United States
                                  Environmental Protection
                                   Industrial Environmental Research
                                   Cincinnati OH 45268
                                  Research and Development
                                  EPA-600/S2-81-066  Sept 1981
Project  Summary
                                  Wood  Preserving   Industry
                                  Multimedia  Emission
                                  Bruce DaRos, Bill Fitch, Carole Franklin, Mike Friedman, Richard Merrill, and
                                  Dean Wolbach
                                    Restriction of wastewater discharge
                                  generated during the preservation of
                                  wood has resulted in the increased use
                                  of evaporation techniques by  the
                                  wood preserving industry. The Project
                                  Report that is summarized here  dis-
                                  cusses emissions that may occur during
                                  evaporation and projects the pollutant
                                  burden on the environment. The in-
                                  formation presented in the full report
                                  includes a description of the wood
                                  preserving industry, its products,  the
                                  regulations impacting its emissions,
                                  and the nature of its emissions.  The
                                  application of preservatives is discussed
                                  in detail  and includes discussions of
                                  the waste streams generated during
                                  the treatment process. Disposal of the
                                  generated wastewater is the primary
                                  topic of discussion, supported by
                                  laboratory  and field sampling data.
                                  The measured emissions are compared
                                  to evaporation models, followed by an
                                  industry wide projection of the emis-
                                  sion of organics if evaporation is used
                                  for the disposal of wastewater. The
                                  impact of regulations on future emis-
                                  sion rates is also projected.
                                   The primary conclusion of this work
                                  is that organic compounds are emitted
                                  to the atmosphere during evaporation.
                                  The rate of release is based on the type
                                  of evaporation system used: solar
                                  ponds, thermal (pan) evaporators,
                                  spray ponds, or cooling towers;  the
                                  temperature (thermal) driving force
                                  used; the molecular weight and vola-
                                  tility of the substances; and the con-
                                  centration of each component in solu-
                                  tion following wastewater pretreat-
                                    This Project Summary was devel-
                                  oped by  EPA's  Industrial  Environ-
                                  mental Research Laboratory, Research
                                  Triangle Park, NC. to announce key
                                  findings of the research project that is
                                  fully documented in a separate report
                                  of the same title (see Project Report
                                  ordering information at back}.

                                    There are approximately 475 wood
                                  preserving plants in the United States
                                  The principal product of these plants is
                                  chemically treated wood for use  as
                                  utility poles, railroad ties, and construc-
                                  tion materials. Chemicals used to treat
                                  the wood are toxic, and waste  from
                                  these plants can cause environmental
                                    Wastewaters are generated  as a
                                  result of the preservatives used, plant
                                  operations, surface runoff, and excess
                                  process water discharge. Solid residues
                                  include waste sludges from wastewater
                                  treatment, insoluble inorganic materials
                                  from waterborne salts, and contaminated
                                  soils from spills or drippage. Air emis-
                                  sions result when the retort is opened
                                  during charge change or from the vacuum
                                  vents. Other air emissions occur during
                                  wastewater evaporation processes
                                    Industry's technical response to re-
                                  quirements for control of process waste-

water has included increased recycling
and evaporation of water using thermal
evaporators, spray and solar ponds, and
cooling towers to decrease aqueous
discharges. The primary purpose of this
program  is to determine  if organic
chemicals are emitted to the atmosphere
during evaporation and to quantitate
                           these emissions. Table 1 summarizes
                           this program.

                             Organic constituents contained in
                           wastewater from pressurized wood
                           preserving processes using organic
                           preservatives can be  emitted to the
atmosphere during wastewater evapo-
  Thermal (pan) evaporation tests
showed that fractions of the organic
constituents present, including penta,
naphthalene,  chemical phenol, and
other nonvolatile organics were dis-
charged to the atmosphere.  Cooling
Table 1.     Summary Information
 Process of Concern—Pressure treating with organic preservatives.

 Pollutants—Polynuclear aromatic hydrocarbons (i.e., naphthalene), chlorinated phenolic compounds (i.e., pentachlorophenol),
            waterborne inorganic salts.

 Pollutant Media—Air emissions, wastewater, waste solids.

