Environmental Engineering Reference
In-Depth Information
3.3.4.3 Synopsis of 1,4-Dioxane Biodegradability Studies
The key studies of 1,4-dioxane biodegradation listed in
Table 3.18
are briel y summarized in this
section.
One of the earliest studies of the degradation of ethers was by Fincher and Payne (1962). The study
was conducted as part of a waste-stream treatability test for efl uent from manufacturing processes
that produced ether glycols as a by-product, such as in the manufacturing of explosives, glues, cos-
metics, pharmaceuticals, shampoos and sundries, and synthetic detergents. In this study, the authors
evaluated utilization of ethers for growth by using a presumed
Pseudomonas-Achromobacter
mem-
ber (designated TEG-5). The test assayed cells for oxidative activity in cultures maintained at 30°C
for 72-96 h in a glycol-basal salt medium. No oxidative activity or other symptoms of growth were
observed in the assay for 1,4-dioxane. Fincher and Payne determined that 1,4-dioxane was not uti-
lized by the bacteria for growth and therefore was not directly degraded by the bacteria studied.
Klecka and Gonsior (1986) observed negligible oxygen consumption in a 20-day test for bio-
chemical oxygen demand for 1,4-dioxane. They also did not observe any biodegradation of 1,4-
dioxane by mixed cultures of sewage microorganisms exposed for 1 year in a wastewater treatment
plant where inl uent concentrations of 1,4-dioxane ranged from 100,000 to 900,000
μ
g/L. No
toxicity to microorganisms from 1,4-dioxane concentrations up to 300,000
g/L was observed.
Klecka and Gonsior also conducted an aerobic shaker bath test at 30°C and measured 44.5%
removal of 1,4-dioxane after 32 days of treatment, including an initial 10-day lag time during
which there was little respirometric response. Their study coni rmed that aerobic bacteria in
sludge could degrade 1,4-dioxane as a primary source of carbon and energy. However, instead of
complete destruction, their data suggested conversion of 1,4-dioxane to intermediates and not
complete mineralization; they inferred that the metabolic by-products may be toxic to microor-
ganisms and inhibit their growth.
Bernhardt and Diekmann (1991) studied degradation of 1,4-dioxane, THF, and other cyclic ethers
by the actinobacterium strain
Rhodococcus
from forest soil or sludge that was obtained from the
settling basin of an aerobic wastewater purii cation plant at a chemical i rm. Despite considerable
effort, no strains were enriched or isolated when 1,4-dioxane or cyclohexane was the sole carbon
substrate. Six strains belonging to the genus
Rhodococcus
that degrade THF were isolated and clas-
sii ed. A strain that degraded dioxane instead of or in combination with THF was further character-
ized.
Rhodococcus
Strain 219 grows fast and degrades 1,4-dioxane at an optimal temperature of
30°C. The maximum growth rate,
μ
μ
max
, of Strain 219 on 1,4-dioxane in the presence of 7.5 mM THF
was 0.019 h
−1
. Growth occurred in as little as 0.22 mM (16,000
g/L) THF. In the shaker test, at the
end of the logarithmic growth phase, no THF or 1,4-dioxane could be detected by gas chromatography;
COD measurement in the supernatant after centrifugation was zero, which was interpreted to mean
that no intermediates had accumulated and the substances were totally destroyed. A total of 34
compounds containing nitrogen or oxygen, including the stabilizers 1,3-dioxolane, morpholine, and
n
-methyl morpholine, were tested. Oxygen demands were 0.37 and 2.32 for 1,3-dioxolane and 1,4-
dioxane, respectively, and zero for the morpholine compounds. The presumed primary products of
THF and 1,4-dioxane degradation were THF-2-ol and 1,4-dioxane-2-ol, but these compounds were
not analytically identii ed.
Burback and Perry (1993) used a pure culture of the propane-oxidizing actinobacterium
Mycobacterium vaccae
[ATCC 29678 (JOB-5)] to demonstrate the biodegradability of 1,4-dioxane.
A total of 100 ppm 1,4-dioxane was added to 100 mL of a 1 mg/mL cell suspension and incubated
at 30°C in a rotating shaker. Vials were removed at 12, 24, and 48 h, with zero hours as the control,
and extracted with ethyl ether for analysis. The bacterium was able to use propane, acetone, and
toluene as a sole carbon source, but 1,4-dioxane and the other contaminants evaluated could not
sustain growth and were therefore determined to be only cometabolically degraded.
Roy et al. (1994) published a study on the biodegradation of 1,4-dioxane and diglyme in industrial
waste. They recorded complete degradation of 1,4-dioxane at 150,000
μ
g/L based on an oxygen-uptake
curve. Roy et al. interpreted the data to mean that microbes utilized 1,4-dioxane as the sole source of
μ
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