Introduction: Wastewater flow and its characteristics, Wastewater collection systems, Estimation and variation of wastewater flows. Problems of industrial wastewaters, sampling protocol, equalization, neutralization, proportioning processes, volume and strength reduction. Preliminary, primary, secondary and tertiary wastewater treatment processes. Theory and design of screens, grit chambers, sedimentation, coagulation, flocculation

1. DEPARTMENT OF CHEMICALENGINEERING
CHAPTER- 1
“Introduction of Wastewater”
PROF. DEVARSHI P. TADVI
ASSISTANT PROFESSOR
CHEMICAL ENGINEERING
DEPARTMENT
S S AGRAWAL INSTITUTE
OF
ENGINEERING & TECHNOLOGY,
NAVSARI
WASTEWATER ENGINEERING

2. OUTLINE
• Introduction
• Objectives of water treatment
• Conventional water treatment plantlayout
• Various Methods of purification ofwater
• Screening
• Plain Sedimentation
• Sedimentation aided withcoagulation
• Filtration
• Disinfection
• Aeration
• Softening

3. What is Wastewater ?
• Wastewater is a term that is used to describe waste material
that includes industrial liquid waste and sewage waste that is
collected in towns and urban areas and treated at urban
wastewater treatment plants.

4. Where does wastewater come from?
• Residences
― human and animal excreta and waters used for washing, bathing, and cooking.
• Commercial institution
• Dairy and industrial establishment
― slaughterhouse waste, dairy waste, tannery wastewater, etc.

5. Where does it all go!
Where does the
water from the
washer go?
When you flush the
toilet where does the
contents go?
By gravity flow, the waste is on its way to your
local wastewater treatment plant!

6. Wastewater treatment
• A process to convert wastewater - which is water no longer needed or
suitable for its most recent use - into an effluent that can be either
returned to the water cycle with minimal environmental issues or reused.
• Water treatment is the process of making water suitable or acceptable for
an end-use.
• It removes existing water contaminats and so, reduce their concentration
that the water becomes fit for it’s desired application.
• The amount & type of tretment process (Treatment Train) depends upon
quality of Raw Water and various standards Required after treatment.

7. Wastewater Contaminants
• Suspended solids
• Biodegradable organics (e.g., BOD)
• Pathogenic bacteria
• Nutrients (N & P)

8. Objectives of water treatment
• Theobjectivesofwatertreatmentaretoproduce:
• Waterthatissafeforhumanconsumption
• Waterthatisappealingaestheticallytotheconsumer
• Wateratareasonablecost

9. Indian Standards for drinking water

10. Screening
Coagulation
Flocculation
Sedimentation
Filtration
Disinfection
Storage
Distribution
Raw water
Alum Cl2
sludge
sludge
sludge
7

11. Functions of Water Treatment Units

12. Selection of treatment process-Train
 The types of treatmentrequired fordifferentsourcesaregiven in the
following table:

13. WHY TREAT WASTEWATER ?
• Causes a demand for dissolved oxygen (lower DO
levels of streams)
• Adds nutrients (nitrate and phosphate) to cause
excessive growth
• Increases suspended solids or sediments in
streams (turbidity increase)

14. • Reduce organic content i.e., BOD
• Removal/reduction of nutrients i.e., N,P
• Removal/inactivation of pathogenic
microbes
OBJECTIVES OF WWT

15. LEVELS OF TREATMENT
• Primary
– removal by physical separation of grit and large objects (material to
landfill for disposal)
– Sedimentation and screening of large debris
Secondary
– Biological and chemical treatment
– aerobic microbiological process (sludge)
organic matter + O2 CO2 + NH3 + H2O
NH3 NO3
-
aquatic nutrient
Mostly dead
microbes

17. Treatment stages - Primary treatment
• typical materials that are removed
during primary treatment include
– fats, oils, and greases
– sand, gravels and rocks
– larger settle-able solids including human
waste, and
– floating materials

18. Methods used in primary treatment
• Bar screens
• Grinding
• Grit Chamber
• Sedimentation Tank-primary Settling tank
• Chlorination of effluent

20. Sedimentation Tank- Primary Settling tank
– Remove grease, oil
– Fecal solid settle, floating material rise to the surface
– Produce a homologous liquid for later biological
treatment
– Fecal sludge are pumped to sludge treatment plant

