EPA/540/R-92/080
December 1992
SITE-Emerging Technologies:
Laser Induced Photochemical Oxidative
Destruction of Toxic Organics in Leachates
and Groundwaters
by
Energy & Environmental Engineering, Inc,
Research and Development Division
Somerville, MA 02143
Cooperative Agreement No. CR 815330020
Project officer
Ronald F. Lewis
Buperfund Technology Demonstration Division
Risk Reduction Engineering Laboratory
Cincinnati/ Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.8.ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
The information in this document has been funded in part by
the United States Environmental Protection Agency under Cooperative
Agreement No. CR 815330020 to Energy and Environmental Engineering,
Inc. The document has been subjected to the Agency's administrative
and peer review and has been approved for publication as an EPA
document. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
11
-------
FOREWORD
The U.S. Environmental Protection Agency (EPA) is charged by
congress with protecting the Nation's land, air, and water
resources. As the enforcer of national environmental laws, the EPA
strives to balance human activities and the ability of natural
systems to support and nurture life. A key part of the EPA's effort
is its research into our environmental problems to find new and
innovative solutions.
The Risk Reduction Engineering Laboratory (RREL) is
responsible for planning, implementing, and managing research,
development, and demonstration programs to provide an
authoritative, defensible engineering basis in support of the
policies, programs, and regulations of the EPA with respect to
drinking water, wastewater, pesticides, toxic substances, solid and
hazardous wastes, and superfund-related activities. this
Publication is one of the products of that research and provides a
vital communication link between the researcher and the user
community.
Now in its sixth year, the Superfund Innovative Technology
Evaluation (SITE) Program is part of EPA's research into cleanup
methods for hazardous waste sites around the nation. Through
cooperative agreements with developers, alternate or innovative
technologies are refined at the bench-and pilot-scale level and
then demrnstrated at actual sites. EPA collects and evaluates
extensive performance data on each technology to use in remediation
decision-making for hazardous waste sites.
This reports documents the results of laboratory and pilot-
scale field testing of Laser Induced Photochemical Oxidative
Destruction of toxic wastes in groundwater. It is the first in a
series of reports sponsored by the SITE Emerging Technologies
Program.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
ill
-------
ABSTRACT
Laser Induced Photochemical Oxidative Destruction of Toxic Organics
in Solution
Organic compounds and specifically chlorinated aromatic and
unsaturated organics are major contarainants in groundwaters. These
latter species also tend to rank hxgh on the list of EPA priority
pollutants, even at the low (ug/1) concentrations that they are
normally found in groundwaters. The technology described in this
report has been developed under the Emerging Technologies section
of the Superfund Innovative Technology Evaluation (SITE) Program to
photochemically oxidize organic compounds in wastewater by applying
ultraviolet radiation using an excimer laser. The photochemical
reaction is capable of producing the complete destruction of
moderate to extremely low concentrations of toxic organics in
water. The energy supplied by the laser is sufficient to stimulate
photochemical reactions between the organics and hydrogen peroxide
employed as a chemical oxidant, causing photo-oxidation and/or
phototransformation of the toxic species to carbon dioxide, water,
and the corresponding halogenated acid. Additionally the radiation
is not absorbed to any significant extent by the water molecules in
solution. The process has been developed as a final treatment step
to reduce organic contamination in groundwater and industrial waste
waters to acceptable discharge limits.
Optimum conditions for the complete destruction of several
different classes of compounds were developed and demonstrated in
the laboratory.
This report is submitted in fulfillment of cooperative agreement
number CR-815330-02-0 by Energy & Environmental Engineering, Inc.
under partial sponsorship of the USEPA. This report covers the
period from October 1988 to September 1990, with the completion of
work in September 1990.
IV
-------
TABLE OF CONTENTS
Page
Disclaimer ii
Foreword iii
Abstract iv
Figures vi
Tables vii
Acknowledgements viii
I. Executive Summary 1
II. Introduction 2
III. Conclusions and Recommendations 3
IV. Background Information 4
A. Process Description 4
B. Potential Applications 7
1. Introduction 7
2. Superfund Sites 7
3. Industrial Waste Streams 8
C. Competitive and complementary Technologies 9
1. Physical Treatment Processes 9
2. Chemical Treatment Processes 10
3. Biological Methods 10
4. incineration 11
V. Experimental Results 12
A. Experimental Procedures 12
B. Initial Irradiation and Oxygenation Experiments 17
c. Hydrogen Peroxide Results 25
D. Status 37
VI. Quality Assurance 42
VII. Evaluation of The LIPOD Process 43
-------
LIST OF FIGURES
PAGE
1. Process Flow Scheme 5
2. Overall Reaction Chemistry 6
3. Impact of Irradiation Dose and Inlet Concentration on
Extent of Reaction (Chlorobenzene saturated with air) 19
4. Schematic of Test Facility for Non-Aerated Fluids 21
5. Schematic of Aerated Recycle Apparatus 22
6. Process Flow Oxygenation Schemes 24
7. Destruction of Chlorobenzene by various Oxygenation
Schemes 26
8. impact of Irradiation Dose on Extent of Reaction 28
9. Impact of Hydrogen Peroxide Concentration on
Reaction Rate 29
10. Extent of Reaction During the Initiation Stage 31
11. Impact of Irradiation on the Reaction Rate of
Several Organics During the Propagation Stage 32
12. Impact of Feed Concentration on Reaction Rate
(Solution Irradiated at 1 Photon/Molecule) 34
13. Impact of Feed Concentration on Reaction Rate
(Solution Irradiated at 10 Photons/Molecule) 35
14. The Impact of Irradiation Wavelength on the
Destruction of Chlorobenzene 36
15. impact of Irradiating a Portion of the Fluid 38
16. Destruction of M8W Waste Leachate 41
vi
-------
LIST OF TABLES
PAGE
1. Toxic Concentration and Absorbance 15
2. Ionic Species concentration and Absorbance 16
3. Calculation of Maximum Extents of Reaction as
Limited by Dissolved Oxygen 18
4. Batch Photolysis of Chlorobenzene Solutions
Saturated with Air 19
5. Destruction of Various Toxics by Laser 30
6. Semivolatile GC/MS Analysis of Real Waste 6/19 39
7. Semivolatile GC/MS Analysis of Real Waste 6/28 40
8. Operating Comparison of UV Oxidation Processes 44
9. Cost Comparison of LIPOD to Other Toxic Organic
Removal and Destruction Processes 46
10. Lipod cost as a Function of Capacity 47
Vll
-------
ACKNOWLEDGEMENTS
This document was prepared under cooperative agreement number
CR-815330-02-0 by Energy & Environmental Engineering, Inc.,
Somerville Massachusetts under the sponsorship of the USEPA.
Ronald Lewis of the Risk Reduction Engineering Laboratory,
Cincinnati, Ohio was the project officer responsible for the
preparation of this document and is deserving of special thanks for
his helpful comments and advice throughout the project.
Participating in the development of this report for E3I, were Dr.
Michael Mohr, and Dr. William Jackson. Special thanks and
recognition are deserving of Dr. James Porter for his innovative
thoughts, Gopi Vungarala, Dave Tremblay. Ann Jeffries, Don Streete
and our Laboratory staff for their endless efforts.
Vlll
-------
I EXECUTIVE SUMMARY
In the two-year period from October 1988 to September 1990, Energy
and Environmental Engineering, Inc. conducted a laboratory
investigation of a new process for destroying toxic organic
compounds in dilute waste water solutions. In this process, Laser
Induced Photochemical Oxidative Destruction (LIPOD), solutions
containing 10 to 200 ppm of organic compounds were irradiated with
laser generated ultraviolet radiation in the presence of the
oxidant hydrogen peroxide.
The effects of organic concentration, irradiation exposure,
wavelength and oxidant concentration on the destruction efficiency
were determined for a series of representative organic
contaminants, and a preliminary design for a larger scale process
was completed.
