Study On Environmental Behavior Characteristics Of Viruses In Vadose Zone

Groundwater is an indispensable natural resource for human survival.Because of the development of production and the improvement of living standards,the pollution of soil and groundwater is becoming more and more serious.The environment of the groundwater is being impacted by more and more pollution.The vadose zone is the hub of the exchange of water and energy between the atmospheric water and the surface water with the groundwater in the saturated zone.And it is also the passage of surface pollutants into the groundwater.The vadose zone,unsaturated soil,as the first line of defense for protecting drinking water,is unavoidable to be contaminated by pathogenic microorganisms.Viruses in the underground environment have smaller volume than bacteria and protozoa,and can migrate to the farther distance in the vadose zone.Therefore,it is necessary to study the environmental behavior characteristics of viruses in the vadose zone,so as to provide the necessary theoretical basis for ensuring the safety of underground water quality.At present,there have been a lot of studies of migration and transformation of viruses in saturated porous media,but there are still insufficient studies on the migration behavior of viruses under unsaturated soil conditions.Therefore,this study selected E.coli phage as an indicator virus and medium and coarse sand as the lithologic medium,the effect of saturation,pH,ionic strength,ion composition and SiO2 colloid on the migration of enterovirus colloids in the vadose zone was investigated by dynamic simulation of indoor soil columns.Based on DLVO theory and colloid filtration theory,this paper analyzed the changes of potential energy at the air-water interface(AWI)and the solid-water interface(SWI),and quantitatively expressed the migration process of enterovirus colloids in the vadose zone.The main parameters that characterize the migration of enterovirus colloids were obtained.Through the research of this thesis,we achieved the main results:(1)Biological characteristics and physicochemical properties of enteric virus colloids:The enterovirus,Escherichia coli phage vB_EcoM-ep3,selected in this study is a gentle bacteriophage belonging to the family of long-tailed phage.v B_EcoM-ep3 is a double-stranded DNA phage with an icosahedral head of approximately 53±2 nm in diameter and a contractile tail of approximately 107±3 nm in length consisting of tail and tail filaments,with a total length of 160 nm.Its head structure consists of a gpE(cleaving enzyme protein),an icosahedral symmetrically arranged capsid,and a gpD(decorative protein)containing a raised surface,both covalently linked by non-disulfide bonds.Under different influencing factors,the colloidal particle size and Zeta potential of the enteric virus showed different results.With the increase of pH,the particle size of enterovirus colloid decreased;with the increase of ionic strength,the size of colloidal particles increased;the higher the concentration of SiO2 colloid,the larger the colloidal particle size.Among them,the effect of divalent cations on the colloidal particle size of enteroviruses is greatest.Zeta potential shows a decreasing trend with the increase of pH.The addition and concentration of monovalent and divalent cations increase the overall Zeta potential.With the addition of SiO2 colloid,the Zeta potential shows a decreasing trend.All potentials are in an unstable state(ZP <±30 mV).(2)Characteristics of environmental behaviors,such as deposition and release for enterovirus colloids in vadose zone:Different water environmental influence factors will change the behavior of enterovirus colloids in the vadose zone.As the degree of saturation decreases,still water will form within the pores of lithologic medium,and the degree of retention of enterovirus colloids will increase significantly.The lower the degree of saturation,the less pronounced the release phenomenon is.The deposited colloidal enterovirus no longer migrates with the suspension.There is also evidence that adsorption to the SWI increases as the water saturation decreases.Adsorption to AWI is considered an irreversible process at lower saturation conditions.With the increase of pH,the potential energy of the solid-water interface and the gas-water interface increased,and the stability of the enterovirus colloids increased,which were not conducive to adsorptions.The increase of cation concentration neutralized more negative charges on the surface of AWI,weakened the electrostatic interaction force and promoted the adsorption of enterovirus colloids.With the increase of cation concentration and the decrease of saturation,enterovirus colloids are more easily adsorbed on the surface of medium,solid-water interface and gas-water interface.The addition of SiO2 colloids adsorbed on lithologic medium occupied the adsorption site of enterovirus colloids,which promoted the migration of viruses.