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Wastewater story Class 7 Notes Science Chapter 13

Water is essential for many things we do every day. But before we drink it, we need to make sure it's clean because water can have tiny things in it that we can't see. Hence, it is essential to clean water before using it.

Water, Our Lifeline

Water gets contaminated by humans and it is not safe for drinking. Drinking contaminated water results in diseases such as cholera, typhoid, and diarrhea. Polluted water can also prove fatal.
Water gets contaminated and scarcity of clean water is due to the following reasons:
Water getting polluted in various waysWater getting polluted in various ways

  • People take baths and wash clothes in rivers and lakes.
  • Many people bathe their animals in rivers and lakes.
  • Increase in the population, industries, and improper disposal of waste.

It was on March 22, 2005, that the United Nations declared 2005-2015 as the International Decade for the Action "Water for Life". Hence, March 22nd is celebrated as World Water Day. 

Clean water is needed not only for drinking but also for cooking, washing and bathing. A lot of waste water is produced at home, which should be cleaned before it drains into rivers or lakes and also before it is reused.
Uses of clean waterUses of clean water

Question for Chapter Notes: Wastewater story
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Why is it essential to clean water before using it?
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Process of Cleaning Water

The process of cleaning water, known as sewage treatment, involves several stages to remove pollutants before it enter a water body or is reused. Waste water released from homes, industries, hospitals and offices, and water collected during rains from rooftops or streets, is collectively termed Sewage.

This sewage is liquid waste containing dissolved impurities, and the impurities are called contaminants, which contain many harmful substances.

What is Sewage? 

Sewage is dirty water that comes from homes, businesses, hospitals, and other places. It includes rainwater that flows down the streets during storms. This water collects harmful stuff as it washes off roads and rooftops.  
Sewage WaterSewage Water

  1. Organic impurities: Organic impurities include animal waste, urine, oil, vegetable and fruit waste, faeces, pesticides and herbicides.
    Inorganic impurities: Inorganic impurities include phosphates, nitrates and metals.

    Vibrio cholera causes cholera Vibrio cholera causes cholera
  2. Bacteria: Bacteria like vibrio cholera which causes cholera and salmonella
    paratyphi which causes typhoid.

    Salmonellatyphi causes typhoidSalmonellatyphi causes typhoid
  3. Nutrients: Sewage contains some useful nutrients, such as phosphorus and nitrogen.
  4. Other microbes: Microbes such as protozones which cause dysentery are also present in sewage water.
    Wastewater story Class 7 Notes Science Chapter 13

Question for Chapter Notes: Wastewater story
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What are some of the impurities found in sewage water?
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Water Freshens Up an Eventful Journey

The network of small and big pipes that carry wastewater is called sewers, and all sewers together form the sewerage. Wastewater is carried from home to the point of disposal, that is the wastewater or sewage treatment plant.

After the treatment of wastewater, the clean water is released into nearby water bodies. Sewerage has manholes that can be used to clear blockages. Manholes are located every 50 - 60 metres in the sewerage. If there is no sewage facility, then wastewater is directly drained into nearby streams and lakes, which results in water contamination.

Water Treatment

Waste water needs to be treated before it can be reused, or released into a water body. Wastewater has many impurities and these impurities should be removed by water treatment.

Wastewater Treatment Plant(WWTP)Wastewater Treatment Plant(WWTP)

Question for Chapter Notes: Wastewater story
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What is the purpose of wastewater treatment?
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Wastewater Treatment Plant(WWTP)

Wastewater treatment involves physical, chemical, and biological processes to remove contaminants. Following are steps of water treatment:

Wastewater Treatment Process

  1. Bar Screening:

    • Wastewater passes through bar screens to filter out large items such as rags, sticks, cans, plastic packets, and napkins.
      Bar ScreeningBar Screening
  2. Primary Sedimentation:

    • Wastewater is directed into a large tank with a sloped bottom, allowing solids like faeces to settle to the bottom.
    • Solid waste is removed using a scraper, forming sludge.
    • Floatable solids like oil and grease are skimmed off the surface, leaving behind clarified water.
      Grit and Sand Removal TankGrit and Sand Removal Tank
  3. Sludge Treatment:

    • Sludge is transferred to a separate tank where anaerobic bacteria decompose it, generating biogas.
    • Biogas produced can be used as fuel or for electricity production.
      Sludge TreatmentSludge Treatment
  4. Aeration:

    • Air is pumped into the clarified water to support the growth of aerobic bacteria.
    • Aerobic bacteria consume remaining human waste, food waste, soaps, and other unwanted matter, further purifying the water.
  5. Secondary Sedimentation:

    • Suspended microbes settle at the tank bottom, forming activated sludge.
    • Water is separated from the top of the tank.
      Secondary SedimentationSecondary Sedimentation
  6. Sludge Dewatering:

    • The activated sludge, containing about 97% water, is removed using sand drying beds or machines.
    • Dried sludge is utilized as manure, enriching soil with organic matter and nutrients.
  7. Discharge of Treated Water:

    • Treated water, with minimal organic material and suspended matter, is released into the environment such as seas, rivers, or the ground.
    • Nature continues the cleaning process.
    • Sometimes, water may require disinfection with chemicals like chlorine or ozone before distribution.
      Discharge of Treated WaterDischarge of Treated Water
Question for Chapter Notes: Wastewater story
Try yourself:
What is the purpose of the primary sedimentation process in wastewater treatment?
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Better Housekeeping Practices

To prevent waste and pollutants from entering drains, follow these practices:
  1. Avoid pouring cooking oil and fats down the drain as they can harden and block pipes. In open drains, fats can clog soil pores, reducing their ability to filter water. Dispose of oil and fats in the dustbin.
  2. Chemicals like paints, solvents, insecticides, motor oil, and medicines should not be poured down the drain as they can kill microbes that help purify water.
  3. Solid waste such as used tea leaves, leftover food, soft toys, cotton, and sanitary towels should also be disposed of in the dustbin. These items can clog drains, restrict oxygen flow, and hinder the degradation process.

