BACKGROUNDPersistence of ammonium nitrogen in landfill leachate still remains a challenge. The Autotrophic Nitrogen Removal (ANR) system has shown promise and become one of the treatments used for removing nitrogen from high strength wastewater. Less well known is the fact that the nitrifying-denitrifying inoculum can readily be grown in large quantities and can be used in the ANR system directly to treat real leachate without adaptation. As such, a scale-up study from lab-scale to pilot-plant scale was performed using nitrifying-denitrifying sludge to analyse the feasibility. RESULTSResults showed on average 72 mg N L-1 d(-1) was effectively removed in the lab-scale bioreactor and up to 36.6 mg N L-1 d(-1) in pilot-scale reactors. When the leachate was treated to reduce the ammonium content, it was found to be possible to reach a chemical oxygen demand (COD) removal of roughly 40% in both lab- and pilot-scale reactors. Operational costs were decreased by 37% costs when combining ANR and nitrification-denitrification compared with individual conventional nitrification-denitrification. CONCLUSIONSThis study demonstrates that high-rate ammonium nitrogen and organic matter removal from landfill leachate by ANR is possible and this will allow a significant decrease in operational costs without significant investment costs. (c) 2014 Society of Chemical Industry