Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Biological and Irrigation Engineering


Conly L. Hansen


The Induced Bed Reactor (IBR) was developed at Utah State University to apply high-rate anaerobic digestion techniques to high solids content substrates. This technology has been successfully implemented at full-scale multiple installations in the United States and Canada as a waste treatment and energy production technology, but the physical processes necessary to further optimize the system were not well understood. Bench scale IBRs were operated as anaerobic digesters at 35°, 45°, and 55° C under three organic loading rates and three corresponding hydraulic retention times. Reactor performance was monitored at steady state for residence time distribution and substrate reduction. The results show that the IBR behaves as a retained biomass reactor with fluid mixing that 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.