Mineralization of hydrocarbons in soils under decreasing oxygen availability

Techniques for remediation of soils contaminated with hydrocarbons (HCs) can be improved when the factors that control the decomposition rate are identified. In this study, the effect of O-2 availability on the decomposition rate of hydrocarbons in soils is examined. A kinetic second-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 calculated analytically as a function of time in a three-phase closed system. These calculations are compared with measurements of repetitive O-2-depletion experiments in dosed jars containing a layer of soil contaminated with HCs. About 80% of the HC decrease could be attributed to mineralization, while the other 20% was assumed to be converted into biomass and metabolites. After calibration, model calculations agree with the experimental results, which makes the concept of O-2 concentration and biomass concentration as rate-controlling variables plausible. The parameter values that are obtained by calibration have a clear biochemical significance. It is concluded that attention has to be paid to the O-2 Supply in closed-jar experiments to avoid erroneous interpretation of the results.