Effects of Phosphate on the Transport of Escherichia Coli in Saturated Quartz Sand

Abstract

Bacterial deposition and survival in porous media is a crucial phenomenon in various environmental processes including bioremediation, water treatment, and pathogen contamination. The fate of bacteria in porous media may be greatly influenced by ionic strength and phosphate. Although phosphate is widespread in the natural environment, the influence of phosphate on the transport of three strains of ESCHERICHIA COLI O157:H7 cells in the groundwater system remains unknown. Experiments were performed in saturated sand packed columns with and without phosphate to examine the transport of bacteria, deposition rate coefficient, interaction energy between bacteria and sand, and bacteria surface charge. Experimental results indicate that phosphate could enhance the transport of three strains of ESCHERICHIA COLI O157:H7 cells under the ionic strengths varied from 10 to 100 mM. Under higher ionic strength, three strains of ESCHERICHIA COLI O157:H7 cells displayed lower retention in sand. According to interaction energy profiles, majority of deposition of three strains of ESCHERICHIA COLI O157:H7 cells in the packed-bed system occurred in the secondary energy minimum. The response of three strains of ESCHERICHIA COLI O157:H7 cells to different phosphate concentrations and ionic strength conditions were explained by the extended DLVO (XDLVO) theory and the steric repulsion caused by extracellular macromolecules. It was concluded that phosphate could broaden the spread of three strains of ESCHERICHIA COLI O157:H7 cells, and potentially other types of bacterial cells, within the soil groundwater system.