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| Titel |
Evaluating potential chlorinated methanes degradation mechanisms and treatments in interception trenches filled with concrete-based construction wastes |
| VerfasserIn |
Diana Rodríguez-Fernandez, Clara Torrentó, Mònica Rosell, Carme Audí-Miró, Albert Soler |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096069
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| Publikation (Nr.) |
 EGU/EGU2014-11553.pdf |
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| Zusammenfassung |
| A complex mixture of chlorinated organic compounds is located in an unconfined carbonated
bedrock aquifer with low permeability in a former industrial area next to Barcelona (NE
Spain). The site exhibited an especially high complexity due to the presence of multiple
contaminant sources, wide variety of pollutants (mainly chlorinated ethenes but also
chlorinated methanes) and unknown system of fractures (Palau et al., 2014). Interception
trenches were installed in the place of the removed pollution sources and were filled with
construction wastes with the aim of retaining and treating the accumulated contaminated
recharge water before reaching the aquifer. Recycled concrete-based aggregates from a
construction and demolition waste recycling plant were used to maintain alkaline
conditions in the water accumulated in the trenches (pH 11.6±0.3) and thus induce
chloroform (CF) degradation by alkaline hydrolysis. An efficacy of around 30-40% CF
degradation in the interception trenches was calculated from the significant and
reproducible CF carbon isotopic fractionation (-53±3o obtained in batch experiments
(Torrentó et al., 2014). Surprisingly, although hydrolysis of carbon tetrachloride (CT) is
extremely slow, a significant CT carbon isotopic enrichment was also observed in the
trenches. The laboratory experiments verified the low capability of concrete to
hydrolyze the CT and showed the high adsorption of CT on the concrete particles
(73% after 50 days) with invariability in its δ13C values. Therefore, the significant
CT isotopic fractionation observed in the interception trenches could point out
the occurrence of other degradation processes distinct than alkaline hydrolysis.
Geochemical speciation modelling using the code PHREEQC showed that water
collected at the trenches is supersaturated with respect to several iron oxy-hydroxides
and therefore, CT degradation processes related to these iron minerals cannot be
discarded. In addition, the combination of alkaline conditions in the trenches with in
situ chemical oxidation (ISCO), which would be able to remove the rest of the
accompanying pollutants, is proposed and merits evaluation. Preliminary batch
experiments were performed to evaluate the feasibility of different chemical oxidation
reactions (permanganate, persulphate, hydrogen peroxide and Fenton) on the complex
contaminated recharge water which were, in general, more effective for degrading
the chlorinated ethenes than for the chlorinated methanes (Torrentó et al. EGU
2012).
Therefore, this study seeks to improve the understanding of CF and CT degradation
mechanisms/processes that are going on in the interception trenches as well as to
select between the two most effective chemical oxidation remediation treatments
(persulphate and permanganate) taking into account their efficiency respect the
chlorinated methanes removal, the generated acute toxicity and the applicability of the
carbon isotopic fractionation as an indicator of the effectiveness of the future in situ
remediation.
Additionally, ongoing batch experiments are expected to elucidate if CT is undergoing
abiotic reductive dechlorination by Fe-bearing minerals such as hydrophobic green rust
(Ayala-Luis et al., 2012) which transform CT into non-chlorinated substances such as formic
acid and carbon monoxide. This unstable iron compound might be formed in the interception
trenches during chloride induced corrosion of iron mineral phases present in the
concrete-based construction wastes (Sagoe-Crentsil and Glasser, 1993). The role of other
minerals like iron oxy-hydroxides, carbonates or sulphides cannot be discarded at all. The
potential of δ13C values to assess the efficiency of this abiotic CT degradation reaction will
be also evaluated.
References
Ayala-Luis, K.; Cooper, N.; Bender C. and Hansen. H. (2012) Efficient dechlorination of
carbon tetrachloride by hydrophobic green rust intercaled with dodecanoate anions.
Environmental Science & Technology 46, 3390-3397.
Palau, J.; Marchesi, M.: Chambon, J.: Aravena, R.; Canals, A.; Binning, P. J., Bjerg P. L.;
Otero, N.; Soler, A. (2014) Multi-isotope (carbon and chlorine) analysis for fingerprinting
and site characterization at a fractured bedrock aquifer contaminated by chlorinated ethenes.
Science of the Total Environment 475, 61–70.
Sagoe-Crentsil, K.K.; Glasser, F.P. (1993) ”Green Rust”, Iron Solubility and the Role of
Chloride in the Corrosion of Steel at High pH,” Cement and Concrete Research, 23(4),
785–91.
Torrentó, C., Audí-Miró, C., Marchesi, M., Otero, N. and Soler, A. (2012) Comparison of
four oxidation processes for the treatment of water contaminated with a mixture of
chlorinated volatile organic compounds. EGU General Assembly 2012. Vienna. Geophysical
Research Abstracts, 14: EGU2012-11310.
Torrentó, C.; Audí-Miró, C.; Bordeleau, G.; Marchesi, M.; Rosell, M.; Otero, N.; Soler,
A. (2014) The use of alkaline hydrolysis as a novel strategy for chloroform remediation: the
feasibility of using construction wastes and evaluation of carbon isotopic fractionation.
Environmental Science & Technology, Just Accepted Manuscript (DOI: 10.1021/es403838t) |
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