Initial simulations were conducted for the base-case
scenario (Figure 2), considering only one equipment per
stage, adopting starch medium for inoculum propagation
and assuming that the concentrated enzyme stream is
the only revenue source (fermented cake being a waste).
Therefore, streams 17, 18, and 20 in Figure 2 were treated
as waste streams, with a treatment cost for disposal of
0.0005 USD kg−1, for each stream. All solid streams were
transported using belt conveyors. Centrifugal pumps used
for transporting liquid streams are not shown in the flowsheet, but were accounted for in the economic analysis.
Inoculum propagation and main fermentation were
conducted in tray bioreactors, as in the lab-scale experiments.
After fermentation, enzymes were extracted using
a CSTR and then separated from the fermented cake by
a hydrocyclone, considering 80% of extract recovery. The
overflow stream was directed to a microfiltration (MF)
unit and finally to ultrafiltration (UF) modules for enzyme
concentration. The total enzymes concentration of the UF
retentate was assumed to be 50% (m/m), in order to yield
a final product with a total protein concentration in the
same order of magnitude as found in commercial preparations.
Denaturation during these filtration procedures was
assumed proportionally to all groups of enzymes and was
adjusted to 5% forMF, while for UF a lower extent (2%) was
used, based on experimental results reported by Mores et al