Produção metanogênica a partir da codigestão anaeróbia de silagem de capim - elefante com vinhaça em reator em batelada

Abstract

The use of biomass as a substrate in anaerobic digestion for energy production purposes has been highlighted in the last three decades, considering climate emergency and the impacts arising from non-renewable energy sources. In this context, sugarcane vinasse and elephant grass have significant potential for biogas production, but their application via anaerobic co-digestion has been little investigated. Therefore, the aim of this study was to evaluate the methane yield of the co-digestion of these substrates in batch reactors, using Box-Behnken experimental design. The adopted factors were ensiling time of elephant grass (40, 80 and 120 days), silage:vinasse ratio (25:75, 50:50 and 75:25), and concentration of alkaline pretreatment of elephant grass (NaOH 0.5%, 2.25% and 4%w/v). Most reactors showed COD and carbohydrate removal greater than 60%, indicating significant removal of organic matter and efficiency of anaerobic digestion. Cumulative methane production data was properly fitted to the modified Gompertz sigmoid model (R2 ≈ 0.99). Cumulative methane yield values ranged from 190.77 to 1,729.80 mLCH4/gSV. The highest yields were observed in the reactors which used silage:vinasse ratio equal to 25:75, ensiling time between 80 and 120 days, and pre-treatment solution of NaOH 2.25%w/v to 4.00%w/v. According to ANOVA, proportion between substrates was the only factor with a significant effect (p < 0.05) on cumulative methane yield. The regression model proposed to estimate the yield as a function of the adopted factors showed a high regression coefficient (R² = 0.93). It is expected that the results will contribute to the optimization and implementation, on a larger scale, of bioenergy generation projects from the anaerobic treatment of sugarcane vinasse and elephant grass silage.