EMERGING  TECHNOLOGY REPORT:

    DESTRUCTION OF ORGANIC CONTAMINANTS IN AIR
      USING ADVANCED  ULTRAVIOLET  FLASHLAMPS
                        by
Mark D. Johnson, Werner Haag and  Paul  G.  By1stone
                    Purus,  Inc.
                San Jose, CA 95134

                        and

                  Paul  F. Daley
      Lawrence  Liver-more National Laboratory
                Livermore, CA 94550
           Contract No. CR-818209-01-0
                 Project  Officer

                   Norma  Lewis
        Emerging Technology  Section,  SDEB
      Risk  Reduction  Engineering  Laboratory
               Cincinnati,  OH 45268
      RISK REDUCTION  ENGINEERING  LABORATORY
        OFFICE  OF RESEARCH AND DEVELOPMENT
       U.S. ENVIRONMENTAL PROTECTION  AGENCY
               CINCINNATI, OH 45268

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                             NOTICE
The information in this document has been funded in part by the United States
Environmental Protection Agency under Contract No. CR 8 18209-01-0.  It has
been subjected to the Agency's peer and Administrative review, and it has been
approved for publication as an EPA document.  Mention of trade names or
commercial products does not constitute endorsement or recommendation for
use.

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                            FOREWORD

    The Superfund Innovative Technology Evaluation (SITE) Program was
authorized in the 1986 Superfund Amendments:  The purpose of the Program
is to assist the development of hazardous waste treatment technologies
necessary to implement new cleanup standards which require greater reliance
on permanent remedies. A key part of 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.

    The SITE Program is part of EPA's research into cleanup methods for
hazardous waste sites around the nation. Through cooperative agreements with
developers, alternative or innovative technologies are refined  at the bench-and
pilot-scale level then demonstrated at actual sites. EPA collects and evaluates
extensive performance data on each technology to use in remediation  decision-
making for hazardous waste sites.

    This report documents Purus Inc.'s laboratory and field studies of the use
of photolytic oxidation for destruction of volatile organic compounds (VOCs)
in air. Field tests were performed at the Lawrence Livermore National
Laboratory Super-fund site in Livermore, California on soil zones contaminated
with trichloroethene

    Copies of this report  can be purchased from the National Technical
Information  Service, Ravensworth Bldg., Springfield, VA, 22161, 703-487-
4600. You can also call the SITE Clearinghouse hotline at 1-800-424-9346 or
202-382-3000 in Washington, D.C. to inquire about the availability of other
reports.
                  E. Timothy Oppelt, Director
                  Risk Reduction Engineering Laboratory
                              in

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                                      ABSTRACT

       This paper describes a new process for photo-oxidation of volatile organic compounds
(VOCs) in air using an advanced ultraviolet source, a Purus xenon flashlamp. The flashlamps
have greater output at 200-250 nm than medium-pressuer mercury lamps at the same power and
therefore cause much more rapid direct photolysis of VOCs , including methylene chloride
(CH2 Cl 2), chloroform (CHC13), carbon tetrachloride (CC1 4 ) , l,2dichloroethane (1,2-
DCA), 1,1,  1-trichloroethane (TCA), Freon  113 and benzene .  The observation of quantum
yields greater than unity indicate the involvement of chain reactions for trichloroethene (TCE),
perchloroethene (PCE), 1,1 -dichloroethene (DCE), chloroform, and methylene chloride.
       TCE was examined more closely because of its widespread occurrence and very high
destruction rate. Two full  scale air emission control systems for TCE were constructed at Purus
and tested at a Lawrence Livermore National Laboratory  (LLNL)  Superfund Site.  The systems
were operated at flash frequencies of  1 - 30 Hz, temperatures of 33  - 60 °C, flows up to 300
scfm (260 ppmv TCE) and concentrations up to 10,600 ppmv (100 scfm). Residence times
ranged from 5 to 75 seconds. In all cases except at the lowest flash frequency, greater than 99%
removal of TCE was observed.  Careful attention was paid to product formation and  mass
balances. The main initial photo-oxidation product of TCE was dichloroacetyl chloride
(DCAC),  which upon further photolysis was converted in part to dichlorocarbonyl (phosgene or
DCC) and possibly formyl chloride, and ultimately to  HC1 and  CQz. Further treatment of photo-
oxidation products is recommended for full-scale operation.
                                       IV

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                                     CONTENTS


Foreword	      iii

Abstract	      iv

List of Figures	yi

List of Tables	     vi

Acknowledgments 	     vii

    1.  Introduction	     1
    2.   Conclusions	     3
             Kinetics of VOC Photo-oxidations	   3
             TCE Photo-oxidation	   3
             Estimation of Process Parameters for Remediation	  4
    3.  Recommendations	     4
    4.  Experimental Methods	    5
             Laboratory Experiments	    5
             Field Measurements	    6
    5.   Results and Discussion	    13
             Laboratory Experiments	    13
             Field Experiments	    25
             Estimation of Parameters to Achieve Recommended
                 Treatment Levels at LLNL Site 300	   28


References	     30

Appendix
    Tables
    A-l Air-2 Results	    31
    A-2 Air-3 Results	    32

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                                      FIGURES
Number
    1   Lawrence Livermore Site 300 Building 834 soil venting apparatus.. .................  7
    2   Details of plumbing connections to the photoreactors .......................................   8
    3   Schematic of Air-2 photochemical reactor [[[  9
    4   Schematic of Air- 3 photochemical reactor [[[   10
    5   Emission spectrum for a mercury lamp vs. a xenon ...........................................
        flashlamp [[[     14
    6   VOC absorbance spectra compared to xenon flashlamp  .....................................
        spectrum [[[     15
    7   Photolysis plots for individual VOC's in the 208-L
        reactor [[[     16
    8   Photolysis plots for chloroolefins in  the 208-L
        reactor [[[     16
    9   Chlorine atom scavenging with ethene in the 208-L
        reactor [[[    21
    10  Photolysis  of TCE and 1,1-DCE as a mixture in the 208-L reactor.. .............. 23
    11  Product yields from the photo-oxidation of TCE in the ......................................
        spectrophotometer cell [[[   23
    12  DCC yields from the photo-oxidation of DCAC in the ......................................

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                               ACKNOWLEDGMENTS
       We thank Ken Kramasz,  Bill Maxfield, Marc van den Berg, Minggong  Su, and Jim
       of Purus, Inc. for engineering and technical support.  We also thank John Greci of LLNL
for his assistance during the field demonstrations. This work, in part, has been sponsored by the
U.S.  EPA's Emerging Technology Program (Project Officer, Norma Lewis). Although the
research described in this article has been funded in part by the EPA, it has not been subject to
agency review and therefore does not necessarily reflect the views of the agency and no official
endorsement should be inferred.
                                      Vii

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                                          SECTION  1

