Monday, April 30, 2007

Simultaneous saccharification and co-fermenation of paper mill sludges into ethanol by cellulase and recombinant E. coli

Li Kang and Y. Y. Lee. Department of Chemical Engineering, Auburn University, 207 Ross Hall, Department of Chemical Engineering, Auburn, AL 36849

Paper mill sludges are solid waste material composed of pulp residues and inorganic additives associated with paper making. Because of high carbohydrate content, the pulp mill sludges have been considered as a potential feedstock for bioconversion into value-added products. The carbohydrate portion of the sludges has similar chemical and physical characteristics as pulp. Therefore the bioconversion may be applied without pretreatment, a significant economic benefit. On the other hand, the sludges also contain high level of ash content, which may adversely affect the bioconversion process. In this study, primary and recycle sludges were collected from various pulp mills and investigated as feedstock for bioconversion to ethanol. The sludges were subjected to standard enzymatic digestion test with and without pH adjustment. The feedstocks were then put through simultaneous saccharification and Co-Fermentation (SSCF) using Spezyme-CP and recombinant E. coli (KO11). The yield of ethanol from the SSCF operated without pH control generally exceeded the yield of ethanol calculated from the enzymatic digestion data. The overall yields based on total glucan and xylan were in the range of 70-80% of theoretical maximum. The SSCF proceeded well without pH control whereas the enzymatic digestion required pH control. It is speculated that the ash content, which is alkaline, is being neutralized by the acidic components produced during the SSCF. The SSCF data were further analyzed to determine the optimum conditions and assess the overall performance.