This goal of this research is to develop an innovative passive barrier remediation technology that will reduce the costs, risks, and time required for contaminated site cleanup. The proposed research will characterize the performance of a novel passive barrier that relies on the use of an innovative membrane technology for the controlled dissolution of hydrogen (H₂). The research will employ special woven hollow-fiber membranes for the passive dissolution of H₂. in order to accelerate the in-situ bioremediation of groundwater contaminated with chlorinated compounds.

The objective of this project is to examine the gas transfer behavior and performance of hollow fiber membrane curtains that are installed as passive barriers. The proposed research will assess the suitability and effectiveness of the membrane for delivering H₂ to accelerate the in-situ remediation of chlorinated organic compounds like trichloroethene and perchloroethene.

The proposed research will investigate the behavior of the membranes in a systematic way to determine what factors control the overall remediation process. These tasks include the following: (1) the study of the gas dissolution behavior of membranes, (2) the evaluation of the impact of gas composition changes and condensation, (3) the evaluation of impact of biofilm growth on gas transfer, (4) the evaluation of solvent transformation, (5) the development of mathematical models, and (6) the development of pilot reactor studies.

The column reactors have been designed and currently are being constructed. Membrane modules for use in the column reactors have been designed and will be constructed once the column reactors are complete (to ensure correct sizing). A recirculating-gas loop has been designed and constructed to control the partial pressure of H₂ at a very low and constant level in the membranes. A model has been built incorporating both halorespiration and methanogenesis and the subsequent competition for H₂. This model is applicable to the batch system. A model for the column system currently is under development.

Passive barrier remediation systems are an attractive treatment option for the transformation of contaminated groundwater. H₂ appears to be an effective electron donor for the biodegradation of halogenated aliphatics when it is sufficiently bioavailable. However, it is difficult to provide sufficient H₂ to organisms because of its low solubility. Gas permeable membranes, used as a passive treatment barrier, could be used to provide H₂ as an electron donor for in-situ bioremediation. This method of H₂ delivery would be expected to provide controlled levels of bioavailable H₂ that should provide the same benefits as cathodically-derived H₂, without the associated problems. In addition, the project will yield the engineering data required to complete a cost analysis and transition the membrane-module remediation system technology into field-scale application.