Transport Of Bacteria And Spores During Managed Aquifer Recharge And Spores Inactivation Mechanism

Regeneration of urban sewage and sustainable recycling of water resources have become an important strategy to solve the problems of water shortages and water pollution for many countries and regions in the world.Secondary effluent of cities,rain floods and other surface water were reclaimed and recharged into underground aquifers.It was a new way for the recycling of water resources in the world.Reclaimed water underground recharge was also a topic actively promoted by national strategies such as China State Council's"Water Pollution Prevention Action Plan"and"13th Five-Year Plan"for building a water-saving society.Studying water quality safety risks and critical control technologies for reclaimed water reuse was a core scientific issue in this afield.Due to the diversity of reclaimed source water,regional differences and the limitation of reclaimed treatment technology,some pathogenic microorganisms may be contained in the reclaimed water.The risk of expanding the pollution range of pathogenic microorganisms in the storage process can cause infectious diseases by water transmission through drinking,contact and other ways,bringing great harm to human health.The researches on the water quality risks of reclaimed water underground storage in the world mainly focus on the transport and diffusion risks of chemical substances,which were rare on biological safety under the recharge seepage system.Based on the difference of reclaimed water quality and the characteristics of groundwater recharge process,the transport behavior of pathogenic microorganisms under different types of reclaimed water recharge systems may be quite different,and systematic comparative study was urgently needed.At the same time,bacterial sporulation(endospore or spore)resistance phenomenon may also be generated under the stress of oligotrophic and low dissolved oxygen conditions on the seepage path.It was unclear of the difference between the transport mechanism of bacteria and their spores along the flow,and the risk of pollution diffusion.Further more,considering the limited inactivation effect of the conventional disinfection process on spores,developing new technical methods and effectively controlling the concentration level of spores(and other pathogenic microorganisms)in reinjection water were important contents for avoiding water quality biosafety risks.Based on the above three major issues,this paper had carried out targeted research.The main results were summarized as follows:(1)The transport behavior of Escherichia coli cultured in different water sources and compared the risk of microbial diffusion in the process of re-irrigation in different water sources were studied in this paper.The secondary effluent from the sewage treatment plant in the northern suburb of Changchun city,the Yitong river water in Changchun city and natural rainwater were selected as the reclaimed water recharge sources,and the one-dimensional quartz sand column seepage experiment was used to simulate the underground recharge process of reclaimed water,revealing the transport mechanism of bacteria in different water sources.The study found that the interception of E.coli was the highest in the secondary effluent recharge process,followed by reclaimed water,and the interception of bacteria was the lowest in the rainwater recharge process.The surface properties of E.coli had a certain effect on the bacteria deposition,and the difference of organic matter composition and hydro-chemical background of reinjection water sources had a major effect.The difference of ion composition(IS)in the water source played a leading role in the interception of bacteria.The XDLVO theory was used to analyze the interaction energy between bacteria and granular media.The minimum value of second order energy in secondary effluent was higher than that in surface water and the value was minimal in rainwater.The larger of the minimum value of secondary energy was easier to deposit on the surface of granular medium for bacteria.The research showed that the different chemical conditions of water in different recharge water sources lead to the difference of bacteria transport behavior and diffusion risk,and the transport risk of bacteria in rainwater is relatively high.(2)Based on the above researches,Bacillus subtilis and their spores were selected as indicator bacteria.The transport mechanism of bacterial and spore under different IS conditions was explored.We simulated the transport behavior of typical bacteria in the recharge process of reclaimed water,and compared the transport mechanism and proliferation risk of bacteria and spores.One-dimensional quartz sand column seepage experiment was used to simulate the transport process of bacteria and spores.And the ADR(advection dispertion retention)equation was used to fit the results.When the ionic strength in aqueous solution was 1 m M,bacteria and spores had strong fluidity and the high mass recovery rate(>75%).When the ionic strength was 100 m M,the mass recovery rate of bacteria decreased to 58.05%,while the spore recovery rate remained at 74.54%.In the higher range of IS,the mobility of spores was significantly higher than that of bacteria.Analysis of the surface properties and breakthrough curves of bacteria and spores showed that adsorption force,shear force and blocking mechanism had certain effects on the deposition of bacteria.XDLVO theory showed that EDL force affected particle deposition when IS was 1 m M.VDW and AB force dominated particle deposition with 100 m M ionic strength.The VDW of bacteria was higher than spores,which was more easy to deposit.The above researches showed that the mobility of spores was much higher than that of bacterial cells and was not affected by hydro-chemical conditions.Spores had a high pollution risk during underground recharge of reclaimed water.(3)In this paper,the effective control of spore concentration in reinjection water source was realized by studying new technical methods.The risk of microbial pollution in the process of reinjection of reclaimed water could be reduced.Microbubbles enhanced photocatalysis method was used to achieve effective and clean sterilization effect.In the experiment,Ag and N doped Ti O₂ were used for visible light photocatalytic reaction.After 7 h of photocatalysis,the inactivation efficiency of spores reached 92.3%and 63.3%.In the process of microbubble enhanced photocatalysis,the removal efficiency of spores reached 66.7%and 43.7%respectively.The catalytic efficiency increased 65%and 77%respectively when the reaction time was 1h.The micro-nano bubble method accelerated the reaction process by increasing DO in water to generate more·OHand·O₂^-which were strong oxidizing radicals(ROS).3D-DEM and TEM results showed that ROS could destroy the outer wall of spores which caused intracellular dissolved substances to flow out,and degraded organic matters.The study found that microbubbles enhanced visible light catalytic reaction could promote the inactivation of spores,which was conducive to reducing the risk of microbial contamination in the recharge water source.