The Effects Of Chemical Cleaning On The Performance Of Ultrafiltration Membranes In Drinking Water Treatment And The Control Methods

Due to the development of Ultrafiltration(UF)membranes and application of UF technology in drinking water treatment industry,the stability of UF membrane and membrane process have aroused many attentions.In the practical applications,the frequent chemical cleaning and disinfection were proved to have significant impacts on the properties and performance of UF membranes,these irreversible changes happened on membranes were also regarded as membrane ageing,which have great impacts on the water quality and running cost of UF plant.However,the investigations on this area were scarce,which hindered the application of UF technology.Firstly,this paper shows how the surface chemistry evolution of membranes can lead to the formation of distinct membrane properties when exposed to sodium hypochlorite solutions.The surface physicochemical evolutions of aged membranes are characterized based on chemical composition(ATR-FTIR and XPS),water contact angle analysis,and surface potential test.The results indicate the ageing mechanism and evolutions between each membrane are totally different.In addition,the retention ability and fouling propensity of the aged membrane are also investigated by three typically foulant.Surface hydrophilization of aged membrane enhanced its retention toward hydrophilic charged foulant.In terms of a small hydrophobic foulant,the mechanical sieving of membrane pores played an important role in its retention.Moreover,the fouling types of the aged membranes were changed,which can ascribe to its distinct surface properties and the interfacial behaviors of the foulant molecules.Secondly,we also investigated the impact of NaClO on the performance of polysulfone membranes.The performance of aged PSF membranes was studied under different transmembrane pressures,and three critical TMPs related to the filtration efficiency,retention ability and sieving capacity were innovatively proposed,respectively.In terms of an aged membrane,the filtration efficiency and retention ability were decreased,while,the response relationship between the retention ability and TMPs were increased significantly.Thirdly,a NaCl coagulation bath(SCB)has been successfully employed to enhance the performance of UF membranes with amphipathic Pluronic F127(F127).The resultant membrane exhibits an excellent stability,and most of the F127 still anchored into the membrane matrix after NaClO treatment.On the other hand,the resultant membrane also shows a great surface porosity of 7.2%,and its permeability can reach to 1405 L/m~2/h/bar.Moreover,a unique micro-nano structure was observed on the membrane surface,which endows the membrane with a remarkable hydrophilicity and antifouling performance.Also,base on the ternary phase diagram analysis,we propose the distinct effect of SCB on the F127 can be ascribed to the intensified hydrophobic-hydrophobic interaction between the F127 and the polymer chains.