Comprehensive model of anaerobic digestion of swine manure slurry in a sequencing batch reactor

An improved mathematical model of anaerobic digestion in a sequencing batch reactor (SBR) process is developed. The model simulates the interactions between the biological, liquid (physicochemical) and gas phases. These phenomena are supported by experimental data. The advanced model assumes: (1) six populations of bacteria, including two populations of acetoclastic bacteria, are present in the bioreactor; (2) hydrogen in the gaseous phase is not in equilibrium with dissolved hydrogen; (3) production of volatile fatty acids (VFA) is regulated by the concentration of hydrogen in the liquid phase; and (4) the process is not affected by large concentrations of VFA and ammonia. The model contains a large number of kinetic constants and has the capability to predict the pH and methane production, as well as the concentrations of acetic (Ac), propionic (Pr) and butyric (Bu) acids; dissolved and gaseous hydrogen and soluble chemical oxygen demand (SCOD) in the SBR as a function of time. The model coefficients were determined for data, gathered from pilot scale digesters operated under psychrophilic conditions. The calibrated model was able to simulate methane production, SCOD, Ac and Pr acid concentrations in the dynamic conditions of an SBR, operated over a range of operating conditions.