The periodic anaerobic baffled reactor

The most common bioreactor type used for anaerobic digestion is the Continu ously Stirred Tank Reactor (CSTR). The main problem of this reactor type, i .e. the fact that the active biomass is continuously removed from the syste m leading to long retention times, has been overcome in a number of systems based on immobilization of the active biomass. Two representative types ar e the Upflow Anaerobic Sludge Blanket Reactor (UASBR) and the Anaerobic Baf fled Reactor (ABR). The success of these reactor systems rests on the highl y flocculated, well settling, compact methanogenic sludge granules which de velop in these reactors. A novel reactor type named Periodic Anaerobic Baff led Reactor (PABR) has been designed, offering the following major advantag e: it may be operated as an ABR, a UASBR or at an intermediate mode. The PA BR hydraulic behavior has been characterized using residence time distribut ion experiments at different retention times. Simulating the PABR behavior, the dependence of the reactor performance on the switching frequency is de termined as a function of the retention time. In particular, it is found th at for high retention times the ABR made is superior, whereas for low reten tion times, the UASBR mode should be preferred. In order to establish the a ccuracy of the predictions of the simulation study, the PABR behavior was e xperimentally verified using three different stable periodic states. (C) 19 98 IAWQ Published by Elsevier Science Ltd. All rights reserved.