Dynamic model simulations as a tool for evaluating the stability of an anaerobic process

The association of a wall growth factor with a dynamic model based on Andrews' work (1969), without pH restrictions, is used herein to study the inhibition of methanogenesis by high concentrations of volatile acids. The model considers the methanogenic bacteria as being representative of the biological phase of the anaerobic digestion, and assumes a continuous feed of acetic acid to the continuously stirred anaerobic reactor. The model can be used for simulations on transient conditions, namely the effect of initial conditions on the start-up of a digester, as well as for studying the significant improvements in stability when wall growth occurs in the reactor. The effect of changing the feed characteristics to a digester was studied in two situations: with and without wall growth. The presence of wall growth allows a better behaviour of an anaerobic process in any case, namely when a step increase in the feeding substrate concentration or in flow rate is performed. WaterSA Vol.27(1) 2001: 109-114