540SR92080
&EPA
United States
Environmental Protection
Agency
February 1993
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology
Summary
Laser Induced Photochemical
Oxidative Destruction of Toxic
Organics in Leachates and
Groundwaters
Organic compounds, specifically
chlorinated aromatic compounds and
unsaturated organic compounds, are
major contaminants in groundwater.
These specific species also tend to rank
high on the list of the U.S. Environ-
mental Protection Agency (EPA) prior-
ity pollutants, even at the low (mg/L)
concentrations that are normally found
In groundwater. The technology de-
scribed in this report has been devel-
oped under the Emerging Technology
Program of the Superfund Innovative
Technology Evaluation (SITE) Program.
Organic compounds in wastewater are
photochemically oxidized by applying
ultraviolet (UV) radiation using an
excimer laser. The photochemical re-
action Is capable of producing the com-
plete mineralization of a variety of or-
ganic compounds at moderate to ex-
tremely low concentrations of the toxic
compounds in water. The energy sup-
plied by the laser is sufficient to stimu-
late photochemical reactions between
the organics and the hydrogen perox-
ide employed as a chemical oxidant,
causing photooxidation and/or
phototransformation of the toxic or-
ganic species to carbon dioxide, water,
and in the case of the chlorinated sol-
vents, the halide ion. Additionally, the
radiation is not absorbed to any sig-
nificant extent by the water. The pro-
cess has been developed as a final
treatment step to reduce organic con-
tamination in groundwater and indus-
trial wastewaters to acceptable dis-
charge limits.
Optimum conditions for the complete
mineralization of several different
classes of compounds were developed
and demonstrated In the laboratory.
This summary was developed by the
EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the Emerging Technol-
ogy Program that Is documented In a
separate report (see Project Report or-
dering information at back).
Introduction
This report summarizes the results of a
2-yr bench-scale evaluation of the laser
induced photochemical oxidative destruc-
tion (LIPOD) process sponsored by the
SITE Emerging Technologies Program.
The LIPOD process is based on the
photochemical destruction of toxic organic
chemicals in dilute aqueous solutions. En-
ergy is supplied by an excimer laser and
is absorbed by the organic molecule and
hydrogen peroxide, thus initiating the oxi-
dation of the organic compound by the
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hydrogen peroxide. The advantage of this
process is that the narrow band UV radia-
tion is preferentially absorbed by the or-
ganic molecules and hydrogen peroxide;
little is absorbed by the surrounding water
molecules; and the organic compounds
are completely oxidized to carbon dioxide,
water, and the inorganic ions present.
Unsaturated organic compounds, and
particularly chlorinated organics, are ma-
jor contaminants in groundwater at or near
hazardous waste sites. These species also
rank high on the EPA's list of priority pol-
lutants, even at the parts per billion con-
centrations often found in wastewaters.
Because of the very low concentrations,
removal of these compounds from these
waters is difficult and expensive. Carbon
adsorption and UV-hydrogen peroxide or
ozonation are currently used to detoxify
these toxic wastes. The LIPOD process
shows promise of excellent performance
at a lower cost.
Process Description
LIPOD is a process developed to oxi-
dize low levels of toxic organic compounds
in contaminated waters to nontoxic spe-
cies. The process has been under devel-
opment for the past seven years, and its
efficacy relies on the use of a coherent
electromagnetic radiation source in the UV
portion of the spectrum to activate an exo-
thermic process in the presence of an
oxidant so as to initiate a chain oxidation
reaction. The UV source is an excimer
laser that provides a high intensity coher-
ent energy source. The oxidant is hydro-
gen peroxide, which is miscible with water
in all proportions, hydroxyl radicals which
are very powerful oxidants are produced
when the laser beam impacts the hydro-
gen peroxide, and sufficient oxygen and/
or hydroxyl radicals are formed to com-
pletely mineralize the organic compounds.
Unlike other UV irradiation processes in
which the toxic molecules must be ex-
posed continually to the UV radiation with
both hydrogen peroxide or ozone present
as the chemical oxidants, this process re-
quires no ozone and the contaminant is
exposed to the UV light source for only a
very short time (< 50 sec) to initiate the
oxidative chain reaction. The investiga-
tions have shown that only a portion of
the fluid to be decontaminated needs to
be exposed to the UV radiation source in
the presence of hydrogen peroxide. This
exposed fluid can be contacted with unex-
posed fluid and additional hydrogen per-
oxide and the entire fluid pool will un-
dergo the chain oxidation reaction.
A typical process flow scheme is shown
in Figure 1. The feed stream containing
Waste
Water
Initiation
Decontaminated
Effluent
Figure 1. Process flow scheme for the laser induced photochemical oxidative destruction process.
the toxic species and the hydrogen perox-
ide flows in a direction countercurrent to
the laser beam in a photochemical reactor
where the toxic compounds are irradiated.
When oxidizing halogenated solvents, the
reaction byproducts are carbon dioxide,
water, and the corresponding halide ion.
Process Performance
The test compounds selected for this
project are frequently found in wastewa-
ters and have the ability to absorb the
energy from the wave length chosen for
this excimer laser; other wave lengths can
be produced by other excimer laser beams
to react with other compounds. The ability
of the process to destroy a given toxic
compound is defined in terms of the per-
cent destruction achieved.
