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Filtration Theory

Filtration theory discusses slow sand filters and filtration processes. Slow sand filters work by passing water through layers of sand and gravel to remove contaminants. They consist of an enclosure tank, underdrainage system, base material, filter media (usually sand), and appurtenances. Water enters the filter and is purified as it passes through the sand, then collected in an outlet chamber. Filters are cleaned when the filtration head reaches a specified limit, usually every 1-3 months. The rate of filtration for slow sand filters is typically 100-200 liters per hour per square meter.

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Aman Bhatti
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604 views17 pages

Filtration Theory

Filtration theory discusses slow sand filters and filtration processes. Slow sand filters work by passing water through layers of sand and gravel to remove contaminants. They consist of an enclosure tank, underdrainage system, base material, filter media (usually sand), and appurtenances. Water enters the filter and is purified as it passes through the sand, then collected in an outlet chamber. Filters are cleaned when the filtration head reaches a specified limit, usually every 1-3 months. The rate of filtration for slow sand filters is typically 100-200 liters per hour per square meter.

Uploaded by

Aman Bhatti
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Filtration Theory

Filtration
• The process of passing the water through the
beds of granular materials is known as
filtration.
• Filtration may help in removing colour, odour,
turbidity, and pathogenic bacteria from the
water.
Classification of filters

Pressure Filters
The filters are
classified into Slow sand filters
two categories:
Gravity Filter

Rapid sand filters


Sand filter
Sand Filter
Characteristics of Sand
• The sand to be used for filter should be free
from clay, loam, vegetable matter, organic
impurities, etc.
• It should also be uniform in nature and size.
Filter Sand Classification

The filter sand • Effective size


is classified on • Uniformity
the basis of its: coefficient
Effective size
& Uniformity coefficient
• The effective size of sand indicates the size of sieve in mm
through which ten percent of the sample of sand by weight
will pass.
• The uniformity coefficient of sand is the ratio of sieve size in
mm through which 60 per cent of the sample of sand by
weight will pass to the effective size of sand.
• For example, suppose the effective size of a sample of sand is
0·50' mm. If 60 per cent of sand from the same sample passes
through 0·60 mm sieve, the uniformity coefficient will be
0.6/0.5 =1.20
• Instead of sand, sometimes anthrafilt is used. It is made from
anthracite which is a stone-coal .that burns nearly without
flame or smoke.
Slow sand filters
Essential parts

A slow •Enclosure tank


sand •Underdrainage system
filter •Base material
consists •Filter media of sand
•Appurtenances.
of :
Cross-section through outlet chamber
Working and Cleaning of Filter
• The water is allowed to enter the filter through
the inlet chamber.
• It run down through the filter media and during
this process, it gets purified.
• It is then collected in the outlet chamber and
taken to clear water storage tanks.
• It is to be noted that water should not be
treated with coagulants in sedimentation tanks.
Working and Cleaning of Filter
• This is due to the fact that dirty skin formed by
floc and carried to the filter considerably
affects the economical working of the filter.
• The depth of water on filter is to be carefully
decided. It should neither be too small nor too
high. Generally, it is kept as equal to the height
of filter media of sand.
Cleaning Interval
• The slow sand filters are usually worked for a
maximum filtration head of 75 cm or so.
• But from the view point of safety, the maximum
filtration head desired is obtained by multiplying the
depth of filtering sand with a factor of 0·67 to 0·80.
• Thus, when specified limit of filtration head
reached, the filter requires cleaning.
• The interval between two successive cleanings
depends mainly on the nature of impurities present
in water to be treated and the size of filtering sand.
• It usually varies from 1 to 3 months.
Rate of filtration
• The rate of filtration for a normal slow sand
filter varies from 100 to 200 Iitres per hour per
m2 of filter area.
Problem
• Find the area of slow sand filters required for a
town having a population of 15000 with an
average rate of demand as 160 liters per head
per day.
• It is solved on paper
Thanks

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