 Multimedia Emission Points—Vacuum vent, retort charge changes, charge cooling, open process vessels, wastewater evaporation,
            condensed retort discharge during treating cycle, surface runoff, boiler blowdown. wastewater treatment
            processes, contaminated soils, housekeeping wastes.

 Purpose of Work Conducted—To evaluate organic emissions to the air during wastewater evaporation and quantitate multimedia
            environmental impacts.

 Predictive Models—Surface vaporation model based on Pick's law of evaporation. Droplet evaporation based on free falling
            drop evaporation. Verification with laboratory and field testing programs.


                                   Thermal (Pan) Evaporation Concentrations (mg/l)
Temperature pH



Filter Water Air
Cake Evaporated Emission
1 6
Rate (gmoles/hr-m2)
5.28 x 10'&
5.36 x 10~7
1.15* 10~5
1.07 x 10's

3.44 x 10~*
8.92 x 10'3
1.11 x 10'3
4.25 x 10~*

—Droplet evaporation models predict 1.9x 10 6 and 1x10 8 gmoles/min versus 7.2 x 1O~5and1.2x
phenol and penta.
                                                                                                     measured for
 Magnitude of Problem — Potential increase in organic emissions if forced evaporation at elevated temperature is
            technology employed.

 Value of Results — Confirmed release of organics during processing and has led to method of evaluation of potential organic
            emissions from point sources.

tower tests showed that phenol was the
only organic material emitted in the air
stream. The cooling tower represents a
lower  source of  emissions than the
thermal (pan) evaporator and may be
lower  than spray pond systems  (not
tested) because atomization and drift
are expected to be less.
  The  effect  of molecular  weight on
evaporation losses was also determined
As the molecular weight increased, the
potential for evaporation decreased. As
thermal  driving force increased,
increasingly higher molecular weight
substances were evaporated. Acidifying
the wastewater (to pH 2), coupled with
filtration, significantly reduced the
volume of organic material available for
  On an  industry-wide basis, it is
projected that approximately 20,000
kg/yr of organic  material may be dis-
charged to the atmosphere when waste-
water  is evaporated. These emissions
primarily consist of volatile organics. If
thermal evaporation  techniques are
used, the emission rate will be increased
as the nonvolatile components are dis-
charged. The projected use of creosote is
expected to decline slightly and penta
and  waterborne  preservatives  to in-
crease slightly, resulting in the continued
emission of organics to the atmosphere
for the  near-term  future. Other potenti-
ally greater sources of organic emissions
to the  atmosphere (from the retort and
vacuum vents) were not tested during
this  program.

  To better qualify the mass emissions
from wood treating  sources, it is
recommended that sampling and anal-
ysis studies be  initiated to further
evaluate the fraction of organic emis-
sions from thermal evaporation devices
and  spray ponds. The data  collected
should be used to further evaluate the
effects of solution pH, molecular weight,
and  thermal driving force for each
evaporation device applicable to waste-
water disposal. In addition, tests char-
acterizing fugitive emissions should
also  be conducted. This is especially
necessary for gases discharged at ele-
vated temperature and pressure,  and
those that have come in contact with the
preservatives. Fugitive emission sources
include vacuum vents, hoods, retort
doors, and storage vessels.
  To qualitatively determine each com-
ponent  potentially discharged during
the evaporation of wastewater contain-
ing creosote, careful separation of
creosote into basic, acidic, and neutral
extractables should  be conducted to
identify  the  species  present in the
coaltar-derived mixture. Other analytical
activities include the disappearance of
OCDD during cold storage. In addition,
analytical work to qualitatively identify
organic components contained in surface
runoff should be conducted.
  Solar  evaporation  ponds,  the  most
widely used evaporation devices, should
be tested  to confirm the release of
volatile components. Other field testing
activities recommended include the
evaluation of oil-water separators. This
work should be directed to yield informa-
tion to maximize the removal of free oils
from the wastewater, ultimately reducing
the emission of organic species.

