United States
Environmental Protection
Agency
Municipal Environmental Research -
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-056 August 1982
Project Summary
Volatile Organics in Aeration
Gases at Municipal Treatment
Plants
Edo D. Pellizzari
When the volatility of certain priority
pollutants is considered, it could be
assumed that these compounds would
be transferred from the aqueous solution
to the atmosphere during treatment at a
municipal treatment plant. When this
study began, there were virtually no data
that either qualitatively or quantitatively
addressed this process. The purpose of
this study was to develop sampling
techniques to monitor emissions of
organics from biological aeration basins.
Additionally, an attempt was made to
correlate emissions with aqueous con-
centrations and to investigate the influ-
ence on volatility of the sorption of the
compounds on sludge solids.
14C-Radiolabeled compounds were
used to determine sorption by solids in
raw wastewater and mixed liquor sus-
pended solids (MLSS). The Freundlich
adsorption isotherm relationship was
used to describe the sorption capacity
and intensity. The results indicated large
variations in K (capacity) and n (inten-
sity) among differing solids and different
compounds. It was concluded that the
sorption of volatile compounds to the
solid phase in activated sludge cannot be
ignored when attempting to predict the
concentration in the off-gas by using li-
quid phase concentrations. In contrast,
sorption on solids in raw wastewater
was considered to have a negligible
effect.
A pilot study and two experiments
were conducted to determine the levels
of volatile priority pollutants in the off-
gas from aeration basins in activated
sludge and raw wastewater at the North-
side Treatment Plant in Durham, North
Carolina. Some 13 volatile compounds
were detected in the off-gas. In general,
the concentrations of the compounds in
the off-gas were higher (by a factor of 2
to 3) at the front end of the aeration
basin than at either the middle or end of
the basin. In contrast, the concentra-
tions of the same priority pollutants in
the mixed liquor of the activated sludge
showed no change at the same sampling
points.
The emission of compounds from the
entire composite aeration tank area of the
plant was computed for a number of pri-
ority pollutants. Four compounds exhib-
ited emission rates of > 1 kg/hr, with
the highest observed for chloroform and
tetrachloroethylene with emission rates
attaining 5.7 and 7.0 kg/hr, respectively.
The effect of superchlorination of
sludge was also investigated. Sampling
and analysis for chlorinated compounds
in superchlorinated sludge revealed the
presence of several hundred constituents.
Analysis of the solid phase after super-
chlorination indicated the presence of
2% to 5% organic chlorine.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a sep-
arate report of the same title (see Project
Report ordering information at back).
-------
Introduction
It would be simpler if the concentra-
tions of volatile organics in the off-gas
from aeration basins could be predicted
from their concentrations measured in
the liquid phase; acquiring liquid samples
from the treatment facility presents
fewer problems. To predict the concen-
trations of volatiles in the off-gas, it is
necessary to recognize the potential
equilibria of compounds between the
solid, liquid, and gas phases that exist in
the aeration basins of the activated
sludge process. A material balance
equation of the interactions leads to a
first-order rate expression that allows
the calculation of the concentration at a
point in time (t). The integrated form of
the equation is given by:
w(t) ~~ ^w(o)6 ' vv i i
Cw = concentration of the chemical
in water
KjL = mass transfer coefficient
PI = partial pressure of the chemical
= Henry's Law Constant
H
It follows that the concentration of the
chemical in the liquid phase should de-
crease with the time of forced air aera-
tion in a body of liquid such as an acti-
vated sludge aeration basin.
Sorption on Sludge Solids
A study was conducted to determine
the sorption of selected 14C-labeled pri-
ority pollutants onto the solids in activated
sludge. The purpose was to determine
whether sorption could be ignored and
the simple Henry's Law relationship
could be used to approximate the rate of
volatilization. At the same time the
sludge was sampled, the concentrations
of the liquid flow were also determined
at the entrance and exit of the aeration
basin to determine whether the above
equation indeed applies.
