Air lift pumps are prone to plugging, especially as low return flow rates. Thus, operators should closely monitor these pumps to ensure sludge is being returned at all times.

• A. False
• B. It depends on flow rate
• C. It is generally not a concern
• D. True

Answer: (D)

Air lift pumps move sludge using air to lift a column of liquid and solids. When return flow is low, solids tend to settle and accumulate in the pump and piping, increasing the risk of plugging. If the pump becomes clogged or its discharge is reduced, sludge isn’t returned as intended, which can upset the biological process and reduce treatment efficiency. Because plugging can happen more readily at low return flows, operators must monitor the pump closely to ensure sludge is being returned continuously and to spot signs of restriction early. This is why the statement is true.