Industry  Profile
  Presently, the wood preserving
industry  uses three types of  preserva-
tives:  creosote, waterbprne salts, and
penta. While research concerning new
preservatives or alternate meth'ods is
continuing, new preservatives are not
considered realistic options for the near
term  due to long  periods  of required

Preservative Usage and
Industrial Growth
  Creosote is a distillate of coal tar. It is
a mixture of many compounds, mostly
aromatic hydrocarbons. As a wood
preservative, it is primarily used to
improve the weathering characteristics
of wood, provide protection from insects
and fungi, and promote  insolubility in
water. The primary disadvantages of
creosote-treated wood products are
color,  odor, oily unpaintable  surfaces,
and tendency to bleed.
  Penta is a crystalline compound
dissolved in light petroleum oil. Wood
treated with penta is resistant to insects
and fungi and is more paintable  than
  Waterborne preservatives are com-
pounds of arsenic, chromium, copper,
zinc, and fluoride. The principal pre-
servatives  include  chromated  copper
arsenate (CCA), fluor-chrome-arsenate-
phenol (FCAP), chromated zinc chloride,
and acid copper ohromate. They produce
a clean, odorless, paintable product.
One disadvantage is that the wood  must
be dried before it is treated rather than
using  a simultaneous processing step.
  A projection of 0.2 percent/year will
be used to describe the  growth of the
wood treating industry. Within that
sector, creosote is projected to decrease
at a rate of 1.5 percent/year and penta
and waterborne salts will increase at a
rate of 6.8 percent/year and 5.8 percent/
year, respectively. These projections are
based on historical consumption data
and do  not reflect future regulation  of
waste streams or preservation use.

Regulation Review
   The Federal Water  Pollution Control
Act (FWPCA) of 1972, as amended  by
the Clean Water Act of 1977, and the
Resource Conservation and Recovery
Act (RCRA) of  1976 are the two primary
federal  laws carried  out by EPA that
regulate the effluent and sludge disposal
practices of the wood preserving industry.
Overlapping laws administered by EPA
are the Clean Air Act (1972), The Federal
Insecticide, Fungicide, and Rodentcide
Act (1972), and the Marine Protection,
Research, and Sanctuary Act (1972).

Future Regulations
   Considering the current wood pre-
serving waste  management methods, it
is reasonable to assume that the primary
area of  concern regarding future envi-
ronmental regulations will be the dispos-
al and handling of solid wastes (sludges)
and air emissions that result from the
treatment processes.

State and  Local Regulations
   RCRA (Section 3006) provides au-
thority for state management of haz-
ardous  waste  programs.  According  to
RCRA regulations, states must initiate
programs equivalent and consistent
with federal programs. Therefore, state
legislation will not be less complex than
RCRA regulations. It is conceivable that
some states will promulgate more
stringent regulations than the federal

Health and Environmental
  Considerable evidence exists associ-
ating wood preservative contact with
adverse health effects, and although the
impacts of continued,  long-term expo-
sure to  low levels of these toxic com-
pounds are still under investigation,
there is evidence indicating that they
may be mutagenic, teratogenic, and
carcinogenic.  It is  imperative that the
fate of these  toxic chemicals, their
generation,  disposal, environmental
transport mechanisms, and emission
rates be thoroughly understood.

Treatment Process
Descriptions and Wastes
  The treatment of wood with preser-
vatives requires impregnation of the
wood with foreign materials designed to
protect it from attack by insects, fungi,
weather, or fire. The processing steps
include wood preparation (debarking,
shaping, drying) and treatment.

Waste Treatment or Disposal
Technology and Emissions
  This  section  presents options for
wastewater treatment or disposal. Char-
acterization, through field test programs
and theoretical model analysis, of evap-
orative technology and the emissions
that  ultimately escape control, is pre-
sented. In wood preserving plants,
wastSwater generated by wood treating
processes  contains the largest amount
of pollutants requiring disposal. To
comply with  zero pollutant discharge
regulations, the wastewater is usually
contained within the plant's boundaries.
Reflecting the scope of work performed,
the primary topics of discussion are
devoted to the evaporation of waste-
water and resulting gaseous and solid

