Effect Of Trivalent Iron Salt And Aluminum Salt On Fouling Behavior Of PVDF Ultrafiltration Membrane With Typical Dissolved Organic Matter

In order to unravel the mechanism of the effects of trivalent iron salt and aluminum salt on ultrafiltration membrane fouling behavior with typical organic pollutants,humic acid,bovine serum albumin and sodium alginate were selected to represent the ubiquitous humic,protein and polysaccharide organic pollutants in wastewater and the fouling behavior on PVDF ultrafiltration membranes under different dosages of Fe Cl₃/Al Cl₃were systematically investigated.Finally,the following conclusions are drawn:（1）The effects of trivalent iron salt and aluminum salt on the fouling of ultrafiltration membranes with the organic pollutants were not the same:For pollutant BSA,the removal rate and corresponding flux decay rate in 2 h filtration time without adding Fe Cl₃or Al Cl₃were 89.5%and 64%,respectively.When adding Fe Cl₃or Al Cl₃,the removal rate of BSA increased to 96.1%and 96.5%,respectively.However,after adding Fe Cl₃,a loose fouling layer was formed on the membrane surface,which was accompanied by a reduction of the flux decay rate to 53%,while after adding Al Cl₃,a dense fouling layer was formed on the membrane surface,which was accompanied by an increase of the flux decay rate to more than 83%.Obviously,Fe Cl₃could reduce membrane fouling caused by BSA,while Al Cl₃could aggravate membrane fouling.Similarly,for SA,although both Fe Cl₃and Al Cl₃could reduce membrane fouling,compared with Al Cl₃,Fe Cl₃was more likely to form a loose fouling layer on the membrane surface,which could significantly reduce membrane fouling.（2）The dosage of trivalent iron salt and aluminium salt was one of the key factors to control membrane fouling behavior.For Fe Cl₃,whether hydrophobic HA,amphoteric BSA or hydrophilic SA,in the range of low dosage,the density of fouling layer could be increased,and the corresponding membrane fouling would be aggravated with the increase of Fe Cl₃dosage.On the contrary,when Fe Cl₃dosage reached a certain value,loose fouling layer could be formed on the membrane surface,and the corresponding membrane fouling began to reduce significantly.Similarly,when the dosage of Al Cl₃increased to 0.02m M and 0.05m M,the flux decay rates of fouling membranes caused by HA and SA increased to 60%and 70%respectively,but when the dosage continued to increase to 0.05m M and 0.07m M,corresponding flux decay rate both began to decrease.This was mainly due to the formation of more small flocs when the dosage of Fe Cl₃or Al Cl₃was small,the formation of a denser fouling layer on the membrane surface and easy to cause blockage of the membrane pore,resulting in increased membrane fouling;with the increase dosage of Fe Cl₃or Al Cl₃,it was easier to form large flocs,forming a loose fouling layer on the membrane surface,accompanied by the reduction of membrane fouling.（3）In addition,the effects of trivalent iron salts and aluminium salts on membrane fouling behavior were closely related to the nature of organic pollutants.For example,at the same dosage of Fe Cl₃,a dense fouling layer was formed on the membrane surface caused by amphoteric BSA,which aggravated membrane fouling;on the contrary,a looser fouling layer was formed caused by hydrophobic HA,and the corresponding membrane fouling also slowed down.Similarly,under the same dosage of Al Cl₃,compared with hydrophobic HA,it was more likely to form a dense fouling layer on the membrane surface caused by hydrophilic SA,which corresponded to a more serious fouling.This may be due to the different physical and chemical properties of surface functional groups,chargeability and molecular structure of different pollutants,resulting in different complexation ability with trivalent ions,accompanied by different membrane fouling behavior.