Estimation of Biokinetic Parameters for Unsaturated Soils

Abstract

Model predicting gas phase concentrations of an organic substrate and of carbon dioxide in unsaturated soil microcosms was developed. The model included equilibrium partitioning of organic between soil, water, and gas phases; consumption of organic and production of carbon dioxide due to biological activity; pH-dependent carbon dioxide partitioning between the water and gas phases; and biomass growth. A Bayesian estimation method was coupled to the microcosm model to allow determination of biokinetic parameters from carbon dioxide and organic vapor concentration measurements. The Bayesian estimation method was applicable to multiresponse data with missing observations; a common occurrence in environmental monitoring. A microcosm configuration was developed for determination of biokinetic constants in unsaturated soils. Results of studies on biodegradation of toluene at two moisture contents were analyzed with the parameter estimation model. Observations of both carbon dioxide and toluene concentrations were used in parameter estimation to allow the simultaneous determination of yield and initial biomass concentrations, as well as reaction rate parameters and half-saturation constants. Parameter confidence intervals and joint confidence regions for pairs of parameters were estimated by integration of the Bayesian posterior density functions.