                                       INTRODUCTION
        Many environmental remediation  sites suffer from pollution with volatile organic
compounds (VOCs). Some of these sites are amenable to remediation by vacuum-induced soil
venting and groundwater air stripping methods. However, treatment of off-gases from such
operations  can be problematic.  Because of environmental legislation, air quality management
districts require  VOC air emission controls  at restoration activities. Activated carbon adsorption is
often utilized to control emissions. However, once breakthrough occurs, the spent carbon must be
regenerated on-site  or transported  to the limited  number  of disposal or regeneration locations.   In
addition, this practice can be costly for sites  that contain  VOCs like methylene chloride or acetone
with low adsorption  characteristics, thereby  requiring large  amounts of carbon.   A permanent
treatment  would involve complete oxidation  of the VOC, so that subsequent disposal would  be
unnecessary. Remediation technologies that destroy VOCs  on-site, such as thermal and catalytic
combustion, also have limitations, particularly  for sites with  chlorinated  VOCs.
        Oxidation of organic molecules can  be initiated by  photolysis. Unlike thermally  initiated
oxidation, very little is known  about the feasibility of photo-oxidation of VOCs in air as a
commercial process.  The lack of an intense and  highly efficient light  source that emits in the deep
ultraviolet (<250nm) is the reason that this has not been investigated as a process. Previously, the
only light source that was routinely used for ultraviolet photolyses  on a large scale was the mercury
discharge  lamp.  Flash lamps can also  be made to emit high intensities of ultraviolet light, but  their
use as sources for initiating photo-oxidation  has  previously been limited to  the  laboratory.
        Pulsed inert-gas lamps  (flashlamps) have been  used  for many  applications including  pump
sources for lasers (EG&G,  1988). Lasers themselves have relatively low overall efficiency  and
therefore are  not likely to find application in large-scale  commercial or treatment processes.  A
flashlamp  is an arc  lamp that operates  in the pulsed mode by alternately storing electrical energy in
a capacitor and discharging  it through  a gas contained in  a chamber of UV transmissive quartz
         1988). The discharge quickly heats the gas to a very high temperature (> 13,000 K) and
pressure, causing ionization  and creating a plasma that  emits light.  The spectral  properties of the
plasma approach those of an ideal black body radiator which has  a peak emission wavelength
defined by its characteristic temperature. Increasing  energy discharged into the plasma increases its

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 temperature, which lowers  the  wavelength  of its emission  maximum.
        As opposed  to non-specific blackbody radiation,  most continuous  sources emit lines that
 are characteristic of  the electronic transitions of the unionized fill gas. For example, almost all the
 radiation emitted by  a low pressure mercury lamp is resonance radiation of mercury vapor at 254
 and 185 nm, arising from the  electronic transitions 63Pi—»61So and 6'Pi—> 61So (Phillips,
 1963).  A major advantage of mercury lamps for low power applications is that they are very
 efficient at these two wavelengths. A disadvantage of continuous sources is that they can only be
 operated at relatively low intensities because the number  of photons emitted is proportional to the
 fill gas  pressure. Because the photons are in resonance with electronic transitions, they can be
 reabsorbed by the fill gas.
        We report the application of a xenon plasma flashlamp as a UV light source for the photo-
 oxidation of some VOCs in air. Initially, laboratory experiments were performed on saturated and
 unsaturated chlorinated hydrocarbons in air to screen compounds for treatability. The kinetics of
 photo-oxidation were studied, and apparent  quantum yields were determined for the disappearance.
 Efforts  were made to characterize the photo-oxidation products of one of these chlorinated
 hydrocarbons, trichloroethene  (TCE).
        A full scale photoreactor  was built for the photooxidation of TCE and was tested at
 Lawrence Livermore National  Laboratory (LLNL) Site 300. This report contains a summary of the
 laboratory screening  studies and performance data collected  at the LLNL site on the photochemical
 treatment process for trichloroethene (TCE). The TCE destruction effectiveness and the yields of
 the main  oxidation products  were characterized  under various operating conditions, including:
        *  Process flow:  100 to 290 cfm
        * TCE concentration: 30  to 10,000 ppmv
        * Flash lamp frequency:  1 to 30 Hz
        * Temperature: 33-60 °C
        These results, in combination with toxicological data, were used to estimate the operating
 conditions suitable for reducing  the total toxicity from TCE and  residual products by 99% using
UV photolysis alone.

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                                        SECTION 2

                                      CONCLUSIONS

 KINETICS OF VOC PHOTO-OXIDATIONS
        The low-wavelength emission of the pulsed xenon lamps (Xmax = 230 nm) allows direct
 photolysis of many VOCs, particularly chlorinated compounds and freons, that was not possible
 with commercial  mercury lamps. The quantum yields for photolyses of simple carbon-chlorine
 bonds are quite high, near unity. Nevertheless, light absorption by such compounds is still weak
 enough at 230 nm that either photosensitization or an even  lower-wavelength source is  needed  for
 the photolyses to  be rapid enough for commercialization at present.  On the other  hand, very rapid
 destruction is observed for compounds that undergo chain reactions initiated by  light, notably
 TCE, PCE, DCE, chloroform and methylene chloride (in order). Therefore, full-scale reactors
 were designed for the treatment of the chloro-olefins  DCE, TCE and PCE.

 TCE PHOTO-OXIDATION
       The initial steps of TCE photo-oxidation involve  a chlorine  atom  propagated chain  reaction
 Sanhueza, et al., 1976, Blystone et al., 1991). The apparent quantum yield for this process is
 about 31, which makes the disappearance of TCE extremely rapid and efficient (Blystone et al.,
 1991). The main  product (> 85%) from this chain photo-oxidation is dichloroacetyl chloride
 (DCAC). Products from the initial photolysis of TCE are insignificant because most of the
 products are formed via Cl atom attack.
       Further oxidation of DCAC  is approximately 100 times slower than the photolysis of TCE.
 The  concentration  of DCAC decays  exponentially with dose,  and may be  a result  of both direct
 photolysis and chlorine atom reactions. The products of further photo-oxidation  after DCAC is
 fully formed include dichlorocarbonyl (DCC) in about 20% yield, trichloroacetyl chloride (< 2%),
 CHC13 (-0.65%), CC4 (~0.15%),CH2Cl2(~0.05%), and possibly formyl chloride and
 dichloroacetic acid. The yield of DCC  can be substantially enhanced by the  addition  of chlorine,
 indicating that this product may be formed by chlorine atom reaction with DCAC. At even higher
 light doses, DCC  also decays, suggesting that the low yield is  a result of its concurrent formation
 and  destruction. Evidence  was  found that the carbon-containing products are eventually converted
to CO2 with enough exposure.

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 ESTIMATION  OF  PROCESS PARAMETERS FOR REMEDIATION
       Although both full-scale  reactors demonstrated very efficient removal  of TCE, remediation
 of the LLNL site to toxicity level goals was not attained because of the formation of intermediate
 toxic products. A reduction in toxicity for TCE of 99% requires that the residual DCAC
 concentration be 0.026% the  TCE input concentration, and the DCC concentration  must be 0.45%
 the TCE input concentration.  While it is possible to estimate the UV dose required to eliminate
 DCAC to this level, sufficient data does not exist to determine the dosage  at which the
 concentration of DCC is reduced to the required level.
       The  maximum flow rate that  meets the  DCAC reduction goal under standard lamp operating
 conditions is between 13 and 20 cfm. At this level of treatment, the DCC concentration would still
 be excessive and additional treatment would be needed. Scrubbing with water under these
 conditions would rapidly hydrolyze the DCC to COi and HC1 and the DCAC to dichloroacetic acid
 (DCAA) and HCI. However, the accumulation of even a trace dichloroacetic acid may result in a
 disposal problem for the water because the  expected EPA drinking water limit  for DCAA is so  low
 (-0.2 ppb; Bull R., University of Washington, personal communication, 1991).
                                       SECTION 3

                                 RECOMMENDATIONS
       Further studies on the use of low-wavelength lamps for the destruction of VOCs should be
directed at 1) examining the use  of shorter-wavelength UV lamps  or catalysts for photolysis of a
broader range of VOCs, 2) in the oxidation of chloro-olefins, verify the effectiveness of dry or wet
scrubbers for removing acidic photooxidation products, and 3) developing methods for post-
treatment of products such as DCAA present in the water after scrubbing. Purus will examine
some  of these issues together with Argonne National Laboratory in continued demonstrations at the
Department  of Energy  Savannah  River site.

