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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

Answer:

The answer is (c) Both biogas and sludge

Explanation:

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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