MINERALIZATION OF HYDROCARBONS IN SOILS UNDER DECREASING OXYGEN AVAILABILITY

Techniques for remediation of soils contaminated with hydrocarbons (HC s) can be improved when the factors that control the decomposition rat e are identified. In this study, the effect of O-2 availability on the decomposition rate of hydrocarbons in soils is examined. A kinetic se cond-order model with the O-2 concentration and biomass concentration as rate-controlling variables is used to quantify HC decomposition, O- 2 consumption, and CO2 production. Concentrations of O-2 and CO2 are c alculated analytically as a function of time in a three-phase closed s ystem. These calculations are compared with measurements of repetitive O-2-depletion experiments in dosed jars containing a layer of soil co ntaminated with HCs. About 80% of the HC decrease could be attributed to mineralization, while the other 20% was assumed to be converted int o biomass and metabolites. After calibration, model calculations agree with the experimental results, which makes the concept of O-2 concent ration and biomass concentration as rate-controlling variables plausib le. The parameter values that are obtained by calibration have a clear biochemical significance. It is concluded that attention has to be pa id to the O-2 Supply in closed-jar experiments to avoid erroneous inte rpretation of the results.