In a clarifier, increasing the influent flow rate generally results in a higher

• A. Weir overflow rate
• B. Tank depth
• C. Diameter
• D. MLSS concentration

Answer: (A)

Weir overflow rate is the rate at which water leaves a clarifier over the weir per unit area. It’s set by the influent flow divided by the clarifier’s surface area. When you increase the influent flow but keep the same surface area, more water must pass over the weir for each square foot of surface, so the weir overflow rate goes up. The other dimensions, like tank depth or diameter, are fixed by the design and don’t automatically increase with flow. MLSS concentration reflects how much suspended solids are present, which can vary with loading, but the direct, immediate effect of higher inflow on a clarifier is the higher weir overflow rate.