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.     

Membrane processes for water reuse from the effluent of industrial park wastewater treatment plant: a study on flux and fouling of membrane

Both the relationship between the flux and the fouling mechanism of ultrafiltration (UF) membrane and the effects of pretreatment before reverse osmosis (RO) process on the treatment of the effluent of industrial park wastewater treatment plant (IPWTP) were investigated to examine the application of membrane processes on the water reuse treatment. For the former, the flux data was first fitted to the Hermia model to give the implication of the fouling mechanism. Then, the fouling mechanism was further identified with the aid of the SEM morphology of membrane surfaces. For the latter, the changes of both water characteristics (turbidity, TOC, conductivity, particle size distribution, and organic solute molecular weight) and membrane properties (surface zeta potential and surface morphology) before and after the treatment of membrane processes were measured. It was found that the major blocking mechanisms of UF membrane process at initial and final stage were standard blocking of pore (causing from colloid materials) and cake blocking of pore (causing from suspended particles), respectively. On the other hand, it was concluded that the permeate from 1 μm/UF/RO process was suitable for the reuse of cooling water and low pressure boiler water.     

Effect of slow sand filtration of treated wastewater as pre-treatment to UF

Ultrafiltration (UF) of treated municipal wastewater has been used to produce high-quality reuse water for different applications. However, without pre-treatment, secondary treated wastewater effluent shows high fouling potential and reduces the performance of UF membrane filtration significantly. To remove foulants prior to UF, slow sand filtration (SSF) was investigated in the present work. Two pilot-scale slow sand filters were operated in tandem with UF. The performance of the UF plant was improved to a large extent by delivering slow sand filtrate compared to direct secondary effluent filtration. Removal of common organic fouling indicators (i.e., proteins, carbohydrates, and biopolymers) by SSF was significantly higher at 0.25 m/h versus 0.5 m/h filter loading rate. Results of a comparative analysis of SSF effluent characteristics and UF performance showed that the biopolymer content detected by size exclusion chromatography displayed a good correlation with the filterability of corresponding water sample by UF, while photo-metrically detected proteins and polysaccharides did not present any relationship with UF performance.     

截留分子质量和材质对浸没式超滤膜过滤性能的影响

针对截留分子质量和材质对浸没式超滤膜处理微污染地表水过滤性能的影响问题,研究了两者对膜去除水中颗粒物和有机污染物的特性及其对膜污染的影响。结果表明,随着膜截留分子质量的减小,超滤膜对浊度和各有机物指标的去除率逐渐升高,但超滤膜对溶解性有机物的去除率较低;不同材质的超滤膜对有机物的去除率存在差异。不同截留分子质量和材质的超滤膜过滤原水时的污染程度不同,截留分子质量较小的超滤膜污染程度较轻,但容易引起不可逆膜污染;聚砜(PS)膜抗污染的能力要强于聚偏氟乙烯(PVDF)和聚氯乙烯(PVC)膜,在实际应用中应根据不同水质特点合理选择超滤膜的截留分子质量和材质。     

Analysis of deposition mechanism during ultrafiltration of glycerin-rich solutions

Clarification of glycerin-rich solution is one of the potential applications of membrane within the oleochemical industry. However, one of the barriers in successfully utilizing the use of membranes such as ultrafiltration (UF) has been due to the fouling. In this work, flux decline during ultrafiltration of the glycerin-rich solutions was studied by using commercialized polymeric polyethersulphone (PES) membrane. Influence of fatty acids as foulants model (palmitic acid, stearic acid and oleic acid), pH of feed solution (3-10) and molecular weight cut-off (5 kDa, 20 kDa and 25 kDa) were analyzed. All the experiments were performed at constant pressure (2 bar) and temperature (40 °C). The Hermia's model was used to analyze the fouling mechanism during the flux decline which involve cake layer model due to adsorption of solute as well as pore blocking model. All the different types of flux decline kinetics were found to occur during the permeation of glycerin-rich solutions. However, the contribution of resistance due to cake layer formation was small for all the conditions studied. The fouling mechanisms were found to depend on the hydrophobicity of the PES membrane itself as well as the nature of foulants used in the study.     

