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Disposal of Wastes

  1. Solid wastes include garbage (food wastes), rubbish (paper, plastics,
    wood, glass etc), sewage treatment residue (sludge) etc. Per capita
    solid waste production ranges from 0.25 – 2.5 kg.
  2. Common methods of their disposal are –
    1. Dumping – refuse is dumped in low lying areas; causes pollution.
      City of Kolkata disposes its waste in this fashion.
    2. Controlled tipping or sanitary landfill – it differs from dumping
      in that the refuse is compacted and placed in a dug out trench and
      adequately covered later. Eg: Trench method, area method, ramp
      method . Temperature rises to >60 degree C within 7 days, kills all
      pathogens & hastens the decomposition. Cools down in 2-3 weeks &
      after complete decomposition of organic matter it turns into an
      innocuous mass in 4-6 months.
    3. Incineration or burning – mainly used in hospitals. Method of
      choice where suitable land is not available.
    4. Composting – this method combines the disposal of refuse and
      night soil or sludge.
      1. The bacterial action results in formation of a stable inert matter,
        compost which can be used as manure.
      2. Two processes are commonly used – Bangalore method
        (anaerobic method) Recommended for municipalities
        with <100,000 population
      3. and Mechanical composting (aerobic method).
    5. Manure pits – can be useful in rural areas by digging
      pits for individual houses.
    6. Burial – useful for small camps.
  1. Excreta disposal
    1. Sewage: waste water from the community containing
      solid & liquid excreta.
    2. Sullage: waste water without human excreta.
    3. Trap: provide water seal depth is 2 cm /¾ inch.
      It prevents access to flies/ smell.
Methods of excreta disposal
  1. Unsewered areas
    1. Service type Latrines
    2. Non service type (sanitary latrines)
      1. Bore hole latrine
      2. Water seal types – PRAI type, RCA type, sulabh sauchalaya
      3. Septic tank
      4. Aqua Privy
  1. Latrines suitable for camps & Temporary use
    1. Shallow trench latrine
    2. Deep trench latrine
    3. Pit latrine
    4. Bore hole latrine
  1. Sewered areas
    1. Water Carraige system & sewage treatment
      1. Primary T/t
        • ​​Screening
        • Removal of grit
        • Plain sedimentation
      2. Secondary T/t
        • Trickling filters
        • Activated sludge process
      3. Other methods
        • ​​Sea outfall
        • River outfall
        • Sewage farming
        • Oxidation pond
    2. ​​Strength of sewage is expressed in terms of
      1. Bio-Chemical Oxygen demand (BOD): amount of oxygen
        absorbed by a sample of sewage during a specified period
        (5 days) at 20 degree C for aerobic destruction or use of
        organic matter by living organism.
      2. Chemical Oxygen Demand (COD): measures the oxygen
        equivalent of that portion of the organic matter in a sample
        which is susceptible to oxidation by a strong chemical oxidizer.
      3. Suspended solids
        Sludge: organic matter, which settles down.

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