Tuesday, May 3, 2011
A Kraft paper mill produces chemical pulp by treating wood chips with white liquor, a mixture of sodium hydroxide, sodium sulfide, and sodium carbonate. Most of the hemicellulose fraction of wood chips released into liquor during pulping process. The resulting black liquor is combusted to recover chemicals and generate of steam and electricity. It is technically feasible to recover this fraction of carbohydrate and enhance its value by converting it into value-added products. Paper mill sludge is a solid waste material composed of short and fine fibers rejected in the paper making process. Because of its high carbohydrate content and well-dispersed structure, the sludges can be biologically converted to ethanol without pretreatment by Simultaneous Saccharificaton and Fermentation (SSF). Use of the mixture of prehydrolysate and pulp mill sludges as the fermentation feed can increase the product concentration. In bioconversion of the sludge, a certain amount of water is added to attain fluidity required for fermentation operation. In this study, prehydrolysate, in place of water, was added into the bioreactor along with the sludge. Under the proposed scheme, there was a net increase of total sugar input to the bioreactor above that of the base case, which led to increase of ethanol concentration. The experimental data detailing the proposed SSF bioprocess converting the mixed-feed to ethanol are presented.