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Bioethanol Production from Alkali-Treated Cotton Stalks at High Solids Loading Applying Non-isothermal Simultaneous Saccharification and Fermentation

Chilari, Despoina, Dimos, Konstantinos, Georgoula, Georgia, Paschos, Thomas, Mamma, Diomi, Louloudi, Argiro, Papayannakos, Nikolaos, Kekos, Dimitris
Waste and biomass valorization 2017 v.8 no.6 pp. 1919-1929
X-ray diffraction, alkali treatment, cellulose, cotton, ethanol, ethanol production, fermentation, glucose, hydrolysis, lignin, saccharification, sodium hydroxide
Ground cotton stalks at a solid loading of 15% (w/v) were subjected to alkali pretreatment with different concentrations of NaOH (0–10% NaOH, w/w) at 121 °C/15ss psi for 60 min. Compositional analysis of the pretreated material revealed 31.9% lignin removal at the highest NaOH concentration applied, while structural changes in native and pretreated CS were evaluated through XRD analysis. Alkali-treated cotton stalks (ATCS) was hydrolyzed at 15% (w/v) ATCS concentration using 1–80 FPU/g cellulose Cellic® CTec 2. Glucose concentration reached 68.19 g/L at the highest enzyme loading. Factors affecting ethanol production namely enzyme loading (7–80 FPU/g cellulose), substrate concentration (15% and 20%, w/v) and pre-hydrolysis time (6–36 h) where evaluated implementing non-isothermal simultaneous saccharification and fermentation (NSSF). Ethanol production at different enzyme loading exhibited almost the same trend as in hydrolysis. When operating NSSF at 15% (v/w) ATCS increase in pre-hydrolysis time from 6 to 14 h resulted in increase on ethanol production which reached 21.85 g/L. In an attempt to increase ethanol production, ATCS at 20%, w/v substrate concentration was pre-hydrolyzed for 14, 24 and 36 h. The highest ethanol concentration was 34.80 g/L (55.40% of the maximum theoretical) in the NSSF preceded by 14 h pre-hydrolysis.