Wastewater Treatment
  In general, the wastewater generated
will vary in volume as well as  content,
depending on the treatment process and
degree of dilution from other sources. The
design of a disposal system isdependent
on the characteristics of the wastewater.
Such wastewater typically contains free
and emulsified oils, organic compounds,
toxic materials, and  heavy metals. A
decrease in the volume of wastewater
traditionally requiring disposal can be
achieved and is quite cost effective.
There are in-plant changes that can
result in both a  volume and pollutant
burden reduction. These changes include:
  • Closed steaming—The switch from
    open to closed or modified closed
    steaming can result in  a  large
    water volume reduction as well as
    a decrease in the formation of oil-
    water emulsions.
  • Separation of effluent streams—
    When a plant uses more than one
    preservative it is necessary to keep
    the different effluent streams from
    these  preservatives separate. This
    improves recovery of preservatives.
  • Reuse of cooling water—The recy-
    cling of cooling and process water.
     as opposed to treating it as waste,
     will reduce the volume of effluent.
     This is essential for plants using
     barometric condensers.
  •  Plant sanitation—Wastewater vol-
     umes can be reduced by eliminating
     leaks, spills, and drips from retort
     doors, and by segregating storm-
     water runoff and improving general
     plant maintenance.

Oil-Water Separators
  Oil-water separators operate as gravity
separators allowing for the continuous
removal of segregated liquids. To achieve
maximum  recovery of free oil, devices
can be staged. Removal efficiencies of
60 to 95 percent can be  achieved in a
single stage.

  Following free oil removal, a primary
disposal  option is to evaporate the
remaining wastewater. Evaporation is a
viable disposal option to reach  zero
discharge because of the relatively low
volumes of wastewater generated at a
typical plant. There are  four types of
evaporation techniques used: contain-
ment with solar evaporation, thermal
evaporation,  spray pond evaporation,
and  cooling tower evaporation.  In a
survey of 183 plants  using pressure
treating technology, 93 plants disposed
of their accumulated  wastewater  by
evaporation. Of this number, 39  used
containment ponds, 16  used thermal
evaporation, 30 used spray pond evap-
oration, and 8 used cooling towers.
  The principle behind the evaporation
of the wastewater is to dispose of the
water fraction while leaving the organic
constituent for subsequent recycling to
the process or disposal.  Since volatile
and other low-molecular-weight organic
constituents are present in the waste-
water, the potential exists for the release
of organic compounds to the atmosphere.
The  Project Report presents the results
and data analysis of laboratory and field
testing programs designed to character-
ize evaporation technology!
  Several conclusions can be drawn
from this discussion and data presen-
  •  Organic compounds, including
     penta, naphthalene, phenol, and
     similar molecular weight substances,
     can be volatilized and discharged to
     the atmosphere during evaporation
     of water, or at lower than expected
     temperatures based solely on vapor
  • Adjustment of the pH and filtering
    the wastewater prior to evaporation
    can remove significant quantities
    of  organic material  that might
    otherwise be emitted  into the at-
  • Reductions in the liquid tempera-
    ture can reduce the volitalization of
    the organics  by three orders of
    magnitude, indicating that solar
    evaporation ponds (T < 35°C) may
    result in significantly less emissions.
    A solar pond was not tested during
    this program.

Droplet Evaporation Emissions
  A second test program was undertaken
to determine if organic compounds
were emitted from a cooling tower. The
cooling tower operates by exposing the
surface of water to air, thus creating the
necessary conditions for evaporation of
organics. A Boulton drying process was
identified and a testing program initiated.
In this test series, phenol, the most
volatile compound present, was emitted
from the tower. In  addition, no phenol
accumulations  occurred in the tower
sump, indicating that  the material
vaporized at the same rate it entered the
  Several conclusions  can be drawn
from this effort:
  • Low-molecular-weight compounds
    can be emitted to the atmosphere
    from a cooling tower.
  • Phenol is emitted at the same rate
    it enters the tower.
  • The molecular weight of chlorinated
    phenols is sufficiently high so that
    they were not volatilized at atmos-
    pheric  temperature.
  Though a field test program to quantify
organic emissions has not been con-
ducted,  it  is expected  that organic
emissions may be higher than those for
cooling  towers. This is  based on the
following considerations:
  • Forced ejection of the liquid, result-
    ing  in the generation of larger
    surface areas for evaporation.
  • High potential for drift (carryover of
    droplets from the pond  by the

Summary of Wastewater
Treatment Technologies
   Laboratory and field data have been
presented  showing that organic con-
stituents in the wastewater are emitted
to the atmosphere. In addition, treatment
of the wastewater, by flocculation (pH
adjustment) and filtration prior to evap-

oration can lead to reductions in the
-mission rates of the toxic substances.
  iodegradation, chemical flocculation,
carbon adsorption, and soil irrigation
have also been reported  to reduce the
COD and organic content in the waste-

