Modelling of the periodic anaerobic baffled reactor (PABR) based on the retaining factor concept

The fact that the active biomass is continuously removed from the continuously stirred anaerobic digesters, leading to long retention times, has been overcome in a number of high rate systems based on immobilisation of the active biomass, such as the Upflow Anaerobic Sludge Blanket Reactor (UASBR) and the Anaerobic Baffled Reactor (ABR). A kinetic model of glucose consumption, which was developed based on a batch kinetic experiment, was used for the development of a dynamic model for the prediction of the behaviour of the recently developed flexible reactor called the Periodic Anaerobic Baffled Reactor (PABR) [(1998) Wat. Sci. Technol. 38(8–9), 401–408]. The PABR may be operated as a UASBR, an ABR or at an intermediate mode. The key assumption of the model is that the hydraulic behaviour of a PABR is equivalent with the behaviour of CSTRs in series as concerning the dissolved matter, whereas the biomass is allowed to be retained in the PABR through a retention factor accounting for precipitation. The model adequately predicted the experimental behaviour of a glucose fed PABR. The model was subsequently used to examine the behaviour of the PABR as a function of operating conditions, both for constant and varying loading rates. It was shown that for different cases, the reactor should best be operated as a UASBR or as an ABR.