The document provides an overview of sewage treatment plants. It defines sewage and its components. It describes various pollutants found in sewage and their impacts. It outlines typical characteristics of raw sewage and treated sewage standards. It then discusses various unit processes involved in sewage treatment plants including preliminary treatment like screening and grit removal, secondary treatment processes like activated sludge process, UASB, MBBR, and SBR. It also discusses membrane bioreactor, stabilization ponds, and sludge handling. Diagrams and figures are included to illustrate the various treatment processes.

1. SEWAGE TREATMENT
PLANT – A PERSPECTIVE
by
Vishal Duggal
PATIALA (Punjab)
Ph.: 98 140 059 33, 98766 05933
Email: visduggal@gmail.com, v.duggal@live.com
for
Training Program
Operation and Maintenance of Wastewater Treatment
Plants (ETPs/CETPs/STPs)
NATIONAL PRODUCTIVITY COUNCIL
New Delhi

2. SEWAGE
(domestic sewage/domestic wastewater/municipal wastewater)
 A type of wastewater that is produced by a community of
people
 Consists of wastewater discharged from residences and
from commercial, institutional and public facilities that
exist in a locality
 Greywater: from sinks, bathtubs, showers, dishwashers,
and clothes washers (reject water having lesser organic
pollution load)
 Blackwater: the water used to flush toilets, combined with
the human waste that it flushes away, and kitchen
wastewater (reject water having higher organic pollution
load)

3. POLLUTANTS
 Oxygen Demanding substances
 Biochemical Oxygen Demand, or BOD: Organic matter and
ammonia are “oxygen-demanding” substances
 Demand is placed on the dissolved oxygen of the receiving
waters by the microbial population in an effort to consume
them as food
 Nutrients
 Carbon, nitrogen, and phosphorus are essential to living
organisms and are the chief nutrients present
 An excess of these nutrients overstimulates the unwanted
growth of aquatic plants, causes unsightly conditions,
interferes with drinking water treatment processes, and causes
unpleasant and disagreeable tastes and odours

4. POLLUTANTS…
 Inorganic and recalcitrant organic substances
 A vast array of chemicals
 Many of these substances are toxic to life and are also
harmful to humans
 May be poisonous at very low concentrations
 Pathogens
 Infectious micro-organisms, or pathogens
 Causes the occurrence of waterborne diseases
 Suspended solids
 Insoluble matter present
 May be inert
 Can cause deposits, chokings, anaerobic conditions

5. RAW SEWAGE CHARACTERISTICS

6. TYPICAL CHARACTERISTICS
Parameter Average quantity
a) BOD3, 27C 200-250 mg/l
b) COD 300-400 mg/l
c) Total suspended solids 400-500 mg/l
d) Total dissolved solids 800-1500 mg/l
e) Total kjeldahl nitrogen (as N) 30-45 mg/l
f) Total phosphorus (as P) 5-15 mg/l
g) Feacal coliform count 1 x 107 MPN/100 ml
h) Soluble fraction of BOD 55-60%

7. TREATED SEWAGE STANDARDS
Parameter Average quantity
a) pH 6.5-8.5
b) BOD3, 27C <10 mg/l
c) COD <50 mg/l
d) Total suspended solids <10 mg/l
e) Ammoniacal nitrogen (as N) <5 mg/l
f) Total nitrogen (as N) <10 mg/l
g) Feacal coliform count <100 MPN/100 ml

8. TREATMENT REQUIREMENTS
 Preliminary treatment
 Removes materials that can cause operational problems
 Primary treatment
 Typically meant to remove ~60% of suspended solids and
~35% of BOD
 Secondary treatment
 Typically meant to remove ~85% of BOD and suspended
solids
 Advanced treatment
 Typically meant to remove >85% of BOD, solids, and
nutrients
 Final treatment (polishing) – disinfection
 Solid management – sludge handling

9. TYPICAL P.F.D. OF AN S.T.P.

10. RAW SEWAGE PUMPING
 Receiving chamber
 Coarse screening
 Wet well (raw sewage sump)
 Pump house
 Raw sewage pumps

11. PUMPING STATION CONFIGURATIONS

12. PRIMARY TREATMENT
 Screening
 Objective: Removal of coarse solids
 Types of screens: Fine/medium/coarse
 Cleaning of screens: Manual/mechanical
 Benefits: Protection of pumps
 Coarse Screening: 20 mm clear spacing in bars
 Fine screening: 6 mm clear spacing in bars

