Biomedical Engineering Reference
In-Depth Information
required places for microorganism growth. The most prominent advantages of solid-
state fermentation include that it is a simple process, it requires less investment, and
it has high output. Its specific characteristics are summarized as follows:
(1) The fermented cost is low because cheap raw materials can be directly used,
such as industrial and agricultural residue (cellulosic feedstock, renewable
resources) as substrates.
(2) It simulates natural growth environment to keep microorganism growing simi-
larly to their natural status.
(3) The three waste discharges of wastewater, waste residue, and waste gas do not
exist.
(4) Postprocessing for the product is simple. Products are easy to store and
transport. (Table
11.4
).
Currently, solid-state fermentation is adopted by the vast majority of Chinese
manufacturers. Figure
11.3
is a production process for cellulase with rice straw as
the raw material and solid-state fermentation.
(1) Solid-state fermentation type
Solid-state fermentation can be divided into shallow tray fermentation, drum solid-
state fermentation, gas dual-dynamic solid-state fermentation, and so on.
①
Shallow tray fermentation
Shallow tray fermentation uses straw powder, wastepaper, and corn straw powder
as the main raw materials. When seed leaven is mixed into feedstock, the mixture
is loaded into a dish or curtain and spread in a thin layer (a few centimeters to tens
of centimeters thick). It is fermented in the training room under certain temperature
and humidity (90-100 %) conditions. The heat conduction of dish fermentation is
easily restricted. The presence of a medium temperature gradient will result in the
generation of natural convection, which will affect the transfer of heat and oxygen
and carbon dioxide and the transfer of moisture. In shallow tray fermentation, heat
transfer is the biggest bottleneck. The best solution is to reduce the thickness of the
substance. Reactor enlargement can only be achieved by increasing the amounts of
trays, so it is not suitable for large-scale production.
Zhang et al. [
115
] took spent grains as the main raw material to produce cellulase
by
T. reesei
Rut C230 with shallow tray fermentation (platter loading 300-400 g dry
matter). The fermentation process was optimized by controlling temperature and
pH. The preliminary temperature was controlled at 27-30
ı
C, and the maximum
temperature of the late stage of fermentation does not exceed 35
ı
C. When the
pH of feed materials rose from 4.3 to 4.5, dilute hydrochloric acid was sprayed
for control. With optimized pH and temperature, FPA activity reached 508 U
g
1
g
1
substance, equivalent to 2,120 U
cellulose.
②
Drum solid-state fermentation
The basic form of a drum reactor is a cylindrical container held in a rotating system.
The rotational system mainly plays the role of support and provides dynamic action.
