Techno-economic analysis of using microalgae to treat streams from fish RAS farming and replace fish meal: A case study

Aquaculture streams contain nutrients that can cause eutrophication problems if released to the environment. However, microalgae can absorb these compounds from the water. In this study, an autotrophic microalgae bloom was cultured outdoors in a High-Rate Algal Pond (20 m2) using an aquaculture stream. The process proved to be technically feasible, removing 90 % of nutrients (nitrogen and phosphorus). In addition, the characterisation of the produced microalgae showed suitability to replace fish meal in Solea senegalensis fattening feeds (up to 21.4 % inclusion). The techno-economic analysis of the process at large scale (10.19 ha) resulted in a water treatment cost varying from 1.37 to 1.66 € m−3 depending on the assumptions. The capital costs were mainly driven by the production stage (76–84 % cost of equipment), while labour represented 28–36 % of the operational expenditures. In case microalgae biomass was sold as high-value ingredient for fish feed, total costs could be covered between 21 and 81 %.