The document discusses wastewater treatment processes for removing nitrogen. It describes the forms of nitrogen found in wastewater and explains why nitrogen needs to be treated. The nitrogen cycle and key processes like nitrification, denitrification, and biological nitrogen removal are summarized. Physicochemical and biological approaches to secondary treatment are compared.

2. Wastewater Treatment Plant
A WWTP is the place where wastewater is treated to
remove pollutants before it enters a water body or
reused.
It includes physical , chemical & biological processes
to remove physical , chemical and biological
contaminations.

5. Forms Of Nitrogen In Wastewater
• Ammonia – NH3
• Nitrite – NO2
-
• Nitrate – NO3
-
• Organic nitrogen

6. • Total Kjeldal Nitogen-TKN
Sum of organic nitrogen + ammonia
• Total Inorganic Nitrogen-TIN
Sum of Ammmonia + Nitrite + Nitrate

7. Why is it necessary to treat the forms of
nitrogen?
• Improve receiving stream quality
• Increase chlorination efficiency
• Minimize pH changes in plant
• Increase suitability for reuse

8. • Prevent ammonia toxicity
• Protect groundwater from nitrate contamination
• To control the growth of algae
• To prevent the DO depletion
• Odor problems

9. • To prevent imbalance of natural ecological systems and
increase of eutrophication
• increase risks to human health, such as NO3-N concentration
in the groundwater for potable use.

11. • Nitrification is the biological oxidation of ammonia or
ammonium to nitrite followed by the oxidation of the nitrite to
nitrate

12. Nitrification
NH3-N
Ammonia N
NO2-N
Nitrite N
NO2-N
Nitrite N
NO3-N
Nitrate N
Nitrosomonas
Nitrobacter
Nitrification of Ammonia Occurs in
Two Steps

13. Heterotrophic Bacteria Break Down Organics
Generate NH3, CO2, and H2O
Autotrophic Bacteria Utilize Inorganic Compounds
(and CO2 as a Carbon Source)
Assimilation Some Nitrogen Will Be
Removed By The Biomass

14. Nitrogen cycle
Nitrogen is present in the environment in a wide variety of
chemical forms including
• ammonium (NH4
+)
• nitrite (NO2
-)
• nitrate(NO3
-)
• nitric oxide (NO) or
• nitrous oxide (N2O)
• inorganic nitrogen gas (N2)
• organic nitrogen

15. • Organic nitrogen may be in the form of a living
organism, humus or in the intermediate products
of organic matter decomposition.
• The processes of the nitrogen cycle transform
nitrogen from one form to another.
• Many of those processes are carried out
by microbes, either in their effort to harvest
energy or to accumulate nitrogen in a form
needed for their growth.

16. The processes of Nitrogen cycle
1. Nitrogen Fixation
2. Assimilation
3. Ammonification
4. Nitrification
5. Denitrification
N-
CYCLE

17. Nitrogen Fixation
• Some fixation occurs in lightning strikes, but most
fixation is done by free-living
or symbiotic bacteria known as diazotrophs
• These bacteria have the nitrogenase enzyme that
combines gaseous nitrogen with hydrogen to
produce ammonia , which is converted by the bacteria
into other organic compounds
• Example of N-fixing bacteria includes:
 free-living bacteria is Azotobacter
 Symbiotic nitrogen-fixing bacteria such
as Rhizobium usually live in the root nodules
of legumes

18. Assimilation
• Plants take nitrogen from the soil by absorption
through their roots in the form of
either nitrate ions or nitrite ions
• Plants cannot assimilate ammonium ions
• nitrate is absorbed, & reduced to nitrite ions and
then ammonium ions for incorporation into amino
acids, nucleic acids, and chlorophyll
• Animals, fungi, and other heterotrophic organisms
obtain nitrogen by ingestion of aminoacids,
nucleotides and other small organic molecules

19. Nitrification
• Nitrification is a microbial process by which
reduced nitrogen compounds (primarily
ammonia) are sequentially oxidized to nitrite
and nitrate
• The conversion of ammonia to nitrate is
performed primarily by soil-living bacteria and
other nitrifying bacteria
• The nitrification process is primarily
accomplished by two groups of autotrophic
nitrifying bacteria

20. In the first step of nitrification,
ammonia-oxidizing bacteria oxidize
ammonia to nitrite according to
equation
NH3 + O2 → NO2 - + 3H+ + 2e-
Nitrosomonas is the most frequently
identified genus associated with this
step, although other genera,
including Nitrosococcus, and
Nitrosospira

21. In the second step of the process, nitrite-oxidizing
bacteria oxidize nitrite to nitrate
NO2 - + H2O → NO3 - + 2H+ +2e-
Nitrobacter is the most frequently identified genus
associated with this second step, although other genera,
including Nitrospina, Nitrococcus, and Nitrospira can also
autotrophically oxidize nitrite

22. Denitrification
Denitrification is the reduction of nitrates
back into the largely inert nitrogen gas (N2),
completing the nitrogen cycle. This process
is performed in anaerobic conditions

23. Total Kjeldahl
Nitrogen
(TKN)
NITROGEN CYCLE

24. PHYSICO-CHEMICAL NITROGEN REMOVAL
 Physico-chemical methods of nitrogen removal
have not been widely applied in waste water
treatment because
 They are generally more expensive to operate
than biological treatment;
 they produce a poorer effluent quality than
biological treatment

25. Air stripping of Ammonia
As the pH increases, a greater proportion of
ammonia converts fromNH4to NH3
NH3+H20 NH4 + OH

26. Ion exchange
Zeolites have been found effective in waste water treatment as
molecular filters which can distinguish molecules
at the ionic level.
For example, the natural zeolite
clinoptilolite is selective for the ammonium ion in
preference to other ions present in solution. A
filtered waste water can be passed through a bed of zeolite to
effect a 90- 97% ammonium removal

27. Breakpoint chlorination
By adding chlorine to a
wastewater, a stepwise
reaction takes place which
results in the
conversion of ammonium
to nitrogen gas

29. N
Secondary “Treatment”
(Biological)
WASTEWATER “TREATMENT”
Of
Nitrogen

30. APPROACHES
TO SECONDARY TREATMENT
Fixed Film Systems
Suspended Film Systems
Lagoon Systems
organic matter + O2  CO2 + NH3 + H2O
NH3  NO3
- aquatic nutrient

31. • Biofilm
– a biological slime layer
– bacteria in biofilm
degrade organics
– biofilm will develop
on almost anything

32. Stir & suspend microorganisms in waste
water.
They absorb organic matter &nutrients from
waste water.
After hours, they settle as sludge……..
Ex…..activated sludge system..etc

33.  Consist of in-ground earthen basins in which the waste is detained for a specified
time and then discharged.
 They take advantage of natural aeration and microorganisms in the wastewater to
remove sewage.

34. Can be achieved in any
• Aerobic-biological process at low organic loadings
• Suitable environmental conditions
Nitrifying bacteria are slower growing than the heterotrophic
bacteria
Key requirement for nitrification to occur, therefore, is that the
process should be so controlled that the net rate of accumulation
of biomass is less than the growth rate of the nitrifying bacteria

35. 1.
• Trickling Filters
2.
• Rotating Biological Contractor
3.
• Fixed Bed Reactor
4.
• Conventional Activated Sludge Processes at Low Loadings
5.
• Two-stage Activated Sludge Systems with Separate Carbonaceous
Oxidation and Nitrification Systems

36. Wastewater treatment system that
• Biodegrades organic matter
• Used to achieve nitrification
Consists of
• a fixed bed of rocks, lava, coke, polyurethane foam, ceramic, or plastic
media
Aerobic conditions are maintained by splashing, diffusion, and either by
forced air flowing through the bed or natural convection of air if the filter
medium is porous.

