Analysis Of Microfiltration Membrane Fouling By Soluble Microbial Products Using XDLVO Theory

Membrane fouling restricts the application of MF membrane, and soluble microbial product was a kind of foulant which causes irreversible fouling in the MF membrane filtration. In order to study the role of interfacial interactions in the MF membrane fouling, the XDLVO theory was used to calculate the interfacial free energy of membrane-foulant and foulant-foulant, and the membrane filtration experiment was also performed, with the varied solution pH.For alginate fouling, in the pH extant involved by the experiment, among the three interactions, the AB interfacial free energy (ΔGAB) plays a dominate role on membrane-alginate interfacial free energy of adhesion and alginate-alginate interfacial free energy of cohesion, and determines the attractive or repulsive character of the total interfacial energy. The absolute value of LW interfacial free energy (ΔGLW) is minor, and the absolute value of EL interfacial free energy (ΔGEL) is minimum. As a result, it can be concluded that the AB interaction plays a dominate role in the influence of interfacial free energy by pH. The interaction between hydrophobic PVDF membrane and alginate is attractive while the interaction between hydrophilic PES membrane and alginate is repulsive, and this results in the higher resistance removal by back washing of fouled PES membrane. The difference of alginate fouling performance at different solution pH is influenced by the change of AB interfacial free energy. For the same membrane, as pH raised ΔGADTOT was rising because the rising ΔGADAB at adhesion stage, as a result, the interfacial attraction enhanced and the interfacial repulsion weaken. There is a similar situation at the cohesion stage. The fouling potential (k) of adhesion stage for one membrane in alginate filtration experiment at different solution pH is pH5>pH7>pH8>pH9, and there is a strong correlation between the calculated membrane-alginate free energy of adhesion and the first stage fouling potential and the second stage fouling rate potential is influenced by the alginate-alginate free energy of cohesion. The irreversible fouling can be explained by the XDLVO theory. The attractive PVDF membrane-alginate free energy of adhesion caused lower flux recovery of back washing, while the repulsive PES membrane-alginate free energy of adhesion caused higher flux recovery. The fouling performance of alginate filtration can be demonstrated by XDLVO theory.For BSA fouling, in the pH extant involved by the experiment, among the three interactions, the AB interfacial free energy (ΔGAB) plays a dominate role on membrane-BSA interfacial free energy of adhesion and BSA-BSA interfacial free energy of cohesion, and determines the attractive or repulsive character of the total interfacial energy. The absolute value of LW interfacial free energy (ΔGLW) is minor, and the absolute value of EL interfacial free energy (ΔGEL) is minimum. As a result, it can be concluded that the AB interaction plays a dominate role in the influence of interfacial free energy by pH. In adhesion stage, the value of dominating AB interfacial free energy ΔGADAB is pH10>pH7>pH3>pH4.7, and caused the same sequence of total interfacial free energy ΔGAdTOT, and this means the attraction is maximum at pH4.7, and the repulsion increases at pH10. In cohesion stage the sequence is similar. There is correlation between the fouling potential and the total interfacial free energy in both adhesion stage and cohesion stage. The irreversible fouling of PVDF membrane is more severe than PES membrane for the attractive interfacial free energy in adhesion stage, and the irreversible fouling mainly takes place in adhesion stage.