Produção biológica de hidrogênio e metano a partir de vinhaça e torta de filtro da cana-de-açúcar

Abstract

The Brazilian economy is strongly based in the agro-industrial sector, with sugarcane occupying a prominent position on the global stage. In this industry, substantial volumes of effluents and residues are generated, notably vinasse and filter cake, which are predominantly applied via fertigation, a practice associated with potential environmental risks. Anaerobic codigestion (CoAD) of these residues emerges as a promising alternative: filter cake can supply essential nutrients to vinasse, thereby adding value while enabling the generation of clean and renewable energy. In this study, biological hydrogen (H₂) and methane (CH₄) production were evaluated under both single-stage and sequential mode using vinasse and filter cake as substrates. During the H2 production phase, the effects of the organic matter-to-inoculum ratio (COD:VSS), thermal pretreatment of the inoculum, and vinasse supplementation were investigated. H2 production was found to be directly proportional to the COD:VSS ratio, with a ratio of 3:1 yielding a productivity (Qp) 173% higher than that obtained at 1:1. The use of untreated sludge outperformed inoculum pre-treated at 65 °C for 30 minutes, achieving an 80% higher yield. Preliminary assessment of vinasse supplementation indicated a 24-hour reduction in the lag phase. Based on these findings, co-fermentation of vinasse and filter cake was conducted to replace exogenous supplementation and explore potential synergistic effects. The adopted strategy involved evaluating different substrate proportions (Vx/Ty), where “x” and “y” represent the percentage contribution of COD from vinasse (V) and filter cake (T), respectively. The V50/T50 condition, conducted at 50 °C using untreated sludge, exhibited the best performance. Compared to vinasse mono-fermentation, this condition increased Qp by 362% (reaching 707 N-mL H₂·L⁻¹·d⁻¹) and reduced the lag phase by 80% (from 72 to 14 hours), achieving a maximum cumulative hydrogen production of 894 N-mL·L⁻¹ within 5 days. Furthermore, the process was successfully scaled up to stirred-tank reactors of 1.5 L and 7.27 L, yielding 687.3 ± 10 N-mL·L⁻¹ of H₂ within 2 days, while maintaining both Qp and lag phase duration, thus demonstrating high reproducibility (p > 0.05). In direct methanogenesis at 35 °C, lower COD:VSS ratios were more favorable: the 1:1 ratio achieved a higher yield (278 mL CH₄ per gram of COD consumed, gCODc) and an 80% shorter lag phase compared to the 3:1 ratio (172 mL CH₄/gCODc). When comparing methanogenic processes, sequential digestion of the effluent (EPH V50/T50) at 35 °C outperformed single-stage digestion. Relative to CoAD of the same mixture (V50/T50), which reached 226 mL CH₄/gCODc, the two-stage configuration increased the yield to 347 mL CH₄/gCODc. The sequential pathway also ensured highly efficient organic matter degradation, achieving an 80% COD removal and surpassing single-stage CoAD (70.3%). These results demonstrate that sequential production not only enables energy recovery from the fermentative phase but also maximizes methane conversion. It is concluded that the integrated valorization of these residues enhances overall energy recovery and supports the transition of the sugar-energy sector toward a sustainable, zero-waste biorefinery model.