EQUIPMENT
Smart technology for water purification in recirculating aquaculture systems Eleonora Buoio, University of Milan, Giulia Moretti, Aquatrade, Daniela Bertotto, Giuseppe Radaelli, University of Padua, Alessia di Giancamillo, Elena Selli, Gian Luca Chiarello, University of Milan, Nadia Cherif, National Institute of Marine Sciences and Technologie, Tarek Temraz, Canal Suez University, Annamaria Costa, University of Milan Global fish production reached 82.1 million tonnes in 2018 and, supported by the rising global population and food demand, is expected to rise to 261 million tonnes by 2030, with 62% of the overall quantity coming from aquaculture production (FAO, 2020). The effects of this economic sector on the environment could be significant: the main problems concern water pollution and waste generation, and possible health risks for biodiversity and humans if its expansion is not based on sustainable farming systems. Recirculating aquaculture systems (RAS) are a good solution to increase food production while lowering negative environmental impacts (Thomas et al., 2018). In RAS, fish are reared in tanks in a controlled indoor environment and the water is purified by filtration, to remove uneaten feed, fish excretion and other wastes generated by farming activities, before being returned to the system. The water is mechanically and/or biologically filtered, sterilized, and oxygenated to guarantee a high quality of water to maximize operational efficiency and productivity. The characteristics of the biofilters determine the main maintenance requirements and management techniques needed for production. Different levels of sophistication and efficiency can be achieved, but in general, all RAS show high levels (>90%) of water reuse (Badiola et al., 2012). Water and energy are the most employed resources in aquaculture and the increasing production requires more sustainable
management, i.e., using green energy, and minimizing water discharges, maintaining water quality parameters suitable for the cultivated species. A high concentration of nitrogen compounds in RAS represents the most important challenge to face. Organic nitrogen derived from fish catabolism is potentially toxic for aquatic organisms, especially in the ammonia form. Its accumulation could be potentially lethal for fish and can cause different problems in the ecosystem. A desirable goal of the fish culture industry would be to discover a method that converts total ammonium nitrogen (TAN) into nontoxic molecular nitrogen (i.e., gaseous N2).
An innovative purification system Photocatalytic reactions are initiated on semiconductor materials by the absorption of light. This provokes the formation of reactive electron–hole pairs in the photocatalyst that can promote redox reactions: electrons photo promoted in the conduction band can reduce electron acceptor species while the holes in the valence band can oxidize electron donor species. Photocatalysis has been successfully employed in the removal of several pollutants of water or air by their full mineralization or for solar energy conversion and storage through the production of solar fuels. The photocatalytic treatment of ammonia-containing water was demonstrated to be able to lower ammonia and nitrite in laboratory conditions (Livolsi et al.,
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