Effects Of Coexisting Components On PAEX Control Of Sodium Alginate Ultrafiltration Membrane Fouling

Natural organic matter(NOM)causes serious membrane organic fouling in the ultrafiltration(UF)technology,which increases the operating cost of ultrafiltration technology.In recent years,the ability of anion exchange resins(AEX)to mitigate membrane fouling caused by NOM has been widely proven,and the integrated process combining AEX with UF technology has also received more attention.However,the effectiveness of ion exchange technology to control membrane fouling is affected by the coexisting components in the influent,which limits the applicability of the technology.In this study,sodium alginate(SA)was used to simulate the polysaccharide components in NOM to investigate the influence of fulvic acid(FA)and SO₄^2-coexistence on the membrane organic fouling formed by SA in PAEX+UF integrated process.The influence mechanism of coexisting components in solution and near membrane surface was analyzed,and the water quality suitability of ion exchange technology to control membrane fouling was obtained.Stoichiometric experiments show that PAEX removes SA,FA and SO₄^2-through ion exchange mechanism.Therefore,the existence of FA and SO₄^2-would compete for the exchange sites on PAEX,thus inhibiting the SA removal effect of PAEX in the solution,and the inhibition effect of SO₄^2-with high charge density was more significant.When the concentration of SA and coexisting component is 10 mg?L^-1,the presence of SO₄^2-and FA reduces the adsorption rate of SA to 0.27 mg?min^-1 and 0.40mg?min-1 from 0.55 mg?min^-1 in the rapid adsorption stage,respectively.In the adsorption equilibrium stage,the removal rate of SA by PAEX decreased from 90%to46%and 82%,respectively.Similar to that in solution,the SO₄^2-?FA in PAEX+UF process can reduce the membrane fouling control effect of PAEX,and the influence of SO₄^2-is more significant.Compared with the separated process,the integrated process has more obvious control effect on membrane fouling due to the interaction between PAEX and SA fouling layer.However,the existence of coexisting components in the solution will affect the interfacial force between PAEX and SA contaminated layer,and the binding between SO₄^2-and PAEX exchange site is stronger,which will significantly reduce the interfacial force.However,the binding between FA and PAEX exchange sites is relatively weak.When PAEX with FA exchange is exposed to SA fouling layer,SA will replace FA and enhance the control effect of membrane fouling.PAEX treated with a mixture of 10 mg?L^-1 SA and 10 mg?L^-1 FA showed an interaction force of 3.95 m N?m^-1,which was 5 times that of PAEX treated with 10 mg?L^-1 SA.And the ability of the former to control membrane fouling near the membrane surface is 11 times higher than that of the latter.In conclusion,PAEX+UF integrated process is affected by the coexisting components in the water,and the degree of influence is related to the charge density of the coexisting components.When the charge density of the coexisting component is high,it binds closely with PAEX,which significantly inhibates the removal of SA from the solution and weakens the interaction between PAEX and the fouling layer near the membrane surface,thus reducing the membrane fouling control effect.However,when the charge density of coexisting components is low,although the SA removal rate in the solution is slightly reduced,the exchange sites"protected"by coexisting components will continue to play the role of displacing SA near the membrane surface,so as to generate stronger interfacial forces and achieve the effect of slowing down membrane fouling.