Micro-polluted water resources treatment by PVDF-TiO2 membrane combined with Fe2+/sodium dithionite (DTN)/O2 pre-oxidation process

Abstract

Modifying PVDF membrane by blending hydrophilic nano TiO2 has been highly concerning, but its practical application is not well investigated. In this study, PVDF-TiO2 membrane was employed in two modes to treat micro-polluted raw water for the first time, direct membrane filtration and pre-oxidation assists membrane filtration. At two filtration modes, the PVDF-TiO2 membrane had comparable rejection capability to the unmodified PVDF membrane, as the removal of permanganate index (CODMn) was 0.26–0.72 mg/L, UV254 was 0.0070–0.0618 cm−1, turbidity was 1.60–4.49 NTU, and the total number of colonies was 360–23,780 CFU/mL. As for raw water treatment, using Fe2+/sodium dithionite (DTN)/O2 system as the pre-oxidation process to assist the filtration of the PVDF-TiO2 membrane was feasible. After optimization, the applicable conditions of the Fe2+/DTN/O2 process were DTN dosage at 100 mg/L and a CFe/CDTN of 1:4. As a result, the effluent qualities of the PVDF-TiO2 membrane significantly improved. It was investigated that atrazine (ATZ), CODMn, UV254, and turbidity reduced, which was realized by the synergic effects of the pre-oxidation by free radicals and flocculation by iron. Pre-oxidation of the Fe2+/DTN/O2 process could also enhance the permeability of the PVDF-TiO2 membrane from 53.6 to 58.0 L/(m2·h), nearly two times the PVDF membrane. Besides, the practical fouling of the PVDF-TiO2 membrane was stably alleviated by the reduced Rt, Rre, and Rir, mainly due to constraining the internal pore fouling effectively.