United States
Environmental Protection
Agency
Research and Development
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
EPA-600/S2-84-080 May 1984
Project Summary
Evaluation of VOC Emissions
from Wastewater Systems
(Secondary Emissions)
R.D. Cox, J.I. Steinmetz, D.L. Lewis, and R.G. Wetherold
This study was performed to develop
and evaluate procedures for measuring
or estimating VOC emissions from
wastewater treatment facilities. The
report describes the results of field
sampling at two wastewater treatment
facilities and a comparison of measured
VOC emissions with emissions data ob-
tained through predictive modeling. One
of the facilities tested used aerobic
biological treatment, whereas the sec-
ond used anaerobic treatment. The field
measurement techniques and equip-
ment, laboratory measurement techni-
ques, data reduction, and the predictive
model are described. Also, a thorough
quality control/quality assurance pro-
gram that documents the data quality is
described. The results of this study pro-
vide information on the errors to be ex-
pected when using predictive models to
estimate VOC emissions from waste-
water treatment facilities as well as
when measuring VOC emissions using
the Concentration-Profile technique.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory, Cincinnati, OH, 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).
Introduction
Few data are available concerning quan-
titative definition of VOC emissions during
treatment of chemically contaminated
wastewaters. In general, wastewater treat-
ment systems are evaluated only with
respect to concentrations of pollutants in the
water effluent. Emissions of pollutants to the
atmosphere are usually ignored or even con-
sidered a means of increasing water treat-
ment efficiency. To properly evaluate VOC
emissions during wastewater treatment re-
quires accurate techniques for identifying
and quantitating emissions, as well as a good
understanding of the volatilization and
dispersion processes.
The quantitation of VOC emissions from
water basins requires consideration of two
processes: emission and dispersion. Surface
emission measurements can be divided into
direct and indirect. Direct measurements in-
volve only measuring emission processes
directly over the water surface. Indirect
measurements involve determining VOC
concentrations in the air above the surface
or downwind of the basin and using
micrometeorological dispersion modeling to
relate measured concentrations to emission
rates.
An understanding of the thermodynamic
principles associated with emissions during
wastewater treatment has led to the develop-
ment of models for predicting VOC emis-
sions. These models require significantly less
testing than the testing required to actually
quantitate.emissions. These models gener-
ally only require inputs such as VOC concen-
trations in the water, ambient temperatures
and wind speeds, engineering functions of
the treatment facility, and thermodynamic
properties of the compounds of interest.
However, little information is available con-
cerning the accuracy of predictive models
when applied to real-world wastewater treat-
ment conditions.
The technical objective of this study was
to examine and refine a method for the in-
direct sampling of volatile organic carbon
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(VOC) emissions from wastewater treatment
facilities for the synthetic organic chemicals
manufacturing industry (SOCMI), and to
evaluate a predictive model using actual
emissions data. The method that was refined
and used to measure VOC emissions was the
Concentration-Profile (C-P) technique. This
procedure involved field determinations of
temperature, wind speed, and time-averaged
concentrations of VOC and specific com-
pounds, all as a function of distance above
the wastewater pond surface using a
logarithmic interval design. VOC species and
chemical class concentrations were
measured at two sites using the C-P techni-
que. These concentrations were compared
to emissions obtained using predictive
models. The sampling and predictive techni-
ques were applied to two sites, one using
subsurface aeration, and the second, an
anaerobic treatment facility.
Approach
The approach of this study involved an
evaluation of the sampling restrictions of the
C-P technique and a modification of the sam-
ple collection and analysis portion of the
technique. This was followed by screening
of several sites by visits and limited testing,
selection of two sites for extensive testing,
and development of site-specific test plans
and a quality assurance project plan. Field
sampling was then performed at two sites,
and results of the emissions measurements
were compared to emission rates obtained
from predictive modeling. A thorough quality
assurance program and statistical treatment
of experimental data allowed the establish-
ment of confidence limits for the comparison
of experimental and predictive results.
An evaluation of the C-P technique
demonstrated that minimum requirements
for the wastewater basin and atmospheric
stability were necessary for proper applica-
tion of the technique. The criteria used for
proper sampling are:
• The location selected for C-P testing
must be at least 50 (and preferably 200)
times the distance of the height of the
dike or other significant obstacle away
from the edge of the pond along the
direction of average wind. Profile mea-
surements taken closer than this cannot
reflect the log profile assumed in the
methodology and, consequently, the
emissions data will not be valid.
