Concentration effects on biotic and abiotic processes in the removal of 1,1,2-trichloroethane and vinyl chloride using carbon-amended ZVI

• Degradation half-life decreased 5-fold after a reduction of 1,1,2-TCA concentration.
• Isotopic enrichment factor changed from − 14.6 ± 0.7‰ to − 0.72 ± 0.12‰.
• Degradation mechanism changed from abiotic reductive degradation to biodegradation.
• Co-culture of Desulfitobacterium and Dehalococcoides responsible for biodegradation

A permeable reactive barrier, consisting of both zero valent iron (ZVI) and a biodegradable organic carbon, was evaluated for the remediation of 1,1,2-trichloroethane (1,1,2-TCA) contaminated groundwater. During an 888 day laboratory column study, degradation rates initially stabilized with a degradation half-life of 4.4 ± 0.4 days. Based on the accumulation of vinyl chloride (VC) and limited production of 1,1-dichloroethene (1,1-DCE) and 1,2-dichloroethane (1,2-DCA), the dominant degradation pathway was likely abiotic dichloroelimination to form VC. Degradation of VC was not observed based on the accumulation of VC and limited ethene production.After a step reduction in the influent concentration of 1,1,2-TCA from 170 ± 20 mg L− 1 to 39 ± 11 mg L− 1, the degradation half-life decreased 5-fold to 0.83 ± 0.17 days. The isotopic enrichment factor of 1,1,2-TCA also changed after the step reduction from − 14.6 ± 0.7‰ to − 0.72 ± 0.12‰, suggesting a possible change in the degradation mechanism from abiotic reductive degradation to biodegradation. Microbiological data suggested a co-culture of Desulfitobacterium and Dehalococcoides was responsible for the biodegradation of 1,1,2-TCA to ethene.