The document summarizes the key steps and components involved in sewage treatment. It discusses primary treatment which uses settling and screening to remove solids. Secondary treatment uses biological processes like activated sludge to break down organic matter via aerobic bacteria. This produces a treated water that can be further processed or released, and a sewage sludge byproduct. Grit chambers and sedimentation tanks are also outlined which employ gravity and flow velocities to separate inorganic materials.

1. Sewage treatment

2. • process of removing contaminants from municipal wastewater,
containing mainly household sewage plus some industrial wastewater.
• Constituents: black water(from toilets and contains human waste)
and grey water(from domestic activities such as laundry, dishwashing,
and bathing)
• A by-product of sewage treatment is a semi-solid waste or slurry,
called sewage sludge.

3. Steps involved
• Sewage treatment generally involves three stages
1. Primary treatment,
2. Secondary treatment and
3. tertiary treatment.

4. Primary treatment
• consists of temporarily holding the sewage in a basin where heavy
solids can settle to the bottom while oil, grease and lighter solids float
to the surface.
• The settled and floating materials are removed and the remaining
liquid may be discharged or subjected to secondary treatment.
• Some sewage treatment plants that are connected to a combined
sewer system have a bypass arrangement after the primary treatment
unit.

5. screens

6. Grit chamber

7. Working principle
• work as a sedimentation tank which is designed to separate the
intended heavier inorganic materials
• The horizontal velocity of flow of 15 to 30 cm/sec is used at peak
flows. This same velocity is to be maintained at all fluctuation of flow
to ensure that only organic solids and not the grit is scoured from the
bottom.

8. Conditions that affect Composition of Grit
• Types of street surfaces encountered
• Relative areas served
• Climatic conditions
• Types of inlets and catch basins
• Amount of stormwater diverted from combined sewers at overflow points
Sewer grades
• Construction and condition of the sewer system
• Ground and groundwater characteristics
• Industrial wastes and
• Social habits.

9. Use of grit chamber
1. reduce formation of heavy deposits in aeration tanks, aerobic
digesters, pipelines
2. reduce the frequency of digester cleaning caused by excessive
accumulations of grit
3. protect moving mechanical equipment from abrasion and
accompanying abnormal wear.

10. Types of grit chambers
1. Vortex type cone and the centrifugal action plummets the grit to
the bottom
2. Aerated Grit Chamber

11. Vortex type

12. Aerated Grit Chamber

13. clearing and disposal of the Grit
• Manual clearing of the grit is to be avoided except in the case of very
small STPs of less than 1 MLD
• disposed of by dumping or by a sanitary landfill.
• The method of disposal is selected on the basis of physical and
chemical characteristics of grit, quality, availability of land for
disposal, etc.

14. Advantages of grit chamber
• To protect moving mechanical equipment from abrasion and
abnormal wear.
• To reduce maintenance cost in the frequency of digester cleaning
caused by excessive accumulation of grit.
• To prevent heavy deposits in pipelines and channels.

15. Sedimentation tank
• Sedimentation is the act of depositing sediment. (Or)
• Sedimentation is a physical water treatment process using gravity to
remove suspended solids from water.

16. Types of Sedimentation Tanks
1. Based on methods of operation
• a. Fill and draw type tank
• b. Continuous flow type tank
2. Based on shape
• a. Circular tank
• b. Rectangular tank
• c. Hopper bottom tank

17. • 3. Based on location
• a. Primary tank
• b. Secondary tank
• 4. based on flow direction
• a. horizontal flow:
• b. vertical flow:

18. Fill and draw type tank

19. Continuous flow type tank

20. Circular tank

21. Rectangular tank

22. Hopper bottom tank

23. Primary and secondary tank

24. Design parameters
• Detention period
• Displacement efficiency
• Surface loading
• Basin dimensions
• Inlet and outlet arrangements
• Sludge removal devices

25. Secondary treatment
• Secondary treatment is the portion of a sewage treatment sequence
removing dissolved and colloidal compounds measured as BOD.
• It can be aerobic (municipal wastewater treatment.) or
anaerobic(high-strength wastewater treatment )
• Aerobic treatment : Aerobic lagoons, Activated sludge, Rotating
biological contactor, Trickling filter (suspended growth and attached
growth process)
• Anaerobic treatment: Anaerobic digestors, UASB reactors
• selection of the secondary treatment may depend on several factors

26. Aerobic treatment Vs Anaerobic treatment

27. suspended growth Vs attached growth
• suspended growth process- the waste flows around and through the
free-floating microorganisms, gathering into biological flocs that settle
out of the wastewater( eg- aerated lagoons, activated sludge process
and aerobic digestion)
• attached-growth process- uses a medium to retain and grow
microorganisms(Trickling filters and rotating biological contactors
(RBCs))

28. Activated sludge process
• The activated sludge process is the biological process by which non-
settleable substances occurring in dissolved and colloidal forms are
converted into settleable sludge which is removed from the liquid
carrier (water).
• The process uses a groups of microorganisms in contact with the
organic matter in the waste water in an aerobic environment.
• The mass of microorganisms present in the system -biological solids
or mixed liquor suspended solids (MLSS).

29. components
1. an aeration tank, which serves as bio reactor;
2. a settling tank ("final clarifier") for seperation of AS solids and
treated waste water;
3. a return activated sludge (RAS) equipment to transfer settled AS
from the clarifier to the influent of the aeration tank

31. Operating Problems
• Sludge Bulking and Rising
• cloudy effluent
• pin floc or stragglers in effluent
• ash on clarifier surfaces

33. OXIDATION POND