Simultaneous saccharification and fermentation of spruce–a comparison of pretreatment conditions and different enzyme preparations

Bioethanol production from softwood has been a subject of a lot of research, but yet no large-scale production plant is operating. So far is seems like the pretreatment is the part of the entire process that is most difficult to run satisfactorily in a large-scale process. In this study a set of simultaneous saccharification and fermentation (SSF) experiments were conducted in order to compare two materials pretreated in the pilot plant in Örnsköldsvik, Sweden with an optimally preatreated material produced in a process development unit (PDU) in Lund. The materials were also examined in a Scannning Electron Microscopy study. In addition, it was investigated which of two enzyme preparations (Celluclast 1.5L and Saf-ISIS) was most efficient in SSF. The need for addition of extra β-glucosidase was also investigated. The study proved that the pretreatment in the pilot plant was not optimal. The highest ethanol yield achieved in the SSF was 69 % of the theoretical, which should be compared to the PDU material where over 90 % of the theoretical yield was achieved. The most evident reason was the low degree of hydrolysis of the pilot materials. Lower fermentabilities of these materials also seemed to contribute to the lower yields. Several possible explanations of the results are proposed; the residence times and scaling up-effects probably being the most reasonable ones. The SEM study also generated a possible explanation why the PDU material was more easily hydrolysed. The cellulose seemed to be more exposed and to contain larger pores. The enzyme comparisons indicated that Celluclast was a more efficient enzyme preparation initially. It was also proved that β-glucosidase addition do not affect the performance when using cellulases from Saf-ISIS, if high SSF yields are desired. 1