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                                         SECTION  4

                                EXPERIMENTAL  METHODS

 LABORATORY EXPERIMENTS

 Chemicals
        The following chemicals were used  without further purification  and were obtained from the
 following sources: from Aldrich trichloroethene 99+%, tetrachloroethene HPLC grade, 1,1,1-
 trichloroethane 99%, 1,2- dichloroethane HPLC grade, dichloromethane HPLC grade,
 trichlorofluoromethane 99+% , dichloroacetyl chloride 99%, and chloroform HPLC grade were
 obtained; from Chem Service 1 ,1,2-trichloro- 1,2,2-trifluoroethane, and 1,1 -dichloroethene were
 obtained, and carbon tetrachloride AR grade was purchased from Mallinkrodt.
        Dichloroacetanilide  was synthesized by reaction  of excess aniline with  dichloroacetyl
 chloride in toluene. The precipitated product was filtered, washed with 0.1 M HC1,  recrystallized
 from methanol/water, and its identity verified by GC/MS

 Lamp Spectra
       Flashlamp emission spectra were measured on an Oriel InstaSpec 111 1024 diode-array
 detector fitted with a 77410 MultiSpec Grating.  A Molectron J25 pyroelectric calorimeter was used
 for absolute intensity determinations. Total lamp output at X < 300  nm was measured by H2C>2
 actinometry (Nicole et al., 1990).

 Bench-Scale  Photolvses
       Photolyses were carried out in specially made 32-mL  (10 cm in length, 2 cm in diameter)
 cylindrical quartz spectrophotometer cell, which had a Teflon stopcock sealed  on  one  end and  a
threaded glass adapter sealed on the  other. The threaded glass adapter was capped with a Teflon
lined septum. Liquid  TCE  or dichloroacetyl  chloride (DCAC) aliquots were injected  into the cell
by microliter syringe through the septum and were allowed to evaporate. The front face of the cell
was then placed 4 cm from a xenon flash lamp, and the sample was  irradiated. TCE concentrations
were determined by drawing a sample with a gas tight syringe and directly injecting into a gas
chromatograph. Acid chloride products were analyzed by derivitization with methanol, which was

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 injected  into the  cell  after  irradiation.  Gas chromatography with electron  capture or electrolytic
 conductivity  detection was  used  for quantitation.  DCC was  analyzed by  derivatization with aniline
 using a modification EPA method TO-6 (Winberry et al., 1990). A 2% v/v aniline/toluene  solution
 was injected into the cell following irradiation. The solution was rinsed from the
 spectrophotometer cell, blown to dryness, and diluted to 1.2 mL with acetonitrile. Carbanilide, the
 product of the reaction of DCC with aniline, was analyzed by HPLC with UV detection at 254 nm.

 Pilot-Scale  Photolvses
       Air mixtures were irradiated in a 208-liter steel cylindrical reactor. A high intensity six-inch
 xenon flash lamp was inserted in the middle of the reactor through its side.  The reactor contained
 two electric fans inside to facilitate mixing. All photolyses were performed at atmospheric
 pressure, and the gas temperature ranged from 300 K to approximately 340 K.
       Known volumes of reagents were injected into the reactor by syringe, and were given time
 to evaporate and mix. Analyses of reactant concentrations were performed by gas chromatography
 after successive exposures of known duration.  Samples were drawn from the reactor by gas tight
 syringe after turning off the lamp. No reaction was observed in laboratory light or in the reactor
 with the  lamp off. Samples were directly injected into an HP5890 model 2 gas chromatograph
 equipped with a 30-m J&W model 624 fused silica column  and using either photoionization or
 electron  capture detection.  CC>2 measurements were made in one run using a Horiba PIR-2000
 C02  monitor.

 FIELD  MEASUREMENTS
       Figure 1 is a schematic diagram of the Building 834  Complex chosen for the field studies at
 the southeast portion of Site 300 at  Lawrence Livermore  National Laboratory  (LLNL).  The
 process stream was pumped from the wells at Site 300 using the blower located as shown in
Figure 1. Figure 2 gives details of the connections to the photoreactors. The air stream was
passed through a heat exchanger  to cool, and sent into two types of photoreactors (Figures 3 and
4). Air-2 is a large steel cylinder 4 feet in diameter by 8 feet in length with a volume of 101 cu. ft.
Four xenon lamps are  distributed  about the center of the cylinder  and point  radially inward. The
process stream flows from one end of the cylinder to the other. Air-3 is a               reactor
consisting of four disc shaped stainless steel chambers. Each chamber is 42 in. in  diameter by 6.1
in. high with a volume of 4.1 cu. ft. exposed to the light source. The lamps  in Air-3 are positioned
in the center axis of each chamber. The process flow enters the bottom of each chamber, around a
deflection plate, in towards  the lamp, and then out the top. The chambers in Air-3 are configured

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Exhaust
Well ID
D3
D4
D5
D13
D14
D3, D4, D5
D3, D4, D5, D14
D13 D14
All
Maximum
Flow
(scfm)
70
9
15
19
19
23
30
35
>250
Maximum
[TCE]
(ppmv)
420
30
14
19
10
150
100
25
11
Figure 1. Lawrence Livermore Site 300 Building 834 soil venting apparatus

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    Pressure  gauge

Temperature  gauge

         Valve

Laminar flow element
Iflowmeterj
Heat exchanger
TCE
output
port 1
t
lmping<
output
port 1
(
I
I
I
i
TC
inp
po
Air-2
3r
Impinger
output
Air-3 P°rts 2,3,4
v2 x
5S
E i Sol
ut IX
rt1 -*- JC
TCE H
Cj/ ^ injection
_^© P2
V3 ^l
V
TCE input
Jb*— Port 2
S> T4 TCE
JC^ 	 output
DO V6 port 2
M ***
^-x X>< I
J 	 V5
X_ 1 V7
^1 f?5 1 ?S3
W ^ XX
^)__ T5 VS
)>-<(_ Heat exchanger
                                                                V1
  Carbon canisters
      Figure 2. Details of plumbing connections to the photoreactors

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Figure 3. Schematic of Air-2 photochemical reactor

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Valve
Xe flashlamp assembly
	 OO Process flow output
>o<-
i
TCEo
septur
TCEi
^ tff
Impinaer ' 	 ' —
ports ill!
'I1
n port ~i — 	 —
i
I
^

nput septum port
1 Valve
	 ^-Process flow input l\)
Cylindrical
photo-reactor
rn I

1 	 -H— T Suprasil lamp
i II !"^ 	 ' 	 *1OUS
N^
[ , 1 1
f \ i|
— 1 	 1 Valve 1 —

oT)
v-\

ing
Xenon
flashlamp

5"


                Figure 4.  Schematic of Air-3 photochemical reactor

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 so that the flow is split through two sets of chambers in series. Some experiments were conducted
 with an enriched TCE air stream by gas injection  from a pressurized liquid TCE-filled stainless
 steel bubbler before the reaction chambers.
        The process flow rate was measured on LFE-2 (Figure 2), a Meriam Model 50 MC2-4
 laminar flow element. Initially, the entire output from the pump was measured by closing valve
 V2, thus sending the entire flow around the reactors and into the carbon cans. The flow was then
 sent through either Air-2 or Air-3 by opening V2. Valve VI was set so part of the flow was sent
 through the bypass. The flow rate through the reactors was thus the difference between the full
 capacity and the residual flow through the bypass  when valve VI was partly closed.
        A typical sampling session involved  setting the process flow rate,  adjusting the TCE
 concentration, and alternately taking  at  least  three input and output TCE samples while
 photolyzing. The impinger samples  were collected during the monitoring of the TCE
 concentration, and were usually run for 30 minutes at a flow rate of approximately 100 mL/min.
 For the sampling performed in Air-2, the impingers were connected to the reactor port by 0.25
 inch i.d. Teflon tubing that was split by a Teflon tee into two sets of impingers. The total length of
 tubing was approximately 1  meter. Even when warmed with heat tape, water tended to condense
 on  the internal surface of the tubing, which  might  have prevented  some of the  reactive compounds
 from reaching the impingers. In order to minimize this problem, the impingers that were used on
 the tests performed on Air-3  had separate connections to the sampling ports that were less than  3
 cm in length.

