Experimental Self-Tuning Proportional Integral Derivative pH Control: Application to a Bioprocess

pH control has received considerable attention in preparation of cheese whey drink, by fermentation with kefir yeast, because of its critical role in quality assurance. To improve the rheological and sensory properties of this drink, milk and grape juice are added to the bioprocess medium. Cheese whey drink was produced from the pasteurized mixture, which contains cheese whey, glucose, grape juice and milk. The fermentation of this mixture with kefir yeast in a batch bioreactor was investigated. The pH was monitored during the production of cheese whey drink. Experiments show that kefir yeast is very resistant to contamination. A self-tuning proportional-integral-derivative control was applied to the bioprocess. The software of controller was developed by using the autoregressive moving average exogenous model. The model parameters were evaluated from input-output data by using a pseudo random binary sequence. The experimental results illustrate that the controller can maintain the pH at the desired value. It is noted that the self-tuning proportional-integral-derivative pH control results with the best controller tuning parameters and provides very good results, compared to initially adjusted case, without control. The best tuning parameters were found as t₁=0.1, t₂=0, t₃=0, by comparing experimental application results.