Study On Membrane Fouling Mechanism Of Oily Wastewater Treated By Coagulation-hydrophilic And Oleophobic Membrane

In recent years,due to factors such as petroleum industry,food processing industry and oil field exploitation,oily wastewater is produced in large quantities and environmental pollution is increasingly serious.The water quality of oily wastewater is complicated,and the traditional treatment technology can not meet the treatment requirements,so it is necessary to explore new treatment technology.Due to its advantages of simple operation,low energy consumption and green environmental protection.membrane separation method has been widely used in the field of oily wastewater treatment.However,the membrane fouling problem restricts the membrane separation process.In order to solve the problem of membrane fouling,membrane modification into hydrophilic and oleophobic membranes can effectively alleviate membrane fouling.Coagulation technology has been widely used in the field of sewage treatment,as a pretreatment means before membrane separation can reduce the content of pollutants.effectively reducing membrane fouling.Therefore,this subject adopts coagulation-hydrophilic and oleophobic membrane combined process to treat oily wastewater.The main research contents and conclusions are as follows:(1)Four inorganic coagulants and one organic flocculant were selected to compare their coagulation pretreatment performance,and the performances of three different dosing modes and different pH values on the coagulation process were investigated.The research results showed that the best coagulation performance was achieved when polyaluminum chloride(PAC)and polydimethyl diallyl ammonium chloride(PDMDAAC)were combined dosing,PAC was 6mg/L and PDMDAAC was 0.5mg/L.When pH value is 6,turbidity removal rate and DOC removal rate are optimal.(2)The flocculant characteristics under different coagulant/flocculant dosage methods and different pH values were measured,and the relationship between flocculant characteristics and membrane fouling was studied.The results showed that the membrane fouling was the lightest when the composite coagulant was used as the pretreatment coagulant.The main reason was that the flocculant produced by the composite coagulant was the largest and had loose structure.(3)Polyether sulfone/tannic acid/iron ion(PES/TA/Fe3+)modified membrane was prepared by chemical deposition method by dipping tannic acid(TA)and iron ion(Fe3+)on polyether sulfone(PES)membrane.The modified membrane was characterized by Fourier transform infrared spectrometer(FTIR),X-ray photoelectron spectrometer(XPS),scanning electron microscope(SEM)and contact angle tester.The results showed that tannic acid and iron ions were successfully modified on the membrane,the modified layer showed loose porous structure,and the membrane’s hydrophilic and oleophobic properties were also improved.(4)The hydrophilic and oleophobic membranes were applied to the combined coagulation-ultrafiltration process,and the effects of direct ultrafiltration and coagulation-ultrafiltration on membrane fouling were compared,and the effects of different pH values and different operating pressures on membrane fouling were studied.The results show that coagulation pretreatment can effectively alleviate membrane fouling.The coagulation mechanism and membrane fouling mechanism are different under different pH values.Operating pressure is positively correlated with membrane flux and membrane fouling.