Nitrogen waste from rainbow trout (Oncorhynchus mykiss) with particular focus on urea |
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| Institution: | 1. Division of Marine Bioscience, College of Ocean Science and Technology, Korea Maritime and Ocean University, Busan 606-791, Republic of Korea;2. Inland Research Institue, National Institute of Fisheries Science, Changwon 51688, Republic of Korea;1. National Institute of Aquatic Resources, DTU Aqua, Section for Aquaculture, Technical University of Denmark, 9850 Hirtshals, Denmark;2. DTU Environment, Department of Environmental Engineering, Bioenergy Group, Technical University of Denmark, Anker Engelunds Vej 1 – Building 101A, 2800 Kgs. Lyngby, Denmark;1. DTU Aqua, Technical University of Denmark, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark;2. NIVA, Norwegian Institute for Water Research, Section for Aquaculture, Thormøhlensgate 53D, 5006 Bergen, Norway;3. NTNU, Norwegian University of Science and Technology, Department of Biotechnology and Food Science, N-7491 Trondheim, Norway;1. Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark;2. Aalborg University, Department of Biotechnology, Chemistry and Environmental Engineering, Sohngårdsholmsvej 49, DK-9000 Aalborg, Denmark;1. Technical University of Denmark, DTU Aqua Section for Aquaculture, Hirtshals, Denmark;2. Aquaculture and Fisheries Group, Wageningen University, The Netherlands |
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| Abstract: | Particulate and dissolved nitrogen (N) waste components are removed in recirculating aquaculture systems (RAS) using different cleaning technologies, and to dimension and optimize their removal efficiency requires that the expected daily load of the different waste forms can be estimated. Using a laboratory, mass-balance approach, the current study examined the effects of commercially applied feeding levels on the loading of different N waste forms, including daily fluctuations in dissolved total nitrogen (TN), total ammonia nitrogen (TAN), urea-N, and non-characterized, dissolved N deriving from juvenile rainbow trout (Oncorhynchus mykiss). In addition, the study examined whether there was a removal of urea-N across a moving bed biofilter operated as end-of-pipe under commercial conditions. The laboratory, mass-balance study showed that there were no effects of feeding levels (1.3, 1.5 or 1.7% of the biomass per day ) on the excretion of dissolved N components, which constituted the majority of total N waste (>81.6% on average). The excretion of urea-N and non-characterized, dissolved N components constituted 12–13% and 9–11%, respectively of dissolved TN. The excretion of urea-N was largely constant and independent of the daily feeding practice, whereas that of non-characterized N appeared to reflect the daily feeding activity, following the trends in TN and TAN. The time limited feeding regime applied in the laboratory study resulted in a pulse in the excretion of TAN that a biofilter may be unable to fully level out, potentially resulting in unnoticed, critical water quality conditions in intensive RAS during certain times of the day. Particulate N waste constituted a minor fraction of total N waste (<18.4% on average), and the actual loading depended on the digestibility of dietary protein/nitrogen. Results from the commercially operated, nitrifying biofilter showed that urea-N was removed at a rate of 0.014 g N m2 day?1. Compared to the removal of TAN (0.208 g N m2 day?1), the moving bed biofilter was 1.07 times more active in removing dissolved N than immediately expected when only considering TAN. |
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| Keywords: | Daily fluctuations Feeding level Nitrogen waste TAN Urea Waste form |
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