National Research Council of Canada. NRC Biotechnology Research Institute
The 9th International FZK/TNO Conference on Soil-Water Systems, ConSoil 2005, October 03-07, 2005, Bordeaux, France
Application of the electrolytical methanogenic/methanotrophic coupling (eMaMoC) process for the in-situ treatment of tetrachloroethene (PCE)-contaminated waters was achieved in both a single-stage and a two-stage technology. A water electrolysis cell was placed directly in the effluent recirculation loop for the supply of both O2 and H2 to the system: H2 serving as the electron donor for both carbonate reduction into CH4 and reductive dechlorination. The concurrent presence of O2 and CH4 could be used by the methanotrophs for co-metabolically oxidizing the chlorinated intermediates left over by the anaerobic transformation of PCE. Lab-scale studies were carried out on both single-stage and two-stage coupling of the methanogenic/methanotrophic processes. In the single-stage study, at a PCE inlet of 26-52 μM and a hydraulic residence time (HRT) of 1 and 6.3 days, PCE dechlorination to dichloroethene (DCE) was over 95% with a maximum DCE mineralization of 83%. Degradation kinetics were further evaluated in a twostage prototype, where methanogens and methanotrophs were segregated at the bottom and in the upper part of the reactor, respectively. The two-stage system was operated with a PCE inlet concentration varying from 22 to 59 μM. PCE dechlorination to DCE was always between 95% and 100% in the methanogenic stage while DCE mineralization in the methanotrophic stage improved from 49% to near 100% as HRT increased from 1 to 47 days. Although these findings confirm possible kinetics limitations of a single-stage eMaMoC system, they clearly demonstrate degradation is feasible so long as methanotrophic density and HRT are accordingly optimized. The eMaMoC concept was then implemented at the pilot-scale as a single-stage permeable bioreactive barrier installed in a 2.4 m x 2.4 m x 1.5 m stainless steel box filled with coarse sand in which was simulated a PCE-contaminated aquifer moving at a linear velocity of ~15 cm/d. The 600 L removable bioactive cassette packed with peat granules and volcanic rocks was inoculated with anaerobic sludge and methanotrophic enrichment. H2 and O2 were generated by an electrolysis cartridge placed in the groundwater recirculation line. At an HRT of 4-5 days and for an influent PCE concentration of 1 to 22 μM, the system was capable of a PCE mineralization of over 97% and a DCE removal down to below 50 ppb, and vinyl chloride removal down to 150 ppb.
CONSOIL 2005 : Proceedings of the 9th International FZK/TNO Conference on Soil-Water Systems (2005): 1488–1496.