Practical Solutions for the Design of Accelerated In Situ Bioremediation

Bioremediation is potentially a cost-effective and environmentally friendly approach for clean-up of hazardous chemicals from polluted geoenvironments, especially toxic organic compounds, like perchloroethene (PCE) and trichloroethene (TCE) from low-permeability strata at depths. The use of Hydrogen Release Compound (HRC) or Oxygen Release Compound (ORC) is a common practice to accelerate anaerobic bioremediation or aerobic bioremediation, depending on the chemical forms of pollutants to be treated. An effective remediation, however, needs effective mixing of, and interaction between the bacteria, target compound(s), injected HRC or ORC as well as other substances if necessary. An understanding of migration behavior of dissolved hydrogen and dissolved oxygen in geological formations is, therefore, an important research subject for predicting potential areas of remediation during acceptable time periods. In this study, 3 practical solutions to the plane source, point source and line source diffusions which correspond to the semi-infinite, spherical and cylindrical models were derived and used to discuss the diffusive transport through low permeability geological media. A series of parameter studies using feasible values for the diffusion coefficient obtained from both literature survey and independent laboratory experiments were performed. Expected areas of hydrogen or oxygen migration were assumed to be from several tens of centimeters to a few meters with consideration of practical pollution problems, and acceptable remediation time periods were considered to be from several months to the maximum of 10-15 years. The results obtained from this study illustrated that transport of chemical substances, like dissolved hydrogen or oxygen used for accelerated bioremediation, due to diffusion is very sensitive to the magnitude of diffusion coefficient. The area of migration due to natural diffusion could be very limited. To effectively design and perform an accelerated bioremediation, a combination of natural migration with pressurized injection and/or other approaches, like electro-migration, for stimulating mass transport could be necessary depending on the hydraulic properties, like porosity and permeability of a stratum.