Environmental Protection Technology Series
Nitrogen Removal By
Ammonia Stripping
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Monitoring, Environ-
mental Protection Agency, have been grouped into five series. These
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2. Environmental Protection Technology
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This report has been assigned to the Environmental'Protection Technology
Series. This series describes research performed to develop and
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pollution. This work provides the new or improved technology required
for the control and treatment of pollution sources to meet environmental
quality standards.
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For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 2M02 - Price 65 cents
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EPA-670/2-73-040
September 1973
NITROGEN REMOVAL BY AMMONIA STRIPPING
By
Thomas P. O'Farrell
Dolloff F. Bishop
Alan F. Cassel
Contract No. 14-12-818
Project 11010 EYM
Program Element 1B2033
Project Officer
Dolloff F. Bishop
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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ABSTRACT
Ammonia removals of up to 90% from lime clarified, filtered wastewater
were obtained in a five stage counter current cross flow stripping
tower using air to liquid rates of 400 to 500 ft /gal. Decreases in
operating temperatures from 78 F to 43 F during the cold weather
reduced the stripping efficiency by 30% and caused icing in the tower.
The variation of stripping efficiency'was also studied as a function
of the inlet pH of the water and the ratio of the air to liquid rate.
The rate of calcium carbonate scaling on the tower was determined for
wastewater pH's of 11.5 and 10.5. The heights of transfer units (HTU)
were estimated by using a mathematical model and a computer iterative
technique.
This report is submitted in partial fulfillment of Project 11010 EYM
and Contract No. 14-12-818 by the Department of Environmental Services/
Government of the District of Columbia under the sponsorship of the
Office of Research and Monitoring, Environmental Protection Agency.
Work was completed as of October 1971.
11
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CONTENTS
Abstract ii
List of Figures iv
List of Tables v
Acknowledgments vi
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Experimental 5
V Temperature Effects 10
VI pH Effects 12
VII Scaling Effects 14
VIII Transfer Coefficients 19
IX References 21
X Publications 22
XI Glossary 23
111
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FIGURES
No. Page
1 Advanced Waste Treatment Pilot Plant 4
2 Ammonia Strippers 6
3 Lime Precipitation and Ammonia Stripping System 8
4 Effect of Temperature on Ammonia Removal Efficiency 11
5 Effect of pH on Ammonia Removal Efficiency 13
6 Continuous Operation at pH 11.5 15
7 Effect of Nitrification on Ammonia Removal Efficiency 17
8 Effect of Scaling on Air Rate at pH 10.5 and 11.5 18
9 Height of Transfer Unit 20
IV
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TABLES
No.
Page
I. Secondary Effluent Characteristics
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ACKNOWLEDGMENTS
The ammonia stripping tower was constructed by the Marley Company of
Kansas City, Missouri. The system was constructed and operated by the
staff of the EPA-DC Pilot Plant under the direction of Robert Hallbrook,
chief mechanic; Walter Schuk, chief instrument technician and
George Gray, chief operator.
Special data collection was conducted by P.P. Frauson, chemical
engineer. The height of unit transfer was determined from the data
by J.F. Roesler, sanitary engineer.
VI
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SECTION 1
CONCLUSIONS
1. Air stripping of ammonia in cross flow cooling towers with water
temperatures of 80°F removed 90%- of the ammonia from a non-nitrified
lime clarified secondary effluent at pH 11.5 with an air to liquid
rate of 500 ft3 air/gallon liquid.
2. At an inlet water temperature of 77°F and an air to liquid rate
of 327 ft? air/gallon liquid, efficiencies of ammonia removal at pH's
11.7, 10.5, and 9.7 were 86.2, 80.2 and 51.8%, respectively.
3. At pH 11.5, heavy calcium carbonate scale was produced within the
stripping tower from the C02 ^n the air as the amount of excess calcium
removed from the water was approximately 125 mg/1 as CaCOj. The scale
reduced air rates which lowered the efficiency of ammonia removal. In
addition, the scale was very hard. Because it could not easily be
removed, it caused severe maintenance problems.
