Question

A qualitative analysis of the bioreactor modes of operation, outlining their advantages and limitations.

1. batch

2. fed-batch

3. continuous mode (chemostat)

4. perfusion system

Answer 1

1) Batch: A batch system does not have an inflow or outflow. It is operated for a particular time and the products are removed. It is useful in case of small production rates and products which have small life cycles in the market. It however requires large manual labour for operation and also, the purity of products can vary from batch to batch and hence, cannot be used for high purity product requirements.

2) Fed-batch: It is a semi-batch system where there is an inlet but no outlet. It is usually when the concentration of one of the reactants should be very low compared to other reactants and so on. It is also semi-batch system and hence has the same disadvantages of batch such as high labour cost and time and inconsistent purity of products.

3) Continuous mode: Here, there is a continuos flow inlet and outlet of reactants and products. They gurantee high purity products and high production rates and is used for products which have a very long life cycle in the market. The disadvantages are that they are costlier to maintain and control, requires skilled personnel in control room, frequent maintanence cannot be performed easily.

4) Perfusion system: These systems are recycle systems in which some of the products is recycled back to the reactor. This is to increase the conversion of the reactants, in case of autocatalytic reactions some of the products is recycled to provide catalyst and also, to dilute the feed stream.