Approach for estimating microbial growth and the biodegradation of hydrocarbon contaminants in subsoil based on field measurements: 1. Model development and verification.

An approach was developed to represent the microbial growth and corresponding biodegradation of hydrocarbons (HCs) during the natural attenuation process based on field measurements of in situ microbial biomass and residual HC concentrations in unsaturated subsurface soil. A kinetic model combining Monod and logistic kinetics represents microbial growth under the limitation of HCs as substrates and environmental factors at actual contaminated sites by the introduction of two new kinetic parameters, the effective rate and the self-limiting coefficient of microbial growth. The correspondence between microbial growth and the biodegradation of HCs in the soil is obtained by dividing the amount of HC and the corresponding degrading microbial groups into two classes: saturated HCs as inert components and aromatic HCs that form a contamination plume as dissolved components. The respiratory quinones were used as indicators of microbial biomass. The biodegradation capacity of contaminated sites was evaluated by the maximum microbial biomass obtained by field measurements, which is considered as the integrated results from measurements of HCs, degrading kinetics, and environmental factors at the site. The feasibility of the proposed approach was verified at two hypothetical contaminated sites. The results suggested that the proposed approach is feasible for application at actual HC-contaminated sites.