REMOVING IMPURITIES FROM WATER
• Water purification is the process of removing undesirable chemicals, biological contaminants, and suspended solids from contaminated water.
• Water is purified for human consumption (drinking water) but water purification may also be designed for a variety of other purposes.
Removing Insoluble Impurities:
• Insoluble impurities such as sand can be separated by:
• Sedimentation is a physical water treatment process used to settle out suspended solids in water under the influence of gravity.
Figure 7: Sedimentation process
It involves the following Steps:
(1) In this method, the mixture is allowed to stand undisturbed in a container.
(2) After some time, the insoluble substances such as mud settle down at the bottom of the container as sediments. This process is called sedimentation.
• Clean water can then be poured out into a separate container. This is called decantation.
Figure 8: Decantation process
• The rate of sedimentation can be improved by adding special chemicals such as alum. This process is called loading.
• Loading can be used to separate dirt particles suspended in muddy water.
Figure 9: Loading process is carried out to separate dirt particles
• Filtration is the act and science of using filters.
• In this method, insoluble impurities can be removed by passing the impure water through a filter paper.
Figure 10: Filtration process
• There are many different methods of filtration, but all processes aim to attain the separation of two or more materials.
• This is achieved by some form of interaction between the substance or objects to be removed and the filter.
• In addition to this, the substance that is to pass through the filter must be a fluid, i.e. a liquid or gas.
Figure 11: Filtration process
• A mixture of sand and water can be separated using filtration.
Removing Soluble Impurities:
• It is more difficult to separate soluble impurities than insoluble ones.
• Soluble impurities can be separated by:
• Evaporation takes place, as molecules of water escape from a collective body of water like puddle, lake, or a stream.
• Water molecules evaporate by taking up heat from the atmosphere.
• The solution containing soluble impurities such as salt or sugar is heated.
• After some time, the water changes into steam, leaving the impurities behind.
Figure 12: Evaporation process
• Distillation is a widely used method for separating mixtures based on differences in their boiling points.
• To separate a mixture of liquids, the liquid can be heated to change the components (which have different boiling points) into the gas phase.
Figure 13: Distillation process
• The water collected by this process is called distilled water.
• Distilled water is the purest form of water and does not contain any impurities or germs.
• It is widely used in car batteries, injections, and medicines.
Purifying Drinking Water:
• Water may contain germs that can cause diseases.
• Therefore, drinking water needs to be purified.
• Drinking water can be purified using some methods like boiling, chlorination, filtration etc.
• One of the simplest ways to purify drinking water is by boiling it.
• Boiling water for about 10 minutes kills the germs present in water, making it safe for drinking.
• Boiled water should be stored in clean and covered pots or pans.
• Another method of purifying water is by adding a chemical called chlorine.
• These days, chlorine tablets are easily available.
• Adding chlorine tablets in water kills germs and makes the water pure.
• This process of purifying water is called chlorination.