Biological nitrogen removal from municipal landfill leachate in a pilot scale suspended carrier biofilm process

Leachate from a municipal landfill receiving both household and industrial waste was treated in pilot scale suspended carrier biofilm reactors for removal of nitrogen and organic matter. Nitrification was studied in two parallel aerated reactors, filled to 60% (v/v) with two different models of carrier media with specific surface areas of 210 and 390 m2/m3 media, respectively. Denitrification was carried out in a mechanically stirred, anoxic reactor filled to 40% with the carrier media having a surface area of 210 m2/m3. Nitrified leachate from one of the aerobic reactors was fed to the anoxic reactor together with external carbon source, initially acetic acid and later methanol, to promote denitrification. The leachate temperature varied between 10 and 26°C during the study. Nitrification proceeded well in this temperature range. The highest volumetric nitrification rate, 24 g N/m3 reactor h (16°C), was obtained for the media with the largest surface area. The maximum denitrification rate with methanol as carbon source was approximately 55 g N/m3 h. As the process had reached optimal operation, inorganic nitrogen was almost completely removed and the removal of total nitrogen was approximately 90%. The chemical oxygen demand (COD) removal was around 20% during the study.