How much Oxygen in Needed for Aerobic Cometabolism of PCE?
Aerobic Cometabolism of PCE
CL-Out bioremediation degrades PCE without the production of vinyl chloride under a wide aerobic range. The degradation pathway is via organic acids. The following compilation of data from 14 locations shows PCE removal with ORP levels in ground water ranging from -150 to 250 standard units. The concentration removed PCE concentrations ranging from 10 to nearly 1,000 ug/L. The amount removed does not appear to be dependent on the ORP level. The amount of PCE removed is probably a function of the initial concentration, with higher mass removal correlating with higher initial concentrations.
The relationship between the starting mass and amount of PCE removed appears to be unrelated to the ORP levels. The following chart shows nearly 100% of the PCE concentration is removed at all ORP levels, even at less than -50. The PCE removal rate appears to decrease at ORP levels above +200, but sites with that level of ORP are rare.
The following chart shows the vinyl chloride concentrations at the same 14 sites. As the PCE is degraded the vinyl chloride concentrations increased slightly at some locations. The increase in vinyl chloride was 10 ug/L or less at most locations. A high increase in vinyl chloride was observed at a location where the ORP was less than -50. This result suggests that there may be a threshold relationship between a low ORP less than -50 and a significant increase in vinyl chloride.
As a percentage of the amount of PCE removed, the increase in vinyl chloride is much less than 10% except when the starting ORP was less than -50.
This compilation of data from different sites shows that with a starting ORP above -50, CL-Out bioremediation will be effective in PCE removal without the production of vinyl chloride. These results should be significant in selecting a remediation option to prevent vinyl chloride vapor intrusion risk by source removal.
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