Downstream processing: Concentration
In this series of articles on downstream processing, we had talked about first two steps of downstream processing, namely -solid-liquid separation and Release of Intracellular Products.
Now, in this article, we are going to talk about the Concentration which is the third step of downstream processing.
The process of Concentration is needed to be done because the filtrate that we get from the previous step usually contain over 80% of water in it. And water has to be removed to get the high concentration of desired product which is done in this process of concentration.
Techniques used in Concentration are as follows: -
1. Evaporation: It is one of the traditional and easiest method of removing water from broth filtrate. In this technique, a heating device has used the size of which depends on the scale of the industry. Concentrate product and steam are separated in another unit followed by a condenser to condense water vapours. Some commonly used evaporators are:
• Plate evaporators
• Centrifugal forced film evaporators
• Forced film evaporators
• Falling film evaporators
2. Membrane Filtration: Membrane Filtration is another convenient method for getting the concentrated product. It makes use of a semi-permeable membrane to restrict bigger molecules to pass through its pores and allow smaller ones to pass through it resulting in separation of the two. Types of Membrane filtration techniques are: -
• Membrane absorbers
3. Precipitation: Precipitation is another technique employed for the concentration of bimolecular products. In this technique, organic solvents are used. It can be done by use of following: -
• Neutral salts
• Organic solvents
• Ionic polymers and Non-Ionic polymers
• Change in pH
• Precipitation by ligands
4. Liquid-liquid extraction: We can also get concentrated product by using the method of liquid-liquid extraction. In this technique, one liquid phase is changed into other. This technique provides a partially purified product. This technique can be categorised in terms of lower and higher molecular weight products as given below:
• Extraction of low molecular weight products
• Physical extraction
• Dissociation extraction
• Reactive extraction
• Supercritical fluid (SCF) extraction
• Extraction of high molecular weight compounds
• Aqueous two-phase systems (ATPS)
• Reverse micellar systems
5. Adsorption: Biological products can also be concentrated by this method. It makes use of either active charcoal or cellulose-based adsorbents. It can be used efficiently to separate biological products like proteins.