Anaerobic digestion of hemicellulose hydrolysate produced after hydrothermal pretreatment of sugarcane bagasse in UASB reactor

In the context of a sugarcane biorefinery, sugarcane bagasse produced may be pretreated generating a solid and liquid fraction. The solid fraction may be used for 2G bioethanol production, while the liquid fraction may be used to produce biogas through anaerobic digestion. The aim of this study consisted in evaluating the anaerobic digestion performance of hemicellulose hydrolysate produced after hydrothermal pretreatment of sugarcane bagasse. For this, hydrothermal pretreatment was assessed in a continuous upflow anaerobic sludge blanket (UASB) reactor operated at a hydraulic retention time (HRT) of 18.4 h. Process performance was investigated by varying the dilution of sugarcane bagasse hydrolysate with a solution containing xylose and the inlet organic loading rate (OLR). Experimental data showed that an increase in the proportion of hydrolysate in the feed resulted in better process performance for steps using 50% and 100% of real substrate. The best performance condition was achieved when increasing the organic loading rate (OLR) from 1.2 to 2.4 g COD/L·d, with an organic matter removal of 85.7%. During this period, the methane yield estimated by the COD removal would be 270 L CH₄/kg COD. Nonetheless, when further increasing the OLR to 4.8 g COD/L·d, the COD removal decreased to 74%, together with an increase in effluent concentrations of VFA (0.80 g COD/L) and furans (115.3 mg/L), which might have inhibited the process performance. On the whole, the results showed that anaerobic digestion of sugarcane bagasse hydrolysate was feasible and may improve the net energy generation in a bioethanol plant, while enabling utilization of the surplus sugarcane bagasse in a sustainable manner. - Highlights: • Hemicelluloses were obtained after hydrothermal pretreatment of sugarcane bagasse. • Anaerobic digestion of hemicellulose hydrolysate was assessed in a UASB reactor. • Hydrolysate dilution and OLR were varied for studying the process performance. • The highest COD removal (86%) was obtained at an OLR of 2.4 g COD/L·d. • Methane yield was estimated at 270 L CH₄/kg COD during the best process condition.