The role of oxygen diffusion in passive bioremediation of petroleum contaminated soils

Abstract

In passive bioremediation of petroleum hydrocarbon contaminated soils, oxygen diffusion is the primary mechanism for supplying the oxygen which is required for microbial hydrocarbon biodegradation processes. It is the objective of this research to theoretically evaluate whether passive bioremediation can be a feasible treatment alternative for petroleum contaminated soils. In this paper we derive equations for the steady-state oxygen concentration profiles which are expected to develop as a result of simultaneous oxygen diffusion and consumption in hydrocarbon contaminated soils. These equations are used to estimate the maximum oxygen penetration distance and the total cleanup time for several environmental scenarios such as surface and subsurface soil contamination as well as contaminated soil piles. It was found that oxygen is expected to penetrate most contaminated soils for up to several meters if hydrocarbon biodegradation rates are similar to those measured during bioventing respiration tests, i.e. approximately 2.5–10 ppm TPH day −1. Both the depth of oxygen penetration and the total passive bioremediation cleanup time were found to be strongly dependent on the magnitude of the diffusion coefficient for oxygen in soil ( D s). As expected, increased oxygen penetration distances and decreased cleanup times 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 the effectiveness of passive bioremediation treatment. Passive bioremediation is expected to be a feasible and cost-effective treatment alternative for TPH contaminated soils in cases where the minimization of cleanup times is not a major remediation objective.