THE ROLE OF OXYGEN DIFFUSION IN PASSIVE BIOREMEDIATION OF PETROLEUM-CONTAMINATED SOILS

In passive bioremediation of petroleum hydrocarbon contaminated soils, oxygen diffusion is the primary mechanism for supplying the oxygen wh ich is required for microbial hydrocarbon biodegradation processes. It is the objective of this research to theoretically evaluate whether p assive bioremediation can be a feasible treatment alternative for petr oleum contaminated soils. In this paper we derive equations for the st eady-state oxygen concentration profiles which are expected to develop as a result of simultaneous oxygen diffusion and consumption in hydro carbon contaminated soils. These equations are used to estimate the ma ximum oxygen penetration distance and the total cleanup time for sever al environmental scenarios such as surface and subsurface soil contami nation as well as contaminated soil piles. It was found that oxygen is expected to penetrate most contaminated soils for up to several meter s if hydrocarbon biodegradation rates are similar to those measured du ring bioventing respiration tests, i.e. approximately 2.5-10 ppm TPH d ay(-1). Both the depth of oxygen penetration and the total passive bio remediation cleanup time were found to be strongly dependent on the ma gnitude of the diffusion coefficient for oxygen in soil (D-s). As expe cted, increased oxygen penetration distances and decreased cleanup tim es are associated with increased D-s values. Since the magnitude of D- s is inversely related to the soil moisture content, it is imperative to maintain moderately low soil moisture levels in order to maximize t he effectiveness of passive bioremediation treatment. Passive bioremed iation is expected to be a feasible and cost-effective treatment alter native for TPH contaminated soils in cases where the minimization of c leanup times is not a major remediation objective.