Wastewater Story Class 7 Notes CBSE Science Chapter 18 (Free PDF Download)

Water that has been drained out from the sink, showers, toilet, laundries etc. is called wastewater 

It is of black brownish colour which is rich in a lather, oil, suspended impurities etc.

Clean water is a basic need of a person for survival.

Earth has $71\%$ water still there is water scarcity and clean water is not available to everyone.

Inability to access clean water leads to many water-related diseases.

Cleaning of water is a process of removing pollutants before it enters a water body or is reused, pollutants are substances that cause contamination.

This process of treating wastewater to remove pollutants is usually referred to as sewage treatment.

Sewage is a liquid waste produced by the community of people.

 Sewage is essentially the wastewater that is released by houses, industries, hospitals, offices and rainwater that has run down the street during a storm or heavy rainfall.

Sewage contains disease-causing bacteria and other microbes which can spread a lot of diseases.

Discharging of sewage into the river body contaminates our source of freshwater and leads to water scarcity and other problems.

It is also threatening the life of aquatic animals and plants.

Therefore, sewage should be treated before discharging into water bodies. 

The liquid waste i.e., sewage goes to the point of disposal from the point of being produced through the network of big and small pipes called sewers.

These sewers form sewerage.

Manholes are a small covered opening in a paved area allowing access beneath, especially one leading to a sewer and are located at every 50 m to 60 m within the sewerage.

Manholes are found at the junction of two or more sewers and at points where there is a change in direction.

Wastewater through the sewerage reaches the wastewater treatment plant where it has to go through a different method of treatment.

After treatment and purification, it is discharged into water bodies and available for use.

It is a facility where physical, chemical and biological processes are used to treat the wastewater.

In the wastewater treatment plant, firstly wastewater is passed through bar screens which removes large objects like rags, sticks, cans, plastics etc.

Water then goes to a grit and sand removal tank. The process of removing grit and sand is known as screening.

The water is then allowed to settle in the large tank which is sloped towards the centre to separate sludge.

After this, the sludge is transferred to an aeration tank where it is decomposed by the anaerobic bacteria and air is pumped to assist aerobic bacteria to grow.

Bacteria consume unwanted matter still remaining in the water.

The activated sludge contains $97\%$ water this water is removed by sand drying beds or machines.

It is necessary to disinfect water chemically with chlorine and ozone to kill unwanted bacteria and microbes.

Sewage formation should be decreased as it leads to the pollution of water.

We must adopt some measures such as:

Not throwing vegetable oil and fats down the drain

Chemicals should not be discharged into the drain as they may kill the microbes that help purify water.

Throwing used tea leaves, kitchen wastes, soft toys, sanitary towels, etc. in the dustbin.

Poor sanitation and contaminated drinking water are the major cause of the spreading of various diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

Excreting in open areas leads to water and soil pollution and these untreated human excreta are harmful to our health which indirectly goes into our body.

These toilets do not require scavenging.

Excreta from these toilets are directed into a biogas plant. 

The biogas produced is employed as a source of energy.

The government has laid down certain standards of sanitation in public places.

We all should contribute to maintaining sanitation in public places.

We should not scatter litter anywhere as it will lead to pollution.