ANS:D - all the above.

The temperature indeed affects various aspects of sewage and its treatment processes. Let's explore how temperature influences each of the factors mentioned:

1. Biological Activity of Bacteria in Sewage:
   • Temperature has a significant impact on the biological activity of bacteria present in sewage. Most biological processes, including those involved in sewage treatment, are highly temperature-sensitive.
   • Higher temperatures generally promote faster rates of biological activity and microbial metabolism. This means that at higher temperatures, bacteria can break down organic matter more rapidly, leading to more efficient sewage treatment.
   • Conversely, lower temperatures can slow down biological processes, reducing the rate of sewage treatment. In cold climates, wastewater treatment plants may experience decreased efficiency during winter months due to lower temperatures.
2. Solubility of Gases in Sewage:
   • Temperature affects the solubility of gases in water, including those present in sewage. Generally, as temperature increases, the solubility of gases decreases.
   • In sewage treatment processes, the solubility of gases such as oxygen (O2) and carbon dioxide (CO2) is crucial for aerobic and anaerobic processes.
   • Higher temperatures can lead to reduced oxygen solubility in sewage, which may affect aerobic biological treatment processes. Conversely, warmer temperatures can increase the solubility of gases such as methane (CH4), which is produced during anaerobic digestion processes.
3. Viscosity of Sewage:
   • Viscosity refers to the resistance of a fluid to flow. Temperature influences the viscosity of sewage, with higher temperatures generally resulting in lower viscosity.
   • Warmer temperatures can reduce the viscosity of sewage, making it flow more easily through pipes and treatment processes. This can improve the efficiency of pumping and mixing operations in wastewater treatment plants.
   • Conversely, lower temperatures can increase the viscosity of sewage, making it thicker and more difficult to pump and process. This can lead to operational challenges and may require adjustments to treatment processes.

Therefore, temperature affects the biological activity of bacteria in sewage, the solubility of gases in sewage, and the viscosity of sewage. Each of these factors plays a critical role in wastewater treatment processes, and temperature management is essential for optimizing treatment efficiency and performance.