Hydraulic Modeling of the Liquid Flow Pattern in a Bench-scale Uasb Reactor

All bioreactor configurations are affected by mixing and transport phenomena and consequently the bioreactor’s hydraulics governs the reactor’s configurations as well as performance. For instance, to provide good conditions for substrate transport to, and from, the microbial aggregates, an even mixing pattern at the macro-level is desirable. However, the available data that either describe UASB flow regime or relate process performance to mixing characteristics are not that much. The global objective of this paper is to determine the liquid flow model of UASB via a tracer study to characterize the overall flow behavior in this reactor. In particular, a tracer study has been utilized in this study to figure out the flow pattern in the UASB reactor and to determine the difference between theoretical and actual hydraulic retention time. The specific objectives of the present work have been reached through four steps; namely: (1) UASB bench-scale model setup, (2) tracer experimental study, (3) results statistical analysis to determine the reactor dispersion and actual retention time, and (4) selection of the model that can be used to describe the investigated reactor. Among the main findings of the present study is that the CSTR model with some degree of short-circuiting, dead zones and bypassing flows seems to describe the overall hydrodynamics of UASBs. Also, the mean residence times were 87.68%, 80.35%, and 72.66% of the theoretical hydraulic retention times 6, 8, and 10 hours, respectively.