Introduction to Water Treatment Practices



Why Treating Water is a Necessity?


Water is the most basic requirement for any form of life on the earth; let it be humans, animals or flora and fauna. Around two third of human body consists of water and presence of water, even at cellular level is quite essential for proper working of our body. Water is also a source of numerous salts and minerals. Through our water consumption, we are also consuming these other micro nutrients.


Ensuring availability and supply of good quality water is absolutely necessary for the society to survive and thrive. Though water is a source of life and nutrients, water might also contain traces of or even significantly large quantities of impurities. These impurities might include presence of salts, toxins or have metals like Nickel, Cadmium, Lead, Zinc etc. These impurities adversely affect human health and can lead to diseases like cancer, damage to nervous system etc. Water can also be contaminated by microbial pathogens. Drinking such contaminated water can cause rapid spread of waterborne diseases.

Along with the natural contaminants in the water, poor industrial water treatment efforts also lead to a large number of contaminants and hazardous chemicals entering the drinking water. Many of these impurities affect the normal functioning of various glands in our body and lead to hormonal imbalances.


Apart from human consumption, a large number of animals, plants and trees and agricultural activities depend on the availability of contamination free water.



Aerial View of Water Treatment Plant

How is Water Treatment Done?

Water treatment is not a blanket activity which covers a set of actions; rather, course of water treatment is decided after analysis of the water constituents and local conditions. A large number of methods are available to treat water. Normally, the commonly available methods like filtration, coagulation, disinfection, sedimentation and softening remove most of the commonly present impurities and ensure that the water is potable. In some cases, other treatment practices are also administered to remove other impurities like manganese, iron, odour, taste, color, various dissolved gases etc.

Another important point to note is, as water needs to be treated and purified, the water supply also needs to be treated. In this article, we will understand which are some of the commonly used methods to treat water, as well as the water supply.

Here are some methods which are commonly used to remove unwanted minerals from water :

Removal of Manganese and Iron :

Generally, metals are present in water in form of their salts. Manganese and Iron are also present in water in form of their salts. Normally, if these salts are present up to 3 mg/L, no treatment is required. Quantities higher than mentioned above can lead to skin disorders.


Water aeration is simplest and most recommended method to remove iron salts by oxidizing them. Ferric oxide is insoluble in water and can be easily separated out via sedimentation tanks. Sprinklers, sprays, and fountains can be used to oxidize the iron salts.


If not iron and manganese salts are present, a strong bond exists between two of them and just aeration is not enough. In such cases, lime is added to break the bond and once the bond is broken, the salts are removed using oxidation and sedimentation as described above.

Removal of Colour, Odours and Taste

Change in taste, colour or odour indicate that the water contains impurities in the form of dissolved gases like hydrogen, sulphide or other impurities like organic matter, industrial wastes etc. Presence of chlorine and phenols can also lead to unwarranted smell and colour. Here are some of the commonly used treatments for colour, odour and taste removal:


  1. Aeration

  2. Treatment with activated carbon

  3. Oxidation of organic matters

In the next article, we will solely focus on methods of removal of colour, odour and taste.


Purification of Water Supply

As we briefly mentioned earlier, while supplying water on a large scale, the source of water and the store house of the water must be purified periodically. In fact, large scale water purification happens by carrying out the purification activities at the water supply level. Once this water is treated, it is made available for domestic, commercial or industrial consumption.


Here are some of the methods which are commonly used to large scale water supply purification:

1) Screening

2) Sedimentation and Coagulation

3) Filtration

4) Disinfection

5) Aeration

6) Softening


1. Screening:

a. Coarse or fine screens:

These screens are fitted in front of the pumps so as to prevent large sized particles from entering the water supply network. These are very effective against large sized contaminants like animals, branches, bushes, debris etc. Fine screens are installed after the coarse screens for sequential removal of the impurities.


b.  Movable or travelling bar type screens:

They are often used for fine screen for passing the water coming out from the coarse screens. A stationary fine screen is cleaned by raising it out of the water and washing off the collected material.

2. Sedimentation and Coagulation:

Sedimentation, sometimes along with coagulation, is the most suitable way for removing suspended solids and organic contents from the water.

3. Filtration:


The process of passing the water through the beds of granular materials. It can help to remove colour, odour, turbidity and some pathogenic bacteria. Types of filters used are as follows:


a. Sand gravity filters

Slow sand gravity filters can remove larger percentage of impurities and bacteria from water. The water from the coagulation sedimentation plant is directly fed into rapid sand filter and the resultant supplies are disinfected for complete killing of germs and for colour removal.


b. Pressure filter

Pressure filter are just like small rapid gravity filters placed in closed vessels through which water to be treated is passed under pressure.


4. Disinfection or Sterilization:

The chemicals used for killing these bacteria are known as disinfectants and the process is known as disinfection or sterilization. Chlorine is found to be the best disinfectant. Minor methods of disinfection are as follows:

- Boiling

- Treatment with lime

-Treatment with Ozone

- Exposure to UV radiation

- Treatment with Iodine, Bromine, or Potassium permanganate.


Conclusion:


Water treatment is important to lower the presence of many of the harmful contaminants. There are home treatment alternatives that can purify drinking water to a greater extent than city treatment plants. The microbial quality of drinking water should not be compromised because of concern over the potential long term effects of disinfectants and DBPs.


In the next article in this series, we will discuss in more details, the various methods used to remove odour, colour and taste from the water.


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