37. • Not a true filtering or sieving process
• Material only provides surface on which bacteria to grow
• Can use plastic media
–lighter - can get deeper beds (up to 12 m)
–reduced space requirement
–larger surface area for growth
–better air flow
–less prone to plugging by accumulating slime

39. • Tank is filled with solid media
– Rocks
– Plastic
• Bacteria grow on surface of media
• Wastewater is trickled over media, at top of tank
• As water trickles through media, bacteria degrade BOD
• Bacteria eventually die, fall off of media surface
• Filter is open to atmosphere, air flows naturally through media
• Treated water leaves bottom of tank, flows into secondary clarifier
• Bacterial cells settle, removed from clarifier as sludge
• Some water is recycled to the filter, to maintain moist conditions

44. Efficient nitrification (ammonium oxidation)
Small land area required

45. Requires expert design and construction
Requires operation and maintenance by skilled personnel
Requires a constant source of electricity and constant
wastewater flow
Flies and odours are often problematic
Risk of clogging, depending on pre- and primary treatment
Not all parts and materials may be locally available

46. o Temperature
o Dissolved oxygen
o pH
o Presence of inhibitors
o Filter depth
o Media type
o Loading rate
o Wastewater BOD

48. • A rotating biological contactor or RBC is a biological treatment
process used in the treatment of wastewater following primary
treatment.
• The RBC process involves allowing the wastewater to come in
contact with a biological medium in order to remove pollutants in
the wastewater before discharge of the treated wastewater to
the environment.
• A rotating biological contactor is a type of secondary treatment
process.

49. • The first RBC was installed in West Germany in 1960,
later it was introduced in the United States and
Canada.
• In the United States, rotating biological contactors
are used for industries producing wastewaters high
in Biochemical Oxygen Demand (BOD)(e.g.,
petroleum industry and dairy industry).

50. • Microorganisms grow on the surface of the discs where biological
degradation of the wastewater pollutants takes place.
• It consists of a series of closely spaced, parallel discs mounted
on a rotating shaft which is supported just above the surface of
the waste water.
• Aeration is provided by the rotating action, which exposes the
media to the air after contacting them with the wastewater,
facilitating the degradation of the pollutants being removed.
• Biofilms, which are biological growths that become attached to
the discs, assimilate the organic materials in the wastewater.

51. OPERATION
• The rotating packs of disks (known as the
media) are contained in a tank or trough and
rotate at between 2 and 5 revolutions per
minute.
• Commonly used plastics for
the media
are polythene, PVC and
expanded polystyrene.
• The shaft is aligned with the flow of
wastewater so that the discs rotate at right
angles to the flow with several packs usually
combined to make up a treatment train.
• About 40% of the disc area is immersed in the
wastewater.

53. • Biological growth is attached to the surface of the disc and forms a
slime layer. The discs contact the wastewater with the atmospheric air
for oxidation as it rotates.
• The discs consist of plastic sheets ranging from 2 to 4 m in diameter
and are up to 10 mm thick. Several modules may be arranged in parallel
and/or in series to meet the flow and treatment requirements.
• Approximately 95% of the surface area is thus alternately
submerged in waste water and then exposed to the atmosphere
above the liquid.

55. • Carbonaceous substrate is removed in the initial stage of
RBC.
• Carbon conversion may be completed in the first stage of a
series of modules, with nitrification being completed after
the 5th stage, when the BOD5 was low enough.
• Most design of RBC systems will include a minimum of 4 or
5 modules in series to obtain nitrification of waste water.
• The rotation of the disks contacts the biomass in the
wastewater ,then with the atmosphere for adsorption of
oxygen.
• Biomass uses the oxygen & organic matter for food thus
reducing the BOD in the wastewater.

56. • Ammonia oxidizers could not effectively compete with the
faster-growing heterotrophs that oxidize organic matter.
• Nitrification occurs only when the BOD was reduced to
approximately 14 mg/L, and increases with rotation speed.
• RBC performance was negatively affected by low dissolved
oxygen in the first stages and by low pH in the later stages
where nitrification occurred.

57. A schematic cross-section of the contact face of the
bed media in a rotating biological contactor (RBC)
• The degree of wastewater treatment is related to the amount
of media surface area and the quality and volume of the
inflowing wastewater.

59. Fixed Bed Reactor
A type of continuous reactor in which the reactants are
feed continuously into the reactor at one point, allow
the reaction to take place and withdraw the products at
another point.

60. Working Principle
• In these reactors, the reaction takes place in
the form of a heterogeneously catalyzed gas
reaction on the surface of catalysts/in biofilms
that are arranged as a so-called fixed bed in
the reactor.

