Influence of hydraulic gradient and temperature on the migration of E. coli in saturated porous media during bank filtration: a case study at the Second Songhua River, Songyuan, Northeastern China.

River bank filtration can effectively reduce the number of pathogenic microorganisms infiltrating into groundwater from surface water. Groundwater seepage velocity and temperature are considered to be important factors affecting the process, but the magnitude and mechanism of their impacts have not been clear for a long time. Based on the actual monitoring data of the Escherichia coli concentrations and soil samples of Second Songhua riverside source area, the migration of E. coli in saturated porous media under different velocities and different temperatures was studied using saturated soil column transport experiments. Concurrently, the migration characteristics of E. coli in the riverside source area were replicated by mathematical simulation. According to the field monitoring results, the concentration of E. coli decreased in the riverbank infiltration zone, and the removal rate was greater than 96%. The column experimental results showed that the lower the flow velocity was and the higher the temperature was, the greater the removal rate of E. coli was. And the flow velocity was the main factor affecting the removal of E. Coli. The mathematical simulation results showed that under the conditions of the largest hydraulic gradient (20%) and the highest concentration of E. coli (2500 MPN/100 mL) in river water, the safe exploitation distance of groundwater that did not cause a risk of E. coli pollution was more than 7 m away from the river bank. These findings are expected to provide a scientific basis for the design of water intake schemes and the optimization of mining technology.