CBSE Class 7 Science Revision Notes Chapter 18

CBSE Class 7 Science Revision Notes Chapter 18 – Wastewater Story

CBSE Class 7 Science Chapter 18 Notes are concise and easy to understand. It covers various topics such as wastewater, clean water, sewage, and wastewater treatment plants with necessary terms and explanations. These notes are created in a simple and lucid manner, while adhering to the CBSE guidelines. Students can access it from the Extramarks website. It is ideal for last-minute revisions for a brief overview of the concepts without missing out on any topic while preparing for the exams.

Revision Notes for CBSE Class 7 Science Chapter 18

Access Class 7 Science Chapter 18 – Wastewater Story

Waste Water

  • Water used by human beings for various activities and becomes dirty is called wastewater.  Household wastewater from the sink, showers, faeces, toilets, and so on are examples of wastewater.
  • Wastewater is of black brownish colour and is filled with foam, combined with oil, and suspended impurities.
  • This contaminated water can be treated and should not be wasted. We can clean it up by extracting the pollutants.

Water Our Lifeline:

  • A basic need for survival is access to clean water.
  • Earth contains 71 percent water, yet there is a water shortage and clean water is not accessible to everyone.
  • People face many water-related diseases as clean water is not accessible.
  • Before water enters a water body or is utilised again, it must be cleaned to remove pollutants, which cause pollution.
  • The procedure of treating wastewater to get rid of pollutants is called sewage treatment.

What is Sewage?

  • Sewage is generally liquid waste generated by homes, industries, hospitals etc..
  • These houses, industries, hospitals, offices, etc,  release a certain amount of wastewater which is considered to be sewage including the rainwater that runs down the street amid heavy rainfall.
  • Sewage consists of disease-causing bacteria and other microbes that can spread a lot of diseases.
  • Disposing of sewage into the river body pollutes sources of freshwater and leads to water shortages. 
  • It also puts the life of aquatic plants and animals at risk.
  • Thus, sewage should be treated and get rid of pollutants before disposing of in water bodies. 

Water Freshens Up-An Eventful Journey:

  • Sewage is the term for liquid waste that is released from a source. The term “sewers” refers to the network of pipes of various diameters that carry liquid waste away from the source of generation.
  • These big and small sewers further create sewerage. It creates a kind of system that carries sewage from the point of being produced to the point of disposal.
  • Manholes are placed every 50 m to 60 m near the sewerage, which are minute-covered openings in a paved area permitting access beneath, specifically one leading to a sewer.
  • Usually, manholes are spotted at the crossing of two or more sewers and at points where there is a shift in direction.
  • Wastewater from the sewerage is transported to the wastewater treatment plant, where it undergoes a diverse treatment method.
  • After going through treatment and purification, it is released into water bodies and can be used by anybody.

Wastewater Treatment Plant:

  • This treatment involves physical, chemical, and biological processes to treat wastewater.
  • Firstly wastewater goes through bar screens which get rid of large objects like sticks, cans, plastics, etc in this wastewater treatment plant.
  • Water further goes through a grit and sand removal tank. The procedure of extracting grit and sand is called screening.
  • The water is further enabled to settle in the massive tank which is sloped close to the centre to split up sludge.
  • Later, the sludge is moved to an aeration tank where it is disintegrated by the anaerobic bacteria, and the air is pumped to aid the aerobic bacteria to develop.
  • Bacteria ingest unwanted matter even while remaining in the water.
  • The activated sludge has 97% water present in it;
  • Dried sludge is used as manure, returning nutrients to the soil.
  •  This water is taken off by sand drying beds or machines. Dried sludge returns to the soil as manure.
  • The treated water has a low level of organic matter and suspended particles. It is further discharged into the sea, river or water and gets cleaned naturally.
  • Water must be chemically disinfected with chlorine and ozone to get rid of undesired bacteria and microbes.

Better Housekeeping Practices:

The generation of sewage should be diminished as it causes water pollution. These are some of the measures:

  • Avoid throwing vegetable oil and fats disposed of through the drain.
  • Chemicals can kill the microbes that help purify water so they should not be run down the drain.
  • Having a habit of disposing of waste such as used tea leaves, kitchen waste, sanitary towels, etc. in the dustbin.

Sanitation and disease:

  • The major cause of the spreading of various diseases like cholera, typhoid, etc is poor sanitation and contaminated drinking water.
  • Water and soil pollution is caused by excreting in open areas. Untreated human excreta indirectly affects our health. It can be a major health hazard and can lead to a number of diseases.
  • The surface water and groundwater get contaminated. 

Alternative Arrangement for Sewage Disposal:

  • On-site sewage disposal system:

  • Scavenging is not needed in these toilets.

  • Excreta are channelised directly into a biogas plant from these toilets. 

  • The biogas generated is used as a form of energy.

  • Sanitation at Public Places:

  • Certain standards of sanitation are laid by the government in public places.
  • All must be equally responsible and supportive in maintaining sanitation in public places.
  • One should be mindful of not littering around as it can lead to massive pollution.
  • Everyone should make use of the dustbin. While travelling, make sure not to dispose of litter here and there. Be mindful and try to keep the environment clean and healthy.

FAQs (Frequently Asked Questions)

1. What is sewage treatment and what does cleaning of water mean?

The technique or process of wastewater treatment is normally called sewage treatment. Cleaning of water is a procedure of getting rid of pollutants before it joins a water body or is reused.

2. What are contaminants?

Households, industries, hospitals, offices, etc, dispose of wastewater that is considered to be sewage. During a storm or heavy rain, the sewage also involves rainwater that runs down the street. The washed-off water from roads and rooftops contains harmful substances in it. Sewage is considered to be a liquid waste. Usually, a large portion of sewage contains water, which has liquified and suspended impurities. These impurities are known as contaminants.

3. What is wastewater?

Foam-filled water, water combined with oil, black–brown water that is usually washed down the drain by people from showers, toilets, and sinks is contaminated. It is called wastewater. This contaminated water should not be wasted and can be treated for reuse.

4. What are some of the better housekeeping practices?

One of the ways to reduce or completely dispose of waste and impurities at their source is to be mindful of discharging down the drain.

  • Some substances like cooking oil and fats should not be thrown down the drain. They can solidify and obstruct the pipes. In a septic tank, the fats block the soil pores decreasing their efficacy to infiltrate water. Oil and fats can be safely disposed of in the dustbin. 
  • The microbes that help purify water may be terminated by chemicals like paints, solvents, insecticides, motor oil, and medicines. So do not dispose of these chemicals down the drain.
  • Worn-out items like one-time used tea leaves, solid food leftovers, soft toys, sanitary towels, etc. should be disposed of in the dustbin. These wastes can clog the drains. They also do not permit the flow of oxygen freely. It eventually leads to hindrances in the degradation process.