Effects On Fouling Control Mechanism Of Ultrafiltration Membrane Based On UV/ClO₂ Pre-oxidation

The problems of membrane fouling in the application of ultrafiltration membrane in water treatment severely restrict the application and development of ultrafiltration technology.In the face of a series of management and operation problems caused by membrane fouling,it can be effectively solved by oxidation pretreatment before ultrafiltration process.Through the oxidation of the influent organic matter,the characteristic of the raw water can be changed,the membrane fouling caused by the nature organic matter can be effectively alleviated,and the effluent quality after the membrane could be improved.In this paper,the new ultraviolet/chlorine dioxide（UV/ClO₂）technology is used as the pre-oxidation technology,and the control mechanism of chlorine dioxide and UV/ClO₂ pretreatment on ultrafiltration membrane pollution and water purification efficiency are systematically investigated.In this paper,the humic acid,sodium alginate and bovine serum albumin were selected as the typical natural organic compounds to investigate the effect of chlorine dioxide pre-oxidation on ultrafiltration membrane fouling control.The membrane fouling mechanism was analyzed by filtration specific flux curve and reversible and irreversible resistance change,combined with the change of interface free energy and membrane surface morphology and membrane fouling model fitting.The influence of chlorine dioxide on the physicochemical properties of organic matter was explored.The results showed that chlorine dioxide pre-oxidation at low concentration（1-2 mg/L）could alleviate the decrease of membrane flux caused by humic acid,polysaccharides and mixed organic pollutants.Meanwhile,chlorine dioxide oxidation could activate the sheltered fluorescent functional groups in raw water,resulting in the increase of fluorescence value of humic acid,However,it can remove the fluorescence intensity of bovine serum albumin effectively;When the dosage of chlorine dioxide was 8 mg/L,the attraction between organic pollutants will increase,and it is easy to deposit on the membrane surface,resulting in serious flux decline and membrane resistance increase;Chlorine dioxide（1 mg/L）pre-oxidation can make the membrane fouling mechanism from cake layer formation to intermediate pore blocking.Then,the UV/ClO₂ oxidation technology was used to investigate the control effect of membrane fouling and removal of trace organic matter in raw water.On the basis of various factors and conditions for the control of ultrafiltration membrane fouling by chlorine dioxide,the hydrophilic and hydrophobic classification of raw water after UV/chlorine dioxide oxidation and the generation content of disinfection by-products were also explored.The results show that compared with chlorine dioxide pre-oxidation,UV/chlorine dioxide oxidation can effectively alleviate the flux decline of ultrafiltration membrane caused by humic acid,sodium alginate,bovine serum albumin and their mixed solution,and significantly control the reversible and irreversible membrane fouling resistance;UV/ClO₂ can preferentially oxidize the hydrophobic substances in humic acid raw,increase the proportion of transition and hydrophilic substances in the solution,reduce the proportion of hydrophobic substances by 27%,and increase the proportion of transition substances by 20%;It can inhibit the formation of chloroform,Trichloroacetonitrile and chloronitromethane.In addition,in order to investigate the mechanism of UV/ClO₂ oxidation to alleviate membrane fouling,this paper also analyzed the surface morphology of ultrafiltration membrane and the free energy of membrane interface,fitted the membrane fouling model,and investigated the removal efficiency of trace organic matter.The results indicated that,UV/ClO₂ oxidation can effectively reduce the content of sulfamethoxazole（SMX）in water,and the retention rate can attain more than 85%within 6 min.Moreover,it can effectively improve the removal efficiency of SMX by ultrafiltration membrane and increase the safety of the process;Through the fitting model analysis of membrane fouling,it shows that UV/ClO₂ pre-oxidation can change the fouling mechanism caused by organic matter in the early stage of filtration,delay the formation time of cake layer fouling,reduce membrane fouling and prolong the service life of membrane.In this paper,chlorine dioxide and ultraviolet/chlorine dioxide pre-oxidation were used respectively.Through various characterization,detection and simulation,the control mechanism of membrane fouling caused by typical natural organic matter was systematically studied.The research results can provide guidance and suggestions for the actual operation of such pre oxidation combined process.