Effect of pH on anionic polyacrylamide adhesion: New insights into membrane fouling based on XDLVO analysis

pH can affect the physicochemical properties of the membrane and the anionic polyacrylamide (APAM), thus changing the degree and situation of membrane fouling. However, limited research has been conducted to determine its mechanism based on the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. Here, the effects of pH on the membrane fouling caused by APAM and the roles of pH were comprehensively studied. It was found that, the acid–base component greatly affected the membrane fouling behavior in a short range. The value of energy barrier decreased with decreasing the pH value, and there existed a critical pH (3.5) below which the energy barrier would disappear, facilitating attachment of the APAM. The APAM–APAM energy barrier was lower than that of APAM–membrane at the same pH, indicating that the membrane fouling at the later stage of filtration was more serious. Moreover, the filtration resistance of the original membrane and pore blockage decreased slightly with an increase in pH, whereas that of the cake layer decreased significantly. Furthermore, the potential for membrane fouling and the total interfacial interaction free energies had an obvious linear dependence. The obtained results provide important guidance for mitigating membrane fouling.