Control of fermentation of lignocellulosic hydrolysates

In this work substrate feeding rate to a fermentation of lignocellulose hydrolysate for production of ethanol has been studied. During hydrolysis of lignocellulose inhibitors are formed that effect the microorganism (here Saccharomyces cerevisiae) that ferments the sugar to ethanol in a negative way. To make the hydrolysate fermentable the inhibitors are often removed by detoxification prior to fermentation, but an alternative to detoxification is to use fed-batch fermentation. The reason for this is that the yeast can convert the inhibitors to less toxic compounds, if high concentrations of the inhibitors are avoided. To get a successful fermentation the substrate feed rate should be controlled so that severe inhibition is avoided and the production of ethanol is maximal. In this work on-line measurement of carbon dioxide evolution rate (CER) was used to control the feed rate of hydrolysate in fed batch fermentation of wood hydrolysate. A control algorithm was created for the feed rate of the hydrolysate and the results showed that the in-situ detoxification worked for moderately inhibiting hydrolysates but not for more severely inhibiting hydrolysates.