Thermophilic Anaerobic Digestion of Vinasse in Pilot Plant UASB Reactor

Abstract

Vinasse from sugar-cane alcohol production is generated in great amounts in Brazil and is disposed on soil “in natura”. Only a few distilleries use mesophilic anaerobic digestion, so far, for gas recovery and vinasse treatment or conditioning, due to an unfavorable economical balance. Thermophilic anaerobic digestion was studied in a large-scale pilot-plant (75 m3 UASB reactor), since vinasses are generated at high temperatures, and no experiments on this subject are reported in the literature, except for a few laboratory assays using pure substrates and other wastewaters. This work demonstrates the feasibility of sugar-cane vinasse thermophilic anaerobic digestion in UASB reactors. The reactor was operated for 280 days, as far as possible like a full-scale plant; at applied organic loading rates of 25-30 kg COD/m3.day, 72% COD removal and 10 Nm3gas/m3.day could be achieved. Granulation of the sludge was essential in order to maintain good stability of the process; almost no soda was necessary for pH control. For full-scale implementation, re-start of the thermophilic process, after several months without feeding, has to be studied yet.