Màster d'Enginyeria Ambiental, Facultat de Química, Universitat de Barcelona, Curs: 2015-2016, Tutor: Isaac Fernández RodríguezThe application of partial nitritation/anammox process to remove nitrogen from wastewater is a cost effective and sustainable approach since it can save energy and resources. It was applied successfully in treating ammonium rich waste streams (Wett, 2007). This is worth to use deammonification (partial nitritation/anammox) process in sewage treatment to create an energy positive environment and therefore, this has been studied extensively for last few years to investigate its applicability in mainstream condition where both temperature (10-20 °C) and nitrogen concentration (<100 mg N/L) are very low. Systems based on Anammox can be of great help to comply with stricter wastewater discharge regulations and reduce environmental problems caused by nutrients discharges (e.g. eutrophication). In this regard, a study of one-step Partial Nitritation/Anammox process was carried out in a moving bed biofilm reactor by using municipal-like wastewater with the aim to conduct the start-up of Partial Nitritation (PN) process in the MBBR and then stabilize it, subsequently perform the Anammox process in the same MBBR system. Finally, optimise the PN/Anammox MBBR to have higher BNR rate. PN/Anammox process was successfully tested in a 4.5 L lab-scale MBBR for 141 days at 20 °C, with about 20% filled with Kaldnes K1 carriers. The feeding was prepared and calculated to have 50 mg NH4+/L, the source of the wastewater was from the rejected water of anaerobic digester from a municipal wastewater treatment plant. Several changes were made to achieve our objectives step by step. The analysis shows that the efficiency of NH4+ removal has reached a maximum of 95% while the maximum overall percentage of nitrogen removal of 32.9% after the addition of Anammox bacteria to the reactor