Performance Analysis of Semifluidized Bed Biofilm Reactors with Liquid Phase Oxygen (LPO) Utilization

Performance Characteristics of Semifluidized bed biofilm reactors that deal with aerobic processes with liquid phase oxygen (LPO) Utilization have been simulated both mathematically as well as experimentally. Dispersed flow has been assumed in both packed section as well as fluidized section of the bioreactor. Accordingly, the reactor becomes equivalent to two plugflow dispersion reactors (PFDRs) in series, each with a different value of axial dispersion co-efficient. The values of design parameters of the bioreactor computed using the developed software package have been found to agree closely with experimental data collected on laboratory scale and pilot plant scale bioreactors, the maximum deviation being 12.5%. INTRODUCTION Semifluidized bed bioreactors have manifested themselves as a veritable compromise between fixed bed and fluidized bed bioreactors. A semifluidized bed consists of an expanded bed [fully fluidized bed] whose expansion is restricted by a restraint (porous plate) at the top. The particles that reach the top restraint accumulate there forming a packed bed. The system thus consists of a well-fluidized bed at the bottom and a packed bed at the top. In spite of the fact that semifluidized bed bioreactors combine the merits of both packed bed and fluidized bed reactors and they function equivalent to a CSTR-PFR combination, their characteristics have been so far studied mainly experimentally and only empirical correlations are available for estimating their basic operating parameters such as semifluidization velocity, fractional fluid holdup, heights of packed section and that of fluidized section etc. A further bottleneck is that most of the experiments have been conducted on semifluidized beds employing air or water as the fluidizing medium (1) and little work has been reported on performance characteristics of semifluidized bed reactors, least of all bioreactors. Worst still, many of the experimental correlations reported predict conflicting and unacceptable values of operating parameters (1, 2), thereby making selection of the most reliable correlation difficult and confusing. The chief operating parameters associated with semifluidized bed reactors are minimum semifluidization mass velocity ( ), maximum semifluization mass velocity ( ), voidage of fluidised section ( ) and volume ratio of packed section to fluidized section. Based on their experiments on a semifluidized bed composed of spherical particles and granules fluidized with water, Murthy and Roy(1) have developed the following correlations: