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-TiO 2 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-TiO 2 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-TiO 2 membrane. In brief, the J C and J TH of PVDF-TiO 2 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-TiO 2 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 J C 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-TiO 2 modified membrane.