Sorption Tests
Sorption tests were conducted on
solids obtained from raw wastewater
and from activated sludge; the solids
were placed in contact with solutions of
14C-labeled volatile organic compounds
in capped centrifuge tubes that were
maintained at 4 °C to minimize biodegra-
dation. Analysis for residual compound
was determined with a liquid scintillation
spectrometer. Results were expressed
by using the Freundlich equation as
follows:
Cs = KC^ or log Cs = log K + n log Cw
where:
Cs = concentration of the organic on
the solid phase in /jg/g
Cw = concentration in the liquid
phase at equilibrium expressed
at /ng/L
Kandn = parameters of the equation
Table 1 shows results of the sorption
tests on a single compound, chloroform,
for sludge sampled during two different
time periods and from three locations in
the aeration basin. These data and re-
sults obtained with other compounds
show that there is a variation in sorption
capacity of activated sludge taken at
two different times (Periods 1 and 2) and
indicate a decline in capacity with loca-
tion in the aeration basin starting at the
front end (1), middle (2), and exit (3).
Sorption data were obtained for the
following compounds: chloroform, car-
bon tetrachloride, chlorobenzene, tol-
uene, benzene, and trichloroethylene.
Table 1. Freundlich Adsorption Parameters for Chloroform on Activated Sludge*
Period
1
1
1
2
2
2
Initial Cone.
Location ffJff/L)
1 5.0
49.8
99.5
2 5.0
49.8
99.5
3 4.6
46.1
92.2
1 5.0
49.8
99.5
2 5.0
49.8
99.5
3 4.6
46.1
92.2
LogCw
0.432
1.253
1.746
0.512
1.536
1.754
0.441
1.521
1.797
0.455
1.438
1.783
0.498
1.438
1.811
0.538
1.470
1.608
LogCs
0.894
2.026
2.164
0.766
1.711
2.154
0.788
1.634
1.935
0.855
1.873
1.983
0.894
1.873
2.065
0.583
1.743
2.236
Slope Intercept Corr. Coef.
(n) LogK(K)** (r)
1.002 0.55(3.54) 0.961
1.057 0.20(1.58) 0.988
0.828 0.41 (2.57) 0.998
0.890 0.48 (3.02) 0.987
0.921 0.46(2.88) 0.992
1.435 -0.21 (0.62) 0.985
* Sludge concentration 0.3 g/L
**K expressed as ng/g of dry sludge solids.
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Emission of Volatiles
Studies were conducted to determine
the levels of purgeable priority pollutants
in raw wastewater, activated sludge,
and the off-gas from aeration basins
stripped by the aeration process. The ob-
jective was to determine the relationship
of off-gas concentrations at the front
end and exit of an aeration basin to the
concentration in the activated sludge
collected at the same locations in the
basin.
The sampler and analytical techniques
were the same as those previously devel-
oped and described for off-gas determi-
nation. * A pilot test and two studies con-
ducted on different days were obtained
at the Northside Treatment Plant, Dur-
ham, North Carolina. In tests No. 1 and
2, the air streams were sampled in tripli-
cate at three locations (beginning, mid-
dle, and end). The two sampling periods
covered a total of 4.5 hr. Concurrently,
at the beginning, middle, and end of the
air sampling period, activated sludge
samples were taken from the same loca-
tions in the tank.
Selected results of two time periods of
the sampling and analysis are shown in
Table 2. Samples were taken at the en-
trance (L1) end of the aeration tank.
Complete sampling data show a de-
creasing concentration of compounds in
the off-gas between flow entrance (L1)
and exit of the tank. Further, concentra-
tions in the sludge were relatively con-
stant or slightly increased at each of the
locations.
From these data, the mass emission
rate of the priority pollutants in the off-
gas from the entire plant aeration tank
surface area could be calculated. The re-
sults for selected compounds are shown
in Table 3. The highest rates were ob-
served for chloroform and 1,1,2,2-tetra-
chloroethylene with emissions reaching
5.7 and 7.0 kg/hr, respectively.
Superchlorination of Sludge
Superchlorination of sludge for stabili-
zation is being practiced in some plants.
