Effect Of Ozone Oxidation Pretreatment On Bovine Serum Albumin Fouling Behavior Of Ultrafiltration Membrane

In this study,bovine serum albumin(BSA)was selected to represent the ubiquitous protein pollutants in wastewater,and the BSA solution was oxidated with ozone under various conditions.Fouling behavior to ultrafiltration membranes of polyvinylidene fluoride(PVDF)caused by BSA were investigated systematically,before and after ozone oxidation.Conbined with the physico-chemical characteristics of BSA,the dynamic adsorption process of foulants on the PVDF surface,the structural characteristics of the adsorption layer and the change of the interfacial forces under corresponding pretreatment conditions,the effect mechanism of ozone oxidation pretreatment on ultrafiltration membrane fouling caused by protein contaminants were studied.And the main conclusions are as follows:(1)First,the conventional aeration pre-ozonation method was employed to pretreat the BSA solution.With the ozone contact time of 0,5,10,and 20 minutes,the corresponding membrane flux decline rates were 73%,70%,66% and 64%,and the flux recovery rates were 37%,43%,51%,and 50%,respectively.Obviously,with the extension of ozone contact time,the fouling rate and irreversible fouling of ultrafiltration membranes caused by "BSA" gradually decreased.This was mainly because,in the process of aeration pre-ozonation,on the liquid surface of the BSA solution,a large amount of floc-like aggregation was formed,which left in the reactor top and inner wall.This led to the decrease of concentration of contaminated solution entering the ultrafiltration system,in other words,the foulant load of the ultrafiltration membrane was reduced,and the corresponding membrane fouling was mitigated.(2)In order to clarify the fundamental reason of formation of floc-like aggregation which mitigated membrane fouling,based on the fact that aeration and ozonization were simultaneous during aeration pre-ozonation process,BSA fouling behavior of PVDF ultrafiltration membrane were investigated after the only aeration and only ozonization pretreatment,separately.The results indicated that the formation of large size aggregations and mitigation of membrane fouling during aeration pre-O3 process,was mainly attributed to combination of ozonization and aeration.During aeration preozonation,ozonization could effectively open the BSA molecular chains and promoted the cross-linking of each molecular chain and formation of smaller-sized aggregation.Meanwhile,the microbubbles generated by aeration linked each other to form floc-like aggregation of water,air bubbles,and BSA,and allowed these floc-like aggregation to float on BSA solution,which ultimately remained on the inner wall of the reactor.This reduced the load of pollutants in the ultrafiltration system and mitigated membrane fouling.(3)Membrane fouling behavior was controlled by the change of disulfide bonds between BSA-BSA molecules for pure ozone oxidation pretreatment.In lower ozone dosage rank,with increasing of ozone dosage,BSA-BSA was obviously weakened and the electrostatic repulsion force was increased,however,the disulfide bond and hydrogen bonding force between BSA molecules were increased,a coocalent bond,the disulfide bond was increased significantly,especially,which resulted in a comprehensive force between BSA-BSA gradually increased.Eventually,the increase of adsorption rate of BSA on the membrane surface was promoted,and a block-like dense foulant layer was formed on the membrane surface,accompanied by the deterioration of membrane fouling.In contrast,with ozone dosage continued to increase,the disulfide bonds between BSA molecules was greatly destroyed,and the interaction force between BSA and BSA had been reduced,which led to decrease of adsorption rate of BSA on the membrane surface and formation of relatively loose and porous foulant layer,and the corresponding membrane fouling began to mitigate.