BIOG-C: Modeling the volumetric methane production in the anaerobic digestion process applied to swine wastes

The implementation of models to forecast the occurrence of phenomena, especially the long-term ones, is a very important tool, since the time consumed in field experiments may be greatly reduced. The models cannot replace the experiments, but complement them. It is possible with modeling to consider a large number of factors that affect a particular process and their combinations, which would be impossible in conventional experiments. The first models for the anaerobic digestion process of animal wastes were reported in 1974, however, these models required many kinetic parameters. The aim of this work was to model volumetric production of methane from swine wastes, based on a bacterial growth kinetic model modified by Chen and Hashimoto (1979), using the results from laboratory experiments and literature data. The main variables were the bacteria specific growth rate, the effluent volatile solids concentration, the hydraulic retention time, the temperature, and the substrate mixing. The simulation was accomplished using "Modelmaker" software, version 2.0-SB technology (1994). The substrate temperatures imposed ranged from 25 to 40°C, hydraulic retention times ranged from 10 to 30 days, and the simulation of methane production rate was made for a 150 day period. The volumetric methane production was satisfactorily estimated by that model, called BIOG-C. It was noted that the methane production pattern was significantly controlled by the effluent volatile solids concentration. The model was tested by comparing the error correlation between the observed volumetric methane production obtained under similar conditions and those predicted by the model. The comparisons showed a close agreement.