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

Helsinki University of Technology, Laboratory of Environmental Engineering, Helsinki, Finland

Mikko Kotro

Helsinki University Development Services, Koetilantie 3, FIN-00710 Helsinki, Finland

Jukka Rintala

University of Jyvaskyla, Department of Biological and Environmental Science, Jyvaskyla, Finland

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 (1ha). A single-stage pilot process was used for nitrification studies. The leachate characteristics were as follows: COD 740 to 2400 mg 1^-1 (chemical oxygen demand), BOD₇ (biochemical oxygen demand) approximately 1000 mg 1 ^-1, N_tot 40 to 120 mg 1^-1 and the temperature was between 2 and 21°C. The results show that 45 to 50% COD removal could be achieved in the UASB reactor even at temperatures below 10°C. The activated sludge process was operated with a 1.1 to 2.2 d hydraulic retention time and at between 8 and 21°C. The removal efficiencies were 80 to 90% for COD, 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 7 D_M m^-3 and 17 to 30 D_M [kg N removed] ^-1) for a landfill representing circumstances in Southern Finland with an annual average flow of 50 m³ d^-1.

Key Words: Anaerobic pretreatment • biological treatment • costs • landfill leachate • low temperature • nitrogen removal • seasonal variation

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