Each step of the transformation process from fish wastes to energy generates some by-products besides the fuel product. These by-products and their possible valorisation pathways are described hereafter.
Figure 1: Fuel products, by-products and their potential market application
The main by-product from oil extraction is protein waste (Fig.2) whereas the oil to biodiesel process generates crude glycerol (Fig.3) These by-products can be recycled and utilised in other production processes.
The crude glycerol contains methanol, salts and organic residues. Its utilisation depends on the glycerol market situation. Depending on the preferred valorisation routes, different refining stages are required, as depicted below:
There is a clear distinction between the markets for crude glycerol and refined glycerine. In 2008 there was oversupply of crude glycerol to the chemicals industry but the demand for refined glycerine was still growing. The volume of refined glycerine was not growing according to the demand growth. The growth of refined glycerine usage in the fine chemical industry is expected to rise creating a favourable market environment for the refined glycerine compared to the crude glycerol (Frost and Sullivan 2008, Voegele 2009).
Figure 5: Crude and refined glycerine (http://www.crowniron.com):