Two-stage semi-continuous hydrogen and methane production from undetoxified and detoxified acid hydrolysates of agave bagasse

Previous works showed the positive effect of detoxification on fermentative hydrogen production using acid hydrolysates of agave bagasse in batch assays. However, the influence of detoxification on process stability and energy recovery through a subsequent methanogenesis stage that allows bringing this technology closer to fullscale applications has yet to be addressed. Therefore, this work aimed to compare the performance of detoxified and undetoxified agave bagasse acid hydrolysates for two-stage hydrogen and methane production in semicontinuous reactors. First, hydrogen was produced in an anaerobic sequencing batch reactor (AnSBR), achieving volumetric hydrogen production rates (VHPR) of 10 and 26.30 mL H2 L-1 h-1 for the undetoxified and detoxified hydrolysates, respectively. The energy recoveries (as hydrogen) were 0.02 kJ g-1-bagasse for the undetoxified hydrolysate and 0.18 kJ g-1-bagasse for the detoxified one. Secondly, the effluents from hydrogen production reactors were used as a substrate in methanogenic AnSBRs, where similar volumetric methane production rates (VMPR) and energy recoveries (as methane) were obtained for undetoxified (0.48 L-CH4 L-1 d-1 and 3.82 kJ g-1-bagasse) and detoxified (0.44 L-CH4 L-1 d-1 and 4.09 kJ g-1-bagasse) hydrolysates. Results demonstrated that detoxification considerably increases the overall process stability and hydrogen production. Conversely, the detoxification process did not significantly enhance methane production. Additionally, unlike the detoxified hydrolysates, the use of undetoxified hydrolysates showed similar global energy yields (H2 + CH4) with or without nutrients addition (3.84 vs. 3.21 kJ g-1-bagasse), pointing out that detoxification is only suggested for processes where hydrogen is the target product.