Pd-Catalyzed TCE Dechlorination in Groundwater: Solute Effects, Biological Control, and Oxidative Catalyst Regeneration

Abstract

The performance of a Pd-on-γ-Al 2 O 3 catalyst for dechlorination of trichloroethylene (TCE) was evaluated in synthetic and real groundwater. Low initial TCE conversions were used to provide maximum sensitivity to changes in catalyst activity. TCE conversions of >24% were maintained in DI water for 60 days using 0.5 g of 1% (w/w) Pd-on-γ-Al 2 O 3 and a retention time of 4.3 min. Slow catalyst deactivation was reversed by treatment with a dilute sodium hypochlorite solution. The presence of high concentrations of H 2 CO 3, HCO 3 -, CO 3 2-, SO 4 2-, and Cl - did not adversely affect catalyst activity. TCE conversion increased 30% upon increasing the solution pH from 4.3 to 11. The presence of 87 mg/L SO 3 2- or 0.4 mg/L HS - caused rapid catalyst deactivation, presumably due to chemisorption to active sites. Dilute sodium hypochlorite solutions regenerated catalysts deactivated by HS - and SO 3 2- . Sulfate-reducing bacteria that developed in natural groundwater amended with H 2 deactivated the catalyst, but activity was restored after flushing with a dilute sodium hypochlorite solution. TCE conversion remained stable between 20 and 28% during a 63-day experiment using natural groundwater and periodic (4−7-day intervals) 90-min pulses of a dilute sodium hypochlorite solution.