Comparative Food/Microorganism Ratio Aspects of Hydrogen Production Through Pentoses Liquor from Sugarcane Bagasse at Mesophilic and Thermophilic Temperatures
Creators: name: Vasconcelos Ferreira, Filipe
name: Peixoto, Guilherme
name: Mattiello Francisco, Luisa
name: Mockaitis, Gustavo
name: Zaiat, Marcelo
Publisher: name: figshare
Year: 2023
Subjects: classificationCode: 300109
subject: Non-genetically modified uses of biotechnology

description: To date there is no industrial process that use pentoses liquor from sugarcane bagasse to produce biofuels. Thus, the present study aims to produce biohydrogen from pentose liquor fermentation. The H<sub>2</sub> production was carried out in 2-liter batch reactors with reaction volume of 1 L at different temperatures (30 and 55 ºC) using thermally pretreated UASB inoculum. At both mesophilic and thermophilic conditions (represented here for codes “m” and “th”, respectively) were made the same set of experiments: the food/microorganisms (F/M) ratios were used for evaluation of fermentable by-products (volatile acids, solvents and biogas). All reactors were maintained under constant agitation in reciprocating shakers (100 min<sup>-1</sup>) with initial pH 6.0 over 35 days. The main source of carbon came from xylose obtained from pentose liquor (quite 85% of liquid content is composed by xylose). For comparative effects, blank samples of pure Xylose (Sigma) were used. Different substrate and microorganisms relations (F/M) were applied in reactors varying organic matter loadings (1000 – 20000 mg O<sub>2</sub>·L<sup>-1</sup>) and fixing biomass concentration at same time (500 mg SVT<sup>-1</sup>). Thus, the F/M ratios were 2, 10, 20 and 40 mg O<sub>2</sub>·L<sup>-1</sup> · mg SVT<sup>-1</sup> corresponding to Ia, IIa, IIIa and IVa conditions, respectively. The extraction of pentoses liquor was carry out by hydrolysis of lignocellulose material with diluited acid: H<sub>2</sub>SO<sub>4</sub> solution (1% v/v) onto dry bagasse (1:9 w/w). This study adopted the residual first-order model for substrate's kinetic and the simple dose-response sigmoidal model for evaluation of accumulated hydrogen production. In general, the xylose reactors (XRs) had greater H<sub>2</sub> productions at mesophilic conditions than thermophilic ones when were compared corresponding conditions (same F/M ratio); meanwhile, pentose liquor reactors (PLRs) showed the highest H<sub>2</sub> productions at 55 ºC. The highest hydrogen yields (HYs) were at thermophilic temperature in both type of reactors (except in the tXR-I condition). The highest HY was recorded in the tPL-I condition with value of 1.9 mol-H<sub>2</sub> molxylose-1. We proposed the novel acetate-butyrate-ethanol fermentation type on H<sub>2</sub> production for mXRs due to main byproducts were acetate, butyrate, and ethanol. The rest of reactors (mPLRs, tXRs and tPLRs) followed the butyric-acetate type fermentation. The main drawbacks for H<sub>2</sub> production were: furfural and hemifurfural compounds, initial acetic acid concentration, sulfate-reducing bacteria presence, homoacetogenic reactions and probable low number of non-specific xylose degrading bacteria in sludge. Substrate degradation rates were comparatively (pairwise comparison for same F/M ratio) greater at mesophilic temperature than thermophilic one owing to the mesophilic characteristic of innoculum. At both temperatures, PLRs had higher kinetic constants than XRs once the first ones had less concentrated solutions. Finally, the pentoses liquor can be considered a suitable residue for biohydrogen production.