Liquid level control in an aerated continous-flow fermentor

An electronic liquid level control system was developed to maintain constant working volume in a continuously fed and aerated fermentor from which spent medium was continously withdrawn by microfiltration in an external recycle loop. The level control system was comprised of an admittance sensor in the fermentor and an external transmitter and controller, which together regulated the speed of a recycle pump and thus the rate of liquid withdrawal from the fermentor. During test bacterial culture the liquid level was maintained usually within +/- 1% and always within +/- 5%. The control system could be applied to various other types and scales of continuous-flow fermentors.