KINETICS OF BIOGAS GENERATION FROM MICROBREWERIES ORGANIC WASTES

Abstract

The kinetics of methane generation was studied based on the anaerobic digestion of organic waste from a microbrewery. In particular, the effect of temperature and the concentration of total solids (TS) were analyzed through assays carried out in an anaerobic batch digester. The experiments were done using initial TS contents of 3%, 6%, and 10% at a digestion temperature of 30°C, and at temperatures of 20, 30, and 40°C with initial TS of 6%. The results indicated that temperature does not affect the total methane generated with 6% TS, but it does affect the initial speed of generation, which increases at higher temperatures. However, the concentration of TS affected both the total volume of methane generated, which increased at higher TS due to the greater availability of substrate, and the initial speed of generation, resulting in lower values with high TS concentrations, and indicating the inhibition of the reaction at high concentrations. Based on the experimental data, a kinetic model was applied that considers the availability of substrate as a limiting factor for biogas generation and assumes that the maximum methane generation is achieved immediately after the onset of each experiment. In addition, a model based on zero-order kinetics was developed for the first stage of the process in the case of 10% TS. The model was validated by comparing the theoretical and experimental values, resulting in a deviation of less than 20% in 73% of the cases, indicating that the model predicts satisfactorily the generation of methane under the conditions studied.