In wastewater engineering, temperature variation most significantly affects which of the following characteristics of sewage?

Introduction / Context:
Temperature is a master variable in wastewater systems. It influences biological kinetics, oxygen transfer and solubility, and hydraulic behavior through viscosity changes, impacting both treatment efficiency and conveyance.

Given Data / Assumptions:

• Municipal sewage subject to normal seasonal temperature swings.
• Typical treatment processes include biological reactors and sedimentation.

Concept / Approach:

• Biological activity: Reaction rates often follow an Arrhenius-type temperature dependence; warmer conditions accelerate biodegradation up to optimal limits.
• Gas solubility: As temperature increases, oxygen solubility decreases, reducing available DO for aerobic processes.
• Viscosity: Warmer temperatures reduce viscosity, generally improving settling and mixing while altering headloss.

Step-by-Step Solution:
Recognize temperature's triple role in biology, chemistry (gas solubility), and fluid mechanics.Each listed factor is temperature-dependent in a way that materially affects plant performance.Therefore, the combined option is correct.

Verification / Alternative check:
Operations data show wintertime oxygen demand rises (due to slower kinetics) while oxygen solubility increases; conversely, summer operations see higher kinetics but lower DO solubility and different viscosity behavior—consistent with the stated effects.

Why Other Options Are Wrong:
Focusing on only one parameter ignores the coupled impacts observed daily in treatment plants.

Common Pitfalls:
Assuming temperature helps in every way; in reality it improves kinetics but can impair oxygen availability and change hydraulics simultaneously.

Final Answer:
All of the above.