 TCE
       Trichloroethene  was  analyzed by gas  chromatography  with photoionization detection.
 Samples were drawn by gas tight syringe at  septum sealed sample ports where the process flow
 entered or exited the reactor. They were injected into a Hewlett-Packard model 5890-2 gas
 chromatograph equipped with a 30-m J&W 624 capillary column and a photoionization detector.
 TCE  standards were prepared in volume-calibrated  glass sampling bulbs by injecting  liquid TCE
 into the bulbs. The TCE detection limit was approximately 0.01 ppmv.

DCC
       Dichlorocarbonyl was analyzed by EPA method TO-6 (Winberry et al, 1990). A small
fraction  of the  process stream was split off through  a  Teflon tube into two impingers connected  in
series. The impingers were filled with 30 mL of a  2% v/v aniline/toluene  solution, which reacts
with DCC to give carbanilide. The flow was measured by a rotameter placed after the impingers

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 and before the pump. Volumes were determined by taking the product of the flow rate with the
 acquisition time. The rotameter was calibrated with a bubble flowmeter. Typical flow rates were
 about 100 mL/min, and typical gas volumes sampled were about 3 liters.
        Samples for TO-6 analyses were evaporated to dryness  at 60 °C under a stream of nitrogen
 and taken up in 1 or 10 mL of acetonitrile. Carbanilide was determined by high pressure liquid
 chromatography (HPLC) on a Perkin Elmer 410 instrument with a 15-cm octadecylsilyl column
 and a UV detector set at 254 nm.  The eluent, a 37/63 v/v acetonitrile/water  solution, was run at
 0.3 mL/min. Injections of 5 |lL gave a detection limit of about 0.02 ppmv DCC, when the samples
 were diluted with 10 mL of acetonitrile. The average recovery of carbanilide based upon standard
 samples run through the blow down procedure was 106 ± 19% (95% confidence interval).

 DC AC
       Analyses of dichloroacetyl chloride (DCAC) for experiments in Air-2 were performed as
 part of the TO-6, with care taken to not blow the samples completely to dryness.  Under these
 conditions, DCAC reacts with aniline to form dichloroacetanilide, which was measured by HPLC
 in the same runs as for DCC. The estimated detection limit was 0.1  ppmv DCAC. Recovery
 based upon standard samples run through the blow-down procedure was 104 ± 69%  (95% Cl).
 These large variations in yield were probably a result of volatilization losses, which were
 minimized by not blowing the samples down to complete dryness. However, this approach left
 some aniline in the samples, which gave a large HPLC peak and which may have given a positive
 error in the DCAC  measurement.
       For these reasons the methanol trap method was used in the subsequent testing of Air-3.
 Two methanol impingers were used in series, and flow rates and acquisition volumes were similar
 to the DCC method. The methyl dichloroacetate that formed was analyzed by gas chromatography
 with electrolytic conductivity detection. The detection limit for this  method,  for gas  volumes of
 about 3 liters and 30 mL of methanol in each trap, was approximately 0.05 ppmv DCAC.

 Chloride  and Hvdrolyzable  Chlorine
       Another impinger method was used to measure free     plus the sum of all carbonyl
 chloride bonds, which hydrolyze in water to yield HCI. A set  of three (Air-2) or four (Air-3)
 impingers were tilled with deionized water and  connected in series.  Chloride was analyzed using
EPA method 325.3,  a titrimetric method  using mercury nitrate.
                                           12

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 VOCs
       Volatile organic compounds were analyzed in one set of experiments by EPA method TO-
 14, a whole air sampling method (Winberry, er al., 1990). The evacuated stainless steel
 (SUMMA) canisters, which were obtained from Coast to Coast Analytical Services, San Luis
 Obispo, CA, were filled during an experiment by connecting a 1 -foot long 0.25-inch OD Teflon
 tube to the swagelock fittings  of the canister and the reactor port. Two samples were taken of the
 process flow with and without the lamps operating. A third sample was taken from a 20.0 ppmv
 standard cylinder of TCE obtained from Scott Specialty Gases. After filling, the canisters were
 sent to Coast to Coast Analytical Services for analysis. Agreement was reasonable; the Purus
 analyses agreed with the  standard within 10% and the Coast to Coast analyses within 25% (see
 VOC results below)
                                      SECTION 5


                             RESULTS  AND DISCUSSION

LABORATORY  EXPERIMENTS

Flashlamp Emission Spectrum
       Figure 5 compares the emission spectrum of a 6-inch Purus 3675-W xenon flashlamp with
that of a 7500-W medium pressure mercury lamp taken from the Peroxidation Systems, Inc.
(Tuscon, AZ) literature. The data are presented as the output power integrated over the total area of
the lamp and normalized to the same input power. The xenon flashlamp has a maximum at 230 nm
and significant output at wavelengths as low  as 200 nm, whereas the mercury lamp has most of its
output at wavelengths above 250 nm. Using peroxide actinometry, we determined an overall
electrical efficiency of 18.6% for generation  of light below 300 nm by the Purus lamp, compared
to 11.4% for the commercial Hg lamp used in UV oxidation. For the same power, the flashlamp
allows a seven-fold smaller reaction  chamber  and thus has an advantage in capital costs.  Lamp  life
for both lamps  is  on the order of 1000 hours.
                                          13

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           E
           c
               15
               10
           CD
           o
           0_
           +-•
           Q.
           5    5
                0
 Xe Flashlamp
18.6% <300 nm
Med. Pressure Hg Lamp
    11A % «300 nm
                 180       200       220       240       260
                                       Wavelength  (nm)
                              280
                      300
       Figure 5. Emission spectrum for a mercury lamp vs. a xenon flashlamp. (All lamps
                 corrected to 3675 W input).
       Figure 6 compares the emission spectrum of the flashlamp with the absorption spectra of
several VOCs  (Baulch et a/., 1980, Hubrich and Stuhl, 1980). Note that the lamp spectrum is
given on a linear  scale while the absorption spectra are on a logarithmic scale. The halomethanes
and TCA are weak absorbers, whereas TCE and other chloro-olefins absorb strongly in the deep
UV region. The VOCs all absorb strongly below 200 nm. A shift in peak output from 254 to 230
nm is significant because it corresponds  to a 1 to 2 order of magnitude increase in absorptivity of
many VOCs, thereby greatly enhancing the rates of direct photolysis.

Photolysis Kinetics
       At low total absorbance   0.1) the direct photolysis of a compound results in the
exponential decrease in concentration of the  compound with photolysis  time  (Zepp and Cline,
1977):
                                            14

-------
                                      dt
                                           =   2.3I0 is the  apparent disappearance quantum yield, £ is the
molar extinction  coefficient, 1 is the light pathlength, and [C] is the contaminant concentration.   or
a fixed reactor size and light intensity,  a simple first-order decrease in concentration  of the
photoreactant  with irradiation time  is consistent with a simple  direct photoreaction.  Anon~
exponential decay indicates that the loss of the reactant involves additional reactions whose
efficiency  is  changing  during the photolysis period.
       The photolysis plots shown in Figures 7 and 8 display both exponential and non-
exponential behavior. Compounds whose decay kinetics are first order include benzene, carbon
o
£
8
o
c
 0
-I
               20000
               10000
                 1000

                   100

                    10
                   0.1
.<9    0.01
o
     0.001

   0.0001
                        50
                                                 Lamp
                                                 Spectrum
                                                          CFCI3
                                                      CH2CI2
                                                         0.8
                                                                     0.6
                         200           250
                         Wavelength  (nm)
                                                      300
                                                              co
                                                              c
                                                              CD
                                                              Q.

