Abstract:
Water quality is one of the most critical determinants of fish health, performance, and mortality in aquaculture facilities. Among all water-quality parameters, real-time monitoring of ammonia is particularly important due to its acute toxicity in its unionised (NH3) form. Ammonia is naturally produced through the nitrogen cycle and exists in equilibrium with its ionised form, ammonium (NH4+), depending on pH and temperature. In aquaculture environments, even short-term elevations in unionised ammonia or total ammonia nitrogen (TAN) can disrupt cellular processes, cause stress, suppress feeding, and ultimately lead to mortality. This challenge extends beyond facilities: ammonia released into receiving waters contributes to nutrient imbalance, eutrophication, and wider ecosystem impacts, linking reliable monitoring directly to licensing and environmental compliance.
To date, the measurement of nitrogen species has been difficult for RAS end users, where high costs are met with unreliable data due to the challenges some technologies face from interference and biofouling. Current practice relies heavily on manual colorimetric tests or unstable ion-selective electrode (ISE) probes, both of which suffer from drift, fouling, interference from salinity and pH, and require constant recalibration. These limitations leave operators with low-frequency, low-confidence ammonia data that often misses rapid spikes caused by feeding events, biofilter instability, disease treatments, or equipment failures. Additionally, sporadic analysis does not arm the operators with the granular data required to be in total control of water quality, and the grow out processes.
Researchers at Aquamonitrix have developed a novel methodology for the detection of Ammonia, based on the conversion of ammonia to a UV-chromophore. Ammonia cannot directly be measured by standard UV-Vis spectroscopy (200 nm – 1,100 nm), due to its absorbance lying outside this window*. However, indirect detection (i.e. converting ammonia into another chemical form) however, is a proven, robust method for ammonia detection. This allowed for the development of an analyser that delivers simultaneous detection of ammonia, nitrite, and nitrate. The proposed method, which employs rapid, high-capacity ion chromatography with UV-LED detection, has been tested and validated in the laboratory at Aquamonitrix facilities, through the construction of a prototype analyser, that is able to in-situ convert ammonia into a UV-active chromophore, while simultaneously measuring and quantifying all three primary inorganic nitrogen species. This analyser was demonstrated at a flow-through aquaculture farm where it monitored ammonia, nitrite, and nitrate for a period of weeks. In summary, the work here-in will present a real-time, online total inorganic nitrogen (TIN) analyser with low maintenance requirements (with uptimes of ≥85%), that is highly accurate (≥90%) and precise (≥90%), resistance to bio-fouling and can operate in both fresh and saline RAS farms without any user-level actions. The analyser has a low environmental impact and provides real-time data through IoT connectivity.
This technology will facilitate new possibilities for improved control of the aquaculture facilities and will deliver increased resource utilisation efficiency The real-time monitoring of ammonia, (alongside nitrate and nitrite), provides important information that can be used to implement process controls with regard to feeding. Next to energy, feed is one of the biggest green-house emitters for the aquaculture industry, and with the general trend towards renewable energy, it is increasingly becoming the largest source of environmental burden. Thus, the implementation of this technology, will help to improve the feed-conversion ratios (FCR) of RAS operators, and as a result, reduce their overall environmental burden. Equally, by allowing RAS operators to optimise their stocking densities, the CO2 cost per fish will be reduced, thereby reducing the overall greenhouse green-house burden of the farm, while also minimising energy consumption across RAS operations, mainly by optimising stock density and reducing water exchange.
*in the condensed phase
Acknowledgment
The authors would like to thank project partners Havland and MOWI for their expertise and assistance with this work. They would also like to thank and acknowledge FHF – Norwegian Seafood Research Fund and Bord Iascaigh Mhara for the help, aid and support for this work.