Effect of zero valent metals and water miscible solvents on reductive dechlorination of polychlorinated biphenyls
Abstract
The use of polychlorinated biphenyl (PCBs) was discontinued in the 1970's; however, PCB contamination of soils and sediment remains widespread. Many physical, chemical, and biological methods have been developed and evaluated for PCB degradation in the past three decades. Due to PCB's low aqueous solubility, high sorption affinity, recalcitrance and environmental persistence, environmental PCB remediation continues to be economically prohibitive. The use of zero valent iron (ZVI) in dechlorination of PCBs has been reported in several solution systems, but the effectiveness of ZVI to degrade sorbed PCBs has not been addressed in the literature to date. This research focused on developing a zero valent metal (ZVM) system that would be feasible for PCB dechlorination in sediment and soils. PCB dechlorination using nano-scale ZVMs (Fe 0, Zn0, Al0, Fe/Pd, Fe/Ag, Fe/Cu, Fe/Pt) combined with various cosolvents (tetrahydrofuran, ethanol, and acetone) were explored in soil-free and Aroclor 1242 contaminated sediment systems. Fe, Zn, and Al degraded highly chlorinated congeners to less chlorinated congeners. Bimetals, except for Fe/Pt, completely degraded 2,3,4,6-PCB, but at various rates. The dechlorination pathway was affected by the ZVM, not the cosolvent. Nano-scale Fe/0.5% Pd in 30% acetone completely dechlorinated Aroclor 1242 within two minutes in solution, and less than three days in a sediment system. Recoveries of biphenyl and chloride were 90.1 ± 2.3% and 74.4 ± 14.5%, respectively, in solution; and 82% and 56%, respectively, in the sediment. Aroclor 1242 removal increased with increasing percentage of Pd and metal to soil ratio. Aqueous chloride and bromide at seawater concentrations reduced removal of Aroclor 1242 with acetone-Fe/Pd system from 89.3% to 18.0% and 9.4%, respectively. In a bench-scale feasibly test simulating a confined storage facilities (CSF) with Aroclor 1242 contaminated sediment, were 82.2 ± 4.5% and 56.3 ± 15.2% of PCBs were degraded in 28 days in an aqueous and 30% acetone Fe/0.5% Pd system, respectively. This research identified an environmentally friendly Fe/Pd-cosolvent system that has a high potential to be a feasible alternative technology for in-situ and ex-situ remediation of PCB contaminated soils and sediments.
Degree
Ph.D.
Advisors
Lee, Purdue University.
Subject Area
Environmental engineering
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