                                                             I
                                                              CD
                                                         0.4 |
                                                              CD
                                                             DC
                                                                     0.2
                                                                     0
           Figure 6. VOC absorbance spectra compared to xenon flashlamp spectrum.
                                              15

-------
                    1,1,1-TCA^v   "CH2CI2     -1,2-DCA

                                   CCI4
 0.001
                   500          1000         1500
                      Irradiation Time  (seconds)
2000
    Figure 7. Photolysis plots for individual VOCs in the 208-L reactor.
0.01
             12345       6
                 Irradiation Time (seconds)
 7
    Figure 8. Photolysis plots for chloroolefins in the 208-L reactor.
                                16

-------
 tetrachloride,  trichlorofluoromethane,  1,1,1-trichloroethane,  l,2dichloroethane, and 1,1,2-
 trichloro- 1,2,2-trifluoroethane.   Non-first order decays were observed for methylene chloride,
 chloroform, tetrachloroethene, trichloroethene, and 1,1 -dichloroethene. These differences in the
 decay behavior provide evidence that the photolysis mechanism for these sets  of compounds  is
 different.

 Disappearance Quantum Yields
        The magnitude of the quantum yield  () for the elimination of the photoreactant also gives
 some mechanistic information.  The ratio of the disappearance quantum yield divided by the
 primary yield would be unity in the case of  a  direct photoreaction that  contains no subsequent
 reactions that consumes the reactant. This ratio is greater than unity when later dark reactions
 consume additional photoreactant, and is substantially  greater than unity in the  case of a chain
 reaction.
        Table 1 shows apparent wavelength-averaged quantum yields for the compounds studied
 determined using carbon tetrachloride as an  actinometer. From rate equation 1 for disappearance of
 the photoreactant in the low absorbance  limit, the following expression  for the  quantum yield  can
 be  derived:
                                                                                          (2)
Because a broad band source was used for the excitation light, this expression incorporates the
summation over the emission band of the  lamp multiplied with the corresponding extinction
coefficients of  the  compound.  The disappearance quantum yield for carbon tetrachloride was taken
as 1.0, based on the literature data at 214 nm (Rebbert and Ausloos, 1976).   For compounds that
displayed non-first order decay, the quantum yield  was calculated  from the initial rate determined
from the first time  point.

        Comparison of the data in Table 1 and Figures 7 and 8 show that compounds that display
non-first order  decays  also exhibit  apparent quantum  yields greater than unity. These compounds
include CH2C12, CHC13,  TCE, 1,1-DCE, and PCE. Furthermore, the other compounds including
benzene, CCLt, CFC13, 1,1,1-trichloroethane, 1,2-dichloroethane, and  1,1,2-trichloro- 1,2,2-
trifluoroethane,  have decays that are first order and apparent quantum yields near unity.  We
                                              17

-------
 TABLE 1. FIRST ORDER DECAY COEFFICIENTS AND WAVELENGTH-AVERAGED
 DISAPPEARANCE QUANTUM YIELDS WITH A 2.756 kW XENON LAMP
Compound
CCU
CCI2FCCIF2
Benzene
CH2CICH2CI
CFCI3
CCI3CH3
CH2CI2
CHCI3
1 ,1-DCE
PCE
TCE
TCE + ethene
k (sec'1)*
0.00432
0.00093
0.0019
0.0024
0.0036
0.0041
0.0070
0.0366
1.24
1.7
5.5
0.075
^-* * CwM
2A£x
Zi V^^C
'XEx
1 .0
5.09
0.067
N.D.#
1.18
0.79
4.60
1.79
0.0389
0.0134
0.0236
0.0236
KKE

1.0
0.22
0.44
N.D.
0.84
0.94
1.62
8.47
287
394
1300
17
Apparent

-------
Although the reactions in their studies were initiated by Cl2 sensitization as opposed to  direct
photodissociation, similar chain propagation steps should occur in both cases. Because most of
the oxidation takes place  in the chain steps, the types of products formed are essentially
independent of whether the chain is initiated by  direct photolysis or Cl;! photolysis. In the case of
TCE, the main carbon containing products were shown to be dichloroacetyl chloride (DCAC),
dichlorocarbonyl @CC), and carbon monoxide (Sanhuenza et al, 1976). Chloroform, carbon
tetrachloride,  and uichloroethylene oxide  were also identified but at much lower yields
(Huybrechts and Meyers, 1966). Adopting their mechanisms  as the most probable, we propose
the following mechanisms  for VOC photo-oxidation in  air:

       The pathways for photo-induced  chain reactions are consistent with the  observed decrease
in efficiency  as the reactant concentration drops,  because the fourth steps have a second order
dependence on  the concentration of the  peroxy radical  intermediate. As their concentration drops,
they become more likely to react in other ways that do not regenerate CK
                         TCE Photo-induced Chain Reaction
                     HC1C=CC12  +  hv  	»HC1C=CC1' +  Cl'
                        Cl'  +  HC1C=CC12	»HCl2C-CCl2*
                      HC12C-CC12*  +  O2 	> HC12C-CC1200»
                    2HC12C-CC12OO" 	> 2HC12C-CC12O*  +  C>
                    HC12C-CC12O*	>HC12C-CC1O +  Cl'
                                           (DCAC)

                       CH2C12 Photo-induced  Chain  Reaction
                         CH2C12  + hv  	>CH2C1* +   Cl'
                        C1'   +  CH2C12	> CHC12' + HC1
                           CHC12*  +  O2 	> CHC1200*
                         2CHC12OO* 	> 2CHC12O*  +  O2
                                      >  HCOCI   +   Cl'  	»
                                     (formyl  chloride)
                                          19

-------
                               TCA Non-chain  Photolysis
                        H3C-CC13 + hv 	> H3C-CCl2* +  C 1 '
                        C 1'   +  C13C-CH3	> C13C-CH2* + HC1
                          C13C-CH2*  +   O2 	>  C13C-CH200
                        2C13C-CH2OO*  	> 2C13C-CH2O'   +   O2
                       C13C-CH2O*  + O2	> C13C-CHO  +
                                             (trichloroacetaldehyde)
       A common feature  of the mechanisms for TCE and methylene chloride is  that O atom
reacts with them to generate a carbon-centered radical that has chlorine substitution. These carbon-
centered radicals are then oxidized in two steps to alkoxy radicals that can then cleave a  O atom
and propagate the chain. By contrast, the carbon radical formed from TCA has no chlorine
substitution and upon oxidation it can only cleave H02» instead of CK H02* is a much less
reactive radical  and engages predominantly in termination  steps with itself and other radicals. All
the compounds  listed in  Table  1 fit this general rule, with  the exception of 1,2-DCA.  1,2-DCA
appears  to deviate from  the rule because it gave first-order photo-oxidation kinetics,  but the
quantum yield is yet undetermined and may still prove to be greater than one. Cl» atoms do not
react with C-C1 or C-F bonds and therefore freons and perchloroalkanes will not form a chain.

