Which of the following is NOT a constituent of bio-gas produced in anaerobic sludge digester in a sewage treatment plant?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Nitrogen
Option (1) Hydrogen sulphide — A constituent.
Option (2) Nitrogen — Not a constituent. NCERT names the gases made in the anaerobic sludge digester as methane, hydrogen sulphide and carbon dioxide. Nitrogen is not among them.
Option (3) Methane — A constituent.
Option (4) Carbon dioxide — A constituent.
NCERT Extract:
Microbes in Sewage Treatment – “… Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as source of energy as it is inflammable.”