Multiphase Bioreactor Design

Isoelectric trapping: the enzyme is trapped between two isoelectric membranes with
isoelectric point values far apart as to trap the enzyme by an isoelectric mechanism
(Righetti et al., 1997; Nembri et al., 1997; Bossi et al., 1999)
Alternatively the enzyme can be rendered insoluble by the direct immobilisation onto
the surface and/or within the matrix of the membrane. This can be achieved in the
following ways (Figure 6.3):
Chemical coupling: the enzyme is bound to membranes which carry reactive
functional groups -OH, -COOH, -NH 2 (Nakajima et al., 1989, 1993; Lozano et al., 1990;
Harrington, et al., 1992; Hausser et al., 1983; Okada et al., 1994a; Ulbricht & Papra,
1997)
Adsorption: the enzyme adheres to the membrane surface via Van der Waals forces
(Garcia et al., 1992; Habulin, 1991; Malcata, 1991; Vaidya et al., 1993; Prazeres et al.,
1992, 1994; Ulbricht & Papra, 1997)
Entrapment: the enzyme is entrapped within the matrix during membrane preparation
by the phase inversion technique (Chen et al., 1994)
Electrostatic interactions: charged enzymes are electrically bound to membranes with
opposite charges (Furusaki & Asai, 1983; Furusaki et al., 1990)
Immobilisation on a macroscopic carrier: enzyme molecules are immobilised
(adsorption, covalent binding, electrostatic interaction) on a macroscopic carrier (beads,
pellets) (Shefer et al., 1993; 1995; Alfani et al., 1998; Xin et al., 2000).

Substrate Retention and Product Separation

The presence of a membrane in a continuous membrane reactor, apart from enabling
enzyme retention may allow for the retention of substrate molecules to a certain extent,
thus increasing their concentration and residence time in the system. In such a situation,
and for the case of enzyme kinetics without substrate inhibition, a membrane reactor
operates at higher reaction rates than an equivalent CSTR (Prazeres, 1995). This situation

Figure 6.4 Theoretical steady state

conversion degree (X) in a continuous

enzymatic membrane reactor operating

with first order kinetics (rate constant

Multiphase bioreactor design 150