61. Fixed bed reactor:
Raschig rings are pieces
of tube used in large
numbers as a packed
bed to support biofilms.

62. • Ammonia and nitrite oxidizer communities are
fixed on the bed material (Raschig rings, Pall
rings, Hiflow, Flocor) to form biofilms.
• AOB occupied the outside layers of the
biofilm, whereas NOB which found in the
deep layers of the biofilm
• A high cell concentration is possible with
immobilized biomass, because of large solids
retention time.

63. Schematic of cross-sectional view of bioflim presenting spatial
distribution of ammonia oxidizing bacteria (AOB) and nitrite
oxidizing bacteraia (NOB) species and diffusion of substrate across
the biofilm.

64. Schematic diagram of experimental setup of up-flow fixed-
bed reactor

65. Basics Setup for FBRs
• The wastewater reaches the first tank (chamber) of the
treatment plant via the inlet sewer.
• The second tank absorbs hydraulic fluctuations
• A filling pump (pneumatic or electrical) feeds the
biological stage evenly (over a period of 24 hours).
This ensures that in the event of subsequent load
fluctuations the most favourable operating mode can
always be set

66. • Gravity pipes are used to fill standard treatment plants,
and there is no buffer pump.
• A biological layer (micro-organic colonisation) forms on
the fixed-bed material after the start-up period.
• The aeration system installed underneath the fixed-bed
material supplies the organisms with sufficient air

67. Ammonia Oxidizers:
Ammonia N Nitrite N
• Four major groups of ammonia oxidizer microorganisms
are known:-
• Ammonia-oxidizing Archaea (AOA): e.g Nitrosopumilus
maritimus, Nitrososhaera gargensis, Nitrosocaldus
yellowstonii
• Ammonia-oxidizing bacteria (AOB): e.g N. eutropha, N.
oligotropha, Nitrosospira multiformis
• Heterotrophic nitrifiers: e.g Paracoccus pantotrophus
• Anammox bacteria: e.g microbes of the order
Planctomycetales

68. Nitrite oxidizers:
Nitrite N Nitrate N
• Nitrite-oxidizing bacteria (NOB): e.g
Nitrobacter, Nitrococcus, Nirtospira

69. Conditions for Optimal Nitrification
• Nitrification significantly consumes oxygen.
oxidation of 1 mg liter-1 NH4+ to nitrate -------------- 3.6
mg liter-1 oxygen is required
• Most strains of nitrifying bacteria are pH sensitive.
optimal growth ------------ pH 7 to 8
• Reduction of carbonaceous BOD (cBOD) is a
preliminary requirement:
Best results ------------- when cBOD < 30 mg/L.
• Temperature
Min. 59 Degrees F. (15oC) ----------- 90 % Nitrification

70. • The hydraulic retention time (HRT) is the
average retention time of wastewater in the
reactor.
“the ratio of liquid volume (V liquid) in the
reactor and the flow rate (Q)”
Depend on: Liquid Volume
Flow Rate

71. Drawbacks of FBRs
Traditional fixed-bed reactors can be easily
blocked through:
• excessive growth of microorganisms
• crystalization of dissolved matter
• solids which are fed in.

72. CONVENTIONAL ACTIVATED
SLUDGE PROCESS

73. ACTIVATED SLUDGE
sludge particles produced by the growth of
microorganisms in aerated tanks as a part of the
activated sludge process to treat wastewater

74. Activated Sludge Process
The most common suspended growth process used
for municipal wastewater treatment is the
activated sludge process

75. In activated sludge process wastewater containing organic matter is
aerated in an aeration basin in which micro-organisms metabolize the
suspended and soluble organic matter.
Part of organic matter is synthesized into new cells and part is
oxidized to CO2 and water to derive energy.
In activated sludge systems the new cells formed in the reaction are
removed from the liquid stream in the form of a flocculent sludge in
settling tanks.
A part of this settled biomass, described as activated sludge is
returned to the aeration tank and the remaining forms waste or
excess sludge are discharged off as effluent.

