Passive Ozone Injection through Gas-Permeable Membranes for Advanced In Situ Groundwater Remediation

In this work, we examine an alternative ozone delivery method for groundwater remediation using permeable membranes. A cylindrical polydimethylsiloxane (PDMS) membrane was used for passive ozone injection in a two-dimensional system simulating in situ groundwater treatment. Liquid velocity and presence of ozone consumers (e.g., nitrite) were found to regulate the ozone diffusion rate through the membrane and the resultant dissolved ozone concentration. A higher liquid velocity (examined in a 340-920 cm day-1 range) resulted in an increase in ozone diffusion rates (up to 2 mu mol s-1 m-2) and a decrease in dissolved ozone concentration due to a dilution effect. Similarly, increasing the nitrite concentration from 0.5 to 25 mM enhanced the ozone diffusion rate by up to 5.64 mu mol s-1 m-2. To examine the membrane performance, carbamazepine was used as a fast-reacting model pollutant. Up to 80% carbamazepine removal was obtained for the lowest liquid velocity examined, which is also relevant for typical groundwater velocities. However, a low ratio of carbamazepine-removed to ozone-delivered was obtained, which was associated with reactions occurring close to the membrane surface that may enable additional reactions of ozone with carbamazepine transformation products. Overall, this study provides new insights to support planning and design of groundwater applications using permeable membranes in reactive permeable barrier mode.