Transport Of Escherichia Coli In Saturated Porous Media

Pathogens exist in livestock manure, domestic wastewater, landfill sites, septic tanks and housphal sewage. The pathogen-contaminated water can pose a risk to human and animal health when it used as a source for drinking. Escherichia coli(E.coli) are often chosen as a common indicator of environment pollution. Column experiments were performed under environmentally relevant conditions to understand the influence of various hydrochemiscal and physical factors on the transport of E.coli in saturate quartz sand and natural sand. The findings from this study provided theoretical and model basis to discuss E.coli transport in groundwater environment.The influence of cell concentration on E.coli transport in quartz sand has been examined using D21f2g and K12 C600 under environmentally relevant conditions. The suitable injection concentration for the exprimental system was 107 cells/mL. Then, the influence of particle size and pore water velocity was discussed. A variety of column experiments were performed in both quartz sand and natural sand under various hydrochemical and physical conditions. Finally, a two-site transport model was used to fit the breakthrough curves (BTCs) collected with experiments of various flow rates and water chemistry. The main results were summarized as follows:(1) When the injection concentration of BTCs of both D21f2g and K12 C600 is 108 cells/mL, the blocking phenomenon was occurring. The suction ratios of breakthrough curve increase with time. As D21f2g is more negatively charged than K12 C600, the suction ratios of breakthrough curve of D21f2g are higher than that of K12 C600.(2) Both ionic strength increasing and Ca2+ can increase the deposition of both E.coli strains. While the influence of ionic strength and Ca2+ on D21f2g was more significantly than that on K12 C600. The influence of ionic strength and Ca2+ on K12 C600 changed less. It is possible that the O-antigen on the K12 C600 could shield charged functional groups, which would otherwise influence electrostatic double-layer interactions. Thus, D21f2g was utilized to study the influence of various hydrochemistry and physical factors on E.coli transport.(3) Particle size and pore water velocity could affect the transport and deposition of E.coli in porous media. The decrease of particle size could enhance the straining effect, which could increase the deposition ratio and retention ratio of E.coli. Moreover, the enhanced straining effect resulted in lower release of E.coli from the smaller grains. When the pore water velocity slows, the deposition ratio and retention ratio of E.coli would increase. The influence is more significations when the ionic strength is higher.(4) Both increasing ionic strength and Ca2+ would increase the deposition rate coefficient of E.coli in both quartz sand and natural sand, while the influence of ionic strength and Ca2+ on deposition in quartz sand was more significantly than that in natural sand. The size distribution of natural sand is highly nonuniform while the size distribution of quartz sand is quite uniform. The mean particle size of natural sand is smaller than quartz sand. And there is a spot of clay mineral and organic matter in natural sand, which responded to changes of ionic strength and ionic species differently than quartz sand. Decreasing pore water velocity had little effect on E.coli transport through quartz sand, but significantly inhibited the transport through natural sand. The difference can be attributed to both the smaller particle size and the more irregular and rougher shapes of natural sand, and can be explained with the shadow zone effect theory.(5) A two-site transport model that takes into account both the blocking and straining effects can effectively model the BTCs of E.coli. When the ionic strength is lower, the results could reflect the characteristics of transport of E.coli. The fitted parameters, provided insights the influence of various hydrochemical and factors on the kinetic transport of E.coli in saturate porous media.This study discusses the influence of geochemical and physical factors on the transport of E.coli based on the simulated groundwater system. As groundwater system is complex and diversiform, it is useful to research the transport of E.coli in real groundwater environment.