The Study Of Escherichia Coli Transport In Saturated Porous Media During River Water Infiltration

With the continuous development of industrialization and urbanization,the microbial pollution of the surface water is becoming more and more serious,which will pose a serious threat to the groundwater quality for riverside pumping,so it is urgent need to study the attenuation of pathogenic microorganisms under the action riverbed percolation.As a kind of pathogenic microorganisms,E.coli possess a certain degree of pathogenicity to human body.By collecting and testing the river water and groundwater samples of riverside source fields in Songyuan City Jilin Province,it is found that the E.coli concentration in river water samples exceeded standard badly,although the E.coli concentration in groundwater samples is less than river water samples significantly,there still are some wells have been tested out.The existing research on the migration regularity and mechanism of E.coli during the process of river water infiltration is not clear yet,therefore need to explore it to provide a scientific basis for the technology of riverside pumping and optimizing exploitation.The article is based on the state water pollution control and management key scientific and technological project “The Songhua river water quality security key technology and demonstration”,selecting Songyuan riverside source fields as the study area.Collect the river water and groundwater samples,testing and analyzing the concentration of E.coli,and summarize the space-time distribution and variation characteristics of E.coli during the river water infiltration.Explore the influence of the lithology,temperature,p H and ionic strength on the adsorption characters of E.coli by carrying out static adsorption experiments,and explore the migration regulation of E.coli by carrying out dynamic soil column simulation experiments.Predict the transport of E.coli based on different hydraulic gradient and concentration of E.coli in river water by numerical simulation,and then provide a scientific basis for the development and protection of groundwater sources for riverside source fields.The results show that in the direction of the river water recharging the groundwater,the concentration of E.coli decrease gradually,and the removal rate is more than 96%.The static adsorption experiments show that the lithology of medium,water temperature,p H and ionic strength will affect the adsorption of E.coli.The adsorption rate and the adsorption quantity of E.coli for each experiment fits the regular: the loamy sand> little gravelly soil> much gravelly soil,12 ? > 8 ? > 4 ?,close to neutral condition(p H=7)>partial acid condition(p H=5)> partial alkaline condition(p H=9),high ionic strength(EC=27000?s/cm)> medium ionic strength(EC=2700?s/cm)> low ionic strength(EC=270?s/cm).The adsorption equilibrium time is 90 min,the adsorption kinetics characterstics conform to the pseudo-second-order model,and the equilibrated adsorption capacity range between 164-209MPN/g,the adsorption thermodynamic characterstics conforms to Henry.The dynamic soil column simulation experiment results show that the aqueous medium has a good removal effect to E.coli during the process of the river water infiltration.Taking 50 cm as example,the removal rate reach to 97.06-99.92%.The removal rate increases with the increase of migration distance.Under the condition of 4 ?,the migration distance and removal rate of E.coli conform to logarithmic relationship,and the retention mechanism includes filtration and adsorption,in which the filtration effect occurring on the surface of the medium is stronger.The strength of filtration and adsorption were affected both by the lithology and the velocity.The smaller is the aqueous medium particles and the flow velocity,the stronger is the filtration and adsorption,and the greater is the removal rate of E.coli.In other temperatures(8? and 12?),the removal rate of E.coli increases with the increasing of migration distance,but it is not in conformity with the logarithmic relationship.It is because that under these temperature conditions,the retention mechanisms include not only filtration and adsorption but the growth and decline.At the same time,the higher the hydraulic gradient and temperature,the faster the decline rate of E.coli and the stronger the aquifer medium adsorption ability,so as to the greater the removal rate of E.coli.The mathematical modeling results show that the hydraulic gradient and the concentration of E.coli in river water can both affect the transport of E.coli.The higher the hydraulic gradient and the concentration of E.coli in river,the greater the concentration of E.coli in groundwater and the longer the transport distance for E.coli.When the hydraulic gradient was 20%,and the concentration of E.coli in the river water is 2500MPN/100 m L,the migration distance of E.coli is about 7m.