In municipal wastewater engineering (Indian conditions), what is the typical average temperature of domestic sewage used for design and process calculations?
-
A10°C
-
B15°C
-
C20°C
-
D25°C
-
E30°C
Answer
Correct Answer: 20°C
Explanation
Introduction / Context:Sewage temperature directly affects biochemical reaction rates, viscosity, oxygen transfer, and gas generation. For Indian design problems and exam standards, a representative average temperature is used when site-specific data are unavailable. This question checks that reference value.
Given Data / Assumptions:
- Domestic sewage in tropical/subtropical Indian climate.
- Average, not peak summer or winter extremes.
- Steady-state assumptions for textbook calculations (e.g., BOD rate constants, oxygen solubility).
Concept / Approach:
Design manuals tabulate typical sewage temperatures by climate. For India, many standard texts take about 20°C as a reasonable annual-average for calculations. This anchors temperature correction factors for reaction rates (e.g., k_T = k_20 * θ^(T-20)).
Step-by-Step Solution:
Identify typical Indian ambient-water temperatures for municipal systems.Select the widely adopted average value used to normalize kinetic parameters.Hence choose 20°C as the standard average figure.Verification / Alternative check:
At 20°C, oxygen solubility and viscosity values match common tables used for aeration and hydraulics, confirming consistency with design norms.
Why Other Options Are Wrong:
10–15°C are too low for most Indian cities; 25–30°C represent warm-season conditions but are not used as a single average baseline.
Common Pitfalls:
Confusing wastewater temperature with air temperature; using peak temperatures for all-year kinetic design without correction factors.
Final Answer:
20°C