Effects of carbon source amendment on the anaerobic degradation of 1,1,1-trichloroethane (TCA) in a contaminated aquifer

We conducted a 10-month anaerobic microcosm test and a 15-month field test to investigate the effects of carbon source addition on the in-situ 1,1,1-trichloroethane (TCA) degradation in a polluted aquifer at an industrial site near Antwerp, Belgium. In the microcosms TCA decreased from 15000 mu g/L to 1500 mu g/L. 1,1-Dichloroethane (DCA) end-concentrations were about the same as the concentrations at the start of the tests (1500 mu g/L). 1,1-Dichloroethene (DCE) decreased from 1200 mu g/L to 800 mu g/L. Carbon source unamended and amended microcosms showed equal concentration trends. Neither chloroethane (CA) nor vinyl chloride (VC) were produced in the microcosms. In the field test TCA dropped from 15000 mu g/L to below 2000 mu g/L. Upstream, TCA levels remained elevated proving that the C-source injection had stimulated degradation. Sulphate reducing bacteria were stimulated; FeS was produced in the microcosms and aquifer. Dehalococcoides species were stimulated in some microcosms and in the HRC-amended aquifer. Neither sulphate reducers nor Dehalococcoidesspecies are however believed to be responsible for the observed TCA degradation. The carbon source injection however did yield environmental conditions that increased TCA degradation.