4. At pH 10.5 with a reduced calcium ion concentration the rate of
calcium carbonate scale was reduced to 16 mg/1 CaCOj.
5. The efficiency of the tower for ammonia removal depended upon air
temperature. A decrease in air temperature from 80°F to 43°F, reduced
the efficiency of ammonia removal by approximately 30% for air to
liquid rates from 100 to 500 ft3 air/gallon liquid.
6. Freezing occurred when the wet bulb temperature within the tower
reached 32 °F, and produced a shut-down of the system.
7. The height of a transfer unit was developed and is described in
the following equation.
HTU = K () 1.322
HTU = Height of Transfer Unit, ft.
2
G = Air Rate, Ibs. moles/hr./ft .
L = Liquid Rate, Ibs. moles/hr./ft .
K = 2.929 ft.
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SECTION II
RECOMMENDATIONS
The use of air stripping for ammonia removal requires warm climates
or summertime operation, a high lime process, and a low nitrate or
non-nitrified wastewater. Because of these requirements the use of
ammonia stripping within the USA as a means of continuous ammonia
nitrogen removal is limited.
Where conditions permit the use of air stripping, additional studies
are necessary to determine local scaling characteristics.
(fhile calcium carbonate scale can be reduced by stripping the
recarbonated effluent at pH 10.5 it probably can not be eliminated.
Thus future work should aim at developing suitable contacting systems
to improve the mass transfer efficiency and to allow easy cleaning of
the calcium carbonate scale. As an alternate approach, a search for
chemical inhibitors to prevent the formation of calcium carbonate
scale could also be performed.
-------
SECTION III
INTRODUCTION
In raw wastewater and in effluents from secondary treatment plants
without nitrification, ammonia, produced by enzymatic action on the
waste product urea, accounts for approximately 90% of the total soluble
nitrogen concentration. The remaining soluble nitrogen and all of the
insoluble nitrogen are combined with organic compounds. Most of the
ammonia may be removed from the wastewater by air stripping (1) . A
high pH is needed for efficient stripping and is achieved by combining
the stripping process with lime clarification (1) . The addition of
lime in the clarification of wastewater for phosphorus and solids
removal increases the wastewater's pH and converts ammonium ion to
ammonia as follows:
NH+ + Off" » NH OH ^ » NH + HO
Unfortunately, ammonia is highly soluble in water and its volatility
decreases markedly with decreasing temperatures. For these reasons
effective air stripping requires warm temperatures and the use of
large volumes of air per gallon of water.
To reduce power requirements, cooling towers, which provide a low
pressure drop, have been used for air stripping of ammonia at South
Lake Tahoe (1) and Pretoria, South Africa (6). The ammonia removal
efficiency of the system at South Lake Tahoe has been reduced both by
low temperatures and CaCO^ scaling. The low winter temperatures reduce
the ammonia removal to less than 60% by decreasing the ammonia
volatility and also by icing the tower. Calcium carbonate scale at
Tahoe also increases the pressure drop through the tower reducing air
rates and the stripping efficiency. In contrast, the warm climate in
Pretoria, South Africa, eliminates the temperature problems for most of
the year. Severe CaCO3 scaling does not occur (7).
With the variation in the performance of air stripping systems, a pilot
study was performed in the EPA-DC Pilot Plant to evaluate temperature,
pH, and scaling in the stripping process, and to determine the mass
transfer characteristics (height of the transfer unit) of a poly-
propylene grid packing in crossflow towers. The stripping process was
included in a tertiary system (Figure 1) which consisted of lime
precipitation, air stripping of ammonia, filtration/ carbon adsorption,
and solids handling.
