Problems to be solved in CLEANAQ

Overall, the problems to be solved for practical and operational cost-efficient removal of nutrients in brackish/saline discharge water from recirculating aquaculture systems are related to:

  • Denitrification using external carbon sources such as methanol is expensive (constitutes some 0.2 €/kg fish produced) and energy-consuming.

  • Organic waste produced in the recirculating aquaculture systems can potentially substitute external carbon via anaerobic sludge hydrolysis, however this process has to be further studied and optimized for brackish water.

  • Carbon-free removal of nitrate using wood-chips has very recently been successfully implemented in freshwater recirculating aquaculture systems. The processes, operation, and potential removal capacity has not been investigated in effluents from neither brackish- nor saltwater recirculating aquaculture systems.

  • Although particles (and concomitantly particulate P) can be removed, there is still considerable P in effluents from recirculating aquaculture systems, and sludge hydrolysis might attenuate the problem. Phosphorus removal/precipitation is realistic since water volumes are smaller and more concentrated than in traditional open aquaculture system. The applicability and efficiency of new renewable flocculants or filter media needs to be examined.

  • Denitrification systems and processes (in brackish and marine waters) is still a “black box” as the exact microbiological mechanisms are poorly studied.
27 OCTOBER 2021