Submitted to: Industrial Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/13/2011
Publication Date: 8/1/2011
Citation: Murthy, G.S., Rausch, K.D., Johnston, D., Tumbleson, M.E., Singh, V. 2011. Industrial evaluation of a dynamic controller for simultaneous saccharification and fermentation process. Industrial Biotechnology. 7(4):298-307. Interpretive Summary: The US corn to ethanol industry uses added enzymes and yeast to convert the starch in corn kernels into ethanol. The hydrolysis of the starch and the fermentation into ethanol is done simultaneously in a large processing tank. Due to its complexity, the fermentation process is not completely controlled in existing facilities. In order to better control the process, a dynamic controller was developed and used to monitor critical factors such as pH, temperature and enzyme dosing and to use these values to make predictive processing adjustments. Use of the dynamic controller during a 3 month trial at a 40 million gallon per year facility, resulted in a reduction of one enzyme (glucoamylase) by 25% with improvements in yeast performance and no loss in ethanol production. Estimated annual savings in enzyme costs for a 40 million gallon per year ethanol facility was $240,000. Based on the results in the industrial-scale fermentors, it can be concluded that the use of the dynamic controller could reduce operating cost and improve fermentation efficiency. This information will be useful to fuel ethanol producers as well as research scientist in the fuel ethanol industry.
Technical Abstract: 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.