Water Treatment Process Step

The Water Treatment includes the treatment of water supplied to the household for drinking and other utility purposes and also the wastewater to be disposed of in the water sources.

The Water Treatment involved in both the supply of water and wastewater different in many ways. Here, we will be discussing the processes included in the water treatment process steps.

Water Treatment Process Steps

Let us see the drinking water treatment process in detail here and the various processes involved in the same. The water treatment process starts with the collection itself.

There are two types of sources of water. One is the surface water source like a river, reservoir, etc. the other one is a groundwater source like a bore well. The water treatment process differs for these systems considerably.

1. Collection of Water

The water is collected from the sources like a lake, rivers, or reservoirs. The water is to be transported from this source to the water treatment plant for the water treatment process. This is included in the collection of water.

Generally, water treatment plants are built near the water source itself.

Collection of Water
Collection of Water

2. Screening

Screening is done to remove the floating matter from the water during the water treatment process. Surface water contains a large number of suspended particles that increase the unnecessary load on the treatment plant units.

Screening is mostly done at the intake point itself. The large-sized suspended particles like dried leaves, fallen twigs, and other floating debris.

Two types of screens are used for screening:

  • Coarse Screens/ Bar screens
  • Fine Screens/ Automatic Strainers

3. Sedimentation

The sedimentation process removes the heavy particles that can settle down under gravity. The weights of the particles increase as they aggregate and then settle down.

A sedimentation tank is so designed that the velocity of the flowing water is reduced. As the water is discharged into the sedimentation tank, the cross-section area of the water flow is in the case and therefore, velocity reduces.

Sedimentation is also of two types: One is Plain sedimentation without the addition of chemicals while the other is sedimentation with coagulation in which chemicals are added.

The efficiency of the sedimentation tank depends upon the following factors:

  • Design considerations for the tank
  • Shape and size of the sedimentation tank
  • Detention period
  • Size of suspended particles
  • Characteristics of suspended particles
  • The flow velocity of water

4. Clarification or Sedimentation with Coagulation

The sedimentation with coagulation is termed clarification. It is required to increase the efficiency of sedimentation as stated above during the water treatment process. Plain sedimentation consumed too much time.

How does clarification work?

The colloidal particles suspended in the water have a negative or positive charge around them. Coagulants neutralize this charge and allow these particles to coagulate.

Steps in Clarification in Water Treatment Process:

  • Addition of measured amount of chemicals  to the water
  • Thorough mixing of water
  • Formation of precipitates in water
  • Formation of flocs which is formed by coagulation initiated by the precipitates
  • Sedimentation

Types of Coagulants used in Water Treatment Process:

  • Alum
  • Ferrous sulfate and lime
  • Magnesium carbonate
  • Polyelectrolytes
  • Sodium aluminate

Alum is most commonly used as a coagulant.

Devices used for Carrying out Mixing of Coagulants:

  • Centrifugal pump
  • Compressed air agitation
  • Mixing basin

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5. Filtration

Filtration is one of the most crucial steps of the water treatment process.

The flocs formed during flocculation are not removed entirely by sedimentation. Hence, to remove the finely sized particles and flocs, filtration is required. And the particulate matter which was retained in the sedimentation tank previously is removed, especially the non-settleable particles.

Types of Filters

The following type of filters are available based on the time taken for filtration:

  • Slow Sand Filter
  • Gravity Type Rapid Sand Filter

Read More: 4 Types of Water Distribution System | Advantages & Disadvantages Water Supply Distribution System

6. Disinfection

After filtration, the next step of the water treatment process is disinfection. Disinfection includes the inactivation of pathogenic bacteria and other microorganisms that can cause diseases. This step is essential to control water-borne diseases.

A disinfectant is added in this step to filtered water. Skilled operators are required to carry out the process of disinfection so as to maintain the appropriate dosage.

Some of the Important Characteristics of A Disinfectant

  • It should be effective in killing the microorganisms in the contact time provided.
  • It should be easily available in the market.
  • It should not be expensive.
  • It should not make the water toxic
  • Its application should not be complicated involving a series of processes
  • It should not impart any objectionable color to the water
  • It should have the ability to remain in the water for a residual amount so that the water is not contaminated again

7. Water Softening

Water softening is done to make the hard water soft. Surface water usually does not contain much hardness. However, the water taken from underground sources like bore wells contains hardness due to the presence of ions. The hardness of water prevents the water from forming lather and also causes problems in the plumbing system.

It even affects the taste of water and even food cooked with hard water tastes tough or rubbery. There are two types of hardness of water and their treatment methods also vary with it.

Types of Hardness and Their Removal

i. Temporary Hardness

Methods of Removal of Temporary Hardness:

  • by boiling
  • by the addition of lime

ii. Permanent Hardness

Cause: calcium sulfate, magnesium sulfate, calcium chloride, and magnesium chloride ions

Methods of Removal of Permanent Hardness:

  • By Lime Soda process
  • Zeolite process
  • Demineralization or Deionization process

8. Other Treatment Methods

There are a few other characteristics of water to be adjusted as per the quality standards set by the guidelines. Some of these characteristics of water to be brought under the limit are:

To Remove Color, Odor, and Taste:

This is necessary when objectionable color, odor, or taste is imparted to the water, which may be because of one of the following reasons:

  • Organic and vegetable matter
  • Dissolved gases beyond a certain limit
  • Dissolved mineral matter
  • Industrial waste
  • Microbes like molds, bacteria, etc.

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