Lagoons and stabilization basins – Aerated lagoons-activated sludge processes – Trickling filtration – Rotating biological contactors – Anaerobic decomposition-laboratory evaluation of anaerobic treatment – Adsorption – Theory of activated carbon– Sludge quality considerations – Stripping of volatile organics – Nitrification and denitrification.

1. Unit-Iv
BIOLOGICAL
WASTE WATER
TREATMENT
PROCESS

2. SYLLABUS

3. LAGOONS
A lagoon is a shallow body of water separated
from a larger body of water by barrier islands,
reefs (ridge of material or near the surface of the
ocean), isthmuses(An isthmus is a narrow strip of
land that connects two larger landmasses and
separates two bodies of water) or peninsulas (an
area of land that is almost surrounded by water)..
When barrier bars and spits form at the mouth of
a bay and block it, a lagoon forms.
The lagoons would gradually get filled up by
sediments from the land giving rise to a coastal
plain.

4. Lagoon – Types
• Coral lagoons, and
• Barrier Island or coastal lagoons
• River Mouth Lagoons
• Artificial Lagoons

5. Coral Lagoons – Locations
 Coral lagoons have the conditions necessary for coral growth.
 For many island communities in the Pacific, the coral lagoons
are of great importance.
 Coral lagoons are restricted to tropical open seas.
 Coral lagoons are mainly found within 25° latitude of the
Equator.
 Coral lagoons are found in the isolated places of the
Caribbean, parts of the Indian Ocean, and found widely in
the western Pacific.
 • The atolls of the Pacific Ocean are the most spectacular
examples of coral reefs.
 • The Great Barrier Reef of Australia is another example
where coral lagoons are found.
 • These are the most common type of lagoon that find in the
coastal regions.

6. Coastal or Barrier Island Lagoons –
Locations
Coastal or Barrier Island lagoons are formed only
where there is abundant sediment for construction of
the protective barrier islands.
Coastal or Barrier Island lagoons rarely occur where
high cliffs form the coast.
These lagoons are usually associated with low coasts.
They occur where the swells are usually less violent.
Coastal or Barrier Island lagoons are characterized by
brackish marshes, fine-grained sedimentation, and
quiet water conditions.

7. Barrier Island Lagoons

8. River Mouth Lagoons
They form at the mouths of the coastal rivers.
These can also be considered coastal lagoons.
They have brackish water which means partly
fresh water and partly saltwater.
These can be seen most commonly in
Newzealand and South Pacific islands.

9. Artificial Lagoons
These are man-made and not natural.
These are increasing and becoming popular.
These can be used for recreation or residential or
other purposes.
They are more controlled and safe as they can be
made anywhere with suitable conditions and
requirements.
The only freshwater can also be found here
rather than brackish water.

10. STABILIZATION BASINS

11. STABILIZATION BASINS
• Waste or Wastewater Stabilization Ponds
(WSPs) are large, man-made water bodies in
which blackwater, greywater or faecal sludge
are treated by natural occurring processes and
the influence of solar light, wind,
microorganisms and algae .
• The ponds can be used individually, or linked
in a series for improved treatment

12. There are three types of ponds,
(1) anaerobic,
(2) facultative and
(3) aerobic (maturation), each with different
treatment and design characteristics.
WSPs are low-cost for O&M and BOD and
pathogen removal is high.
However, large surface areas and expert design
are required.

13. • WSPs should be linked in a series of three or more with
effluent being transferred from the anaerobic pond to
the facultative pond and, finally, to the aerobic
pond.
• The anaerobic pond is the primary treatment stage
and reduces the organic load in the wastewater.
• The entire depth of this fairly deep man-made lake is
anaerobic.
• Solids and BOD removal occurs by sedimentation and
through subsequent anaerobic digestion inside the
accumulated sludge.
• Anaerobic bacteria convert organic carbon into
methane and through this process, remove up to 60%
of the BOD.

