Environmental Engineering Reference
In-Depth Information
contaminated aquifer exhibited high levels of bromide, which exacerbated the bromate formation
issue. Above-ground treatment using ozone and peroxide can be adjusted to control the reactions,
whereas subsurface reactions cannot be adequately controlled to ensure that bromate levels do not
become a problem.
7. 7. 3 H
YDROGEN
P
EROXIDE
AND
U
LTR AVIOLET
L
IGHT
Ultraviolet
peroxide oxidation systems cleave the hydrogen peroxide molecule (H
2
O
2
) into two
hydroxyl radicals (OH
∙
) by direct photolysis caused by the energy absorbed from an ultraviolet lamp.
Experiments performed by Stefan and Bolton (1998) dei ned the degradation pathways for 1,4-dioxane
by hydroxyl radicals generated by direct ultraviolet photolysis of hydrogen peroxide. They determined
that the destruction of 1,4-dioxane by ultraviolet
+
peroxide follows pseudo i rst-order kinetics and was
more rapid than direct photolytic destruction of 1,4-dioxane using ultraviolet light. Within the i rst 5 min
of irradiation, almost 90% of the initial concentration of 1,4-dioxane was depleted.
Ultraviolet
+
peroxide is a reliable, demonstrated
ex situ
technology, that is commercially avail-
able from a number of vendors. A case study presented in
Pollution Engineering
in July 1999
described a system installed to remove 1,4-dioxane following an air stripper that removes chlori-
nated compounds. The system demonstrated 1,4-dioxane removal from an initial concentration of
600
+
g/L to below unspecii ed detection limits at a rate of 100 gpm.
An improvement to the typical ultraviolet
μ
peroxide system was proposed and tested by
Safarzadeh-Amiri et al. (1996), who used an ultraviolet
+
hydrogen peroxide system
for treatment of highly contaminated waste streams. The ferrioxalate complex [Fe(C
2
O
4
)
3
3-
] is
widely studied and is used to measure light intensity. The photolysis of ferrioxalate yields ferrous
iron, which then reacts with the hydrogen peroxide to generate the hydroxyl radicals and provide a
constant source of Fenton's reagent (discussed further in the following section). Safarzadeh-Amiri
et al. (1996) demonstrated removal of 1,4-dioxane, among other contaminants, to below unspecii ed
detection limits at substantially higher efi ciency than that of ultraviolet
+
ferrioxalate
+
peroxide systems. This
greater efi ciency would result in fewer ultraviolet bulbs being needed and therefore lower mainte-
nance and energy costs.
In a German application, bench testing for 5000 gallons per day of process wastewater contain-
ing 15,000,000-20,000,000
+
g/L 1,4-dioxane achieved a 99.95% removal efi ciency by using ultra-
violet light and peroxide (Sörensen and Weckenmann, 2006).
μ
7. 7. 4 H
YDROGEN
P
EROXIDE
AND
F
ERROUS
I
RON
Fenton's chemistry involves catalyzing hydrogen peroxide, typically with a transition metal such as
ferrous iron, to produce hydroxyl radicals, which are strong, nonspecii c oxidizers. For the reaction
to work properly, water must be acidii ed to a pH between 3 and 5. The iron catalyst is typically
added as iron sulfate (FeSO
4
), and then hydrogen peroxide is slowly added to control generation of
heat from the reaction.
Pall Corporation (2004) performed multiple phases of i eld testing to evaluate Fenton's chemistry
for the treatment of 1,4-dioxane
in situ
. Initial testing of hydrogen peroxide injections, which would
have relied on naturally occurring ferrous iron, indicated that the 1,4-dioxane was completely bro-
ken down in the test area, without the production of bromate. However, a follow-up i eld study
concluded that the 1,4-dioxane could not be destroyed
in situ
to a signii cant extent by peroxide
injections alone. Potential injections of ferrous iron and peroxide were evaluated but are not docu-
mented in the literature.
Rushing et al. (2006) performed large-scale batch experiments using contaminated soil and
groundwater from a coastal-plain pharmaceutical site. Naturally occurring ferrous iron was sufi cient
to catalyze the hydrogen peroxide injected at a concentration of 10 g/L into the reactors that were
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