Because the sludge cake generated from
this process can eventually be deposited
in a landfill or used as a fertilizer, it is im-
portant to know whether potentially toxic
compounds are generated by this process.
Sampling and analysis were conducted
at two plants on sludges before and after
Superchlorination and on sludge cake
from drying beds. Total organic chlorine
Table 2. Priority Pollutant Levels in Airstreams and Activated Sludge Northside
Treatment Plant, Durham, NC
Location LI
1200-1 41 5 hr
Priority Pollutant
Chloromethane
Dichlorofluoromethane
Bromomethane
Vinyl chloride
Chloroethane
Methylene chloride
Trichlorofluoromethane
1, 1 -Dichloroethylene
1 , 1 -Dichloroethane
trans- 1,2 -Dichloroethylene
Chloroform
1,2 -Dichloroethane
1, 1, 1 -Trichloroethane
Carbon tetrachloride
Bromodichloromethane
Bis(2-chloroethyl)ether
1 , 2-Dichloropropane
trans- 1,2-Dichloropropene
Trichloroethylene
Dibromochloromethane
cis- 1 ,3-Dichloropropane
7,7,2- Trichloroethane
Benzene
2-Chloroethyl vinyl ether
1, 1,2,2- Tetrachloroethylene
Bromoform
1, 1 ,2.2-Tetrachloroethane
Toluene
Chlorobenzene
Ethylbenzene
Acrolein
Acrylonitrile
m -Dichlorobenzene
o-Dichlorobenzene
Air
NO"
ND
NO
ND
ND
27.7±6.3C
ND
8.0±0.2
2.8±0.5
ND
125±47.7
1.1 ±0.1
27.6±7.4
ND
4.7 ±0.8
ND
ND
ND
10.7 ±0.4
ND
ND
ND
21.2±4.2
ND
119±26.3
ND
ND
136±52.4
T
26.4±8.4
ND
ND
38.1 ±13.2
1 1.3±2.4
Sludge*
ND
ND
ND
ND
ND
18.5±7.8
ND
4.0±0.4
ND
ND
27.8±13.2
ND
1.4±0.3
0.2±0
ND
ND
ND
ND
0.4±0
ND
ND
ND
1.0±0.2
ND
4.3±0.7
ND
ND
3.1±1.1
ND
0.7 ±0.2
ND
ND
3.6±0.4
2.5±0.6
1415-1630 hr
Air
ND
ND
ND
ND
ND
23.7 ±2.0
ND
6.8±0.2
3.8±0.5
ND
108±13.8
T<
34.0±4.4
T
3.4±0.1
ND
ND
ND
9.4±2.8
T
ND
T
18.8±1.5
ND
281 ±20.4
ND
ND
130±15
T
23.4±6.6
ND
T
36.3±6.9
10.5±2.6
Sudge
ND
ND
ND
ND
ND
34.2±21.6
ND
3.9±0.8
ND
ND
16.7±5.8
0.2±0
1.2±0. 1
0.3±0.1
ND
ND
ND
ND
0.6±0.1
ND
ND
ND
1.1 ±0.1
ND
12.2±2. 1
ND
ND
3.5±1.0
ND
0.4±0.4
ND
ND
3.9±1.2
2.5±0.8
a Priority pollutants were measured in sludge at the beginning and end of time period
with mean value of quadruplicate analyses reported.
"NO - not detected.
cmean values are in ppb with standard deviation.
dr= trace.
"'Collection and Analysis of Purgeable Organics
.milled from Wastewater Treatment Plants,"
EPA-600/2-80-017.
was determined by a combustion tech-
nique, volatile organics by purge and
trap, and chlorinated organics by elec-
tron impact and negative ion chemical
ionization capillary GC/MS.
The organic chlorine content of the
sludge solids before chlorination was
<0.6 ± 0.3%, which was at the limit
of detection by the SchBniger method;
after chlorination, the concentration
ranged from 2.15% to 5.28%.
