Shellfish processing wastewater: characterization of a group of wastewater resources for future valorisation

The seafood processing industry generates large volumes of wastewaters that are released to the environment following variable treatment processes. The composition of shellfish (e.g., mussel, crab) processing wastewater is dependent on the processing technology used, shellfish species and quantities processed, as well as the final desired food product, among other factors. Mussel processing wastewater, for example, can contain up to 860 mg L^-1 biochemical oxygen demand (BOD₅), 250 mg L^-1 ammonia (NH₃-N) and ammonium (NH₄-N), 2000 mg L^-1 total nitrogen (TN), 2400 mg L^-1 sulphates (SO₄^2-) and 20 g L^-1 chloride (Cl^-). This review reveals marked differences in concentrations of BOD₅, chemical oxygen demand (COD), total suspended solids (TSS), NH₃-N, and fats, oils and grease (FOG) in the processing wastewaters from different shellfish group of species. Ranked from high to low concentration are wastewaters from: mussel > crab > fish > scallop > shrimp > clam > sea snail > oyster > lobster ≥ squid. In most cases, concentrations exceed the international standards and limits for effluent discharges. Yet, this study shows that processing wastewater is a rich source of nutrients and minerals that can be utilised. Another innovative approach is to cultivate complementary species, e.g., plants or algae, on wastewater resulting in remediation and valorisation. These approaches are aligned with circular economy principles and can contribute towards the goal of a zero-waste industry.