Most of the bacteria in sewage are saprophytic.

Explanation:
- Saprophytic bacteria are bacteria that obtain their nutrients from dead or decaying organic matter. They play a crucial role in the decomposition process and are responsible for breaking down complex organic materials into simpler compounds.
- Sewage is primarily made up of organic waste, including human and animal feces, food scraps, and other organic matter. As a result, it provides an abundant source of nutrients for saprophytic bacteria.
- These bacteria thrive in anaerobic (oxygen-deprived) environments, which are commonly found in sewage systems. They are able to carry out the process of decomposition in the absence of oxygen.
- Saprophytic bacteria secrete enzymes that break down complex organic molecules, such as proteins, carbohydrates, and lipids, into simpler forms that can be absorbed and utilized by the bacteria.
- By decomposing organic matter, saprophytic bacteria help to reduce the volume of sewage and break down potentially harmful substances.
- Additionally, they play a vital role in the nutrient cycle by releasing essential elements, such as nitrogen and phosphorus, back into the environment.
- While some pathogenic bacteria may be present in sewage, they are typically present in much lower numbers compared to saprophytic bacteria. Pathogenic bacteria are capable of causing diseases in humans and animals.
- The treatment of sewage involves the removal of both saprophytic and pathogenic bacteria, as well as other contaminants, to ensure the water is safe for reuse or discharge into the environment.
- Various treatment processes, such as primary sedimentation, biological treatment, and disinfection, are employed to remove or inactivate bacteria and other harmful microorganisms present in sewage.
- Overall, the presence of saprophytic bacteria in sewage is beneficial as they aid in the natural decomposition process and help to break down organic waste.