21. Secondary treatment
• Biological treatment
– activated sludge
– trickling filter
– oxidation ponds

22. Activated sludge process
• Primary wastewater mixed with bacteria-rich (activated)
sludge and air or oxygen is pumped into the mixture
• Both aerobic and anaerobic bacteria may exist
• Promotes bacterial growth and decomposition of
organic matter
• BOD removal is approximately 85%
• Microbial removal by activated sludge
• 80-99% removal of bacteria
• 90-99% removal of viruses

23. 5 physical components
• Aeration tank
• oxygen is introduced into the system
• Aeration source
• ensure that adequate oxygen is fed into the tank
• provided pure oxygen or compressed air
• Secondary clarifiers
• activated-sludge solids separate from the surrounding
wastewater
• Activated sludge outflow line
• Pump activated sludge back to the aeration tank
• Effluent outflow line
• discharged effluent into bay or tertiary treatment plant

25. Aeration
and rapid
mixing
Settling collects
sludge on
bottom
Secondary process
iriffuser
From
primary
process
To
tertiary
process

26. • Trickling filters are beds made of coke (carbonized coal),
limestone chips or specially fabricated plastic media
• Optimize their thickness by insect or worm grazing
• The primary wastewater is sprayed over the filter and microbes
decompose organic material aerobically.
• Low pathogen removal
- Bacteria, 20-90%
- Viruses, 50-90%
- Giardia cysts, 70-90%
Trickling filters

28. Stabilization or oxidation
PONDS
•
•
•
•
•
Oxidation ponds are a few meters deep, and up to a hectare
in size.
They are low cost with retention times of 1 to 4 weeks. Odor
and mosquitoes can be a problem
Pathogen removal:
- Bacteria, 90-99%
- Virus, 90-99%
- Protozoa, 67-99%
Mechanisms include the long detention time, high pH (10- 10.5)
generated by photosynthesis, predation, sunlight, temperature

29. Continued…
Stabilization ponds are the preferred
wastewater treatment process in developing
countries due to low cost, low maintenance.
This is balanced by larger land requirement.

30. When the treatment is done…
• Effluent back to stream after
– a final carbon filtration and
– chlorination/de-chlorination
• Sludge – very nutrient rich
– applied directly to land as fertilizer
– incinerated (good fuel after drying)
– composted

31. Sludge Treatment Processes
Thickening (water removal)
Digestion (pathogen inactivation and odor control)
Conditioning (improved dewatering with
alum and high temp, 175-230o C)
Dewatering (pathogen inactivation and odor control)
Incineration (volume and weight reduction)
Final disposal

32. • Septic Tanks
•
• Constructed
Wetlands
Composting
Wastewater
Treatment
Alternatives

33.  Removes large solids logs
branches rags fish
 Simpleprocess
mayincorporateamechanizedtrashremoval system
 ProtectspumpsandpipesinWaterTreatmentPlants

34. Plain Sedimentation
 Sedimentation is the removal of suspendedparticles
by gravitationalsettling.
 Types of Sedimentation Tanks
1) Fill And Draw Type
2) Continuous Flow type

35. Shape of sedimentation tank
1. Rectangular
tank with
horizontal flow.
2. Circular tank
with radial or
spiral flow.
3. Hopperbottom
tank with
vertical flow.

36. SEDIMENTA
TION
 Water flows to a tank called a
sedimentationbasin
 Gravity causes the flocs to settle
to the bottom
 It would take a very long time for
all particles to settle out and that
would mean we would need a
verylarge sedimentationbasin.

37. Sedimentation aided with coagulation
 Sedimentation added with comprises of three step
Addition of measured quantity of chemicals called
coagulants to water and their through mixing ( rapid
mixing ).
Formation of precipitate which coagulates and forms a
flow ( flocculation)
Sedimentation

38. Coagulants
 AluminumSulfate
Al2(SO4)3
 Ferrous Sulfate FeSO4
 Ferric Sulfate Fe2(SO4)3
 Ferric ChlorideFeCl3
 LimeCa(OH)2
Aluminum salts are cheaper
but iron salts are more
effective over widerpH range
15

39. Aeration Unit
 Work : Diffusion of Air
 Removes odour andtastes
 Oxidizes iron and manganese, increases dissolved oxygen content in
water, removes CO2 and reduces corrosion and removes methane and
other flammablegases.
 Types of Aerators
1. Gravityaerators
2. Fountainaerators
3. Diffused aerators
4. Mechanical aerators.

