Produção de biohitano a partir da vinhaça e melaço de cana-de-açúcar via digestão anaeróbica em dois estágios

Abstract

The search for alternative and sustainable energy sources has intensified, especially in the context of the energy transition and the need to reduce dependence on fossil fuels. Among these alternatives, biohythane stands out, a biological mixture of hydrogen (H₂) and methane (CH₄) generated through the anaerobic digestion of organic waste. Its combustion mainly results in the emission of water vapor, in addition to presenting a higher energy content compared to fossil fuels. Moreover, its production from renewable substrates, such as industrial and domestic waste rich in carbohydrates, becomes a promising solution for clean energy generation. In this scenario, the present research aimed to evaluate the production of biohythane in anaerobic fluidized bed reactors (AFBRs), using the co-digestion of vinasse and sugarcane molasses as substrate. These agro-industrial residues, originating from sugarcane processing, have high carbon concentrations, favoring anaerobic digestion and the conversion of organic matter into biogas. Molasses, a byproduct rich in organic matter, is widely used in biogas production by biological processes, while vinasse, resulting from ethanol production, also stands out as a potential source for biohythane generation. Thus, the integration of these residues in anaerobic systems constitutes a viable and environmentally sustainable alternative for renewable energy generation. For the study, two AFBRs were operated under progressive increase of the organic loading rate (OLR), with hydraulic retention times (HRT) varying between 6 h, 4 h, and 2 h for the acidogenic reactor while the methanogenic reactor was maintained constant with fixed HRT of 16 h. The reactors had total and useful volumes of 1.2 L and 0.9 L, respectively. Sludge from a UASB reactor used in domestic sewage treatment was used as inoculum and crushed expanded clay (diameter between 2.8 – 3.35 mm) was employed as support material for microbial adhesion. The first reactor was operated for 102 days and the second for 51 days, with feed proportions of 50% vinasse and 50% molasses, maintaining the influent COD concentration fixed at 25 g.L⁻¹. The results indicated that hydrogen production was significantly influenced by the hydraulic retention time, reaching its highest average yield in the third experimental phase. A significant increase in volumetric hydrogen production was observed from 0.20 L.h⁻¹.L⁻¹ (HRT of 6 h) to 8.90 L.h⁻¹.L⁻¹ (HRT of 2 h), with an increase in yield from 0.74 mol H₂.mol⁻¹ glucose to 1.12 mol H₂.mol⁻¹ glucose at HRT of 2 h. As for methane production, the results showed an average yield of 1.22 ± 0.64 L CH₄/g COD and volumetric production of 1.9 ± 4.6 L CH₄/L. During the operation of the acidogenic reactor, the presence of acetic acid (HAc) and ethanol (EtOH) was observed in all phases, with relative HAc concentrations varying between 74.2 ± 73.0% at HRT of 6 h, between 70.2 ± 54.8% at HRT of 4 h and 68.7 ± 64.4% at HRT of 2 h. As for EtOH concentrations, they ranged between 25.8 ± 11.5% at HRT 6 h, between 29.8 ± 9.6% at HRT 4 h and 31.3 ± 11.8% at HRT 2 h. The data highlight the potential of co-digestion of vinasse and molasses in two phases for biohythane generation, constituting a viable and sustainable alternative for renewable energy production.