FILTRATION

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filtration

Filtration removes fine particles, turbidity, colloidal matter, dissolved minerals, and microorganisms.

Types of Filters:-

A. Slow Sand Filter

  • Generally designed rectangular having L/B ratio of 1.5 to 3
  • Depth of filter is 2.5 to 3.5 m
  • Plane area of the filter is 100 to 2000 m2 having its’ size of the order of 30m *60m
  • 2 ≤ 1 of sand ≤ 4mm
  • Coefficient of uniformity D60/D10= 3 to 5
  • Design period =10 years
  • Depth of sand is 90 to 110 cm
  • Below the sand gravel-based of 30 to 75cm thick is used.
  • The frequency of cleaning is 1 to 3 months.
  • Rate of filtration =very slow 100 to 200lit/hr/m2
  • The efficiency of bacteria removal = 98 to 99%
  • It can be removed turbidity up to 50 ppm.
  • Cleaning of the filter is done manually once in 1-3 months in which top 1.5 cm to 3 cm layer is scrapped and washed manually.
  • It is designed for maximum daily demand.
  • The number of filter beds required to depend on the total filter area but usually 1 filter bed is provided at the stand by

B. Rapid Sand Filter

  • The number of Filter unit is computed using as N = 1.222√Q
  • Water to be treated must be Coagulated and Sedimented
  • Sand layer depth is about 75 cm.
  • Below the sand gravel-based of 60 to 90cm thick is used.
  • 1 of sand is 0.35 to 0.55 mm.
  • Depth of tank = 2.5 m to 3.5 m.
  • Area = 10 to 80 m2 each unit.
  • The rate of washing is 15 to 90 cm rise/ minute.
  • Rate of filtration 3000 to 6000 lit/hr/ m2 approx 30 times of slow sand filter.
  • Less efficient in the removal of bacteria (80- 90%)

C) Pressure Filter

Pressure filters are just like small rapid gravity filters placed in closed vassals, and through which water to be treated is passed under pressure.

Rate of filtration – 6,000 to 15, 000 liter/hr/m2

The pressure

is less efficient than the rapid gravity filters, in removing bacteria and turbidities.

FILTRATION

FILTRATION

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