Intensification of Bioethanol Production by Simultaneous Saccharification and Fermentation (SSF) in an Oscillatory Baffled Reactor (OBR)

Bioethanol is an alternative transport fuel produced mainly by the biochemical conversion of biomasses. This can be carried out efficiently and economically by simultaneous saccharification and fermentation (SSF): a process which integrates the enzymatic saccharification of the cellulose to glucose with the fermentative synthesis of ethanol. However, the SSF unit operation still contributes nearly 50% to the cost of ethanol production. For cellulosic ethanol to be cost competitive, there is the need to intensify the production process in smaller, more efficient and more economical bioreactors. In this work, SSF was performed in an intensified form of plug flow reactor, called the Oscillatory Baffled Reactor (OBR). The OBR is a continuous tubular reactor fitted with equally-spaced orifice plate baffles. An oscillatory component, provided by moving bellows in this design, is superimposed on the net flow through the reactor, generating short-lived vortices due to the interaction of the oscillating fluid with the baffles. This results in uniform mixing in each of the inter-baffle regions, with each behaving as a stirred tank reactor (STR), producing a plug flow residence time distribution (RTD) for the reactor as a whole, in which the mixing effects are largely decoupled from the mean flow (unlike conventional PFRs). The process was evaluated using 2.5% SigmaCell cellulose, 40 FPU cellulase loading/g of cellulose and 10% cellobiase. Saccharomyces cerevisiae was employed as the fermenting organism at 38 C and pH 4.8. In the first part of this work the use of the OBR resulted in a 7% increase in glucose yield compared to a shake flask, after 48 h of saccharification and 8.0 g/L ethanol in the OBR. This represented 89.8 % of the theoretical yield, as compared to 7.7 g/L in the shake flask representing 81.29%, a difference of 9 percentage point. This increased glucose yield is attributable to better mixing in the OBR.