Hydrodynamic Modeling of the Induced Bed Reactor Anaerobic Digester

The Induced Bed Reactor (IBR) was developed at Utah State University (USU) to apply high-rate anaerobic digestion techniques to highly-suspended solids content substrates (6-12% total solids). This technology has been successfully implemented at multiple full-scale installations in the United States andCanada as a waste treatment and energy production technology. Residence Time Distribution (RTD) studies for 58 L lab-scale reactors operated at a 3.8-d hydraulic retention time were conducted at three temperatures (35°, 45°, and 55°C) under both control (no active biomass, no reaction taking place) and active digestion conditions. Rhodamine WT and Li+ were used as tracers. Rhodamine appears to interact with the digester contents, raising questions about its suitability as a tracer in this context.The results show that the IBR most closely approximates Completely Stirred Tank Reactor (CSTR) behavior when operated under the study conditions. A compartment real CSTR model, incorporating elements of dead zone and bypass flow appears to be the most appropriate representation of the data. Mixing is likely due to a combination of energy inputs from thermal gradients induced by heat flux through the reactors and reactor and shear rates induced by gas evolution in the sludge bed.