NCERT Exemplar Solutions Class 7 Science Solutions for Wastewater Story - Exercise in Chapter 18 - Wastewater Story

Question 14 Wastewater Story - Exercise

Which of the following is/are products of wastewater treatment?

(a) Biogas

(b) Sludge

(c) Both biogas and sludge

(d) Aerator


The answer is (c) Both biogas and sludge


During wastewater, treatment water is allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water. The sludge 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 or can be used to produce electricity.

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