Control of a Thiobacillus denitrificans bioreactor using machine vision

A PC-based machine vision system has been used to continuously monitor changes in biomass concentration and to control the undesirable production of colloidal elemental sulfur (a reactor upset condition due to an excessive concentration of inhibitory sulfide substrate) in a bioreactor containing Thiobacillus denitrificans. A field of view of a video camera was established which contained regions of different background lighting. Mean values of the distribution of red, green, and blue intensity components within corresponding regions of a digital image image captured from the camera were used to monitor color changes associated with changes in biomass concentration, and to determine if the reactor was in an upset condition. The ration of red to blue intensity components was an important parameter in detecting the formation of an elemental sulfur precipitant. Using a stepper motor-driven pressure regulator, intelligent process control was performed by altering the hydrogen sulfide feed flow rate setpoint on the vision system measurements.