The results of analysis for purgeable
organics (Table 4) are for two sets of
samples from one plant and for sludge
-------
Table 3. Estimated Emission Rates Calculated for Selected Priority Pollutants
from Aeration Basins at Northside Treatment Plant, Durham. NC
Priority Pollutant
Emission Rates (g/hr)
August 19, 1979 January 29, 1980 May 14, 1980
Methylene chloride
1. 1 -Dichloroethane
Chloroform
1,2-Dichloroethane
1 , 1 , 1 -Trichloroethane
Bromodichloromethane
Trichloroethylene
Benzene
1, 1 ,2,2-Tetrachloroethylene
Toluene
Ethylbenzene
o-Dichlorobenzene
572
—
5,756
—
301
288
704
668
7,007
4,819
• 871
280±86
14±4
703±11
10±7
191±27
130±42
103±11
62±9
940±15
264±216
16±8
148±3
205±3
19±2
944±103
±2
252±23
43±1
111±8
122±8
1,969±710
741 ±86
171±21
478±71
4,689
m -Dichlorobenzene
609±44
155±13
cake from the drying beds. Comparison
of the concentrations of the purgeable
organics between the unchlorinated in-
fluent and the chlorinated effluent sludge
indicates that several compounds in-
creased appreciably: notably, chloroform,
carbon tetrachloride, and p-chlorotoluene.
The remaining compounds remained
relatively constant.
Extensive analyses were also con-
ducted for the nonvolatile compounds
using GC/MS techniques. In addition,
sample fractions that are normally ex-
cluded by EPA's analytical protocol were
also analyzed. Certain compounds were
identified but not quantified, but most of
the results are presented as GS/MS
profiles. These profiles reveal the pres-
ence of "hundreds" of unidentified
compounds resulting from chlorination.
Conclusions
Certain 14C-radiolabeled priority pol-
lutant compounds were used to deter-
Table 4. Levels* of Selected "Purgeable" Organics in Liquid Sludge Before and After Superchlorination (ppbf
Compound
INF/1S*
EFF/1S*
INF/2S
EFF/2S
Bed Samples
Chloromethane
Dichlorodifluoromethane
Bromoethane
Methylene chloride
Trichlorofluoromethane
1 , 1 -Dichloroethylene
1, 1 -Dichloroethane
Freon 1 13
Chloroform
1.1,1 - Trichloroethane
Carbon tetrachloride
Bromodichloromethane
trans- 1,3-Dichloropropene
Trichloroethylene
Benzene
1. 1,2,2- Tetrachloroethene
1, 1.2,2- Tetrachloroethane
Toluene
Chlorobenzene
Ethylbenzene
p-Chlorotoluene
Dichlorobenzene isomer
20±15
8±8
3±2
260±110
390±229
10±3
24±22
15±2
9±7
175±51
NO"
ND
ND
86±5
50±23
139±32
ND
778±64
ND
9±8
ND
11±10
32±9
27±8
Ta
376±12
118±26
16±2
39±10
14±1
1.037±140
211 ±23
847±47
ND
9±7
81±1
48±20
182±18
ND
1.213±66
15±1
13±1
951 ±90
25±1
54±32
4±4
T
203±40
74±26
9±1
41±41
11±0
6±5
69±34
ND
ND
ND
66±1
354±279
102±24
ND
1,432±127
11±11
6±6
T
9±9
15±1
20±4
T
264±27
276±86
15±3
32±6
15±5
1,104±125
179±17
989±135
6±4
10±8
85±10
39±11
149±10
T
739±14
16±1
12±0
1.586±269
32±1
27±5
14±1
T
338±28
135±50
15±5
15±4
12±1
490±110
86±28
395±140
ND
T
75±18
39±11
106±34
ND
2,165±644
12±2
14±0
762±273
23±8
"Based on total sample.
"Mean values in parts per billion with standard deviation.
CINF = unchlorinated influent liquid sludge; EFF = chlorinated effluent liquid sludge.
dr= trace.