13. PRIMARY TREATMENT (SCREENING)

14. PRIMARY TREATMENT (SCREENING)

15. PRIMARY TREATMENT
 Grit removal
 Objective: Removal of inorganic solids, e.g., pebbles/sand/
silt to protect moving mechanical equipment
 Principle: Gravity separation (effective size – 0.15 mm;
specific gravity – 2.65)
 Types:
 Manual grit removal – Rectangular channel
 Mechanical grit removal - Circular tank
 Grit removal mechanism: Screw classifier/reciprocating
classifier

16. PRIMARY TREATMENT (GRIT REMOVAL)

17. PRIMARY TREATMENT (GRIT REMOVAL)

18. PRIMARY TREATMENT (GRIT REMOVAL)

19. SECONDARY TREATMENT
The microorganisms are cultivated in the wastewater. The
microorganisms use organic matter from sewage as their food
supply. This process leads to decomposition or biodegradation
of organic wastes.
 Activated Sludge Process (ASP)
 Up-flow Anaerobic Sludge Blanket Reactor (UASBR)
 Moving Bed Biofilm Reactor (MBBR)
 Sequential Batch Reactor (SBR)
 Membrane Bio-reactor (MBR)
 Lagoons/stabilisation ponds
 Constructed wetland systems

20. SECONDARY TREATMENT
 High density of microorganisms – keep organisms in system
 Good contact between organisms and wastes – provide
mixing
 Provide high levels of oxygen (for aerobic processes) -
aeration
 Favorable temperature, pH, nutrients – design and operation
 No toxic chemicals present – control or pre-treat inputs

21. ACTIVATED SLUDGE PROCESS
 Proven and tested for more than 7 decades all over world
 Several modifications/advances possible to meet specific
requirements
 Comprises of;
 Aeration tank containing micro organisms in suspension in
which reaction takes place.
 Activated sludge recirculation system.
 Excess sludge wasting and disposal facilities.
 Aeration systems to transfer oxygen
 Secondary sedimentation tank to separate and thicken
activated sludge.
 Performance is critically dependent on sludge settling
characteristics and design of secondary clarifier

22. ACTIVATED SLUDGE PROCESS…
 Sludge settling characteristics are typically influenced by
bio-flocculation which in turn depends on growth rate of
micro-organisms
 Growth rate is generally controlled by controlling biological
solids retention time/food to micro-organism ratio
 Requires careful monitoring of the reactor sludge levels and
sludge withdrawal

23. ACTIVATED SLUDGE PROCESS…
 Advantages
 Performance is not significantly affected due to normal
variations in wastewater characteristics and seasonal changes
 Less land requirements
 Disadvantages
 High recurring cost
 High energy consumption
 Performance is adversely affected due to interruption in power
supply even for a short period
 Foaming, particularly in winter season, may adversely affect
the oxygen transfer, and hence performance
 Nitrogen and Phosphorous removal requires additional anoxic
tank and >3 times internal recirculation
 More land requirement than SBR & MBBR

24. UPFLOW ANAEROBIC SLUDGE BLANKET
REACTOR
 UASB uses an anaerobic process whilst forming a blanket of
granular sludge which suspends in the tank
 Wastewater flows upwards through the blanket and is
processed (degraded) by the anaerobic microorganisms
 The upward flow combined with the settling action of
gravity suspends the blanket with the aid of flocculants
 The sludge in the UASB is tested for pH, volatile fatty acids
(VFA), alkalinity, COD and SS. If the pH reduces while
VFA increases, the sewage should not be allowed into the
UASB until the pH and VFA stabilise.
 The reactor may need to be emptied completely once in five
years, while any floating material (scum) accumulated
inside the gas collector channels may have to be removed
every two years to ensure free flow of gas.

