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Licensed Unlicensed Requires Authentication Published by De Gruyter February 17, 2015

Studies on Computer-Aided Design and Analysis of Three-Phase Semifluidized Bed Bioreactors

C. M. Narayanan


Attempts have been made to perform computer-aided analysis and simulation of the performance of a three-phase semifluidized bed bioreactor. The bioreactor is of biofilm type. Cocurrent operation with liquid (substrate solution) forming the continuous phase has been considered. Both air and feed solution are thus admitted from the bottom, the air moving up as tiny bubbles. Being semifluidized, the bioreactor is composed of a fully fluidized bed at the bottom and a packed bed at the top. The performance of the bioreactor is analysed by assuming it to be equivalent to two plug flow dispersion reactors (PFDRs) in series, each with a different value of dispersion number/axial dispersion coefficient. The performance equations (assuming dispersed flow) for both sections are written separately and then solved numerically using fourth-order Runge–Kutta method/successive over-relaxation method, based on appropriate boundary conditions. The specific case considered is the aerobic synthesis of Xanthan gum from cheese whey permeate, which follows Contois-type kinetic equation. The fractional gas holdup in both sections, height ratio of fluidized section to packed section and the semifluidization velocity are computed at the outset from selected experimental correlations (compiled from available literature). The results obtained from the developed software package, after verifying experimentally, are used to study and illustrate the performance characteristics of the bioreactor. It is observed that the three-phase semifluidized bed biofilm reactor of proposed design provides substantially large fractional conversion of substrate at large capacities, with relatively low reactor volume requirement.


This paper has been presented in the International conference on Bioprocess Engineering (Bioprocess-2014) held at Valencia, Spain, during June 26–27, 2014 and has been modified based on the discussion and interactions during the conference. The author is thankful to all the participants of the conference, to all of his fellow members of IRG (International Research Group), to a large number of consultancy firms and software companies of India and abroad for their valuable assistances towards the successful completion of this project.



cross-sectional area of reactor column, m2

CS (z)

substrate concentration at any z, g/L


substrate concentration at the exit of the fluidized section (or entrance to the packed section) of the bioreactor, g/L


substrate concentration in product solution leaving the bioreactor, g/L


substrate concentration in feed solution entering the bioreactor, g/L


substrate concentration at the biofilm–liquid interface, g/L


diameter of the support particle, m


diameter of particle-biofilm aggregate, m


diameter of reactor column, m


axial dispersion co-efficient for the fluidized section of bioreactor, m2/s


axial dispersion co-efficient for the packed section of bioreactor, m2/s


volume fraction of biofilm in particle-biofilm aggregate, dimensionless


drag coefficient, dimensionless


kinetic constant, dimensionless

KC (app)

parameter defined in eqs (27) and (28), g/L


height of initial static bed, m


characteristic dimension (see eq. (35)), m


height of fluidized section of bioreactor, m


height of packed section of bioreactor, m


total height of semifluidized bed, m


volumetric flow rate of substrate solution, m3/s


intrinsic rate of biochemical reaction, g/(L.s)


bed expansion ratio, dimensionless


modified Reynolds number (see eq. (6)), dimensionless


particle Reynolds number, dimensionless


superficial velocity of gas, m/s


minimum fluidization velocity for a liquid–solid fluidized bed, m/s


operating superficial velocity of liquid through the bioreactor (liquid phase semifluidization velocity), m/s


cell mass concentration in biofilm, g/L


parameter defined in eq. (29), g/L


parameter defined in eq. (30), g/L


overall yield coefficient for cell mass production, g/g


axial coordinate, m


fractional conversion of substrate, dimensionless


parameter defined in eq. (36), dimensionless


thickness of biofilm, m


total voidage of fluidized section of bioreactor, dimensionless


fractional gas holdup in the fluidized section of the bioreactor, dimensionless


fractional liquid holdup in the fluidized section of the bioreactor, dimensionless


total voidage of packed section of bioreactor, dimensionless


fractional gas holdup in the packed section of the bioreactor, dimensionless


fractional liquid holdup in the packed section of the bioreactor, dimensionless


parameter defined in eq. (33), dimensionless


effectiveness factor at any z, dimensionless


viscosity of substrate solution, kg/(m.s)


kinetic constant, s–1

μm (app)

parameter defined in eqs (25) and (26), g/(L.s)


density of substrate solution, kg/m3


density of microbial solution, kg/m3


density of support particle, kg/m3


density of particle-biofilm aggregate, kg/m3


Thiele-type modulus, dimensionless


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Published Online: 2015-2-17
Published in Print: 2015-3-1

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