Reductive Dechlorination of Octachlorodibenzo-p-dioxin by Nanosized Zerovalent Metals

Abstract

Polychlorinated dibenzo-p-dioxins (PCDDs) among widespread persistent organic pollutants (POPs) are liberated into the environment as a result of incineration process and byproducts during chlorinated chemical manufacture. They are of environmental issues because of their high toxicity, bioaccumulation, long half-lives, and recalcitrance to degradation. Hence, the effective and feasible remediation technologies are necessary to transfer these compounds into environmentally non-toxic forms. Dechlorination of PCDDs by zerovalent metals is thermodynamically favorable, but the dechlorination pathways of PCDDs with 256 reactions linking 76 congeners have not been clearly described in the literature. In this study, dechlorination of octachlorodibenzo-p-dioxin (OCDD) was investigated by using various nanosized zero-valent metals as catalyst like aluminum, zinc, iron and nickel under ambient conditions. After 2 days, nickel and iron, aluminum among nZVMs couldn’t dechlorinate PCDDs whereas zinc shows relatively rapid stepwise dechlorination of OCDD. The formation of tetra- to hepta- dechlorinated congeners was observed. With the help of experimental data, a modeling process developed in previous study was applied to assess reductive dechlorination by the electron transfer for PCDDs degradation. The experimentally observed results mostly correspond with the predicted modeling, considering the complexity of the OCDD dechlorination pathway with 256 theoretical reactions. Reductive dechlorination of PCDDs form dechlorinated products that can be further degraded to lower chlorinated congeners which are readily oxidized by aerobic microorganisms and by a radical oxidation.