Comparison of two systems on water quality, ammonia and GHG emissions in RAS for rainbow trout

Aquaculture is a rapidly expanding sector, driven by growing demand for fish products, but it is important to recognise that this farming system has significant ecosystem impacts and needs to be managed appropriately. It can directly affect aquatic environments, contributing to biodiversity loss, deep water, and air pollution. Greenhouse gas (GHG) emissions from aquaculture can vary depending on several factors, such as the species cultivated, management practices, and production system efficiency. To reduce the environmental impact of aquaculture and its related greenhouse gas emissions, sustainable practices and technologies have been developed. These include the use of recirculating aquaculture systems (RAS), sustainable feeds, and responsible waste management to achieve more sustainable production by reducing water consumption. Additionally, because they are land-based, they limit direct interaction between aquaculture practices and the environment. Although RAS has advantages in terms of climate change adaptation for supporting seafood production, it also has a greater negative impact on climate change for the energy consumed by the systems. RAS relies on physical and biological filtration tools to filter water. Biofiltration is an effective method for water purification, but it can be challenging to develop the necessary bacterial population to oxidize ammonia to nitrite and then to nitrate. Recently, scientists have explored alternative water purification systems, including advanced oxidation processes such as photo-electrocatalysis. This technique accelerates the removal of ammonia, reducing its accumulation in water systems. This study compares two filtration systems: a classical plant equipped with biofiltration, and a plant equipped with a biofilter coupled with a photo-electrocatalytic system. The objective is to evaluate the differences between the two solutions in terms of the physical-chemical parameters of the water, with particular attention to the kinetics of nitrogen compounds, as well as the levels of ammonia and greenhouse gasses (methane, nitrous oxide and carbon dioxide) emissions from the water surface of the tanks, measured through the floating chamber method, in the grow-out phase of Rainbow trout reared at low density (15 kg/m3).