14. • In a series of WSPs, the effluent from the
anaerobic pond is transferred to the facultative
pond, where further BOD is removed.
• The top layer of the pond receives oxygen from
natural diffusion, wind mixing and algae-
driven photosynthesis.
• The lower layer is deprived of oxygen and
becomes anoxic or anaerobic.
• Settleable solids accumulate and are digested on
the bottom of the pond.
• The aerobic and anaerobic organisms work
together to achieve BOD reductions of up to
75%.

15. Anaerobic and facultative ponds are designed
for BOD removal, while aerobic ponds are
designed for pathogen removal.
An aerobic pond is commonly referred to as a
maturation, polishing, or finishing pond
because it is usually the last step in a series of
ponds and provides the final level of treatment.

16. Anaerobic Treatment Ponds (APs)
• The main function of anaerobic ponds is BOD
removal, which can be reduced 40 to 85 %
(WSP 2007).
As a complete process, the anaerobic pond
serves to:
Settle undigested material and non-degradable
solids as bottom sludge
Dissolve organic material
Break down biodegradable organic material

17. Facultative Treatment Ponds (FPs)
• Facultative Treatment Ponds are the simplest
of all WSPs and consist of an aerobic zone
close to the surface and a deeper, anaerobic
zone.
• They are designed for BOD removal and can
treat water in the BOD range of 100 to 400
kg/ha/day corresponding to 10 to 40 g/m2/day
at temperatures above 20°C.

18. The facultative pond serves to:
• Further treat wastewater through sedimentation
and aerobic oxidation of organic material
• Reduce odour
• Reduce some disease-causing microorganisms
if pH raises
• Store residues as bottom sludge

19. Advantages of Stabilization basins
• Lower operating cost in terms of operators and
chemicals
• Large settling zone – less susceptible to poor
settling or sludge bulking
• Minimal operator attention
• Takes up less area – Smaller footprint
• Faster process
• Higher BOD reduction efficiency
• More concentrated bacterial population
• Can treat higher loaded waste streams

20. Disadvantages of Stabilization basins
• Harder to remove accumulated biological solids
• Poorer removal efficiencies , particularly in
cold weather
• Takes up more area – larger footprint
• More initial capital
• Higher operational cost – dewatering chemicals &
solids disposal
• Must be properly managed to better handle
upsets
• Susceptible to sludge settling Issues (bulking)
• Need for highly trained operators – more
testing to control & requires more attention.

21. AERATED LAGOONS
• An aerated lagoon (or aerated pond) is a
simple wastewater treatment system consisting
of a pond with artificial aeration to promote
the biological oxidation of wastewaters.
• There are many other aerobic biological
processes for treatment of wastewaters, they
all have in common the use of oxygen (or air)
and microbial action to reduce the pollutants
in wastewaters.

22. Types of Aerated Lagoons
Aerated lagoons are deep waste stabilization ponds in
which sewage is aerated by mechanical aerators to
stabilize the organic matter present in the sewage,
rather than relying only on photosynthetic oxygen
produced by algae.
 Thus aerated lagoons represent a system of sewage
treatment that is intermediate between oxidation
ponds and activated sludge systems.
• Depending on how the microbial mass of solids is
handled in the aerated lagoons the same are classified
as:
(i) Facultative aerated lagoons and
(ii) Aerobic aerated lagoons.

23. Characteristics of Aerated Lagoons

24. Advantages of Aerated Lagoons
(i) The aerated lagoons are simple and rugged in
operation, the only moving piece of equipment
being the aerator.
(ii) The removal efficiencies in terms of power
input are comparable to some of the other
aerobic treatment methods.
(iii) Civil construction mainly entails earthwork, and
land requirement is not excessive. Aerated lagoons
require only 5 to 10 percent as much land as
stabilization ponds.
(iv) The aerated lagoons are used frequently for
the treatment of industrial wastes.

