NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story

NCERT solutions for class 7 science chapter 18 wastewater story exercise:

  1. Fill in the blanks:
    (a) Cleaning of water is a process of removing ____________.
    (b) Wastewater released by houses is called ____________.
    (c) Dried ____________ is used as manure.
    (d) Drains get blocked by ____________ and ____________.


(a) Cleaning of water is a process of removing contaminants .
(b) Wastewater released by houses is called sewage .
(c) Dried cow dung is used as manure.
(d) Drains get blocked by plastic and fats .

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


Sewage is wastewater coming out of households, public places, farms and industry. It also includes rainwater which has flown into the sewers.

Untreated sewage contains harmful chemicals which if released directly into the rivers or seas would pollute them harming the ecosystem of the water bodies and making the water unfit for drinking or further use.

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


Oils and fats are insoluble in water. When released in the drain, it causes hardening and blocking of the sewage pipes. In an open drain, the fats block the soil pores which is required for filtering water. That is why oil and fats should not be released in the drain.

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


The treatment of wastewater includes the following steps:

(i) First, the physical waste like plastic, rags, pebbles, wood etc is removed by passing the water through a bar screen.

(ii) Then water is sent into sand removal tank for removing sand, pebbles, grit etc. through the process of sedimentation.

(iii) Then the rest of the solid waste is allowed to settle at the bottom of a large settling tank. This waste deposited at the bottom is called sludge and is removed through a scraper.

(iv) The harmful microorganisms in this water are killed through chlorination or UV rays.

(v) Through aerator, air is pumped into this water so that aerobic bacteria can grow and decompose any remaining organic wastes.

(vi) This treated water is then released into the water bodies.

. What is sludge? Explain how it is treated.


Sludge is the solid waste which has settled at the bottom of settling tanks during the process of wastewater treatment.

It is treated by decomposition by anaerobic bacteria. This activated sludge further can be used as manure.

. Untreated human excreta is a health hazard. Explain.


Untreated human excreta contains many harmful organisms which can cause lots of health-related problems. Untreated human excreta pollutes air, water and soil. Epidemics like cholera, meningitis etc. can be spread by untreated human excreta.

. Name two chemicals used to disinfect water.


Two chemicals used to disinfect water are Chlorine and Ozone.

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


Bar screens filter most of the large-sized solid waste like plastic, cans, wood etc from wastewater.

  1. Explain the relationship between sanitation and disease.


Sanitation refers to the availability of clean drinking water and proper treatment of human waste and sewage.

Without proper sanitation various diseases like cholera, typhoid, diarrhoea, etc. would spread and proper sanitation ensures that these diseases do not spread.

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


As an active citizen, we should ensure that proper sanitation facilities are available in our home and workplaces, should make people aware about the necessity of sanitation and should not throw garbage in the open as it will block the drains and restrict the flow of the sewage.

  1. Here is a crossword puzzle: Good luck!

. Liquid waste products
. Solid waste extracted in sewage treatment
. A word related to hygiene
. The waste matter discharged from the human body
. Used water
. A pipe carrying sewage
. Micro-organisms which causes cholera
. A chemical to disinfect water



  1. Study the following statements about ozone:

(a) It is essential for breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its proportion in air is about 3%.

Which of these statements are correct?
(i) (a), (b) and (c)
(ii) (b) and (c)
(iii) (a) and (d)
(iv) All four


(ii) (b) and (c) are correct.

Responsive Table
Chapter No. Chapter Name
Chapter 1 NCERT solutions for class 7 science chapter 1 Nutrition in Plants
Chapter 2 NCERT Solutions for class 7 science chapter 2 Nutrition in Animals
Chapter 3 NCERT solutions for class 7 science chapter 3 Fibre to Fabric
Chapter 4 NCERT solutions for class 7 chapter 4 science Heat
Chapter 5 NCERT solutions for class 7 science chapter 5 Acids Bases and Salts
Chapter 6 NCERT solutions for class 7 science chapter 6 Physical and Chemical Changes
Chapter 7 NCERT solutions for class 7 science chapter 7 Weather Climate and Adaptations of Animals to Climate
Chapter 8 NCERT solutions for class 7 science chapter 8 Winds, storms and cyclones
Chapter 9 NCERT solutions for class 7 science chapter 9 Soil
Chapter 10 NCERT solutions for class 7 chapter 10 Respiration in Organisms
Chapter 11 NCERT solutions for class 7 science chapter 11 Transportation in Animals and Plants
Chapter 12 NCERT solutions for class 7 science chapter 12 Reproduction in Plants
Chapter 13 NCERT solutions for class 7 science chapter 13 Motion and Time
Chapter 14 NCERT solutions for class 7 science chapter 14 Electric Current and its Effects
Chapter 15 NCERT Solutions for class 7 science chapter 15 science Light
Chapter 16 NCERT solutions for class 7 science chapter 16 Water A Precious Resource-
Chapter 17 NCERT solutions for class 7 science chapter 17 Forests Our lifeline
Chapter 18 NCERT solutions for class 7 science chapter 18 Wastewater Story

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NCERT Solutions for Class 7 Science Chapter 18 Waste water Story
The CBSE NCERT Solutions for Class 7 Science Chapter 18 Waste water Story are very useful for students to prepare for final exams. Click to download.
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