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.