Environmental Engineering Reference
In-Depth Information
7. 7. 6 P ERMANGANATE
Potassium permanganate (KMnO 4 ) is a common oxidizer used in water treatment. A recent survey
of surface-water treatment systems serving more than 10,000 people reveals that 36.8% of the treat-
ment systems use potassium permanganate for the removal of organic compounds (Waldemer and
Tratnyek, 2004). Although ISCO with potassium permanganate is an accepted and widely used
remedial method for chlorinated VOCs, it has been generally thought that the oxidation potential
(1.7 V) of potassium permanganate is too low to have an impact on 1,4-dioxane. However, Waldemer
and Tratnyek (2006) determined the kinetics of permanganate oxidation for a number of environ-
mental contaminants and found that the secondary rate constant for permanganate oxidation of
1,4-dioxane was four orders of magnitude lower than that found for TCE or perchloroethylene.
Although at a very slow rate, oxidation of 1,4-dioxane was nonetheless observed. Given the very
rapid destruction of chlorinated VOCs (on the order of minutes), an oxidation rate for 1,4-dioxane
four orders of magnitude slower would be on the order of months, which may be suitable for some
applications.
Evidence from an ongoing ISCO pilot study at Air Force Plant 44 (AFP 44), in Tucson, Arizona—a
site contaminated with chlorinated VOCs and 1,4-dioxane—indicates long-term decline in 1,4-di-
oxane concentrations following injection of potassium permanganate (Earth Tech, 2008). 1,4-Diox-
ane levels in two monitoring wells located near the center of the KMnO 4 injection area (M-96 and
M-98) declined from 250 to 100 mg/L and from 650 to 170 mg/L, respectively, between May 2004
and May 2007. Although the permanganate oxidation kinetics for 1,4-dioxane are slow, the reaction
is likely occurring and, given enough time, could reduce concentrations sufi ciently to meet regula-
tory standards. KMnO 4 oxidation of 1,4-dioxane was further studied at AFP 44 through a bench-
scale test using site groundwater contaminated with 1,4-dioxane in the range of 40
g/L. Triplicate
samples analyzed quarterly, where one sample was an untreated control, one sample was acidii ed
to sterilize and eliminate possible bioactivity, and one sample was treated with approximately
4 mg/L of KMnO 4 , intended to approximate the KMnO 4 concentrations maintained in site ground-
water since 2004. Results from the i rst quarter indicate 1,4-dioxane reductions of ~20% in the
control and the acidii ed control, likely because of interactions with dissolved minerals in the site
groundwater. The KMnO 4 -treated replicate indicated ~30% reduction over the same time period,
which suggested that oxidation was occurring. Results from subsequent quarters were ambiguous,
indicating that 1,4-dioxane destruction was not unequivocal. Therefore, the test was terminated.
μ
7. 7. 7 P HOTOCATALYTIC O XIDATION
In aqueous solutions, ultraviolet light activates a catalyst, such as titanium dioxide (TiO 2 ), to produce
hydroxyl radicals on its surface from oxygen in air or dissolved oxygen in water.
Hill et al. (1996) determined that 1,4-dioxane in water can be completely broken down by expo-
sure to oxygen and ultraviolet light, in the presence of titanium dioxide as a catalyst. No reaction
occurred in any experiment conducted that omitted any one of the three requisite elements. The
study focused on degradation intermediates, particularly ethylene diformate, which appears to be
created more readily than it is destroyed. Formate esters, which are likely present even in “pure”
1,4-dioxane, should therefore be considered in toxicological studies of the effects of 1,4-dioxane.
Mehrvar et al. (2000) further evaluated the photocatalytic destruction of 1,4-dioxane, alone and
in an aqueous solution combined with THF, which is associated with 1,4-dioxane at many sites.
They dei ned the hypothetical reaction mechanism pathways for both THF and 1,4-dioxane and
developed kinetic models to predict degradation behavior. They concluded that 1,4-dioxane is con-
verted to hydroxylated 1,4-dioxane; this process leads to ring opening and formation of organic
acids, which ultimately convert to CO 2 and water.
Yanagida et al. (2006) evaluated the effect on an applied voltage to a titanium dioxide-
impregnated screen exposed to ultraviolet light for the enhanced treatment of 1,4-dioxane. They
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