Which of the following is mainly produced by the activity of anaerobic bacteria in sewage?

Explanation

Marsh gas or methane gas is mainly produced by the activities of anaerobic bacteria in sewage. Sewage contains large amounts of organic matter and microbes, many of which are pathogenic. These microbes (bacteria and fungi) are digested during the secondary treatment process of sewage by anaerobic bacteria. During digestion, bacteria produce a mixture of gases such as methane, hydrogen sulfide, and carbon dioxide. These gases are called biogas and can be easily used as a source of energy as it is inflammable.