(782a) Lactic Acid Production From the Mixture of Kraft Paper Mill Sludge and Hemicellulose Prehydrolysate

Paper mill sludge is a solid waste composed of pulp residues and ash generated from pulping and paper making processes. The carbohydrate portion of the sludge has chemical and physical characteristics similar to pulp. It can be biologically converted to value-added products without pretreatment. Most of the hemicellulose fraction of pulp mill feedstock is released into black liquor during the pulping process and combusted to recover energy. It is feasible to recover this fraction of carbohydrate for bioconversion. The prehydrolysate can be produced by steam or hot-water treatment. The sugar concentration, however, is far below the level usable as fermentation feed. In this study, we have investigated a bioconversion scheme in which the mixture of these two feedstocks is converted to lactic acid. For this purpose, simultaneous saccharificiaton and fermentation (SSF) was applied using Lactobacillus delbrueckii (ATCC 7830) and cellulose enzyme (Novozyme CTec-2). The bioreactor feed was prepared mixing Kraft pulp mill sludge and the prehydrolysate generated from pine wood by hot-water extraction. The prehydrolysate was detoxified by overliming and charcoal treatment. The SSF was carried out without pH control since calcium carbonate in the sludge, the main inorganic ingredient in the ash, acted as a neutralizing reagent. The main carbohydrate in the prehydrolysate, mannose, and the Kraft sludge were converted efficiently giving above 80% of theoretical yield with enzyme loading less than 10 FPU/g-hexose. The performance data and the details of the bioprocess, prehydrolysate preparation, and detoxification procedures are presented in this paper.