United States
                      Environmental Protection
                      Office of Water
                      Washington, D.C.
September 2000
Waste water
Technology  Fact Sheet
Ammonia  Stripping

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/.,

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):
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


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
                                           \^~*	AIR INLET
                                      ~J	—--—-TL WATER
                                            I COLLECTING BASIN
                                   COUNTERCURRENT TOWER
                     Source: Gulp, et. al, 1978.

                       FIGURE 1 TWO TYPES OF STRIPPING
                     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).


                     The following advantages and disadvantages should
                     be considered when comparing ammonia stripping
                     with other ammonia removal systems.

      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

      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.
     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.


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

       pH of wastewater (10.8-11.5).

       Air pressure drop (0.015"  - 0.019"  of

       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.


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).


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

     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

•    Clarifying the influent before stripping.

•    Monitoring and  controlling noise from the
     stripping equipment.

Table  1 lists sources and  solutions  to noise


The  cost of  ammonia  stripping depends  on the
manufacturer, the site, the capacity of the plant, the
 Noise Source
Possible Solutions
 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.


Other Related Fact Sheets

Other EPA Fact Sheets  can be found at  the
following web address:

1.     "Air Stripping" [http://www.scana.com/sce

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.

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].


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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