76. ACTIVATED SLUDGE PLANT
Activated sludge plant involves:
• wastewater aeration in the presence of a
microbial suspension
• solid-liquid separation following aeration
• discharge of clarified effluent
• wasting of excess biomass
• return of remaining biomass to the aeration
tank

77. ACTIVATED SLUDGE PLANT

78. Weismann (1994) studied the nitrification in a conventional
activated sludge system and found that it was relatively low for
carbon removal and nitrification of sewage because carbon removal
and nitrification occurred in the same reactor with an activated
sludge system.
This resulted in a population mixture of mainly heterotrophs and
few autotrophs. In this kind of treatment system, it was not possible
to enrich the autotrophic bacteria because the slower growing
autotrophs were removed with the surplus sludge. It was necessary
to separate the autotrophic from the heterotrophic biomass in order
to increase the specific nitrification rate.

79. Suwa, et al. (1989), conducted a research on simultaneous
organic carbon removal-nitrification by an activated sludge
process with cross-flow filtration.
Because of the recycle of sludge with cross-flow filtration, this
process made the sludge retention time very long; simultaneous
carbon removal-nitrification was achieved quite well under the
loading rate of about 0.10 g BOD/g VSS/d. The efficiency of
dissolved organic carbon removal was more than 95%, and
nitrification was sufficient

80. Two Stage Activated Sludge System
With Separate Carbonaceous
Oxidation and Nitrification System

81. Activated sludge
• Activated sludge is a process for
treating sewage and industrial wastewaters
using air and a biological floc composed of
bacteria and protozoa.

82. Purpose
• In a sewage (or industrial wastewater)
treatment plant, the activated sludge process
is a biological process that can be used for one
or several of the following purposes:
• oxidizing carbonaceous biological matter
• oxidizing nitrogenous matter
mainly ammonium and nitrogen in biological
matter.
• removing phosphates

83. Purpose
• driving off entrained gases such
as carbondioxide, ammonia, nitrogen, etc.
• generating a biological floc that is easy to
settle.
• generating a liquor that is low in dissolved or
suspended material.

84. The process
• The process involves air or oxygen being
introduced into a mixture of screened
• and primary treated sewage or industrial
wastewater (wastewater) combined with
organisms to develop a biological floc which
reduces the organic content of the sewage.
• This material, which in healthy sludge is a brown
floc, is largely composed of saprotrophic bacteria
but also has an important protozoan flora mainly
composed of amoebae and a range of other
species.

85. The process
• In poorly managed activated sludge, a range of
filamentous bacteria can develop which
produces a sludge that is difficult to settle and
can result in the sludge blanket decanting over
the weirs in the settlement tank to severely
contaminate the final effluent quality.
• This material is often described as sewage
fungus but true fungal communities are
relatively uncommon.

86. The process
• The combination of wastewater and biological
mass is commonly known as mixed liquor.
• In all activated sludge plants, once the
wastewater has received sufficient treatment,
excess mixed liquor is discharged into settling
tanks and the treated supernatant is run off to
undergo further treatment before discharge.

87. The process
• Part of the settled material, the sludge, is
returned to the head of the aeration system to
re-seed the new wastewater entering the
tank.
• This fraction of the floc is called return
activated sludge (R.A.S.). Excess sludge is
called surplus activated sludge (S.A.S.)
or waste activated sludge (W.A.S).

88. • W.A.S is removed from the treatment process
to keep the ratio of biomass to food supplied
in the wastewater in balance, and is further
treated by digestion, either under anaerobic
or aerobic conditions prior to disposal.

89. Activated sludge control
• The general method to do this is to monitor
• sludge blanket level
• SVI (Sludge Volume Index)
• MCRT (Mean Cell Residence Time)
• F/M (Food to Microorganism), as well as
the of the activated sludge and the major

90. • Nutrients
• DO (Dissolved oxygen),
• Nitrogen
• Phosphate
• BOD (Biological oxygen demand)
• COD (Chemical oxygen demand).

91. • In the reactor/aerator + clarifier system:
• The sludge blanket is measured from the bottom
of the clarifier to the level of settled solids in the
clarifier's water column; this, in large plants, can
be done up to three times a day.
• The SVI is the volume of settled sludge in
milliliters occupied by 1 gram of dry sludge solids
after 30 minutes of settling in a 1000 milliliter
graduated cylinder.

