Chapter 4.0 Water Purification Process

4.0  Water Purification Process

In order to make water more acceptable for a desired end-use, it is vital for it to undergo some purification processes.  Also known as water treatment, water purification includes various processes of removing existing contaminants in the water. Water purification is done in order to produce drinking water that is pure enough for its intended uses.

General Methods of Water Treatment:

This usually occurs in the intake where untreated water passes through a series of screens as it enters a water treatment plant.  The series of screens basically prevents debris and other solids from entering the water treatment system.

 Fig.8. Water Filtration Tanks

Chemical treatment method includes the pumping of water into a discharge basin where it is subjected to several types of chemical treatment.  Various disinfectants are used in the chemical treatment method.

Most common disinfectants

4.1 Sedimentation

This process allows matter suspended in water to settle. In order to speed up the sedimentation process, coagulants like aluminum sulfate are added to the water.  When a coagulant is added to the water, the small particles that are present in the water are caused to cling together.  These clumps are called floc.  In order to promote the formation of the floc, water has to be gently stirred in a mixing basin before it passes into the settling basin. In the settling basin, the floc slowly settles into the bottom forming a sludge which can be easily taken out.

Types of sedimentation processes

In this type, every particle settles independently

Type 2 sedimentation is when particles can flocculate as they settle

This is where sludge thickening happens.

Sludge thickening progresses.

4.2  Filtration

After the separation of the floc and the water, the water is further filtered in order to remove the remaining suspended particles.  In the filtration process, water passes on to filter beds.  These beds are usually made up of a layer of gravel that is 18 to 24 inches thick and covered with sand or crushed anthracite.  As the water is drained, the remaining particles suspended in the water are trapped in the filter.

Filtration Processes:

This process involves a pre-filter which screens the water source at the point of entry.

In this process, the water passes through a sediment filter.  The sediment filters provide an added 5-micron filtration which removes unseen sediment that will prematurely clog the carbon filter.

Sediment filters remove

This filtration consists of two different procedures which are chemical bonding and mechanical straining.

4.3 Disinfection

Water disinfection is practically the final stage in the water treatment process.  This process aims to limit the effects of organic material, contaminants, and other suspended solids present in water.

Primary methods for disinfecting water:

Fig.9. UV Radiation Water Treatment Plant

Alternative methods for disinfecting water:

Media for disinfection

Disinfectants that can be used

Disinfectants that can be used

Influencing factors in chlorination practices: