Simulation of a periodic anaerobic baffled reactor (PABR): steady state and dynamic response K. Stamatelatou and G. Lyberatos Department of Chemical Engineering, University of Patras, GR-26500 Patras, Greece (E-mails: stamatelatou@chemeng.upatras.gr, lyberatos@chemeng.upatras.gr) Abstract The Periodic Anaerobic Baffled Reactor (PABR) is a novel high-rate configuration for wastewater treatment. The reactor resembles an ABR with the compartments arranged in a circular manner. The feeding and effluent points are periodically set in different compartments by proper manipulation of valves that determine the flow pattern. This way of feeding makes the reactor response oscillating and gives the PABR a great flexibility in the operation mode. A 15 litre PABR was operated on a gelatin based medium under steady and variable organic loading rate. The experimental conditions were simulated using a mathematical model whose primary feature was that each compartment was considered as a two-section tank, each section with a different biomass concentration in them. The degree of biomass accumulation was determined indirectly by the operating conditions and the reactor dynamics and was not set a-priori. Keywords Gelatin; high-rate system; modeling; periodic anaerobic baffled reactor Introduction Anaerobic digestion has become a very popular microbial process for wastewater treat- ment, mainly because of the development of high-rate reactors that allow slow-growing anaerobic microorganisms to remain inside the reactors under short hydraulic retention times. The Anaerobic Baffled Reactor is a high-rate system that has been tested on a variety of wastewaters under a wide range of organic loading rates with success (Barber and Stuckey, 1999). Based on the ABR design concept, the PABR (Periodic Anaerobic Baffled Reactor) is an innovative reactor, initially developed by Skiadas and Lyberatos (1998). The PABR interior space is separated into compartments, each consisting of one downflow and one upflow part. The compartments are arranged in a circular manner in the annular region between two concentric cylinders (Figure 1a). In the PABR, the influent and effluent ports are not fixed as in the ABR, but they can be switched in a periodic mode within a certain time interval (switching period), so that each compartment becomes the first, taking in the influent, in the series within a fraction of the period (switching sub-period) (Figure 1b). The frequency of the influent and effluent points switching is an operational parameter which can be manipulated to optimize the PABR performance. Depending on the switching frequency, the PABR can operate as an ABR (zero frequency) or as a UASBR (infinite fre- quency) or at an intermediate mode. Skiadas et al. (2000) studied the effect of the switching frequency on a glucose fed PABR at various dilution rates. At high dilution rates, the PABR performs better at a high switching frequency and vice versa. At intermediate dilution rates, there is a specific value of the switching frequency at which the PABR yields its optimal performance. The periodic behavior of the PABR, as simulations indicate, may be benefi- cial over the ABR in the case of severe overloading (Skiadas et al., 1998, 2000). In the present paper, the behavior of a lab-scale PABR is presented under steady and changing conditions, while fed on a gelatin based medium. The PABR was operated at nor- mal organic loading rates (between 3.125 and 6.25 g COD/l/d) at various conditions: 100% step change in the feed concentration or the hydraulic retention time and at steady state. In order to predict the experimental results, an improved modeling frame was developed Water Science and Technology Vol 45 No 10 pp 81–86 © IWA Publishing 2002 81 Downloaded from https://iwaponline.com/wst/article-pdf/45/10/81/425019/81.pdf by guest on 04 November 2018