Perspectives for improving circular economy in brackish shrimp aquaculture

Shrimp farming in South-East Asian and Latin American coastal regions generates economic benefits for the producer countries and contributes to a healthy nutrition of consumers. However, shrimp farming uses great amounts of fish meal and fish oil in the feed for the provision of essential proteins and polyunsaturated fatty acids during growth. This practice contributes to the environmental burden of the production process, as it is estimated that 25% of the total wild capture fish is used to produce these compounds. Also, intensive brackish water farming in coastal regions promotes the shrinkage of mangrove forests and the contamination of surrounding soil and water resources, causing further environmental degradation. In this work, several concepts for wastewater and sludge treatment in brackish water aquaculture are reviewed, and a novel concept that combines aquaculture with the production of macroalgae and microalgae is proposed to achieve a circular system. Macroalgae can assimilate nitrogen and phosphorus in the wastewater stream, which enables the recirculation of the salty water. Solid residues are converted via anaerobic digestion into several short-chain carboxylic acids and methane. While methane can be used for electric energy and heat provision, the acids can be consumed by heterotrophic microalgae. Both macroalgae and microalgae can be applied as feed additives in shrimp aquaculture, providing proteins and polyunsaturated fatty acid sources. This integrated concept can enable the production of shrimp without the addition of fish meal and oil, enhance nutrient recycling in brackish aquaculture, and minimize the contamination of coastal land and water.