25. ACTIVATED SLUDGE PROCESSES
Activated sludge treatment can define as a
conventional method, which can separate the
solid wastes, suspended organic matter, soluble
matter and parasites.
Activated sludge treatment involves a series of
stages, which firstly separates the raw or
primary sludge, then separates the waste
activated sludge and finally involves disinfection
and clarification of the effluent.
Therefore, it contributes a significant role in the
control of water pollution by eliminating the
undesired chemicals, particulate matter and
parasites from the sewage and industrial waste.

26. Activated sludge treatment can define as the
wastewater treatment plant, which eliminates
the particulate matter like sand, unwanted
inorganic and organic wastes and harmful
microorganisms from the sewage waste.
The process is followed by the primary,
secondary and tertiary treatment methods.

27. • Primary treatment is a physical method, which
involves the separation of large solid matter like
leaves, sand, gravel particles etc.
• Secondary treatment is a biological method,
which separates the suspended and soluble
organic matter by making the use of bacterial
flocs.
• Tertiary treatment is a chemical method, which
is a final stage to disinfect the secondary effluent
by making the use of chlorine gas.

28. Flow Diagram of Activated Sludge Process

30. Advantages
• The process of activated sludge treatment releases high-
quality effluent (wastewater released from the sewage).
• It ensures the maximum reduction of BOD and
parasites upto 99% during the secondary treatment of
wastewater.
• Activated sludge process can resist different organic and
hydraulic shock load.
• The activated sludge treatment plant can be
established in the minimal land area compared to the
water stabilization pond.
• It also ensures maximum removal of nutrients like N2,
K, Ph from the organic matter.

31. Disadvantages
• The activated sludge process requires high capital.
• It also requires a continuous electricity supply.
•Its operation and maintenance require skilled
labour-power.
•The process cannot be established at the
community level.
•The construction of an activated sludge plant
requires expert design, and generally, all are
equipment’s are not locally available.
•Effluent from the wastewater requires proper
disinfection and appropriate discharge.

32. Trickling filtration
• Trickling filter process is one of the types of
aerobic wastewater treatment.
• It is a fixed-bed bioreactor that is the part of
secondary wastewater treatment, which
eliminates the coarse particles, suspended
organic and inorganic waste, small colloids etc.
• out of the primary effluent. A trickling filter is
also called biological filter, as it makes the use of
active microbial mass as a bioweapon to degrade
the waste out of primary sewage.

33. • Trickling filter process can define as the
biological system, which tends to separate or
degrade the maximum organic and inorganic
waste (up to 85%) out of the primary or raw
sludge via the slime layer.
• The designing of a trickling filter unit includes
a support structure, pebble or plastic filled
media and rotary distributor.

34. Trickling Filter Process

35. Trickling Filter Unit

36. Layout of Trickling Filter

37. • Depending upon the hydraulic and organic
shock load, trickling filters can be categorized
into two types, namely
–high rate and low rate trickling filter.
The hydraulic loading rate can define as the
sewage flow (Q) per unit volume (V) of filter bed
in a day, while the organic loading rate can define
as the kilograms of BOD (Y5) introduced into the
per unit volume (V) in a day.

38. Advantages
• It is a simple and reliable secondary treatment unit of the
wastewater.
• It can be used to degrade a variety of organic waste.
• Trickling filter can resist shock loadings.
• It efficiently oxidizes the ammonia or efficient in
ammonium oxidation.
• Trickling filter aids to produce effluent free of BOD,
COD, nutrients, suspended colloids etc.
• Its construction requires a small land area, unlike
constructed wetlands.

39. Disadvantages
 Its designing requires high capital costs.
 The designing of a trickling filter requires expert skills
 Its operation and maintenance require regular
attention by the skilled labour personnel.
 The trickling filter process is a continuous process,
which needs an uninterrupted supply of electricity and
wastewater distribution.
 It sometimes causes flies breeding and odour problem.
 The effluent produced by the trickling filter needs to
treated further by the chemical disinfectants.
 Accumulation of excessive biomass may cause clogging
of the TF-unit.
 Not all parts and materials may be locally available.

