Class 7 Science Notes for Waste Water Story

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CLASS 7
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WASTEWATER STORY

1. Waste Water
 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.
2. Water Our Lifeline:
 Clean water is a basic need of a person for survival.
 Earth has 71%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.
3. What is Sewage?
 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.
4. Water Freshens Up-An Eventful Journey:
 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.

KVS ZIET CHD Class VII-Science 2023-24 Page 67

5. Wastewater Treatment Plant:
 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.
6. Better Housekeeping Practices:
 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.
7. Sanitation and disease:
 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.
8. Alternative Arrangement for Sewage Disposal:
a. On-site sewage disposal system
 These toilets do not require scavenging.

KVS ZIET CHD Class VII-Science 2023-24 Page 68

 Excreta from these toilets are directed into a biogas plant.
 The biogas produced is employed as a source of energy.
b. Sanitation at Public Places:
 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
References:-

KVS ZIET CHD Class VII-Science 2023-24 Page 69

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