Influences of substrate concentration and Fe-loaded zeolite/bentonite on the methane yield in sugarcane vinasse anaerobic digestion

Every liter of sugarcane-based bioethanol production discharges 8–20 liters of liquid waste called vinasse, which is suitable for biogas production. However, biogas production from vinasse is hindered by the presence of phenolic compounds as inhibitors in anaerobic digestion. In this study, we investigated the improvement of specific methane yield in the anaerobic digestion of vinasse by adding a solid structure as a microbial immobilization medium. The ring-shaped zeolite/bentonite mixture loaded with particular amounts of Fe(II) cations was used as the medium. The medium was tested in vinasse anaerobic digestion with initial substrate concentrations ranging from 7,500 to 35,000 mg sCOD/L. The substrate concentrations affected both the soluble chemical oxygen demand (sCOD) removal rate and the methane yield. However, the amount of Fe(II) loading in the medium only affected the methane yield. Specific methane yields 85% higher than the control was obtained with the solid medium, i.e., 399.78 mL CH4/g sCOD, by adding 45 g media/g sCOD with an Fe(II) loading of 0.0016 mg Fe/g media. Based on the results, it was possible to increase biogas productivity by adding an Fe-loaded zeolite/bentonite medium to make the anaerobic digestion of vinasse more economically feasible.