Remediation Technologies - Environmental Investigation and Remediation - page 343

and more rapid 1,4-dioxane degradation. IESI did not observe any evidence that the 1,4-dioxane was
directly degraded as the sole carbon and energy source during the 88-day test period.
Global BioSciences, Inc. (2007) evaluated the capability of butane biostimulation to enhance the
degradation of 1,4-dioxane in groundwater from a browni eld site in Massachusetts. Samples were
enriched by using standard microbiological subculturing techniques and incubated at ~10°C in a
BSM for four weeks. Microcosm studies were performed by using static headspace methods over a
i ve-day period to evaluate butane consumption and 1,4-dioxane degradation. Duplicate serum bottles
of the biostimulated and control microcosms were sacrii ced each day for analysis. Samples demon-
strated 1,4-dioxane losses from 6.73 to 7.66 mg/L over the 5-day period, whereas the control bottles
exhibited losses from 1.35 to 2.07 mg/L, which were attributed to abiotic losses, specii cally leaks
through a serum bottle septum. The difference between the total loss and abiotic loss was attributed
to undei ned microbial activity, either direct metabolism or cometabolism. After 2 days, the 1,4-diox-
ane concentrations in the serum bottles were below the laboratory detection limit of 0.1 mg/L.
A pilot project is being initiated involving the use of cometabolic propane biosparging at an
industrial manufacturing site in the southeast with 1,4-dioxane levels ranging from 18,000 to
580,000 mg/L (T. Renn, AECOM, personal communication, 2009). As is discussed in Section
7.6.4 , gasotrophic bacteria have been demonstrated in the laboratory to cometabolically degrade
1,4-dioxane to low levels; therefore, this approach has the potential to achieve the 1,4-dioxane
groundwater protection standard through bioremediation.

7.6.5 B IOREACTORS AND B IOBARRIERS
Building on the laboratory work related to the bacterial degradation of 1,4-dioxane, several authors
have constructed and tested bioreactors or have proposed the use of bacteria in a biobarrier concept.
Zenker et al. (2004) demonstrated the effectiveness of a trickling i lter inoculated with bacteria
derived from a 1,4-dioxane-contaminated site. The bacteria were grown in an RBC in the presence
of THF and 1,4-dioxane at concentrations of 20,000 and 30,000 g/L respectively. The bacteria

were then inserted into the trickling i lter system, which was maintained at 35°C. Various THF and
1,4-dioxane concentration regimes were evaluated; 1,4-dioxane levels were tested at 1000 and
200

μ

g/L. Removal efi ciencies for 1,4-dioxane were 93% at both concentrations. Zenker et al.
(2004) coni rmed the obligate presence of THF because biodegradation of 1,4-dioxane slowed and
then disappeared once THF was depleted.
A bioreactor for ex situ cometabolic biotreatment of 1,4-dioxane was designed and implemented
at the Lowry Landi ll, in suburban Denver, Colorado, following a series of bench-scale studies
described in Stani ll et al. (2004). An existing multiprocess treatment plant, including ultraviolet
oxidation and GAC, was effective at removing other organic contaminants, but did not effectively
remove 1,4-dioxane because of low light transmittance of the inl uent groundwater and potential inter-
ference by inorganic compounds. Groundwater at the landi ll contained high levels of 1,4-dioxane (up
to 60,000

μ

g/L) and other organic contaminants. The extracted groundwater was fortuitously con-
taminated with THF (up to 200,000

μ

g/L), which had been shown by Zenker et al. (2000, 2004) and
others to foster cometabolic degradation of 1,4-dioxane. The bioreactors were constructed to operate
in a batch processing mode, with an anoxic initial stage, which created activated sludge. The sludge
l owed to a multichamber aerobic reactor, the i rst stage of which was aerated and agitated; the sec-
ond stage was designed as a clarii er. The reactors were seeded with biomass derived from a polyester
manufacturing facility that treats 1,4-dioxane. Two distinctly different feed waters were used: One
was from the toe of the contamination plume and contained high levels of 1,4-dioxane and THF, as
well as other organic compounds, and the other was a combination of the high-organic-content water
and water from an extraction trench with much lower organic contamination levels. This combination
was used to evaluate 1,4-dioxane degradation in the potential combined inl uent that would be used
in a full-scale operating system. A signii cant proportion of the organic content in both tested waters
was attributable to the high concentrations of 1,4-dioxane and THF, which were demonstrated to be

μ