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INFLUENT STRIPPING
CLARIFICATION
CO,
SOLIDS
HANDLING
T
LIME WASTE
FILTRATION
V V V V
I C°2
A
EFFLUENT
CI2 ADSORPTION
Figure 1. Advanced Waste Treatment Pilot Plant
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SECTION IV
EXPERIMENTAL
In the stripping process (Figure 2) , a series of five Marley crossflow
cooling towers were each packed with forty, 4 ft. x 5 ft. x 1/2 inch
polypropylene grids. The layers of each grid were spaced every
2 1/2 inches and the grids were packed to promote waved air flow
through the system. The air was drawn through the towers by a 24-inch
centrifugal fan operated by a 5-HP motor. The water was pumped to a
distribution box located on the top of each tower and flowed downward
over the grids. The water flow between towers was controlled by
automatically maintaining a constant level in the collection basin of
the preceding tower. The air was drawn countercurrent to the flow
of water between towers and cross flow within the packing of each tower.
Two types of secondary effluents were fed to the (lime precipitation
and ammonia stripping) treatment system: first, the effluent from the
District of Columbia's Water Pollution Control Plant (modified
aeration) and later, the effluent from the EPA-DC Pilot Plant step
aeration process.
The District of Columbia's modified aeration system (270 MGD) , with
2 hours of aeration time and 500 mg/1 of mixed liquor suspended solids,
never nitrified and approximately 12 mg/1 of NH^-N was available for
air stripping. The EPA-DC Pilot plant's step aeration system (0.1 MGD),
however, with 3.8 hours of aeration time and with 3000 to 4000 mg/1 of
mixed liquor suspended solids, produced nitrification in warm weather
and reduced the available'ammonia for air stripping. The quality of
these effluents and the nitrogen contents are given in Table 1.
During the operation of the ammonia stripping process, lime precipi-
tation, operated in two stages with intermediate recarbonation
(Figure 3), included liming (300 to 400 mg/1 as CaO) the water in the
first stage reactor to produce a pH greater than 11.5, recarbonating
with carbon dioxide to pH 10.5 for precipitation of the excess calcium
ions, and finally flocculating and clarifying the precipitated calcium
carbonate in a reactor identical to the first stage reactor. The
effluent from either the first (pH 11.5) or the second (pH 10.5)
stage clarifier (Figure 3) was fed to the stripping system. In the
temperature study, the system was operated at various air to liquid
rates (G*/L') during periods of warm and cold temperatures. Liquid
loading rates were varied from 1.0 to 2.44 gpm/ft2. Air rates were
varied from 100 to 750 ft air/gallon liquid by a damper setting.
With the available capacity of the fan, G'/L' rates of greater than
400 ft-3 air/gallon liquid could be achieved only at a liquid loading
rate of 1 gpm/ft2.
In the pH study, influent wastewater at pH's 11.7, 11.3, 10.5
-------
AIR
OUT
ttt
WATER
IN
I
AIR
IN
BLOWER
1
WATER
OUT
Figure 2. Ammonia Strippers
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TABLE 1
SECONDARY EFFLUENT CHARACTERISTICS
EFFLUENT
BOD SUSPENDED SOLIDS TKN-N NH3-N (NO + NO )-N
mg/1
District of Columbia 48.0
(modified)
68
20.4 12.0
0.14
EPA-DC
(Step non-nitrified) 13.4
27
10.9 9.5
0.9
EPA-DC
(Step nitrified)
20.7
44
5.3 2.0 10.0
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STRIPPING
CO
INFLUENT
LIME
rvn
ITi
FIRST STAGE
CO.
WASTE
A
TO
FILTER
SECOND STAGE
Figure 3. Lime Precipitation and Ammonia Stripping System
-------
and 9.7 were fed to the tower at a liquid loading of 2 gpm/ft2 (32 gpm)
with an average air to liquid rate (G'/L') of 327 ft3 air/gallon liquid.
