Monitoring management criterion of an anaerobic digester using an explicit model based on temperature and pH

In this paper, the stability analysis of an anaerobic digestion process is presented. The analysis is performed using a simplified mathematical model, which includes explicit temperature and pH dependence on kinetic growth rates. A detailed nonlinear and bifurcation analyses are performed in order to study the effects of temperature and pH parameters on the process behaviour. In addition, both safety and optimal operation regions of the bioreactor are established. Based on bifurcation diagrams, it is observed that the washout condition occurs by combining a fold bifurcation and a transcritical bifurcation. Consequently, to prevent the washout and guarantee optimal operation conditions of the bioreactor, a risk criterion oriented to monitor the bioprocess on-line is proposed, allowing to detect the system destabilisation.