Summary of Results
The experiments showed that the LIPOD process is capable of
destroying from 90 to 99 percent of the organic contaminants in
dilute waste water solutions. The destruction process occurs in
two steps. Some of the contaminant is destroyed during the
irradiation period of about one minute. The destruction continues
after the solution is removed from the radiation field for a period
of hours until essentially complete destruction is achieved.
Economic comparison of the LIPOD process with competitive processes
indicates that the LIPOD process can offer significant cost savings
over other ultraviolet treatment processes and carbon adsorption.
-------
II INTRODUCTION
The Superfund Innovative Technology Evaluation (SITE) Program was
implemented to accelerate the development and application of
innovative cleanup technologies at hazardous waste sites across the
country. The SITE Program is comprised of the following five
component programs:
. Demonstration Program
. Emerging Technologies Program
. Measurement and Monitoring Technologies Development Program
. Innovative Technologies Program
. Technology Trensfer Program
This report surmarizes the results of a two-year bench-scale
evaluation of the Laser Induced Photochemical Oxidative Destruction
(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. Energy
supplied by an excimer laser is absorbed by the organic molecules,
rendering them oxidizable by the oxidant hydrogen peroxide w^ich is
added to the solution. The advantage of this process is that the
narrow band ultraviolet radiation is preferentially absorbed by the
organic molecules and hydrogen peroxide, with little being absorbed
by the surrounding water molecules.
Aromatic and aliphatic organic compounds, and particularly
chlorinated organics, are major contaminants in ground waters at or
near hazardous waste sites. These species also rank high on the
Environmental Protection Agency's (EPA) list of priority
pollutants, even at the parts per billion concentrations often
found in the waste waters. Because of the very low concentrations,
detoxification of these waters is difficult and expensive. Carbon
adsorption and UV ozonation are currently in use. The LIPOP
process shows promise of better performance at a lower cost.
-------
Ill CONCLUSIONS AND RECOMMENDATIONS
CONCLUSIONS
Laboratory scale testing of the LIPOD process has shown that
the process is capable of destroying 90 percent or more of
toxic organic compounds in dilute water solutions. The
effects on destruction efficiency of organic concentration,
oxidant concentration and irradiation dosage have been
determined for a series of representative organic compounds.
On the basis of these results, the cost of a commercial scale
process has been estimated and found to be very competitive
with existing technologies which are now in use for waste
water detoxification.
The chemistry of the LIPOD process proceeds in two steps, an
initiation step followed by a propagation step. In the
initiation step, some destruction of the organic occurs during
the short duration of the irradiation. when the solution is
removed from the radiation field, propagation of the oxidative
destruction continues over a period of hours until more than
90 percent of organic har been destroyed.
RECOMMENDATIONS
Results to date suggest that the LIPOD process has excellent
potential for effective removal of organics from dilute waste
waters and that further development of this process is
warranted. Treatability studies in the laboratory using
actual waste water samples from hazardous waste sites are
needed to establish how the process performs on waste
containing a variety of organic compounds and inorganic salts.
Successful completion of these treatability studies would lay
the groundwork for larger scale field testing of the process.
-------
IV BACKGROUND INFORMATION
A. Process Description
Laser Induced Photochemical Oxidative Destruction (LIPOD) is
a process^developed at Energy and Environmental Engineering,
Inc. (E3I) to oxidize low levels of toxic organics in
contaminated waters to non-toxic species. The process has
been under development 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 exothermic process in the presence of an oxidant so as to
initiate a chain oxidation reaction. The UV source is an
excimer laser which provides a high intensity, coherent energy
source. The oxidant is hydrogen peroxide which is miscible
with water in all proportions and thus provides sufficient
oxygen and or hydroxyl radicals to completely oxidize the
toxic molecules.
Unlike other UV irradiation processes in which the toxic
molecules must be exposed continually to the UV radiation with
both hydrogen peroxide and ozone present as chemical oxidants,
this process requires no ozone and the contaminant is exposed
to the UV light source only for a very short time (< SOsec) to
initiate the oxidative chain reaction. Our investigations
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 unexposed fluid and additional hydrogen
peroxide and the entire fluid pool will undergo the chain
oxidation reaction.
A typical process flow scheme is shown in Figure 1 , the reed
stream containing the toxic species and the chemical oxidant,
hydrogen peroxide, flow countercurrent to the laser beam in a
photochemical reactor where the toxic compounds are
irradiated. The overall reaction chemistry is depicted in
Figure 2 . When oxidizing halogenated organics, the reaction
byproducts are carbon dioxide, water, and the corresponding
halogen acid.
-------
WASTE
WATER
CHEMICAL
OXIDANT
STORAGE
FC
INITIATION
PHOTOCHEMICAL
REACTOR
SOLID
RESIDUE
METERING
PUMP
LASER
^
EFFLUENT
STORAGE TANK AND
PROPAGATION
REACTOR
DECONTAMINATED
EFFLUENT
Figure 1. Process Flow Scheme
-------
UV Coherent Light Source
Photolysis Reactor
Oxygen Source
CaHbX + ( a + 0.25(b-1))O2 » a CO2 + H2O + HX
0.5(b-1))H2O2 » a CO2 + (2a+b-1) H2O + HX
Figure 2. Overall Reaction Chemistry
-------
B. Potential Application
1. Introduction
Since the industrial revolution in the United States,
industrial waste products have been generated in ever
increasing amounts and, in general, have been discarded in a
very haphazard manner. Little thought was given to the
suitability of the industrial and municipal landfills that
were typically used for disposal. The Times Beach and Love
Canal cases have dramatically illustrated the folly of past
practice.
In the 1970s, increasing public concern with the quality of
the environment led to federal legislation to manage newly
generated hazardous wastes as well as a separate program to
deal with the cleanup of existing uncontrolled waste sites.
This legislation is commonly known as the Resource
Conservation and Recovery Act (RCRA) of 1976 and the
Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) of 1980, respectively. CERCLA
established the Superfund program to provide a mechanism for
expeditious cleanup of the worst of these sites and has
provided the focal point for marketing a wide range of
services involved with the cleanup effort.
Ground water contamination at hazardous waste sites results
from leaching action from those landfills containing hazardous
materials and can be composed of a variety of toxic organics.
Among the most difficult of these to deal with are a class of
chemicals known as aromatic organic compounds. They are
pervasive; they are not biodegradable; they are among the most
toxic chemicals to be dealt with in the Superfund Program; and
they do not lend themselves to simple destruction techniques.
In addition to the cleanup of Superfund sites, a market exists
for the neutralizing of toxic wastes in those industries that
can no longer dump their waste products in landfills or
discharge contaminants into water streams. To a large extent,
these industries have been able to recycle the hazardous
chemical compounds, but small amounts of these materials must
be destroyed prior to release of the effluent to the
environment.
2. Superfund Sites
The clean up of existing hazardous waste sites represents one
of the most difficult and costly problems facing our society
over the next fifty years. The clean up activity associated
with the Superfund program is estimated by the Office of
Technology Assessment to be more than $100 billion with the
cost of treating ground water contamination comprising more
7
-------
than 50 percent of the total.
Typically, the ground water at these sites will contain trace
amounts of organic contaminants that have leached from old
landfills. The ground water clean up program will normally
consist of the following elements:
* Taking measures to prevent further leaching of
contaminants into the aquifer.
* An Assessment of the plume of contamination in the
aquifer as well as the nature and amounts of
contamination.
* Removal and treatment of contaminated groundwater with
the treated water either discarded or returned to the
aquifer.
Much of the early effort at cleanup has involved relocation,
removal, or on-site containment of hazardous materials and not
permanent destruction. To some extent, this only serves to
transfer the problem to another location to be dealt with
another day- The expressed desire is for destructive
treatment or a permanent stabilization of the hazardous
materials. However, little progress has been made toward this
end, particularly for the expensive, difficult and uncertain
task of contaminated waste and ground water cleanup.
