Page 1 :
(Chapter - 18) (Wastewater Story), (Class - VII), » After several hours, the suspended microbes settle at the bottom of the tank as activated, sludge. The water is then removed from the top. The dried activated sludge is used as manure., >» Water is removed from the top and is stored in a tank. The treated water has low level of, organic material and suspended matter. It is discharged into a sea, a river or into the ground., Sometimes it is disinfected through chemicals like Chlorine and ozone and then distributed to, towns., , Question 5:, , What is sludge? Explain how it is treated., , € Answer 5:, , Sludge is human waste (like faeces) 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 97%, 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., , Question 6:, , Untreated human excreta is a health hazard. Explain., , €. Answer 6:, , 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., , €. Answer 7:, , 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., € Answer 8:, , Bar screens are used to remove large objects like rags, sticks, cans, plastic packets napkins, etc., , Question 9:, , Explain the relationship between sanitation and disease., , €. Answer 9:, , 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., , Question 10:, Outline your role as an active citizen in relation to sanitation.