vvEPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA832-F-00-019
September 2000
Waste water
Technology Fact Sheet
Ammonia Stripping
DESCRIPTION
Ammonia stripping is a simple desorption process
used to lower the ammonia content of a wastewater
stream. Some wastewaters contain large amounts
of ammonia and/or nitrogen-containing compounds
that may readily form ammonia. It is often easier
and less expensive to remove nitrogen from
wastewater in the form of ammonia than to convert
it to nitrate-nitrogen before removing it (Gulp et a/.,
1978).
Ammonia (a weak base) reacts with water (a weak
acid) to form ammonium hydroxide. In ammonia
stripping, lime or caustic is added to the wastewater
until the pH reaches 10.8 to 11.5 standard units
which converts ammonium hydroxide ions to
ammonia gas according to the following reaction(s):
NH4++OH-
Figure 1 illustrates two variations of ammonia
stripping towers, cross-flow and countercurrent. In
a cross-flow tower, the solvent gas (air) enters
along the entire depth of fill and flows through the
packing, as the alkaline wastewater flows
downward. A countercurrent tower draws air
through openings at the bottom, as wastewater is
pumped to the top of a packed tower. Free
ammonia (NH3) is stripped from falling water
droplets into the air stream, then discharged to the
atmosphere.
APPLICABILITY
Ammonia stripping works well with wastewater
that has ammonia contents between 10 to 100mg/l.
For higher ammonia content (more than lOOmg/1),
•-COLLECTION BASIN
CROSS-FLOW TOWER
-u
»;
7
\^~* AIR INLET
~J —--—-TL WATER
I COLLECTING BASIN
COUNTERCURRENT TOWER
Source: Gulp, et. al, 1978.
FIGURE 1 TWO TYPES OF STRIPPING
TOWERS
it may be more economical to use alternate
ammonia removal techniques, such as steam
stripping or biological methods. Air stripping may
also be used to remove many hydrophobic organic
molecules (Nutrient Control, 1983).
ADVANTAGES AND DISADVANTAGES
The following advantages and disadvantages should
be considered when comparing ammonia stripping
with other ammonia removal systems.
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Advantages
The operation is relatively simple and not
affected by wastewater fluctuation if pH and
air temperature remain stable.
Ammonia stripping is a mechanical
procedure and creates no backwash or
regeneration.
Ammonia stripping is unaffected by toxic
compounds that could disrupt the
performance of a biological system.
Ammonia stripping is a controlled process for
selected ammonia removals.
Disadvantages
Water must be re-pumped to the stripping
tower. Pumping requires higher maintenance
and power requirements.
Scale formation can be removed hydraulically
in most cases but not all, resulting in a need
to pilot test at most locations.
Ammonia stripping cannot be performed in
freezing conditions (unless sufficient heated
air is available). Fogging and icing result in
a significant reduction in ammonia removal.
While ammonia is usually discharged to the
atmosphere at low level (6 mg/m3), this may
be unacceptable in certain locations due to air
quality concerns or regulations.
Ammonia stripping does not remove nitrite
and organic nitrogen.
Air pollution problems may result from
ammonia and sulfur dioxide reaction.
Air stripping often requires the addition of
lime to control pH, which may create
operation and maintenance concerns.
Noise may be a problem.
• High pH wastewater will corrupt the wood
packing of the stripping tower.
DESIGN CRITERIA
The following criteria should be considered when
designing ammonia stripping systems. Optimum
conditions are noted in parentheses.
Hydraulic wastewater loading (0.1 to 0.2
1/min/m3 or 1 to 2 gal/min/ft2).
• Stripping air flow rate (32 to 54 1/min/m3 or
300 to 500 ft3/min/gal).
• Packing depth (6.1 to 7.6 meters or 20-25
ft).
pH of wastewater (10.8-11.5).
Air pressure drop (0.015" - 0.019" of
water/ft).
Blower type.
Site and land requirements.
Packing material (plastic or wood).
Packing spacing (approx. 5 cm or 2"
horizontal and vertical).
