In the population loading example, what is the influent volume?

• A. 100 gallons
• B. 1000 gallons
• C. 10 gallons
• D. 50 gallons

Answer: (A)

The essential idea is that influent volume in a population loading scenario is the total wastewater entering the plant over a set period, usually per day. You get it by multiplying the number of people by how much wastewater each person contributes per day. So the formula is Q_in = P × q_p, where Q_in is the influent volume (gal/day), P is the population, and q_p is the per-capita daily production (gal/person-day).

If the example uses 4 people producing 25 gallons per person per day, you’d have 4 × 25 = 100 gallons per day, so the influent volume is 100 gallons daily. The other numbers would only fit if the population or the per-person daily yield were different than what the example specifies.