Solid Waste Disposal
  The  amount of solid waste material
generated by the wood preserving
industry depends on the preservative
used and the treatment technologies
employed. The water effluent from
waterborne salt processes is recycled to
the process. Insoluble materials con-
tained  in the process water are filtered
out and disposed. However, since the
preservative category does not generate
waste  containing organic compounds,
the treatment category will not be
discussed further.
  Each of the treatment processes
discussed for wastewater result  in the
formation of a sludge material. The
volume of material generated is pre-
sented. This material is typically disposed
in landfills; onsite, if land is available; or
offsite. Incineration of solid waste is not
currently practiced. Additional testing of
the combustion of these preservatives is
to be conducted.

4/r Emissions
  Emissions from the wood preserving
industry include boiler exhaust and a
variety of fugitive  source emissions.
Boiler stack emissions will be regulated
under  the Office of Air Quality Per-
formance Standard's (OAQPS's) new
source performance standards for non-
fossil or industrial boilers. Reports of
work quantifying the organic constit-
uents in fugitive air emissions from the
wood preserving industry were not
identified These sources include the
dense  vapor plumes emitted as the
pressure vessel is opened and wood
charge removed, the treated wood as it
cools, and the vacuum exhaust. Testing
programs to quantify these emissions
are to be conducted.
  A control technique  for emissions
from the retort and treated wood consists
of a water blanket around the opening.
The blanket  is formed  using spray
headers mounted a few centimeters
from the open end of the retort. The
sprays  cover the end of the retort and
the emerging wood. The wood is cooled
to approximately 45°C thereby reducing
the  driving force for emission of  high-
molecular-weight compounds.  The or-
ganics are transferred  to the water
phase which then must be treated prior
to ultimate disposal.
  The evaporation  devices used to
reduce wastewater  volumes are not
equipped with devices to remove organic
compounds from air  emissions. This is
due to the low concentrations of organics
present  per volume  of gas.  Control of
these organics, as described previously,
would most likely be by flocculation and
filtration or other treatment techniques
for the wastewater prior to possible air
  Information was  not identified or
collected in the field that  would  allow
quantification or estimation of the drift
from either the cooling tower or a spray
pond. The cooling  tower tested was
designed and operated such that no drift
was detected during  the test sequence.
Drift is  expected to contain organic
constituents similar to the  recirculating
liquid. Therefore, the impact on air
emissions could be estimated from the
charge material composition and an
assumed amount of drift.

Impact of Evaporation on
Multimedia  Emissions
  The primary emphasis  of the  work
conducted during this program has
been the evaporation of wastewaters
generated during wood preserving
operations. The impact of evaporation
technology on the inventory of industry
emissions is developed from data on
established industry practices and
research results. To establish the mass
emissions of  organic material from a
typical wood treating plant, the projected
wastewater generation rate and con-
stituent concentrations identified are
coupled  with the fractional  emission
rates. Major operational factors affecting
these projections are also presented.
These factors include the organic  emis-
sions due to operation of  spray ponds
and the projected probability of plant
closure under the burden of promulgated
wastewater discharge regulations.

Fractional Emission Rates
of Evaporation Devices and
Emission Projections
  For solution temperatures near atmo-
spheric  temperature, such as in the
case of spray ponds, cooling towers, and
solar ponds, it has been shown that the
low-molecular-weight organics, such
as benzene, toluene, and  phenol, may
be emitted. As the molecular weight of
an organic constituent increases, the
probability that the constituent will
remain in the sludge fraction also
increases. Likewise, as the solution
temperature increases, such as in pan
evaporation, the probability of additional
organic emissions exists. For penta
solutions,  it has also been shown that
reductions in the organics in solution
can be obtained by pH adjustment and
  Review  of the data shows several
impacts of treatment and/or evapora-
tion. Primarily, it is expected that all
volatile organics, including phenol, will
be emitted from the wastewater. Though
quantitative data are not available at the
time of this report, other sources,
primarily vacuum vents from the retorts,
may represent more significant emis-
sion sources for volatiles than does the
evaporation of  the wastewater.
  The second  impact is the increased
emissions  of heavier organics at elevated
temperatures. Without pretreatment of
the wastewater, significant  organics
could be emitted to the atmosphere. The
use of wastewater treatment, whether
acidification and filtration or floccula-
tion and gravity settling, is expected to
reduce the emissions of nonvolatile
organics during evaporation. Clearly,
evaporation of  wastewaters with min-
imal use of thermal enhancementdunng
poor weather operation represent the
lowest source  of air emissions. Since
creosote components are not readily
removed by pH adjustment and filtration,
and penta components are, the decreased
use of creosote and increased use  of
penta (coupled with pretreatment) may
result  in  an overall decrease in air

