Paper sludge is a solid residue arising from wood pulping and paper-making operations. Sludge treatment is costly and poses a disposal problem in the paper mill industries. Therefore, this by-product could be an attractive raw material for ethanol production due to its high and accessible cellulose content [4]. However, the high ash content of paper sludge could cause handling problems
and the economy of the process is mainly dependent on the utiliza-tion of the solid residue, lignin, which constitutes approximately 25% (w/w) of the raw material [5].