Environmental Engineering Reference
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maintained at a pH of 4. Samples were collected before adding peroxide and after 24 h of reaction
time. The concentration of 1,4-dioxane, which was not the focus of the study, was reduced 99%
from 15,000 to 110
g/L. Rushing et al. (2006) also noted a relatively small decline in COD and
total organic carbon (TOC) compared to the large reductions in the targeted contaminants of
concern. They concluded that the parent compounds were degraded, but complete destruction of the
organic compounds was not achieved.
An additional Fenton's reagent pilot study was performed to address 1,4-dioxane in saprolitic
soils and groundwater at an active printing facility in North Carolina (Masten, 2004). Analytical
data, which were collected 45 days postinjection, demonstrated that 1,4-dioxane was decreased
by 98% in the pilot-testing area and similar concentration reductions were coni rmed down
gradient.
Laboratory bench-scale tests using modii ed Fenton's chemistry (Isotec, 2008) resulted in
greater than 99% reduction in 1,4-dioxane levels in groundwater from 26,500
μ
μ
g/L to ND at
55.1
g/L. Although this detection level is well above many states' promulgated groundwater
standards, this level of reduction, with one application, of a demonstrated aggressive oxidant sug-
gests that achievement of lower concentration standards is likely. Soil remediation testing was
also performed with comparably positive results, with 1,4-dioxane declining from 330 to less
than the 1.1
μ
g/kg detection limit. This removal from soil took two doses of the modii ed Fenton's
oxidant to achieve.
μ
7. 7. 5 P ERSULFATE
Persulfate is a strong oxidizer, with a standard oxidation potential of 2.1 V, which is higher than that
of hydrogen peroxide (1.8 V) and the permanganate anion (1.7 V) (Block et al., 2004). Persulfate
can be “activated” in a number of ways to create sulfate radicals (SO 4 - ) that have an oxidation poten-
tial (2.6 V) almost as high as that of the hydroxyl radical (2.7 V). Activation methods for persulfate
include heat, alkali, chelated iron, and hydrogen peroxide. Reactions involving the sulfate radical
are kinetically fast, and the sulfate radical is more stable, and therefore longer lived, than the
hydroxyl radical. The hydroxyl radical has a half-life of minutes to hours, whereas the sulfate radi-
cal has a half-life of hours to weeks, depending on aquifer geochemistry (Huling and Pivetz, 2006),
allowing greater migration distances in the subsurface when injected. Persulfate also has a lower
afi nity for natural soil organic matter than some other oxidizers, most notably permanganate, and
would therefore be more effective in highly organic soils. Note that the sulfate formed through
activation has a secondary drinking water standard of 250,000
g/L for taste.
Evaluation of the effectiveness of alkaline activation of sodium persulfate (Na 2 S 2 O 8 ) for 1,4-
dioxane degradation was performed by Block et al. (2004); in this study, potassium hydroxide
(KOH) was used as the base to increase pH to
μ
10. Several contaminants were tested, including
chlorinated VOCs and oxygenated compounds (e.g., MTBE, TBA, and 1,4-dioxane), at a range of
molar ratios of KOH:persulfate. The laboratory-scale studies demonstrated that alkaline activation
of persulfate, in addition to the buffering effect of the KOH, resulted in signii cant declines in target
compound concentrations ( Figure 7.13 ). Block et al. (2004) additionally reviewed activation with
inorganic compounds and found that Fe 2+ was an effective activator; however, natural conditions
would not favor using ferrous iron for activation because of solubility issues. Evaluation of various
chelating agents and inorganic compounds identii ed a combination of iron and ethylenediamine-
tetraacetic acid (EDTA) to be an effective activator at typical pH ranges found in natural waters.
Félix-Navarro et al. (2007) studied the sensitivity of sodium persulfate oxidation of 1,4-dioxane
at different persulfate concentrations, temperatures, and pH levels. At temperatures ranging from
25°C to 50°C, a 25 mM persulfate solution at pH 7 oxidized 1.13 mM 1,4-dioxane at half-lives rang-
ing from 5 to 64 min; higher temperatures yielded more rapid destruction. Persulfate solutions rang-
ing from 12.5 to 100 mM, at pH 7 and 25°C, oxidized 1.13 mM 1,4-dioxane within half-lives of
38-122 min; the higher-concentration solution oxidized the fastest. Dependency on pH was also
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