Insights Into Interaction Mechanism Of Coagulation Pre-treatment On Ultrafiltration Membrane Fouling By Dextran

Membrane fouling is the major factor inhibiting the development of ultrafiltration(UF)technology.Coagulation pretreatment has been introduced to mitigation the membrane fouling.In this study,extended Derjaguin-Landau-Verwey-Overbeek(xDLVO)approach was employed to analyze the interfacial interactions involved in pre-coagulation-UF membrane fouling with different concentration of PACl(poly aluminium chloride),calcium ion and pH.The contribution of different interactions(i.e.van de Waals interaction,double layer electronic interaction and acid-base interaction)towards fouling was assessed and the main mechanism through which concentration of PACl and calcium ion influenced dextran of UF membrane was examined.In order to abtain a more comprehensive and systematic evaluation of the validity of the xDLVO approach in describing UF membrane fouling by dextran,both qualitative and quantitative studies were conducted on correlations between fouling potential and interfacial interaction energy at various foouling conditions.It was found that acid-base(AB)interaction,which was a short-range interfacial interaction,contributed the most to UF membrane fouling by dextran and turned out to be the major factor through which PACl and calcium ion influenced fouling.Fouling experiments indicated that the UF membrane fouling potential was mainly controlled by the AB(acid base)interaction.The membrane fouling potential followed the order of dexline:6>9>3>0 mg/L PACl pre-coagualtion.And the membrane performance decreased with the increasing concentration of calcium ion.Interfacial interaction energy analysis showed that PACl and calcium ion could weaken the repulsive AB interaction or enhance the attractive AB interaction,and meanwhile the pre-coagulation was able to increase the radius of foulants significantly,which contributed to the increasing of the absolute value of interaction energy.For PACl,calcium ion's concentration and pH,permeate flux during the entire filtration process decreased with the increasing concentration of calcium ion.And the related permeate flux followed the order of dexline:6>9>3>0 mg/L PACl pre-coagualtion.Decline of related filtration flux during initial and subsequent stage correlated well with the interaction energy of membrane-foulant and foulant-foulant combinations,respectively.This indicated that xDLVO theory was able to predict the fouling potential in pre-coagulation-UF process effectively.Under all the tested conditions,the acid-base interaction was the main interaction.For the reason that dextran is hydrophilic neutral,zeta potential of dextran is close to 0,so the EL interaction has a little influence in membrane fouling.And the LW interaction changed irregularly with the increasing concentration of PACl and calcium ion,which also influenced a little the membrane fouling potential...