滤工艺清洗过程中气液两相流对絮体形成的影响

基于数值模拟的方法研究了不同填充密度和不同曝气强度下短程混凝-膜过滤工艺中膜清洗过程反应器内流场特性。结合絮凝动力学理论,引入微涡旋尺度参数来判定影响絮体形成的流场状态,以评估膜清洗过程中曝气强度对絮体形成及膜清洗效果的影响,并用实时图像技术对模拟结果进行验证。研究结果表明,反应器填充密度为7.38%,气水比为15：1时,反应器内平均有效能耗适中,且形成的微涡旋尺度也适中,不会对絮体产生明显的破坏作用,有利于形成较大尺寸的絮体;同时在膜组件附近产生较强的水流剪切速度,使膜面得到有效的清洗。结合实验分析,反应器填充密度为7.38%,气水比为15：1时,反应器内形成的絮体粒径较大且与数值模拟得到的微涡旋尺度相近,上清液UV₂₅₄和TOC值最低,去除效果最好。     

MBfR中PVDF/pDOPA改性膜耐污染性能研究

针对膜生物膜反应器(MBf R)研究中疏水性微孔膜供氧能力不足、耐污染性较差等问题,采用自聚合法对自制疏水性聚偏氟乙烯(PVDF)中空纤维膜进行表面改性,研究制备适用于MBf R技术的PVDF/p DOPA中空纤维复合膜。选取典型有机污染物牛血清白蛋白(BSA),考察原膜及表面改性膜的抗污染性能,并采用XDLVO理论定量解析BSA对PVDF原膜及PVDF/p DOPA改性膜的污染行为。研究结果表明,改性膜对BSA的吸附速率低于原膜,最终BSA吸附量为原膜的62.1%,进一步的氧传质实验表明BSA污染后,改性膜的氧总转移系数衰减率(14.0%)低于原膜(21.9%),显示出优于原膜的抗污染性能。XDLVO理论所涉及到的三种界面自由能中,粘附阶段和粘聚阶段的极性力界面自由能均起主导作用,决定总界面自由能的性质,范德华力界面自由能和静电力界面自由能绝对值相对较小,对膜污染影响较为微弱;PVDF/p DOPA改性膜与BSA之间的总表面自由能(10.53 m J/m2)远大于PVDF原膜(-12.52 m J/m2),较好的解释了原膜与改性膜耐污染性能的差异。     

计算机模拟技术在絮体分形成长研究中的应用

颗粒聚集形成絮体是水处理混凝过程中的中心现象，絮体的结构、行为和性能与混凝效果密切相关。计算机模拟为研究颗粒聚集过程提供了一条新的途径，而分形理论则提供了新的理论观念。本文对絮体的分形结构模型、絮体成长过程的计算机模拟方法和模拟结果的分析方法进行了系统的介绍，以期推动此项技术的应用研究。     

响应面法优化餐饮废水混凝工艺研究

餐饮废水是一种污染严重、成分复杂的高浓度有机废水。为了降低生化处理的负荷,采用混凝沉淀工艺对餐饮废水进行预处理,利用响应面法优化混凝工艺条件。通过扫描电子显微镜（SEM）、X射线能谱（EDS）及X射线衍射（XRD）分析絮体组成结构的变化,采用三维荧光光谱对比餐饮废水处理前后有机物成分的变化,探究餐饮废水的降解机理。结果表明：在初始pH 7.75,FeCl₃投加量为101.84 mg/L,搅拌及沉降时间分别为42.05 s和25.99 min的条件下,响应面法预测COD去除率为45.34%,与实测值仅相差0.02%（<2%）。由SEM、EDS及XRD分析可知,混凝前原水的悬浮物表面相对平整,混凝后的沉淀物颗粒表面粗糙,且表面呈空间网状结构;混凝前后废水的絮体主要含有C、Cl、Na、O、N、P等元素;混凝后的絮体表面附着铁的氢氧化物。通过三维荧光分析可知,混凝沉淀工艺能有效地去除可溶性微生物副产物和腐殖酸类物质。     

Interaction mechanisms associated with organic colloid fouling of ultrafiltration membrane in a drinking water treatment system

The Extended Derjaguin Landau Verwey Overbeek (XDLVO) approach was introduced to predict organic colloid fouling of membranes in an initial ultrafiltration (UF) phase. Two polymeric UF membranes, made of polyvinylchloride (PVC) and polyvinylidene fluoride (PVDF) respectively, were selected to investigate membrane fouling by filtering water samples with different organic colloid compositions. The experiment was performed to determine the fouling contributions of van der Waals (LW) interactions, electrostatic (EL) interactions, as well as double layer and short-range acid–base (AB) interactions, to the total interaction energy caused by organic colloids attaching to UF membrane surfaces. The results showed that LW interaction energy predominated when the distance between the membrane surface and organic colloid was > 5 nm, while AB accounted for a key contribution to total interaction energy over short distances (< 2.5 nm). The influence of EL interaction energy was ignored in the total interaction energy composition. The surface energy, among all characteristics of membrane material, was a dominant factor affecting membrane fouling. The experimental results of initial ultrafiltration of raw water from the actual water source were in accordance with the predictions based on XDLVO theory, indicating that it was a feasible option for predicting membrane fouling during the initial ultrafiltration phase.     

Natural organic matter fouling due to foulant–membrane physicochemical interactions

An extended DLVO (XDLVO) force analysis was introduced to predict natural organic matter (NOM) fouling in ultrafiltration (UF) membrane processes. Ultrafiltration membrane fouling experiments were performed using two NOM extracts from real waters and two commercial polymeric UF membranes. The hydrodynamic force by permeation drag and three interfacial forces of XDLVO (van der Waals, electrostatic, acid–base energy) were used for the force analysis. Acid–base interaction forces between NOM and UF membranes were dominant in short range (separation distances < 5 nm) and appear to determine the potential of NOM deposition. Relative extents of flux decline were successfully predicted using the short-range force analyses.     

Fractal Dimension Analysis of Flocs in Inline Coagulation-Microfiltration of Natural Organic Matter (NOM)

2D fractal dimension analysis of inline-coagulation (IC) flocs in microfiltration of NOM using power-law relationship and box-counting was done. Different process conditions represented by two types of coagulants (PIX and PAX) at four different hydraulic gradients (G-values of 4, 31, 98, and 300 s^?1) were tested. Fractal dimensions of the flocs formed under the varying process conditions were found to be different. Overall NOM removal was found to be similar for all cases; however, the membrane filtration and fouling phenomenon observed were affected by the process conditions. This study has investigated the relationships between fractal dimensions, aggregate properties, and membrane fouling behavior observed. In general, PIX resulted in higher particle concentrations and the more irregular floc shapes resulted in high irreversible fouling, lower specific cake resistance, and a more compressible cake layer. In contrast, PAX resulted in lower particle concentrations and the more regular floc shapes resulted in a more reversible fouling, higher specific cake resistance and a less compressible cake layer. The fractal dimensions properties were found to be complementary for the analysis of membrane and cake resistances and can be useful tools in membrane fouling elucidation and minimization.     

Slip behavior of liquid flow in rough nanochannels

The molecular dynamics simulation is applied to investigate the liquid flow in rough nanochannels with a focus on interfacial velocity slip via three-dimensional Couette flow system. The typical liquid spatial distribution, velocity profile and slip length for liquid flow in rough nanochannels are evaluated and compared with smooth nanochannel. The effects of liquid–solid interaction, surface roughness and shear flow orientation on slip behavior of liquid flow in rough nanochannels are all investigated and discussed. The results indicate that, regardless of whether the liquid flow in transverse or longitudinal flow configuration, the rough surface induces extra energy losses and contributes to the reduction of interfacial velocity in nanochannel when compared with smooth surface. A larger roughness size introduces a more irregular near-wall flow, which results in a smaller interfacial velocity slip. In addition, irrespective of surface condition, increases in liquid–solid interaction strength lead to small interfacial velocity slip and expand the extent of velocity nonlinearity in wall-neighboring region. In particular, the slip behavior of liquid flow in rough nanochannels is also influenced by the shear flow orientation. Interestingly, we find that interfacial velocity slip at the rough solid surface in transverse flow configuration is smaller than that in longitudinal flow configuration.     

Initial Deposition of Colloidal Particles on a Rough Nanofiltration Membrane

The initial rate of colloid deposition onto semi‐permeable membranes is largely controlled by the coupled influence of permeation drag and particle‐membrane colloidal interactions. Recent studies show that the particle‐membrane interactions are subject to immense local variations due to the inherent morphological heterogeneity (roughness) of reverse osmosis (RO) and nanofiltration (NF) membranes. This experimental investigation reports the effect of membrane roughness on the initial deposition of polystyrene latex particles on a rough NF membrane during cross flow membrane filtration under different operating pressures and solution chemistries. Atomic force microscopy was used to characterize the roughness of the membrane and observe the structure of particle deposits. At the initial stages of fouling, the AFM images show that more particles preferentially accumulate near the “peaks” than in the “valleys” of the rough NF membrane surface.     

基于膜表面与界面作用的膜污染控制方法

膜污染控制是膜技术能否成功应用的关键因素之一。讨论了膜面粗糙度、亲水性和荷电性等性质对膜分离性能的影响,介绍了膜表面性质参数的表征方法,分析了颗粒污染物团聚、颗粒与胶体吸附、胶体大分子的变形等对膜污染形成的影响。最后对面向应用过程的陶瓷膜材料表面与界面控制方法进行了总结。膜污染的研究已从操作参数调节发展到表面与界面作用的控制,对提高膜分离性能,促进膜过程在更多领域的推广应用有重要意义。     

Optimizing the coagulant dose to control membrane fouling in combined coagulation/ultrafiltration systems for textile wastewater reclamation

Optimal coagulation conditions need to be re-examined when coagulation is coupled to membrane filtration for wastewater treatment. This work focused on the optimization of coagulant dosing in order to control membrane fouling in ultrafiltration (UF), following coagulation for the reclamation of textile wastewater. The effects of pore size and coagulant types and dosages on flux decline were investigated using a stirred-cell UF unit. The flux was greatly enhanced for the UF membrane when a coagulant was added, whereas for the microfiltration (MF) membrane the flux decreased. This could be attributed to changes in the size of coagulated particles and their interaction with membrane pores. At a low dosage (e.g., 0.0371 mM as Al), the polyaluminum chloride (PACl) coagulant was found to control the flux decline most effectively for low ionic-strength wastewater. The optimal dose minimized the fouling and cake layer resistances, although it was sharp and dependent on influent composition. The cake layer protected the membrane from fouling, but it provided additional resistance to permeation. Analyses of turbidity, particle size, and membrane surface exhibited the characteristics of coagulated particles and their cake structures that are closely associated with flux behavior.