Remediation Technologies - Environmental Investigation and Remediation - page 341

THF THF (w/1,4-Dx) 1,4-Dx 1,4-Dx (w/THF)

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FIGURE 7.6 Biodegradation of 1,4-dioxane and THF by THF-grown strain ENV478 when the compounds
were added alone or as a 50:50 mixture. The concentration of volatile suspended solids was 0.38 mg/L. [From
Vainberg, S., McClay, K., Masuda, H., et al., 2006, Applied and Environmental Microbiology 72(8): 5218-5224.]

grow on 2HEAA as a sole carbon source. To identify the biodegradation products, radio-labeled
1,4-dioxane was used. Analysis of the culture liquor showed that the [ 14 C] dioxane converted to a
product that coeluted with authentic 2HEAA. The apparent 2HEAA product was not degraded fur-
ther, even after 402 h of incubation at 25°C. Addition of THF to cultures that had depleted the
1,4-dioxane and accumulated 2HEAA also did not result in the further degradation of 2HEAA. At
the end of the experiment, the radioactivity in the supernatant was not less than the radioactivity in
the control. This observation indicated that no carbon dioxide had been produced and no 1,4-diox-
ane was converted to the Strain ENV478 biomass.
Vainberg et al. incubated aerobic aquifer microcosms for 80 days at 15°C to simulate ambient
aquifer temperatures. 1,4-Dioxane at ~700

g/L was rapidly degraded in the augmented micro-
cosms before the i rst sampling time (day 20); when repeatedly added at ~1000

μ

g/L, the 1,4-dioxane
was also rapidly degraded. Fresh groundwater was added to the microcosms after 53 days of incuba-
tion to replace the volume that had been removed for sampling. This addition created an ~30% dilu-
tion of the resident microbial population in the microcosms, with a commensurate decrease in
1,4-dioxane degradation. In the study by Zenker et al. (2000), the system required augmentation
with relatively large amounts of THF on a continuous basis to maintain 1,4-dioxane degradation
activity. The ability of Strain ENV478 to maintain 1,4-dioxane degradation activity in microcosms
for 80 days without THF was, therefore, surprising and encouraging; however, additional work is
needed to coni rm whether inoculating contaminated aquifers with Strain ENV478 will be effective
for economical remediation.
Strain ENV478 is phylogenetically related to Strains CB1190 and K1, but is not able to grow on
1,4-dioxane as a sole carbon source even though it appears that the same enzyme or enzymes in
the strain are required to oxidize both substrates. The inability of Strain ENV478 and other
THF-degrading bacteria to grow on 1,4-dioxane alone could be related to a lack of induction of the
requisite enzyme(s) by 1,4-dioxane or to an inability to efi ciently process metabolites for energy
production. The research team focused on evaluating why this strain cannot grow on 1,4-dioxane
and on whether this strain can be used to degrade 1,4-dioxane in contaminated environments.

μ