(624d) Butanol Production from Paper Mill Sludge By Simultaneous Saccharification and Fermentation (SSF)

Paper mill sludge is a solid waste material composed of pulp residues and ash generated from pulping and paper making process. The carbohydrate portion of the sludge from Kraft paper mill has chemical and physical characteristics similar to those of commercial wood pulp, making it an attractive feedstock for bioconversion to value-added products. In this study, the paper mill sludge was investigated as a feedstock for production of butanol. For this purpose, simultaneous saccharification and fermentation (SSF) was applied to the sludge under various conditions using Clostridium acetobutylicum (ATCC-824) and cellulase (Novozyme, C-Tec 2). The results indicate that the overall bioconversion efficiency under optimal conditions is similar to those obtainable from pure cellulose (Avicel or Solka Sloc), and it is only slightly lower than those attainable from pure glucose. Also notable is that the bioconversion of the sludge does not require pretreatment because of its high carbohydrate content and well-dispersed structure. The only obstacle of concern was the inhibitory effects of the ash content to enzymatic hydrolysis. A partial separation of ash was therefore necessary for efficient conversion of the sludge. The representative performance indices of the SSF of the sludge were: 15.5 g/L of total solvents (Acetone+Butanol+Etahnol) from the sludge loading equivalent to 58 g-glucan/L, 10 FPU/g-glucan, and 120 h of SSF. The details of the SSF performance including product yield, distribution of ABE, product concentration, and productivity are presented, and the effects of enzyme loading, solid loading, and ash content are discussed.