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

(1) Semi-solids such as faeces that settle down during wastewater treatment are called sludge.

(2) This sludge is removed using a scraper and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas.

(3) This biogas is used as a low-cost fuel for heating, cooking, etc. It is also used to produce electricity.