NCERT Solutions for Class 7 Science Chapter 13 – Wastewater Story

Wastewater Story Long Summary

What is Wastewater?

Wastewater is essentially used water that contains various impurities. It is the liquid waste that flows out of households, industries, hospitals, and offices. This water is often rich in contaminants such as food scraps, detergents, and even harmful chemicals.

Composition of Sewage

Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, and disease-causing bacteria.

• Organic Impurities: Human faeces, animal waste, oil, and fruit/vegetable peels.

• Inorganic Impurities: Nitrates, Phosphates, and metals.

• Bacteria: Microbes that cause diseases like cholera and typhoid.

Importance of the Wastewater Treatment Plant 

The main goal of treating wastewater is to remove pollutants so the water can be safely returned to the water cycle. The wastewater story class 7 NCERT solutions sets often focus on the mechanics of this treatment process.

Steps in Wastewater Treatment

1. Bar Screens: Large objects like rags, sticks, cans, and plastic packets are removed.

2. Grit and Sand Removal: The speed of the incoming wastewater is decreased to allow sand, grit, and pebbles to settle down.

3. Sedimentation Tank: Water is allowed to settle. Solids like faeces (sludge) sink to the bottom and are removed with a scraper. Floatable solids like oil and grease are removed with a skimmer.

4. Aeration: Air is pumped into the clarified water to help aerobic bacteria grow. These bacteria consume remaining organic waste.

5. Chlorination: Before water is released into the sea or rivers, it is often disinfected using chemicals like chlorine or ozone to kill harmful germs.

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Better Housekeeping Practices

We can reduce the load on treatment plants by being mindful of what we pour down our drains. This is a common theme in wastewater story class 7 science question answer sections.

• Cooking oil and fats should not be thrown down the drain as they can harden and block pipes.

• Chemicals like paints, solvents, and insecticides can kill the helpful microbes that purify water.

• Solid food remains and tea leaves should be thrown in the dustbin to prevent clogging.

Sanitation and Disease

Poor sanitation and contaminated drinking water are the leading causes of various diseases. When sewage is not treated, it can mix with groundwater or surface water.

• Water-borne diseases: Consuming contaminated water leads to Cholera, Typhoid, Polio, Meningitis, and Hepatitis.

• Alternative Sewage Disposal: In areas where sewerage systems are unavailable, low-cost onsite sewage disposal systems like septic tanks, chemical toilets, and composting pits are used.

Vermi-processing Toilets

In India, a design of a toilet in which human excreta is treated by earthworms has been tested. It has been found to be a novel, low water-use method for safe processing of human waste. The operation of the toilet is very simple and hygienic, converting human excreta into high-quality vermicompost.

Role of an Active Citizen

• Keep surroundings clean

• Avoid throwing waste in drains

• Use toilets properly

• Spread awareness about hygiene

Read More - NCERT Solutions for Class 7 Science Chapter 1 Nutrition in Plants

Wastewater Story Class 7 Question Answer

Question: What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Answer: Sewage is liquid waste containing various impurities, including organic and inorganic contaminants, nutrients, and disease-causing bacteria. Discharging untreated sewage into water bodies is harmful because:

• It pollutes the entire water source.

• It spreads water-borne diseases like cholera and dysentery.

• It harms aquatic life by depleting oxygen levels in the water.

Question: Why should oils and fats not be released in the drain? Explain.

Answer: Oils and fats should not be released in the drain because:

• They can harden and block the pipes in the sewerage system.

• In open drains, they clog the soil pores, reducing the effectiveness of the soil in filtering water.

Question: Describe the steps involved in getting clarified water from wastewater.

Answer: The process includes:

• Passing water through bar screens to remove large debris.

• Using a grit and sand removal tank.

• Allowing solids to settle in a sedimentation tank to remove sludge.

• Aerating the water to allow bacteria to decompose organic matter.

Question: What is sludge? Explain how it is treated.

Answer: Sludge is the solid waste, such as faeces, that settles at the bottom of the sedimentation tank during sewage treatment. It is transferred to a separate tank where it is decomposed by anaerobic bacteria. The biogas produced during this process can be used as fuel or to produce electricity.

Question: Name two chemicals used to disinfect water.

Answer: The two chemicals commonly used to disinfect water are Chlorine and Ozone.

Question: Untreated human excreta is a health hazard. Explain.

Answer: Untreated human excreta contains harmful microorganisms. When it is released into open areas, lakes, or rivers, it pollutes water and soil. This increases the spread of diseases such as cholera, typhoid, and hepatitis. This is an important point in wastewater story class 7 question answer because safe sanitation protects both people and the environment.

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Question: Explain the function of bar screens in a wastewater treatment plant.

Answer: Bar screens are placed at the start of the treatment process. They remove large objects such as rags, sticks, cans, napkins, and plastic packets from sewage. This prevents damage to machines and helps the rest of the treatment process work smoothly.

Question: Explain the relationship between sanitation and disease.

Answer: Poor sanitation leads to dirty surroundings, contaminated water, and the spread of germs. Stagnant wastewater also becomes a breeding ground for flies and mosquitoes. As a result, people may suffer from water-borne and insect-borne diseases. This makes sanitation a key part of class 7 chapter 13 science question answer preparation.

Question: Outline your role as an active citizen in relation to sanitation.

Answer: An active citizen should keep surroundings clean, avoid throwing waste into drains, use toilets properly, and spread awareness about hygiene. Students can also encourage family members and neighbours to follow safe sanitation practices. These simple habits support cleaner communities and healthier living.

Question: Study the following statements about ozone and choose the correct option.

a) It is essential for breathing.

b) It is used to disinfect water.

c) It absorbs ultraviolet rays.

d) Its proportion in air is about 3%.

Answer: The correct statements are **b and c**. Ozone is used to disinfect water, and the ozone layer helps absorb harmful ultraviolet rays. It is not essential for breathing, and its amount in the atmosphere is extremely small.

Question: Solve these one-word answers from the chapter.

Question: Liquid waste product

Answer: Sewage

Question: Solid waste removed during treatment 

Answer: Sludge

Question: A word linked to cleanliness 

Answer: Sanitation

Question: A pipe carrying sewage 

Answer: Sewer

Question: Used water 

Answer: Wastewater

Wastewater Story Class 7 Fill in the Blanks

a) Cleaning of water is the process of removing ________.

b) Wastewater released by houses is called ________.

c) Dried ________ is used as manure.

d) Drains get blocked by ________ and ________.

Answer:

a) contaminants

b) sewage

c) dung

d) plastic, sludge

Benefits Of Wastewater Story Class 7 Question Answer

• Builds a clear understanding of how wastewater is collected, cleaned, and released safely.

• Helps students revise key ideas such as sewage, sludge, sanitation, and water treatment in simple language.

• Makes exam preparation easier with direct explanations of important chapter concepts.

• Supports better retention through step-by-step coverage of treatment stages and hygiene practices.

• Encourages awareness of cleanliness, safe water use, and responsible public behaviour in daily life.

• Gives students a quick revision aid for school tests, homework, and class discussions on Chapter 13.