Oxygen dynamics in petroleum hydrocarbon contaminated salt marsh soils: III. A rate model

A model describing oxygen dynamics due to crude oil biodegradation under flooded conditions in saltwater wetlands was developed. The model is composed of three non-linear ordinary differential equations (ODEs) that simulate oxygen uptake, cell growth, and oil degradation simultaneously. The model equations were solved by using a stiff version of ODE solver, ODEPACK, which employs a multistep method and allows the change of step sizes and order of methods (ie., Gear's method). The results of model simulation were compared with experimental data obtained from a fully aerated microcosm study. The results of model simulation indicate that dissolved oxygen concentration in the overlying water rapidly depleted below 3 mg l(-1) unless the reaeration coefficient was higher than 2.0 day(-1). Active aerobic biodegradation of crude oil did not occur under flooded conditions because (i) dissolved oxygen is rapidly depleted, (ii) reaeration is not sufficient enough to replenish dissolved oxygen and (iii) the oil dissolution rate constant decreases over time. The model may lead to better understanding of oxygen demand for a long bioremediation period. The results of this study may be applicable for the establishment of an engineered bioremediation strategy.