Use of colloid filtration theory in modeling movement of bacteria through a contaminated sandy aquifer

Abstract

A filtration model commonly used to describe removal of colloids during packed-bed filtration in water treatment applications was modified for describing downgradient transport of bacteria in sandy, aquifer sediments. The modified model was applied to the results of a small-scale (7 m), natural-gradient tracer test and to observations of an indigenous bacterial population moving downgradient within a plume of organically contaminated groundwater in Cape Cod, MA. The model reasonably accounted for concentration histories of labeled bacteria appearing at samplers downgradient from the injection well in the tracer experiment and for the observed 0.25-jum increase in average cell length for an unlabeled, indigenous bacterial population, 0.6 km downgradient from the source of the plume. Several uncertainties were apparent in applying filtration theory to problems involving transport of bacteria in groundwater. However, adsorption (attachment) appeared to be a major control of the extent of bacterial movement downgradient, which could be described, in part, by filtration theory. Estimates of the collision efficiency factor, which represents the physicochemical factors that determine adsorption of the bacteria onto the grain surfaces, ranged from 5.4 X 10'3 to 9.7 X 10~3.

Revisiting the Cape Cod Bacteria Injection Experiment Using a Stochastic Modeling Approach

“…Details of the conditions of the injection test are provided in Harvey and Garabedian [14]; information on the site hydrogeology is provided in LeBlanc et al [20]. In brief, a 90-L volume of bromide solution (150 mg/L) and stained bacteria was injected at a rate of 0.85 L/m simultaneously at depths of 8.5 and 9.1 m below land surface in the saturated zone; breakthrough was measured at these elevations 6.8 m downgradient from point of injection.…”

“…For attached bacteria, the mass balance equation is given by period following collection, growth and death were not significant [14]. Although significant advances have been made in understanding the effect of bacterial chemotaxis at the pore scale [23], much about the macroscale significance of chemotaxis for bacteria is still poorly understood [24].…”

“…Gains have also been made in the area of field-scale modeling by coupling porous-media transport models with a realistic representation of the microbial attachment process (e.g. [14,15]). Less progress has been made in coupling the known non-idealities of microbial transport with a realistic representation of aquifer heterogeneity to quantify the effects of heterogeneity on the transport process (e.g.…”

“…[14]), considerable advances have been made in (1) quantifying, statistically, aquifer heterogeneity; (2) capturing heterogeneity using numerical methods incorporating finely-gridded systems and grid-free transport algorithms; (3) refining the relationship between colloid filtration (sorptive removal) and physical heterogeneity, and (4) parameterizing the colloid filtration process. The purpose of this paper is to utilize improvements in these four areas to revisit the data interpretation from the 1991 paper by Harvey and Garabedian.…”

Bacteriophage transport through a fining-upwards sedimentary sequence: laboratory experiments and simulation

“…Many workers have noted that tracer responses with time (breakthrough curves) observed on different scales may not be consistent with one another (Harvey and Garabedian, 1991;Bales et al, 1995;Schijven et al, 2002). These differences are often attributed to heterogeneity.…”