EFFECT OF INOCULUM SOURCE ON THE ANAEROBIC DIGESTION OF MEZCAL VINASSES AT DIFFERENT SUBSTRATE-INOCULUM RATIOS

Abstract

Vinasses are a very harmful residue for the environment if no treatment takes place before their discharge. The present study focuses on the anaerobic digestion (AD) of mezcal vinasses for treatment and energy generation. The effect of two inoculum sources, anaerobic sludge and cattle manure, were assessed by biochemical methane potential assays (BMP), testing different substrate to inoculum ratios (SI-ratios). Mathematical modeling was performed using three sigmoidal bacterial growth curves (Gompertz, transference and logistic), in order to understand the kinetics of methane production. Anaerobic sludge was digested with vinasses at SI-ratios of 0.1, 0.3 and 0.4 and cattle manure at 0.3, 0.5 and 0.7. When using a 0.3 SI-ratio, the digestion of vinasses with manure showed the highest results regarding biogas (1025.44 ± 33.80 L/kgVS), methane (up to 81 %) and organic matter removal (54 % volatile solids removal). Manure indicated a higher specific methane yield growth, with a longer lag phase. Concentrations containing low vinasses content resulted in an inefficient AD due to the lack of organic matter, whilst concentrations with high vinasses content resulted in AD inhibition. The present work shows that cattle manure is an alternative inoculum source to achieve a more efficient anaerobic digestion. The optimal SI-ratio to be used for the digestion of vinasses is 0.3, at which the bacterial population has enough substrate to work efficiently.