Waste Water Treatment Objectives Outline of treatment process (flow diagram) Preliminary treatment Primary treatment (sedimentation) Secondary treatment (activated sludge, filtration) Sludge treatment Disinfection Tertiary treatment

1. Waste Water Treatment
(Sewage Treatment)

2. Outline
• Objectives
• Outline of treatment process (flow diagram)
• Preliminary treatment
• Primary treatment (sedimentation)
• Secondary treatment (activated sludge, filtration)
• Sludge treatment
• Disinfection
• Tertiary treatment

3. Objective of Sewage Treatment
 To prevent pollution of the receiving water
 To prevent offensive odour in the water
 To prevent the destruction aquatic life
 If the sewage has to be disposed of on land,
the soil will become sewage sick after some
time and cannot take any more sewage

4. Outline of Sewage Treatment
 Preliminary treatment
 Primary treatment
 Secondary treatment
 Disinfecting
 Tertiary Treatment

5. Preliminary Treatment
• Waster water contains floating suspended
solids such as rags, wood, metal, plastic, etc.
• these suspended impurities have to be
removed as they interfere with the treatment
processes or mechanical equipment.

6. Primary Treatment
• consists of mainly the sedimentation
process to remove suspended organic solids
• Chemicals are sometimes added in primary
clarifier to assist in the removal of finely
divided and colloidal solids or to precipitate
phosphorous

7. Secondary or Biological
Treatment
• Activated sludge process
• Filtration

8. Activated sludge process
• the sewage is biologically treated.

9. Filtration
• is done in contact beds or intermittent sand
filters or tricking filters.
• It removes finely divided suspended matter.

10. Sludge & Effluent
• The semi-solid that settles down at the
bottom after treatment,is called sludge
• liquid to be discharged is called effluent.

11. Disinfecting
• Disinfecting is carried out if necessary by
chlorination to kill the bacteria which
remain in the effluent of sewage

12. Tertiary Treatment
• If the receiving water provides only little
dilution or there is a need to preserve a
particularly high quality of effluent, tertiary
treatment can be used.

13. PRELIMINARY TREATMENT

14. Objectives
Remove coarse suspended and floating
matter such as rags, plastic, pieces of wood,
etc., by means of screening
Remove grit, sand, broken glass, etc., in grit
chambers
Remove grease, and oil substances by
floatation in skimming tanks

15. Processes
Screening
Silt and grit removal
Oil and grease removal

16. PRIMARY TREATMENT

17. PRIMARY TREATMENT
Primary sedimentation tank
(Secondary sedimentation tank) -
sedimentation after activated sludge process

18. Advantages
• The advantages of coagulation over plain
sedimentation are:
Sedimentation by coagulation is more
effective
BOD, colour and turbidity are reduced
Less capacity of sedimentation tanks
The process is simple

19. Disadvantages
• The disadvantages are:
Chemicals destroy the bacteria that digest
the sludge
Chemicals increase the cost of
sedimentation
Skilled supervision is required
Large quantity of sludge is produced

20. SECONDARY TREATMENT

21. SECONDARY TREATMENT
• The secondary treatment converts the
remaining organic matter into stable form
by putting aerobic and anaerobic bacteria
into action

22. Processes
Filtration
Activated sludge process

23. Filtration
• Aerobic bacteria need a contact surface to
live and carry out their activities

24. Filtration
Contact beds
Intermittent sand filters
Trickling filters

25. Contact Beds
• A contact bed consists of filtering medium.
• When the sewage is passed over the
medium, a thin film is produced around the
particles.
• The bacteria present in the film oxidise the
organic matter.

26. Intermittent Sand Filter
• the filtering medium consists of sand.
• The action of the filter is due to:
Mechanical straining and
– Bacterial action

27. Trickling Filters
• A trickling filter is an artificial bed of stone
or broken brick material
• waste water is distributed an applied in
drops, films or spray
• A zoogleal film is formed on the surface
media.

28. ACTIVATED SLUDGE
PROCESS
• is a biological sewage treatment process
• a mixture of sewage and activated sludge is
agitated and aerated.
• The activated sludge is subsequently
separated from the treated sewage by
sedimentation

29. What is ACTIVATED SLUDGE
• is that sludge which settles down after the
sewage has been freely aerated and agitated
for a certain time.

30. How Activated Sludge works
• Activated sludge contains numerous
bacteria and other microorganisms. When it
is mixed with raw sewage saturated with
oxygen, the bacteria perform:
– Oxidise the organic solids
Promote coagulation and flocculation and
convert the colloidal and suspended solids into
settable solids

31. Steps in Activated Sludge process
• Treat raw sewage in the primary settling
tank
• mix sewage with the activated sludge and
aerated for 4-10 hours
• final (secondary) settling tank
• dispose of effluent
• return some sludge to the aeration tanks
• dispose of the rest of the sludge

32. Advantages
• Gives clear sparkling treated effluent
• Effluent free from offensive odour
• Degree of purity can be varied as desired
• Cost of installation lesser than for a
trickling filter
• Small loss of head in the process

33. Disadvantages
Skilled supervision and constant check on
the return sludge is necessary
When there is change in the quality or
quantity of sewage, the process is upset
The process does not work for some
industrial wastes
Large volume of sludge increases difficulty
in disposal

34. Methods of Aeration
• The success of the activated sludge process
depends on the aeration provided.
Diffused air aeration
Mechanical aeration
Combination of the above two methods

35. TERTIARY TREATMENT

36. TERTIARY TREATMENT
• MICROSTRAINERS
• RAPID GRAVITY SAND FILTERS
• UPWARD-FLOW “MEDUIM” SAND
FILTERS
• SLOW SAND FILTERS
• PEBBLE-BED CLARIFIERS
• SETTLEMENT
• GRASS PLOTS
• LAGOONS

37. SLUDGE TREATMENT AND
DISPOSAL

38. Sludge
• Sludge is a semi-liquid
• Sludge produced by plain sedimentation
• Sludge produced by chemical
precipitation
• Trickling filter
• Activated sludge

39. Methods of Disposal
• Disposal on land
• Drying on drying beds
• Dumping into the sea
• Heat-drying
• Incineration
• Lagooning or ponding
• Sludge Digestion

40. Sludge Digestion
• It transforms a portion of solids into
liquids and gases, thereby reducing the
sludge volume to be dealt with
• It breaks the organic matter of sludge
into simpler compounds by the action of
anaerobic bacteria.