**4. Conclusions**

Different control strategies and parameters are reported in the literature to monitor system stability as a result of changes related to the feedstock. Several strategies have been implemented, reactor operating time extensions, lowering of OLRs, or supplementing enough alkalinity to buffer possible pH shocks. A longer operation time could allow the choice of a transition strategy to microbial community adaptation. Also, systems operation with low OLRs is less disturbed by instabilities. In any case, the transitory state is when the process needs to be carefully controlled not to reach a point of irreversible inhibition. The control parameters that should be monitored to prevent this situation would be pH and VFA/TA ratio. The microbial population analysis provides interesting information on its adaptation, although it does not reveal enough details for daily monitoring. Developing protocols for substrate changeover strategies could be of great interest to expand the use of existing anaerobic digestion facilities. It would improve the potential of this technology in the treatment of seasonal substrates that are generally not treated by anaerobic digestion. Concerning anaerobic digestion process robustness, changes in the type or composition of feedstock fed to the reactors are possible, although cautiously.