投加粉末活性炭对超滤膜去除海水中有机物的影响

超滤膜的有机污染问题是膜法海水预处理技术在海水淡化工程应用面临的重要挑战,粉末活性炭吸附是目前常用的膜前预处理手段之一。本文对比分析了直接超滤和投加粉末活性炭后对海水中有机物的截留能力,利用三维荧光光谱分析了投加粉末活性炭对超滤膜截留有机物的影响机制,并考察了海水超滤过程中通量变化及膜污染情况。研究结果表明,投加粉末活性炭能够强化超滤膜对海水浊度和有机物的去除,当粉末活性炭投量为200mg/L时,整个系统对海水中DOC去除率从直接超滤时的55.1%提高到77.6%。利用粉末活性炭的吸附作用及其在超滤膜表面形成的疏松滤饼层能够显著提高超滤系统对海水中腐植酸类有机物的去除能力。与直接超滤相比,粉末活性炭-超滤系统对改善膜通量的作用有限,但粉末活性炭形成的滤饼层能够避免超滤膜与有机物直接接触,可显著减缓超滤膜的不可逆污染。     

Effect of different operating parameters on the recovery of proteins from casein whey using a rotating disc membrane ultrafiltration cell

In this study, effects of different operating parameters in ultrafiltration (UF) of casein whey in rotating disk ultrafiltration module, fitted with a 30 kD followed by a 5 kD molecular weight cut-off (MWCO) membrane have been analyzed and the benefits of membrane rotation with respect to stationary membrane module are highlighted. Prior to UF, centrifugation and microfiltration (MF) were carried out with the raw casein whey with an aim to remove the major membrane foulants like colloidal matters, suspended casein particles and lipid. The effects of pH, membrane rotation and transmembrane pressure (TMP) on UF flux and rejection were studied thoroughly, giving an emphasis on the effect of operating conditions in pressure and mass transfer controlled region as well. It was observed that solution pH was having a strong effect on UF flux and rejection for treating casein whey, which was explained in terms of prevailing monomer-dimer equilibrium of β-lactoglobulin, a major constituent of casein whey, as well as due to conformational changes of protein molecules with respect to isoelectric point. It was observed that for the 30 kD membrane, after 20 min of operation, 28.5% higher flux was obtained at pH 2.8 compared to pH 5.5 at a pressure of 490 kPa for stationary membrane, whereas the same figure for rotating membrane was 49.5%. Further, 38.7% higher UF flux at 300 rpm membrane speed compared to stationary membrane in 20 min of operation at pH 2.8 and TMP 490 kPa suggests the importance of shear across the membrane in minimizing the effects of concentration polarization. In the 5 kD membrane α-lactalbumin, which was mainly in the permeate stream from the 30 kD membrane, was separated from the other low molecular weight component of whey, such as lactose.     

Coagulation–bubbling–ultrafiltration: Effect of floc properties on the performance of the hybrid process

A novel hybrid process of coagulation–bubbling–ultrafiltration was proposed to study membrane fouling phenomena by surface water. Relationship of bubbles, flocs and the hollow fibers was explored. When applying less than 20 mL/min gas flow rate, membrane fouling was accelerated with air bubbles introduced. When gas flow rate increased further to 40 mL/min and 60 mL/min, TMP showed a two-stage development trend, which was a fast development in the first few hours followed with a relatively slow development after about 4 h. Unified membrane fouling index (UMFI) increased from 0.00216 (without bubbles) to 0.00274 m²/L (40 mL/min gas flow rate) and 0.00219 m²/L (60 mL/min gas flow rate). As gas flow rate increased, bubble size became bigger, and its distribution range became wider, resulting in higher shear rate in the ultrafiltration column, which led to severe floc breakage. Flocs of small size and compact structure accelerated membrane fouling, resulting in highest UMFI value under 40 mL/min gas flow rate. However, under 60 mL/min gas flow rate, with largest bubbles and highest shear rate examined in this study, concentration polarization was effectively limited. As a result, TMP development slowed down when pore blockage reached equilibrium.     

