Research: Industrial evaluation of a dynamic controller for simultaneous saccharification and fermentation process

The dry grind corn industry is the largest ethanol producer in the US. Simultaneous saccharification and fermentation (SSF) is one of the most critical process steps that determines the ethanol yields and conversion efficiency of the whole process. Due to its complexity, the SSF process is not completely controlled in dry grind corn processing plants. Previously, a dynamic optimal controller to control of the fermentation process was developed and demonstrated on a 15 L laboratory-scale system. The dynamic controller (DC) was used to determine fermentor temperature, pH and amount of glucoamylase to achieve optimum performance. Validation of this optimal controller was conducted in a commercial dry grind ethanol plant. During commercial trial, DC maintained average peak glucose concentration of 3.15 ± 0.58 (% w/v) for the SSF process compared to 7.9 ± 0.36 (% w/v) for conventional SSF process (no DC). There was no difference (p value = 0.077 for a two tailed, unequal variance, unpaired students t-test) in the final ethanol concentrations with/without the use of DC. The numbers of live and budding yeast cells were higher in fermentors with DC compared to the fermentor without the DC. Based on 39 runs over a 3 month period, use of DC resulted in a 25% reduction in glucoamylase usage. Installation costs for the DC are estimated to be USD$10 000 to $15 000 for a 40 million gal per year ethanol plant. Estimated savings in enzyme costs for a 151 million L/yr (40 million gal/yr) ethanol plant was $240 000. Based on the results in the industrial-scale fermentors, it can be concluded that the use of DC could reduce operating cost and improve fermentation efficiency by maintaining low glucose concentration during SSF.