Photolysis of Chloro-olefin Mixtures
       As a further test  of the occurrence of a chain reaction with TCE,  we photolyzed TCE in the
presence of a 500-fold molar excess of ethene as a Cl* atom scavenger.  Because  ethene contains
no chlorine, it cannot propagate a Cl* atom chain. Figure 9 and Table 1  show that the ethene
decreased the TCE photolysis rate  by a factor of about 75.  Moreover, the rate constant in the
absence  of ethene decreased with time  until at very long times  ([TCE]     ppmv) it approached the
rate constant in the presence of ethene (data not shown). Under both of these conditions chain
propagation is inefficient  and therefore we believe that the  reaction observed in these  cases  is
predominantly direct photolysis.
                                            20

-------
             c
             o
             I
             o
            O
             0)
            QC
               0.01
                         1:500
                      TCE:Ethene
                               10        20         30         40
                                    Irradiation  Time  (seconds)
              Figure 9. Chlorine atom scavenging with ethene in the 208-L reactor
       Figure 10 shows a photolysis experiment with an equimolar mixture of TCE and  1  ,1 -DCE.
Comparing these results with those presented in Figure 8 shows that in the mixture the rate of TCE
loss is slightly reduced but the rate of 1,1-DCE loss is considerably enhanced. We interpret this to
be a result of photo-initiation predominantly by TCE because  it absorbs UV light more strongly,
but with chain propagation predominantly by 1,1-DCE because it reacts with chlorine atoms more
rapidly (Atkinson and Aschmann, 1987):
        cr   +  H2c=cci2
      cr  + HCic=cci2
> HC1C-CC12*    kocE =  14 x 10-11cm3molec-1s-1
 HC12C-CC12' kTCE =  8.1  x  10'11 cm3 molec-1 s"
When chains are long compared to the primary photolysis event, the relative rates of loss of 1,1-
DCE and TCE should be in the same ratio as their Cl» atom reaction rate constants of 14/8.1=1.7.
This value is in good agreement with the observed ratio of rates of 1.5 and presents further
evidence that Cl» atom is the rate-limiting oxidant in the system.
       The  experiments with olefin  mixtures demonstrate that  co-contaminants can cause both
                                            21

-------
 sensitization and inhibition of photolysis. Increasing chlorine substitution on the olefin results in
 stronger light absorption and thus more rapid chain initiation. On the other hand, greater chlorine
 substitution decreases the rate of the propagation reaction with O atom thereby reducing chain
 length. Finally, as chlorine substitution decreases, the statistical chance of regenerating a free O
 atom and propagating a chain drops sharply. Thus, TCE and PCE can be expected to sensitize the
 photo-oxidation of the dichloroethene isomers and vinyl  chloride  because the former are better light
 absorbers and the latter react with Cl* atom more readily. However, addition of chloroolefins will
 not sensitize  the  photoreactions of the chain promoters  chloroform  and dichloromethane, because
 the chloroolefins enhance the rate of Cl* atom scavenging as well as production.  In principle, any
 chlorocarbon that  photolyzes to form Cl*  atom  can  be expected to sensitize the  oxidation of another
 hydrocarbon, although the effect will be small if a chain  reaction is not sustained or the reaction
 rate constant between Cl* atom and the hydrocarbon is low compared to that between Cl* atom and
 its precursor.

 Photo-oxidation Products of TCE
       Some products of the  photo-oxidation of TCE in  air were investigated by irradiating TCE in
 a Teflon-sealed, quartz  spectrophotometer  cell, to allow  efficient  collection of the reactive  products.
 Methanol was  injected into the  cell  following  irradiation, which  derivatized the  main  oxidation
 product DCAC to methyl dichloroacetate (MDCA). Analysis by GC/MS of the methanol solution
 revealed that at low UV doses, DCAC (measured as MDCA)  was formed at a yield exceeding 90
 mole % from TCE. The identity of MDCA peak was verified by mass spectrometry.
 Trichloroacetyl chloride (measured as methyl trichloroacetate) was also identified by GC/MS but
 the yield was < 2% of the DCAC yield based on the relative  ion signal. Further photolysis of TCE
 in air revealed an approximately exponential decrease in the DCAC concentration (Figure 11). The
pattern of the TCAC concentration suggests that it is formed  from DCAC but then also  photolyzes.

DCAC Photo-oxidation
       Because the main intermediate product from  TCE photo-oxidation  is dichloroaceryl
chloride, subsequent products are largely determined by the photochemistry of DCAC. One
product formed from the photo-oxidation of DCAC is DCC,  as shown in Figure 12. Note that
these experiments  were  conducted  by starting with DCAC instead of TCE in  the  specuophotometer
cell, and measuring the yield of DCC in the absence and presence of added Cl2 gas. The DCC
                                            22

-------
      1000
                                    Cl  +  IJ-DCE 	t>k = 14e-11
                                    CI + TCE  	>  k = 8e-11
    Q.
    Q.
    2
    •t-^

    CD
    O
    O
    o
                                                           TCE
                              Irradiation  Time (seconds)
     Figure 10.  Photolysis of TCE and 1,1-DCE as a mixture in the 208-L reactor
                               ,  ... i  i i  i  i i  i i  i i  i i  i i  . t  i i
        0.001
              0       5      10     15     20      25     30      35

                             Irradiation Time  (seconds)


Figure 11. Product yields from the photo-oxidation of TCE in the spectrophotometer cell
                                    23

-------
                             10
  20       30       40        50
Irradiation Time (seconds)
     Figure 12. DCC yields from the photo-oxidation of DCAC in the spectrophotometer cell
yield increases slowly to about 15 mole % and then begins to decrease with light dose. Addition of
chlorine greatly increases the DCC yield by a factor of 24 when a 3.7:  1 mole ratio of  C\2 to DCAC
is photolyzed for 7 seconds. Its formation might be caused by chlorine atom attack upon DCAC:
                   c r  + ci2HC-C(O)Ci -
                              DCAQ
                       C1(O)C-C12C'  +  O2
                    2  Cl(O)C-Cl2COO*	3
                         Cl(O)C-Cl2CO* 	
        —-> C1(O)C-C12C* +  HC1
        	> Cl(O)C-Cl2COO'
        O2 +  2 C1(0)C-C12CO*
        >  CbCO  +  OC1C
          (DCC)
       The low of DCC suggests that it is either photolyzed  simultaneous with its  production from
DCAC, or that an additional DCAC reaction pathway exists that does not lead to DCC, or both. A
possible additional  mechanism involves  photolytic cleavage of the  chlorine-carbonyl bond followed
by reaction with oxygen:
                                           24

-------
                    hv  +  Cl2HC-C(O)Cl	>Cl2HC-C(Or  +  Cl'
                       C12HC-C(O)*  +  02  	> C12HC-C(O)00*
                     2 C12HC-C(O)OO*	> O2 +  2 C12HC-C(O)O'
                          C12HC-C(0)0«	>C12HC*  +  CO;!
                             C12HC'  +  O2  	» C12HCOO»
                          2  C12HCOO'	> 02+2 C12HCO*
                             C12HCO'	»C1HCO  +  Cl'
                                         (formyl   chloride)
This mechanism  predicts CO2 and formyl chloride  as the carbon-containing products.  A
preliminary CO2 measurement in the 208-L pilot reactor indicated ^ 50% yield of C02 after 170
seconds of irradiation. Formyl chloride was not analyzed for, but it is the most likely missing
product because it contains only hydrolyzable chlorine. The field data  described below indicate
that all of the chlorine not accounted for by DCAC is readily hydrolyzable, i.e., forms Cl- rapidly
on reaction with water. Formyl chloride hydrolyzes to give formic acid and HC1.

FIELD EXPERIMENTS
       TCE disappearance data and product data from Air-2 and Air-3, are given in the Appendix.
Most of the  discussion will be limited to  results from Air-3, because sampling conducted during
the  testing of Air-2 was impaired by high  moisture levels in the system.  Because the two principal
oxidation products, DCAC and DCC, could react with water prior to sampling, they were readily
lost on the reactor surface and sampling tubing. Measurements of TCE concentrations should not
be influenced by this problem, however. As described in the Methods section, these difficulties
were overcome before sampling for Air-3 measurements were begun.