Regulatory Impact on
Emissions Burden and Control
  EPA's Effluent Limitations will require
further industry wastewater discharge
control that will impact industry emis-
sions. Capital and operating cost data
was examined for three evaporation
systems:  pan evaporators, cooling
towers, and spray ponds. Pretreatment
of process wastewater is usually re-
quired before disposal into these sys-
tems. Often gravity oil and water re-
moval, flocculation, filtration, aerated
lagoons, spray cooling ponds, and hold-
ing ponds may also be connected  in
series or parallel with each other.
  Cooling  towers have the highest
capital expenditure and also the highest
total annual costs. The latter is due  to

the high amortization rate of the initial
capital investment. Forced evaporation
systems are the second most costly.
These systems will become more ex-
pensive to operate as energy costs
increase. It should be noted  that pan
evaporation may  represent the least
economic  impact  of any of the three
technologies, but  also is the greatest
emitter of organic pollutants to the

Regulatory Impact on Existing
  An interagency analysis  of EPA's
proposed effluent limitations shows
that the projected costs of compliance to
best available technology regulations
falls disproportionately on the smaller
plants (i.e., those with a lower sales
volume are impacted more heavily).
Twelve plants with sales under  $3.5
million would not  be able to afford the
control  equipment required  for  the
wastewater disposal options considered.
This evaluation is based on a plant likely
to incur operating  losses as a result of
compliance costs  or  being  unable to
finance the investment for the necessary
control equipment.
  Eleven plants are likely to shut down
and 10 others face potential shutdown if
zero discharge regulations are imple-
mented. Though the closure of any plant
would be significant to individuals
directly impacted, it is expected that the
lost treating capacity could be replaced
by excess capacity at other facilities. In
addition, potential plant closures are not
expected to initiate additional research
efforts to  identify new treatment
processes or preservatives.

Review of Ongoing Wood
Treating Preserving and
Waste Disposal Studies
  EPA, the Department of Agriculture
(USDA), and the National Institute for
Occupational Safety and Health (NIOSH)
are presently studying the effects of the
disposal of wood treating wastes on the
environment, the impact of using treated
products, and other questions relating
to the use of creosote, penta, and other
  To determine if additional study is
required to characterize the multimedia
emissions from the wood treating indus-
try , Table 2 has been prepared. This
table presents a summary of work that
has been or is being performed. Infor-
mation was obtained from the literature
and  project officers conducting the
work.  In addition, if work  is being
conducted, it should be qualitative or
quantitative for the organic constituents
in the waste stream to be included.
Table 2.    Study Areas Defining the Multimedia Emissions from the Wood Treating and Wood Treating Products Industry

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Process wastewater
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air emissions

Still ponds
Pan evaporators
Spray ponds
Cooling towers


Fugitive air
Chemical storage
Chemical transport
Open treatment vessels
Opening pressurized ret
Gas purging of retorts
Vacuum exhaust gas
Hoods and vents




Bruce DaRos,  Bill Fitch, Carole Franklin. Mike Friedman, Richard Merrill, and
  Dean Wolbach are with Acurex Corporation, Mountain View, CA 94042
Donald L. Wilson is the EPA Project Officer (see below).
The complete report, entitled "Wood Preserving Industry Multimedia Emission
  Inventory," (Order No. PB 81 -205 999; Cost. $20.00, subject to change) will be
  available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
The EPA Project  Officer can be contacted at:
        Industrial Environmental Research Laboratory
        U.S. Environmental Protection Agency
        Cincinnati, OH 45268
                                                                                   > US GOVERNMENT PRINTING OFFICE 1981 -757-012/7299

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