Application of Zirconium/PVA Modified Flat-Sheet PVDF Membrane for the Removal of Phosphate from Aqueous Solution

Control of phosphate in natural waters is very important to prevent eutrophication. In this study, a novel zirconium/PVA modified adsorptive flat-sheet PVDF membrane was applied for phosphate removal from simulated contaminated water. The uptake of phosphate decreased with an increase in solution pH; the best performance was observed at pH 2.0. Most of ultimate uptake occurred in 10 h, and the adsorption equilibrium was established in 30 h for both pH 2.0 and pH 7.0. The Langmuir adsorption isotherm better represented the experimental observation than the Freundlich adsorption isotherm; the maximum adsorption capacity of 73.99 and 21.64 mg P/g was achieved at pH 2.0 and pH 7.0, respectively. The adsorption occurred rapidly in the first 10 h, leading to 90% of the ultimate removal. The uptake of phosphate was inhibited by the commonly existing anions with a sequence of CO₃^2- < SiO₃^2- < humic acid < F^- < Cl^- < SO₄^2-. The membrane with an area of 12.56 cm² could treat 4.63 and 1.82 L phosphate solution through a filtration mode with an influent phosphorus concentration of 216 μg/L and pH 2.0 and pH 7.0, respectively, to meet the USEPA requirement for a reservoir of 25 μg/L. The membrane demonstrated a good regeneration-reuse capacity through a series of regeneration-reuse studies. It was found that the uptake was mainly due to an ion exchange process between chloride and phosphate ions.