40.  Gravity Aerators (Cascades): In gravity aerators,
water is allowed to fall by gravity such that a large area
of water is exposed to atmosphere, sometimes aided by
turbulence.
Aeration Unit

41.  Injection or Diffused Aerators : It
consists of a tank with perforated
pipes, tubes or diffuser plates, fixed
at the bottom to release fine air
bubbles from compressor unit. Time
of aeration is 10 to 30 min and 0.2 to
0.4 litres of air is required for 1 litre
of water.
Aeration Unit

42.  Fountain Aerators : These are also known as spray
aerators with special nozzles to produce a fine spray. Each
nozzle is 2.5 to 4 cm diameter discharging about 18 to 36
l/h. Nozzle spacing should be such that each m3 of water
has aeratorareaof 0.03 to 0.09 m2 forone hour.
Aeration Unit

43.  Mechanical Aerators
f locculation are used.
: Mixing
Paddles
paddles
may be
as in
either
submerged or at thesurface.
Aeration Unit

44. Types of Mixing Devices
 Mixings basins with bafflewalls

45.  Mixing Basins Equipped with Mechanicaldevicies

46. Flocculation
 Flocculation is a slow mixing or agitating process in which
the destablished colloidal particles are brought into
intimatecontact in order to promote the floc formation .
 Rate of flocculation dependsupon
 Types and amount of turbidity
 Types of coagulant
 Dosages of coagulant
 Mean velocity gradient inbasin

47. Clariflocculator
Clarifier and flocculator are provided in single unit
called clariflocculator.
The flocculating chamber is provided in the centre
and clarifier component is formed by the peripheral
space.
Velocity of flowof water around 0.3 m/min.
Mechanical scrapper provided to removesludge.

49. Filtration
The process of passing the water through the beds of
such granular material is known asfilteraton
 Types of Filtration
Slow sand gravityfilter
Rapid sand gravityfilter
1. Rapid sand gravityfilter
2. Pressure filter

52. Method of disinfection
 Physical method
By heat
By U.V.rays
 Chemical method
Oxidizingchemicals
Metal ions
Alkalis andacids
 Minor method
Boiling of water
Treatment with excesslime
Treatment withozone
Treatment with iodine and bromine
Treatment with ultra-violet rays
Treatment with potassiumpermanganate

53. Water softening
 Water is said to be hard when it contains relatively large
amounts of bicarbonates, carbonates, sulphates and
chlorides of calcium and magnesium dissolved init.
 Types of Hardness
 Temporary hardness
 Permanent hardness

54. Types of Hardness
caused by dissolved
 Temporary Hardness-
bicarbonates of Ca and Mg.
-AKA ‘alkaline or carbonatehardness’
 Permanent Hardness – caused by dissolved
chlorides and sulphates of Ca, Mg, Fe and Aletc.

55. Removal of Hardness
 Removal of temporary hardness
1. Boiling
2. By adding lime
 Removal of temporary hardness
1. Lime-soda process
2. Zeolite process
3. Demineralization or De-ionizationprocess

56. Disinfection
 The filtered water may
normally contain some
harmful disease producing
bacteria in it.
 These bacteria must be
killed in order to make the
water safe fordrinking.
 The process of killing these
Disinfection
bacteria is known as
or
Sterilization.

57. Methods of Disinfection
 Boiling: The bacteria present in water can be destroyed by boiling it for a long
time. However it is not.
 Treatment with Excess Lime: Lime is used in water treatment plant for
softening. But if excess lime is added to the water, it can in addition, kill the
bacteria also. Treatment like recarbonation for lime removal should be used
afterdisinfection.
 Treatment with Ozone: Ozone readily breaks down into normal oxygen, and
releases nascent oxygen. The nascent oxygen is a powerful oxidizing agent and
removes theorganic matteras well as the bacteria from thewater.
 Chlorination : The germicidal action of chlorine is explained by the recent
theory of Enzymatic hypothesis, according to which the chlorine enters the cell
walls of bacteria and kill the enzymes which are essential for the metabolic
processes of living organisms.

58. Reference
• Mahajan Publishing House
 http://web.iitd.ac.in/~arunku/files/CVL100/L8.pdf
 http://nptel.ac.in/courses/105104102/Lecture%2020.ht m
 http://www.sswm.info/sites/default/files/reference_at
tachments/SCHUTTE%202007%20Handbook%20for
• %20the%20Operation%20of%20Water%20Treatment
• %20Works.pdf
-4th
 Water & waste water Engineering edition By

59. Thank You