NCERT Class 7 Science Chapter 18: Wastewater Story YouTube Lecture Handouts

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NCERT Class 7 Science Chapter 18: Wastewater Story (NSO/NSTSE)

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Brain Teasers

  • What are organic and inorganic impurities?

  • Differentiate Sewer and Sewerage.

Sources of Wastewater

Preserve water

Preserve Water

Preserve water

Sources of wastewate: Bathing

Sources of Wastewate: Bathing

Sources of wastewate: Bathing

Sources of wastewate: Cleaning

Sources of Wastewate: Cleaning

Sources of wastewate: Cleaning

Cleaning Wastewater

Image result for impure water cleaning gif

Cleaning Wastewater

Image result for impure water cleaning gif

  • Don’t waste water

  • Remove pollutants

  • 1 billion people don’t have safe drinking water

  • 22 March – World Water Day

  • 2005-2015 – Water for Life

  • Sewage Treatment





  • Waste water from homes, industries, hospitals and offices

  • Dissolved and Suspended Impurities

  • Sewer – Network of pipes (from production to disposal); Manholes located 50 to 60 m

  • Organic impurities –Human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste, etc.

  • Inorganic impurities – Nitrates, Phosphates, metals.

  • Nutrients – Phosphorus and Nitrogen.

  • Bacteria – Such as vibriocholera which causes cholera and salmonella paratyphi which causes typhoid.

  • Other microbes – Such as protozoans which cause dysentery.

Treatment of Water

Water testing

Water Testing

Water testing

  • Before treatment

  • After aeration

  • Chlorination

  • Sedimentation

Waste Water Treatment Plant

Bar Screens for large plastics and cans:-

Filtering sewer water

Filtering Sewer Water

Filtering sewer water

Grit and Sand Removal – reduce speed

Sewer water

Sewer Water

Sewer water

  • Solid feces settle on bottom and is removed by scraper – sludge

  • Skimmer removes floatable impurities

  • Clear water is clarified water – biogas

  • Aerator - Air is pumped for aerobic growth; Bacteria consume waste

  • Activated Sludge – microbe settle on bottom and is 97% water

  • Dried sludge is used as manure, returning organic matter & nutrients to the soil.

Cover Open Drains

Clean water

Clean Water

Clean water

Plant Eucalyptus to absorb surplus waste water & release pure water

Cholera, Typhoid, Polio,

Meningitis, Hepatitis and Dysentery

Good health

Good Health

Good health

Cleaning garbage

Cleaning Garbage

Cleaning garbage

  • Cooking oil harden and block pipes

  • Chemicals like paints, solvents, insecticides, motor oil, medicines may kill microbes that help purify water. So do not throw them down the drain

  • Solid waste choke drains

  • Swachh Bharat Abhiyan

  • Vermi-processing toilet: A design of a toilet in which humans excreta is treated by earthworms has been tested in India. It has been found to be a novel, low water-use toilet for safe

  • processing of human waste

Alternate Arrangements

  • To improve sanitation, low cost onsite sewage disposal systems are being encouraged. Examples are septic tanks, chemical toilets, composting pits.

  • Septic tanks are suitable for places where there is no sewerage system, for hospitals, isolated buildings or a cluster of 4 to 5 houses

  • By-products of wastewater treatment are sludge and biogas.

  • Open drain system is a breeding place for flies, mosquitoes and organisms which cause diseases.

  • We should not defecate in the open

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