Sanitation & Disease

  1. Poor sanitation and contaminated drinking water cause numerous diseases.
    Contamination of WaterContamination of Water
  2. Many people in our country lack proper sewerage facilities, leading to outdoor defecation in places like dry riverbeds, railway tracks, and fields.
    Poor sanitation system Poor sanitation system 
  3. Untreated human waste poses dangers as it can contaminate water and soil.
  4. Contamination affects surface water and groundwater, with groundwater being essential for wells and rivers.
    Groundwater ContaminationGroundwater Contamination
  5. Groundwater becomes a common route for diseases such as cholera, typhoid, polio, meningitis, hepatitis, and dysentery.
    Diseases caused by drinking polluted waterDiseases caused by drinking polluted water

[Intext Question]

Alternate Arrangement For Sewage Disposal

Following are some of the alternate ways for sewage water disposal.

(i) To enhance sanitation, promoting low-cost onsite sewage disposal systems.
On-site Sewage Disposal SystemOn-site Sewage Disposal System

(ii) Examples include septic tanks, chemical toilets, and composting pits.

(iii) Septic tanks are suitable for areas lacking sewerage, such as hospitals or isolated buildings.It is an underground chamber made of concrete, fiberglass, or plastic that is used to treat sewage from homes and buildings in areas without access to centralized sewer systems. 
Wastewater story Class 7 Notes Science Chapter 13

(iv) Organizations offer innovative toilets that don't require manual cleaning.

(v) Waste from these toilets flows into a biogas plant.A biogas plant is a facility that turns organic waste into biogas through anaerobic digestion. Organic waste, like food scraps or manure, is broken down by bacteria in the absence of oxygen, producing biogas composed mainly of methane and carbon dioxide.

Biogas PlantBiogas Plant

(vi) This biogas can be used as a renewable energy source for cooking, heating, electricity generation, and more.  

Sanitation at Public Places

  • Fairs, railway stations, bus depots, airports, and hospitals are busy places where large amounts of waste are generated due to thousands of daily visitors.
  • Proper waste disposal is vital to stop diseases from spreading, especially since open defecation and poor sanitation can cause epidemics and disease transmission.
  • Although government rules on sanitation might not always be enforced well. 

The "Swachh Bharat" mission initiated by the Government of India in 2016 aims to improve sanitation, including proper sewage disposal and providing toilets for all.

Swachh Bharat Mission Swachh Bharat Mission But everyone can help by avoiding littering and taking their trash to proper disposal places, even if there's no bin nearby.

[Intext Question]


We all have a duty to keep our environment clean and safe. 

Mahatma Gandhi once said, " “No one need to wait for anyone else to adopt a humane and enlightened course of action.” 

Wastewater story Class 7 Notes Science Chapter 13

We must understand our role in keeping water sources healthy by practicing good sanitation habits every day. Each of us can make a significant impact by taking individual responsibility and inspiring others with our energy, ideas, and optimism. When people come together and work collectively, remarkable things can be achieved.

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FAQs on Wastewater story Class 7 Notes Science Chapter 13

1. What is sewage?
Ans. Sewage refers to the wastewater and waste materials that are produced by households, businesses, and industries. It contains a mixture of water, human waste, food scraps, oils, chemicals, and other contaminants.
2. What is a wastewater treatment plant (WWTP)?
Ans. A wastewater treatment plant, also known as a WWTP, is a facility that processes sewage and wastewater to remove contaminants and pollutants. It uses various physical, chemical, and biological processes to treat the wastewater before it can be safely discharged back into the environment.
3. What are better housekeeping practices in relation to sewage disposal?
Ans. Better housekeeping practices for sewage disposal involve proper maintenance and management of household plumbing systems, the regular cleaning of septic tanks or sewer lines, and the responsible use of water and waste products. It also includes avoiding flushing non-biodegradable items down the toilet, such as wipes or sanitary products, as they can cause blockages and damage the sewage system.
4. How does sanitation relate to disease prevention?
Ans. Sanitation plays a crucial role in disease prevention as it helps to remove or reduce the sources of contamination that can lead to the spread of diseases. Proper sanitation practices, such as the safe disposal of sewage and wastewater, the provision of clean drinking water, and the regular cleaning of public spaces, help to eliminate or minimize the presence of disease-causing pathogens, bacteria, and viruses.
5. What are alternate arrangements for sewage disposal?
Ans. Alternate arrangements for sewage disposal may include the use of septic systems, which are individual wastewater treatment systems installed on private properties. These systems treat and dispose of sewage on-site, usually through the use of septic tanks and drain fields. Another alternative is the connection to a centralized sewer system, where sewage is transported and treated at a central facility. Some areas also utilize composting toilets or other innovative technologies for sewage disposal.
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Wastewater story Class 7 Notes Science Chapter 13