Comparative study of pretreated corn stover for sugar production using cotton pulping black liquor (CPBL) instead of sodium hydroxide

• CPBL which contains appreciable alkaline was used to pretreat corn stover.
• Sugar yield of corn stover pretreated with CPBL was comparable to the one with NaOH.
• 82.1% of lignin was removed by CPBL pretreatment with addition of Na2SO3 (SS-CPBLP).
• 81.8% of total sugar yield was obtained after enzymatic hydrolysis by SS-CPBLP.
• Utilization in biomass pretreatment is a useful and environmentally friendly way for the CPBL.

Black liquor is a significant water pollution source, and many investigations related to black liquor have been performed over the years. Recovering cotton pulping black liquor (CPBL) is difficult due to its low lignin content. This study presents corn stover pretreatments using CPBL alone and in combination with other agents to improve the cost-effectiveness of the biomass-to-sugar conversion. The results showed that 78.4%, 74.9% and 82.1% of the lignin was removed after pretreatment with sodium hydroxide (SHP), CPBL (CPBLP) and CPBL combined with sodium sulfite (SS-CPBLP). Accordingly, the glucose and xylose contents in the pretreated corn stover increased to more than 62% and 24% after CPBLP and SS-CPBLP, respectively, which was comparable to SHP. Moreover, the total sugar yield of CPBLP and SS-CPBLP was 66.4% and 75.3%, which was 2.9% and 11.8% higher than that of SHP (63.5%), respectively. The lignin content in the black liquor rose from 6.9 g/L to 17.8 g/L, and the sulfonation degree of the black liquor reached 0.8 mmol/g after SS-CPBLP, which had a positive effect on further lignin utilization. The results indicate that the use of CPBL for corn stover pretreatment not only efficiently produced fermentable sugar products, but also presented a solution to the CPBL pollution issue. Thus, this process represents a method of waste recycling with high industrialization potential.