DEVELOPMENT OF MONITORING AND CONTROL METHODS FOR CONTINUOUS FERMENTATION PROCESSES

A 14 liter batch fermentor was converted for continuous operation and interfaced to a PDP 11/34 digital computer for the purpose of studying continuous pure and mixed culture systems. The experimental system was used to study Candida utilis grown on glucose as the limiting substrate. Using both batch and continuous data, the parameters in a simple growth model of the yeast were determined. The continuous culture of the yeast was subjected to both positive and negative step changes in glucose feed rate. Based on a limited amount of transient data a compound linear model was proposed to model the dynamic response of the growth rate.;The potential use of the Cytofluorograf for determination of cell mass of individual populations in a mixture was also investigated by calibrating the instrument with a pure culture of C. utilis. Cell mass was independently determined by measuring the optical density with a Gilford 2400S spectrophotometer which was interfaced to the computer for on-line operation. Variations in the cell size of the yeast necessitated a correction to be made to the optical density readings to account for the average cell size in the samples.;The need for sterilizing of nutrient feed reservoirs has been elminated by filter sterilizing the feeds and passing them through a custom-built UV sterilizer before entering the fermentor vessel. Off-line tests of the sterilizer show that a 100% kill rate efficiency is possible with a residence time as low as 15 seconds.;A flow-through cell was designed and built to house an immobilized glucose oxidase enzyme probe. The probe was successfully used to measure glucose concentration in the range of 0 to 100 mg/l which is typical of the continuous operation of the fermentor.;Cell size analysis was done with a commercial microphotometer (Cytofluorograf) adapted for on-line operation under computer control. Hardware and software was developed to enable automatic sample delivery and data acquisition with the emphasis on high sampling rates and minimum computer memory requirements. Careful choice of the sampling technique resulted in less than five minute delay in the cell size analysis.;In addition a complete software package was developed to control the experimental system and to automatically collect and store the output data. The package can also be used to guide the system through a predetermined set of experimental steps without operator intervention which makes the experimental system highly productive in terms of data generation.