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mine the extent of their sorption by the
solids in activated sludge and raw waste-
water. The Freundlich adsorption iso-
therm relationship was used to describe
the sorption capacity and intensity of the
solid for each of the radiolabeled com-
pounds. Measurable sorption capacities
(K) were detected for each of the com-
pounds. Sorption studies conducted
over several different time periods indi-
cated large variations in K values (e.g.,
for chloroform it ranged from 0.62 to
3.54). The sorption intensity (n) for sev-
eral chemicals varied by as much as a
factor of 3. The results indicated that
sorption of volatile chemicals to the solid
phase in activated sludge cannot be
ignored when attempting to predict their
concentration in the off-gas by measur-
ing liquid phase concentrations. The
sorption capacity for the same chemicals
to solids in raw wastewater was deemed
negligible.
A pilot study and two experiments
were conducted on different days to
determine the levels of volatile priority
pollutants in the off-gas from aeration
basins in activated sludge and raw
wastewater at the Northside Treatment
Plant in Durham, North Carolina. In
general, the concentrations of priority
pollutants in the off-gas were higher at
the front end of the aeration basin than
at either the middle or end of the basin—
a decrease by a factor of 2 to 3. In con-
trast, the levels of priority pollutants
measured in the activated sludge did not
appear to decrease at the same three
points along the aeration basin. The con-
centrations of priority pollutants in raw
wastewater were higher, however, than
in the activated sludge itself, indicating
that the priority pollutants were partially
lost at other points in the treatment
facility or that a dilution had occurred
before reaching the aeration basin.
Because of a significant sorption for the
priority pollutants to the solids in acti-
vated sludge and the lack of a concentra-
tion gradient across an aeration basin, it
was concluded that a simple Henry's
Law relationship cannot be used to accu-
rately predict the off-gas concentrations
of a priority pollutant from its concentra-
tion in the liquid phase.
The emission rate from the entire com-
posite aeration tank area for the North-
side Treatment Plant in Durham, North
Carolina, was determined for a number
of priority pollutants. The highest rates
were observed for chloroform and tetra-
chloroethylene with emission reaching
5.7 and 7.0 kg/hr, respectively.
Sampling and analysis for chlorinated
compounds in superchlorinated sludge
revealed the presence of several hundred
chlorinated constituents; the super-
chlorinated sludge effluent contained 2%
to 5% organic chlorine. The organic
chlorine content for the unchlorinated in-
fluent sludge solids was at the limit of
detection using the Schb'niger method.
The use of negative ion chemical ioniza-
tion/mass spectrometry (NICI/MS)
made the specific and sensitive detec-
tion of chlorinated compounds easier.
Quantification of purgeable priority pol-
lutants before and after chlorination of
sludge indicated increased concentra-
tions. Chloroform increased from about
6 ppb before chlorination to over 1,000
ppb after; carbon tetrachloride was not
detected in the influent but was mea-
sured at levels up to 989 ppb in the efflu-
ent. Increases of almost three orders of
magnitude were also observed for p-
chlorotoluene, in some cases from only
trace levels to 1,620 ppb. When using
the priority pollutant method for sludge
analysis, acid, base, and neutral frac-
tions yielded only a few chlorinated non-
priority pollutants. In contrast, NICI/MS
examination of the discard fraction gen-
erated by this method indicated that the
majority cf the chlorinated compounds
amenable to gas chromatography were
contained in these fractions. Even
though the chlorinated compounds
detected by NICI/MS were not quanti-
fied, it was evident that a major portion
of the chlorinated organics was not de-
tected by this method since the presence
of up to 5% organic chlorine in the solid
component of the chlorinated sludge
had been demonstrated.
The full report was submitted in fulfill-
ment of Contract No. 68-03-2780 by
Research Triangle Institute under the
sponsorship of the U.S. Environmental
Protection Agency.
Edo D. Pellizzari is with Research Triangle Institute, Research Triangle Park, NC
27709.
James J. Westr/ck and H. Paul Warner are the EPA Project Officers (see
below).
The complete report, entitled "Volatile Organics in Aeration Gases at Municipal
Treatment Plants," (Order No. PB 82-227 760; Cost: $18.00. subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
For information contact H. Paul Warner at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
. S. GOVERNMENT PRINTING OFFICE: I982/559-092/0461
-------
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