There are two main ways to utilize the waste solids – either compost them or
convert them into useful products. Since composts often have relatively little
value, the second route is preferable. Mehta et al. [224] cultivated Pleurotus
florida on rice straw to produce mushrooms. They used the waste solid for
biogas production. In fact they noted that the growth of the fungus increased
the production of biogas from the straw. Singh et al. [225], in reviewing the
traditional production of mushrooms from cereal straws in Asia, pointed out
that residues are often used as animal feeds. However, the acceptance of the
residue by ruminants varied with the type of mushroom produced.
9
Evaluation of the Current Status and Future Prospects
This review has investigated the state of the art of biochemical engineering
aspects of solid state fermentation. It is clear that the development of large-scale
processes is problematic, owing to the limitations of heat and mass transfer
which are intrinsic to the system. Any of a range of factors can potentially be
limiting at different times and places during a fermentation, such as temperature, nutrient concentration, oxygen concentration, pH, and water activity. Due
to this complexity, until recently our quantitative understanding of the system
has been poor, which has limited our ability to design successful large-scale
processes.
Solid-state fermentation technology must be seen as complementary to SLF
technology. In a majority of cases SLF is superior, if not for product yields then
for the ease of handling and control on the large scale. However, there is a need
for SSF technology, because certain products are either not produced in SLF, or
if produced, do not possess desirable features possessed by the product from
SSF. SSF may also be favored in some instances simply because a low technology
process is sufficient and labor costs are low, or because a waste solid material
needs to be utilized for profit rather than simply dumped.
Routine commercialization of those products for which SSF is the superior
technique will require better knowledge about how to design equipment and
how to operate the process. The application of biochemical engineering approaches to SSF is still in its early stages. Despite this, our knowledge of bioreactor design and operation has advanced considerably over the last decade.
Mathematical models of the microscale have given us insights into how intraparticle diffusion of enzymes, hydrolysis products, and oxygen have the potential to limit process performance. Further, mathematical models have been
developed to describe the operation of most types of bioreactors. Although
these mathematical models need many further improvements, they have
already given us valuable insights into how to design and operate bioreactors on
the larger scale.
Much more needs to be done. More attention needs to be given to the
auxiliary operations such as substrate preparation, sterilization, aseptic
transferal of substrate, preparation of inoculum, and downstream processing.
With respect to the bioreactor step itself, mathematical models need to be
improved in order to improve their usefulness as tools in the design process.
Biochemical Engineering Aspects of Solid State Bioprocessing
131
convert them into useful products. Since composts often have relatively little
value, the second route is preferable. Mehta et al. [224] cultivated Pleurotus
florida on rice straw to produce mushrooms. They used the waste solid for
biogas production. In fact they noted that the growth of the fungus increased
the production of biogas from the straw. Singh et al. [225], in reviewing the
traditional production of mushrooms from cereal straws in Asia, pointed out
that residues are often used as animal feeds. However, the acceptance of the
residue by ruminants varied with the type of mushroom produced.
9
Evaluation of the Current Status and Future Prospects
This review has investigated the state of the art of biochemical engineering
aspects of solid state fermentation. It is clear that the development of large-scale
processes is problematic, owing to the limitations of heat and mass transfer
which are intrinsic to the system. Any of a range of factors can potentially be
limiting at different times and places during a fermentation, such as temperature, nutrient concentration, oxygen concentration, pH, and water activity. Due
to this complexity, until recently our quantitative understanding of the system
has been poor, which has limited our ability to design successful large-scale
processes.
Solid-state fermentation technology must be seen as complementary to SLF
technology. In a majority of cases SLF is superior, if not for product yields then
for the ease of handling and control on the large scale. However, there is a need
for SSF technology, because certain products are either not produced in SLF, or
if produced, do not possess desirable features possessed by the product from
SSF. SSF may also be favored in some instances simply because a low technology
process is sufficient and labor costs are low, or because a waste solid material
needs to be utilized for profit rather than simply dumped.
Routine commercialization of those products for which SSF is the superior
technique will require better knowledge about how to design equipment and
how to operate the process. The application of biochemical engineering approaches to SSF is still in its early stages. Despite this, our knowledge of bioreactor design and operation has advanced considerably over the last decade.
Mathematical models of the microscale have given us insights into how intraparticle diffusion of enzymes, hydrolysis products, and oxygen have the potential to limit process performance. Further, mathematical models have been
developed to describe the operation of most types of bioreactors. Although
these mathematical models need many further improvements, they have
already given us valuable insights into how to design and operate bioreactors on
the larger scale.
Much more needs to be done. More attention needs to be given to the
auxiliary operations such as substrate preparation, sterilization, aseptic
transferal of substrate, preparation of inoculum, and downstream processing.
With respect to the bioreactor step itself, mathematical models need to be
improved in order to improve their usefulness as tools in the design process.
Biochemical Engineering Aspects of Solid State Bioprocessing
131