NCERT Class VII Science Solutions: Chapter 18-Wastewater Story Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 5:

What is sludge? Explain how it is treated.


Sludge is human waste (like faces) in waste water left during sewage treatment. Since it is organic waste, it is used to produce bio gas and manure. Sludge is collected by a scrapper. It is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel. After the aerator tank, microbes and human waste settle down and form activated sludge. The activated sludge is about water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.

As Showing in Images is a Result for Sludge

Question 6:

Untreated human excreta is a health hazard. Explain.


Untreated human excreta contains many pathogens and disease causing microbe like cholera, diarrhea, typhoid, polio, meningitis, hepatitis etc. The germs of these diseases can easily reach human population through air, water or insects and through contaminated food and water. Thus, untreated human excreta are a health hazard.

Question 7:

Name two chemicals used to disinfect water.


Chemicals like chlorine (Chlorine dioxide) and ozone (in the pharmaceutical industry) are commonly used to disinfect water.

Question 8:

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


Bar screens are used to remove large objects like rags, sticks, cans, plastic packets napkins, etc.

Bar screens clear the waste water of all the physical impurities. Large size waste like napkins, plastics, cans etc. are removed from the waste water through the bar screens.

Question 9:

Explain the relationship between sanitation and disease.


A large number of diseases is caused due to poor sanitation and contaminated drinking water. Poor sanitation leads to growth of harmful microbes, flies and mosquitoes which are the source of spreading many diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

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