NOVELTY - The method for the treatment of landfill water with high nitrogen and low 5-day biochemical oxygen demand in a two-stage process, comprises mixing the landfill water with nitrifying activated sludge in a first step, oxidizing ammonium contained in the landfill water only in a part to nitrite, and reacting nitrite and ammonium contained in the aqueous phase separated from the activated sludge under exclusion of oxygen in activated carbon fixed bed reactor to molecular nitrogen in a second step. The activated carbon fixed bed reactors turned in rows are flowed one after the other.    USE - Method for the treatment of landfill water with high nitrogen and low 5-day biochemical oxygen demand in a two-stage process.    ADVANTAGE - The method ensures treatment of landfill water with high nitrogen and low 5-day biochemical oxygen demand and high quality in environmental friendly manner.    DETAILED DESCRIPTION - The method for the treatment of landfill water with high nitrogen and low 5-day biochemical oxygen demand in a two-stage process, comprises mixing the landfill water with nitrifying activated sludge in a first step, oxidizing ammonium contained in the landfill water only in a part to nitrite, and reacting nitrite and ammonium contained in the aqueous phase separated from the activated sludge under exclusion of oxygen in activated carbon fixed bed reactor to molecular nitrogen in a second step. The activated carbon fixed bed reactors turned in rows are flowed one after the other. The ammonium content is adjusted in the first step, which is operated under microaerophilic condition. The oxygen content adjusted in the first step is 0.01-0.4 mg/l. The ratio of nitrogen content in the ammonium and in the nitrogen dioxide of 1:1.1 is adjusted in the flow of the first step over a process control. In the first step, temperature is adjusted to 28-39 degrees C. The addition to the second step is same as the addition to the activated carbon fixed bed reactors free from dissolved oxygen. The activated carbon is inoculated to begin the process with planctomycetes containing granular. The ratio of the used activated carbon and the granular is 50:1 related to the volume. The internal surface of the used activated carbon is 600-1800 m2/g. The first and the second step are separated through a membrane filtration. An INDEPENDENT CLAIM is included for a device for the treatment of landfill water with high nitrogen and low 5-day biochemical oxygen demand in a two-stage process.