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Microbial Kinetic Model for the Degradation of Poorly Soluble Organic Materials
Citation:
Yassine, M. H., M. T. Suidan, AND A. D. VENOSA. Microbial Kinetic Model for the Degradation of Poorly Soluble Organic Materials. Mark von Looschrecht (ed.), WATER RESEARCH. Elsevier BV, AMSTERDAM, Netherlands, 47(4):1585 -1595, (2013).
Impact/Purpose:
To develop a simple mechanistic model that adequately explains 90-97% of the aerobic biodegradation kinetics of the fatty acid methyl esters (FAMEs) of soybean biodiesel, and 80-94% of the biodegradation kinetics of the n-alkanes of petroleum diesel in batch experiments by acclimated cultures. The model was developed based on the assumption that the biological reaction occurs with the dissolved fraction of the organic materials.
Description:
A novel mechanistic model is presented that describes the aerobic biodegradation kinetics of soybean biodiesel and petroleum diesel in batch experiments. The model was built on the assumptions that biodegradation takes place in the aqueous phase according to Monod kinetics, and that the substrate dissolution kinetics at the oil/water interface is intrinsically fast compared to biodegradation kinetics. Further, due to the very low aqueous solubility of these compounds, the change in the substract aqueous-phase concentration over time was assumed to approach zero, and that substrate aqueous concentration remains close to the saturation level while the non-aqueous phase liquid (NAPL) is still significant. No former knowledge of the saturation substrate concentration (Ssat) and the Monod half-saturation constant (Ks) was required, as the term Ssat/(Ks + Ssat) in the Monod equation remained constant during this phase. The n-alkanes C10 - C24 of petroleum diesel were all utilized at a relatively constant actual specific utilization rate of 0.01 - 0.02 mg-alkane/mg-biomass-hr, while the fatty acid methyl esters (FAMEs) of biodiesel were utilized at actual specific rates significantly higher with increasing carbon chain length and lower with increasing number of double bonds. The results were found to be in agreement with kinetic, genetic and metabolic evidence reported in the literature pertaining to microbial decay rates, uptake mechanisms, and the metabolic pathway by which these compounds are assimilated into microorganisms. The presented model can be applied, without major modifications, to estimate meaningful kinetic parameters from batch experiments, as well as near source zone field application. We suggest the estimated actual microbial specific utilization rate (kC) of such materials to be a better measure of the degradation rate when compared to the maximum specific utilization rate (k), which might be orders of magnitde higer than kC and might never be observed in reality.
