NEDBRYTNING AV UREA I ET NITRIFISERENDE DYKKET BIOLOGISK FILTER I ET FISKEOPPDRETTSKAR MED KARINTERN RESIRKULERING (SYSTEM BIOFISH) / Removal of Urea in a Nitrifying, Recirculating and Submerged Biological Filter Located in a Fish Tank (The Biofish System)
In a fish tank with a build-in upstreams aerobic biological filter (The BIOFISH System), batch-experiments were made to study whether hydrolysis of urea is a limiting step in the conversion of urea to nitrate. Based on frequent grab sampling and analysis of the different forms of nitrogen in the water, calculations were made for the reaction rate of urea hydrolysis and ammonia and nitrite oxidation (nitrification). The tests demonstrated that urea hydrolysis was a faster process than nitrification. This means that urea hydrolysis was not the limiting step for the conversion of urea to nitrate. Nitrifying biological filters must therefore be designed from the total Kjeldahl (TKN) nitrogen load.