Recirculating aquaculture systems (RAS) have lower water consumption and lower nutrient discharge to the environment than the traditional flow-through systems, making them environmentally sustainable fish-producing systems. However, waste management still need to be improved to reduce environmental impact. Partial nitrification combined with anammox (PNA), which combines the anammox with the partial nitrification, is currently applied for nitrogen removal from wastewater with very high concentrations of TAN, and is characterized by reduced requirements for aeration, no need for addition of carbon source, lower sludge production. In the BlueBio project RASbiome, we investigate the potential for adapting the PNA process to RAS relevant conditions with low TAN concentrations, to seek out an economical and sustainable alternative to solve the nutrient discharging problem of RAS. A continuous PNA moving-bed bioreactor (MBBR, 14L) was started up by applying active AnitaMox carriers, which originated from wastewater treatment plant treating wastewater with approximate 1000 mg TAN and 3000 mg COD per liter. The PNA-MBBR was fed with synthetic water (10 mg/L TAN and 15 g/L COD,) with a hydraulic retention time of 2 days at 20℃. The PNA-MBBR showed an efficient nitrogen removal ability after around 4 weeks adaption. The TAN removal rate gradually increased from around 40% (week 5-week 10) to around 75% (week16-week 23). After decreasing the inlet TAN to 5mg/l, the TAN removal rate has been stable around 90% for 6 weeks with an outlet concentration of TAN at below 0.1mgl/L (0.08±0.03mg/L). No nitrite accumulation was observed during the whole trial. This experiment demonstrated that the PNA process can be applied for removal of nitrogen at RAS relevant TAN concentrations. Bacterial and archaeal biofilm microbiomes of bio-carriers will be characterized by high-throughput DNA sequencing of 16S rDNA amplicons, and the results will be presented at Havbruk 2022.