HOW MUCH DOES
NITROGEN CONTROL COST?
1 IK- chart (right) shows the approximate
nal ioiuil average lotul cosls, including plant
ainoi i i/ation (25 years ul 6 percent), oper-
aiion and nuiinienanee lor biological ni-
n ogcn conirol i ne ill oils. Costs tor nitrogen
removal by breakpoint chlorination (in
addition to cosls for conventional treal-
meni ) are constant at approximately 6c'/
I 000 gallons Mealed. Cosls for amnionia-
sitipping and ion-exchange can vary sig-
inlicanlly depending on plant si/e and
location, availability of materials, etc. A
detailed investigation must therefore be
made to determine exact costs for these
two physical-chemical methods of remov-
ing nitrogen from waslewaler.
WHERE IS CONTROL OF
NITROGEN IN WASTEWATER
BEING APPLIED?
1
25 50
Plain Size (Million Ga
75 10
Ions per Dayl
A. Conventional Treatment
("Ins Nitrification
1'lus Denitrifiailion
K. Conventional Treatment
Plus Nitrification
('. Conventional Treatment
This is a partial listing of full-scale nitro-
gen control treatment plants under design.
construction or operation.
Washington, 1). C.
1 ampa. Horida
Alexandria. Va.
Salt Cieek (Chicago). III.
A i ling! on. Ya.
Madison. Wise.
Ian lax County, Va.
Him. Mich.
\\ankeegaii. III.
Highland Park, 111.
(itirnce, 1II.
Jackson. Mich.
()i atme Count \ . Calif.
lienton Harbor. Mich.
Ovvosso. Mich.
Central Contra C'osta. Calif.
Rosemonl. Minn.
H I am>. Texas
How (Million
Gallons/Day)
.soil
60
54
50
.;o
30
22.5
20
20
18
17
17
15
13
6
Type Facility
Suspended Growth System
Fixed Film Denilrification
Ion-Exchange
F'i.xed Film Denitrificalion
Breakpoint Chlorinaiion
Nitrification
Ion-Exchange
Nitrification
Nitrification
Nitrification
Nitrification
Nitrification
Ammonia Stripping
Nitrification
Breakpoint Chloiinalion
Suspended Growth System
Ion-Exchange
Fixed Film Denilrification
WHERE CAN I GET
MORE INFORMATION?
( ontacl your consulting engineer
nr write to:
Environmental Protection AgencA
'-. Technology Transfer
Washington, D.C. 20460
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HOW CAN NITROGEN IN
WASTEWATER BE CONTROLLED?
Ammonia nitrogen can lie reduced in con-
centration or removed I rom waste water by
several processes. These processes can be di-
vided into I wo broad categories: biological
methods and physical-chemical methods.
BIOLOGICAL METHODS One meth-
od of ensuring a low ammonia content in
treated wastewater diluents is to induce
nitrification to occur in the treatment sys-
tem. Nitrification is merely the biological
conversion ol nitrogen in the lorui ol am-
monia to nitrogen in the form of nitrate.
Nitrification is accomplished by providing
that amount of oxygen required in the
bio-chemical reaction which converts am-
monia nitrogen to nitrate nitrogen. This
is roughly 4.5 pounds of oxygen per pound
of ammonia nitrogen in the wastewater.
'•.quipment required consists basically of
tank through which the wastewater to
e nitrified passes, and oxygen or air gener-
ing. pumping, and diffusion equipment.
When the effluent from a wastewater
eatment plant is discharged to a recciv-
g water with a significant flow, such as
•'ivcr. nitrate nitrogen may not have any
rerse effects upon it. In fact, a nitri-
ii-il effluent free of substantial quantities
of ammonia can oiler several advantages:
I. Nitrate nitrogen provides oxygen to
sludge beds and prevents the forma-
tion of septic odors
2. A nitrified effluent contains less sol-
uble organic material than the same
effluent before nitrification
3. Nitrified effluents are more ef-
ficiently disinfected by chlorine
treatment
4. A nitrified effluent reduces the oxy-
gen demand on the receiving waters
The deciding factor in determining
whether the discharge of a nitrified ef-
fluent to a free-flowing receiving water
is acceptable is the level of nitrate nitro-
gen contained in it. If it is loo high, then
further action is necessary to control the
nitrogen content ol the el fluent. This is
also the case when treated waslewater is
discharged to relatively still bodies of wa-
ter such as lakes, reservoirs, and estuaries.
In these cases even a highly nitrified ef-
fluent can have harmful effects, such as
fostering algal blooms.
