Gas-permeable membranes for delivery of hydrogen to contaminated groundwater: Evaluation of transfer rates

This research evaluated the potential use of membrane-delivered hydrogen to reduce nitrate and chromate in groundwater. The primary objective was to quantify hydrogen transfer rates using gas-permeable hollow-fiber membranes in soil columns designed to simulate groundwater conditions. A second objective was to develop a mathematical model to simulate water vapor and nitrogen back-diffusion into the membranes. Measured dissolved H2 concentrations in the soil columns decreased rapidly with time due to microbial utilization for nitrate and chromate reduction. No detectable methane production or sulfate reduction was observed. Studies with a conservative gas tracer (SF6) suggested that the gas transfer performance of the membranes declined slightly over time due to fouling or water vapor condensation inside the membranes. Finally, the model showed that water vapor back-diffusion could lead to water condensation inside the membranes, which in turn could affect the gas transfer efficiency.