Anaerobic digestion of palm oil, ethanol, and tequila production by products

Abstract

This study explored the interactions between alkaline hydrothermal pretreatment (AHPT) operational conditions temperature (°C), NaOH concentration (M) and residence time (min) on the compositional characteristics of the solid (SH) and liquid hydrolysate (LH) obtained from AHPT of sugarcane bagasse (SCB), empty fruit bunch (EFB) and agave bagasse (AB). The experimental design was carried out with a three factors five levels (−훼, −1, 0, 1, and +훼) central composite rotatable design. Response variables for the liquid hydrolysate included glucose, xylose and arabinose content. Whereas the effects on the solid hydrolysate were evaluated with delignification and solids recovery (%). Biogas production and in situ biogas upgrading by co digestion of SH and NaOH rich LH was evaluated against mono digestion of raw and treated fibers. Therefore, methane production and methane content in the biogas were also considered response variables. Compositional characteristics were fiber dependent. Glucose, xylose and arabinose were found in SCB and AB LHs whereas for EFB LH cellobiose was also detected. A significant (p-value <0.05) linear interaction between treatment temperature and glucose release was found for SCB and AB. EFB showed significant (p-value <0.05) a quadratic interaction between temperature and retention time with glucose release. Arabinose presented a significant (p-value <0.05) linear positive interaction with temperature and NaOH concentration in all fibers. Delignification of SCB had a significant (p-value <0.05) negative correlation with the coupled effect of temperature and NaOH concentration. Solids recovery showed a significant (p-value <0.05) negative interaction with temperature and NaOH concentration for all fibers. Methane production from SCB hydrolysates co digestion presented significant (p-value <0.05) interaction with NaOH concentration and retention time. EFB hydrolysates co digestion presented a significant (p-value <0.05) interaction with temperature and NaOH concentration. Methane content in biogas presented a significant (p-value <0.05) linear interaction with temperature and NaOH concentration. No energy gain from pretreated SCB was observed. A maximum energy gain of 3.5MJ Kg-1 for pretreated empty fruit bunch. Agave bagasse presented a maximum net energy gain of 4.8 MJ Kg-1.Keywords: Empty fruit bunch; sugarcane bagasse; agave bagasse; hexoses; pentoses; lignin degradation.