Methane and hydrogen production from anaerobic digestion of soluble fraction obtained by sugarcane bagasse ozonation

In the present study, the ozonation of sugarcane bagasse (SB) at different operational conditions (pH, time, liquid-to-solid ratio (LSR)) was evaluated with the aim of generating a soluble liquid fraction (SLF) suitable for biogas production (CH4 and H2) via anaerobic digestion and a solid fraction prone to enzymatic hydrolysis and 2G ethanol production. The SLFs obtained were characterized for sugars, total organic carbon (TOC), soluble lignin, furans and other components identified by GC/MS. The results showed that it was possible to solubilize 45.2% of lignin, 48.3% of hemicelluloses and 40.7% of cellulose with the use of ozone (8 mg min−1) at pH 11 for 15 min, employing a LSR of 13.3 mL g−1. The best results of biochemical methane potential (BMP) and biochemical hydrogen potential (BHP) were 2.6 Nm3 of CH4 and 0.18 Nm3 of H2 per kg of TOC, respectively. An energy balance for the best pretreatment conditions indicates that the combustion of such biogas led to an energy surplus of 0.1 MJ kg−1 SB for methane and to an energy deficit of 0.191 MJ kg−1 SB for hydrogen. Potentially inhibitory compounds for anaerobic digestion such as oxalic acid, butanal, xylitol, furanone, benzaldehyde, d-erythrotetrofuranose, d-erythro-pentofuranose and 2,5-furandione were identified in the hydrolysates, which negatively affected the anaerobic digestion and the energy balance. Nevertheless, the energy generated from the hydrolysates (as biogas) and from the ozonized solid fraction (as 2G ethanol) offsets the ozonation energy input and led to positive energy balance.