Nitrogen is a chemical element which can be found in fresh water and wastewater in many different forms. In wastewater for example mainly organic nitrogen which comes from the rejections of food can be found. This nitrogen is an essential nutrient and can lead to algal bloom, eutrophication and water pollution. In its reduced form (ammonium, NH4+ and ammonia NH3), it is transformed into nitrate, a process which consumes a lot of oxygen leading to oxygen depletion in the water. Nitrate (NO3-) is also a drinking water pollutant while nitrite (NO2-) is toxic to fish.