A STUDY OF THE DISSOLUTION RATE-LIMITED BIOREMEDIATION OF SOILS CONTAMINATED BY RESIDUAL HYDROCARBONS

The widespread release of organic chemicals in the environment frequently leads to groundwater contamination with non-aqueous phase liquids (NAPLs) because many of these organic chemicals are barely soluble in water. Understanding the mechanisms of transport and biotic transformation is essential for successful design and implementation of remedial strategies for contaminated soils. A model describing the biodegradation of the contaminants in NAPL-groundwater systems has been developed in this paper. Numerous field data and experimental results have indicated that the non-wetting fluids of the NAPLs in groundwater are trapped, i.e., completely surrounded by the wetting aqueous phase. In the present model, therefore, the NAPLs are treated as discrete blobs, while the aqueous phase is considered to be continuous. Interactions between the two liquid phases are incorporated into the governing equations for the aqueous phase. The rates of dissolution and desorption are assumed to be of the first order. Only aerobic growth of microorganisms is taken into account. This paper focuses on situations in which dissolution is the main rate-limiting factor. An investigation has been carried out on the rates of biodegradation of some common petroleum components such as benzene, ethyl-benzene, toluene, and xylene in the four-phase system. The effects considered are those of the mass-transfer area, specific growth rate of biomass, and velocity of pore-water flow.