抄録
Chlorinated organic compounds such as trichloroethene (TCE) have caused soil and ground water pollution on a lot of sites. Oxidation processes which are produced hydroxyl radical are effective to remediate these contaminated sites, because they are able to degrade TCE. This paper describes photochemical oxidation of TCE with citrate ion and iron ion. Citrate ion and iron ion form some complexes (Fe-citrate complexes) which absorb the light of wavelength below 450nm. The Fe-citrate complexes were able to be decomposed TCE with black light lamp (wavelength: 320-400 nm). Approximately 50% of initial TCE concentration (100mg/L) decomposed within about 7 hours when the molar ratio of iron ion to TCE is 4 and the molar ratio of citrate ion to TCE is 4. The degradation rate of TCE using citrate ion and iron ion was lower than using oxalate ion and iron ion. The excess iron ions inhibited the TCE degradation because some of iron ions formed iron hydroxide and it absorbed lights essential for the photochemical reaction. Therefore, the photodegradation of TCE needs sufficient citrate ion to ensure for forming Fe-citrate complex formation. TCE was degraded between initial pH 2.5 and 10.6. The degradation rate of TCE was higher in the condition of acidity than the condition of alkalinity. In acidic condition, the dominant iron species was [Fe(III)(C6H5O7)] which is the important species for TCE photodegradation. On the other hand, even in alkaline condition, [Fe(II)(C6H5O7)]- existed as an Fe-citrate complex. So, this fact shows strongly that [Fe(II)(C6H5O7)]- photochemically degrades TCE under the condition of alkalinity.
