NCERT Solutions for class 7 Science Chapter-18

Chapter – 18   Wastewater Story

Chapter Exercise

Page no. – (228)

 

Q.1– Fill in the blanks:-

1. Cleaning of water is a process of removing ____.
2. Wastewater released by houses is called ____.
3. Dried ____ is used as manure.
4. Drains get blocked by ____ and ____.

 

Ans.1–

1. Cleaning of water is a process of removing __pollutant__.
2. Wastewater released by houses is called __sewage__.
3. Dried __sludge__ is used as manure.
4. Drains get blocked by __cooking oil__ and __fats__.

 

 

Q.2– What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

 

Ans.2– The sewage is used and waste water released by homes, office, industries and other place. The untreated water should not be discharge untreated into the sea because it may contain harmful chemicals, waste, used and dirty items etc and which will contaminate water cause and harm peoples and animals.

 

 

Q.3– Why should oils and fats be not released in the drain? Explain.

 

Ans.3– The oils and fats be not released in the drain because drains get blocked by cooking oil.

 

 

Q.4– Describe the steps involved in getting clarified water from wastewater.

 

Ans.4– Following steps are involved in getting the clarified water from wastewater:-

• Firstly of all, all bottles, stones, plastic bags etc are removed by bar screen.
• The water is then transported to the grit and sand removal tanks. At that place the impurities are removed by sedimentation.
• Solid impurities and feces etc. are collected from under water. These impurities collected are called sludge mud.
• Aerator water is cleaned of other impurities by the aerator. Chlorination removes all disease causing bacteria.

 

 

Q.5-What is sludge? Explain how it is treated.

 

Ans.5– Solid materials like feces sit at the bottom when treating sewage, and this material is called sludge. At the water treatment plant, the waste is drained from the water at the time of treatment. The sludge is decomposed into a separate tank by anaerobic bacteria.

 

 

Q.6– Untreated human excreta is a healthy hazard. Explain.

 

Ans.6– Untreated human excreta can cause many problems because it contains pollutants, soil, water and disease causing micro – organism. When people use water contaminated with human excreta, they get diseases like Typhoid, Dysentery and Cholera.

 

 

Q.7– Name two chemicals used to disinfect water.

 

Ans.7– The following are two chemicals used to disinfect water:-

• Ozone
• Chorine

 

 

Q.8– Explain the function of bar screens in a wastewater treatment plant.

 

Ans.8– Bar screen remove large objects such as bottles, cans, stones, and plastics.

 

 

Q.9– Explain relation between sanitation and disease.

 

Ans.9– Cleanliness and disease are related to each other. Sanitation includes proper disposal of sewage and refuse from homes and public places. If there is hygiene, then there will be no disease, but if there is no hygiene, then different kinds of diseases will arise and spread. Therefore, hygiene should be maintained to avoid illness.

 

 

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

 

Ans.10– The following are the role as an active citizen in relation to sanitation:-

• First of all, make sure that we keep cleanliness in our house, street, locality, school etc. and prevent others from making a mess.
• We should help the municipal corporations to cover all open drains and remove the materials thrown in the open.
• Sewage systems in the home must be managed properly.
• NCERT Solution for class 7 English Chapter 3