Remediation Technologies - Environmental Investigation and Remediation - page 333

TOD are ubiquitous with the density of MOB ranging from 10 3 to 10 7 cell/mL and TOD ranging
from 10 4 to 10 8 cell/mL. PHE and sMMO are also present at signii cant levels. Based on the pres-
ence of key bacteria and enzymes in all samples collected, further testing for naturally occurring
biodegradation will be performed. Stable isotope probing (SIP) will be conducted using BioTraps™
baited with 1,4-dioxane tagged with the 13 C isotope. The 13 C-1,4-dioxane-baited BioTraps™ will
be evaluated for 13 C fractioning (indicating biodegradation of 1,4-dioxane), incorporation of 13 C
into cell phospholipid fatty acids (i.e., PLFA), and generation of 13 C carbon dioxide. The SIP results
will directly indicate whether or not 1,4-dioxane is being biodegraded in this aerobic aquifer. The
last step of the study will be to assess enzyme activity directly, which should indicate which active
enzymes have the capacity for degrading 1,4-dioxane. This natural attenuation study will assess
the intrinsic biodegradation capability of the aquifer, and will help dei ne whether bioaugmenta-
tion or amendments could enhance this capability.

7.3.4 S UMMARY
Natural attenuation processes may reduce concentrations of 1,4-dioxane in the groundwater under
specii c site conditions. The most likely processes are advection, diffusion (especially into dead-end
pores), and dispersion. Intrinsic biodegradation may also be a viable mechanism, but additional i eld
study is necessary to verify occurrence and effectiveness. Volatilization and sorption to conventional
soil materials are not likely to be signii cant attenuation mechanisms for 1,4-dioxane. Further discus-
sion of MNA is provided in Section 10.4.1.

7.4 ULTRAVIOLET PHOTOLYSIS
The energy from an ultraviolet lamp can often directly break apart the chemical bonds of an
organic contaminant, ultimately resulting in harmless constituent compounds, such as carbon
dioxide and water. When photons are absorbed by a compound, the chemical bonds holding the
elements together may be broken if their energy is less than the energy contained in the photon. On
the basis of historical research into quantum physics by Albert Einstein and Max Planck, the
energy E of a “light quanta” is described by the equation E

hc / x , where h is Planck's constant
(4.14 × 10 −15 eV s), c is the speed of light (3.0 × 10 8 m/s), and x is the wavelength (Tailored Lighting,
2007). Thus, shorter-wavelength light, including ultraviolet light, contains more energy than
longer-wavelength light.
Hentz and Parrish (1971) demonstrated that the decomposition of 1,4-dioxane occurred at a “far”
(ISO, 2005) ultraviolet wavelength of 147 nm, which carries 6.2-12.4 eV of energy per photon.
Ninety-eight percent of the total decomposition yielded ethane and formaldehyde. In general, this
application is restricted to ultrapure, laboratory-grade water, and restricted low wavelengths of
ultraviolet light.
A. Festger (personal communication, 2007) of Trojan Technologies has stated that manufactur-
ers of ultraviolet-peroxide water treatment systems use 1,4-dioxane as a reagent in bench-scale tests
quantifying the effects of ultraviolet energy on oxidation systems because 1,4-dioxane does not
react by strict ultraviolet photolysis at middle ultraviolet wavelengths commonly applied to water
treatment (230-300 nm), without the addition of oxidation chemicals. The middle ultraviolet wave-
lengths contain less energy (4.13-6.20 eV), which likely limits the destructive effect on 1,4-dioxane.
The use of 1,4-dioxane in bench-scale tests allows Trojan Technologies to demonstrate the treatment
efi cacy of ultraviolet plus oxidation, as opposed to limited ultraviolet photolysis, by quantifying the
degradation of 1,4-dioxane.
Although there is some evidence of direct ultraviolet photolysis of 1,4-dioxane, the demonstrated
applications are at wavelengths not typically applied to groundwater treatment and were tested on
extremely pure water. Therefore, direct ultraviolet photolysis is not considered as a viable remedia-
tion technology for 1,4-dioxane.

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