Membrane Fouling Behavior And Mechanism Analysis In Membrane Distillation Process

As a membrane separation technology,membrane distillation has advantage of energy-efficient,convenient in operation and management,and high separation performance which makes it has broad application prospects under the context of the global shortage of fresh water resources.However,the problem of membrane pollution is one of the important factors restriction its industrial development.Aiming to the problem of membrane fouling in MD,this study investigates the anti-pollution behavior of the hydrophobic membrane（PVDF）membrane and the self-made super hydrophobic（SH-PVDF）membrane,analysing the membrane fouling behavior mechanism by using the extended-Derjagui-Landau-Verwey-Overbeek（XDLVO）theory,evaluating the contribution of different interfacial interaction energies which including van der Waals interaction energy（LW）,Lewis acid-base interaction energy（AB）and electrostatic interaction energy（EL）towards membrane fouling,and then,we compare the calculation results with air gap membrane distillation（AGMD）experiment,aiming at providing certain theoretical support for more selections of membrane materials and the control of membrane fouling in the process of membrane distillation.Three different types of pollutants including flocs,organic and inorganic pollutants were used for investigating the membrane fouling behaviors.The flocs is the effluent of kaolin suspension,the organic matter is humic acid（HA）and sodium alginate（SA）,and the inorganic matter includes Ca CO₃,Ca SO₄ and Si O₂.Through theoretical calculation,AGMD experiment and the characterization of polluted membrane materials,the following conclusions are drawn:（1）XDLVO theoretical calculation results reveal that the total interaction between several types of pollutants and membrane materials shows an attraction effect,and these pollutants would contaminate the membranes.The AB interaction energy was dominant and showed an attractive effect in all pollutant systems,while the LW and EL contributed little.The change curve of interaction energy between membrane materials and pollutants with distance showed that there is a repulsive energy barrier between membrane and pollutants,pollutants need to cross a higher energy barrier to reach the surface of SH-PVDF membrane,thus SH-PVDF membrane has a stronger ability to resist different types of pollutants.（2）AGMD experimental results revealed that there were no membrane wetting phenomena during the treatment of several types of pollutants by the two membrane materials.It can be seen that SH-PVDF membrane has better anti-pollution performance through the flux decrease and surface morphology of fouled membranes.The experimental results of AGMD are consistent with those predicted by XDLVO theory.（3）Based on the above conclusions,SH-PVDF membrane shows a better anti-pollution performance by reason of it has stronger electron donor properties than PVDF membrane.It is found that this property has a good correlation with the anti-pollution performance of membrane materials.Therefore,in the selection of membrane materials in the process of membrane distillation,we can enhance the electron donor properties of membrane materials to achieve better anti-pollution effect.