Study On Phosphorus Removal From Water Using An Anion-exchange Membrane

This study investigated the removal of phosphorus from water by Donnan dialysis with anion-exchange membrane, and put forward the three steps of phosphorus transports from feed solution to receiver solution. We analysised the influence of pretreatment of anion-exchange membrane by immersed in NaCl solution and changing the concentration of receiver solution on the three steps of phosphorus transport, preliminarily discussed the influence of temperature, concentration of receiver solution, stirring speed, receiver composition, HRT, flow rate in receiver solution, initial concentration of feed solution, accompanying anions in feed solution, initial pH of feed solution on removal of phosphorus using anion-exchange membrane.This study investigated the influence of pretreatment of anion-exchange membrane by immersed in NaCl solution and changing the concentration of receiver solution on the three steps of phosphorus transport. The results showed:pretreatment of anion-exchange membrane by immersed in NaCl solution could promote the first step of phosphorus transport, finally promoted the whole ion exchange process and improved the phosphorus removal; improve the concentrion of receiver solution could promote the secend and third step of phosphorus transport, but this had little influence on ion exchange process and phosphorus removal.This study also investigated the inflence of various experimental conditions on phosphorus removal. The results showed:when raising temperature from10℃to25℃, the phosphorus removal rate increased from56.8%to69.3%; change the concentration of receiver solution had little influence on phosphorus removal; the removal rate of phosphorus greatly decreased to27.8%when using Na2SO4solution as receiver solution, but using NaHCO3solution as the receiver solution, the phosphorus removal was almost not affected; when decrease the sample injection rate of feed solution, the contact time of phosphorus in feed solution with anion-exchange membrane was prolonged and this promoted the phosphorus removal; when increase the sample injection rate of receiver solution, the concentration of phosphorus in the receiver solution could remain at a low leval but this had little influence on phosphorus removal; when increase the initial concentration of feed solution, although the concentration of phosphorus after Donnan equilibrium was increased, but the removal rate was only slightly affected and the membrane flux was greatly increased; when the accompany ion was added to the feed solution, the thickness of membrane electrical double layer (κ-1) and ξ potential was decreased thus decreased the resistance of membrane boundary layer, so the phosphorus removal rate was increased; under strong acidic condition, part of phosphorus in feed solution was exist as the form of H3PO4molecule which could not permeat the anion-exchange membrane, and this result in phosphorus removal rate significantly decreased to44.5%, when the pH value increased to5and7, most of phosphorus in feed solution was exist as the form of H2PO4-, the phosphorus removal rate was increased to67%, when the pH value futher increased to9, most of phosphorus in feed solution was exist as the form of HPO42-, the phosphorus removal rate was slightly increased; due to the OH-transported form feed solution to receiver solution, the pH value of feed solution decreased and the pH value of receiver solution increased during the experimental process, and this tendency became more obvious when the initial pH value of feed solution increased.