反洗水组分对超滤膜污染的影响
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摘要
超滤反洗如同短时间的"死端过滤",反洗水组分对超滤膜污染进程有重要影响,以腐殖酸(HA)、Na~+和Ca~(2+)模拟反洗水中的小分子有机物、一价和二价金属阳离子,将海藻酸钠(SA)作为典型污染物,通过死端过滤的方式分析了反洗水中的不同组分对PVDF超滤膜污染的影响。同时借助质量守恒定律对膜的反洗效率和反洗后污染物的去除情况进行了定量分析。结果表明,反洗水中单独存在的小分子有机物对膜污染的影响并不显著,但小分子有机物协同金属阳离子对膜污染产生了较为明显的不利影响;一方面Ca~(2+)、Na~+等阳离子能够与带负电的HA小分子吸附结合,形成尺寸较大的聚集体,导致膜内壁污染以及反洗膜孔的堵塞,从而降低反洗效率,加剧膜面污染物的积累;另一方面,通过Ca~(2+)、Na~+等阳离子的"架桥作用"与电荷屏蔽效应,强化了膜表面污染物与膜壁之间的静电吸附作用,导致了更为严重的不可逆污染。
UF backwash is similar to a short-time"dead-end filtration".The composition of the backwashing water has important influences on the process of UF membrane fouling.Humic acid(HA),Na~+and Ca~(2+)were applied to simulate low-molecular-weight organics,monovalent and bivalent mental cations,respectively.Sodium alginate(SA)was selected as the typical contaminant.The experiment was performed under dead-end filtration mode to investigate the effect of different backwash water composition on the PVDF UF membrane fouling.Backwash efficiency and the foulant removal after backwash were quantitatively analyzed according to the mass balance.The results showed that the effect of low-molecular-weight organics in backwash solution alone on membrane fouling were insignificant.However,they interacted with metal cations and then produced mild adverse effect.Ca~(2+),Na~+and other cations combined with negatively charged HA,and formed large aggregates and blocked membrane pores,which subsequently reduced backwash efficiency and increased the accumulation of foulant on the membrane surface.Moreover,through the"bridging effect"and the charge shielding effect of Ca~(2+)and Na~+ions,the electrostatic interaction between the foulant and the membrane surface was enhanced,which resulted in serious irreversible fouling.
UF backwash is similar to a short-time"dead-end filtration".The composition of the backwashing water has important influences on the process of UF membrane fouling.Humic acid(HA),Na~+and Ca~(2+)were applied to simulate low-molecular-weight organics,monovalent and bivalent mental cations,respectively.Sodium alginate(SA)was selected as the typical contaminant.The experiment was performed under dead-end filtration mode to investigate the effect of different backwash water composition on the PVDF UF membrane fouling.Backwash efficiency and the foulant removal after backwash were quantitatively analyzed according to the mass balance.The results showed that the effect of low-molecular-weight organics in backwash solution alone on membrane fouling were insignificant.However,they interacted with metal cations and then produced mild adverse effect.Ca~(2+),Na~+and other cations combined with negatively charged HA,and formed large aggregates and blocked membrane pores,which subsequently reduced backwash efficiency and increased the accumulation of foulant on the membrane surface.Moreover,through the"bridging effect"and the charge shielding effect of Ca~(2+)and Na~+ions,the electrostatic interaction between the foulant and the membrane surface was enhanced,which resulted in serious irreversible fouling.
引文
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[10]Ye Y,Chen V,Le-Clech P.Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[J].Desalination,2011,283:198-205.
[2]孟倩.三种典型污染物对超滤膜的污染研究[D].哈尔滨:哈尔滨工业大学,2014.Meng Qian.Effect of Three Model Fouling Compounds on UF Membrane[D].Harbin:Harbin Institute of Technology,2014(in Chinese).
[3]Li S,Heijman S G J,Verberk J Q J C,et al.Removal of different fractions of NOM foulants during demineralized water backwashing[J].Sep Purif Technol,2012,98:186
[4]Li S,Heijman S G J,Verberk J Q J C,et al.Fouling control mechanisms of demineralized water backwash:Reduction of charge screening and calcium bridging effects[J].Water Res,2011,45(19):6289-6300.
[5]Li S,Heijman S G J,Verberk J Q J C,et al.Impact of backwash water composition on ultrafiltration fouling control[J].J Membr Sci,2009,344(1/2):17-25.
[6]Chang H Q,Qu F S,Liu B C,et al.Hydraulic irreversibility of ultrafiltration membrane fouling by humic acid:Effects of membrane properties and backwash water composition[J].J Membr Sci,2015,493:723-733.
[7]Bessiere Y,Jefferson B,Goslan E,et al.Effect of hydrophilic/hydrophobic fractions of natural organic matter on irreversible fouling of membranes[J].Desalination,2009,249(1):182-187.
[8]Sioutopoulos D C,Karabelas A J.Evolution of organic gel fouling resistance in constant pressure and constant flux dead-end ultrafiltration:Differences and similarities[J].J Membr Sci,2016,511:265-277.
[9]Ding Q,Yamamura H,Murata N,et al.Characteristics of meso-particles formed in coagulation process causing irreversible membrane fouling in the coagulation-microfiltration water treatment[J].Water Res,2016,101:127-136.
[10]Ye Y,Chen V,Le-Clech P.Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[J].Desalination,2011,283:198-205.