AbstractThe effects of pH and sulfonated lignin (SL) on the saccharification of enzymatic hydrolysis were investigated using acid bisulfite (AS)- and green liquor (GL)-pretreated poplar as substrates. The enzymatic sugar conversions of AS- and GL-pretreated poplar could reach high levels at pH 4.8. The sugar conversions of both AS- and GL-pretreated poplar solids increased when hydrophilic SL was used as an additive in the enzymatic hydrolysis. With SL addition, the optimal pH of AS-pretreated poplar moved to 5.1–5.7, while that of GL-pretreated poplar showed no significant difference. The sugar conversions of AS- and GL-pretreated poplar went up and then leveled off with SL charges from 0.05 to 0.3 g/g-substrate. The highest total sugar conversions increased from 76.4% and 86.9% (pH 4.8, without SL) to 83.5% (pH 5.4, SL 0.3 g/g-substrate) and 90.9% (pH 5.0, SL 0.2 g/g-substrate) for AS- and GL-pretreated poplar, respectively.