Concept: Properties and Purification of Water
As we know, water is an important natural resource, and it possesses some unique properties, which are listed below.
Properties of water:
- Pure water is colourless.
- It does not have a characteristic smell and hence, is odourless.
- It can dissolve many substances, making it an excellent solvent.
- It is liquid at room temperature.
- Water assumes the shape of the liquid in which it is poured.
- It constitutes hydrogen and oxygen in a ratio of 2:1.
- Water is a bad conductor of electricity i.e. it does not allow electricity to pass through it. Still, salts in it make water a good conductor of electricity.
- Example: Tap water (which contains salts) is a good conductor of electricity, whereas distilled water (pure water) is a bad conductor.
States of water:
- Water exists in all three states at different temperatures.
- Water freezes and exists in the solid state at 0°C. The change of water from its liquid state to solid state is called solidification.
- Water boils to form water vapour at 100°C.
- Ice starts melting at the temperature of 4°C.
Soluble and insoluble substances:
- The substances that dissolve in water are called soluble substances.
- Soluble substances can be either solid, liquid or gas.
- The substances that do not dissolve in water are called insoluble substances.
- The method of purification of water depends on the type of impurities present in it.
- Soluble impurities are separated using different methods, while insoluble impurities require other purification techniques.
Methods of purification of water:
- The conversion of the liquid state of water into its gaseous state is called evaporation.
- This method is used to separate soluble impurities like salt or sugar.
- Water containing the soluble impurities is heated.
- Meanwhile, the water evaporates, collected separately, whereas impurities like salt or sugar are left behind as the residue.
- Sedimentation and Decantation:
- This method is used for removing insoluble impurities like mud and clay particles.
- The water is taken in a container and left undisturbed for a while.
- As a result, the clay and mud particles gradually settle down.
- The clear water from the top is then poured into another vessel, and this method is called decantation.
- Alum, a transparent rock-like substance, is used to increase the rate of sedimentation.
- Dissolving a tiny amount of alum in water increases the weight of the insoluble impurities, which allows them to settle down rapidly.
- This method is used to separate water from liquid impurities like oil or alcohol.
- During this process, water is heated up to its boiling point. Water evaporates, leaving behind the impurities.
- The evaporated water vapour is then collected in a condenser, where it condenses to form distilled water.
- This method is used to separate insoluble impurities from water by using a strainer, muslin cloth or filter paper.
- The impure water is passed through the above-mentioned things. The impurities accumulate on the strainer, muslin cloth or filter paper while the clear water gets filtered out.
- Impurities like cereals, husk, sand, etc., can be separated by this method.
Water treatment plant
- A water treatment plant is a facility for large scale purification of water.
- The setup consists of various complex machines.
- Water treatment plants are usually built to purify water before it is distributed to the different households in the urban areas.
- These plants also help reduce the impurity levels of industrial wastewater before it is released into nearby waterbodies.
- Water is also recycled in these treatment plants.
Steps involved in the purification of water in a water treatment plant:
- Primary treatment:
- This step involves filtering and removing large insoluble waste like plastics, wrappers etc.
- The water is then allowed to flow through a screen which does not allow the solid waste to flow ahead.
- Then the separated water is transported to the sedimentation chamber.
- The biodegradable solid waste is allowed to digest by the use of bacteria.
- The bacteria consume the waste matter, which makes the water clearer.
- The water is then left in the sedimentation tank for a while so that the remaining impurities settle down.
- The water obtained after the tertiary treatment is treated with chlorine and UV rays is passed through the water which kills the harmful bacteria present.
- This water is then supplied to houses where it is used again and sent back to the water treatment plant through sewage channels.
- In the case of industries, the wastewater, which is released as a result of several chemical processes, is first treated to remove the hazardous chemical substances present in it and then released into the nearby water bodies.
- Such treatment of wastewater is done to reduce the water pollution level.
- We should turn off the tap while brushing our teeth.
- Buckets should be used instead of showers for bathing.
- Plants should be watered early morning or evening so that the water stays in the soil rather than evaporating quickly.
- Water should be reused whenever possible, like the water used for washing vegetables can be used for mopping the floor.
- Leaks in the pipes should be repaired immediately to prevent further water wasting.
- The Bahr El-Baqar wastewater treatment plant is the world’s largest water treatment plant located in Egypt.
- The water that comes from the kitchen, laundries and domestic baths is called grey water, whereas the water that comprises animal, food or human waste is called black water.
- The waste which is removed during sedimentation after bacterial treatment is often used as organic fertiliser.
Judicious use of water:
Implementation of the following habits in daily life would help control the overuse and wastage of water.
Room temperature: In this case, it denotes the temperature of 25°C. In general, room temperature means a range of temperature comfortable to human beings.
Hazardous: Something which is toxic and can cause harm.
Sedimentation: The settling down of heavier particles at the bottom of the container.
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