Outlet of nutrients from the fish laboratory at Norwegian University of Life Sciences (NMBU)
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- Master's theses (IHA) 
Recirculating aquaculture system (RAS) has been more and more applied in aquaculture farms in over the world because of its effectiveness. Like others, the RAS in fish laboratory at Norwegian University of Life Sciences (NMBU) has worked well with 94% of the degree of recirculation, which has economically meaning to the lab. However, the fish lab shall be moved to other location in the near future so it is important to document the amount of nutrients the RAS overflow water contains during a period of normal operation. Therefore, this study was carried out and concentrated on measurements of total Nitrogen (TN), total Phosphorus (TP), Orthophosphate (PO4-P) and Chemical Oxygen Demand (COD) in the overflow of the system. During one month of experiment at fish lab, these parameters were measured carefully to see how they varied in one sample, between samples, through the day and from week to week. The results shown that the concentrations in the outlet of nutrient were always quite stable with the average values around 114.75 gram total nitrogen, 13.18gram total phosphorus, 10.46 gram orthophosphate and 350.54 gram oxygen chemical demand in 34 m3 of overflow water per day. Of these values, the amounts of TP, PO4-P, TN and COD per kg feed were 3.27g, 2.6g, 28.69g and 88.3g, respectively. In addition, 1 kg of biomass discharged 0.04 g TN, 0.03 g PO4-P, 4.28g TN and 0.98g COD to the outlet water. However, the load of total phosphorus needs to be reduced to 0.05mg/l when releasing into the small stream “Brønnerudbekken”, so limiting TP in feed with an acceptable value by using phosphate low containing ingredients and phytase enzyme can be carefully considered.