Anaerobic co-digestion of sugarcane press mud with vinasse on methane yield

The conversion efficiency of high solids waste digestion as sugarcane press mud (P) may be limited due to hydrolysis step. The option of co-digestion with vinasse, main liquid waste generated from ethanol production, was investigated under batch regime at mesophilic conditions (37.5 ± 1 °C) and the best mixture was evaluated under semicontinuous regime in stirred-tank reactors. The maximum values for methane yield in batch tests were for V75/P25 and V50/P50 mixtures (on basis of the chemical oxygen demand (COD) percentage added in the mixture), with an average value of 246 N mL CH4 g−1 CODfed, which was 13% higher than that of press mud alone. A highest methane production rate of 69.6 N mL CH4 g−1 CODfed−1 d−1 was obtained for the mixtureV75/P25. During the experiment carried out in CSTR reactors, the organic loading rate (OLR) was increased from 0.5 up to 2.2 g VS L−1 d−1. Methane yields of 365 L CH4 kg−1 VS and biogas productivities of 1.6 L L−1 were obtained in co-digestion, which was 64% higher in comparison to mono-digestion. The performance of the process in mono-digestion was less stable than in co-digestion, with a significant fall of methane yield to 1.8 kg VS m−3 d−1, and a partial inhibition of the methanogenic archaeas when the OLR was increased up to 2.2 kg VS m−3 d−1. The co-digestion of vinasse with press mud is a good option for the treatment of streams at the alcohol-sugar industry.