Optimization of Chemical Pretreatments Using Response Surface Methodology for Second-Generation Ethanol Production from Coffee Husk Waste

• Published in: Bioenergy research Vol. 14; no. 3; pp. 815 - 827
• Main Authors: Morales-Martínez, J. L., Aguilar-Uscanga, M. G., Bolaños-Reynoso, E., López-Zamora, L.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2021; Springer; Springer Nature B.V
• Subjects: Acetaldehyde; acid hydrolysis; Alcohol; Alcohol, Denatured; Alternative energy sources; Ammonium sulfate; Analysis; beverage industry; biomass; Biomedical and Life Sciences; carbon; Carbon sources; Cell culture; Cellulose; Coffee; Coffee industry; culture media; delignification; energy; Energy minerals; Enzymes; Ethanol; ethanol production; exocarp; Fermentation; Fossil fuels; Glucose; Hemicellulose; hulls; Hydrogen peroxide; Hydrolysis; International economic relations; Life Sciences; Lignin; liquids; Methods; Nutrients; Optimization; Pericarp; Plant Breeding/Biotechnology; Plant Ecology; Plant Genetics and Genomics; Plant Sciences; Potassium phosphate; Potassium phosphates; Pretreatment; Production data; Production processes; Raw materials; Renewable energy; Response surface methodology; Sulfuric acid; wastes; Wood Science & Technology; Renewable source; Response surface methodology; Glucose; Enzymatic hydrolysis; Cellulose
• ISSN: 1939-1234; 1939-1242
• DOI: 10.1007/s12155-020-10197-6

Within the strategies of substitution of energy from fossil fuels by renewable energies, the research is based on second-generation ethanol production (2G ethanol). One of the raw materials considered for this is residual biomass of the coffee industry, being the subject of study here. The cellulose contained in the coffee husk (coffee husk or coffee skin or coffee exocarp or pericarp) was maximized using pretreatment processes. In dilute acid hydrolysis (DAH), using a fixed 1:6 w:v solid to liquid ratio (SLR), process times (35, 45, 55 min) and H 2 SO 4 concentrations (3, 4, 5% v/v) were evaluated, achieving 53.63% hemicellulose removal. A delignification process resulted in 58.82% lignin removal, evaluating the effect of process times (30, 35, 40 h) and SLR (1:8, 1:10, 1:12 w:v) at a fixed concentration of 8% v/v H 2 O 2 . A 115.59 g/L glucose concentration was obtained with an interaction of fixed concentrations of 4–6% w/w Cellic CTec3 enzyme and 6:1 to 1:12 v:w SLR. The fermentation process considered the composition variation of the culture medium (enriched culture C1 and non-enriched culture C2), generating ethanol at 48.19 and 29.02 g/L concentrations, respectively. Fermentation efficiency ( η f ) was improved from 21.99 to 81.74% with the addition of inorganic nutrients (KH 2 PO 4 , (NH 4 ) 2 SO 4 , and MgSO 4 ·7H 2 O). These results confirmed that the optimization of the pretreatments in coffee husk waste favored the cellulose production and facilitated the enzymatic process to produce a high glucose concentration, revealing these residues as a carbon source promising for second-generation ethanol production.