40. ROTATING BIOLOGICAL CONTACTORS

41. • A rotating biological contactor (or RBC) is a type
of fixed media filter which removes both organic
matter and ammonia from water.
• It can be added to a packaged plant for more
efficient ammonia removal, replacing the aerator
in both location and function.
• Although RBC's are less prevalent than trickling
filters or oxidation ditches, they produce a high
quality effluent and wastewater operators should
be familiar with them.

42. Advantages
• High contact time and high effluent quality (both
BOD and nutrients)
• High process stability, resistant to shock hydraulic or
organic loading
• Short contact periods are required because of the
large active surface
• Low space requirement
• Well drainable excess sludge collected in clarifier
• Process is relatively silent compared to dosing
pumps for aeration
• No risk of channelling
• Low sludge production

43. Disadvantages
• Continuous electricity supply required (but uses
less energy than trickling filters or activated sludge
processes for comparable degradation rates)
• Contact media not available at local market
• High investment as well as operation and
maintenance costs
• Must be protected against sunlight, wind and rain
(especially against freezing in cold climates)
• Odour problems may occur
• Requires permanent skilled technical labour for
operation and maintenance

44. ANAEROBIC DECOMPOSITION
• Anaerobic digestion can be described as biological oxidation
of biodegradable waste by microbes under anaerobic
conditions or in simpler terms it is the process of converting
complex organic molecules into simpler molecules with the
help of microorganisms in absence of oxygen.
• The end product of this product has a high concentration of
carbon dioxide and methane.
• Anaerobic digestion is a biochemical process, it mainly utilizes
substrates with high organic matter, such as sludge, domestic
waste, sewage, and waste from a feedstock of cattle.
• It is mainly used in fermentation technology and the
management of waste.

45. Anaerobic Digestion Process
• Anaerobic decomposition is performed in anaerobic
digesters mainly by a group of anaerobic bacteria called
methanogens and acetogens, the group of bacteria do
not use oxygen as their source of electron donor rather
they accept electrons from acetate and methane for their
ener
1. Hydrolysis
2. Acidolysis or Acidogenesis
3. Acetogenesis
4. Methanogenesis

46. Hydrolysis

47. Hydrolysis
 It is also known as the liquefaction of complex
molecules.
 The process of breaking the chains with the help of
hydrolyzing enzymes is known as hydrolysis.
 High molecular weight polymeric components are
broken down into simple sugars and monomers which
can be readily accessible to bacteria.
 Acetate, hydrogen, and some VFAs (Volatile Fatty Acid)
produced during these steps.
 VFAs can not be directly used by the microorganisms so
they are first catabolized into small molecules that can
be utilized by the bacteria.

48. Acidolysis or Acidogenesis
• It is the process of acidic breakdown of oligo
polymers and compounds into simpler
molecules.
• Acidogenesis performed by acidogenic
bacteria, during this reaction ammonia,
carbon dioxide, and hydrogen sulfide, as well
as other byproducts, are formed.

49. Acetogenesis
Acetogenesis is the process of formation of
acetic acid with the help of acetogens.
This reaction produces carbon dioxide and
hydrogen as the main byproduct.

50. Methanogenesis
• This is the final step of anaerobic
decomposition.
• It is a pH sensitive reaction that occurs
between the range of pH 6.5 to pH 8. During
this step, the intermediate product from other
steps is used to produce methane, carbon
dioxide, and hydrogen.

