The Atlantic case aims at producing BBF’s from fish by-products using ThermoMechanoChemical (TMC) fractionation by twin-screw extrusion. Configured as an extraction tool, extrusion represents an industrial continuous process providing simultaneously a solid and a liquid fraction. The use of TMC process for fertilizers production from fish by-products is an innovative approach that enables the recovery of not only BBFs but also fish oil to reach a ZERO-waste process. The biorefinery scheme integrates the extruder as main technology but also includes pretreatment units and downstream processes. The process was developed from TRL4 to TRL7. The optimization of the TMC process included the following operating parameters: screw profile, screw speed, temperature, fish by-products feed rate, L/S ratio, enzymes introduction. The efficiency was evaluated by measuring the yield and selectivity in N, P, K and lipids in the different fractions.
To assess the properties of the final products and to avoid microbial development, the raw materials must be kept under the cold chain: +4°C (direct use) or frozen (delayed fractionation).
Up to TRL7, grinding the fish by-products is necessary to introduce them into the extruder. This can be avoided at TRL8-9 on larger extruders. Nevertheless, grinding allows fractioning all fish heads and frames, independently of species and their morphology (size, shape,…).
If we want also to process viscera, they should be sorted, to remove impurities such as stones that can severely damage the extruder. And so whatever the TRL.
Figure 1: Biorefinery scheme
The solid/liquid separation in the TMC process is very sensitive. Little modification in the operating parameters could be responsible in losing the dynamic equilibrium.
Figure 2: Principle of the fractionation by twin-screw extrusion
