Stability Parameters

The FOS/TAC parameter is used to monitor process stability by focusing on the pH value. FOS/TAC is defined as the ratio of the amount of volatile fatty acids that accumulate during anaerobic digestion to the alkalinity present in the system (Lili et al. in Analele Univ Din Oradea Fasc Protecția Mediu 17:713–718, 2011). Since volatile fatty acids accumulate during the acidogenesis phase, they can lead to a consumption of alkalinity and consequently a decrease in pH. For this reason, it is of fundamental importance to have a buffer solution that can counteract the pH decrease bringing it back to neutral values, as the optimal pH value for an anaerobic digester is around 7 (Pontoni et al. in Chem Eng Trans 43:2089–2094, 2015).