Protein recovery during the overall treatment of wastewaters from fish-meal factories

The suspended solids contained in the wastewaters generated by fish-meal industries (5–40 g VSS/l) are composed mostly of protein, which could be recovered to optimise the manufacturing process. In this work, settling, centrifugation and coagulation-flocculation were studied as alternative treatment processes to attain this objective. Settling experiments showed that the flotation of a high fraction of suspended solids occurred (up to 45%), even with previous alkalinisation or the addition of a coagulant such as chitosan. Centrifugation at 10 000 rpm for 12•5 min gave optimum results, TSS and soluble COD removal efficiencies of 45–82% and 10%, respectively, being obtained. The amino acid profile of the solids was quite similar to fish meal, indicating the feasibility of solids reuse. Results obtained after coagulation-flocculation followed by centrifugation showed that among the different compounds assayed sodium polyacrylate and chitosan produced the best results, operating at pH 4 and 7•2–7•8, respectively, and giving TSS removal efficiencies up to 97 and 75%, respectively.