Fresh sewage may become stale in

ANS:C - three to four hours

Fresh sewage may begin to show signs of staleness within approximately three to four hours under normal conditions. Here's a detailed explanation:

1. Microbial Activity: After sewage is generated, microbial activity begins almost immediately. Bacteria and other microorganisms present in the sewage start to metabolize organic matter, breaking it down into simpler compounds. As microbial populations grow and metabolic processes intensify, the sewage's composition begins to change.
2. Odor Formation: One of the key indicators of sewage staleness is the formation of foul-smelling gases such as hydrogen sulfide and ammonia. These gases are byproducts of microbial metabolism and decomposition processes. As the microbial activity continues, the concentration of these odorous compounds increases, leading to the characteristic foul odor associated with stale sewage.
3. Temperature and Environmental Factors: The rate of microbial activity and sewage decomposition is influenced by environmental factors such as temperature, oxygen availability, and organic content. Warmer temperatures generally accelerate microbial processes, hastening the onset of sewage staleness.
4. Observation and Monitoring: In wastewater treatment and management practices, it's essential to monitor the condition of sewage regularly. Monitoring parameters may include odor, appearance, and biochemical characteristics such as biochemical oxygen demand (BOD) and total suspended solids (TSS). These indicators can provide insights into the freshness and quality of sewage and help determine appropriate treatment and management strategies.
5. Management Practices: Effective sewage management practices involve timely collection, transportation, and treatment of sewage to prevent odor issues, environmental contamination, and public health risks associated with stale sewage. Proper treatment processes, such as biological treatment, can help reduce odor and remove organic pollutants from sewage before discharge or reuse.

In summary, while fresh sewage may initially have a relatively neutral odor and appearance, it can begin to show signs of staleness within approximately three to four hours due to microbial activity and decomposition processes. Monitoring and managing sewage effectively are essential to mitigate odor issues and maintain environmental and public health standards.