Performance and Applications of Semifluidized Bioreactors – A Review

What is it about?

This paper reviews the design features and performance characteristics of semifluidized bed bioreactors. Both biofilm reactors and immobilized enzyme bioreactors have been analysed. Also, both two phase ( liquid – solid ) and three phase ( gas – liquid – solid ) operations are considered. Apart from the hydrodynamic parameters ( semifluidization velocity, bed expansion ratio, height of packed section formed, fractional fluid holdups in both fluidized and packed sections ), all other operating / system parameters affecting reactor performance such as axial dispersion, intrinsic kinetics of bioconversion ( mostly nonlinear ), the effectiveness factor and Thiele – type modulus have also been surveyed. The specific advantages and attractive features of these bioreactors have been highlighted based on data from successful case studies such as bioplastic synthesis, biodiesel manufacture, Xanthan gum production and aerobic waste water treatment with and without LPO ( Liquid Phase Oxygen ) utilization.

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Why is it important?

The technology of semifluidization has been known since last four decades. However, utilization of this concept for the design of industrial bioreactors / chemical reactors is a relatively recent development. Semifluidized bed bioreactors, in fact, have distinctly improved features over conventional fluidized bed bioreactors, their higher operating cost notwithstanding. This paper reviews the recent developments in the design, construction and analysis of two phase and three phase semifluidized bed reactors, the bioreactors in particular. To illustrate the industrial applications of these bioreactors, results from successful case studies are presented, with special reference to synthesis of polymer – grade lactic acid from molasses and cheese whey by microbial fermentation( Narayanan, Das and Pandey, 2017), biodiesel synthesis using immobilized lipase (De et.al, 2017), Xanthan gum production from cheese whey permeate( Narayanan, 2015) and aerobic treatment of effluents from process industries for BOD degradation (Narayanan and Biswas, 2016)..

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