絮体表面形态对膜污染预测的影响

现有对混凝-膜过滤过程中膜污染的预测分析,一般采用XDLVO理论对光滑界面的作用能进行计算,但混凝絮体表面形态会对预测结果产生较大的影响。利用正弦波球体模型对粗糙腐殖酸(HA)絮体表面进行模拟,并通过表面元素积分法(SEI)结合XDLVO理论与复合辛普森规则,对不同粗糙程度的混凝絮体与聚偏氟乙烯(PVDF)膜的界面作用能进行量化模拟;并将结果与传统XDLVO理论模拟的光滑界面作用能进行了比较。实验结果表明,该模型适用于混凝-膜过滤体系中絮体界面作用能的模拟,同时在模拟过程中,由于粗糙度的不同会导致界面作用能在数值上存在1~2个数量级的差异;并且粗糙的絮体较完全光滑的絮体与膜污染趋势的拟合程度更高,即引入絮体表面形态对利用絮体与膜界面间相互作用能表征膜污染趋势的置信度更高。     

Membrane fouling formation when treating effluent by ultrafiltration

The objective of this study is to investigate membrane fouling caused by ultrafiltration (UF) when reusing tertiary effluent in an industrial park. A bench-scale membrane system was performed. Experimental results showed that the removal of iron, manganese, and turbidity were 62%, 30%, and 77%, respectively. From the infrared ray analysis of membrane fouling, one can see that the organic functional groups were aromatic rings and a few linear chain compounds of chromophore and auxochrome found in dyestuff. Therefore, tertiary effluent may induce both colloidal and organic fouling into the UF system.     

超滤膜处理乳化油废水的研究进展

综述了近年来国内外超滤膜分离技术应用于乳化油废水处理的研究进展,着重介绍了超滤处理工业乳化油废水的分离性能,以及超滤过程存在的问题和解决途径.针对实际运行过程中产生的膜污染现象,在新膜材料、膜组件改进和耦合工艺3方面进行了阐述.最后对今后的研究方向提出了建议.     

氧化预处理延缓超滤膜污染试验研究

分析了膜前氧化对超滤膜污染规律和水中有机组分构成的影响,并对延缓膜污染的机理与方法进行探讨。结果表明,试验所用3种氧化剂KMnO4、高锰酸钾复合盐(PPC)、H2O2均能延缓膜污染进程,在投加量为1 mg.L-1条件下,预处理效果PPC>KMnO4>H2O2;KMnO4和PPC对UV254的去除效果优于溶解性有机物,表明2种氧化剂优先去除含有双键的疏水性有机物;通过研究氧化剂投加量对比紫外吸光度变化的影响,说明氧化作用使水中腐殖质类成分向非腐殖质类成分转化。     

Amelioration of ultrafiltration process by lime treatment: Case of landfill leachate

Nowadays membrane ultrafiltration process is generally used in effluents treatment. However, at industrial level, this process has major limitations such as important membrane fouling. In this study, a pre-treatment with lime upstream ultrafiltration was envisaged. The effluent considered is landfill leachate. The final waste storage centres produce leachates resulting from the percolation of waters through the hidden waste mass. These effluents strongly charged in mineral and organic matters, must be treated before their release into natural environment. Concerning the cleaning up, results have shown that the selectivity of membranes has an important influence on elimination of pollution from organic source. As expected, any action of retention on salts and heavy metals has been shown. During the filtration of raw leachate, the fouling of membranes turns to be very important and does not allow reaching satisfactory productivity no matter the cut-off limit. There seems to be no impact from hydrodynamics on velocity circulation higher than 4 m s^− 1; this shows the existence of a dense and adhesive deposit on the membrane. The pre-treatment by lime allows (i) to precipitate carbonates under calcium carbonates form and ii) to eliminate by co-precipitation humic acids that are responsible for irreversible membrane fouling. Industrially, the implementation of the pre-treatment may allow reducing the costs of an ultrafiltration unit at about 50% in terms of investment and from 5 to 30% for operating costs.     

Integration of immersed membrane ultrafiltration with the reuse of PAC and alum sludge (RPAS) process for drinking water treatment

Effects of PAC and alum sludge generated from water treatment process on the effluent quality and fouling of immersed UF membrane were systematically investigated with representative source of natural water and the efficiency of coagulation, PAC adsorption and RPAS to treat natural surface water prior to UF were compared. It was found that the average turbidity removal by RPAS could reach up to 80.2%, and the turbidity removal of immersed membrane UF was independent of the influent, which could be kept at 99%. Particulates were reduced after being pre-treated by different processes, and particles with sizes ranging from 0.5 to 3.5 μm and larger than 13.5 μm were effectively removed by RPAS. UF coupled with RPAS pre-treatment got the best removal for DOM compared to other processes with average DOC and UV₂₅₄ removal 54.1% and 47.2% due to the high removal in the influent of UF. The residual alum content in the effluent of RPAS with UF was less than coagulation and bacteria were almost all removed by membrane. The membrane-fouling was mitigated by pre-treatment processes at different degrees, TMP of UF coupled with RPAS process was relatively stable in 15 d of run, the adsorption of PAC and large number of Al(OH)₃ complexes and precipitates for the foulant molecules might be an important mechanism.     

pH adjustment for seasonal control of UF fouling by natural waters

Natural surface waters in Algarve, Portugal, have important seasonal variations in natural organic matter (NOM) content, that influences ultrafiltration (UF) performance. This paper addresses the evaluation of the pH adjustment for seasonal control of UF fouling at a laboratory scale, using a plate and frame polysulphone membrane of 47 kDa MWCO. Results of two types of natural water (clear water, 3-5 NTU, and turbid water, 33-34.6 NTU) and three different water pH values (acid, neutral and basic) demonstrated that the pH adjustment could be used for seasonal control of UF fouling: when the water has less NOM (in dry periods, clear water), the acid pH will improve the UF performance, while during and after intense rainfall periods (turbid water with high NOM concentration) basic pH will be advantageous, because it minimizes membrane fouling. This behaviour is explained for clear water in terms of charge effects on membrane size. For turbid water, the electrostatic repulsion between membrane surface and NOM and turbidity particles is reduced at pH 4.13 and protonation of the NOM functional groups decreases the hydrodynamic radii of humic substances while increasing their hydrophobicity and their tendency to adsorb. Therefore, a dense fouling layer develops and flux is lower at pH 4.13 than at pH 8.33. These results together with the observed raw water feed concentrations decline and rejection decrease with WRR confirm the extensive adsorption on the membrane enhanced by the moderate hardness cation of this water.     

Membrane evaluation for the treatment of acidic clear filtrate

The total effluent load of a paper mill can be significantly decreased by recycling of purified clear filtrate (CF) back to paper-making process. The CF treated with membranes can be reused, for instance, as wire section shower water and in the dilution of chemicals. The main requirements for a membrane in CF treatment are high filtration capacity, high retention of turbidity and low fouling tendency. Previous studies have shown that the regenerated cellulose (RC) ultrafiltration (UF) membrane C30F (current trade name UC030T) is especially suitable for the treatment of paper mill process waters. Every paper-making process is, however, different. Thus, filtration experiments are required in order to find the most optimal membrane for the treatment of a certain process water. In this study the best membrane for the treatment of acidic clear filtrate (ACF) was searched. The performance of the C30F membrane was compared with five UF and three microfiltration (MF) membranes. The results revealed that in addition to the C30F membrane, also some other membranes produced high filtration capacity with ACF (approximately 200 L/(m²h bar)). All the tested membranes also retained over 90% of turbidity. The extremely hydrophilic C30F membrane had, however, lower fouling tendency compared to the other tested membranes. Therefore, it was concluded that the C30F membranes were the best possible membrane for the ACF treatment.     

