Iron-mediated reactions of polychlorinated biphenyls in electrochemical peroxidation process (ECP)

A study was conducted to explore some of the basic processes of polychlorin ated biphenyl (PCB) destruction by a new technology termed electrochemical peroxidation process (ECP). ECP represents an enhancement of the classic Fe nton reaction (H2O2 + Fe2+) in which iron is electrochemically generated by steel electrodes. Focus was on the extent of adsorption of a mixture of Ar oclor 1248 on steel electrodes in comparison to iron filings. Commercially available zero-valent iron filings rapidly adsorbed PCBs from an aqueous so lution of Aroclor 1248. Within 4 h. all the PCBs were adsorbed at 1%, 5%, a nd 10% Feo (w/v) concentrations. Little difference in adsorption was found between acidic (2.3) and unamendcd solutions (pH 5.5), even though signific ant differences in iron oxidation state and Fe2+ concentrations were measur ed in solution. PCB adsorption also occurs on steel electrodes regardless o f the pH or electric current applied (AC or DC), suggesting the combination of oxidizing (free radical-mediated reactions) and reducing (dechlorinatio n reactions) iron-mediated degradation pathways may be possible. Extraction of the iron powder after 48 h of contact time yielded the progressive reco very of biphenyl with increasing Fe mass(from 0.4% to 3.5%) and changes of the PCB congener-specific pattern as a consequence of dechlorination. A var iety of daughter congeners similar to those accumulated during anaerobic mi crobial dechlorination of Aroclor 1248 in contaminated sediments indicate p referential removal of meta- and para-chlorines. (C) 2001 Elsevier Science Ltd. All rights reserved.