The LIPOD process is well suited to the ground water cleanup
problem. It is capable of destroying the low levels of
organic contaminants normally found at a lower cost than
competing processes. LIPOD represents a vast improvement in
the currently available technologies because it:
* More effectively destroys organic compounds than
competing technologies.
* Does not require significant post treatment as do
competing physical separation technologies.
* Can be built in such a manner as to be easily transported
and operated at individual waste sites.
industrial Waste Streams
The Resource Conservation and Recovery Act of 1976 (RCRA) , as
amended by the Hazardous and Solid Waste Amendments of 1984
(HSWA) prohibits continued placement of RCRA regulated wastes
in or on the land, including placement in landfills, land
treatment areas, waste piles, and surface impoundments. This
has resulted in the need for new waste management techniques
8
-------
to deal with the 3-5 billion gallons of waste solvents
generated annually. Additionally each year about 70 billion
pounds of chemicals considered hazardous under RCRA are used
in the United States. Of this, about 80 percent are organic
compounds used in pesticide formation; paint and adhesives;
cleaning; and chemical intermediates. Of the hazardous
materials to be treated the treatment process chosen for use
will normally be custom designed for each application and will
depend on the following:
* The type of chemical involved
* The concentration of the waste stream
* The potential uses for recovered chemicals
In most cases, an aqueous stream containing trace amounts of
contaminants must be treated further prior to unrestricted
release to the environment. Present practice, in most cases,
is to use activated charcoal post treatment for these waste
streams. In some cases, this will remain the best practice.
However, for most of the organic compounds encountered, the
LIPOD process will be more cost effective.
C. Competitive and Complementary Technologies
The technologies described below can also be used to treat
contaminated waste waters. They may be used prior to LIPOD
treatment to reduce high concentrations of contaminants, or
they may be competitive with the LIPOD process in treating
very dilute solutions, or they may be used after the LIPOD
process to capture organics that may not be easily destroyed
by the LIPOD process (e.g. aliphatic saturated and conjugated
organic compounds).
1. Physical Treatment Processes.
These processes are based on physical methods of separation
and generally do not result in destruction of the contaminants
in the waste feed stream. The most common of these processes
are distillation, stripping, and adsorption.
Distillation processes are applicable to high organic content
wastes but usually generate a large volume residual that
Contains appreciable organic contamination. Incineration is
often the principal means of handling this type of residual.
Air stripping is generally used on waste streams containing
inw levels of volatile contamination with steam stripping
for streams containing somewhat higher levels of
-ion However, some level of residual contamination
additionaei treatment can often be expected from
-------
these technologies.
^S30? an* rSSin adsorPtion are commonly used to remove trace
amounts of contaminants to achieve low organic concentration
levels. The adsorptive materials will contain the
contaminants and must either be incinerated or put through a
restorative process leaving a slurry mixture that can be
incinerated.
2. Chemical Treatment Processes.
Most of the chemical processes of interest for the treatment
of organic hazardous wastes make use of oxidation to render
the wastes harmless. The methods use either high temperature
conditions or a catalyst to bring this about.
The Wet Air Oxidation process and a somewhat similar
Supercritical Water Oxidation process cause reaction of the
organic contaminants with free oxygen in the waste stream by
raising the temperature and pressure of the aqueous wastes to
very high levels. The organic materials are generally
converted completely to carbon dioxide and water by these
processes .
UV/ozonolysis and other oxidation processes such as peroxide,
potassium permanganate, and hydrogen peroxide treatments do
not normally achieve total destruction and must be considered
as a pretreatment step for a second treatment technology,
usually a biotreatment process.
3. Biological Methods.
Biological treatment processes used for the removal of organic
solvents and other volatile organic compounds from industrial
waste streams can be divided into two major categories: (l)
aerobic processes, and (2) anaerobic processes. In aerobic
systems microorganisms use oxygen to biologically oxidize
compounds. Anaerobic, or oxygen-free, biotreatment systems
make use of a reducing metabolic process. Typically a series
of reactions involving acetogens (acid generating) and
methananogenic bacteria cause organic compounds to be broken
down into methane and simple organic acids.
F*ch of these processes can be further subdivided into
suspended growth or attached growth systems. Suspended growth
systems are characterized by microbes moving freely within the
w^te stream or being suspended by mechanical agitation.
Attached or "fixed film" growth systems have layers of
microbes attached to a suitable medium that comes into surface
contact with the waste stream.
10
-------
™™ t5eatment systems are generally open surface
impoundments which require large land areas and considerable
capital investments. Aerated processes have the potential to
produce significant air (and odiferous) emmisions. Being open
to the environment, the treatment plants are subject to
weathering and their design features and biological kinetics
are stressed by precipitation and temperature extremes.
4. Incineration.
Incineration is the principal disposal alternative for
nonrecoverable, flammable solvent hazardous wastes.
Incineration possesses several advantages as a hazardous waste
disposal technology, including the following:
Thermal destruction by incineration provides the ultimate
disposal of hazardous wastes, minimizing future liability
from land disposal:
Toxic components of hazardous wastes can be converted to
harmless or less harmful compounds:
The volume of waste material may be reduced significantly
by incineration: and
- Resource recovery (i.e., heat value recovery) is possible
through combustion.
While incineration as a hazardous waste management technique
possesses many potential advantages, there are also two major
potential drawbacks: environmental impacts and costs.
Incineration has the potential to affect both air and surface
waters via stack emissions and fugitive emissions of volatile
compounds, and the production of solid wastes (ash and
scrubber liquors and scrubber sludge).
Incineration facilities permitted to operate by EPA under the
provisions of RCRA are required to meet environmental
standards in the following areas:
They must meet destruction and removal efficiency (ORE)
standards.
They must meet standards for the release of acid gasses
from the stack, including HC1.
They must meet standards for the emission of particulates
from the stack.
They must meet standards for limitation of emission of
toxic air pollutants (e.g., toxic metals) from the stack.
11
-------
Costs of incineration are higher than most hazardous waste
management alternatives. Incineration costs more because of
the large energy input requirements and the high cost of
environmental controls. These costs vary widely depending
upon waste characteristics, incinerator design, and various
operational considerations.
Y EXPERIMENTAL RESULTS
A. Experimental Procedures
Laser destruction experiments were carried out on a series of
hydrocarbons in dilute solutions, using air, dissolved oxygen,
sodium nitrate, and hydrogen peroxide as oxidants.
The performance of these processes was measured in terms of
its ability to destroy toxics, relative to the maximum
achievable toxic destruction capability. This capability is
measured as the difference between relative destruction with
the light on and with the light off.
The relative destruction achieved is defined as:
E =
— c
^-out*
where C- = Inlet Feed Toxic Concentration to reactor
C .= Outlei: Feed Toxic Concentration, with Irradiation
-out*
C = Outlet Feed Toxic Concentration, no Irradiation
which is°the relative destruction of the toxic with the light
on less the destruction obtained in the absence of light.
This latter term accounts for evaporation, absorption and
other processes which can occur in the absence of light.
The maximum achievable value of E, (E^J , is obtained when C
out
= 0.
The process performance is then measured in terms of the
destruction efficiency, defined as .
in terms of concentrations, the expression reduces to:
Percent destruction achieved = 100X --- = 100 X
c - c
^-out '"o
F C
'-'ma* out
12
-------
usedfo^r^3^6 measure °f Process performance and
used for all the data presented herein.
H^ reP°rted< the percent of destruction achieved
was determined as a function of:
. Toxic Compound speciation
. Oxidant speciation
. Aqueous concentration of toxic
. Concentration of oxidant
. Irradiation Dosage
. Irradiation wavelength, and
. Time
To assist in the understanding of the results, absorbance
coefficients were measured for each of the hydrocarbons
studied, and for a number of common ionic species which might
be present in contaminated waste water.
A Lambda Physik excimer laser was used to produce the coherent
light source. The laser was calibrated and optimized to
produce energy at specific wavelengths. The laser was
calibrated daily before each experimental run, monitoring the
input energy to the reactor and the output energy from the
reactor.
