In packed bed reactors, cells are immobilized on large particles. These particles do not move with the liquid. Packed bed reactors are simple to construct and operate but can suffer from blockages and from poor oxygen transfer.
 
 

Packed Bed Bioreactor

figure taken from http://www.np.ac.sg/~dept-bio/biochemical_engineering /fermentation_tutorial/fermentation_technology_bioreactor.htm

Continuous packed bed reactors are the most widely used reactors for immobilized enzymes and immobilized microbial cells. In these systems, it is necessary to consider the pressure drop across the packed bed or column, and the effect of the column dimensions on the reaction rate.

There are three substrate flow possibilities in a packed bed and they are illustrated below:

   1. Downward flow method

   2. Upward flow method

   3. Recycling method

The recycling method is advantageous when the linear velocity of the substrate solution affects the reaction flow rate. This is because the recycling method allows the substrate solution to be passed through the column at a desired velocity.

For industrial applications, upward flow is generally preferred over downward flow because it does not compress the beds in enzyme columns as downward flow does. When gas is produced during an enzyme reaction, upward flow is preferred.

A continuous packed bed reactor has the following advantages over a batch packed bed reactor:

   1. Easy, automatic control and operation

   2. Reduction of labor costs

   3. Stabilization of operating conditions

   4. Easy quality control of products

Excel Worksheet Simulators for Packed-Bed Reactors

Bohmann et. al. (Ref. 1) described a bioreactor system for continuous cultivation with a high potential for scale up. This reactor system consists of radial-flow fixed-bed units coupled with a dialysis module. The dialysis membrane enables the supply of low-molecular-weight nutrients and removal of toxic metabolites, while high-molecular-weight nutrients and products (e.g. monoclonal antibodies) are retained and accumulated. This concept was investigated on the laboratory scale in a bioreactor with an integrated dialysis membrane. The efficiency of the reactor system and the reproducibility of the cell activity under certain process conditions could be demonstrated in fermentations up to 77 days.
 

Reference:

A. Bohmann, R. Pörtner, H. Märkl, Performance of a membrane-dialysis bioreactor with a radial-flow fixed bed for the cultivation of a hybridoma cell line, Applied-Microbiology and biotechnology, 43(5), 772-780, 1995
 

Last modify: 05/01/2000, by Xuezhen Kang