Retention Mechanisms Of Escherichia Coli Transport In The Soil

Migration behavior of microorganisms in soil is an important factor affecting soil andgroundwater contamination, as well as the critical issues in microbial remediation ofcontaminated soil and groundwater. A clear understanding of mechanisms of microorganismsbehavior in soil, not only can indicate microbial contamination of the soil and groundwater,but can provide a favorable basis for the groundwater protection and pollution management. Italso can provide a theoretical basis for judgment if microorganisms could reach to thecontaminated areas or sources, as to guide microbial remediation work of soil andgroundwater.Five sizes of quartz sands (351,319,217,71,27μm) and E. coli were used to stduy theimpacts of soil texture on retention behavior of microorganisms in soil, batch adsorptionexperiment and migration experiment were adopted, were studied.The comparative experiment results showed batch adsorption experiments should adoptstanding to separate E. coli which was not adsorbed from quartz sands in the particle sizerange of this study. Results of batch adsorption-desorption experiment showed that quartzsands had great adsorption quantity of E. coli. The adsorption ratio could reach above95%,when the initial microbial concentration was109cfu/mL. With the decreased of the quartzsand particle size, the adsorption quantity increased, and adsorption reached balance faster.However, quartz sands had small desorption ratio of E. coli，the desorption ratio increased asquartz sands particle size increased, the largest desorption ratio was only3.6%. Desorption ofE.coli on quartz sands existed obvious hysteresis. It indicated there existed irreversibleadsorption between E. coli and quartz sands.The Pseudo-second-order rate equation is optimal to describe adsorption and desorptionkinetics of E. coli on quartz sands, and the isothermal processes is suitable to describe usingHenry equation. The average particle size and specific value physical clay content/physicalsand content of quartz sand have some relevance with the parameters of Henry equation andPseudo-second-order rate equation. This shows that adsorption and desorption heavily dependon particle size.In migration experiments, the retention amounts of E. coli in the quartz sands were verylarge, the retention amount of E. coli in small particle size quartz sand could even reach morethan90%. The breakthrough curves of E. coli in quartz sands could be described byBoltzmann equation. The parameters show that E. coli may breakthrough completely in thethe quartz sand which size is351,319μm, and may not breakthrough completely in otherthree quartz sands.The results of forward elution experiment showed retention amount of E. coli caused byreversible adsorption was small. This proves the conclusion that adsorption is irreversible inbatch adsorption experiment.The results of reverse elution experiment and the distribution of E. coli in the column show E. coli would form straining layer and gradually thicken, this is asignificant “cake” layer (here defined as“crust”). Although reverse elution can not reflect thestraining strength of E. coli in soil, but can reflect the stability of “crust”, this stability isdetermined by straining and adsorption.The migration experiment shows, in the size range studied, the role of straining inretention much greater than the adsorption, and heavily depends on the geometry of soilparticles. Meanwhile, on the basis of straining, adsorption remained the microorganisms nearthe straining layer to enhance the overall retention. This is the retention mechanism ofmicroorganisms transport in the soil.