Analysis of the toxic solutions before and after irradiation
was performed on a Hewlett Packard 1090 HPLC. The HPLC was
calibrated daily before each run and compared to a five point
calibration curve generated for each organic compound.
Preparation of standards and HPLC analysis were performed in
accordance with the methods approved by the EPA in the final
QA/QC plan accepted by the EPA for chemical analysis of water
and waste water. Water blanks and 50 ppm solutions of the
toxic compounds as standards were all analyzed before each
experimental batch of irradiated samples, thus, ensuring some
degree of accuracy and precision in the observed toxic
concentration changes.
Toxic concentration changes in the water solutions, by-
nroducts and column effluents were determined and monitored
bv observing any changes on the five point calibration curves
apnerated for each of the toxic species. Complementary
?nalvses were carried out in our GC/MS laboratories on the
nCre and irradiated samples to identify any irradiated
products, while observing the changes in initial toxic
13
-------
concentrations .
Tnn HP*LC System used included a reversed phase RP18 Lichospher
iuu, 5 micron column with 100 by 2.1 mm dimensions and a
variable wavelength Diode Array UV Detector. Irradiated
samples were collected in duplicate at five time intervals of
u, 10, 30 50, & 80 minutes. Upon collection the samples were
analyzed on the HPLC and then stored in amber colored vials.
The samples in the vials were monitored over time to determine
the continued destruction.
50 ppm solutions of the toxic compounds were made up in a 17
liter bottle. The solutions were fed to the photochemical
reactor by a variable speed peristaltic pump, set at 30
ml/min. When using hydrogen peroxide as the oxidanr the toxic
solutions were mixed at a mixing tee with the peroxide
solution and then fed into a I meter by 2 . 3 cm by 0 . 8 cm flow
reactor. The solutions flowed countercurrent to the laser
beam and were irradiated in the reactor. The irradiated
samples were then collected from an exit port in amber colored
vials with teflon lined caps for analysis.
Total organic carbon (TOC) analysis was carried out on the
duplicate samples collected, on a Dohrman carbon analyzer,
which measures any change in the total organic carbon content
of a compound as the reaction proceeds over time.
PH measurements were continuously taken of the toxic solutions
before and after irradiation.
Toxic Components
The compounds listed in Table 1 were selected as
representative of toxic organics found in waste water. UV
absorbance was measured for each compound in the concentration
range of 10 to 200 ppm. Absorbance values are shown in Table
1. The absorbance measurements were carried out in the 190 to
250 nm range of the spectra on a UV spectrophotometer . The
absorbance at the standard irradiation wavelength is reported
in Table 1.
-------
Table 1. Toxic Concentration and Absorbance
Toxic Compound Concentration,ppm Absorbance
Chlorobenzene 50 1.49
Dichloroethene 50 1.30
Dichloroethane 50 0.33
Benzidene 50 1-44
Hexanoic Acid 50 0-41
Bis-2-chloroethylether 50 0.37
Methyl Ethyl Ketone 50 O-38
Chlorobenzene Cone. Absorbance
200 1.580
150 1.548
100 1.526
50 1.492
10 1.260
Additionally the absorbance at the standard wavelength of 100 ppm
solutions of some common ionic species which may be present in
contaminated waste water were also obtained, (Table 2).
15
-------
ionic species Concentration^* Absorbance
Magnesium Chloride 100 Q
Magnesium Sulphate 100 0>289
Magnesium Nitrate 100 1 546
Sodium Chloride 100 0_751
Sodium Sulphate 100 0.609
Sodium Nitrate 100 1.560
Calcium Chloride 100 0.727
Calcium Sulphate 100 0.362
Calcium Nitrate 100 1.564
Water 0.253
Table 1 results showed that Benzidine, t-Dichloroethene and
Chlorobenzene exhibited high absorbances, Hexanoic Acid and Methyl
Ethyl Ketone showed modest absorbance values while Bis-2-
Chloroethyl Ether and t-Dichloroethane showed low absorbances.
The absorbances of the ionic species showed very low absorbance
values in aqueous solutions and except for solutions containing
nitrates, the spectral values were not significantly different from
that of pure water. Therefore, only nitrate containing solutions
were expected to have any adverse or impeding effect on the
process. This adverse effect may be overcome by shifting the
irradiation wavelength. Because of its high absorbance
coefficient, Chlorobenzene at 50 ppm concentration was selected as
the representative compound on which most of our experimental
studies were carried out.
50 ppm solutions of Chlorobenzene were made up and a five point
calibration curve established, from which all concentration changes
were measured. Analysis and close monitoring of the standard 50
ppm solution with time showed that even after a 3 month period the
concentration had only changed by a factor of < 10%. This enabled
us to monitor concentration changes of the laser irradiation
process during irradiation and for long periods after, since there
was not a significant change in the standard 50 ppm solution.
The standard 50 ppm solutions were run on the HPLC before and after
each set of the irradiated samples were analyzed each day. It was
observed that there was no significant changes in the standard with
16
-------
theeiaserSs^Tf ^ W6re observed in the samples were due to
the laser stimulated reactions initiated by the LIPOD process.
B. Initial Irradiation and Oxygenation Experiments.
Initial experiments on the process were carried out employing
various concentrations of chlorobenzene solution in a batch mode
using a quartz cell. The emphasis of these tests was to obtain
samples of the irradiated toxics to determine the formation of any
by-products, and to establish run conditions and equipment design
rcr the continuous flow system. As these experiments were
exploratory and preliminary in nature, a batch cell system was
used, thereby avoiding complications that could arise from a
continuous flow system.
The oxidation process was initially thought to be produced by
dissolved oxygen in solution. Calculations summarized in Table 3
show the maximum extent of reaction that should be achievable ••'ith
various toxic species as is limited by saturated oxygen dissolved
in solution. Table 4 and Figure 3 show the destruction obtained
for air saturated chlorobenzene solutions at different
concentrations and irradiation dosages. These results indicated
that at very low toxic concentrations <12.5 ppm, competitive
absorption takes place between the water and the toxic molecules.
Under these conditions the ratio of light absorbed by the water
molecules to the light absorbed by the toxic molecules becomes an
important limiting factor in the photolysis process. At higher
toxic concentrations >50 ppm the amount of oxygen dissolved in the
solution is too low to allow complete oxidation of the toxics.
Therefore best results were achieved at concentrations between 12.5
and 50 ppm.
These results led us to investigate two schemes for effectively
oxidizing the toxic solutions, recycle aeration and chemical
oxygenation. The baseline case against which all of the
oxygenation methods were compared, is the system shown in Figure 4
where the feed solution is saturated with air but no further
aeration occurs. For all of the aeration experiments, 50.0 ppm
chlorobenzene solutions were fed into the system and irradiated at
0 (method Blank), 1, 3, 5, and 10 photons per molecule. Figure 5
shows a schematic of the recycle aeration system, using air and
pure oxygen as the oxidant.
Aerated Recycle systems
In cases where the oxidant was insoluble in water (air, oxygen)
aeration rates were achieved by aerating a recycle stream to its
saturation value and then controlling the recycle rate. At 0.208
atm and 70°F, the oxygen concentration in an oxygen saturated
solution is 2.9X10-7 gmmoles/ cc, based on the Henry's law
constant. In this system the feed solution flows in the reactor
17
-------
Table 3
Table 3. Calculation of Maximum Extents of Reaction as limited by
dissolved oxygen
Basis: Toxic + a02 — > bH20 + cC02 + dHCl + e N02
Oxygen saturation concentration = 2.90E-07 gmol/cc
Toxic
Chlorobenzene
Benzidine
Dichloroethane
Dichloroethene
Hexanoic Acid
Bis-2-Chloroethyl Ether
Methyl Ethyl Ketone
Toxic
Chlorobenzene
Benzidine
Dichloroethane
Dichloroethene
Hexanoic Acid
Bis-2-Chloroethyl Ether
Methyl Ethyl Ketone
7
17
2
2
9
5
5
1
17
2
2
9
5
5
a
. 0
. 0
.5
. 0
. 0
.0
.5
a
.0
. 0
.5
. 0
.0
.0
.5
M
112 .
