Population equivalent based on 5-day BOD at 15°C: A town discharges 100 kg/day of 5-day BOD. If standard per-capita 5-day BOD at 15°C is 0.1 kg/day per head, what is the population equivalent?

Introduction / Context:
Population equivalent translates an industrial or combined wastewater load into an equivalent number of persons, using a standard per-capita biochemical oxygen demand (BOD) contribution. This helps compare loads and size treatment units accordingly.

Given Data / Assumptions:

• Total 5-day BOD load = 100 kg/day.
• Standard per-capita 5-day BOD = 0.1 kg/day per head (at 15°C).
• Objective: compute population equivalent (PE).

Concept / Approach:

Population equivalent is defined as total load divided by per-capita load. This is a direct proportion, requiring no further adjustments when temperature and measurement basis match the standard.

Step-by-Step Solution:

Verification / Alternative check:

Units: kg/day divided by kg/day per head gives heads; arithmetic is straightforward.

Why Other Options Are Wrong:

100, 5000, 10000, and 750 do not satisfy the simple ratio; only 1000 matches the calculation.

Common Pitfalls:

Using BOD5 per capita values at different temperatures or confusing BOD with COD; mixing daily and hourly loads.

Final Answer:

1000