Effective nutrient waste management is a key driver of profitability in recirculating aquaculture systems (RAS), particularly in handling nitrogenous wastes. While nitrifying biofilters are widely established and integrated into RAS, the development of denitrifying biofilters holds promising opportunities for further enhancing system efficiency and sustainability.
Denitrification, carried out by facultative anaerobic microorganisms, converts oxidized nitrogen compounds like nitrite and nitrate into nitrogen gas (N₂). This critical process can be fueled by organic carbon (heterotrophic denitrification) or inorganic sources (autotrophic denitrification), depending on the electron donors available. Heterotrophic denitrification is typically supported by external carbon sources, such as carbohydrates or alcohols, or by endogenous carbon from fish waste.
Beyond its primary function of nitrate removal, denitrification contributes to several vital processes in RAS. It raises alkalinity, thereby compensating for the inorganic carbon lost through nitrification, while also reducing organic carbon discharge. Furthermore, denitrifying organisms play roles in phosphorus and sulfur cycling. Some denitrifiers can accumulate excess orthophosphate, leading to substantial reductions in the ambient phosphorus levels. In marine systems, autotrophic denitrifiers also prevent the accumulation of toxic sulfides by mitigating sulfate reduction.
In today’s world of increasingly stringent environmental regulations, denitrification offers a natural, efficient solution to control nitrogen emissions and comply with regulations while minimizing the need for external chemical treatments or costly infrastructure modifications. By leveraging denitrifying biofilters, aquaculture operations can maintain high productivity while meeting environmental standards, reducing their ecological footprint, and enhancing public perception of the industry.
This presentation will delve into the multifaceted benefits of denitrification in RAS, illustrating how the optimization of this process can lead to improved water quality control, resource efficiency, and overall system sustainability.