Hydrothermal pretreatment and acid hydrolysis of coconut pulp residue for fermentable sugar production

Abstract

Coconut pulp residue is the waste generated after the extraction of milk and oil. This material became an interest as feedstock for the production of biofuels and other bioproducts in a biorefinery context. The present study aimed to improve the release of sugar from coconut pulp residue through the optimization of sequential hydrothermal and acid pretreatment. An experimental design was constructed with the central composite design (CCD) response surface method using factors of the hydrothermal residence time of 20, 40, 60min and post-acid treatment concentration of 1%, 2% and 3% (v/v) in constant temperature and time of 121°C and 20min. Total sugar yields of 32.47, 27.51 and 26.72g/L were observed after hydrothermal pretreatment time of 20, 40 and 60min, respectively. Furthermore, when the pretreated solid residues were subjected to acid pretreatment, the results revealed an increment of 90% on reducing sugars after reaction with 1%, 2% and 3% H2SO4. Statistically, the optimum condition for the two-stage hydrolysis of coconut pulp residue was 60min hydrothermal pretreatment followed by 3% H2SO4 acid hydrolysis with maximal reducing sugar release of 120.71g/L. In addition, the degree of polymerization achieved was 1.2, indicating no further hydrolysis required. The current study demonstrates that two-stage pretreatment improves saccharification and provide sufficient sugars for the fermentation process.