Kinetics of anaerobic digestion of pig excreta to obtain biogas in the laboratory

Abstract

Anaerobic biodigestion is a natural biochemical process, through which complex organic materials are broken down by some microbial communities to produce elementary biomolecules and biogas, in the absence of oxygen. The process is carried out in four stages: hydrolysis, acidogenesis, acetogenesis and methanogenesis. The generation of CH4 can be followed by analysis and kinetic models such as those of Gompertz and Monod. The objectives were to evaluate the kinetic behavior of biogases: CH4, CO2, H2S, produced by anaerobic biodigestion of pig excretes treated with microbial inoculum, using Gompertz and Monod kinetic models. We worked with data collected in the field from a geomembrane biodigestor installed on a property near Fusagasugá, in Cundinamarca, Colombia, and with three prototypes of biodigesters located in the laboratory, whose tributaries were pig excreta and microbial inoculum (IM), biogas production was monitored using a digital thermohygrometer and a multiparametric gas meter A-ALT5X-ALKB. Significant differences (p <0.05) were found between the kinetic parameters evaluated using DCA, expressed through the kinetic models worked on, being attributable to the control of variables such as: type and composition of the tributary, biodigest temperature, pH and evolution of COD. The best kinetic behavior was observed in the biodigester that operated at a temperature close to 38 ºC, given that the change in biogas volume and the concentrations of CH4, CO2, H2S and NH3 in time were adequately explained by the kinetic models of Gompertz and Monod.