This document discusses different types of water filtration processes. It describes slow sand gravity filters and rapid sand gravity filters. It explains the filtration materials used like sand, gravel and anthracite. Sand used as a filter material should be hard, uniformly sized, free from impurities and resistant. Gravel and anthracite are also used. Filters are classified as gravity filters like slow sand and rapid sand filters, and pressure filters like horizontal and vertical pressure filters. Slow sand filters have low filtration rates but are suitable for rural areas. Rapid sand filters have higher filtration rates and require less space. Pressure filters operate under pressure within a closed cylinder.

1. GOVERNMENT ENGINEERING
COLLEGE BHAVNAGAR
FILTERATION
Mayank Oza

2. FILTERATION
• screening and sedimentation process removes a large
percentage of the suspended solids, organic matter and
a small percentage of bacteria.

3. Types of filteration
1.The slow sand gravity filters
2.The repid sand gravity filters

4. Theory of filteration
• mechanical straining
• sedimentation
• biological action
• elctrolytic action

5. *
Filteration materials
 sand, either fine or coarse, is generally
used asfilter media. the layers of sand
may be supported on gravel, which
permits the filtered water to move freely to
the under drains, and allows the wash
water to move uniformly.
1. send
2. gravel
3. anthracite

6. sand
 The sand used for filters should have the following
properties:
1. it should be obtained from hard rocks such as
quartzite, trap, basalt etc.
2. it should be free from clay, loam, lime and organic
matter.
3. it should be of uniformly size and nature.
4. it should be hard and resistant.

7. Gravel
 the gravel which may be used below the
sand should be hard, durable free from
impurities, properly rounded and should have
a density of about 1600 kg/m3

8. Anthracite
 crushed anthracite has been successfuly
used as filter media as a substitute for sand
in same filters and may be used in conjuction
with sand. it is more costly per tonne than
sand, but its greater volume per unit weight
and lower transportation cost per unit volume
may make it more economical at some
locations.

9. Classification of filters
 filters may be classified as follows
 ( A) Gravity filters
(1) Slow sand filters
(2) Rapid sand filters
(B) Pressure filters
(1) Horizontal pressure filters
(2) vertical pressure filters

10. Slow sand filters
 Slow sand filters was the earliest type of
filters introduced in 1829. slow sand filters are so
called because the rate of filtration thtoughthem
may be 1/20 or less of the rate of filtration
through rapid gravity filters or pressure
filters.because of low filtration rates, they require
large area of land and are costly to install.

11.  they are well suited for rural areas in
devloping countries because of its simple
operation and maintenance procedures.the
effect of the slow sand filter is to remove
turbidity by straining and to remove bectaria
by biological action.it is not particularly
effective in removing colloidal matter.

12. Repid sand filters
 The main defect of slow sand filter is its low
filteration rate due to which large filter area is
required. I. order to reduce the requrement of
space and to increase the rate of filtration, a
lot of research was conducted, which finally
led to the development of repid sand filters,
or sometimes called mechanical sand filters.

13. pressure filters
 The pressure filters is a type of rapid sand
filter placed within a closed, watertight steel
cylinder. the water passes through the
sandbed under a pressure greater than
atmospheric. all the operation of this filter is
similar to rapid gravity filters, except that the
coagulated water is directely applied to the
filter without mixing and flocculation.

14.  These filters are used on small supplies
where water is received under pressure,
which can be used to force the water through
the filter.mostly pressure filters are used for
industrial plants, but are not economical on
large scale.

15. * Water filtration *

16. Thank you