Remediation Technologies - Environmental Investigation and Remediation - page 342

Degradation of 1,4-dioxane by Strain ENV478 was greatest after its growth on THF; the presence
of THF inhibited the degradation of 1,4-dioxane by this strain. During 1,4-dioxane degradation,
Strain ENV478 appeared to accumulate 2HEAA, an expected product of a monooxygenation reac-
tion with 1,4-dioxane. The research team therefore concluded that the degradation of 1,4-dioxane
and THF by Strain ENV478 involves an initial oxidation of the cyclic ether by a monooxygenase
that presumably is homologous to the THF monooxygenase of Strain K1 (Vainberg et al., 2006).

7.6.3.2 Degradation of 1,4-Dioxane
Parales et al. (1994) isolated CB1190, a pure culture of a nocardioform actinomycete, likely of
the family Pseudonocardia , in mixed cultures of bacteria from industrial sludge generated at a
1,4-dioxane-contaminated site in Darlington, South Carolina. Bacteria were then grown aerobically
on BSM, yeast extract, and THF. CB1190 was demonstrated to have a specii c activity for dioxane
degradation at a rate of 0.33 mg dioxane/min/mg of protein. Initial concentrations of 5.5 mM
1,4-dioxane (48.4 g/L).

Parales et al. also coni rmed the complete destruction of 1,4-dioxane by CB1190, when 4000

μ g/L) were degraded to less than 0.55 mM (4.84 μ

μ M

1,4-dioxane and CB1190 were incubated at 30°C for 18 h and degraded to less than 10 M. About

60% of the carbon in the dioxane molecule was converted to carbon dioxide. CB1190 was also found
to degrade the ethers THF, tetrahydropyran, 1,3-dioxane, diethyl ether, and 2-methyl-1,3-dioxolane,
as well as the alcohols ethanol, isopropanol, 1-butanol, and 2-butanol. CB1190 would not degrade
1,4-dioxane at temperatures higher than 42°C. Moderately increased salinity did not affect
the growth of CB1190 on 1,4-dioxane; 2% NaCl did not slow the growth at all, and some growth was
observed at up to 4% NaCl. No growth was observed at 8% NaCl.
Attempts to grow the organism directly on 1,4-dioxane were unsuccessful. Early experiments
apparently cometabolized 1,4-dioxane in the presence of THF. Long-term attempts eventually
yielded a culture capable of growth on 1,4-dioxane alone, but THF remains the preferred substrate
for growth of CB1190. Once the THF was exhausted and only 1,4-dioxane was provided, the cul-
tures were capable of degrading 10 mM 1,4-dioxane daily (Parales et al., 1994).

μ

7.6.4 G ASOTROPHIC B ACTERIA : C OMETABOLIC B IODEGRADATION
Propane-utilizing aerobic bacteria (propanotrophs) capable of cometabolic 1,4-dioxane degradation
in laboratory studies have been cultured from contaminated groundwater at several sites (Fam et al.,
2005). Natural enzyme systems within these cultures, which are designed to oxidize propane, are
capable of cometabolically converting 1,4-dioxane to carbon dioxide. Propane degradation occurs
initially, and the destruction of 1,4-dioxane occurs only after most of the propane has been destroyed.
The bacterial cultures are able to degrade up to 10,000 g/L of 1,4-dioxane, but higher concentra-

tions inhibit degradation. The aerobic propanotrophs compete for oxygen with other aerobically
degraded contaminants such as acetone, Freon, and chlorinated solvents; therefore i eld applications
with competing contaminants may inhibit propanotroph growth on 1,4-dioxane.
Innovative Engineering Solutions, Inc. (IESI) (2008) performed microcosm studies using ground-
water from a 1,4-dioxane-contaminated industrial facility in Michigan and designed a i eld pilot
study as a follow-on. Baseline conditions indicated that the site groundwater was only slightly
anaerobic, in the range of nitrate and iron reduction, and therefore was conducive to bio-enhancement
to stimulate aerobic propanotrophs. Aerobic microcosms were constructed and i lled with site
groundwater and nutrients. The presence of propane-utilizing bacteria was coni rmed through the
addition of propane and observation of species growth. Subsequently, 1,4-dioxane was added to the
reactors at the rate of approximately 3 mg/L, and 1-4% propane was sparged through the test solu-
tion. Two of the well samples were coni rmed to have the appropriate propanotrophic bacteria in
sufi cient quantities and were observed to reduce 1,4-dioxane concentrations. Bioaugmentation with
SL-D, IESI's proprietary propanotrophic bacteria consortium, resulted in greater microbial growth

μ