2.2. Analysis of paper sludge
The paper sludge was dried to constant weight at 90 ◦C, followed
by cooling in a desiccator, and weighed. The carbohydrate content
of the dried paper sludge was determined by a t wo-step quantita-tive hydrolysis starting with 30 ◦C in 72% (w/w) H2 SO4 for 1 h. The
solid residue was rins d and dried, followed by a second hydrolysis
at 121 ◦C in 4% (w/w) H2 SO4 for 1 h. The hydrolyzed composi-tion was determined via HPLC using an Aminex column HPX-87H
(30 0 mm × 7.8 mm) (Bio-rad, Richmond, CA) [2]. Values for wt% cel-lulose in samples were calculated by adding the results from the
two quantitative hydrolysis from the following equation [4]: