Abstract
Chlorinated ethenes are among the most frequently occurring groundwater contaminants. Pump and granular activated carbon (GAC) treatment is frequently applied to limit the spreading from point contaminations. Perchloroethene (PCE) and trichloroethene (TCE) sorb well to GAC, but dichloroethene (DCE) and vinyl chloride (VC) sorb poorly, thereby defining a low efficiency seen as amounts of GAC used. On the other hand, ozone reacts fast with VC and DCE, but slowly with PCE and TCE. We utilise for the first time the synergy between ozonation and GAC to treat chlorinated ethenes-contaminated groundwater as an upgrade to an existing GAC treatment installation. Laboratory experiments confirmed that VC and trans-DCE could be >90% removed with just 0.23 g O3/m3, corresponding to 0.18 mg O3/mg DOC. For cis-DCE, 1,1-DCE and TCE, ozone doses of 0.86, 0.87 and 2.8 mg O3/mg DOC, respectively, were required to remove 90%. In full-scale, trans-DCE and 1,1-DCE were completely removed with 1.6 g O3/m3, while only 90% of cis-DCE and 50% TCE were removed with this ozone dose. A relationship between extinction of fluorescence from naturally occurring organic matter with ozone, was used to gauge the ozone dose delivered in the full-scale system. This approach predicted precisely the removal of chlorinated ethenes. Finally, based on the obtained results, we estimated that an optimised ozone treatment would increase the lifetime of an activated carbon filters from 1.0 years to 7.2 years.
Highlights
Perchloroethene (PCE) and trichloroethene (TCE) were previously widely used, for example in dry-cleaning and as degreasers in the metal industry
More than 90% of vinyl chloride (VC) and trans-DCE was removed at 0.18 mg O3/mg dissolved organic carbon (DOC), while the ozone doses required to remove 90% of cis-DCE, 1,1DCE and TCE were 0.86, 0.87 and 2.8 mg O3/mg DOC, respectively
In full-scale experiments, the removal of the chlorinated ethenes increased in line with an increase in ozone dose, and both trans-DCE and 1,1-DCE were completely removed at 1.6 g O3/m3, while only 90% of cis-DCE and 50% TCE were removed with this ozone dose
Summary
Perchloroethene (PCE) and trichloroethene (TCE) were previously widely used, for example in dry-cleaning and as degreasers in the metal industry. Their intensive use has resulted in a high number of polluted sites in locations where they were stored, used or disposed. Excavating soil from pollution hotspots and limiting the spread to groundwater through pump and treatment operations are the most widely used abatement methods. The sorption of VC is often the limiting condition when designing and operating GAC This is unfortunate, as VC is – by far – the most toxic hydro carbon and has the lowest water quality criteria concentration [6]
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