Versatility of soil column experiments to study biodegradation of halogenated compounds under environmental conditions

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Deposition of Pseudomonas putida mt2 and Rhodococcus strain C125 during transport through columns packed with Teflon grains was investigated. Deposition was analyzed in terms of the clean bed collision efficiency α0 (the probability of a cell to attach upon reaching a cell-free substratum) and the surface area blocked by attached cells. Blocking was quantified by a blocking factor B, the ratio of the blocked area per cell to the geometric area of a cell. At an average interstitial fluid velocity of 200 μm s-1, α0 is close to unity (0.83 ± 0.01) for both strains, indicating that cell−solid interactions are almost completely favorable for deposi tion. Values for B of 1.6 ± 0.1 and 12.0 ± 0.8 were obtained for Ps. putida and Rhodococcus strain C125, respectively. This difference is consistent with differences in cell size and cell−cell repulsion, which were both smaller for Ps. putida than for Rhodococcus strain C125. At coverages close to saturation, multilayer adhesion and/or pore clogging occurs for the weakly blocking Pseudomonas cells but not for the strongly blocking Rhodococcus cells. The collision-blocking concept succesfully explains the breakthrough of Bacillus cells in coarse sand columns, as reported by Lindqvist and Enfield, for which adhesion is less favorable (α0 = 0.10 ± 0.01) and blocking is relatively strong (B = 5.8 ± 0.8). The general conclusion is that deposition of microbes during their transport through coarse grain media is adequately described by the collision-blocking model in cases of strongly blocking cells or weakly blocking cells at low coverage conditions.

Section: Introductionmentioning

confidence: 99%

Bacterial Deposition in Porous Media Related to the Clean Bed Collision Efficiency and to Substratum Blocking by Attached Cells

Rijnaarts

Norde

Bouwer

et al. 1996

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“…Control of microbial transport and retention in porous media is required for effective and safe bioremediation of contaminated soil and groundwater (1)(2)(3)(4). A significant step toward a better understanding of bacterial mobility in porous media was made in the preceding paper in which the basic mechanisms contributing to microbial deposition in coarse grain media were analyzed (4).…”

Section: Introductionmentioning

confidence: 99%

Bacterial Deposition in Porous Media: Effects of Cell-Coating, Substratum Hydrophobicity, and Electrolyte Concentration

Rijnaarts

Bouwer

Lyklema

et al. 1996

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Deposition of seven bacterial strains on spherical glass and Teflon collectors was studied in vertical downflow columns at an ionic strength (I) of 0.1 M. The various bacteria had either one of the following types of major cell-surface constituents: nonpolysaccharide (NP), amphiphilic (AMPH), or anionic polysaccharide (AP) macromolecules. Deposition was analyzed in terms of the clean bed collision efficiency R 0 (the probability of a cell to attach upon reaching a substratum free of cells) and a blocking factor B (the ratio of the area blocked by an attached cell to the geometric area of a cell). The value of R 0 decreased from 1.0 to about 0.01 in the following order of cell-surface constituents/collector combinations: NP/Teflon and AMPH/Teflon > NP/glass > AMPH/ glass, AP/Teflon, and AP/glass. The value for B, at a Peclet number of 1 × 10 5 , increased from about 3 to 18 in the order NP/low cell charge < NP or AMPH/ high cell charge < AP/high cell charge. This indicates that cell-cell repulsion enhances blocking. Blocking is higher on Teflon than on glass. Most likely cell-surface macromolecules adsorb in the surroundings of the attached cells and enhance blocking on Teflon. The deposition of four bacterial strains was investigated at 0.0001 M e I e 0.1 M. For I values smaller than a critical level, R 0 decreased with decreasing I. The critical I is determined by the range over which cell-surface macromolecules can penetrate the repulsive Gibbs energy barrier between cell and solid. The value for B increases about 1 order of magnitude upon changing I from 0.1 to 0.001 M. Maximal control of microbial mobility in porous media can be reached in systems for which B and R 0 are high at high I (0.1 M): the high B value minimizes the occurrence of pore-clogging whereas the dependencies of R 0 and B on I allow manipulation of deposition by varying the ionic strength.

“…This latter observation is of concern, as aromatic growth substrates (phenol and toluene) are themselves regulated chemicals. Theoretically, in such a system, growth substrates are removed to a residual or threshold concentration equal to S min ( , ). Based on the findings presented here, this residual will increase in relation to residual CAH concentra tion.…”

Section: Resultsmentioning

confidence: 99%

Effect of Chlorinated Ethenes on S_min for a Methanotrophic Mixed Culture

Anderson

McCarty

1997

The presence of chlorinated aliphatic hydrocarbons (CAHs) was found to increase the minimum methane concentration for net growth (S min ) of a methanotrophic mixed culture expressing particulate methane monooxygenase (pMMO). Without CAHs, S min was 5 µg/L methane. S min , however, increased to 20-25 µg/L in the presence of 0.05 mg/L 1,1-dichloroethylene (1,1-DCE), 2 mg/L trans-1,2dichloroethylene (t-DCE), or 4 mg/L trichloroethylene (TCE). A lower maximum methane oxidation rate was required to model growth rates at these low methane concentrations, a result that was attributed to reducing energy limitation. A derived equation for possible factors by which CAHs increased S min included reducing energy limitation, competitive inhibition, and transformation product toxicity. However, a simplified model that incorporated these effects into a single parameter was adequate to model the overall effect on growth rate and S min .