For an influent at pH 11.7, the system was fed effluent from the first
stage chemical clarifier. Influents at pH's 11.3, 10.5, and 9.7 were
provided from the second stage clarifier with the pH controlled by the
appropriate addition of carbon dioxide in the recarbonation tank.
During the two continuous operations to determine the effect of scale,
the influent to the system was continuously fed at pH 11.5 and later at
pH 10.5 with a liquid loading rate of 2 gpm/ft^. At both pH levels,
the initial air to liquid rate was approximately 350 ft air/gallon
liquid.
The high pH scaling test was initiated in late July, 1969 on limed
(D.C. modified aeration) effluent from the first stage lime clarifier
which contained an excess calcium ion concentration of 150-200 mg/1
Ca++. The scaling test at pH 10.5 was initiated in late March 1970
and continued into mid July 1970 on limed (Pilot Plant step aeration)
effluent from the second stage lime clarifier with inlet calcium ion
concentrations of approximately 50 mg/1 Ca++.
During both the temperature and pH studies, liquid samples of the
influent and effluent from each tower were analyzed for ammonia,
calcium, temperature, pH and alkalinity. The relative humidity of the
influent air and the temperature of the air between each stage were
also recorded. The ammonia concentrations were determined by an
automated Technicon procedure (2). The calcium concentrations were
determined on a Perkin-Elmer Model 303 Atomic Adsorption Spectrophoto-
meter. The alkalinities were determined by the procedure in Standard
Methods (5).
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SECTION V
TEMPERATURE EFFECTS
In warm weather tests at pH 11.5 with inlet air and water temperatures
averaging 78 and 79°F, respectively, air stripping cooled the outlet
water temperature by evaporation of the liquid within the tower to an
average of 72°F. In a similar test with the inlet air temperature
averaging 43°F and the inlet water temperature averaging 61°F, the air
stripping cooled the outlet water to an average temperature of 41°F.
The efficiency of the tower (Figure 4) for ammonia removal was directly
dependent upon the air and water temperature. The efficiency of the
system during the warm weather tests increased from 50% at 100 ft
air/gallon liquid to 90% at approximately 500 ft air/gallon liquid.
During the cold weather tests, however, the removal efficiency increased
from 20% at 100 ft air/gallon liquid to 60% at 500 ft air/gallon
liquid. The decrease in efficiency from the warm to cold temperatures
was approximately 30% over the entire air to water flow range. In
addition to the decreased stripping efficiency, tower operation was
also interrupted by icing. Since the ammonia stripping system is an
efficient cooling tower, evaporation within the tower cooled the outlet
water and air temperatures. Thus, icing within the tower occurred when
the wet bulb temperature of the air within the tower reached 32 F even
at inlet air temperatures greater than 32°F.
10
-------
o
UJ
o:
<
O
80
60
40
20
0
0
72
o -
---
LIQUID RATES
(GPM/FT2)
• 2.44
* 2.00
• 1.50
• 1.00
200 400 600
G'/l!.. FT3AIR/GAL LIQUID
Figure 4. Effect of Temperature on Ammonia•Removal Efficiency
800
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SECTION VI
pH EFFECTS
The effect of influent pH on the removal efficiency of ammonia was
determined during the summer with the inlet water and air temperatures
averaging 77 and 76°Ff respectively. During air stripping, the water
was cooled to an average outlet water temperature of 69°F. The results
of air stripping through various packing depths with influents at pH's
9.7, 10.5, 11.3, and 11.7 are shown in Figure 5. As seen, the
efficiency of removal rvas dependent upon pH with the highest removal
(86.2%) obtained at pH 11.7. However, the decrease in efficiency of
removal from pH 11.7 to 10.5 was approximately 6%. The decrease in
inlet pH from 11.7 to 9.7, however, produced a marked decrease in
total efficiency from 86.2 to 51.8%.
