After a four-day treatment, cellulose, hemicellulose and lignin contents in the ground poplar processing residues were decreased considerably, especially for lignin. The decrease of which ranged from 11.1% to 20.5%, with NaOH dose increased from 3.0% to 7.0%, respectively (Table 3). Lignin is closely linked with cellulose and hemicellulose in cell wall and protecting cellulose from destruction (Zhu et al., 2010). The removal of lignin by NaOH released cellulose and improved poplar processing residues biodegradability. The characteristics of polar processing residues after NaOH treatment are shown in Table 4.