Bioconversion of pretreated sugarcane vinasse into hydrogen: new perspectives to solve one of the greatest issues of the sugarcane biorefinery

Abstract

Currently, the disposal of sugarcane vinasse is one of the greatest issues of sugarcane biorefineries in Brazil because of the large volumes produced. To contribute with an alternative energy recovery process from this by-product, this study proposed a physicochemical pretreatment and adjustment of operating conditions to improve the performance of the acidogenic stage of the anaerobic digestion of sugarcane vinasse. Therefore, this study evaluated the influence of hydraulic retention time (decreasing from 8 to 6, 4, 2, and 1 h) on the bioconversion of pretreated sugarcane vinasse (5000 mg COD L−1) to hydrogen and value-added products. Two anaerobic fluidized bed reactors were operated under mesophilic (AFBR-M, 30 °C) and thermophilic (AFBR-T, 55 °C) conditions. Despite the low similarity between the bacterial populations of AFBR-M and AFBR-T (40% similarity), the maximum hydrogen production rates (0.27 ± 0.07 and 6.42 ± 1.46 L H2 day−1 L−1) and hydrogen yields (0.27 ± 0.07 and 1.06 ± 0.15 mmol H2 g COD−1) occurred at the hydraulic retention time of 2 h by reducing the values from 8 to 2 h. The highest COD/SO42− ratios of 17.4 and 25.1 were also observed in the effluents of the AFBR-M and AFBR-T, respectively, at the hydraulic retention time of 2 h. Under both mesophilic and thermophilic conditions, a similar metabolic distribution was observed at the HRT of 2 h (acetic, propionic, and butyric acids, for AFBR-M and acetic, propionic, butyric acids, and ethanol for AFBR-T). This finding indicates the functional similarity between bacterial populations in both reactors.