The aquaculture industry has been very slow to adopt denitrification methods. Present practice is to convert the toxic metabolic waste product ammonia via nitrite to nitrate in a nitrifying bio-filter. This microbial process demands oxygen and reduces the pH, requiring expensive buffering treatment. The accumulating nitrate is generally flushed from the farm into recipient waters without pollutant removal. The DeammRecirc proposal is based on the recent experiences and success of using deammonification to convert ammonia to nitrogen gas in other waste water treatment applications. This method will in the proposed project be adapted for use in recirculation aquaculture systems (RAS) for fresh- and marine water species. By using a deammonification reactor within RAS, ammonia will be converted to nitrogen gas in one step. Deammonification bacteria enriched in granules will be adapted to RAS water qualities. The advances compared to current SoA include reduced oxygen use, reduced cost for buffering chemicals, lower carbon footprint, reduced levels of nitrate rich effluent released to the environment, reduced pumping cost and treatment need of new exchange water. The project includes 11 participants, of which four are industrial SMEPs, which will produce, develop and distribute the DeammRecirc system post project, one is a large enterprise end user, one participant is from S. Africa who plans to transfer the technological development to the aquaculture industry to their continent and four are RTD participants, which will be responsible for the RTD work.