184 .
98.
96.
116.
142.
72.
M
112.
184.
98.
96.
116.
142.
72.
56
20
96
96
10
40
10
56
20
96
96
10
40
10
Toxic Cone.
(12.5 PPM)
gmol/cc
1. 11E-07
6 . 79E-08
1. 26E-07
1.29E-07
1. 08E-07
8.78E-08
1.73E-07
Toxic Cone.
(12.5 PPM)
gmol/cc
4 .44E-07
2.71E-07
5.05E-07
5. 16E-07
4 .31E-07
3 . 51E-07
6.93E-07
Maximum
Extent
of
Reaction*
0 .
0 .
0 .
1 .
0.
0 .
0.
Maximum
Extent
37
2 5
92
00
30
66
30
Of
Reaction*
0.
0.
0.
0.
0.
0 .
0.
09
06
23
23
07
17
03
a = Stoichiometric coefficient of oxygen for oxidation reaction
M = Molecular weight of toxic compound
PPM = Parts per million, mass:mass
* Reaction extents for oxidation reactions are calculated
as follows ,,4.1
[-Moles Oxygen Present]
Extent of reaction =
Id
-------
Table 4
Table 4. Batch Pnotolysis of Chlorobenzene Solutions Saturated with Air
Coutlet/Cinletat Vari°US Inlet Concentrations
Photons
molecule
Photons
molecule
1
3
5
10
1
3
5
10
3.125
0.53
0.39
0. 37
0.24
1 -
inlet
12.5
out
/ c
0. 43
0.2
0 .09
0.06
50
inlet
0. 49
0. 29
0. 15
0. 09
(C / C )
( out inlet)
0. 47
0.61
0.63
0.76
0.57
0.8
0.91
0. 94
0. 51
0.71
0.85
0. 91
100
0. 72
0.72
0. 58
0. 22
0. 28
0. 28
0.42
0.78
-------
|0
ORE
468
Photons / Molecule
12
Inlet Concentration
—3.125 PPM —12.5 PPM ^-50 PPM -*- 100 PPM
Figure 3. Impact of Irradiation Dose and Inlet
Concentration On Extent of Reaction
(Chlorobenzene saturated with air)
-------
Outlet
Collection
Tank
Sample
Syringe
Laser
Mini
Controller
Sample
Withdrawal
[Septum
Sample
Syringe
Peristaltic Pump
Inlet
Collection
Tank
Power
Photochemical
etectorn Test Cel1
Power
Detector
'Sample
Withdrawal
Septum
Power
Meter
Chart
Recorder
Figure 4. Schematic of Test Facility for Non-Aerated
Fluids
-------
reactor Th x^i? Solution' takes place at the inlet end of the
Ul
x °f the "action, however, occurs at the
?I,?/H mixln<3 zone between the toxic and the aerated
"^ the Ught ^"sion P°rt of the reactor. The
reacted ""id leaves the reactor and is split into
nnn^nrr af recycle stream and a product stream. The
concentration of air and/or oxygen in the recycle stream is
restored to saturation levels by the aerator. The recycle rate is
controlled independently of the toxic solution feed rate, and thus
controls the rate of oxygen to toxic in the reaction zone.
Chemical Oxygenation
The next oxygenation technigue examined was that of chemical
oxygenation employing hydrogen peroxide and sodium nitrate as the
oxygenating source, (Figure 6).
First considering Sodium Nitrate, absorbance experiments indicated
that aqueous solutions of dissolved sodium nitrate, absorbs energy
in the ultraviolet region of the spectrum. It was further known
that nitrates can act as electron acceptors, and so could act as an
oxidant for the toxic solutions. Since sodium nitrate is highly
soluble in water, the problem of dissolved oxygen solubility
limitation could be overcome with the use of the sodium nitrate as
an oxygen carrier. In these experiments, SOppm solutions of a
mixture of sodium nitrate and chlorobenzene were fed into the
reactor and irradiated.
The next experiments were conducted with hydrogen peroxide as the
chemical oxidant. In these experiments (Figure 6) hydrogen
peroxide is mixed at a mixing tee with the toxic solutions prior to
entering the reactor. The mixed solutions of hydrogen peroxide and
toxic then flows down the reactor towards the laser. The hydrogen
peroxide is very soluble in aqueous solutions and the oxidant level
can be set at any desired value. The general chemical reaction
equation, involving hydrogen peroxide as the oxidant is shown in
Figure 2,
C6H5X + 14 H202 — hv ---- > 6 C02 + 16 H20 + HX
and was used to determine stoichiometric requirements.
For each experiment run, the laser pulse frequency and toxic feed
flow rate were set to deliver the desired irradiation dosage of
0135 and 10 photons / molecule. The toxic and oxidizing agent
concentrations were continuously monitored at the feed and effluent
nnrtsbv the HPLC. The irradiated and non-irradiated reactor
erfluent were collected and analyzed within thirty minutes after
the samples were collected from the reactor.
22
-------
Outlet
Collection
Tank
Peristaltic
Pump
Air Reservoir
ro
Sample
Syringe
Sample
Withdrawal1
Septum
Laser
Mini
Controller
^ . Return
Recycle Air
1
Aerato
\
/
c
r
S
n
Blower
Sample
Syringe
Inlet
Collection
Tank
Peristaltic
Pump
Sample L3
Withdrawal
J Photochemical |_
Power Test Cell
Detector
Power septum
M Detector
Power
Meter
Chart
Recorder
Figure 5. Schematic of Aerated Recycle Apparatus
-------
Recycle Oxidation
Reactor
Toxicant Feed Solution
in Equilibrium with
0.208 atm Oxygen
A) Air
Chemical Additive Oxidation
Reactor
Chemical Additive
Hydrogen Peroxide
Laser Beam
Effluent
Oxygenator
B) Oxygen
-TX. Laser Beam
=i Effluent
Figure 6. Process Flow Oxygenation Schemes
-------
e
conditions had b«n achieved in%h
-"ruction
e"SUre Steady State
HPLC
"
sodium nitrate as a potential oxidant, no destruction occurred. It
was deduced that sodium nitrate is such a strong absorber of the
radiant energy at the wavelength used, that very little radiation
was available to interact with the chlorobenzene
When considering air and oxygen in recycle aeration, destruction
was achieved, increasing with oxygen partial pressure, but only at
the expense of high irradiation dosages. These results were
discouraging, however, the results obtained with hydrogen peroxide
as the oxidant led to unique discoveries discussed in the next
section.
c. Hydrogen Peroxide Results
The toxic destruction using hydrogen peroxide as the oxidant
(Figure 7) shows destruction equivalent to using oxygen as the
oxidant. However, these data are the results of samples analyzed
immediately after being collected from the reactor.
Upon review and reanalysis of some of the experimental samples, in
November 1989, the following discovery was made, which was used to
set the final research objectives and experimental parameters.
For most of the experiments run before November 1989 on
chlorobenzene, our specific target compound, samples were only
analyzed right after they were collected. However, these samples
were stored in amber colored teflon lined capped vials, and so were
available to be reanalyzed at a later date. The initial HPLC
analyses gave results that were far from encouraging, but
reanalysis and comparative review of the samples being stored in
the dark to the initial results showed the destruction of the
chlorobenzene had continued during sample storage. Similar results
were observed for all the samples reanalyzed.
It was discovered and confirmed after several analyses that the
chlorobenzene concentration and the Total Organic Carbon content of
the samples sealed in the amber colored vials had diminished to
extremely low levels in comparison to the initial analyses It was
subsequently substantiated that reactions leading to the toxicant
destruction were continuing for extended periods of time after the
initial irradiation exposure period, when varying stoichiometric
concentrations of hydrogen peroxide were present in the toxic feed
solution ? Further ^experimentation and analysis showed that the
25
-------
INITIATION STAGE
ORE o.4
n i i i i i i m
100
Photons / Molecule
-•- Air (2.0) — Oxygen (6.0)
-*-Sodium Nitrate (1.0) ~*~ Hydrogen Peroxide (1.0)
The Figure in Brackets Above Represents the Stoichiometric
Oxygen Fraction Delivered.
