pH对膜污染层EPS污染特征的影响及机理分析

溶液pH值不仅影响溶质的电荷等表面性质,同时也影响膜表面的特性,从而影响溶质与膜表面之间的相互作用和溶质在膜面的沉积量及膜通量.胞外多糖(Extracellular POlvsac-charides,EPS)是膜生物反应器(Membrane Bioreactor,MBR)中主要的膜污染物质之一,从实际MBR膜污染层中分离纯化得到的EPS,在EPS引起膜污染机理分析的基础上,以过滤阻力、EPS在膜表面沉积量及膜通量为评价指标,综合分析不同溶液pH对EPS污染特征的影响,可为揭示MBR中EPS膜污染的成因和机理以及污染膜的清洗提供参考.结果表明,MBR膜污染层EPS的膜污染过程较好地符合沉积阻力模型,EPS在膜表面的污染主要是EPS沉积引起的;EPS溶液的pH越高,其与膜之间的排斥力越大,沉积量越少,沉积阻力越小,膜通量越高.pH为7.0时,沉积阻力为3.34×10~(11) m~(-1),沉积量为1.25 g/m~2,初始相对膜通量为9.8%.

Mechanism analysis and influence of pH on fouling properties of EPS from membrane fouling layer

Solution pH influences the surface charge and structure of solute as well as those of membrane, consequently heavily affects the interaction between solute and membrane, deposited amount of solute on membrane surface and membrane flux. Extracellular polysaccharides (EPS) are one of important foulants of membrane sur face in membrane bioreactor (MBR). EPS were obtained from membrane fouling layer of treating wastewater MBR. Based on the determination of membrane flux, filtration resistances and deposited amount of EPS on the membrane surface as well as the mechanism analysis of membrane fouling, the influence of solution pH on the PVDF membrane fouling of EPS obtained was investigated. The membrane fouling caused by EPS in MBR fol-lows the model of deposition resistance. EPS deposition on membrane surface leads to membrane fouling. As pH of EPS solution increases, the repulsion between EPS and membrane surface goes up, depositing resistance of filtration goes down and deposited amount of EPS increases. When pH is 7.0, deposited resistance of filtration,deposited amount of EPS and flux are 3.34 × 10~(11) m~(-1), 1.25 g/m~2 and 9.8% , respectively.