TCE Removal Effkiencv
       Over the range of  experimental variables covered,  aichloroethene was  photo-oxidized to
>99% conversion except at the lowest flash frequencies and number of lamps. The tables in the
Appendix give the extent  of  conversion under the different experimental  conditions.  Under the
highest exposures and optimal conditions, conversions of 99.9996% were achieved. Estimation of
the  loss of trichloroethene  was limited by  the 0.01 ppmv detection limit of the  gas chromatographic
method.
                                           25

-------
Measured  TCE  Oxidation Products
       Figure 13 shows the evolution of products during the photolysis of TCE in Air-3 at the
field site. In order to  compare total exposure levels in each reactor and to factor in flash frequency
and process flow rate, a dose was calculated under each set of experimental conditions, defined as:
          Dose = Residence time x Flash frequency x No.  of lamps x Energy/flash      (3)

In the case of Air-3 the dose was calculated assuming two lamps, since the flow was split off and
sent through two reactors in series. Again, the principal organic product from the  TCE photo-
oxidation observed in the field studies was dichloroacetyl chloride. At the lower exposure range
(1.2 kJ dose) that is just sufficient to eliminate TCE, a conversion of 86 mole % DCAC and 6.9
mole % DCC was observed in Air-3. At a dose of about 70 kJ, we found a 28 mole % conversion
to DCAC and 23 mole % to DCC. As the dose was increased, by increasing either  the residence
time or the flash frequency, the DCAC yield fell off exponentially (Figure 13), and the DCC
concentration increased. The DCC yield did not equal the DCAC loss, presumably because of
concomitant DCC photolysis or other pathways for DCAC loss, as observed in the laboratory
studies.
                      10      20      30      40       50      60      70      80
                                          Dose (kjoules)
                                           26

-------
                 Figure 13. Product yields from the photolysis of TCE in Air-3
        A mass balance for chlorine can be estimated by using the yield obtained for DCAC  and the
 total chloride yield. If, as the evidence suggests, DCAC is the only organic product with non-
 hydrolyzable chlorine atoms, then the chlorine mass balance may be calculated as follows:

 Fraction chlorine recovered = (moles chloride + 2 x moles DCAC) / (3 x moles TCE lost)  (4)

 The chlorine recoveries taken from Air-3 ranged from 79 mole % to 115 mole %  with the  average
 about 93 ± 23 % (95% confidence interval). This high yield is constant throughout the
 experiment, as can be seen in Figure 1. Within the uncertainty of these measurements most of the
 chlorine is accounted for, indicating that all the  chlorine  other than one of those in  DCAC is in
 hydrolyzable form such as in DCC or formyl chloride.  The chlorine balance in Air-2 experiments
 was more variable due to the higher humidity, causing sampling loss, as mentioned above.
       The  excellent chlorine balance implies that products such as carbon tetrachloride and
 chloroform, which have been detected previously in TCE photo-oxidation (Huybrechts and
 Meyers, 1966), are present in very low yield in our system. The TO-14 whole air  sampling rest
 results given in Table 2 confirm this. The chloroform yield was found to be 0.65  % of the TCE
 input, and the carbon tetrachloride yield 0.15%, and the methylene chloride yield 0.05%.
       A mass balance for carbon cannot be determined based  upon the measurements performed
 in this study. Potential carbon containing products from TCE photo-oxidation that were not
 examined in detail  include CO, CO2» formyl chloride and trichloroethylene oxide.
TABLE 2. TO-14 ANALYSIS SAMPLED ON 28 JAN 1992 AT 30 HZ FROM AIR-2
Sample
Input
output
20 ppmv
Standard
CCI4
(ppmv)
<0.002*
0.200
<0.001
CHCI3
(ppmv)
<0.005
0.840
<0.001
CH2CI2
(ppmv)
<0.050
0.070
<0.01 0
PCE
(ppmv)
0.150 [0.002]*
0.002
<0.001
TCE
(ppmv)
130.0 [0.002]
(182)t
0.024 [O.OOI]
(0.06)
15.0 [0.001]
(18.3)
* Values in brackets or given as upper limits are detection limits.  Detection limits for the output samples
 were the same as for the 20 ppmv standard.
t Values in parentheses were determined  by Purus.

                                            27

-------
 ESTIMATION OF PARAMETERS TO ACHIEVE RECOMMENDED  TREATMENT  LEVELS
 ATLLNL SITE  300
       Because of the formation of toxic products, the efficacy of treatment at LLNL Site 3OO
 cannot be measured simply in terms of TCE removal. Table 3 lists exposure limits for TCE  and its
 photo-oxidation products, as estimated by Environ Corp., a consulting firm in Emeryville, CA
 (Tsai and Libicki, 1992). The estimate for DCAC assumes that this compound hydrolyzes  rapidly
 in the environment or respiratory tract and thus has the same long-term toxiciry as DCAA.  It is
 clear from Table  3 that the major products are  more toxic than TCE and thus would need to  be
 removed by further photolysis or other post-treatment before emission to the atmosphere.
       TABLE 3. EXPOSURE LIMITS FOR TCE AND ITS PHOTO-OXIDATION PRODUCTS

                                              Worker Exposure Limit'
                     Chemical
TCE
DCAC
DCAA
DCC
c o
26.8
0.68
0.68
12
20.6
        Based on a lifetime cancer risk level 10~5
       Because the toxicity of DCAA is 40 times greater than that of TCE (Tsai and Libicki,
1992), the most DCAC one can emit is 1/4000 times the initial TCE concentration, or at most
0.025% DCAC remaining, to reach the goal of 99% reduction in initial toxicity. Similarly, the
concentration of DCC would need to be less  than 0.45% of the initial TCE concentration.  To
estimate the exposure time necessary to reach the required  concentration of DCAC, an  extrapolation
must be made because no conditions used in this study reached these treatment goals. To do this
we assume an exponential decrease with dose, as supported by the data over the parameters studied
(Figures 11 and 13):
                                                 -                                   (5)

where Y = relative concentration, k = first order rate coefficient, and t = time. Because we want to

                                           28

-------
 substitute for the dose, we let dose = Intensity (kJoules/sec) x time (sec), thus:
                                     Y(t) = Y(o) e'^)0                                 (6)

 where D = dose and I = intensity.
        Two important assumptions are made in deriving this expression. The first is that DCAC
 destruction is always first order, which may only be a good approximation if the mechanism for its
 removal is direct phdtolysis. This is not be the only possibility because preliminary experiments
 with added chlorine gas indicated that chlorine  atom attack on DCAC can occur also. The  second
 assumption is that DCAC is  created instantly at zero  time, which is a reasonable approximation
 when the rates of appearance and disappearance of DCAC are compared.
       Table 4 gives the result of this extrapolation along with the first order rate constants
 obtained from the fits to three sets of data. The fit to data from Air-2 data includes only the highest
 yields over the dose range, because lower yields may have resulted from poor sampling recovery
 caused by water reactions. The data indicate that a flow rate of 13 - 20 cfm in Air-2 or Air-3 with
 four 3.7-kW lamps can achieve the desired DCAC reduction.
TABLE 4. TREATMENT PARAMETERS FOR 99% REDUCTION IN TOXICITY BY UV ALONE
AT LLNL SITE 300

Data Source for
Extrapolation
30 Hz Air-3
All Air-3
Highest Air-2

k
(sec'1)
0.128
0.111
0.0267
Calculated
Residence
Time
(seconds)
65
74.8
301
Calculated
Process Flow
(cfm)
15.2
13.2
20.2

TCE Input
Concentration
(ppmv)
30
30
30
       Insufficient  data are available to determine if the DCC concentration would be low enough
when the DCAC treatment goal is reached. DCC could easily be removed with a water scrubber,
where it would rapidly hydrolyze to CO2 and HC1. However, traces of DCAC would also
hydrolyze to dichloroacetic acid (DCAA) and HC1 and, depending on the water flow, the residual
                                            29

-------
 DCAA would still be at least an order of magnitude above the proposed drinking water limit of 0.2

 ppb (Bull R, University of Washington, personal communication, 1991). A relatively dry

 scrubber, such as slaked lime is a possibility because it would trap both DCC and DCAC.

 However, DCAA is likely to leach out when the lime is landfilled. Promising approaches include

 using very small flows of water and treating them by incineration or other thermal processes.
                                     REFERENCES
Atkinson R; Aschmann S.A. Int. J.  Chem. Kinet. 1987,19, 1097,

Baulch D.L.; Cox R.A.; Hampson R.F.; Kerr J.A.; Troe J.; Watson RT. /. Phys. Chem. Ref.
     Data 1980,9,  295.

