In the described sedimentation setup, how many tanks are currently in service?

• A. One
• B. Two
• C. Three
• D. None

Answer: (A)

In a sedimentation system, tanks are often arranged in parallel so they can share the flow, but only the tanks that have an open path from the influent to their effluent are actually in service. If the diagram shows the influent header feeding only one tank and the other tanks are isolated by closed valves or tied into a bypass, then only that single tank is actively processing water. You can confirm by tracing the flow: the path from influent to effluent should go through just one tank, not through multiple ones. This situation can occur during maintenance or when operating at reduced flow. So, in that setup, one tank is in service.