Question

Which of the following are the by-products of wastewater treatment ?

• A. Sewage and biogas
• B. Oil and grease
• C. Sewage and sludge
• D. Sludge and biogas

Answer 1

The correct option is D Sludge and biogas

• Solids like faeces called sludge settle at the bottom of large tanks during primary treatment in a wastewater treatment plant and are removed with a scraper.
• The sludge is then 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.
• The suspended microbes settle at the bottom of the tank as activated sludge which is ~ 97% water. The water is removed by sand drying beds or machines and the resultant dried sludge is used as manure.