Mathematical Simulation of Upflow Anaerobic Fixed Bed Reactors

Abstract

ABSTRACT ANAEROBIC digestion of agricultural wastes using conventional stirred-reactor technology has been unsuccessful in treatment of dilute waste streams. The development of *'fixed bed anaerobic reactors has provided an effective method of utilizing dilute waste for methane production. Anaerobic fixed bed reactors (AFBR), or anaerobic filters, are unique among anaerobic reactor designs in that a fixed support medium is placed inside the reactor vessel, allowing attachment of active bacterial mass responsible for substrate conversion. The resulting attached biofilm allows high hydraulic flow through the reactor vessel without causing bacterial washout and subsequent digester failure, a significant advantage over conventional reactor designs. A mathematical model was developed which simulates dynamic upflow AFBR response to waste characteristics, loading, flow rate, surface area and porosity of the support medium, and temperature. Computer simulations with the model indicate that the AFBR is superior to conventional stirred reactor designs for treatment of dilute wastes. The AFBR provides stable operation, rapid response to transient operational and environmental conditions, and effective treatment at reduced temperatures (20C to 30C).