| Riverbank filtration(RBF)is a kind of natural water treatment process with a long history,green and high efficiency,which has been widely concerned and studied all over the world.However,RBF also has some defects,such as small water yield,poor anti pollution impact ability,easy hardening of filter layer,unstable biological safety and so on,which makes it difficult to be used as a drinking water technology alone.In this paper,aiming at the shortcomings of RBF,the hydraulic retention time is appropriately shortened,RBF and ultrafiltration(UF)technology are coupled.A combined process of RBF and UF is proposed.The Songhua River water in Harbin section is used as raw water to investigate its treatment efficiency and operational stability for natural surface water,and to explore the alleviation mechanism of RBF on ultrafiltration membrane fouling,It provides technical reference for the application and promotion of RBF technology in drinking water treatment.Firstly,the water purification efficiency of RBF was studied and optimized,and the influence of different operation parameters on the effluent quality was investigated.The results show that RBF can effectively remove turbidity,TN,ammonia nitrogen,organic matter and other pollutants in the water,and the removal rate of turbidity is more than92%.The effluent quality can be improved by prolonging the retention time;The removal of turbidity and nitrogen-containing compounds can be enhanced by increasing the operating temperature,but the organic matter content in the effluent increases.In the process of RBF,the argillaceous sediments mainly degrade organic matter and nitrogen compounds,while the sandy aquifers mainly remove turbidity,and the sediments play a major role in RBF.Then,the water purification efficiency and operation stability of the combined process were explored.Compared with direct ultrafiltration,the combined process significantly improved the removal rate of pollutants,alleviated 64.28% reversible membrane fouling and 38.87% irreversible membrane fouling.During the continuous operation of the combined process,the effluent quality is good and stable,the turbidity is always below 0.1 NTU,and 65.07% TN,46.88% TOC and 40.21% ammonia nitrogen can be removed;The results show that the TMP increases gently,the membrane fouling is controlled,the irreversible fouling accumulation slows down,and the total fouling resistance reaches saturation after 25 days of operation.Finally,the alleviation mechanism of RBF for ultrafiltration membrane fouling is studied and elaborated.Through parallel comparison of membrane fouling under different pretreatment methods,it was found that RBF could effectively alleviate ultrafiltration membrane fouling,reduce the resistance of reversible and irreversible fouling,and reduce the thickness of cake layer on membrane surface.RBF could not change the types of organic pollutants on membrane surface,but reduced the relative content of humus,protein and polysaccharide.Through high-throughput sequencing analysis of RBF system,the results showed that the microbial community structure in different depths of the filter layer was slightly different,but on the whole,the microbial population was rich and functional,including a variety of bacteria with the functions of degrading macromolecular organic matter,absorbing ammonia nitrogen,biological nitrogen fixation and so on.The analysis shows that the content of substances causing membrane fouling is reduced through the interception and filtration of turbidity substances,adsorption and biodegradation of natural organic matter,so as to alleviate the membrane fouling.In conclusion,the RBF-UF combined process has an excellent treatment effect on natural surface water,the effluent quality basically meets the requirements of drinking water standards,and the membrane fouling accumulation is slow during operation,which has good operation stability.In the combined process,RBF can reduce the treatment load of UF,so as to alleviate the membrane fouling.UF can further improve the water quality and ensure the biological safety.The two are complementary and cooperative,which makes the combined process have an excellent operation effect. |
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