Optimisation of liquor yield during the hydraulic pressing of sardine (Sardina pilchardus) discards

Fresh sardine (employed as discard model species) was pressed with a hydraulic press in order to obtain a partially dewatered cake (whose volume represents between 55% and 60% of the initial volume of raw material) and a 3-phase press liquor comprising an aqueous fraction, an oil fraction and a variable amount of suspended solids. Pressing conditions, such as final pressure to which the sardine was subjected, compression speed, number of pressing stages and time of relaxation between two consecutive pressing stages, were optimised by means of a statistically designed experiment. The goal of the optimisation problem was to achieve maximal yield of press liquor with a minimum load of suspended solids. The suspended solid content in the press liquor must be kept to a minimum in order to facilitate any further treatment by operations such as membrane filtration. The conflict between these two objectives suggested employing a multiobjective optimisation technique. A Pareto Front was generated in order to find a set of solutions which satisfied both objectives to an adequate degree.