Experimental Study Of Transport Characteristics Of E. Coli In Soils

Pathogens such as bacteria and virus exist in septic tanks, sewage sludge and wastewater. Microbial pollution in the groundwater has been paid more attention all over the country because of its difficulty to remove and purify from soil porous. In this thesis, E. coli. as an indicator of environmental pollution has been studied. Both behaviors of adsportion and transport of bacteria in the soil are studied under conditions of lab. The goals are to clarify character and mechanisms of adsportion and migration of bacteria in the soil and consider the effects of different styles and basic characters of soils to behaviors of bacteria. All of these researches can provide some updated minds and fresh ways to study mutual effects between microbe and soil.In this thesis, MTT method to measure bacteria amount is studied in detail. By applying Static batch equilibrium adsorption test, bacteria behaviors in the soil is described by Isotherm model and adsportion characters and mechanism of bacteria in the soil are analyzed. Bacteria breakthrough curve and distribution in the soil profile are analyzed by using saturated and unsaturated soil column experiment. Meanwhile, the behaviors of bacterial transport in the soil and other factors to behaviors of bacterial transport are studied.Dual-wavelength is constructed to measure E.coli, the appropriate concentration range of live bacteria is 10⁷¹0⁹ cfu/mL, and OD_510-690 and live bacteria amount C are significant correlation, the relationship is OD_510-690=1.006C-0.0187, correlation coefficient is above 0.99. Meanwhile, this method can detect different stage E.coli.Iso-density gradient centrifugation method is adding 4mL 60% sucrose at the bottom of centrifuge tube. Each experimental condition of E.coli. adsorption in the soil is studied by this method. Loam condition: adsorption time 90min, speed centrifugation 2000rpm, time 20min; Sand condtion: adsorption time 90min, speed centrifugation 1500rpm, time 20min.Through stimulating E.coli. adsorption in the soil, F and L equation can show ideal stimulating results. Loam can decrease ability to adsorp E.coli. as concentration of bacteria increased. However, in the sand condition, the adsorption of bacteria is increased as concentration of bacteria increasement. The ability of adsportion E.coli. in the Loam is stronger than that of in the sand by analyzing adsorption parameters.When comparing peak point and time of E.coli. BTC, bacteria holdup is bigger in the loam soil; Bacteria is mainly in the surface soil by analyzing E.coli. distribution in the soil profile, this shows that leaching plays a critical role in the process of E.coli. transport in the soil. Meanwhile, the holdup is much bigger in the loam surface, this can demonstrate that leaching is more important in the loam soil. Flow velocity is the main factor to effect bacteria transport in the soil by calculating average pore velocity in different type soils. Under the high flow velocity, it can move bacteria forcedly and reduce the mutual time between bacteria and soil and increase bacterial outflow.In the sand, convection-diffusion is the main transport way to E.coli. by applying unsaturated soil migration test. Bacteria holdup in the sand is increased as Ionic strength increasement through studying effects of EC and pH to bacteria migration. Under low pH, bacteria holdup is increased.