Figure 7. Destruction of Chlorobenzene by
Various Oxidation Schemes
-------
which con?inutn Her lr/adiati°n source initiates a chain reaction
nronaaaM na ^ ^°nd the exP°su^ period and into a dark
?he toxicantseventually leads to complete destruction of
A further test was carried out, by irradiating a 1 liter solution
of 50 ppm chlorobenzene containing stoichiometric quantities of
hydrogen peroxide. The gas evolved from the solution was
CK ^ f, Calculation show that 64.5 cc • s of carbon dioxide
should be produced under complete oxidation conditions, presuming
that water and hydrogen chloride stay in the aqueous phase. sixty
eight (68) cc's of gas were measured, and this gas was soluble in
caustic solution indicating the presence of carbon dioxide.
Preliminary studies suggested that the reaction rate in the
propagation stage was proportional to the irradiation dosage during
exposure to the laser light source. Further, it was found that
chlorobenzene and eventually the other toxicants tested were also
reduced to non-toxic gaseous species of carbon dioxide and water,
by observing and monitoring the total organic carbon (TOC) content
of the toxicants. The TOC concentration was reduced significantly
as the reaction propagated in the dark, correspondingly we also
monitored and observed similar decreases in the pH as the reaction
continued. These results led to examination of the LIPOD process
as a laser stimulated initiation of the destruction process, which
leads to a propagating destructive oxygenation reaction in the post
exposure period.
After running 50 ppm chlorobenzene solutions at three different
irradiation dosages of 1, 3, and 10 photons / molecule (Figure 8)
and at three different stoichiometric hydrogen peroxide ratios of
0.5, 1.0 & 1.5, (Figure 9) attention was focused on the
experimental parameters of 10 photons /molecule and unit
stoichiometric hydrogen peroxide.
Irradiation of the chlorobenzene solutions under these conditions
showed that after initial laser irradiation, percentage destruction
was only 31%, (Table 5, Figure 10). However, continuous monitoring
of the reaction process with time in the propagating phase without
the light showed that greater than 98% destruction of the
chlorobenzene was achieved after 115.5 hours, (Figure 11).
Similar experiments were run on six other toxic compounds (Table 5,
Fiaure 11) The parameters were calculated for all other compounds
and the experimental conditions set to achieve similar run
parameters as that of the chlorobenzene case. Monitoring and
analysis of these tests were similarly on an initiation and a
propagation phase basis.
All the toxic compounds tested (except for t-dichloroethane) showed
initial destructions between 18 and 30 %, while testing over time
showed thaVthe destructions achieved had increased significantly
27
-------
00
ORE
50 PPM Feed
Concentration of Hydrogen Peroxide = 3.1 x 10"6 g-mole/cc
i i \ i i i
20
40 60 80 100
Reaction Time (Hours)
Photons / Molecule
120
140
Figure 8. Impact of Irradiation Dose on Exient
of Reaction
-------
ORE
1.0
0.8
0.6
0.4
0.2
0.0
* D
50 PPM FEED IRRADIATED AT 10 PHOTONS/MOLECULE
CONCENTRATION OF HYDROGEN PEROXIDE = 3.1 x 10-6 gmole/cc
6.2 x 10"6 gmole/cc
9.3 x 10~6 gmole/cc
0 20 40 60 80 100 120
Reaction Time (Hours)
H2O2 TO CLBZ RATIO
+ 0.5 STOICHIOMETRIC * 1.0 STOICHIOMETRIC
a 1.5 STOICHIOMETRIC
Figure 9. Impact of Hydrogen Peroxide
Concentration on Reaction Rate
(HYDROGEN PEROXIDE ADDED AT 0.5,1.0 AND 1.5 TIMES STOICHIOMETHSC RATE)
-------
Table 5. Destruction of Various Toxic Organic Compounds by Laser
Compound Irradiation Dose
(photons/molecule]
Benzene
Chlorobenzene
Chlorophenol
Dichloroethene
Benzidine
Phenol
10
10
10
10
10
10
Initiation
Destruction
(percent)
29
31
34
18
48
35
Propagation
Time (Hr)
96.0
113.5
72.0
624.0
288.0
72.0
Final Destruction
Achieved after
Propagation
(percent)
91
98
>99
88
88
>99
The system was found to be dependenton an initiation and a prpoagation
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 gieater irradiation dosage.
Analysis and observation of the propagation process showed significant
changes in the final destruction achieved after a number of days depending on the
concentration of the toxic organic compound present, the concentration of the
hydrogen peroxide, and the irradiation dose applied during the initiation
phase.
30
-------
ORE
1.0
0.8
0.6
0.4
0.2
0.0
50 PPM FEED IRRADIATED AT 10 PHOTONS/MOLECULE
20
40 60 80 100
Reaction Time (MIN)
* CHLOROBENZENE
a DICHLOROETHENE
* CHLOROPHENOL
x BENZENE
120 140
Figure 10. Extent of Reaction During the
Initiation Stage
(HYDROGEN PEROXIDE ADDED AT STOICHIOMETRIC RATE)
-------
ORE
50 PPM FEED IRRADIATED AT 10 PHOTONS/MOLECULE
i i i i
100
200 300 400 500
Reaction Time (HOURS)
600
700
+ CHLOROBENZENE * CHLOROPHENOL
x BENZENE O BENZIDINE
n DICHLOROETHENE
A PHENOL
Figure 11. Impact of Irradiation on the Reaction Rate of
Several Organics During the Propagation Stage
(HYDROGEN PEROXIDE ADDED AT STOICHIOMETRIC RATE)
-------
water and a halogenated acid, given by a simplified
equation approximating to: ^j-mpuriea
CAX + (2a + 0.5(b-l))H202 —hv—> aC02 + (2a + b-l)H2O + HX
In July 1990, a series of experiments with chlorobenzene were
begun, to determine the effect of toxic species concentration and
irradiation dosage on the destruction efficiency of the LIPOD
process. Chlorobenzene at concentrations of 10, 20, & 50 ppm
(mg/L) and irradiation dosages of 1 and 10 photons / molecule were
used in these experiments. The data of the results shown in
(Figures 12 and 13) shows that as toxic concentration diminishes,
there is an increase in the destruction in the initiation phase but
there is reduction in the rate of destruction in the propagation
phase.
The observations can be explained as follows. As the toxic
concentration is reduced, the laser beam penetrates further into
the fluid, and a greater fraction of the toxic molecules are
exposed to the laser beam. However, in the dark propagating phase,
the reaction becomes diffusion controlled with the reaction rate
being proportional to the remaining toxic and hydrogen peroxide
concentrations.
This conceptual picture is supported by the data presented in
(Table 5, Figure 11), where the percent destruction achieved
obtained in the initiation and propagation phases of the reaction
for all the compounds studied are presented. The data show that
the components which exhibit high absorption coefficients achieve
the greatest amount of destruction in the initiation phase.
Correspondingly those compounds with compact molecular
configurations and correspondingly high diffusivities tend to show
faster reaction rates in the propagation phase.
Impact of Irradiation Frequency
In order to reduce the possible reaction interferences caused by
nitrates in solution, 50 ppm chlorobenzene solutions were
irradiated at a higher wavelength. In the higher wavelength
region, the nitrate anions in solution show negligible absorption.