12
-------
100
o
Ld
_ cc
80
60
< 40
z
o
2
< 20
0
10
PACKING
15
DEPTH, FEET
20
25
Figure 5. Effect of pH on Ammonia Removal Efficiency
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SECTION VII
SCALING EFFECTS
The system was operated with the influent at a pH greater than 11.5 for
75 days. During the operation, the inlet ammonia concentration averaged
11.5 mg/1 NHj-N. The efficiency of the system (Figure 6) decreased from
80 to 55% (residual NH3-N = 2.5 to 4.5 mg/1) over the 75 days as the
formation of CaCO 3 scale in the tower decreased the air to liquid
(G'/L1) rates from an initial 350 ft3 air/gallon liquid to 250 ft air/
gallon liquid. Near the end of the 75 days of operation, the efficiency
of the system, however, had decreased by approximately 20% more than
that expected for the decrease in the G'/L' at an average air temperature
of 78°F (Figure 4). The additional loss of efficiency was produced by
a decrease in ambient air temperature from 80°F to 59°F.
The accumulation of calcium carbonate scale within the connecting pipes
and control valves forced intermittent shut-down of the system for
maintenance. At the end of the high pH (^^11.5) operation, the towers
were opened for inspection. A heavy scale of calcium carbonate was
evenly distributed throughout the towers, while negligible scaling
occurred in the distribution box of the first tower and associated inlet
piping. Thus, the scaling was not caused by post precipitation of the
effluent from the first-stage clarifier but by the formation of calcium
carbonate from the carbon dioxide in the stripping air.
The average packing grid increased from a tare weight of 2 Ibs. to
22 Ibs. or by 20 Ibs. of calcium carbonate scale. The scale, 1/4 to
3/8 inches thick, contained more than 99% calcium carbonate with traces
of organic carbon and phosphorus. The scale was crystalline, hard, and
could not be removed by a high pressure water hose. Each grid had to
be manually cleaned. With forty grids per tower, the total accumulation
of scale in the five towers was approximately 4000 Ibs. Based on the
accumulated flow through the system, the 2 tons of scale corresponded to
a scale rate of 125 mg/1 of calcium carbonate. Material balances with
alkalinity analyses verified this result.
In addition to the effect of calcium carbonate scaling on maintenance
and reduction in air capacity, the loss of the calcium carbonate
seriously affected the operation of the chemical clarification system
on the D.C. modified secondary effluent. Control of the slurry pool in
the first clarifier (3) required recycle of the solids from the second-
stage clarifier to the first. Since 35% of the calcium carbonate was
lost through scale formation in the stripping tower, the calcium
carbonate produced in the recarbonation process and recycled to the
first-stage clarifier was not sufficient to stabilize the slurry pool
in the first-stage lime clarifier. Hence, periodic overflow of the
solids into the ammonia stripping system also interrupted the stripping
process.
14
-------
(D
ro
h-
UJ
CC
o
350
300
250
200L
100
90
80
70
60
50
40
30
20
IQ
10
20
30
40
DAYS
50
60
70
Figure 6. Continuous Operation at pH 11.5
-------
In the low pH (10.5) operation, the influent to the tertiary treatment
system (chemical clarification and ammonia stripping) was the effluent
from the EPA-DC Pilot Plant's secondary (step aeration) treatment
system. The step aeration process fluctuated through various stages
of nitrification, and thus after chemical clarification provided an
influent of varying ammonia concentration to the ammonia stripping
column (Figure 7) . During the first seventeen days of operation
(Figure 7), nitrification did not occur in step aeration. The average
concentration of ammonia in the inlet and outlet of the tower were
9.5 and 4.2 mg/1 NH -N, respectively, for an average removal of 56%.
During this period, the average outlet water temperature was 4STF with
an average G'/L' value of 347 ft air/gallon liquid. Between the 35th
and 45th day of operation, the step aeration system produced little
nitrification and the percent removal of ammonia averaged 66% (3.1 mg/1
NH -N average residual) with an average outlet water temperature of 57°F.
