Remediation Technologies - Environmental Investigation and Remediation - page 360

compared to an inert powder (SiO 2 ). They found that the titanium dioxide increased both the tem-
perature and cavitation in the aqueous solutions. These changes led to an increase in the ultrasonica-
tion energy consumed in the water and the destruction efi ciency of 1,4-dioxane. Nakajima et al.
(2004) coupled photocatalytic treatment of 1,4-dioxane using ultraviolet and titanium dioxide with
sonication in the presence of titanium dioxide. They also assessed hydrol uoric acid treatment of
titanium dioxide, which had been shown elsewhere to enhance sorption of organic contaminants to
the titanium dioxide surface. The research i ndings indicate that the synergistic effect of these com-
bined methods improves the decomposition rate of 1,4-dioxane. The reaction constant for the
decomposition of 1,4-dioxane using the combination of ultrasound, ultraviolet, and a TiO 2 catalyst
is three times higher than that derived by using only ultraviolet and the TiO 2 catalyst.
7. 7.10 C HEMICAL O XIDATION S UMMARY
Chemical oxidation effectively destroys 1,4-dioxane, and the degradation mechanisms and kinetics
are well understood. Ex situ treatment systems utilizing several of the technologies described in this
chapter are in place and functioning as designed, decreasing 1,4-dioxane concentrations to below
clean-up standards at several sites. In situ applications of chemical oxidation technologies have thus
far been limited to pilot studies and other smaller-scale implementations. The effectiveness of ISCO
application is limited by the oxidation demand of natural organic materials and inorganic elements
in the aquifer, as well as aquifer hydraulic characteristics, which are limitations with all in situ
technologies. Full-scale ISCO projects have not been implemented and operated to complete the
remediation of 1,4-dioxane as of this writing (2009).
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