Discharges of chlorinated solvents into the environments have led to extensive subsurface and groundwater contamination. This study investigates the degradation of trichloroethylene (TCE), one of chlorinated carcinogenic organic compounds, using advanced reduction processes (ARPs). This new technology has been developed by combining activation methods and reducing agents to produce reactive radicals which can destroy many contaminants such as chlorinated organics, perchlorate, nitrate, nitrite, and bromate. Hydrated electrons (eaq), sulfite ion radical(SO3�-), and hydrogen radical (H�) are potential reductant to reduce the target contaminants. Screening experiments were performed using sulfite, sulfide, and dithionite as reducing agents with the combination of each low-pressure mercury UV lamp (UV-L), medium-pressure mercury UV lamp (UV-M), and narrow band mercury UV lamp (UV-N) having a different major peak wavelength. The screening test results showed the highest removal (97.6%) of TCE with the combination of sulfite and UV-L, which was used to investigate the effect of different process variables (TCE initial concentration, sulfite dose, pH, and light intensity) on TCE degradation rates. It was observed that TCE degradation rate was almost independent of its initial concentration, whereas by increasing sulfite dose and light intensity, higher rate of reaction and more efficient TCE removal percentage was found. TCE removal by ARP was investigated at different pH conditions (pH 4, 7, 9, 11). At pH 9 and 11, it showed higher removal compared to at the neutral pH, while at pH 4 no apparent removal was observed. It indicates that sulfite ion at high pH will be dominant and that it will produce the effective radical or hydrated electrons being able to reduce TCE. Chloride recovery, final pH and reaction products were also analyzed. When the concentration of initial TCE and sulfite was 0.23 mM and 4.6 mM, respectively, no chlorinated products were detected by GC-MS after 3hours by UV-L irradiation.

Reductive dechlorination of trichloroethylene in a sulfite-mediated UV photochemical system

248th National Meeting (2014)

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