Fouling Of Nanofiltration Membranes In The Advanced Treatment Of Different Secondary Effluent

With the increasing shortage of global water resources and increasingly strict water quality standards,advanced treatment and reuse of wastewater has become an important measure to solve water shortage problems at home and abroad.In recent years,nanofiltration membrane as a good and stable membrane filtration technology has attracted much attention in the advanced treatment and reuse of wastewater,but membrane fouling is the main factor limiting its promotion and application.The mechanism and control of membrane fouling need further research.In this paper,the secondary effluent of municipal wastewater and meat processing wastewater is taken as the research object,and the NF90 and NF270 nanofiltration membranes are used to treat the wastewater.Study the treatment effect of nanofiltration membrane on different secondary effluent,and carry out nanofiltration fouling research on this basis.By analyzing flux decline,membrane resistance change,membrane fouling substances and contaminated membrane surface,the pollution mechanism of nanofiltration membrane was studied,the commonality and difference of membrane fouling were clarified,and a reasonable cleaning strategy was proposed.In order to provide a scientific basis for promoting and using the nanofiltration membrane in the advanced treatment of different wastewater.Research indicates:(1)There are significant differences in the performance of the NF270 and NF90.The membrane flux of NF270 is much higher than that of NF90 membrane.The two nanofiltration membranes have better interception effect on organic in different secondary effluent,and the TOC of nanofiltration production water is lower than 2mg/L.The desalination rate of the two nanofiltration membranes is quite different.The desalting rate of NF90 membrane can reach more than 96% for different wastewaters.The desalting rate of NF270 membrane is lower.When treating secondary effluent from municipal wastewater and secondary effluent from meat processing wastewater,The salt rejection rates were 54% and 36%,respectively.(2)Membrane fouling study results show that the membrane fouling of NF270 is much larger than that of NF90.When treating different wa stewaters,the flux decay rate of NF270 is greater than 60%,and NF90 is 9-16%.The secondary effluent from the meat processing wastewater caused more pollution to the membrane than the secondary effluent from municipal wastewater,when treated it with NF90,the membrane flux decay rates were 16% and 9%,respectively,when treated it with NF270,the membrane flux decay rates were 64% and 62%,respectively.(3)The membrane resistance analysis results show that when the nanofiltration membrane is used to advanced treatment different secondary effluent,the surface resistance of the fouling membrane is composed of the membrane inherent resistance Rm,the adsorption resistance Ra and the surface gel resistance Rc.The Rm accounts for a large proportion of the total resistance,and the ratio of Ra and Rc of NF270 is larger than that of NF90.When the nanofiltration membrane is used to treat the secondary effluent of the meat processing wastewater the influence of Ra on the membrane surface is relatively large.(4)The results of membrane fouling analysis showed that after the NF90 and NF270 treated the different secondary effluent,there were inorganic pollution and organic pollution on the membrane surface.Among them,the degree of inorganic pollution caused by the meat processing wastewater is greater than that of municipal wastewater,and the degree of organic pollution caused by the two kinds of wastewater is basically the same.The main substances that form organic pollution are dissolved microbial products(SMP)and amino acid substances.Humic acid and fulvic acid in raw water have little effect on membrane fouling.(5)The NF270 and NF90 fouled membranes were cleaned with different cleaning solutions.The results showed that the alkali had the best effect on the organic pollution of the membrane,followed by DI water and the acid.The acid has a better effect on inorganic ions.In practical applications,alkali can be used as the main method to assist acid.