Microwave-Assisted Alkali Delignification Coupled with Non-Ionic Surfactant Effect on the Fermentable Sugar Yield from Agricultural Residues of Cassava

Cassava stem, leaves and peel are agricultural residues generated as waste biomass during the cultivation and processing of cassava. The potential of these biomasses as feedstock for ethanol production depends on the effective deconstruction via pretreatment and saccharification. The effect of alkaline hydrogen peroxide (AHP) treatment on microwave (MW)-irradiated or steam-exposed aqueous slurry was compared with MW-irradiation (300 W) of alkali slurry in delignifying the biomass and degrading the polysaccharides. Cellulose was degraded to a higher extent than hemicellulose in the AHP treatments. The steam-exposed and AHP pretreated residues on saccharification with Cellic (Cellulase complex) alone or Cellic along with Tween 20 resulted in high conversion of carbohydrate to reducing sugars (RS) in leaves (64-70%) and peel (74- 78%), with slightly lower conversion in stem. MW-irradiation of alkali slurry (5 min.) followed by Tween 20 supplemented saccharification was a better strategy degrading cellulose and hemicellulose to very high extent. Tween 20 supplementation was beneficial in enhancing the RS release from the biomasses even when Cellic dosage was halved. Ultrastructural studies indicated the disappearance of starch granules from stem and peel samples after MW-irradiation and saccharification, while fragmented cellulose fibers were visible in leaf samples. The study showed that MW-assisted alkali pretreatment followed by saccharification with Cellic in presence of Tween 20 was very effective in releasing maximum sugars from these biomasses.