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Waste Water Treatment (Sewage Treatment)

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Waste Water Treatment (Sewage Treatment) Outline Objectives Outline of treatment process (flow diagram) Preliminary treatment Primary treatment (sedimentation ... – PowerPoint PPT presentation

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Title: Waste Water Treatment (Sewage 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.
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