During the pH studies, nearly 80% of the ammonia was removed under
similar operating conditions with an outlet water temperature of 69°F.
While stripping efficiencies were affected by nitrification, the rate
of calcium carbonate scaling and its effect upon the reduction in the
air to liquid ratio were unaffected. The calcium carbonate scale -in
the pH 10.5 tests reduced the air to liquid ratio from an initial
350 ft3 air/gallon liquid to approximately 330 ft3 air/gallon liquid
(Figure 8) over the 112 day period. During this period, the inlet and
outlet calcium ion concentrations averaged 48.3 and 41.8 mg/1 of Ca ,
respectively. The calcium ion decrease corresponded to a calcium
carbonate scaling rate of 16 mg/1 CaCO .
It was hoped that operation at the lower pH would produce a softer
scale which could be easily flushed from the packing. Examination of
the scale showed it to be as hard as the scale formed at pH 11.5.
Unfortunately, during this long-term test at low pH, several extended
runs were made at pH 11.5. Consequently, a definitive statement
cannot be made about the relative hardness of the scale at pH 10.5.
16
-------
o>
E
15
12
0
INFLUENT
24
48
72
DAYS
96
120
Figure 7. Effect of Nitrification on Ammonia Removal Efficiency
-------
370
Q
ID
O
(D
340-
310
<£. 280
u.
250
220
/•
—5—
••%
Vx
T 1 1 1 r
•
• A~* -
••i ••
•
1 1—z—r
10.5
/\>
0
A*
i i
I i
24
48
72
96
120
DAYS
Figure 8. Effect of Scaling on Air Rate at pH 10.5 and 11.5,
-------
SECTION VIII
TRANSFER COEFFICIENTS
A mass transfer correlation in crossflow cooling towers has been
developed for air stripping of aimonia by Roesler et al. (4). The
correlation employs an iterative computer procedure to determine the
height of the transfer unit for the packing within the crossflow
cooling tower. The procedure includes both temperature and humidity in
the correlation.
The mass transfer characteristics of the tower were evaluated through
the computer program. Data from fifteen controlled runs on the first
crossflow tower with an influent pH of 11.7 and warm temperatures
were used to calculate the overall gas height of a transfer unit
(Figure 9). The data was collected over a three day period; thus changes
in packing characteristics produced by a gradual increase in scale
formation were minimal.
The equation from a least square regression of the data is:
HTU = K A 1.322
Li
HTU = Height of Transfer Unit, ft.
2
G = Air Rate, Ibs. moles/hr/'ft
2
L = Liquid Rate, Ibs. moles/hr/ft
K = 2.929 ft.
The regression yielded a correlation coefficient of 0.91.
19
-------
h-
U-
cc
LJ
u.
or
u.
O
O
UJ
X
100
80
60
40
20
10
8
6
I
0.3 0.4 0.6 0.8 1.0 2.0 4.0 6.0 8.0 10.0
AIR LOADING RATE / LIQUID LOADING RATE
-------
SECTION IX
REFERENCES
1. Gulp, Russell, "Water Reclamation at South Tahoe," Water and Wastes
Engineering, Vol. 6, No. 4, April 1969.
2. "FWPCA Methods for Chemical Analysis of Water and Wastes," Dept.
of the Interior, Federal Water Pollution Control Admin.,
Cincinnati, Ohio (November 1969).
3. O'Farrell, T.P., Bishop, D.F., and Bennett, S.M., "Advanced Waste
Treatment at Washington, D.C.," presented at the 65th Annual
AIChE Meeting, Cleveland, Ohio, May 1969.
4. Roesler, J.F., Smith, R., andEilers, R.G., "Mathematical
Similation of Ammonia Stripping Tower for Wastewater Treatment,"
Internal Report, Advanced Waste Treatment Research Laboratory,
Cincinnati, Ohio, 1970.
