Shock load modelling in the anaerobic digestion process

A simplified mathematical model for the behaviour of anaerobic digesters under shock loading conditions is derived with a special emphasis on bicarbonate alkalinity. This study was motivated by the development of a novel bicarbonate alkalinity measuring device providing on-line information of this variable, which is particularly well suited for the early detection of organic overloading. The model includes a set of dynamic equations and an extended ion balance to describe the effect of alkali, volatile fatty acids and carbon dioxide. After the structural description, the model is calibrated using specific shock experimental data and its implications are discussed in terms of a variety of shock conditions. Lastly, the feasibility of bicarbonate dosing control is assessed through proportional-integral-derivative (PID) controller design and model simulation.