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

Continuous-flow column experiments with short-pulse inputs of one hydr ophobic and one hydrophilic bacterium were used to study the retention of bacteria on quartz (negatively charged), hematite-coated quartz (p ositively 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 attenu ated compared to a bromide-tracer peak. Maximum bacteria concentration s in the column outlet were 0.08-57% of the peak bromide concentration . A one-dimensional advection-dispersion transport model with first-or der bacteria removal described by colloid-filtration theory was used t o estimate attachment and detachment rate coefficients and the relativ e 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 o f 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 detachmen t could be important in deep subsurface environments where transport o n geologic time scales is important, and in some shallow aquifer recha rge situations where soils are used to eliminate pathogenic bacteria f rom sewage effluent. Values for cu were 0.04-0.4. Slower attachment an d detachment rates were observed for the hydrophilic vs. hydrophobic b acteria, suggesting that hydrophilic bacteria could move further befor e being removed by attachment to soil, but once attached, would be res uspended at a slower rate.