If a nitrified effluent is determined un-
acceptable, there arc two steps which can
be taken. Each of these steps involves
dcnitrification the conversion of nitrate
nitrogen to nitrogen gas.
1. Suspended Growth Dcnitrification.
In this form of dcnitrification. nitrified
wastewater Hows to a tank where an or-
ganic compound (such as methyl alcohol)
is added in proportion to the amount of
nitrate nitrogen present. The end products
of the reaction induced in this tank are
nitrogen gas and carbon dioxide, both of
which are liberated to the atmosphere.
2. Fixed Film Dcnitrification. As in
suspended growth denitrification. an or-
ganic compound is added to the nitrified
wastewater. However, in this form of de-
nitrification, the nitrified wastewater and
organic compound passes through a col-
umn of fine media such as sand. Denitri-
fying bacteria are produced and attach as
a slime to the media surface. The end pro-
ducts again are nitrogen gas and carbon
dioxide, which are released to the atmos-
phere. Fixed-film denitrification has the
added benefit of filtration, and under nor-
mal circumstances will produce an effluent
low in suspended solids concentration.
Biological Methods of Controlling "•';*
Primary
Secondary
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PHYSICAL-CntMICAL METHODS
There aie several other means of removing
nitrogen from wastewater—all of which
are physical-chemical rather than biologi-
cal. They are:
1. Ammonia-Stripping. The ammonia
nitrogen which, as mentioned previously,
is present in wastewater during conven-
tional biological treatment can be removed
by a physical process called desorption
or, more commonly, "stripping." Simply
stated, the wastewater is first made very
alkaline by adding lime, and the ammonia
is then induced to leave the water phase
and enter the gas phase where it is re-
leased to the atmosphere. To accomplish
tliii stripping, the wastewater is merely
contacted with a sufficient quantity of
vnonia free air. This contacting with
air is done in a slat-filled tower very simi-
lar to those used in industry to cool water.
It should be pointed out that ammonia-
stripping is limited to warm weather areas
with little or no prolonged freezing. Also
the impact of ammonia discharge on the
surrounding environment must be eval-
uated on a case-by-case basis.
2. Breakpoint Chlorination. Chlorine
added to wastewater reacts with the am-
monia nitrogen ti m nitrogen gas. This
may be the simplest i itrogen removal pro-
cess, but it has sonn disadvantages. One
of these is the amount of chlorine re-
quired—approximately 10 parts of chlo-
dlfcViic Compound
Wastewater
ation
Fixed Film System
Denitrification
rine to remove one part of ammonia.
Therefore, a city of 100,000 would require
approximately 6 million pounds ot chlo-
rine per year (abotit 30 times that required
for normal disinfection purpo'ses). The
transportation and handling problems are
obvious. Another possible disadvantage is
that this large dose of chlorine may re-
sult in the formation of chlorides which
would have to be eliminated by subse-
quent demineralization.
3. 1'on-Exchange. This nitrogen remov-
al process involves passing ammonia-laden
wastewater through a series of columns
packed with a material called clinoptilo-
lite. The ammonium ion adheres to or is
absorbed by the clinoptilolite. When the
first column in series loses its ammonia
adsorptive capacity, it is removed from
the treatment scheme and washed with
limewater. This step converts the captured
ammonium ions to ammonia gas, which
is then released to the atmosphere by con-
tacting heated air with the wastewater
stream, much the same as described pre-
viously under ammonia stripping.
A. Wastewater Inlet
B. Regenerant Inlet
C. Regenerant Dit'fuser
D. Clinoptilolite
E. Underdrain System
I . treated Wastewater
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Nitrogen in its many forms has long played
a fundamental role in the aquatic environ-
ment. It is now apparent that ecological
imbalances in the natural environment
have been caused, in part, by the exces-
sive discharges of nitrogenous materials to
natural waterways. Along with phospho-
rus, nitrogen occupies a critical role in the
eutrophication of lakes. In certain forms
nitrogen is one of the major nutrients sup-
porting blooms of green and blue-green
algae in surface waters. In addition to the
nutrient value of nitrogen, the oxygen
demand of nitrogen forms can represent
as much as 70% of the total oxygen de-
mand of conventionally treated munici-
pal wastewater.
During conventional biological waste-
water treatment, almost all the nitrogen
contained in the wastewater is converted
into the ammonia nitrogen form. Al-
though ammonia has very little toxicity
to humans, treated wastewater effluent
containing ammonia has several undesir-
able features:
1. Ammonia consumes dissolved oxy-
gen in the receiving water
2. Ammonia can be toxic to fish life
3. Ammonia is corrosive to copper
fittings
4. Ammonia increases the amount ot
chlorine required for disinfection
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