51. The Breakdown of Three Major Food
Groups are as Follows
Carbohydrates → simple sugars → alcohol
and aldehydes → organic acids
Protein → amino acids → organic acid +
NH3
Fats and oils → organic acid

52. The Genera of Microbes Responsible for
Anaerobic Digestion are:
1. Pseudomonas
2. Flavobacterium
3. Escherichia
4. Aerobacter

53. • The Genera of Bacteria Responsible for
Methanogenesis:
1. Methanococcus
2. Methanobacteria
3. Methanosarcina

54. Advantages of Anaerobic Decomposition
1.The lower operating cost of the digester makes it
commercially viable.
2. Sludge occupies less volume and is easier to dry.
3. Reduce production of landfill gas, which when
damaged leads to an outburst of methane (major
greenhouse gas)
4. Methane produced in the digestor can be used as
biogas, an alternative source of energy.
5. It reduces the energy footprint of conventional
wastewater treatment technology.
6. It has reduced the use of chemical fertilizer as the
digestive (the content of the reactor after completion
of digestion) can be used as fertilizer.

55. LABORATORY EVALUATION OF
ANAEROBIC TREATMENT
 Conventional digesters are mainly used for the
stabilization of primary and secondary sludge, originating
from sewage treatment, and for the treatment of industrial
effluents with a high concentration of suspended solids.
 They usually consist of covered circular or egg-shaped tanks
of reinforced concrete.
 The bottom walls are usually inclined, so as to favour the
sedimentation and removal of the most concentrated solids.
 The covering of the reactor can be fixed or floating (mobile).
Since conventional digesters are preferably used for the
stabilization of wastes with a high concentration of particulate
material, the hydrolysis of these solids can become the limiting
stage of the anaerobic digestion process.

56. Depending on the existence of mixing devices
and on the number of stages,
Three main digester configurations have been
applied
• low-rate anaerobic sludge digester
• one-stage high-rate anaerobic sludge
digester
• two-stage high-rate anaerobic sludge
digester

57. Schematic Representation of A Low
Rate Anaerobic Sludge Digester

58. Schematic representation of a one
stage high rate anaerobic sludge
digester

59. Schematic Representation of a Two
Stage High-Rate Anaerobic Sludge
Digester

60. ADSORPTION
• Adsorption may be defined as the process of
accumulation of any substance giving higher
concentration of molecular species on the surface of
another substance as compared to that in the bulk.
• When a solid surface is exposed to a gas or a liquid
molecules from the gas or the solution phase
accumulate or concentrate at the surface.
• The phenomenon of concentration of
molecules of a gas or liquid at a solid surface
is called adsorption.
• "Adsorption" is a well established and powerfull
technique for treating domestic and industrial effluents.
• In water treatment, the most widely method is
"adsorption" once the surface of activated carbon.

61. Types of Adsorbents
1.Oxygen-containing compounds are typically
hydrophilic and polar, including materials such
as:
• Silica gel
• Zeolites

62. Treatment of Waste Water by
Adsorption

63. Mostly two common carbon
adsorption process such as
(1) Granular Activated Carbon (GAC)
(2) Powdered Activated Carbon
(PAC)

64. 2.Carbon-based compounds are typically
hydrophobic and non-polar, including materials
such as:
✓ Activated carbon
✓ Graphite
3.Polymer-based compounds are polar or non-
polar function groups in a porous polymer
matrix.

65. Classification of Adsorbents
1. Engineered adsorbents
»(a) Activated carbon
»(b) Polymeric adsorbents
»(c) Oxidic adsorbents
»(d) Synthetic zeolites
2. Natural and low cost absorbents:
» (a) Mineral absorbents
»(b) Agricultural waste/by products
»(c) Industrial waste/ by products

66. Types of Adsorption
Depending on the type of attractions between
adsorbate and adsorbent, the adsorption can be
divided into two types:
• Physical Adsorption or Physisorption
• Chemical Adsorption Chemisorptions

67. Physical Adsorption (or) Physisorption
• When the force of attraction
existing between adsorbate and
adsorbent are weak undercoal
force of attraction, the process is
called physical adsorption or
physisorption.

