Environmental Engineering Department, Faculty of Engineering,
Zagazig University, Egypt.
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.