Achieving clean technology in the fish-meal industry by addition of a new process step

Fish-meal processing plants use large volumes of seawater to unload the fish from ships. Water to fish ratios range from 5 to 10 (m³ tonne⁻¹), producing an effluent high in chemical oxygen demand (COD) load, which is discharged to the sea. Alternative treatments were studied from economic and environmental aspects. The selected treatment involved two sequential steps: recycling of water during unloading and salvaging of reusable organic matter by chemical coagulation of soluble proteins with FeCl₃ followed by centrifugal separation. The recovered sludge was incorporated into the fish-meal process. Technical feasibility and cost implementation at industrial-scale were assessed. Results obtained at one plant demonstrated overall COD removal efficiencies of 93% for the clarified effluent (91% for proteins and 93% for fats and oil). Incorporation of the precipitated organic matter into the process increased productivity by approximately 7%.