Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Combined production of liquid biofuel and enzymes from fiber sludge originating from sulfite and sulfate pulping processes was investigated. The fiber sludges were fermented to cellulosic bioethanol using simultaneous saccharification and fermentation (SSF). The enzymes and Saccharomyces cerevisiae yeast cells used in the first fermentation were recirculated for a second SSF fermentation with fiber sludge. The ethanol production in the SSF experiment with sulfite fiber sludge (SIFS) was faster than for the experiment with sulfate fiber sludge (SAFS). After 48 h, the concentration of ethanol after the first SSF was 64.7 g/L for the SIFS compared to 45.6 g/L for the SAFS. In the first SSF experiment, an average productivity of 3.1 g/L/h was achieved for the SIFS, while the average productivity for the SAFS was 2.1 g/L/h. The second SSF, which was undertaken using recycled yeast and enzymes from the first SSF and fresh fiber sludges, yielded ethanol concentrations of 38.3 g/L for the SAFS and 24.4 g/L for the SIFS after 72 h. The spent fiber sludge hydrolysates from sulfate (SSAFSH) and sulfite pulping (SSIFSH) were then in turn used as growth medium for recombinant Aspergillus niger carrying the endoglucanase-encoding Trichoderma reesei (Hypocrea jecorina) Cel7B gene. The cellulase activities obtained with SSAFSH and SSIFSH were similar and ranged between 2,700 and 2,900 nkat/ml. Analyses of the recombinant endoglucanase indicate that the main part was glycosylated and had a molecular mass of 76 kDa, while a minor part had a molecular mass of 47 kDa.