10/5/2019

Purification of Water Dr. Jawaid Hussain Deptt of Community Medicine Assistant Professor Peoples Medical University of Health Sciences Nawabshah

The participant will be able to define: Learning Objectives: The participant will be able to define: Purification of Water. 10/5/2019

Purification Of Water Purification of is done by TWO ways: Natural Methods Artificial Methods

NATURAL METHODS Natural Method includes:- Aeration Sedimentation Sunlight Dilution Oxidation Plants & Animals (Aquatic)

Artificial Methods They may be carried out at: Purification of Water on Large Scale Purification of Water on Small Scale

A. Purification of Water on Large Scale At Large scale, it is done by Filtration, which may be Slow sand filtration Rapid sand filtration Desalination

B. Purification of Water on Small Scale / Domestic Level At Small scale or Domestic level, is carried out by: Boiling Chemical disinfection Filtration Solar radiation

A. Purification of Water on Large Scale The purpose of water treatment is to produce water that is safe & wholesome. The method of treatment to use depends upon the nature of raw water & the desired standards of water quality. Ex: Ground water (wells & springs) may need no treatment other than disinfection. Surface water (e.g River water) which tends to be turbid & polluted, require extensive treatment. The components of a typical water purification system comprise one or more of the following measure.

A. Purification of Water on Large Scale A typical water supply carries the following steps in Purifying the water: Storage Sedimentation Filtration Disinfection

I. STORAGE Water is drawn out from the source and impounded in natural or artificial reservoirs. Storage provides of a reserve of water from which further pollution is excluded. As a result of storage, a very considerable amount of purification takes place. This natural purification & we may look at it from three points of view:

I. STORAGE Physical: By mere storage the quality of water improves. About 90% of the suspended impurities settle down in 24 hours by gravity. The water becomes clearer. This also improves the turbidity of water. This allow penetration of light & reduce the work of filters.

I. STORAGE (b) Chemical: Certain chemical changes also take place during storage. The aerobic bacteria oxidize the organic matter present in the water with the aid of dissolved oxygen. As a result the content of free ammonia is reduced and a rise in nitrates occurs.

I. STORAGE (c) Biological: A tremendous drop takes place in bacterial count during storage due to antibiosis and oxidation. The pathogenic organism gradually die out. It is found that when river water is stored the total bacterial count drops by as much as 90 percent in the first 5-7 days. This is one of the greatest benefits of storage. The optimum period of storage of river water is considered to be about 10-14 days.

I. STORAGE (c) Biological: If the water is stored for long periods, there is likelihood of development of vegetable growths such as algae which impart a bad smell and colour to water.

II. SEDIMENTATION Here we add chemical coagulant Alum. ALUM – AL2(So4)3 The Dose is 35 mg/Litre & is kept for 4 – 6 hours. It is very necessary. Prior to filtration and helps in Preventing the Rapid Clogging of filter. The reaction is:- Al2 (So4)3 + Ca (Hco3) → Al(OH)3 + 6Co2 + CaSo4 2) Al2(So4)3 + 3Na2Co3 + H2O → 3NaSo4 + 2Al (OH)3 + 3Co2

III. FILTRATION It is the oldest and Universal method of purification. Filtration is the second stage in the purification of water. This filtration reduces the bacterial content by 98-99%, turbidity by 50 PPM to 5 PPM and colour to colurless.

III. FILTRATION There are two types of Filters: SLOW SAND FILTERATION (BIOLOGICAL FILTER). RAPID SAND FILTERS ( MECHANICAL FILTERS).

SLOW SAND FILTRATION (BIOLOGICAL FILTER) They are cheap and easy to design and occupy less space. Slow sand filters were first used for water treatment in 1804 in Scotland and subsequently in London. During the19th century their use spread throughout the world. Even today they are generally accepted as the standard method of water purification.

SLOW SAND FILTRATION (BIOLOGICAL FILTER) They contain the concrete made basin, which contains the selected graded sand, supported on stones. The contents are Supernatant Water Head 1 – 1.5 meter for Raw Water Sand Bed, which consists of sand particles, supported by fine and coarse gravel. Drainage system Filter Control Valve

1) SUPERNATANT WATER HEAD The supernatant water above the sand bed, whose depth varies from 1 to 1.5 meter, serves two important purpose. 1. It provides a constant head of water so as to overcome the resistance of the filter bed & thereby promote the flow of water through the sand bed. 2. It provides waiting period of some hours (3 to 12 hours) for the raw water to undergo partial purification by sedimentation, oxidation & particle agglomeration. The level of supernatant water is always kept constant.

2. SAND BED It is very important part of the sand bed. The thickness of the sand bed is a about 1 meter. The sand grains are carefully chosen so that they are preferably rounded and have an effective diameter b/w 0.2 to 0.3 mm. The sand should be clean and free from clay & organic matter. The sand bed is supported by a layer of graded gravel 30 to 40 cm deep which prevents the fine grain being drained into the drainage pipes.

2. SAND BED The sand bed presents a vast surface area, one cubic meter of filter sand presents some 15,000 sq.meter of surface area. Water percolates the through the sand bed very slowly, process taking 2 hours or more. It is subjected to a number of purification processes- mechanical straining, sedimentation, adsorption, oxidation & bacterial action, all playing their part. The designed rate of filtration of water usually lies b/w 0.1 to 0.4 m3/ hour/ per square meter of sand bed surface.

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