Enhanced TCDD degradation by Fenton's reagent preoxidation

The dioxin isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been calle d the most toxic compound known to man. Because of its poor bioavailability and low biodegradibility, bioremediation technology cannot effectively deg rade TCDD when used alone. In this study, chemical pretreatment (partial ox idation) in combination with biodegradation technique was developed to effi ciently remediate TCDD-contaminated soils. An oxidizing reagent [Fenton's R eagent (FR)] was applied in a slurry reactor to transform TCDD with a conce ntration of 96 mu g per kg of soil to compounds more amenable to biodegrada tion. Up to 99% TCDD was transformed after the chemical pretreatment proces s. The slurry reactor was then converted to a bioreactor for the following biodegradation experiment. The detected TCDD oxidation byproducts including chlorophenols (CPs) and chlorobenzenes (CBs) were transformed in this bior eactor under aerobic conditions. Two other biodegradation experiments were performed in parallel to investigate the biodegradabiliy of TCDD under aero bic and anaerobic conditions without chemical pretreatment. Approximately 5 3% TCDD was transformed under anaerobic conditions possibly due to the redu ctive dechlorination process using organic materials contained in the activ ated sludge as the primary substrates. No TCDD degradation was observed und er aerobic conditions. Results show that FR can oxidize TCDD to less-chlori nated and less-toxic byproducts, promoting their bioavailability to microbi al communities. The bench-scale results indicate that the two-stage (partia l oxidation followed by biodegradation) system has the potential to be deve loped to remediate TCDD-contaminated soils on-site. (C) 2000 Elsevier Scien ce B.V. All rights reserved.