Study Of Organic/Metal Ion Combined Fouling On Anion Exchange Membrane Based On XDLVO Theory

As an emerging membrane separation technology,electrodialysis technology is widely used in various industries such as chemical industry,medicine,seawater and brackish water desalination,wastewater treatment,etc.But the fouling of ion exchange membrane has become the bottlenecks restricting its further development.The ion exchange membrane fouling would increase membrane resistance and decrease membrane performance,which in turn affects the normal operation of the electrodialysis operation.The types of membrane fouling mainly include inorganic fouling,organic fouling and microorganism fouling.Among them,organic matter is easy to cause irreversible fouling of anion exchange membrane(AEM),and metal ions will chelate with organic matter to affect membrane fouling.In this paper,taking organic matter/metal ion as research objects,the effect of metal ions on organic fouling of ion exchange membrane during the electrodialysis process in artificial water system was explored.The extended Derjaguin-Landau-Verwey-Overbeek(XDLVO)theory was used to study mechanisms of three organic matters(sodium alginate(SA),humic acid(HA),bovine serum albumin(BSA))on the anion exchange membrane fouling.The focus is on the effect of metal ions(calcium ion(Ca2+),iron ion(Fe3+))conceltration on the membranes organic fouling.And XDLVO theory was utilized to quantitatively evaluate the interfacial interactions between anion exchange membrane and organic/metal ion combined foulant.The results indicated the presence of calcium ions induced bridging between NOM components to generate a compact foulant layer,tremendously aggravated anion exchange membrane fouling compared with the absence of calcium ions in aqueous solution.When the calcium ion concentration is 4mmol/L,the interaction energy between fouled membrane by SA and foulant is the lowest,which is-22.09 mJ/m-2;When the calcium ion was 8mmol/L,the interaction energy between fouled membrane by HA or BSA and foulant was the least,which were-18.55mJ/m-2 and-20.57 mJ/m-2,respectively.In addition,the analysis of the interaction energy between membrane and foulant by XDLVO theory reveals that the short-ranged acid-base(AB)interaction plays an important role to the total interaction energy in the ED process.Calcium ions affect the total interaction energy mainly by affecting the AB interaction energy.Moreover,the effect of calcium ions on combined anion exchange membrane fouling by organic/metal ion foulants follows the following sequence:SA>HA>BSA.According to the XDLVO theory,the presence of iron ions also has an effect on ion exchange membrane fouling.Iron ions have a weak effect on ion exchange membrane fouling by sodium alginate.And iron ions have a greater impact on ion exchange membrane fouling by humic acid when its concentration is higher in the influent.The effect of iron ions on membrane fouling by bovine serum albumin increased with the increase of iron ion concentration.All interaction between membrane and foulant is attraction action.When the iron ion concentration is in the range of 4 mg/L,the effect of iron ions on the anion exchange membrane fouling by organic/metal combined foulants follows the following sequence:BSA>HA>SA.In addition,the study showed that membrane fouling was aggravated when the total interaction energy between membrane and foulants was decreased.At the same time,metal ions can bridge with organic matters to form chelation,resulting in an increase in interaction energy and aggravation of membrane fouling behavior.And thus the membrane fouling was more serious,and the electrodialysis desalination performance was worse.