Most likely cause of short-circuiting in a tank?

• A. High incoming BOD
• B. Missing baffle
• C. Low flow
• D. Increased detention time

Answer: (B)

Short-circuiting happens when water moves straight from the inlet to the outlet without circulating through most of the tank, giving portions of water very short hydraulic detention times and poor treatment. A baffle acts like a flow guide; it directs the incoming flow and forces water to travel across the tank rather than shooting straight to the outlet. If the baffle is missing, jets of water can rush directly to the outlet, creating that shortcut through the tank and causing short-circuiting.

Among the options, missing the baffle is the direct structural change that promotes this undesired flow pattern, whereas high incoming BOD, low flow, or longer detention time affect loading, mixing, or residence time but don’t inherently create the straight-through flow path that causes short-circuiting.