Nitrification of anaerobically pretreated municipal landfill leachate at low temperature

Nitrification of anaerobically pretreated municipal landfill leachate (270-1000 mg COD l(-1), 53-270 mg NH4-N l(-1)) was studied in laboratory-scale activated sludge reactors without (AS) and with (ASC) the addition of plastic carrier material. The reactors were run at 10 degrees C (149 d), 7 degrees C (21 d) and 5 degrees C (16 d). With a loading rate of 0.027 g NH4-N g MLVSS-1 d(-1) and a hydraulic retention time of ca. 3 d, at 10 degrees C, complete nitrification was obtained in both reactors. At 7 degrees C, and in loading rate of 0.023 g NH4-N g MLVSS-1 d(-1), both reactors appeared to be overloaded and ammonium removal was only ca. 93%. At 5 degrees C, with a lower loading rate of 0.010 g NH4-N g MLVSS-1 d(-1), complete nitrification was obtained in the ASC reactor but in the AS reactor only 61% of ammonium was removed. Aerobic posttreatment produced effluent with 150-500 mg COD l(-1), less than 7 mg BOD7 l(-1), and, on average, less than 13 mg NH4-N l(-1). In batch assays at 24 and 10 degrees C, maximum nitrification rates were 0.13 and 0.03 g NO3-N g MLVSS-1 d(-1), respectively, while ammonium removal rates were twice as high. The nitrification rates were higher with than without carrier material, suggesting that a large fraction of nitrifying micro-organisms was attached on the surface of the carrier material. The results show that nitrification of anaerobically treated leachate is feasible at temperatures down to 5-10 degrees C. Benefits of the carrier reactor were evident only at low temperatures and under varying loading conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.