USE OF SHORT-PULSE EXPERIMENTS TO STUDY BACTERIA TRANSPORT THROUGH POROUS-MEDIA

Continuous-flow column experiments with short-pulse inputs of one hydrophobic and one hydrophilic bacterium were used to study the retention of bacteria on quartz (negatively charged), hematite-coated quartz (positively charged) and polymer-coated quartz (hydrophobic surface), at pH 7.3. Both bacteria were Gram-negative rods. All breakthrough peaks occurred about one pore volume after the input pulse, and were attenuated compared to a bromide-tracer peak. Maximum bacteria concentrations in the column outlet were 0.08-57% of the peak bromide concentration. A one-dimensional advection-dispersion transport model with first-order bacteria removal described by colloid-filtration theory was used to estimate attachment and detachment rate coefficients and the relative sticking efficiency (cu) of bacteria in each experiment. Attachment was reversible, with rate coefficients for attachment on the order of 10(-4)-10(-3) s(-1), implying that the time scale for attachment was of the same order as the column detention time of 1.2 h. The time scale for detachment was on the order of days to weeks. This slow detachment could be important in deep subsurface environments where transport on geologic time scales is important, and in some shallow aquifer recharge situations where soils are used to eliminate pathogenic bacteria from sewage effluent. Values for cu were 0.04-0.4. Slower attachment and detachment rates were observed for the hydrophilic vs. hydrophobic bacteria, suggesting that hydrophilic bacteria could move further before being removed by attachment to soil, but once attached, would be resuspended at a slower rate.