Inactivation Efficacy And Mechanism Of Escherichia Coli And Cryptosporidium In Water By UV/Trypsin Process

Cryptosporidium is a typical zoonotic coccidian parasite.Its egg sac has thick cyst wall and strong resistance.It is difficult to completely remove it by conventional sewage treatment process or even disinfection process.It enters the natural water environment with the effluent of sewage treatment plant,which may induce Cryptosporidium disease by watermediated transmission,which poses a potential threat to regional water safety.Based on this,a new method of trypsin coupling common UV disinfection process is proposed in this paper.After treating Cryptosporidium oocysts with a certain concentration of trypsin solution,the surface protein is dissolved or even damaged,the internal nucleic acid is leaked,and then the apoptosis rate is accelerated under the action of UV.Taking the common pathogenic microorganism E.coli in water as a reference,this paper systematically explores the efficiency,influencing factors and internal mechanism of the coupling process in inactivating Cryptosporidium in water.(1)Inactivation effect of disinfection process in typical sewage treatment plant on Cryptosporidium.The incoming and outgoing water samples of disinfection processes of four typical sewage plants in Changchun were collected.The concentration of Cryptosporidium in and out of oocyst water was determined by Immuno Concentration sucrose staining.The results show that the average number of oocysts in the disinfection unit of sewage treatment plant a is 3.80/l,the concentration of oocysts in the effluent is 2.96/l,and the average removal rate is 22.0%;the average number of oocysts in the disinfection unit of sewage treatment plant B is 2.52/l,the concentration of oocysts in the effluent is 2.04/l,and the average removal rate is 20.7%;the average number of oocysts in the disinfection unit of sewage treatment plant C is 4.08/l,the concentration of oocysts in the effluent is 3.12/l,and the average removal rate is 25.4%,The average number of oocysts in the influent of D sewage treatment plant is 3.48/l,the concentration of oocysts in the effluent is 2.84/l,and the average removal rate is 18.0%.The infection rates of oocysts in primary and secondary sewage treatment were 87.5% and 90.0% respectively.After disinfection,the infection rate of oocysts in effluent decreased to 76.67%.The infection intensity of Cryptosporidium at the disinfection inlet is higher than that at the outlet.The disinfection process reduces the infection intensity of Cryptosporidium by 71%,but there are still a certain number of infectious oocysts discharged into the urban water supply system.(2)Experimental study on single inactivation of Escherichia coli and Cryptosporidium.In this part of the experiment,UV-LED(14 W,model: x6500)was used as the UV disinfection source,and the suspension quantitative inactivation experiment was used to simulate the effect of inactivating Escherichia coli and Cryptosporidium under different water quality environments.The effects of different water quality conditions such as temperature,p H value,turbidity,organic matter and inorganic ions on the disinfection effect of Escherichia coli and Cryptosporidium were studied.The results showed that when the UV radiation dose was 10 m J · cm-2,the inactivation logarithm of Escherichia coli was 2.2.When the dose increased to 20 MJ · cm-2,the inactivation logarithm was 3.1 and the inactivation logarithm increased by 0.9;When the UV radiation dose was 10 m J · cm-2,the logarithmic inactivation value of Cryptosporidium was 1.2.When the dose increased to 14 MJ · cm-2,the inactivation logarithm value was 2.8.Under the same UV radiation dose,the inactivation logarithm value of Cryptosporidium decreased by 1.0 and 0.3 respectively compared with that of Escherichia coli.This study shows that Cryptosporidium is more resistant to UV stress.(3)Experimental study on inactivation of Cryptosporidium by UV combined with trypsin.After soaking Cryptosporidium with different trypsin concentration solutions(0.1%,0.25%,0.5%,1%)for 10 min,20 min,30 min and 40 min,the UV inactivation experiment was carried out to evaluate the efficacy of UV combined trypsin in inactivating Cryptosporidium.The results showed that the inactivation efficiency of Cryptosporidium increased with the increase of soaking time when the concentration of trypsin was 0.1% and0.25%.The inactivation effect was the best when the concentration of trypsin was 0.25% for30 minutes.When the UV radiation dose was 16 MJ · cm-2,it reached the plateau period,and the inactivation logarithm value was 3.0.The inactivation effect of trypsin at the concentration of 0.5% and 1% after soaking for 20 minutes was not significantly different from that after soaking for 40 minutes.Through comparative analysis,it was determined that the concentration of trypsin 0.25% and soaking time 30 min were the best pretreatment conditions for UV synergistic.The inactivation rate constant was 0.0568 MJ · cm-2 · min-1and the inactivation logarithm was 3.0.(4)Mechanism of inactivation of Cryptosporidium by UV and UV combined trypsinThe mechanism of synergistic action of UF and UA was studied by scanning electron microscopy,dissolving protein experiments and agarose gel electrophoresis.Trypsin is a kind of protease.The experiment found that trypsin can degrade or leak the protein in the egg sac wall.The free radicals produced by UV can effectively destroy the structure of sporozoites,cause damage to substances such as nucleic acids and enzymes,hinder important activities such as replication and transcription,and eventually lead to death.