Biomedical subjects

K A Strevett

Publications and source records attributed to K A Strevett.

4 recordsLinked to original sources

PubMed2001

Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes.

Diffusion, sorption and biodegradation are key processes impacting the efficiency of natural attenuation. While each process has been studied individually, limited information exists on the kinetic coupling of these processes. In this paper, a model is presented that couples nonlinear and nonequilibrium sorption (intraparticle diffusion) with biodegradation kinetics. Initially, these processes are studied independently (i.e., intraparticle diffusion, nonlinear sorption and biodegradation), with appropriate parameters determined from these independent studies. Then, the coupled processes are studied, with an initial data set used to determine biodegradation constants that were subsequently used to successfully predict the behavior of a second data set. The validated model is then used to conduct a sensitivity analysis, which reveals conditions where biodegradation becomes desorption rate-limited. If the chemical is not pre-equilibrated with the soil prior to the onset of biodegradation, then fast sorption will reduce aqueous concentrations and thus biodegradation rates. Another sensitivity analysis demonstrates the importance of including nonlinear sorption in a coupled diffusion/sorption and biodegradation model. While predictions based on linear sorption isotherms agree well with solution concentrations, for the conditions evaluated this approach overestimates the percentage of contaminant biodegraded by as much as 50%. This research demonstrates that nonlinear sorption should be coupled with diffusion/sorption and biodegradation models in order to accurately predict bioremediation and natural attenuation processes. To our knowledge this study is unique in studying nonlinear sorption coupled with intraparticle diffusion and biodegradation kinetics with natural media.

Adsorption↗

PubMed2001

Impact of surface thermodynamics on bacterial transport.

Microbial surface thermodynamics correlated with bacterial transport in saturated porous media. The surface thermodynamics was characterized by contact-angle measurement and the wicking method, which was related to surface free energies of Lifshitz-van der Waals interaction, Lewis acid-base interaction, and electrostatic interaction between the bacteria and the medium matrix. Transport of three different strains of bacteria present at three physiological states was measured in columns of silica gel and sand from the Canadian River Alluvium (Norman, OK, USA). Microorganisms in stationary state had the highest deposit on solid matrix, compared with logarithmic and decay states. The deposition correlated with the total surface free energy (DeltaG132TOT) and the differences in DeltaG132TOT were mainly controlled by the Lewis acid-base interaction. Infrared spectroscopy showed that the increased deposition correlated with an increase in the hydrogen-bonding functional groups on the cell surfaces.

Bacterial Adhesion↗

PubMed1999

Influence of microbial concentration on the rheology of non-Newtonian fermentation broths.

The objective of this study was to quantify the effect of fungal biomass concentration on the rheology of non-Newtonian fermentation systems. Batch fermentations of Penicillium chrysogenum were carried out with glucose as the sole carbon source. The flow behavior of the system was characterized at various fermentation times and was adequately described by the power-law model. The apparent viscosity of the fermentation broth was significantly affected by biomass concentrations in the fermenter. Fermentation broths containing 17.71 g/l biomass as dry weight were characterized by an apparent viscosity of 0.25 Pa s at a shear rate of 50 s-1. Microbial concentration also affected the power-law flow-behavior index and the consistency index. The value of the consistency index ranged from 0.002 Pa sn at a biomass concentration of 0.1 g/l to 6.14 Pa sn at a biomass concentration of 17.71 g/l. The flow-behavior index decreased from an initial value of 1 to a final value of 0.17. Simple empirical correlations have been proposed to quantify the dependence of the power-law parameters on fungal biomass concentration. Experimental data obtained in this study were accurately described by these correlations. The general applicability of these relationships was tested, using previously published rheological data on Aspergillus awamori and Aspergillus niger fermentation broths, and good agreement was seen between experimental data and the predictions from the empirical correlations.

Biomass↗

PubMedDate not supplied

Nutrient conversions by photosynthetic bacteria in a concentrated animal feeding operation lagoon system.

A diurnal examination was conducted to determine the effect of photosynthetic bacteria on nutrient conversions in a two-stage concentrated animal feeding operation (CAFO) lagoon system in west-central Oklahoma. Changes in nutrients, microbial populations, and physical parameters were examined at three depths (0, 1.5, and 3.0 m) every 3 h over a 36-h period. The south lagoon (SL) was anaerobic (dissolved oxygen [DO] = 0.09 +/- 0.12 mg/L) while the north lagoon (NL) was facultative (DO ranged from 4.0-0.1 mg/L over 36-h period). Negative sulfide-sulfate (-0.85) and bacteriochlorophyll a (bchl a)-sulfate (-0.83) correlations, as well as positive bchl a-sulfide (0.87) and light intensity (I)-bchl a (0.89) correlations revealed that the SL was dominated by sulfur conversions driven by the photosynthetic purple sulfur bacteria (PSB). The correlation data was supported by diurnal trends for sulfate, sulfide, and bchl a. Both nitrogen and sulfur conversions played a role in the NL; however, nitrogen conversions appeared to dominate this system because of the activity of cyanobacteria. This was shown by positive chlorophyll a (chl a)-I (0.91) and chl a-nitrate (0.98) correlations and the negative correlation between ammonium and nitrite (-0.88). Correlation data was further supported by diurnal trends observed for chl a, DO, and ammonium. For both lagoons, the dominant photosynthetic microbial species determined which nutrient conversion processes were most important.

Animals↗