Nutrient Removal from Recirculating Aquaculture System Water

• Main Author: Costigan, Eliza M
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2022
• Subjects: recirculating aquaculture systems; phosphorus; adsorption; biofilters; nitrification; Environmental Engineering; Langmuir; Atlantic salmon
• Online Access: https://digitalcommons.library.umaine.edu/etd/3639; https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=4720&context=etd

Recirculating aquaculture systems (RAS), where only approximately 10% of the total system water is exchanged per day, have grown in popularity in recent years due to their potential to provide a high-quality protein source in a contained environment. With increased production comes the need for RAS water treatment to mitigate recirculation and discharge of nutrients produced by fish; mainly phosphorus and nitrogen. When discharged, nutrients can contribute to eutrophication in surrounding water bodies, harming the fish and other aquatic life. Therefore, RAS effluent should be treated before discharge. One method of phosphorus removal is adsorption, a surface phenomenon that is often used to bind dissolved pollutants to a solid-phase medium and remove them from water. Nitrogen is present in RAS as ammonia, which is toxic to fish even at concentrations as low as 0.05 mg L-1. Therefore, the ammonia is transformed to nitrogen’s non-toxic form, nitrate, before recirculation or discharge, by a process called nitrification. Both adsorption and nitrification can be affected by RAS process parameters such as salinity. Many anadromous fish such as Atlantic salmon require a change in salinity over their lifetimes; therefore, both of these processes should be investigated for their response to salinity changes. An adsorption study was performed on an aluminum oxide-based material, RhizoSorb®, to assess its response to different RAS variables. It was found that both film diffusion and intraparticle diffusion are rate-controlling steps in the adsorption process, and the removal efficiencies in batch tests were affected by time, salinity, and phosphate concentration. The Freundlich isotherm fit the equilibrium data better than the Langmuir isotherm, showing that adsorption is a multi-layer process and that the adsorbent is highly heterogeneous. The Clark model was better suited than the Thomas model for predicting the performance of the RhizoSorb® in a flow-through system. The results of this study showed that RhizoSorb® and ...