C -C
Percent destruction achieved = ^ X100
where Ch - feed toxic organic concentration
Com " effluent toxic organic concentration
The UV light initiates a chain reaction.
Part of the destruction occurs during the
initiation phase of the reaction when the
reactants are exposed to the light source
(time 0 on the following figures is after this
initiation); and the remaining destruction
occurs as the reaction propagates in the
absence of light. Table 1 and Figure 2
show the destruction of six compounds
during initiation and propagation periods.
The system was found to be dependent
on an initiation and a propagation phase.
Limited destruction was achieved during
the photochemical initiation phase for all
compounds irradiated. Greater destruction
can be achieved during this phase only
at the expense of applying greater irradia-
tion dosage. Analysis and observation of
the propagation process showed that sig-
nificant changes in the percent destruc-
tion after a number of days depended on
the concentration of the toxic organic com-
pound and of the chemical oxidant, hydro-
gen peroxide, and the irradiation dose ap-
plied during the initiation phase.
Process performance results with chlo-
robenzene as the test toxic compound are
presented in the next several figures. The
impact of chemical oxidant concentration
on reaction kinetics is shown in Figure 3.
The stoichiometric quantities of chemical
oxidant used in typical applications are
minuscule, and in all cases over the range
studied, greater than 95% destruction was
achieved. The effect of irradiation dose
and toxic organic concentration on the
rate of destruction in the propagation
phase are shown in Figures 4 and 5 re-
spectively. The system is cost efficient,
non-labor intensive; reaction byproducts
in the effluent are nontoxic. Percent de-
struction achieved has in some instances
been greater than 99%.
Conclusions
Laboratory scale testing of the LIPOD
process has shown that the process is
capable of destroying 90% or more of a
variety of toxic organic compounds in di-
lute water solutions. The effects of or-
ganic concentration of the toxic compound,
oxidant concentration, and irradiation dos-
age have been determined for a series of
representative organic compounds. On the
basis of these results, the cost of a com-
mercial-scale process has been estimated
and found to be very competitive with
existing technologies that are now in use
for wastewater detoxification. Costs range
from $30 to $70/1000 gal treated for the
complete conversion of toxic organic com-
pounds, present initially at the 50 ppm
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Table 1. Destruction of Toxic Organic Compounds by Laser with H,O2 at the Stoichiometric Concentration
Compound
Benzene
Chlorobenzene
Chlorophenol
Dichloroethene
Benzidine
Phenol
Irradiation
dose, photons
per molecule
10
10
10
10
10
10
Percent
destruction
at end of
initiation
period
29
31
34
18
48
35
Propagation
time (hr)
96.0
113.5
72.0
624.0
288.0
72.0
Percent
destruction
at end of
propagation
period
91
98
>99
88
88
>99
level in the solution, to carbon dioxide and
water.
Recommendations
Results to date suggest that the LIPOD
process has excellent potential for effec-
tive removal of organic compounds from
wastewater and that further development
of this process is warranted. Treatability
studies in the laboratory using actual
wastewater samples from hazardous waste
sites are needed to establish how the
process performs on waste containing a
variety of organic compounds and inor-
ganic salts. Successful completion of these
treatability studies would lay the ground-
work for commercialization of the process.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR
815330020 by Energy and Environmental
Engineering, Inc., under the sponsorship
of the U.S. Environmental Protection
Agency.
1
0.8
2
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100
20
HgOsfchlombenzene ratio
0.5 stoichiometric
B
40 60 80
Reaction Time (hr)
HsOg'chlorobenzene ratio
1.0 stoichiometric
— -A- -
100
120
HzO&chlorobenzene ratio
1.5 stoichiometric
--•0
SOppm feed irradiated at 10 photons/molecule
Figure 3. Destruction of chlorobenzene by laser. Effect of chemical oxidant (H2Cy by concentration.
100
80 -
20
40
60 80
Reaction Time (hr)
100
120
1 photon/molecule 3 photons/molecule
10 photons/molecule
— O—
Figure 4. Destruction of chlorobenzene by laser. Effect of number of photons/molecule of chlorobenzene.
4
140
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100
"I 80
60
40'
20
-7©-
o /
200
Wppm chlorobenzene
_L
400 600
Reaction Time (hr)
20 ppm chlorobenzene
A
H202 added at stoichiometric rate.
Solution was irradiated at 10 photons/molecule.
Figure 5. Destruction of chlorobenzene by laser. Effect of chlorobenzene concentration.
800
1,000
50 ppm chlorobenzene
•U.S. Government Printing Office: 1993-750-071/60194
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This Project Summary was prepared by the staff of Energy and Environmental
Engineering, Inc., Somerville, MA 02143
Ronald Lewis is the EPA Project Officer (see below).
The complete report, entitled "SITE-Emerging Technologies; Laser Induced
Photochemical Oxidative Destruction of Toxic Organics in Leachates and
Groundwaters," (Order No. PB93-131431/AS; Cost: $19.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
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POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/540/SR-92/080
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