Microcosm Experiments and Modeling of Microbial Movement Under Unsaturated Conditions

Conference · Wed Apr 05 04:00:00 EDT 2006

OSTI ID:894942

Brockman, F J; Kapadia, N; Williams, G; Rockhold, M

Colonization of bacteria in porous media has been studied primarily in saturated systems. In this study we examine how microbial colonization in unsaturated porous media is controlled by water content and particle size. This is important for understanding the feasibility and success of bioremediation via nutrient delivery when contaminant degraders are at low densities and when total microbial populations are sparse and spatially discontinuous. The study design used 4 different sand sizes, each at 4 different water contents; experiments were run with and without acetate as the sole carbon source. All experiments were run in duplicate columns and used the motile organism Pseudomonas stutzeri strain KC, a carbon tetrachloride degrader. At a given sand size, bacteria traveled further with increasing volumetric water content. At a given volumetric water content, bacteria generally traveled further with increasing sand size. Water redistribution, solute transport, gas diffusion, and bacterial colonization dynamics were simulated using a numerical finite-difference model. Solute and bacterial transport were modeled using advection-dispersion equations, with reaction rate source/sink terms to account for bacterial growth and substrate utilization, represented using dual Monod-type kinetics. Oxygen transport and diffusion was modeled accounting for equilibrium partitioning between the aqueous and gas phases. The movement of bacteria in the aqueous phase was modeled using a linear impedance model in which the term D{sub m} is a coefficient, as used by Barton and Ford (1995), representing random motility. The unsaturated random motility coefficients we obtained (1.4 x 10{sup -6} to 2.8 x 10{sup -5} cm{sup 2}/sec) are in the same range as those found by others for saturated systems (3.5 x 10{sup -6} to 3.5 x 10{sup -5} cm{sup 2}/sec). The results show that some bacteria can rapidly migrate in well sorted unsaturated sands (and perhaps in relatively high porosity, poorly sorted unsaturated sands--see Figure 5) at volumetric water contents that naturally occur in many sandy vadose zones.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA
• Sponsoring Organization: USDOE - Office of Science (SC)
• OSTI ID: 894942
• Report Number(s): CONF-ERSP2006-73
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
59 BASIC BIOLOGICAL SCIENCES
ACETATES
BACTERIA
BIOREMEDIATION
CARBON SOURCES
CARBON TETRACHLORIDE
DIFFUSION
IMPEDANCE
KINETICS
MICROCOSMS
NUTRIENTS
OXYGEN
PARTICLE SIZE
POROSITY
PSEUDOMONAS
REACTION KINETICS
SAND
SOLUTES
STRAINS
SUBSTRATES