• Water temperature.
• Plant capacity.
• Ammonia concentration of the wastewater.
• Water distribution uniformity.
• Scale removal and ease of cleaning up.
The introduction of air into the system is the major
design difference in the two basic types of towers.
Air enters from the side in the cross-flow tower,
which is less efficient than the countercurrent tower
where the air enters from the bottom of the tower.
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PERFORMANCE
Ammonia stripping performance is highly
dependent on air temperature and air/water ratios.
Efficiency decreases significantly as air temperature
decreases. At 20'C (68' F), there is a 90 to 95%
ammonia removal efficiency, while at 1O C (5O F),
efficiency decreases to 75 percent.
Lake Tahoe EPA Research Project
Lake Tahoe found that the removal rate was 95
percent ammonia nitrogen at 11.5 pH using 53,460
1/m3 (400 gal/ft3) wastewater during warmer
weather (Gulp et al, 1978). Erected in 1969, the
7.3 meter (24-foot) tower uses a cross-flow design
to treat a flow of 28,390 nrVday (7.5 MOD).
OPERATION AND MAINTENANCE
A routine O&M schedule should be developed and
implemented for any ammonia stripping system.
Regular O&M includes the following activities:
• Following all manufacturer O&M
recommendations.
Testing and calibrating equipment.
Maintaining pumps and blowers.
Inspecting the tower periodically for fouling.
Maintain proper air and water flows.
Proper pH adjustment with lime requires safe
handling.
• Clarifying the influent before stripping.
• Monitoring and controlling noise from the
stripping equipment.
Table 1 lists sources and solutions to noise
problems.
COSTS
The cost of ammonia stripping depends on the
manufacturer, the site, the capacity of the plant, the
TABLE 1 SOURCES OF AND SOLUTIONS
TO POTENTIAL NOISE PROBLEMS
Noise Source
Possible Solutions
Motors
Fans
Water Splashing
Proper installation, maintenance,
and insulation
Reduction in tip speed and
installation of exhaust silencers
Water shielding of the tower
packing and air inlet plenum
Source Culpef a/., 1978.
ammonia concentration of the wastewater, the flow
rate desired, the types of blowers, and the water
temperature (water temperature affects design
which affects price). Price comparisons are
possible with a specific set of design criteria.
Operation and maintenance include power,
materials, chemical, and labor.
REFERENCES
Other Related Fact Sheets
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
1. "Air Stripping" [http://www.scana.com/sce
%26g/business_solutions/technology/ewt
wair.htm].
2. Cornwell, David A., 1990. Air Stripping
and Aeration. In Water Quality and
Treatment: A Handbook of Community
Water Supplies. Ed Pontius, Frederick W.,
AWWA 4th Ed. McGraw-Hill, Inc., NY.
3. Culp, Russel L.; Wesner, George Mack; and
Culp, Gordon L., 1978. Handbook of
Advanced Wastewater Treatment. 2nd Ed.
Van Nostrand Reinhold Co., NY.
4. Nutrient Control, Manual of Practice FD- 7
Facilities Design, 1983. Water Pollution
Control Federation.
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5. U.S. EPA, Wickramanayake, G.B.; Evers,
D.; Kittel, J.A.; Gavaskar, A., 1991. Bench-
Scale Evaluation of Ammonia Removal
from Wastewater by Steam Stripping. EPA
600/2-91-046, Washington, D.C.
6. U.S. EPA, 1980. Innovative and
Alternative Technology Assessment Manual.
EPA 430/9-78-009, Washington, D.C.
7. Water Engineering & Management
Ammonia Removal Suppliers
[http ://www. waterem. com].
ADDITIONAL INFORMATION
ResinTech, Inc.
Frank DeSilva
1980 Old CuthbertRd.
Cherry Hill, NJ 08034
Water Equipment Services
Mark Gorrell
6389 Tower Lane
Sarasota, FL 34240
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
1200 Pennsylvania Avenue, N.W.
Washington, D.C. 20460
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