CLEANAQ will develop novel procedures for end-of-pipe nutrient removal to improve the cost-efficiency and to further reduce environmental impact of fish farming in recirculating aquaculture systems in the different salinities prevailing in the Baltic Sea area. The project investigates three methods for end-of-pipe treatment of effluents: single-sludge denitrification, carbon-free woodchip denitrification, and non-microbial nutrient removal.