LABORATORY-SCALE EXPERIMENT MEASURING ESCHERICHIA COLI INFILTRATION IN SATURATED SOIL COLUMNS

摘要

A laboratory-scale experiment measuring the infiltration of Escherichia coli into saturated soils was performed under constant temperatures. Three soil columns were prepared with loamy clay soil using the wet packing method: Column A consisted of a 15-cm soil column with a water head of 5 cm above the soil surface, whereas Columns B and C had a soil column of 10 cm with a water head of 10 cm above the soil surface. Columns A and B were inoculated with autoclaved ultrapure water containing 7.4 × 10~7 colo-ny-forming units/mL of E. coli K12 for 450 and 180 h respectively. Column C was inoculated only with autoclaved ultrapure water and served as an experimental control. Column A presented a steady decrease in infiltration rate, which showed a strong correlation (correlation coefficient = −0.93) with the amount of E. coli accumulated in the soil (clogging). Column B first presented similar results to Column A; however, after eight pore volumes were flushed, the infiltration rate increased rapidly, doubling the initial infiltration rate prior to E. coli inoculation. It is proposed that heterogeneous accumulation and growth of E. coli in the soil led to increased infiltration rate. In Column C, the infiltration rate decreased from 27.7 to 24.0 mL/h over the duration of the experiment, despite not having any other input than autoclaved ultrapure water. Additionally, the measurements of E. coli at the output of the soil columns were compared using spec-trometry, plate counts, and quantitative polymerase chain reaction measurements. The results indicated that spectrometry was the most suitable method for determining breakthrough curves in soil infiltration ex-periments.