Environmental Engineering Reference
In-Depth Information
Patt and Abebe's patent cites two applied examples of 1,4-dioxane degradation using Aureoba-
sidium pullulans. In the i rst application, a 2-million-gallon aeration lagoon containing 1,4-dioxane
at a concentration of 8000
g/L was
treated with a 300-gallon volume of Aureobasidium pullulans inoculum containing about a million
cells per milliliter; hence, ~1.1 trillion cells were added to the 2-million-gallon lagoon. 1,4-Dioxane
concentrations decreased to below an unspecii ed detection limit within 2 months.
In the second example, a l uidized-bed reactor (FBR) was inoculated with 10 billion cells of
Aureobasidium pullulans and supplied with groundwater contaminated with 1,4-dioxane at a con-
centration of 8000
μ
g/L and THF at concentrations between 5000 and 8000
μ
g/L and supplemented with THF. The FBR retention time was 1 h, and the pH
was between 6 and 7. Efl uent contained 1,4-dioxane in concentrations from just a few micrograms
per liter to 2000
μ
g/L detection limit (Patt and Abebe, 1995).
Kim et al. (2006) made a comparison between the destruction of 1,4-dioxane by advanced oxida-
tion technology (AOT) and biodegradation using BAC-TERRA, a i lamentous fungi. AOT was
demonstrated with ultraviolet
μ
g/L and less THF than the 500
μ
hydrogen peroxide and a modii ed Fenton's chemistry, both of
which demonstrated pseudo i rst-order kinetics, with a rate coefi cient of 5 × 10 −4 s −1 . The fungal
degradation also exhibited pseudo i rst-order kinetics, but with a rate coefi cient that was two orders
of magnitude lower (2.38 × 10 −6 s −1 ) than that shown for AOT.
+
7.6.8 E NHANCING B IODEGRADABILITY WITH I N S ITU C HEMICAL O XIDATION
Several authors have performed various studies to determine the effect of in situ chemical oxidation
(ISCO) on the biodegradation of 1,4-dioxane.
Adams et al. (1994) evaluated the use of hydrogen peroxide and ozone to enhance the biodegra-
dation of 1,4-dioxane using a mixed microbial culture obtained from a municipal wastewater treat-
ment plant. Upon subjecting the test cells to hydrogen peroxide/ozone ratios of 0.0 (ozone only), 0.5,
and 1.0, the biological oxygen demand (BOD 5 ) increased, and, following a lag period, the chemical
oxygen demand (COD) decreased. This rise in BOD 5 and the limited drop in COD suggests that
biodegradability of the initial oxidation by-products occurred more readily than the biodegradation
of the original 1,4-dioxane. Biodegradability was also assessed by using shaker-table bioassays to
measure COD removal rates at different hydrogen peroxide/ozone molar ratios. Minimal biodegra-
dation was observed in the samples with no oxidant, but up to 85% reduction in COD was observed
in 57 h in oxidized samples. Higher residual COD (up to 37%) was present in the samples with lower
oxidant input because of residual untreated 1,4-dioxane. The ratio of oxidant to 1,4-dioxane in these
experiments was lower than the ratio required for direct and complete oxidation of the 1,4-dioxane.
Adams et al. (1994) concluded that, for the treatment of 1,4-dioxane in wastewater, signii cant
reduction in oxidant usage could be obtained by optimizing an oxidation system to enhance bio-
degradability of the 1,4-dioxane, rather than full oxidation of the contaminant.
Suh and Mohseni (2004) looked at the kinetics of 1,4-dioxane oxidation with ozone and peroxide
and the relationship of these oxidants to enhanced biodegradability. They also looked at the effects
of 1,4-dioxane concentration, pH, and hydrogen peroxide concentration on 1,4-dioxane biodegrad-
ability. The fact that initial seeded solutions contained minimal BOD 5 indicated that 1,4-dioxane
was not biodegradable if conventional bacterial methods were used. After treatment with hydrogen
peroxide and ozone, 1,4-dioxane and COD decreased and BOD 5 increased, indicating oxidation of
1,4-dioxane and creation of biodegradable intermediates. Oxidation of 1,4-dioxane was found to
follow a Langmuir-Hinshelwood-type model following i rst-order kinetics and transitioning to
zero-order kinetics at higher concentrations (
g/L). The overall kinetics, as well as the
transition from i rst order to zero order, is affected by pH, hydrogen peroxide, and presence of other
intermediate species. Increases in pH, up to ~9, increase biodegradability. Increasing hydrogen per-
oxide levels enhances biodegradability up to a point (0.4-0.45 mol:mol hydrogen peroxide:ozone),
after which the hydrogen peroxide has a negative effect, reduces 1,4-dioxane destruction, and
thereby decreases biodegradability.
>
60,000
μ
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