ELECTRICALLY INDUCED REDOX BARRIERS - BORDEN FIELD EXPERIMENT

The concept of an e-barrier is that of a permeable reactive barrier driven by low amperage low voltage D.C. current. This is accomplished by installing closely spaced (planar) permeable electrodes transverse to flow through a targeted plume. Sequential oxidizing and reducing conditions are generated about the positive and negative electrodes, respectively.

Promising results from laboratory studies conducted over the last three years have suggested that a field-scale evaluation of an e-barrier was needed. Building on column and tank studies, a prototype e-barrier (6 by 8 feet) was designed and constructed in the summer of 2001. The barrier was installed downgradient of a PCE/TCE source at Canadian Force Base, Borden, Ontario, in the fall of 2001. In January of 2002, after a three-month equilibration period, power (5V) was applied to the barrier. Analysis of performance is ongoing.

Data collected through the first five months of operations indicate steady current densities of 1.76 amp/m² at 5.32V. Stable amperage suggests the electrodes are not degrading and that scale control measures are effective. Power consumption is 9.4 watts/m² (~$US 0.01/day-m²). Up and downstream reference electrode values of +1.5 and -1.4 (SHE) suggests the potential to drive mineralization of PCE and TCE via both oxidative and reductive pathways. Observed removal of PCE is in excess of 99%. A complicating factor is that part of the observed removal is likely due to adsorption of PCE in the panel. Analysis of TCE removal is complicated by production of TCE from PCE degradation. Decreases in TCE downgradient of the panel after start up suggest that substantial TCE is also being removed. Minor amounts of cis-DCE have been observed downgradient of the barrier. No VC has been detected.

Current plans are to step-wise increase the applied voltage to ~ 7 and 10 V. This will provide further insight into the efficacy of e-barrier for chlorinated solvents. This will be followed by monitoring during a zero voltage period to differentiate the effects of electrolytic processes from other loss mechanisms. Results of this work forms a basis for a larger scale demonstration funded by the US DoD that will be installed at F. E. Warren AFB Cheyenne, Wyoming in the fall of 2002.