5. "Standard Methods for the Examination of Water and Wastewater,"
12th Ed., American Public Health Association, New York (1965).
6. Stander, G.K., and VanVuuren, L.R.J., "The Reclamation of Potable
Water from Wastewater," Journal of Water Pollution Control
Federation, 3, Vol. 4, pp 355-367, March 1969.
7. VanVuuren, L.R.J. - private communication.
22
-------
SECTION X
PUBLICATIONS
O'Farrell, T.P., Frausonf P.P., Cassel, A.F. , and Bishop, D.F. ,
"Nitrogen Removal Jby Ammonia Stripping," presented at the 160th
National ACS Meeting, Chicago (September 1970).
This paper has been accepted and will be published in the Journal of
the Water Pollution Control Federation.
22
-------
SECTION XI
GLOSSARY
Air Stripping - The transfer of the volatile component ammonia from
water into air by physical contact of the water with air.
Ammonia-Nitrogen (NH -N) - The weight of ammonia expressed in terms of
the nitrogen combined in ammonia, i.e. the weight of ammonia x 14.
17.
Countercurrent Flow - With reference to the air water system, if the
water flows from tower 1 to tower 6 in sequence, the air flowed from
tower 6 to tower 1 also in sequence.
Cross Flow - Refers to the flow of air and water in the column. The
water flowed from top to bottom and the air from one side across to
the opposite side.
G'/L' - Ratio of air to water flow, ft of air/gallon of water.
HTU - Height of a transfer Unit. In terms of a single length dimension,
the height of apparatus required to accomplish a separation of standard
difficulty.
MGD - Million gallons per day.
Mixed Liquor Volatile Suspended Solids - Approximation of the quantity
of micro-organisms present in mg/1.
Modified Aeration - An activated sludge process typified by relatively
low mixed liquor suspended solids, short detention time and high
organic loading.
Step Aeration - An activated sludge process in which the wastewater is
added at the 1/4, 1/2 and 3/4 points along the length of the reaction
basin.
Nitrification - The biological conversion of ammonia under specific
conditions to first nitrite and then nitrate.
Recarbonation - Removal of Ca from limed water by precipitation as
CaCO , achieved by bubbling CO_ through the water.
23
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Rep-rtNo.
w
•i. Title
NITROGEN REMOVAL BY AMMONIA STRIPPING
EPA-DC PILOT PLANT
Department of Environmental Services
Government of the District of Columbia
5000 Overlook Ave. S.ff.
Washington, D.C. 20032
12. Sponsoring Organizaf'in
5. R,-_ortDf-
6.
.'. X.tir/ion's.)
O'Farrell, Thomas P.f Bishop, Dolloff F.r and Cassel, Alan F.
11010 EYM
14-12-818
13. Typet'Repor and
Period Covered
Environmental Protection Agency report number EPA 670/2-73-040 ,
September 1973.
lr>. <4£iT?VfOi
Ammonia removals of up to 90% from lime clarified filtered wastewater were obtained
in a five stage counter current cross flow stripping tower using air to liquid rates
of 400 to 500 ft3/gal. Decreases in operating temperatures from 78°F to 43°F during
the cold weather reduced the stripping efficiency by 30% and caused icing in the
tower. The variation of stripping efficiency was also studied as a function of the
inlet pH of the water and the ratio of the air to liquid rate. The rate of calcium
carbonate scaling on the tower was determined for wastewater pH's of 11.5 and 10.5.
The heights of transfer units (HTU) were estimated by using a mathematical model
and a computer iterative technique.
17a. Descriptors
*Jomaonia
*Mass Transfer
Calcium Carbonate
: Lime
17 b. I dentil i* rs
*Air Stripping
*Ammonia Removal
Wastewater Treatment
* Scaling
05D
19. S
(Report)
20. Secur;:,? C/ass,
<^>
21. ;; -. of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Thomas P. O'Farrell
Environmental Protection Agency
------- |