The forced convection of a monodisperse, monoclonal suspension of bacteria through a uniform, saturated porous medium has been investigated. Bench-scale column studies were carried out to measure the removal of microorganisms from suspension due to attachment to the surfaces of the solid phase. The columns were packed with 40-μm borosilicate glass beads, and bacterial sorption was measured as a function of depth in the column using a leucine radiolabel assay. The strains A1264 and CD1 were examined separately. Colloid filtration theory was used to interpret the data, and the average, or effective, affinity of the bacteria for the glass beads was found to decrease with distance traveled through the column. It is postulated that, under these circumstances, the cell/collector affinity (that is, the collision efficiency α) varied due to intrapopulational differences in bacterial surface characteristics. A simple bimodal probability density function, consisting of two Dirac delta functions, was found to satisfactorily represent the α distribution in the original bacterial population. This form of the distribution function was supported by capillary electrophoresis measurements on the bacteria, which showed intrapopulational differences in the surface charge density under the conditions of the transport experiments. These variations in surface charge density are significant inasmuch as they give rise to substantial differences in the colloidal interaction potentials and, presumably, large differences in cell affinity for negatively charged collectors such as glass beads or quartz.

Transport of bacteria over significant distances through aquifer sediments occurs primarily among bacteria with low affinity for sediment materials. Bacterial affinity for a uniform collector surface has been represented quantitatively by a collision efficiency (α), defined as the fraction of colliding cells that adhere to the collector surface. Using a new method for estimating α during advective transport of monoclonal bacterial populations through a uniform bed of 40‐μm borosilicate glass spheres, we found that α decreased 10‐fold over a bed depth of only 1 cm. Depth‐dependent differences in α were not related to variation in bacterial size or intra‐strain genetic variation. Intra‐population heterogeneity in biocolloid‐collector affinity may be important determinant of subsurface bacterial transport characteristics, with critical implications for pathogen transport and dispersal of bacteria for the remediation of hazardous waste.

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Transport of bacteria over significant distances through aquifer sediments occurs primarily among bacteria with low affinity for sediment materials. Bacterial affinity for a uniform collector surface has been represented quantitatively by a collision efficiency (α), defined as the fraction of colliding cells that adhere to the collector surface. Using a new method for estimating α during advective transport of monoclonal bacterial populations through a uniform bed of 40‐μm borosilicate glass spheres, we found that α decreased 10‐fold over a bed depth of only 1 cm. Depth‐dependent differences in α were not related to variation in bacterial size or intra‐strain genetic variation. Intra‐population heterogeneity in biocolloid‐collector affinity may be important determinant of subsurface bacterial transport characteristics, with critical implications for pathogen transport and dispersal of bacteria for the remediation of hazardous waste.

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