Ozonation of dye wastewater by membrane contacing process using modified PVDF membrane

Abstract

This thesis presented the study of the hydrophobic surface modification of PVDF hollow fiber membrane and membrane stability test of ozone exposure aiming for application as membrane contactor for dye wastewater treatment with ozonation process. For the 7.5M NaOH activation, the contact angle of original membranes (68) was increased to 100 after modification with 0.01M FAS-C8 for 24h. There was no significant change in pore size and pore size distribution. The surface modified membranes under helium plasma activation followed by grafting with 0.01M FAS-C8 for 24h showed higher contact angle and surface roughness than that obtained by NaOH activation method. In the study of membrane stability toward ozone, the four different hollow fiber membranes (original PVDF, modified PVDF by chemical activation/modification (PVDF-CM2) and plasma activation/modification (PVDF-PAM), and PTFE) were exposed to ozone at varied concentration and time. The contact angles of the PVDF-PAM and PVDF-CM2 membranes exposed to ozone decreased, whereas the contact angles of original PVDF membranes were increased at low concentration and duration, and remained constant. The pore size and outer surface of membranes exposed to ozone presented insignificant change. Meanwhile, the properties of PTFE membranes exposed to ozone did not changed. For the study on the decolorization of dye solutions by membrane contactor with ozonation process, the long-term ozone fluxes by PVDF-PAM were higher and more stable than those of the original PVDF membrane. The use of the PVDF-PAM membrane as the membrane contactor with ozonation is very beneficial due to complete decolorization and high degradation efficiency of dye derivative aromatic fragments. Sulfate, nitrate, oxalic and acetic acids were identified as main oxidation products. The reduction of COD and TOC showed partial degradation and mineralization of these dyes.