The effects of equipment dimensions and operation conditions on the liquid circulation now rate in a rectangular airlift bubble column were investigated at relatively low gas velocities, at which few bubbles were entrained into the downcomer. The gas holdup in the downcomer was almost zero, and the gas holdup in the riser decreased with increasing length between (lie tipper end of the partitioning plate and the liquid surface during aeration (tipper clearance) and with increasing length of the partitioning plate. The liquid circulation flow rate increased with increasing tipper clearance, and became constant when the clearance exceeded a certain value. The loss coefficient in the zone above the upper end of the partitioning plate was a function of the upper clearance and the riser width. By using the energy balance and experimental equations [lie liquid circulation flow rate was calculated, and the results agreed with the measured data within an error of +30%.