Environmental Engineering Reference
In-Depth Information
7.6.9 B
ACTERIA
S
UMMARY
Laboratory and i eld pilot studies have identii ed several different types of bacteria that are effective
at either utilizing 1,4-dioxane as an energy source or cometabolically degrading 1,4-dioxane while
consuming some other energy source. Chapter 3 summarized the laboratory studies aimed at
identifying the requisite bacteria and optimal conditions, dei ning degradation pathways, and
determining biodegradation rates. The available literature related to the potential i eld application
for soil or groundwater remediation of 1,4-dioxane indicates that the bacteria are dominantly aero-
bic and, although they may be naturally occurring, the natural conditions generally encountered at
hazardous waste sites are not conducive to high degradation rates without some form of biostimula-
tion. Biodegradation of 1,4-dioxane has been applied
ex situ
in bioreactors at the i eld scale, but to
date, there have been no i eld-scale bioaugmentation or biostimulation projects utilizing
in situ
aero-
bic bioremediation for 1,4-dioxane for an entire groundwater plume.
7.7 CHEMICAL OXIDATION
Oxidation is a contaminant-destruction technology in which oxidation-reduction (redox) chemical
reactions convert hazardous contaminants to nonhazardous or less toxic compounds. Redox reac-
tions involve the transfer of electrons from one compound to another. During chemical oxidation,
the redox reaction oxidizes one reactant (the contaminant, which loses electrons), whereas the other
reactant (the oxidizer, which gains electrons) is reduced. Oxidizing agents that may be used in the
treatment of drinking water, wastewater, and groundwater include ozone, hydrogen peroxide, per-
sulfate, hypochlorite, chlorine, potassium permanganate, and Fenton's reagent (hydrogen peroxide
and iron). Applications of chlorine-based methods for the treatment of groundwater are not com-
mon. The strength of the oxidant—measured as oxidation potential—varies, and oxidation poten-
tials of more than 2.0 V are generally considered to effectively address 1,4-dioxane. The strongest
oxidant is l uoride, which is impractical for water treatment. The hydroxyl radical is nearly as strong
as l uoride and has been effectively employed for both
in situ
and
ex situ
remediation. Table 7.2
presents a compilation of common oxidants, their oxidation potential, and their strength relative to
chlorine. Chemical oxidation for the destruction of 1,4-dioxane
ex situ
is a proven technology dem-
onstrated by numerous full-scale applications.
Because 1,4-dioxane is fully miscible in water, it is an ideal candidate for extraction and
ex situ
treatment (e.g., “pump and treat”).
Figure 7.9
presents a comparison of laboratory simulations of
TABLE 7.2
Oxidation Potentials for Some Common Oxidizers
Oxidation
Potential (V)
Relative Strength
(Chlorine
Oxidant
=
1)
Hydroxyl radical (OH
•
)
2.7
2
Sulfate radical (SO
•
)
2.6
1.8
Ozone (O
3
)
2.2
1.5
Persulfate anion (S
2
O
2-
)
2.1
1.5
Hydrogen peroxide (H
2
O
2
)
1.8
1.3
Permanganate ion (MnO
-
)
1.7
1.2
Chlorine (Cl
-
)
1.4
1
Oxygen (O
2
)
1.2
0.9
Source:
DiGuiseppi, W.H. and Whitesides, C., 2007,
Environmental
Engineer
43(2): 36-41.
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