| Excessive nitrate and phosphate are discharged into the natural water body,causing eutrophication of the water body.Due to its advantages like stable operation and high treatment efficiency and good water quality and friendly environment,membrane bioreactor(MBR),which has been successfully applied in the treatment and reuse of domestic sewage.MBR technology mainly relies on biological treatment to remove nitrate and phosphate,where an ultrafiltration membrane is used to separate activated sludge and other suspended matters.The concentration of the nitrate and phosphate in the effluent still keeps high,which cannot meet the increasingly stringent effluent standard.Moreover,membrane fouling of ultrafiltration membrane seriously restricts its popularization and use in water treatment.In this context,the hybrid membrane can be effectively used as a substitute for the traditional ultrafiltration membrane by introducing additives to improve the adsorption ability of the traditional ultrafiltration membrane for nitrate and phosphate and the anti fouling properties of the original ultrafiltration membrane.In this study,dimethydodecyl[3-(trimethoxysilyl)propyl]ammonium chloride was used to modify zeolites and activated carbons,respectively,and then the quaternized membrane additives were obtained.The results of nitrate and phosphate removal by membrane additives showed that activated carbon prepared by dipping was the best quaternized product.Single-factor optimization experiment showed that activated carbon 5 g,synthesis time 3 h,dimethydodecyl[3-(trimethoxysilyl)propyl]ammonium chloride 4 g,the obtai-ned quaternized activated carbon product was the most excellent(CQA).The specific surface area and the pore volume of the modified activated carbon was 551.670 m2/g and 0.326 cm3/g,respectively.The adsorption of nitrate and phosphate by CQA was well fitted by the Langmuir isothermal adsorption model.The maximum adsorption capacity of nitrate and phosphate was 14.829 mg/g and 8.442 mg/g,respectively.While pH was 4-9,the removal rate of CQA for nitrate and phosphate would be higher.The saturated CQA could be regenerated by 10%sodium chloride solution,and the CQA after 6th regeneration still had a good ability to remove nitrate and phosphate.In this study,a novel quaternized activated carbon-PVDF hybrid membrane,made of PVDF,impregnated with CQA,was prepared by phase inversion.The hybrid membrane was the α-phase PVDF,and the quaternary ammonium group appeared on the surface of the hybrid membrane,then the hydrophilicity of the membrane was improved obviously.The addition of CQA increased the pore diameter and roughness of the hybrid membrane,which was still a typical ultrafiltration membrane structure.After flux experiments,it was known that the hybrid membrane was still a ultrafiltration membrane.The experimental results of simultaneous removal of nitrate and phosphate from 2CQA-PVDF hybrid membrane showed that the membrane can realize advanced treatment of nitrate and phosphate in solution.The 2CQA-PVDF hybrid membrane saturated by nitrate and phosphate could be easily regenerated using 0.1 mol/L of sodium chloride solution and subsequently be reused.The antifouling performance of the modified hybrid membrane was enhanced,the water flux recovery rate(FRR)and the reversible rate fouling(Rr)of the hybrid membrane were obviously improved.The membrane,which could effectively inhibit the adhesion of bacteria on the membrane surface,had obvious inhibitory effect on Escherichia coli.The ion exchange between hybrid membrane and nitrate and phosphate was based on the quaternary ammonium group on the hybrid membrane,so as to achieve the purpose of removing nitrate and phosphate in the solution. |
