Field trials of a TiO2 pellet‐based photocatalytic reactor for off‐gas treatment at a soil vapor extraction well

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Abstract
A field trial of a pilot‐scale TiO2 photocatalytic reactor for treatment of off‐gases from a soil vapor extraction (SVE) well at a chlorinated solvent spill site at the Savannah River Site near Aiken, SC, is described. Trichloroethylene (TCE), perchloroethylene (PCE), 1,1‐dichloroethylene (1,1 ‐DCE), and 1,1,1 ‐trichloroethane (1,1,1 ‐TCA) were treated at flow rates up to 6 1/min and space times of 5.1 x 107 to 1.2 x 109 g/mol. The TiO2 used was in the form of porous pellets with a surface area of 150 m2/g. Operation of the reactor with the undiluted waste stream (5000 ppmv) at 80, 100, and 110°C yielded many undesirable byproducts, such as phosgene, chloroform, carbon tetrachloride, and penta‐ and hexachloroethane, even though the conversion of PCE and TCE approached 100%. After diluting the waste stream with ambient air to below 1000 ppmv and maintaining space times around 5 x 108 g/mol, a conversion >99.5% was achieved with the production of only small amounts (2 determined in the reactor effluent accounted for 80% of the influent carbon.