Injection‐attachment of Methylosinus trichosporium OB3b in a two‐dimensional miniature sand‐filled aquifer simulator

Abstract

For some potentially useful and emerging in situ bioremediation technologies it is important to control bacterial attachment to subsurface materials during the injection of microbial cell suspensions. In this study the attachment patterns of Methylosinus trichosporium OB3b were measured after horizontal injections into a two-dimensional miniature aquifer simulator containing a wet homogeneous sand. In preliminary sand column assays, bacterial attachment to the sand was increased nearly 2 orders of magnitude compared to attachment in the presence of distilled water by raising the concentration of a pH 7.0 sodium-potassium phoosphate buffer to 10 mM.The maximal concentration of attached cells was ---4 x 10 ø cells/g dry sand with both sand minicolumns and the wet sand aquifer simulator. For the latter this occurred on streamlines directly between the horizontal injector and withdrawal ports, where injection-withdrawal velocities were the highest. The effects of a simulated groundwater cross flow during suspension injection on bacterial attachment to the aquifer simulator sands were also studied, and a peristaltic pumping method to counteract these groundwater flow effects resulted in a more localized pattern, i.e., without extensive downstream skewing of the bacterial attachment zone. Phenol red was utilized as a•nonbinding, red-colored tracer compound. It proved to be very convenient for quantitatively measuring the earlier breakthroughs of cells versus an inert tracer during the aquifer simulator and subsequent capillary tube cell injection experiments and also for visualizing the anticipated boundaries of cell attachment in the aquifer simulator. The effect of injection velocity on the observed bacterial attachment patterns in these experiments appears to be accounted for by colloid filtration theory.

A review of visualization techniques of biocolloid transport processes at the pore scale under saturated and unsaturated conditions

“…The effect had [119,98], analyzing earlier breakthrough of microbes relative to a tracer, assigned a lower dispersivity for microbes than for solutes. They noted differences in dispersion that led to faster breakthrough, although they were unable to pinpoint the mechanism that caused these differences.…”

Processes in microbial transport in the natural subsurface

“…Size exclusion effects have been observed in laboratory columns [37,92,114,156,164] and in field experiments [50,172,189]. Exclusion is a phenomenon where transported particles move faster than the mean pore-water velocity, and involves an increase in the transport rate due to the size or charge of the material conveyed.…”

“…Engfield and Bengtsson [37] examined the effects of unaccounted exclusion on the effective value of partition coefficients for macromolecular transport, and Shonnard et al [114] analyzed early breakthrough of microbes relative to phenol red in a capillary in the context of Taylor-Aris dispersion theory [181]. Shonnard et al [114] assign the microbe a lower radial diffusivity than a molecular solute so that the microbial transport is dominated by convection, on the basis of which they use the high Peclet limit solution of the capillary convection-dispersion equation. This approach is critiqued in Ginn [45].…”

Modeling the effects of systematic variation in ionic strength on the attachment kinetics of Pseudomonas fluorescens UPER‐1 in saturated sand columns

“…Effects of cell surface heterogeneity [Simoni et al, 1998] and motile/ nonmotile cells [Camesano and Logan, 1998] on cell attachment in column studies have been recently reported. Studies of microbial attachment in a two-dimensional (2-D) miniature sand-filled aquifer simulator [Shonnard et al, 1994] and a biofilter [Taylor et al, 1993] are reported. Harvey et al [1989] have reported field research on the transport of bacteria in a sandy aquifer.…”