A large number of materials are produced by fermentation processes.
Fermentation process design should be such that the product may be obtained efficiently and economically.
Any fermentation process design must consider three major aspects:
(i) Value creation opportunity,
(ii) Process design analysis and
(iii) Objectives of the design project.
These objectives are discussed in brief below:
(i) Value Creation Opportunity:
It concerns mostly establishment of microbial reaction process and its development recognizing economic opportunity.
Recognition of economic opportunity relates to the appropriateness of the following:
(i) Selection of microbial strains
(ii) Selection of appropriate fermenter design
(iii) Scope of product utilization.
A. Microbial strains:
Exploitation of microbial activity is done considering the following important aspects:
(a) Selection of new stable strains for getting a share in the market by producing useful new products using modern fermentation plant.
(b) Selection of stable strain for known product of the established equipment.
B. Fermenter design:
For production of a substance having established market, combination of an existing stable strain and a simplified fermenter together with new devices need to be used. In almost all fermentation processes the fermenter configuration plays the part of a mediator between energy input variables and physiological reactions of microbial cultures.
As microbial behaviour vary widely, it is difficult to design a versatile fermenter for multipurpose use. This limitation led to the development of various conventional and non-conventional fermenter designs. However, attempts in all designs have been made to meet the requirements as listed in Table. 7.2. High power demand and underutilization of impeller energy input are the two important weak points of conventional designs.
In any new design principles of unconventional fermenter have been to minimize these shortcomings of conventional fermenters. Also, care is needed in the interaction between fermenter design and microbial unit at used physiochemical environment as depicted in Fig. 7.1 to make the downstream processing of the product easier.
C. Scope of the product:
It is associated with the mode of utilization of the product to get an adequate fitness of the product on human needs.
(ii) Process Design Analysis:
In fermentation process analysis major requirements include the following:
(a) Design variables to which similarity concepts are applicable, most important among them requires:
(i) Fermentation time course and profiles of state and control variables.
(ii) Determination of most favourable control variables condition to obtain maximum product yield.
(b) Design variables to which innovation concept is applicable. It requires:
(i) Pilot plant studies for new process development thereby aid in innovation in scale up.
(ii) Investigating possibilities of innovation by the process simplification and by adopting high technology easily and successfully.
(iii) Product development such that marketing is decisive.
(c) Design variables in relation to optimization concept. These concerns:
(i) Yield equilibrium specific rates of fermentation and growth profiles.
(ii) Product concentration in finished broth, fermentation cycle or fermentation rate and product recovery process.
(d) Process economics:
Evaluation of the fermentation process design has to be done on economic basis. As indicated the concept based on financial cash flow and discounted cash flow are useful in economic evaluation of the process. Considering capital cash flow C earns the present value P in n years at a nominal interest rate i and compounding and discounting occurs m times per year
(iii) Objectives of Design Project:
The fermentation process design project deals with:
(i) Aims of:
a) Product development
b) Possibilities of producing new type of microbial group in a known fermenter design
c) Efficiency of new fermenter for known fermentation
d) Process improvement
(ii) Procedure of design project for:
a) Organization of basic idea
b) Structure of design project
c) Other process design requirements
(iii) Projected design and development programme:
Systematic analyses of the points discussed above are essential in developing fermentation processes in bioreactors.