Figure 14 represents the data obtained in this experiment The
reaction shows a similar profile as, was obtained at the lower,
i->=uv->_j.i_ni .JIIWTT^. .. j_j+.j_,4_^^_ -.r,^> nr-ni-iartal-inn
reaction snows a aa.iuj.j-aj. ^^^^.^--— —-
more energetic wavelength, with the same initiation and propagation
Phase reaction characteristics, but at an overall slower rate in
achieving the same percent destruction achieved. This slower
reaction9rate in ^propagation phase can be attributed to the
33
-------
ORE
200 400 600 800
Reaction Time (HOURS)
Chlorobenzene Concentration
Q20ppm <>50ppm
1000
Figure 12. Impact of Feed Concentration
on Reaction Rate
(HYDROGEN PEROXIDE ADDED AT STOICHIOMETRIC RATE)
(SOLUTION IRRADIATED AT 1 PHOTON/MOLECULE)
-------
ORE
200 400 600 800
Reaction Time (Hours)
Chlorobenzene Concentration
MOppm a20ppm <>50ppm
1000
Figure 13. Impact of Feed Concentration
on Reaction Rate
(HYDROGEN PEROXIDE ADDED AT STOICHIOMETRIC RATE)
(SOLUTION IRRADIATED AT 10 PHOTONS/MOLECULE)
-------
ORE
200 400 600
Reaction Time (Hours)
1000
Figure 14. The Impact of Irradiation Wavelength
on the Destruction of Chlorobenzene
(Hydrogen Peroxide Added at Stoichiometric Rate)
(50 PPM CLBZ Irradiated at 10 Photons/Molecule)
(Irradiation Wavelength 28.5% > Normal)
-------
lower energetics of the photons at the higher wavelengths.
Propagating Reaction Effectiveness
To test the effectiveness of and a possible mechanism for the
propagation reaction, an experiment was run in which one fourth of
a 50 ppm chlorobenzene solution was irradiated and then mixed with
the other three fourths of non-irradiated solution,(Figure 15)
This remixed solution was monitored to determine the extent of
reaction initiated by the irradiated molecules and hydrogen
peroxide, to see if the fraction of irradiated molecules were
energetic enough to propagate the oxygenation reaction.
Analysis of the results shown in Figure 15 shows that greater than
25% destruction was achieved. This indicated that a reaction
between irradiated and non-irradiated species does take place which
can eventually lead to the destruction of all species. However,
the reaction rates in the propagation phase is slower than in the
case when the whole fluid pool is irradiated even at one guarter of
the photon /molecule dosage.
Real Waste Testing
In September 1990, the LIPOD process was tested on the leachate of
a landfill from a municipal solid waste burning facility.
A sample from this waste facility was analyzed earlier in the year
for its organic content, (Tables 6 and 7) . The method used for the
real waste testing in September was based on the total organic
carbon (TOC) content of the sample after filtration with 0.45
micron filters. TOC analysis was done on the filtered samples
shortly after arriving at E3I. Based on the TOC results of 1200
ppm total organic carbon in the sample, the concentration of
stoichiometric hydrogen peroxide needed to totally oxidize this
organic carbon content of the sample was calculated and employed
for the tests.
The results of Figure 16 show that at the time of writing this
report, after six days, the destruction achieved was 56 and 75
percent using five and ten photons /molecule irradiation dosages
respectively.- using stoichiometric hydrogen peroxide.
D. status
The process is currently operating at the bench scale level in a
system with 1 GPM capacity when treating a toxic waste stream
containing 32PPM of total organic carbon in solution. The impact
of absorption coefficient, irradiation dosages, toxic
concentration, hydrogen peroxide concentration and the £«""« °J
common ionic species in solution on the destruction achieved and
reaction rate have been determined for the six target compounds.
The ability of the process to destroy a given toxic compound is
37
-------
1.0
0.8
ORE 0-6
0.4
0.2
0.0
D
D
4 6 8 10
Reaction Time (Days)
14
Figure 15. Impact of Irradiating a Portion
of the Fluid
(50 PPM CLBZ Irradiated at 4 Photons/molecule
1 Liter of Irradiated Solution Mixed with
3 Liters of Non-Irradiated Solution)
-------
Table 6. Semlvolatile GC/MS Anal
Compound
Phenol
Benzyl alcohol
2-Methylphenol
Isophorone
Benzoic acid
Dimethyl phthalate
Diethyl phthalate
Di-n-Butyl phthalate
Nitrobenzene
2-F1 uorobi phenyl
Terphenyl
2-Fluorophenol
2,4,6 Tribromophenol
Standards
1,4 Dichlorobenzene
Naphthalene
Acenaphthene
Chyrsene
24.29
7.29
1.49
1.33
162.80
1.06
5.00
1.18
125.46
96.08
102.47
164.37
210.48
Conentration (mg/L)
40.00
40.00
40.00
40.00
40.00
-------
Table 7. Semivol atile GC/MS Analysis of Real Waste (6/28)
Compound
Phenol
Benzyl alcohol
2-Methyl phenol
Isophorone
Benzoic acid
Dimethyl phthalate
Diethyl phthalate
Di-n-Butyl phthalat
Nitrobenzene
2-F1 uorobiphenyl
Terphenyl
2-Fluorophenol
2,4,6 Tribromophenol
Standards
1,4 Dichlorobenzene
Naphthalene
Acenaphthene
Chyrsene
Perylene
Concentration (mg/L
24.60
8.17
1.11
1.41
83.00 1
6.72
3.46
3.90
3.92
5.91
10.37
Concentration (mg/L)
40.00
40.00
40.00
40.00
40.00
-------
ORE
0
2345
Reaction Time (Days)
Photon / Molecule
A 5 D10
Figure 16. Destruction of MSW Leachate
(Hydrogen Peroxide at Stoichiometric Rate)
(1200 ppm Filtered with 0.45 ^m Filter)
-------
measured in terms of the net destruction achieved.
Summarizing results using hydrogen peroxide as the oxidant, the
impact of the hydrogen peroxide concentration on reaction kinetics
is shown in Figure 10. The stoichiometric quantities of H,0, used
in typical applications are small. Propagation phase reaction
rates increased with increasing peroxide concentration but in all
cases over the ranges studied greater than 95% destruction was
achieved. Figure 9 shows the impact of irradiation dosage, showing
that the greater the irradiation dose received in the initiation
phase of the reaction, the more rapid the destruction rate during
the propagation phase. Again, complete destruction is attained in
all cases, but this observation provides a design tr^>de off between
power cost to initiate the reaction and effluent storage reaction
capital cost to contain the reaction while it proceeds to
completion in the absence of light.
Figure 15 shows the impact of toxic concentration on reaction rate.
Higher destruction is seen to occur during the initiation phase as
the toxic concentration diminishes. This is as a conseguence of
the fact that the laser beam is able to penetrate further into the
photochemical reactor at lower concentrations because of less
absorption by a smaller number of toxic molecules. Thus as the
toxic flows through the reactor it is exposed to the beam for a
longer period of time and hence exits the reactor at higher levels
of destruction. However, in the propagation phase, the reaction
rate is species dependent, with the kinetics following the law of
mass action. So, the higher toxic concentrations react more
rapidly during the propagation phase of the reaction.
The impact of common ionic species normally found in waste and
ground water on the destruction^achieved were also determined. Six
ionic species were examined Na , Ca , Mg , Cl , SO42., and N03., of
which only the nitrate showed any form of impedance on the reaction
process at the 193nm wavelength employed. Nitrate ions were found
to absorb the radiation at the lower wavelength, however, tests
done at a higher wavelength showed that we could overcome this
deficiency since the nitrate ions did not absorb at this new
wavelength.
VI. Quality Assurance
A Quality Assurance Project plan for "The Laser Stimulated
Photochemical Oxidative Destruction of Toxic Organics in Water" was
submitted by E3I in December, 1988 to Dr. Ronald Lewis, USEPA
Project Officer. A review of the QA project plan was received in
February 1989. E3I responded to the review comments in a revised
OA nroie'ct plan, which was sent to Dr. Lewis in July, 1989.
