What is sludge? Explain how it is treated.

Semi-solids such as faeces that settle down at the bottom during wastewater treatment are called sludge.

Treatment of sludge:

• Sludge is removed from the bottom of the tank using a scraper.
• It is then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas.
• This biogas is used as a low-cost fuel for heating, cooking etc.
• It is also used to produce electricity.