• The mean wind speed for the 20-minute
sampling period must be greater than 5
mph.
• The maximum wind speed (gust) must
not be greater than three times the mean
wind speed.
• The wind direction standard deviation
(WSD) must not be greater than 45°.
2
• The Richardson number (R,), defining
atmospheric stability, must be greater
than -0.1.
As presented, the C-P technique called for
collecting VOC species using liquid oxygen
traps for field sampling. This method
presented a number of safety and procedural
problems and was therefore not used. In-
stead, air samples were collected in evacu-
ated stainless steel canisters using vacuum
flow regulators to obtain integrated samples.
Extreme care had to be used to minimize
contamination with this technique. Different
types of canisters were found to have sig-
nificantly different blank levels. The canister
technique proved to be a simpler and more
workable technique than liquid oxygen traps.
The determination of chemical flux rates
above waste treatment ponds by the C-P
technique required measurements of wind
speed, temperature, and organic species
concentrations at six logarithmically spaced
heights over the pond surface. In addition,
measurements of humidity, water temper-
ature, and organic composition of the water
were required. A 20-foot pontoon boat was
outfitted with the necessary equipment to
provide these measurements and with safety
equipment for sampling personnel. The
sampling equipment consisted of a 4-meter
mast with six wind speed sensors, six
temperature sensors and seven air collection
probes, a continuous real-time data collec-
tion system, water temperature and sampl-
ing equipment, and an instrument for
measuring humidity.
The work performed during this program
incorporated a comprehensive quality
assurance/quality control (QA/QC) program
as an integral part of the overall sampling and
analytical effort. The primary objective of the
QA/QC program was to provide a system for
defining the measurement data quality in
terms of precision and accuracy. It also pro-
vided a mechanism for assuring that the data
were representative, complete, and com-
parable to other similar data. While the
system of QA activities was necessarily in-
dependent of the technical effort per se, the
QC system was an integral part of the daily
technical effort. It was designed to provide
an overall system for generating data of a
specified quality. The QA/QC program en-
compassed control over daily data genera-
tion as well as a mechanism to assess the
quality of data produced. This ultimately
allowed the establishment of confidence
limits for comparing predictive and ex-
perimental data.
Results and Discussion
VOC emissions were measured using a
modification of the C-P technique at two
chemical waste treatment facilities, one us- U
ing an aerobic bio-oxidation pond (site FB), ~
and the second using a non-aerated pond
(site TB). Three sets of C-P tests were per-
formed at each site. Also, water samples
were collected for applying the predictive
models. Due to an equipment malfunction,
water samples from site FB were destroyed
and a second set of samples was collected
approximately one month after the C-P
sampling. All quality control functions were
performed at both sites and quality
assurance audits were conducted at site TB
and at Radian's laboratories.
Results of the C-P sampling and the pre-
dictive model applications are presented in
Table 1. Emissions from both sites were very
low, near the detection limits for the sam-
pling and analytical methods which were us-
ed (3 ppbv-C). VOC flux rates were
calculated for benzene, diethyl ether, indene,
and styrene at site FB. Also, a flux rate was
determined for the total aromatic content in
the air above the pond surface. Measured
flux rates at this site ranged from 430 kg/Ha-
yr for styrene to 3660 kg/Ha-yr for diethyl
ether. The average flux rate for total
aromatics at this site was 20,400 kg/Ha-yr.
VOC flux rates at site TB were determined
for benzene, cyclohexane, and acetone.
Measured flux rates at this site ranged from ^
130 kg/Ha-yr for benzene to 1550 kg/Ha-yr fl
for acetone. Standard errors and confidence
limits were calculated for all analytical and
meteorological measurements. Because of
the low levels of VOC species that were pre-
sent above the ponds, and sampling and
analytical variabilities, a zero flux rate was
within the 95% confidence level for all flux
measurements.
Flux rates determined using the modified
C-P technique were compared to flux rates
from the predictive models. Results of the
comparison, shown in Table 1, were variable
and appeared to be related to the type of
compound and whether or not aerators were
used. For the site containing aerators (FB),
predictive flux rates for the three aromatic
compounds were approximately 3.5 times
higher than measured flux rates. However,
for diethyl ether, the predicted flux rate was
only 35% of the measured flux rate. Pre-
dicted flux rates for diethyl ether and styrene
were within the 95% confidence limits for
the measured rates, whereas benzene and
styrene were outside the 95% confidence
limits. The predictive model indicated that
85-95% of the overall emissions at site FB
resulted from aeration (turbulent phase).