Revision 1 of the QA project plan was accepted by the USEPA and
adhered to throughout the project. As research proceeded, results
directed attention toward several new areas for investigation. The
work plan for the project was expanded and altered somewhat to
42
-------
were
accommodate additional experimentation. These changes
discussed in detail and approved by the project officer
A technical systems audit of the laser project experimental process
was conducted on August 29-30, 1990. The following areas of
laboratory operation were reviewed for conformance to the quality
assurance project plan and standard good laboratory practice:
Standard Operating Procedures
Sample Collection
Analytical Methods
Preparation of Standards
Instrument Calibration
Quality Control Procedures
Preventative Maintenance
Documentation
Safety
Waste Disposal
Reporting
Laboratory and technical systems for the project were determined to
be in control. Procedures and documentation were found in order.
VII Evaluation of the LIPOD Process
Based on the experimental results, the following criteria were
established for the successful application of the technology:
1. The UV radiation must be at a wavelength where the energy
is not significantly'absorbed by the water molecules.
2 . The UV radiation must be absorbed by the hydrogen
peroxide and the toxic organic.
3. The energy of the absorbed photons must exceed the bond
energy of the absorbing molecule so as to be able to
cause excitation and fragmentation and thereby a
reaction.
4. A source of hydroxyl radicals, such as hydrogen peroxide,
must be present to initiate the oxidative chain reaction.
When using dissolved oxygen in water as the oxidant, the
effective chain reaction does not occur, and the toxic is
oxidized only at the expense of using high dosages of UV
radiation.
Aromatic and unsaturated organics, which normally appear high on
the priority pollutant list, meet the above criteria and are thus
good candidates for the successful application of the technology.
Table 8 shows an operating comparison between the UV oxidation
43
-------
Table 8. Operating Comparison of UV Oxidation Processes
Process
Issue
I r r ad i a t i on
Intensity
(Photons/Molecule)
Input Power
(KUatt-Hr/MGal) *
Hydrogen Peroxide
Requirements
(Crams/Cram "TOC")
Ozone Requi rements
(Gram/Gram "TOC") **
Power Output
Power Input
Power Source
Lou Intensi ty UV
Radiation Processes
Low
.005
27.1
H
1950
.1
High
.OH
79.1
990
2865
.1
Lou Pressure UV Lamp
LI POO
Low
.05
13.4
2.4
0
.01
High
2
53.2
4.8
0
.01
Excimer Laser
High Intensi ty u,"
Radiation Processes
Low
386
371
2.4
0
.1
High
115
-------
processes. The UV processes require an oxidant, normally hydrogen
peroxide, and an energy source to overcome the activation energy
barrier associated with the oxidation reactions. The high
intensity UV process uses the UV light source to supply the energy.
The low intensity UV process uses a combination of the UV light
source and ozone to supply the activation energy. A comparison of
the high and low intensity UV radiation processes and LIPOD shows
a clear advantage of the LIPOD process due to its ability to
initiate a chain oxidative reaction which continues to propagate
the oxidation reaction in the absence of any light. This feature
could possibly allow the LIPOD process the potential of being used
as an insitu "chemical" remediation process. Because the output to
input power efficiency of the laser is less than that for a UV
lamp, the lamp power requirements are equivalent to that for the
low intensity UV process. However, the laser process requires far
less peroxide and no ozone to accomplish the same level of
destruction. Similarly, the high intensity UV process requires
modest peroxide levels and no ozone. However, the irradiation
intensity and hence the power requirements are substantially
greater than in the LIPOD process. This is due mainly to the
coherence of the laser beam, which allows the beam to maintain its
high intensity as it moves further away from its source. It is
also beam coherence and intensity that leads to the ability of the
process to initiate a chain oxidation reaction. Tables 9 and 10
show cost comparisons and projections of LIPOD's costs as a
function of capacity respectively.
Carbon adsorption which is the most commonly utilized technology in
the final clean up of trace contaminants in aqueous waste streams
and LIPOD processes have several components in common. For
example, a typical 10 gpm polishing system would require that both
employ the following:
* Pumps and piping,
* Instrumentation and controls,
* Filtration equipment to remove potentially
interfering suspended solids.
In comparison to carbon adsorption, however, the LIPOD process will
require additional capital for the laser. For the trace amounts of
aromatic compounds for which LIPOD is especially well suited, the
additional capital cost will be offset by the reduced operating
cost of the LIPOD process: eg. The cost will be recovered in a
period of several months. Also the carbon adsorption process
recmires continual supply of activated carbon or alternatively the
use of expensive regeneration equipment. This process also requires
the disposal of spent carbon as a hazardous waste.
Based on previously acquired information, and the effectiveness of
the present technology, it is estimated that the LIPOD process will
45
-------
Table 9.
Cost Comparison of LIPOD to other Toxic Organic Compound Removal
and Destruction Processes
Basic Data
Feed flow rate
Inlet chloroaromatic concentration
Destruction & Removal Efficiency (ORE)
Annual Capacity Factor
Carbon cost
Carbon disposal cost
Carbon Loading
Hydrogen Peroxide Cost
Electric Power costs
UV lamp Replacement
UV lamp life
Capital Recovery factor
Process LIPOD
Capital Cost $78,000
Electric Power
efficiency .01
Annual Operating
& Maintenance costs
(excluding labor)
Electric Power
Peroxide
Laser Gases
Carbon Cost
Lamp Replacement
Other Chemicals
Maintenance &
Insurance (2% of
capital cost)
Capital recovery
Total
Cost per 1000
Gallons treated
.815 GPM
50 ppm
. 99
70 percent
$ 3.00/lb
$ 1.50/lb
10 mg/gram
$ 1.10/lb
7.65 cents/KWHr
$ 65/lamp (65 watts lamp)
1 year
.177 (10 years @ 10%)
Low Intensity
UV radiation
$55,200
.1
High Intensity
UV radiation
$170,000
. 1
776
2,571
1,969
0
0
0
1,560
13.806
$20,682
$68.94
$ 63,538
7,892
0
0
924
0
1, 104
9.770
$83,228
$277.43
$ 39,147
2, 571
0
0
37 , 045
0
3,400
23 .856
$106,019
$353 .40
Carbon
Adsorption
$30,000
175
46, c:
7 , 5 0 C
60C
$59 ,585
$198.61
46
-------
TABLE 10. LIPOD COST AS A FUNCTION OF CAPACITY
Capacity (GPM)
Capital Cost
Annual Operating
Cost (Excluding Labor
and 70% operating factor)
Electric Power
Peroxide
Laser Gases
Maintenance & Insurance
Capital recovery
Total $
Cost Per 1000
Gallons Treated
81,600
952
3, 154
2,415
1, 632
14 ,443
22,596
$61.42
10
360,000
9,518
31,541
24, 151
7,200
63, 720
$ 136,130
$37.00
100
2,160,000
95,183
315,415
241,509
43 , 200
382 , 320
$ 1,077,627
$29.29
LIPOD COST AS A FUNCTION OF CAPACITY
c
A
P
I
T
A
L
C
0
5
T
S^OOQOOO \
11090004
$19,000
0.1
SOppm
BASIC DATA
TOXIC CONC.
ORE : 0.99
ANNUAL CAPACITY FACTOR - 70*
HYDROGEN PEROXIDE COST : J 1,10/18
ELECTRIC POWER COST -• 7.65 CENTS/KWHfl
CAPITAL RECOVERY FACTOR > .177
1 10 100
CAPACITY (GPM)
1000
o
p
£
R
A
T
I
N
G
C
0
5
T
M
G
A
L
47
-------
offer substantial savings in cost over all competing processes in
the applications for which it is designed, with the per gallon
treatment cost estimated not to exceed $0.10-$0.20.
In summary, LIPOD's favorable attributes include complete
conversion of toxic organics to non-toxic species, competitive
costs, and potential to provide in-situ "chemical" remediation to
subsurface contamination. Unfavorable features of the process are
its inability to effectively oxidize non-absorbing species such as
aliphatic saturated and conjugated organic compounds, and as of yet
a lack of thorough understanding of the effect of particulates on
the process performance. Aliphatic compounds are not usually very
toxic, and particulates may be removed by filtration.
48
------- |