68. Characteristics of Physisorption
o Energetic and kinetics.
o Effect of temperature.
o Effect of pressure.
o Specificity.
o Nature of adsorbate
o Surface area of adsorbent.

69. Chemical Adsorption (or)
Chemisorption
• When the force of attraction existing
between adsorbate and adsorbent
are chemical forces of attraction or
chemical bond, the process is called
chemical adsorption or
chemisorption.

70. Characteristics of Chemisorption
• ✓ Energetic and kinetics.
• ✓ Effect of temperature.
• ✓ High of pressure. High specificity.
• ✓ Surface area.

71. Factors Influencing Adsorption
Adsorption on a solid is influenced by a number of
factors such as
✓ Surface area.
✓ Nature of adsorbate.
✓ Hydrogen ion concentration (pH) of the solution.
✓ Temperature.
✓ Mixed solutes.
✓ Nature of adsorbate.

72. Modes of Operation
• ✓ Batch flow system
• ✓ Column flow system.

73. Types of Adsorption Isotherm
• ✓ Type I Adsorption Isotherm
• ✓ Type II Adsorption Isotherm
• ✓ Type III Adsorption Isotherm
• ✓ Type IV Adsorption Isotherm
• ✓ Type V Adsorption Isotherm

74. Theory of activated carbon
 Activated carbon, also known as activated charcoal ,
is a form of carbon processed to have small, low-
volume pores that increase the surface area available
for adsorption or chemical reactions.
 It has high degree of microporosity.
 The word 'active' is also sometimes used for 'activated'.
 The surface area may vary greatly depending upon
precusor (raw material) and the condition of
carbonization for making active carbon
 An activation level sufficient for useful application
may be obtained solely from high surface area.
 Chemical treatment has been found to enhance the
adsorption properties of activated carbon.

75. • AC is usually derived from charcoal.
• When derived from coal, it is referred to as activated coal.
• Activated coke is derived from coke.
• Therefore activated carbon, activated charcoal, activated
coke, active carbon may be said to perform the same
function.
• Chemical or physical activation methods and microwave
radiation methods are the commonly used techniques
adopted for preparation of activated carbon.
• They are used as an adsorbent by the separation and
purification industries.
• They are composed of a micro porous, homogenous
structure with high surface area and show radiation
stability.
• Their adsorption capacity depends on porosity and its
surface chemistry.

76. Activated Carbon Powder
Granules Pellets

77. TYPES OF ACTIVATED CARBON
(1) Powdered Activated Carbon (PAC)
(2) Granular Activated Carbon (GAC)
(3) Extruded Activated Carbon (EAC)

78. Powdered Activated Carbon (PAC)
• Powdered activated carbons generally fall in
the particle size range of 5 to 150 Å, with some
outlying sizes available.
• PAC’s are typically used in liquid-phase
adsorption applications and offer reduced
processing costs and flexibility in operation.

79. Granular Activated Carbon (GAC)
Granular activated carbons generally range in
particle sizes of 0.2 mm to 5 mm and can be
used in both gas and liquid phase applications.
GACs are popular because they offer clean
handling and tend to last longer than PACs.
Additionally, they offer improved strength
(hardness) and can be regenerated and reused.

80. Extruded Activated Carbon (EAC)
Extruded activated carbons are a cylindrical
pellet product ranging in size from 1 mm to 5
mm.
Typically used in gas phase reactions, EACs
are a heavy-duty activated carbon as a result of
the extrusion process.

81. Applications of Activated Carbon (AC)

82. Applications of Activated Carbon (AC)
• Activated carbon is an incredibly diverse material that lends
itself to thousands of applications through its superior
adsorbent capabilities various application of activated carbon
• The availability of high surface area of particles possessed
by AC as well its adsorptive ability makes it a significant
constituent in many industries.
• Industries like; petroleum, fertilizer plants, nuclear,
pharmaceuticals, cosmetics, textiles automobile, and
vacuum manufacturing all uses AC.
• AC has found to be good porous materials, which make it
very effective in adsorption of solutes from aqueous solutions.
• This was suggested to be due to the possession of large
specific surface area.

