Multiphase Bioreactor Design

Table 4.1 General aspects related to the use of

immobilised biocatalysts.

General aspects Specific aspects

Advantages

RETENTION OF THE
BIOCATALYST IN THE
BIOREACTOR

—possible biocatalyst reuse

—product contamination avoided

—high dilution rates allowed without biocatalyst wash-out

HIGH BIOCATALYST
CONCENTRATION

—increased volumetric productivity

—rapid conversion of unstable substrates

—minimised side-reactions

CONTROL OF
BIOCATALYST
MICROENVIRONMENT

—manipulation of biocatalyst activity and specificity

—stabilization of biocatalyst activity

—protection of shear-sensitive biocatalysts

FACILITATED
SEPARATION
OF THE BIOCATALYST
FROM THE PRODUCT

—precise control of bioreaction time

—minimisation of further product transformation

Limitations

INCREASED COSTS
OF
BIOCATALYST
PRODUCTION

—increased requirements of materials and equipment

—need for specific reactor configurations

LOSS OF
BIOCATALYST
ACTIVITY DURING
IMMOBILISATION

—biocatalyst-related —exposure to pH and temperature

extremes

—exposure to toxic reactants

—exposure to high shear or mechanical

strain

—microenvironment
related

—exclusion of macromolecular

substrates

—blocking of the enzymatic active site

—local pH shifts

—mass transfer limitations

LOSS OF
BIOCATALYST
ACTIVITY DURING
BIOREACTOR
OPERATION

—leakage of biocatalyst —matrix erosion or solubilisation

—small support particles carried in the

outflow

—cell growth inside the matrix

—broad pore-size range

—matrix poisoning or
fouling

—build-up of inhibitors in the

microenvironment

—retention of suspended solids

—growth of contaminating species

(biofilms)

—need for a stricter control of feed

Design and modelling of immobilised biocatalytic reactors 91