Which sewer system is described as being used when gravity systems are not feasible, with wastewater conveyed under pressure from the discharge side of a lift station to a point where gravity flow can be accomplished?

Which sewer system is described as being used when gravity systems are not feasible, with wastewater conveyed under pressure from the discharge side of a lift station to a point where gravity flow can be accomplished?

• A. Forced
• B. Gravity
• C. Open Channel
• D. Vacuum

Answer: (A)

When gravity flow isn’t feasible, wastewater is pumped under pressure from a lift station through a force main to a point where gravity flow can take over again. This setup is a forced (pressurized) sewer system. The force main carries sewage under pressure, overcoming elevation or slope challenges, until it reaches a location with sufficient grade to allow gravity to carry it onward to the gravity sewer or treatment facility. Gravity systems rely on slope to move wastewater, so they don’t involve pumping or pressurized pipes. Open channel systems convey sewage in an open, channel-like path rather than a closed pipe under pressure. Vacuum systems move wastewater using suction in a sealed, vacuum-pressurized network, not by discharging from a lift station into a gravity section.

When gravity flow isn’t feasible, wastewater is pumped under pressure from a lift station through a force main to a point where gravity flow can take over again. This setup is a forced (pressurized) sewer system. The force main carries sewage under pressure, overcoming elevation or slope challenges, until it reaches a location with sufficient grade to allow gravity to carry it onward to the gravity sewer or treatment facility.

Gravity systems rely on slope to move wastewater, so they don’t involve pumping or pressurized pipes. Open channel systems convey sewage in an open, channel-like path rather than a closed pipe under pressure. Vacuum systems move wastewater using suction in a sealed, vacuum-pressurized network, not by discharging from a lift station into a gravity section.