GOVERNMENT ENGINEERING COLLEGE BHAVNAGAR

FILTERATION

Mayank Oza

FILTERATION

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

Types of filteration

1.The slow sand gravity filters

2.The repid sand gravity filters

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

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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. send2. gravel3. anthracite

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.

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

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.

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

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.

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.

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.

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.

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.

* Water filtration *

                                                                                                                                     

Thank you