Scale-up of microbial processes
Direct production of microbes on a large or commercial scale has the risk of not only large investments, but also producing products, which may not be of appropriate quality so that there are problems in their commercialisation. To avoid these risks, the manufacturers try to validate laboratory process on an intermediate scale before attempting commercial production. This step is carried out in a pilot plant, which is a mini version of the commercial plant.
Before setting up a commercial scale plant the results, which are derived from pilot plant, are theoretically extrapolated to the commercial scale in terms of equipment size (fermentor / bioreactor), utilities like steam, water, electricity, fittings etc, labour (technical and non-technical) and market surveys. All these data are compiled into a techno-economic report to assess the feasibility of the project. Such a report is also important for seeking financial assistance for the project from banks or other financial institutions.
The following example will give you an idea about the importance of scale-up calculations for the bioprocess industry in terms of reactor size:
Recombinant insulin is produced at 100 mg/L by E. coli at a cell concentration of 1 g/L. Calculate the volume of reactor (size of the fermentor) needed to produce 1 Kilogram of insulin in the following conditions:
(a) When the cell concentration is 1 g/L and insulin production is 100 mg /L.
(b) When the cell concentration is 50 g/L and insulin production is 100 mg /L.
(c) When the cell concentration is 50 g/L and insulin production is 500 mg /L.
(a) Insulin production is 100 mg/L; so fermentor volume needed for 1 Kg of insulin is 1 Kg / 100mg = 1000, 000mg/100,g = 10,000mg = 10,000L.
So we need 10,000-litre fermentor to produce 1 Kilogram of insulin in one batch.
(b) In this case the cell concentration is increased to 50 g/L; so insulin production per liter will be 50 X 100 = 5000 mg = 5 g / L;
Thus, to produce 1 Kilogram of insulin we need 1 Kilogram / 5 g = 1000 g / 5g = 200 g. So, if the cell concentration is increased 50 times, we need 200-litre reactor to produce 1 Kilogram of insulin.
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