Model for bioremediation of oil contaminated soil system-A simulation study

Pollution has reached levels which demand immediate attention and scientific and technological solutions are required on an urgent basis. We are concerned in this report with bioremediation og organically contaminated soil and groundwater. Specifically, we have in mind the situation obtaining in the oil fields where the oil system is contaminated with crude oil during its extraction process. To achieve managed in situ bioremediation in practice, treated water is recycled with added nutrients into the ground surface so that ozygen and nitrogen are carried with the water to the sub surface regions. Sorption, conective-dispersive flow and chemical and biological transformation are the chief processes involved which have to be modelled. A simulation model that combines a completely mixed macropore flow model with a contaminated aggregates bioremediation model ( Dhawan et al., 1993) was employed by us ( Gogoi et al., 1998) in the development of a treatability protocol for bioremediation of contaminated soil at Borhola oil fields. Assam, India, an unusual feature of this simulation model is that it is governed by coupled partial differential equations (PDEs) and ordinary differential equations (ODEs). PDEs model the diffusion and biodegradation process occuring in the micropores of soil aggregates while the ODEs describe the bioremediation in the macropores, the interstital spaces between soil aggregates; both the PDEs and ODEs are nonlinear. Simulation models are a must in this case since laboratory experiments take periods of the order of months. The model was applied to the case of high initial contaminant concentrations as observed at Borhola oil fields, Assam. Sensitivity of the model to the parameters was seen to be nonlinear in nature. Alternate normalisation schemes are required to place in context some of the results. The model was turneed with the experimental results available from Regionl Research Laboratory (RRL), Jorhst, where field pilot studies of a bioremediation system for Borhola were conducted over a period of one year. Over studies showed that the model is inefficient and that it is impractical to use it for high initial contaminant concentration. Ways of improving the model efficiency as well as comprehensiveness are discussed