Solving the bottlenecks of vinasse biodigestion: High-rate year-round methane production driven by fermented sulfate-free vinasse and molasses

This study investigated the use of fermented sulfate-free vinasse (season) and molasses (off season) as substrates to obtain enhanced year-round methane production in sugarcane biorefineries. Two second stage methanogenic structured-bed reactors operated at different temperatures (30oC and 55oC) were subjected to increasing organic loading rate (OLR) levels (1.0 to 20.0 kg COD m-3 d-1) in an experimental simulation of sequential periods of season, off season and season. Pre-fermenting vinasse and molasses was imperative for maintaining efficient organic matter conversion (80 to 90%) into methane, regardless of the significant differences in lactate and phenols availability. Methane content in biogas over or equal 80% and methane yield over or equal 330 NmL CH 4 g-1 COD were observed in both reactors, with no observation of organic overloads. The results point towards a highly efficient strategy to maintain year-round high-rate biogas production from sugarcane vinasse, although the relatively high molasses demands can trigger an internal competition (with ethanol production) for substrate.