83. Applications of Activated Carbon (AC)
• Metal recovery
• Food & Beverage
• Medical
• Air Emission purification
• Biogass Purification
• Remediation
• Waste water purification

84. SLUDGE QUALITY
CONSIDERATIONS
To determining sewage sludge quality it depends
on three following parameters:-
 The presence of pollutants (arsenic,
cadmium, chromium, copper, lead, mercury,
molybdenum, nickel, selenium, and zinc)
 The presence of pathogens (e.g., bacteria,
viruses, parasites)
 The sewage sludge’s attractiveness to
vectors (e.g., rodents, flies, mosquitoes)

85. STRIPPING OF VOLATILE
ORGANICS
Air Stripping and VOC Removal - Moving air
through contaminated groundwater or surface
water in an above-ground treatment system.
Air stripping removes chemicals called
"volatile organic compounds" or "VOCs.“
 VOCs are chemicals that easily evaporate
which means they can change from a liquid to
a vapor (a gas).

86. Sources of volatile organic
compounds
•Man made
•Anthropogenic

87. Man made volatile organic
compounds emissions
• Transportation
• Petroleum and petrochemical industry
• Electrical power generation
• Chemical process industries

88. Effects of VOC’s
• Photochemical smog
• Health effects
• Global warming
• Odour
• Carcinogenicity

89. Harmful chemical of VOC’s
• Benzene
• Toluene
• Xylene
• Phenol
• Pyridine
• Chloroform
• Methyl Ethyl Ketone

90. Flowchart of VOC Removal Technology

91. VOC Organic Component Removal

92. NITRIFICATION AND
DENITRIFICATION
• Nitrification is the
conversion of ammonia
(NH3+) to nitrate (NO3-).
• Denitrification is the
conversion of nitrate (NO3-)
to nitrogen gas (N2).

93. NITRIFICATION AND
DENITRIFICATION
The conversion of ammonia
into nitrites is known as
nitrification.
The conversion of nitrates into
nitrogen is known as
denitrification

94. NITRIFICATION AND
DENITRIFICATION

95. Nitrification
 The process of conversion of ammonia or reduced
nitrogen compounds into the easily absorbable form
of nitrogen that is nitrates and nitrites.
 It is an aerobic process.
 Chemoautotrophic bacteria play a major role in this
process.
 First, the ammonia is converted into nitrite by the
process of oxidation.
 Nitrococcus and Nitrosomonas take part in this
process.
 Nitrite is oxidised to nitrate with the help
of Nitrobacter.
 Then, nitrate is taken up by the root of the plant.

96. Nitrification
Nitrification is a two-step process.
Bacteria known as Nitrosomonas convert
ammonia and ammonium to nitrite.
Next, bacteria called Nitrobacter finish the
conversion of nitrite to nitrate.
Biological nitrification is the process in which
Nitrosomonas bacteria oxidize ammonia to nitrite
and Nitrobacter bacteria oxidize nitrite to nitrate.
This process results in the overall conversion of
ammonia to nitrate.

97. • Nitrification is temperature sensitive. The
optimum temperature for nitrification is
generally considered to be 30°C.
• Nitrification consumes alkalinity and lowers pH
in the activated sludge mixed liquor.
• pH below 6.5 or above 8.0 can significantly
inhibit nitrification.
• Optimum pH values for denitrification are
between 7.0 and 8.5. Denitrification is an
alkalinity producing process.

98. Denitrification
The process of conversion of nitrates and
nitrites into the gaseous form of nitrogen is
called denitrification.
It is mostly converted to nitrogen and nitrous
oxide.
Bacteria participating in this reaction
are Pseudomonas and Thiobacillus.