Operation cycle of an alternating tandem chemostat. Wavy lines, dots and circles in growth chambers represent culture level, live bacteria and air bubbling respectively. The letters 0 and X indicate open and closed valves, respectively. Lines carrying mixed gaseous-liquid flows are in bold. In the tube that connects the two chambers, the dotted arrow indicates the direction of flow. Sterilization and replenishment phases have respective durations of 20 mn and 47 h 40 mn. During each cycle, both growth chambers, their effluent lines and the bridging line are transiently flooded with 10 N NaOH, destroying all cells attached to any part of the device.