For the site not containing aerators (TB),
predictive flux rates for benzene and cyclo-
hexane were greater than measured rates by
factors of 10.0 and 5.9, respectively. The
predicted flux rate for acetone at this site was
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15% of the measured rate. The predicted
flux rate for acetone was within the 95%
confidence limits for the measured value, but
predicted flux rates for benzene and cyclo-
hexane were not.
In summary, predicted flux rates range
from 0.15 to 10 times the measured flux rates
at two sites. Predicted rates for aliphatic and
aromatic hydrocarbons were always higher
than measured rates, whereas predicted
rates for the two polar species, diethyl ether
and acetone, were lower than the measured
rates. The lower predicted flux rates for the
polar compounds may be attributed to low
analytical data on these compounds in
water, since these do not purge efficiently
using routine purge and trap techniques.
Data from site FB should also be viewed in
light of the fact that VOC species concen-
trations in the water (used for predictive
modeling) were not obtained on the same
day as air flux rate data.
Results of the QA/QC portion of this pro-
ject indicated that the overall chemical data
accuracy was -12%, and the combined
sampling and analytical precision (variability)
for ambient species measurements was
±34%. The data accuracy must be viewed
in light of the fact that primary standard
reference materials are not available for ppb
levels of organic vapors in air.
Conclusions and
Recommendations
The C-P technique used to measure flux
rates is an indirect measurement technique,
since it requires micrometeorological model-
ing to convert measured concentrations to
flux rates. Validation of the predictive model
should only be considered a relative com-
parison between the predictive model and
the micrometeorological model used for
measuring flux rates. In the future, it is
recommended that both models be com-
pared to emission rates determined by a
direct measurement technique.
The meteorological and height-to-berm re-
quirements of the C-P technique seriously
limit its applicability on smaller ponds. Some
treatment facilities use small settling and
cooling ponds before larger scale treatment.
Both systems tested had initial settling
ponds. Because of elevated temperatures
and concentrations in these ponds, they can
potentially produce significant emissions. A
measurement technique should be devel-
oped and evaluated for smaller ponds.
R. D. Cox. D. L. Lewis, R. G. Wetherold, and J. I. Steinmetz are with Radian
Corporation, Austin, TX 78766.
Paul de Percin is the EPA Project Officer (see below}.
The complete report, entitled "Evaluation of VOC Emissions from Wastewater
Systems (Secondary Emissions)," (Order No. PB 84-173 780; Cost: $16.00.
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
U S GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7691
Table 1. Comparison of Predicted and Measured Flux Rates
Predicted Flux
Average Measured Flux3 Predicted
Measured Flux
Confidence Limits (95%)b
Species or
Class
Site = FB
Benzene
Diethyl Ether
Indene
Styrene
Total Aromatics
Site = TB
Benzene
Cyc/ohexane
Acetone
ng-C/crrf-sec
0.208
0.0266
0.0889
0.0438
0.586
0.0394
0.0381
0.00458
kg/hectare-yr ng-C/crrf-sec
7,150
1,300
3,010
1,500
20,400
1,340
1,400
240
0.0592 ±
0.0751 +
0.026 1 ±
0.0126 +
0. 120 +
0.0038 ±
0.0065 ±
0.0313 ±
0.0492
0.0561
0.0167
0.0261
0.0829
0.0138
0.0134
0.0168
kg/hectare-yr
2030 ± 1680
3660 ± 2730
880 ± 570
430 ± 890
4180 ± 2890
130 ± 480
230 ± 490
1550 + 860
Measured
3.5
0.35
3.4
3.5
4.8
10.0
5.9
0.15
ng-C / crrf-sec
0-
0-
0-
0-
0-
0-
0-
0-
0.158
0.187
0.0595
0.0647
0.286
0.0313
0.0333
0.0650
kg/hectare-yr
0-
0-
0-
0-
0-
0-
0-
0-
5390
9120
2020
2210
9960
1090
1210
3270
Predictive Flux
Within Limits?
No
Yes
No
Yes
No
No
No
Yes
a Mean + standard error (o).
b Mean + 2o.
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Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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