Study On Enhancing Filtration Efficiency Of Gravity-driven Membrane System And Membrane Fouling Mitigation

Water treatment facilities in rural areas of China were not perfect,and domestic sewage was discharged directly,which caused water environment pollution and endangered residents life and health.Therefore,improving sewage treatment in rural areas and ensuring drinking water safety are great significance to the revitalization of rural areas.According to the characteristics of rural wastewater quality,based on the traditional single function（aerobic or anaerobic）membrane systems,this paper developed an aerobic and anoxic tandem function gravity driven membrane system,which formed microbial community structure differentiation distribution in system.Under the condition of not adding carbon source,the system had efficient removal of organic pollution.The results showed that there were different dominant microbial community structures in the aerobic zone and the anoxic zone.In the anoxic zone,Acidobacteria,Actinobacteria,Thiobacillus and Longilinea were the dominant bacterial communities.These bacteria can effectively degrade complex organic polymers and produce bioactive molecules.Firmicutes can facilitate denitrification.In the aerobic zone,abundant DO and organic matter promoted the proliferation of microorganisms,Rhodanobacter and Nitrospira ensured the realization of heterotrophic nitrite oxidation and nitrification process.Therefore,the removal rate of ammonia nitrogen（NH₄⁺-N）,TOC and COD can reach 93%,77%and 98%,and the removal efficiency of the system was obviously better than the conventional gravity membrane system（NH₄⁺-N,TN and COD removal rates were 18%,17%and 70%）.Different microbial community functions in aerobic and anoxic tandem function gravity driven membrane system enabled the system to achieve efficient removal of organic matter.In order to ensure the safety of drinking water in rural areas,a multi-functional tandem gravity membrane system was developed to improve the nitrogen removal efficiency in low organic matter water.The system can change the flow pathes of influent water,realized the partition consumption of DO through the installation of movable baffles.It constructed different environmental microzones,realizing the coexistence of multiple nitrogen conversion paths,and improving the nitrogen removal effect.The results showed that adjusting the distribution of DO and substrate in the system environment could change the structural superiority of the functional microbial community in the system,and Thaumarchaeota increased from 0.019%in the raw water to 42.58%in the low DO zone and 33.25%in the biofilm zone.Due to Thaumarchaeota’s fast growth rate and ammonia affinity,which was 200 times higher than other ammonia oxidizing bacteria,the system can achieve efficient nitrogen removal under low organic matter load.The average removal rate of NH₄⁺-N in the system is 94.68%.Pearson correlation coefficient analysis showed that there was a functional complementary relationship between nitrogen transforming gene pairs,which promoted the synergistic effect of endogenous denitrification,nitrification,partial nitrification and isnitrite reduction in the system.In order to solve the problem of membrane fouling in gravity membrane system,micro fine particle material was used to deposit on the membrane surface,and the influence of micro fine particle layer on membrane flux stability and membrane pollution was investigated.The results showed that the membrane deposited with micro fine particles can give the membrane a higher hydrophilicity（the contact angle of the membrane decreased from 93±8.31°to 59±4.15°and 50±2.21°,respectively）without damaging the pore structure of the membrane,and improved the stable flux of the membrane.Compared with the original membrane,the pure water fluxes of the deposited membranes were increased by 57%and 48%,respectively.The interfacial free energy（ΔG）was increased from-78.04 m J m^-2 to-41.47 m J m^-2 and-39.34 m J m^-2,respectively.Therefore,the adhesion of biomacromolecules（such as cells and polysaccharides）on the membrane surface was reduced.At the same time,the deposition of miceo fine activated carbon particles on the membrane surface can improve the degradation ability of the fouling layer to macromolecular organic matter and prolonged the membrane filtration time.The deposition of micro fine zeolite particles on the membrane surface made the membrane surface more easily cover by hydrophilic proteins,forming a hydrated film,which effectively prevented the adhesion of hydrophobic pollutants on the membrane surface.This paper constructed the anaerobic-aerobic tandem function gravity driven membrane systems and multi-function area gravity membrane water purification system.The system realized the advantages of microbial function by different environmental micro area,enhancing gravity driven membrane filtering efficiency.The deposition micro fine particles on the membrane surface reduced membrane fouling formation.The study provided an important reference for the selection of wastewater treatment and drinking water security technology in rural areas.