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
Slow sand filtration is a kind of centralized or semi-centralized water purification system. A well-designed and well-maintained gradual sand filter (SSF) efficaciously eliminate turbidity and pathogenic organisms via numerous biological, bodily, and chemical approaches in an unmarried remedy step.
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%)
Rapid sand filtration is an in basic terms bodily consuming water purification method. Rapid sand filters (RSF) offer fast and green elimination of pretty massive suspended particles. Two varieties of RSF are generally used: fast gravity and fast stress sand filters. For the supply of secure consuming water, RSFs require good enough pre-remedy (typically coagulation-flocculation) and post-remedy (typical disinfection with chlorine). Both production and operation are cost-intensive. It is a pretty state-of-the-art procedure typically requiring power-operated pumps, normal backwashing or cleaning, and waft manage of the clear out the outlet. Rapid sand filtration is not unusual to place in evolved international locations for the remedy of massive portions of water in which land is a strongly proscribing factor, and in which material, professional labour, and non-stop strength deliver are available.
C) Pressure Filter
The gravity clear out out is the oldest and most effective type. Gravity sand-mattress filters established in town water flowers are a number of the maximum not unusual place filters. Such filters contain using tanks that typically are built of concrete. At the lowest of the tank is a grating or fake bottom; above that is coarse gravel or overwhelmed rock of graded length; on the very pinnacle are layers of quartz sand of uniform length. In business filtrations overwhelmed coke of graded length is utilized in lead-covered bins to clear out out sulfuric acid, overwhelmed limestone of graded length is used for alkaline liquors, and charcoal beds are used to purify natural drinks via way of means of each filtration and adsorption.
Pressure or vacuum filters typically are utilized in enterprises in choice to gravity filters. The using pressure that may be provided via way of means of stress or vacuum is a good deal extra than gravity, as a consequence allowing better filtration rates. Sand-mattress filters are operated below stress in closed vessels to offer excessive-capability carriers. Pressure filters are automatically utilized in everyday life, consisting of a vacuum purifier with a dirtbag or paper clear out or a car engine with an oil clear out cartridge. Many business operations contain the filtration of slurries that comprise excessive concentrations of suspended solids. Pressure or vacuum filters with a skinny clear-out-out medium consisting of a clear-out-out fabric or woven steel display are desired for such carrier due to the fact clear-out beds fill particularly swiftly whilst used with slurries that have excessive solids content.
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.