Strategy study of critical flux/threshold flux on alleviating protein fouling of PVDF-TiO2 modified membrane

Aiming at the fouling problem of PVDF membrane, one novel integrated strategy was used for the first time, including hydrophilic membrane modification and low-pressure operation. Permeability and anti-fouling ability of PVDF were simultaneously improved by nano-TiO2 embedment. From perspective of operating condition optimization, the concepts of critical flux (J(C)) and threshold flux (J(TH)) were recommended as fouling-control tools. The J(C) and J(TH) of PVDF-TiO2 membrane were tested by two constant pressure-steps methods, i.e. Constant pressure-step method and Alternating constant pressure-step method. Three indicators, consisting of instant FTTT curves, dFlux/dt condition and TMP-Flux(ave) curve, were employed to evaluate the J(C) and J(TH) of PVDF-TiO2 membrane. In brief, the J(C) and J(TH) of PVDF-TiO2 were 10.62 and 23.91 L/(m(2).h), respectively, which were nearly 3 times of PVDF membrane. Fouling resistance results displayed that protein irreversible fouling of two PVDF membranes were effectively reduced by J(C) mode and J(TH) mode. Besides, reversible fouling of PVDF-TiO2 membrane was controlled well by J(C) mode meanwhile. The pure water filtration line (PWF line) and the normalized resistance were both used to judge the form of Jc of two membranes. As compared with PVDF, it was speculated the enhancement of J(C) and J(TH) mainly related to the better hydrophilicity and local hydraulic condition of PVDF-TiO2 modified membrane.