The FOS/TAC ratio is a commonly used indicator for assessing the fermentation process within biogas reactors, where FOS is a measure of the volatile organic acids (measured in mg CH3COOH/l) and is TAC is a measure of the total inorganic carbon i.e. the alkaline buffer capacity of the system (measured in mg CaCO3/l). In simple terms, this ratio looks at acid vs alkaline in the system which helps...