Results

Separation module development and evaluation have resulted in the identification of a module design and operating conditions that result in VOC removal efficiencies greater than 81 percent and as high as 95 percent in some instances. The optimum results thus far resulted from a radial, parallel flow module. These results were used to develop a crossflow module aimed at improving air-side contact efficiency and pressure drop. Both of these modules were coated with a thin (~ 1 micron) layer of plasma-polymerized silicone rubber. Gas residence times in the range of 0.2 to 1.2 seconds are used for these experiments. Several module construction issues will be resolved in the next module version that will be used in pilot-scale testing.

The biotreatment module has been characterized extensively using m-xylene, toluene, and methyl ethyl ketone (MEK) as model compounds and two organisms, X-1 and M-1, which were isolated from contaminated soil and enriched on m-xylene and MEK, respectively. Shake flask studies indicate that consortia of these organisms degrade m-xylene and toluene extremely rapidly. However, degradation of MEK is inhibited significantly in the presence of either aromatic compound.

Biofilms containing one or both of these organisms have been shown to accelerate the transfer of VOCs out of the stripping fluid. Furthermore, the biofilm activity was not inhibited by long-term exposure to the initial stripping fluid, octanol. Degradation of the aromatic compounds investigated was achieved. These compounds were not observed in the aqueous phase above the biofilm. They were consumed concurrently in some mixed substrate experiments but sequentially metabolized in mixtures with MEK.