Blystone P.; Johnson M.; Haag, W.R. Advanced ultraviolet flashlamps for the destruction of
     organic contaminants in air, ACS  Symposium Series, 1992, presented at the ACS I & EC
     Division  Special Symposium, Atlanta, Ga., Oct 1-3, 1991.

EG&G Publication Flashlamp Applications Manual 1988.

Hubnch C; Stuhl F. /.  Photochem.  1980, 12, 93-107

Huybrechts G.; Meyers L. Gas-phase  chlorine-sensitized oxidation of trichloroethylene,
     Transactions of the Faraday Society, 1966,62,2 191.

Nicole I; De Laat I; Dore M.; Duguet IP.; Bonnel C. Water Res. 1990,24, 157.

Phillips, R. Sources and Applications of Ultraviolet Radiation; Academic Press, 1963.

Rebbert RE.; Ausloos P.J.  /. Photochem. 1976/77,6, 265.

Sanhueza E.; Hisatsune I.C.; Heicklen J.  Chem. Rev. 1976, 76, 801

Tsai P.; Libicki S. Environ Corporation Report to Purus, 1992.

Winberry W. T.; Murphy N. T.; Riggan R. M. "Methods  for Determination of Toxic Organic
     Compounds in Air, EPA Methods", Noyes Data Corporation, Park Ridge, New Jersey,
     1990. 153.

Zepp R.G.; Clme D.M. Environ. Sci. Technol 1977, II, 359.
                                          30

-------
      APPENDIX A
TABLE A-l. AIR-2 RESULTS
Res. [TCE] [TC E]
Rrea. No. of Flow Time input output
(HZ) Lamps (cfm) (sec) (ppmv) (ppmv)
4
4
4
4
4
4
4
4
4
4
4
4
4
4
2
2
4
2
4
4
4
4
4
4
2
4
2
21 .0
23.3
30.5
62.5
58.8
56.6
58.3
58.3
59.4
20.6
23.3
30.5
73.9
58.3
57.7
57.7
57.7
57.7
20.6
23.3
30.6
57.7
56.6
57.7
57.7
57.7
57.7
256
138
144
210
31.8
843
10600
182
29.9
113
138
149
246
166
1575
78.1
1562
1562
132
134
167
148
113
84.9
84.9
1236
1236
4.34
dl
0.082
dl
0.28
0.13
0.038
0.06
dl
dl
0.34
0.21
dl
0.06
0.06
dl
0.05
0.06
dl
0.69
1.9
0.33
0.41
dl
0.87
0.13
278
TCE
Destruction
(%)
98.3047
> 99.99
99.94 1
> 99.995
99.1195
99.9846
99.9996
99.96 0
> 99.97
> 99.99
99.7536
99.8591
> 99.995
99.9639
99.9962
> 99.99
99.9968
99.9962
> 99.99
99.4851
98.8623
99.7770
99.6372
> 99.99
98.9753
99.9895
97.7508
DCC
Yield
(ppmv)
26.2
26.7
33.2
186.5
4.2
418
959
112
nd
13
15.2
36.1
167
114
nd
nd
nd
nd
12.5
11.6
24.4
16.6
56.1
nd
nd
nd
nd
DCAC
Yield
(ppmv)
9.6
41.9
4.5
29.5
0.6
4.2
42.5
4
nd
4.5
36.6
63.7
60.7
5.2
nd
nd
nd
nd
40.8
33.6
80.9
12.4
40.5
nd
nd
nd
nd
Mole %
DCC
10.2
19.3
23.1
88.8
13.2
49.6
9.0
61.5
nd
11.5
11.0
24.2
67.9
68.7
nd
nd
nd
nd
9.5
8.7
14.6
11.2
49.6
nd
nd
nd
nd
Chlorine
Mole % Mole Balance
DCAC Cl ( Mole %)
3.8
30.4
3.1
14.0
1.9
0.5
0.4
2.2
nd
4.0
26.5
42.8
24.7
3.1
nd
nd
nd
nd
30.9
25.1
48.4
8.4
35.8
nd
nd
nd
nd
16.2
47.8
28.0
61.7
28.7
75.1
6.6
76.8
nd
26.3
34.7
33.5
42.9
57.3
nd
nd
nd
nd
12.1
34.8
28.6
17.1
76.8
nd
nd
nd
nd
18.7
68.0
30.1
71 .1
30.0
75.4
6.9
78.3
nd
29.0
52.4
62.0
59.3
59.4
nd
nd
nd
nd
32.7
51.5
60.9
22.7
100.7
nd
nd
nd
nd

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TABLE A-l. (CONT.'D)  AIR-2 RESULTS
Freq. No. of Flow
(Hz) Lamps (cfm)
4
4
4
4
4
4
4
4
4
4
2
4
2






















Res. [TCE] [TCE] TCE
Time input output Destruction
(sec) (ppmv) (ppmv) (%)
21.3
23.3
31.1
53.2
58.8
59.4
61.2
56.6
58.3
57.7
57.7
57.7
57.7
149
149
115
147
40.2
34.8
773
109
23.6
35.1
25
7.9
0.96
0.37
166
55
3120 1330
105
105
1466
1466
22.8
31.7
429
596
84
76
78
94
97
98
78
49
57
78
69
70
59
TABLE
Freq, No. of
(Hz) Chambers










4
4
4
2
4
2
4
2
4
2
Fiow
(cfm)
103
97
95
106
97
103
95
103
106
103
Res.
Time
(sec)
9.6
10.1
10.4
4,6
10.1
4.6
10.4
4.6
9.3
4.8
[TCE]
input
(ppmv)
76.4
108.5
98.3
91.7
106.8
101.3
104.9
101.4
101.7
96.5
[TCE]
output
(ppmv)
dl
di
dl
0.07
dl
dl
dl
dl
0.65
13.23










.1611
.4430
.2609
.6259
.6119
.9368
.5252
.5413
.3718
.2857
.8095
.7367
.3452
DCC DCAC Chlorine
Yield Yield Mole % Mole % Mole % Balance
(ppmv) (ppmv) DCC DCAC Cr (Mole%)
7.1 10.3 4.8
10.5 17 7.0
18.1 82.2 15.7
7.9 24.4 5.4
3.1 6.7 7.7
nd nd nd
100.5 120.9 13.0
49.3 76.7 45.2
113 226 3.6
nd nd nd
nd nd nd
nd nd nd
nd nd nd
6.9
11.4
71.5
16.6
16.7
nd
15.6
70.4
7.2
nd
nd
nd
nd
6.8
13.9
35.9
30.9
23.0
nd
36.9
85.6
8.9
nd
nd
nd
nd
11.4
21.5
83.6
42.0
34.1
nd
47.3
132.5
13.7
nd
nd
nd
nd
A-2. AIR-3 RESULTS
TCE DCC DCAC Chlorine
Destruction Yield Yiefd Mole % Mote % Mole % Balance
(%) (ppmv) (ppmv) DCC DCAC C!' (Mole%)
> 9999
> 99.99
> 99.99
99.92
> 99.99
> 99.99
> 99.99
S99.99
99 '16
86.57
nd 20.2 nd
21.3 265 19.6
25.6 34 26.0
15.9 49.2 17.3
22.8 nd 21.3
12.6 65.3 12.4
8.7 75.7 8.3
9.4 76.3 9 3
12.5 83.2 12.3
6.8 84.9 6,9
25.6
24.4
34.6
53.7
nd
64.5
72.2
75.2
81.8
8.6 2
61.6
89.9
91.4
55.3
68.2
43.2
41.9
36.6
35.8
358
78.8
106.2
114.5
91 .1
nd
86.2
90.0
88.8
90.3
93 3

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