Simple approaches to start-up anaerobic digestion systems for biogas production

The start-up of anaerobic digestion processes is a complex problem, which determines the entire evolution of the system. In spite of its importance, this issue has not received so far a significant attention. This paper presents two simple startup strategies for an anaerobic digestion process, which have been developed based on the system dynamics. Both strategies consists of switching the dilution rate between minimum and maximum levels and then to an optimal level to drive the system towards a steady state characterized by maximum production of biogas. The main difference between the two policies consists in the type of measurement assumed: while for the first strategy it is supposed that the entire state of the system is available, for the second approach only the outflow rate of biogas is needed. Simulation results are presented to illustrate the principle of the two approaches.