SANITARY ENGINEERING

1. UNIT-4
CHAPTER 4.1
TREATMENT AND DISPOSAL OF
SEWAGE

2. TREATMENT OF SEWAGE

3. CLASSIFICATION OF WASTE WATER
TREATMENT
• Primary treatment
• Secondary treatment
• Tertiary treatment

4. Primary treatment:
• It removes floating and settable solids from
waste water by screening and sedimentation
Secondary treatment:
• It removes most of the organic matter by
chemical process
Tertiary treatment:
• In this nitrogen and phosphorus which are not
removed by secondary treatment are
removed

5. SCREENING
• The first unit operation carried out in waste
water treatment plants is screening.
• It is used to retain the large particles of
floating or suspended matter present in waste
water
• It should be placed before the grid chamber
• Screens are sometimes accommodated in the
body of the grit camber

6. TYPER OF SCREENS
• ACCORDING TO THE SIZE OF OPENING
Coarse screen- steel, large floating matters,
incineration or dumping
Medium screen– steel, organic matters,
incineration or dumping
Fine screen- electric motor, industrial waste,
dumping
• ACCORDING TO THE SHAPE
Disc screen
Drum screen

7. Wing screen
Shovel vane screen
Wing screen
Band screen
Shovel vane screen
Cage screen
Mesh screen

8. • ACCORDING TO THE CONDITION OF FIXITY
Fixed screen- permanently set in position
cleaned by rakes
Movable screen- lifted while cleaning
Moving screen- continuous rotation
• ACCORDING TO THE METHOD OF CLEANING
 Hand cleaned screens- cleaned using rakes
 Mechanically cleaned screens- cleaned
automatically at fixed intervals by rakes

9. SKIMMING TANKS
• It is a narrow rectangular tank with
longitudinal baffles.
• The sewage enters through the one end and
the water is collected in the other end.
• The compressed air is diffused upwards
through them to separate the floating matters
• Remove the lighter floating matters like oil,
grease, soap, pieces of wood from the waste
water.

10. GRIT CHAMBERS
• Grit cambers are provided to remove grit.
• It consist of sand, gravel, cinders and other
organic matters of food waste
• It prevents the clogging of pipes
• The flow velocity is decreased to settle down
the large organic matters
• The flow velocity is 0.15 to 3 m/s with a depth
of 0.9 to 1.2m and a detention period of 1
minute

12. • REMOVAL OF GRIT
Manual cleaning – It is removed by using
shovel and it is less hygienic.
Hydraulic cleaning – It is removed by the force
of water jet.
Mechanical cleaning – It is cleaned by devices
like scrapers, buckets, elevators.
• WASHING OF GRIT – The removed grit may
contain some organic matter it can be
removed if necessary by washing.
• DISPOSAL OF GRIT – It is a good manure used
for garden crops and it is also used to raise the
low lying areas.

13. SEDIMENTAION TANK
• The separation of settable solids from sewage
is called sedimentation tank.
• The sedimentation process carried out before
biological treatment is called primary settling.
• The sedimentation process carried out after
biological treatment is called secondary
settling.
• If it is carried out with a coagulant it is called
sedimentation with coagulation.

14. CLASSIFICATION OF SEDIMENTATION
TANK
• NATURE OF WORKING
• Fill and draw type
• Continuous flow type
• DIRECTION OF FLOW
• Horizontal flow
• Vertical flow
• Radial flow

15. • SHAPE
• Rectangular
• Circular
• Hopper bottom
• LOCATION
• Primary clarifier – located after the grit
camber, provided to treat the raw sewage
• Secondary clarifier – located after the filters,
provided to treat the treated sewage and are
also known as final clarifiers

16. FILTERS
• The organic matters in sewage is removed by
the biological processes
• Such biological treatment process include
sewage filtration and activated sludge process

17. TYPES OF FILTERS
• Contact beds
• Intermittent sand filters
• Trickling filters
Low rate or standard rate trickling filters
High rate or high capacity trickling filters

18. HUMUS TANK
• It is the secondary settling tank and are similar
to sedimentation tank
• The effluent from the trickling filters are
treated here by sedimentation process
• The effluent from filter media has the finely
divided suspended solids which are oxidized
• So thus it can be settled easily under the tank

19. ACTIVATED SLUDGE DIGESTION TANKS:
• It is the sludge settled at the bottom after the
sewage has been properly activated in the
presence of abundant oxygen
ACTIVATED SLUDGE PROCESS:
• The primary treated sewage is mixed with a small
quantity of activated sludge
• The effluent is collected after this process and the
sludge is treated and disposed of in a suitable
manner

20. ACTION OF ACTIVATED SLUDGE
PROCESS
• When activated sludge is mixed with sewage
containing sufficient quantity of sewage, the
micro organisms present in activated sludge
multiply rapidly and utilise the solids in the
effluent as food
• The colloidal and suspended matters
coagulate the flocculate and get converted to
readily settleable form

21. MODIFIED ACTIVATED SLUDGE
PROCESSES
• Re-aeration
• Step aeration
• Tapered aeration
• Activated aeration
• High rate treatment

22. SEPTIC TANK FOR ISOLATED BUILDINGS
• It is a rectangular water tight under ground
masonry tank
• It is suitable for disposing human waste and
liquid waste from houses, institutions etc.

23. DISPOSAL OF SEPTIC TANK EFFLUENT
• Disposal into soak pit
• Disposal in absorption trench

24. METHODS OF SLUDGE DISPOSAL
• Disposal on land
Ploughing
Trenching
• Distribution by pipe line
• Drying on drying beds
• Dumping into the sea
• Heat drying
• Incineration
• ponding