Ultrafiltration of Wastewater from Isolated Soy Protein Production: Fouling Tendencies and Mechanisms

Membrane separation processes appear to be a good alternative in wastewater treatment systems. One of the biggest limitations is the decrease in permeate flux, which is caused mostly by concentration polarization and fouling phenomena. The extent of these phenomena are dependent on the interactions between the different solution compounds, membrane-solution interactions, and the operating conditions. The fouling tendencies of three different commercial tubular ceramic membranes (5, 20, and 50 kDa) during the ultrafiltration of an isolated soy protein (ISP) wastewater were evaluated through determination of the water permeate flux before and after the wastewater ultrafiltration and using Hermia's Model. The wastewater from ISP production is a complex solution characterized by a very high organic load: reaches COD values greater than 18,000 mg · L^?1. The wastewater proteins are small molecules (8 to 50 kDa) that could not be removed during the industrial processing. The recovery of these small proteins and their return to the ISP production process would result in both economical and environmental benefits by increasing the final product yield and reducing significantly the wastewater organic load. All the membranes tested presented a large fouling tendency: 65% (5 kDa membrane), 69% (20 kDa membrane) and 76% (50 kDa membrane). The best fit to Hermia's Model for all of the UF membranes was obtained by the complete blocking model.     

Chemical control of colloidal fouling of reverse osmosis systems

Fouling of membranes by colloidal organic and inorganic particles continues to be documented as the most common and challenging obstacle in attaining stable continuous operation of reverse osmosis (RO) and ultrafiltration (UF) systems. Much current research is being conducted on physical parameters to mitigate such fouling. The focus has been on membrane synthesis and element design; microfiltration and ultrafiltration pretreatment; electromagnetic devices; correlation with physical factors such as Silt Density Index, zeta potential and critical flux; technique of direct observation of fouling process through a membrane; and classification of macromolecular organics for correlation with fouling characteristics. We report initial successes with chemical control of colloidal fouling. Through screening with a large number of observable coagulations of natural colloids, we have developed a group of proprietary anticoagulants and dispersants that would, at less than 10 ppm dosage to the RO feedwater, control various classes of colloidal foulants. Case studies of the control of humic matter, elemental sulfur and colloidal silicate in problematic RO systems that became stabilized are briefly presented. We conclude that a great need and potential exists in economically controlling the myriads of fouling interactions of colloidal particles during concentration within the brine channels of RO membrane elements. Low dosages of antifoulants can in many cases obviate the need for installation and maintenance of pretreatment unit or operations designed to remove such colloidal foulants from the process stream.     

超滤在饮用水处理中的应用和研究进展

介绍了超滤在饮用水处理中的应用和研究进展;研讨微絮凝+超滤组合工艺、粉末活性炭(PAC)+超滤组合工艺,以及膜污染及其防治技术;从处理效果、经济性能上对超滤工艺与常规过滤工艺进行对比。认为超滤工艺必将成为未来饮用水最重要最有效的处理技术之一;而混凝+超滤工艺比较适合我国国情,具有很好的发展前景。     

Ultrafiltration and nanofiltration membranes applied to the removal of the pharmaceuticals amoxicillin,naproxen, metoprolol and phenacetin from water

BACKGROUND: In the removal of pharmaceuticals present in aquatic systems by membrane processes, some important issues must be explored in order to obtain a better knowledge of the global process. Among these issues, a better understanding of the influences of the operating parameters on the membrane flux, an analysis of membrane resistances and fouling, and determination of the removal of specific substances, must be studied. RESULTS: Four selected pharmaceuticals (amoxicillin, naproxen, metoprolol and phenacetin) were subjected to ultrafiltration (UF) and nanofiltration (NF) processes for their removal from several water matrices. The determined permeate fluxes at the steady state were affected by the main operating conditions: molecular weight cut‐off (MWCO) of the membrane, transmembrane pressure TMP, cross‐flow velocity and temperature. The retention coefficients with the UF membranes followed the sequence naproxen > metoprolol > amoxicillin > phenacetin, and with the NF membranes, followed the trend: amoxicillin > naproxen > metoprolol > phenacetin, due to the role of other mechanisms such as size exclusion and electrostatic repulsion. In the case of the selected water matrices, the retention coefficient was referred to some quality parameters (total organic carbon, chemical oxygen demand and absorbance at 254 nm), leading to moderate (UF) or high (NF) removals of the organic matter content. CONCLUSIONS: The NF CK membrane achieved the highest retention of these pharmaceuticals (excepting phenacetin), and provided retentions for quality parameters around 80% in the four water systems tested. Copyright © 2011 Society of Chemical Industry