Fate And Transport Of Escherichia Coli And Cryptosporidium During Groundwater Recharge With Reclaimed Water

In the process of infiltration and storage of effluent and reclaimed water from urban sewage plants to the surface and then to the underground,how the pathogenic microorganisms migrate and spread is a water safety issue that has attracted much attention.Cryptosporidium is a common zoonotic parasite in the aquatic environment.It is transmitted through contact or drinking.Low doses can cause human or animal infection and cause cryptosporidiosis.At present,less attention has been paid to the removal of Cryptosporidium in different process units in the sewage treatment process.Combined with the geographical conditions in the northeast cold region,the characteristics of Cryptosporidium migration under the low temperature recharge system and the risk of its pollution diffusion are still unclear.Based on the above problems,this paper takes the common indicator pathogenic microorganisms in water Escherichia coli as a reference,and studies the migration mechanism of Escherichia coli and Cryptosporidium under different conditions.The main research results are as follows:（1）Investigate and analyze the removal efficiency and species/genotype distribution of Cryptosporidium by each process unit of the three sewage treatment plants in Changchun City.The results showed that the total removal rates of Cryptosporidium in the three sewage treatment plants were 84.65%,88.70%and 84.01%,respectively.In the sewage treatment process,the improved secondary sedimentation unit has better removal effect on oocysts,with an average removal rate of 62.01%,followed by activated sludge（10.81%）,primary treatment（7.76%）and disinfection（3.67%）The overall removal rate is42.31%higher in summer than in winter.In the end,the average concentration of residual oocysts in the effluent of the whole year was 3.97/L,and the winter（4.27/L）was higher than the summer 2.22/L.A total of 10 species of Cryptosporidium were identified,of which the proportion of Cryptosporidium from bovine origin was close to 90%.（2）The effects of different temperatures and ionic strengths on the migration behavior of Escherichia coli were studied.The results showed that:under specific temperature conditions,when the ionic strength increased from 1 m M to 100 m M,the bacterial migration ability decreased by 24.62%～45.68%,and the retained sediment increased by1.99～2.33 times;under specific ionic strength conditions,the temperature increased from 5When the temperature rose to 25℃,the deposition of Escherichia coli on the surface of the medium intensified,and the adhesion coefficient increased from 0.018 min^-1to 0.091min^-1to 0.050 min^-1to 0.208 min^-1.The reasons for this were analyzed.The types and quantities of surface proteins secreted by bacterial metabolism changed at low temperature,the extracellular polymer increased from 72.29μg/mg to 119.83μg/mg;the surface electronegativity decreased by 55.48%～85.68%;the hydrophobicity decreased by 72.53%～81.58%;in the end,the collision efficiency between it and the medium particles decreases,and the secondary energy hydrazine value of the comprehensive interfacial interaction energy such as electrostatic repulsion,van der Waals attraction and Lewis acid-base interaction decreases,which is not conducive to bacterial adhesion,and further bacterial retention reduced,there is a higher risk of migration and diffusion.（3）The effects of different temperatures and ionic strengths on the migration behavior of Cryptosporidium were studied.Under specific temperature conditions,when the ionic strength increased from 1 m M to 100 m M,the surface electronegativity of Cryptosporidium decreased by 56.09%-69.01%;the hydrodynamic diameter increased7.2%～11.12%;the collision efficiency increases by 1.71%～7.32%,when the ionic strength increases,the electrostatic repulsion of the electric double layer compression decreases,the van der Waals attraction is the main force,the oocysts are more likely to be deposited on the surface of the medium particles,and the interception increases by 28.63%～54.20%.At a specific ionic strength,as the temperature increased from 5℃to 25℃,the extracellular polymer,surface electronegativity,and hydrophobicity showed a similar low-temperature weakening rule（2.8%～90.23%decreased）as Escherichia coli,and finally showed a low temperature.Facilitated migration effect under induction.Compared with the typical indicator organism Escherichia coli,under the same conditions,the collision efficiency of Cryptosporidium was 25.41%～31.57%lower,the adhesion coefficient was 5.8%lower,and the penetration rate was 1.4%～15.67%lower.In the process of migration with the flow,it exhibits a higher mobility and has a higher risk of diffusion.