Influence of zero-valent iron on the biodegradation of 1,2-dichloroethane
Date Issued
2011
Date
2011
Author(s)
Kao, Mei-Lin
Abstract
1,2-dichloroethane (1,2-DCA) is an important chemical intermediate during the manufacturing reaction of chlorinated aliphatic hydrocarbons. 1,2-DCA affects human and environmental health owing to its toxicity and carcinogenicity. The half-life of 1,2-DCA under abiotic hydrolysis reaction is about 5.8 years. A popular method for degrading chlorinated organics is to place a permeable reactive barrier consisting of a reductant such as zero-valent iron (ZVI) in the path of a contaminant plume. However, 1,2-DCA is resistant to degradation processes only by using ZVI. Therefore, this study was aimed to investigate the influence of zero-valent iron on the biodegradation of 1,2-dichloroethane and whether ZVI was practicable for the bioremediation of 1,2-DCA.
The batch experiments were conducted in microcosms spiked with groundwater and aquifer material from a contaminated site either with ZVI or without ZVI. However, no 1,2-DCA transformation was observed in any conditions. Other batch experiments under anaerobic or aerobic conditions were performed with inocula from enriched microbial cultures. The results show that 1,2-DCA was degraded about 60％-70％ within 127 days under anaerobic condition with enriched culture originally from the site or under aerobic condition. 1,2-DCA was degraded about 70％ within 40 days in microcosms with sludge from sewage, and 60％ within 40 days with sludge from industrial wastewater. But 1,2-DCA was not degraded in microcosms spiked with Drunken Moon Lake sediment. In addition, 1,2-DCA was biodegraded in a plug-flow column which was fed with medium equilibrated with H2. The result shows that the concentration of 1,2-DCA was initially 20 mg/L and disappeared within 20 days of incubation. It suggests that 1,2-DCA has been reduced with an anoxic respiratory process. ZVI provides a slow and steady source of low cocwntration of H2, under which dechlorination may be favored over competing methanogenesis. It is concluded that 1,2-DCA can be biodegradated in porous medium under anaerobic condition with ZVI added to stimulate dechlorination.
The first-order rate constant of 1,2-DCA disappearance was 0.24 day-1 with addition of H2 and was 2.5 day-1 by replacing H2 with ZVI. The results suggest that addition of ZVI favors biodegradation of 1,2-DCA and is a promising technology for 1,2-DCA bioremediation. Finally, Carbonate was not able to replaced acetate as the carbon source of bacterial while ZVI is the electron donor. Organic substrate are required for the anaerobic dehalogenation of 1,2-DCA.
Subjects
1,2-dichloroethane
biodegradation
dehalorespiration
cometabolism
zero-valent iron
Type
thesis
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