25. UPFLOW ANAEROBIC SLUDGE BLANKET
REACTOR

26. UPFLOW ANAEROBIC SLUDGE BLANKET
REACTOR
 Advantages
 Requires lesser power than aerobic processes
 Biogas generated can be used as fuel or electricity
 Disadvantages
 UASB alone does not treat the sewage to desirable limits,
therefore downstream aerobic treatment is compulsory
 Requires very large space due to post treatment
 Recovery of biogas is not sufficient to produce substantial
electricity in case of municipal wastewater

27. MOVING BED BIO-REACTOR
 A compact and robust system involving extended aeration
process with submerged aeration
 Biomass growth on fluidized bed of plastic media enabling
retention of biomass and long solid retention time in the
reactor leading to low “food to micro-organism ratio” and
higher organic removal
 Two stage biological oxidation
 The process is intended to enhance the activated sludge
process by providing greater biomass in aeration tank and
thus by reducing volume of the tank
 After aeration tank sedimentation tank is provided for
settlement of sloughed biomass
 Ability to withstand limited organic overload

28. MOVING BED BIO-REACTOR
 Special grade plastic proprietary media custom made for
offering high specific surface area is required
 MBBR is a unique process in which combines suspended as
well as attached growth principles of biological wastewater
treatment
 The biomass responsible for the removal of organic matter
from the wastewater is held in suspension as well as on the
bio carriers provided in the reactor as fixed film
 MBBR provides an unique combination of advantages
provided by both activated sludge system as well as fixed
film system and at the same time trying to minimize the
drawbacks of both the systems
 In MBBR, the biological performance is independent of
solids separations

29. MOVING BED BIO-REACTOR

30. MOVING BED BIO-REACTOR

31. MOVING BED BIO-REACTOR
 Advantages
 Requires lesser space
 Ability to effectively treat dilute domestic wastewaters
 Elimination of the need for sludge recirculation and
monitoring of MLSS in the reactor
 Capacity to handle shock loads
 Low and stabilised sludge production
 Simple and reliable operation
 Disadvantages
 Control of SRT and other process parameters is difficult
 Problems of choking of media
 Problems of media loss

32. SEQUENTIAL BATCH REACTOR (S.B.R.)
 The sequencing batch reactor (SBR) is a fill-and-draw type
activated sludge system operating in batch
 The treatment consists of a cycle of five stages: fill, react,
settle, draw and idle.
 During the reaction type, oxygen is added by an aeration
system. The bacteria oxidise the organic matter just as in
activated sludge systems.
 Thereafter, aeration is stopped to allow the sludge to settle.
 Then the water and the sludge are separated by decantation
and the clear layer (supernatant) is discharged from the
reaction chamber through a special decanter
 Depending on the rate of sludge production, some sludge
may also be purged

33. SEQUENTIAL BATCH REACTOR (S.B.R.)
 After a phase of idle, the tank is filled with a new batch of
wastewater
 At least two tanks are needed for the batch mode of
operation as continuous influent needs to be stored during
the operation phase.
 It performs biological organic removal, nitrification, de-
nitrification and biological phosphorous removal.

34. SEQUENTIAL BATCH REACTOR (S.B.R.)

35. SEQUENTIAL BATCH REACTOR (S.B.R.)
 Advantages
 Controls growth of filamentous bacteria and avoids bulking of
sludge
 Provides stabilised sludge.
 Allows for easy modular expansion for increased flow
 High BOD removal of up to 98%
 Disadvantages
 Compared to the conventional ASP/MBBR/UASB, a higher
level of sophistication and maintenance is associated due to
automation
 The SBR is susceptible to shock loads
 Process start-up stabilisation require very high skills

36. MEMBRANE BIO REACTOR (M.B.R.)
 Combines membrane technology with biological treatment
 Replaces conventional clarification, aeration and filtration
into a single step
 The use of membrane filtration allows an MBR process to
produce a significantly higher quality effluent than that
obtainable from a conventional aerobic treatment process
 The mixed liquor suspended solids concentration (MLSS)
and the solids retention time (SRT) are limited in a other
aerobic processes
 The MLSS and SRT can both be larger for MBR processes
 This results in a smaller aeration tank volume needed for an
MBR process than that needed for other aerobic processes