92. • The MCRT is the total mass (lbs) of mixed
liquor suspended solids in the aerator and
clarifier divided by the mass flow rate (lbs/day)
of mixed liquor suspended solids leaving as
WAS and final effluent
• The F/M is the ratio of food fed to the
microorganisms each day to the mass of
microorganisms held under aeration.

93. Arrangement
• The general arrangement of an activated
sludge process for removing carbonaceous
pollution includes the following items:
• Aeration tank where air (or oxygen) is injected
in the mixed liquor.
• Settling tank (usually referred to as "final
clarifier" or "secondary settling tank") to allow
the biological flocs (the sludge blanket) to
settle, thus separating the biological sludge
from the clear treated water.

94. • Treatment of nitrogenous matter or
phosphate involves additional steps where
the mixed liquor is left in anoxic condition
(meaning that there is no residual dissolved
oxygen).

95. General arrangement of an activated
sludge process

96. Two-stage nitrifying process
• In a two-stage nitrifying process , the first
stage removes most of the carbonaceous
organic matter and the second stage oxidizes
the ammonia. Typically, nitrification systems
have lower F:M ratios than systems designed
for CBOD removal alone.

97. Two-stage nitrifying process

98. Solids Handling control is a first step
•Plant Return Flows are High in BOD and
Ammonia
•It inhibits Nitrification and
Exceed Nitrification Capability of plant
So we must ,
•Return plant flow Slowly
• In Low Quantities
•At Low Loading Times
Operational Controls for Nitrification

99. Air Requirements must be controlled
1.5 lbs of O2 / lb of Biological oxygen demand
4.6 lbs of O2 / lb of Total kaldejhal Nitrogen
Aerobic Reaction Time Must Be Long
Enough……….> 5 hrs.

100. F:M (food to mass) Ratio Must Be Low
Enough
(< 0.25)
BOD Removal is next step
in Aeration Tank DO (dissolved oxygen) must
be increased up to 3 - 5 mg/L

101. Nitrification VS D.O.NH3-NRemoval,%
Dissolved Oxygen, mg/L
0 1 2 3 4 5 6 7 8 9
100
90
80
70
60
50
40

102. Effluent BOD Vs % NH3-N Removal
Effluent BOD, mg/L
0 10 20 30 40 50 60 70 80
NH4-NRemoval,%
100
90
80
70
60
50
40
30
20
10
0

103. Temperature
Substrate concentration
Dissolved oxygen (DO)
pH
Toxic & inhibitory substance
Factors Affecting Nitrification

104. NitrifierGrowthRate
0 5 10 15 20 25 30 35 40
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Temperature, oC
Effect of Temperature on Nitrification
Lower the Temperature, Slower will be the growth rate of Nitrifier

105. 90 % Nitrification requires Minimum of 59 Degrees F. (15oC)
Below 50 Degrees F. (10 oC) Maximum of 50 % Nitrification can be
expected only
Ideal Temperature is between 30oC and 35oC (86oF and 95oF)

106. (Ammonium bicarbonate)NH4HCO3 + O2 HNO3
(nitric acid) + H2O + CO2
7 mg Alkalinity is Destroyed Per mg NH3-N Oxidiation
Chemicals Added For Phosphorus Removal Also Destroy Alkalinity
Adequate Alkalinity is required
Effluent Above 50 mg/L
Influent Above 150 mg/L
5.3 - 13.5 lbs of Alkalinity is added per lb Fe
6.0 - 9.0 lbs of Alkalinity id added per lb Al
pH will decrease If Not Enough Alkalinity is Present
Nitrifiers are pH Sensitive
Optimum pH for Nitrosomonas 7.5 & 8.5 for Nitrobacter
Effect of alkalinity on Nitrification

107. pH VS Nitrification Rate at 68 oF
pH
6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
100
90
80
70
60
50
40
30
20
10
0
%ofMaxNitrificationRate

108. Cyanide, thiourea, phenol and heavy metal, nitrous acid
and free ammonia can inhibit nitrifying bacteria.
Nitrification occur only when DO level is 1.0 mg/L or
more.