INNOVATIVE PHOTOELECTROCATALYTIC REACTOR FOR AMMONIA REMEDIATION AND SUSTAINABLE FISH FARMING

Land based aquaculture generates large amounts of nitrogen rich wastewater, contributing to eutrophication in fresh and seawater environments1. The nitrogen content (nitrite ion NO2- and nitrate ion NO3-) comes from the biological aerobic oxidation of the toxic ammonia NH3 naturally produced by fish. In this work a photoelectrochemical reactor designed for Recirculating Aquaculture Systems (RAS) exploits the UV-electrochlorine advanced oxidation process. Illumination of the photoanode promotes the oxidation of Cl- naturally present in water to highly reactive chlorine species, converting ammonia into NO3- and the more inert N2 2. The aim is to abate the overall nitrogen content in the water, improving water quality, fish welfare and sustainability for aquaculture. The photocatalyst is a thin film of self-assembled vertical TiO2 nanotubes3, synthesized through anodization of a Ti mesh in a HF containing ethylene glycol solution at 30V. 6 h of anodization produces photoanodes yielding currents up to 500 mA at 6 V. Preliminary tests on 100 mgL-1 NH3 5 mM KCl solutions, over the course of 8 h, show NH4+ being completely degraded. The amounts of NO2- and NO3- formed only account up to 50% of the consumed ammonia nitrogen, meaning the selectivity towards N2 formation is above 50%. The reactor prototype has been used in a real-life experimentation of fish farming using rainbow trout4 showing a lower NO3- accumulation compared to the traditional biofilter No visible effects on fish health are reported, and the technology has proven to be biocompatible.