Computer control of an algal bioreactor with simulated diurnal illumination

Design details are presented for the construction of a microcomputer based system to measure and control the growth of an algal population in a continuous‐flow bioreactor. Diurnal variation in the light intensity was simulated by computer control of a Venetian blind placed in front of the solar lamps. An indirect method of biomass estimation was based on balancing the amount of nitrogen (NH 3 ) in and out of the system. The computer‐control system held the algal biomass at a constant concentration while fluctuations in CO 2 partial pressure, turbulence and light intensity occurred. Under diurnal illumination, CO 2 assimilation began without lag when illumination started, although there was a lag before ammonia utilisation began.