Removal and degradation of chlorinated organic compounds in groundwater

The first part of this work demonstrates that membrane air-stripping (MAS) is an efficient method for separating volatile organic compounds from water. The introduction of a membrane barrier to separate the air and water phases provides several advantages without increasing the total mass transfer resistance. Efficient removal can be achieved at lower air/water ratios than are typically required in packed-tower. Mathematical models were developed to simulate the performances of both countercurrent-flow and cross-flow contractors. Model simulations indicate that the cross-flow contractor is more efficient than the countercurrent-flow contractor. The second part of this work demonstrates the degradation of aqueous-phase CT in a continuous-flow reactor with a porous copper electrode. Removal of CT increases with more negative cathode potentials until hydrogen evolution becomes excessive. At that point, the increase in solution potential offsets further change in cathode potential and limits further improvement in reactor performance. Removal efficiency was predicted to vary inversely with the liquid velocity. At solution conductivities less than 1.0 S/m, both experiment and simulation showed that reactor performance is seriously handicapped by solution potential. The model predictions were in reasonable agreement with experimental results for high conductivity solutions (≥1.0 S/m). At lower conductivities, the discrepancies between the predictions and experimental results are due to the loss of validity of the zero-solution-potential boundary condition at the downstream end of the cathode. The third part of this work investigates a cylindrical reactor geometry in which the anode is wrapped closely around the cathode. This arrangement eliminates the solution potential limitation encountered in the downstream-anode configuration, making it a promising tool for remediation of low-conductivity groundwater. Higher removals of CT are achieved under more negative cathode potential. Increasing the hydrodynamic residence time by increasing the cathode length is also an efficient way to improve the CT conversion even for low-conductivity solutions. An intrinsic drawback of this configuration is lowered current efficiency due to the high proton concentration at the perimeter of the cathode where most of the current is generated. However, low energy consumption due to small overall potential drop across the reactor at least partially compensates for the drawback