Table 11.3 Citric acid production by A. niger in a
continuous fluidised bed reactor with different air
pulsation frequency
(^) Frequency (sā^1 )
Time 0.50 0.35 0.20 0.125 0.050 Non-Pulsed
0 0 0 0 0 0 0
3 1.06 1.22 1.78 0.78 0.78 0.89
7 5.11 6.58 5.53 0.61 5.44 5.31
9 8.03 9.85 8.15 7.95 7.06 7.56
13 11.02 14.62 11.85 9.53 7.97 NA
16 16.55 19.55 16.72 13.79 10.86 NA
20 16.83 18.98 17.88 17.38 13.64 NA
NA: Not applicable.
with high levels of activity, comparable with the batch process. The success of the
process depends on its ability to maintain stable secondary metabolism conditions and
control fungal growth. The combination of a proper feed rate and the application of a
pulsation in a packed-bed bioreactor were fundamental in the enhancement and
prolongation of MnP production by P. chrysosporium (Moreira et al., 1998). For this
work, two different configurations were considered: expanded-bed bioreactor operated
with pellets or fixed-bed bioreactor packed with P. chrysosporium BKM-F-1767
immobilised in cubes of polyurethane foam, both bioreactors coupled with oxygen
pulsation.
The comparison of the effect of pulsation on MnP production in pulsed and non-
pulsed bioreactors is highlighted in Figure 11.12. A clear difference is observed when
comparing the operation with and without pulsation. In both pulsed bioreactors,
continuous production of MnP is maintained for a long period (more than 30 days). In the
case of the non-pulsed bioreactor, MnP production is comparatively low and maintained
for a shorter period.
Just as pulsation modifies the morphology of mycelial pellets, the application of the
gas pulsation to the immobilised bioparticle efficiently limits hyphal extension between
foam blocks, and avoids interconnection and aggregation.
Application of the fungal pulsed bioreactor to the decolourisation of
synthetic dyes
Conventional biological technologies have been applied extensively in the treatment and
detoxification of many industrial effluents. However, these treatment alternatives present
specific limitations, especially when applied to the decolourisation of recalcitrant
compounds. The following example seeks to describe another possible application of gas-
Pulsing bioreactors 347