37. MEMBRANE BIO REACTOR (M.B.R.)

38. MEMBRANE BIO REACTOR (M.B.R.)

39. MEMBRANE BIO REACTOR (M.B.R.)
 Advantages
 Better effluent quality, smaller space requirements, and ease
of automation
 Operate at higher volumetric loading rates which result in
lower hydraulic retention times
 The low retention times mean that less space is required
compared to a conventional system.
 The treated effluent contains low concentrations of bacteria,
TSS, BOD, and phosphorus. This facilitates high-level
disinfection.
 High quality water produced for effective reuse

40. MEMBRANE BIO REACTOR (M.B.R.)
 Disadvantages
 Very high level of sophistication and maintenance is
associated
 Higher capital and operating costs
 Problem of membrane fouling and choking drastically reduces
plant efficiency
 Very high operational complexity – require highly skilled
manpower for operation

41. STABILISATION POND
 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
 Three types of ponds: anaerobic, facultative, aerobic
(maturation), each with different treatment and design
characteristics
 WSPs are low-cost for O&M and BOD and pathogen
removal is high
 Very large surface areas are required
 The treated effluent is appropriate for the reuse in agriculture
only

42. STABILISATION POND

43. STABILISATION POND
 Advantages
 Simple to construct, operate and maintain
 Does not involve installation of expensive electro-mechanical
equipment
 Has very low O&M costs
 Extremely robust and can withstand hydraulic and organic
shock loads
 BOD reduction of the order of 90% and more
 Coliform reduction could be up to 6 log units
 High quality effluent at least operating costs
 Low skill requirement for operation of the plant

44. STABILISATION POND
 Disadvantages
 Very large land requirement
 High cost of lining
 Likelihood of odour nuisance and mosquito breeding in
poorly maintained WSPs
 If unlined, likelihood of groundwater contamination in porous
and fractured strata

45. SLUDGE HANDLING
 Involves sludge dewatering
 Sludge drying beds
 Conventional method of sludge drying
 No power requirement
 Substantial area is required
 Difficult to operate in monsoon
 Labour intensive
 Manual scrapping and loading of dried sludge

46. SLUDGE HANDLING

47. SLUDGE HANDLING
 Mechanical dewatering – centrifuge
 Advanced method of solid-liquid separation
 Less area
 Power required for pumping the sludge and operation of
centrifuge
 Less time
 Efficient dewatering

48. SLUDGE HANDLING

49. COMMON PROBLEMS &
TROUBLESHOOTING
 Treated effluent is not meeting total nitrogen targets
 Analyse for Ammonia, Nitrite and Nitrate
 In case of high ammonia look to ensure your plant has
the following;
 Generally, nitrification occurs only under aerobic
conditions at dissolved oxygen levels of more than 1.0
mg/L
 Nitrification requires a long retention time
 A low food to microorganism ratio (F:M)
 A high mean cell residence time (measured as MCRT or
Sludge Age)
 Adequate pH buffering (alkalinity)

50. COMMON PROBLEMS &
TROUBLESHOOTING
 Treated effluent is not meeting total nitrogen targets
 The biological reduction of nitrate to nitrogen gas is
performed by bacteria that live in a low-oxygen
environment. To thrive, the bacteria need biochemical
oxygen demand (BOD) – soluble BOD.
 Adequate carbon source: about five times as much as the
amount of nitrate being denitrified
 Ensure that the nitrification process is working otherwise
there will be no nitrate to denitrify
 Ensure that the anoxic tank has 0 DO. Otherwise Mixed
Liquor Return Rate (MLR) might need to be reduced (as a
rule of thumb this flow rate is usually set at 300% of the
daily incoming flow)

51. COMMON PROBLEMS &
TROUBLESHOOTING
 Treated effluent is not meeting BOD targets
 High effluent BOD levels in the treated effluent can have
a number of causes
 Incomplete wastewater treatment due to organic
overloading
 Low oxygen concentration
 Low hydraulic detention time
 Physical short circuiting
 High algae or sulphur bacteria growth
 Sludge accumulation and loss of old sludge to the effluent

52. COMMON PROBLEMS &
TROUBLESHOOTING
 Sludge overflow from clarifier
 This phenomenon may be related to oxygen deficiency or
nutrient deficiency.
 It can also be adversely affected by the long residence time in
sedimentation tanks when denitrification bacteria can start to
produce nitrogen gas
 Also not sufficient sludge removal from the system might be a
reason of those problems

53. Any Questions …….???