Effect of pre-treatment on membrane fouling of PVDF (Polyvinylidene Fluoride) microfiltration membrane with different structures in a pilot-scale drinking water production system

Two pilot-scale polyvinylidene fluoride (PVDF) microfiltration (MF) membranes with different structures (i.e. symmetric and asymmetric) were operated after coagulation/sedimentation, sand filtration, and chlorination. Turbidity was removed completely. Moreover, humic substances, Al, and Fe were removed very well by the pilot-scale system. An asymmetric membrane (HFS membrane) having a nominal pore size of 0.05 μm showed relatively high removal efficiency of the small organic matter (about 6,000 Da) than a symmetric membrane (HFM membrane) having a nominal pore size of 0.1 μm. However, the extracted inorganic concentrations of the HFM membrane were relatively higher than that of the HFS membrane. Therefore, it could be concluded that the HFS membrane better reduced membrane fouling than the HFM although the nominal pore size of the former was half of the latter. To control microbial growth and mitigate membrane fouling, a NaOCl solution was injected into the effluent of sand filtration before the both membranes. However, it adversly affected membrane fouling due to the oxidization of inorganic substances such as Al, Fe, and Mn.