Biological nitrogen removal from landfill leachate: a pilot-scale study

A pilot-scale two-stage process including an anaerobic pretreatment (up-flow anaerobic sludge blanket, UASB) unit and a pre-denitrification activated sludge process was studied for treating leachates from a municipal landfill (waste aged 4 to 5 years, area 2.5 ha) and from a windrow composting area (1 ha). A single-stage pilot process was used for nitrification studies. The leachate characteristics were as follows: COD 740 to 2400 mg l(-1) (chemical oxygen demand), BOD7 (biochemical oxygen demand) approximately 1000 mg l(-1), N-tot 40 to 120 mg l(-1) and the temperature was between 2 and 21 degrees C. The results show that 45 to 50% COD removal could be achieved in the UASB reactor even at temperatures below 10 degrees C. The activated sludge process was operated with a 1.1 to 2.2 d hydraulic retention time and at between 8 and 21 degrees C. The removal efficiencies were 80 to 90% for GOD, over 98% for BOD7, over 90% for NH4-N and over 70% for N-tot. The dependence of denitrification efficiency on leachate biodegradable COD fraction and COD to N ratio was evaluated. Overall treatment efficiencies were good and applicable for design purposes. The total costs were estimated for a full scale pre-denitrification process at FIM 10 to 20 m(-3) and FIM 50 to 90 (kg N removed)(-1) (3.5 to 1 DM m(-3) and II to 30 DM [kg N removed](-1)) for a Landfill representing circumstances in Southern Finland with an annual average flow of 50 m(3) d(-1).