The feasibility of using microbial fuel cells (MFCs) in landfill leachate treatment and electricity production was assessed under high levels of nitrogen concentration (6033 mg N L-1) and conductivity (73,588 mu S cm(-1)). An air-cathode MFC was used over a period of 155 days to treat urban landfill leachate. Up to 8.5 kg COD m(-3) d(-1) of biodegradable organic matter was removed at the same time as electricity (344 mW m(-3)) was produced. Nitrogen compounds suffered transformations in the MFC. Ammonium was oxidized to nitrite using oxygen diffused from the membrane. However, at high free ammonia concentrations (around 900 mg N-NH3 L-1), the activity of nitrifier microorganisms was inhibited. Ammonium reduction was also resulted from ammonium transfer through the membrane or from ammonia loss. High salinity content benefited the MFC performance increasing power production and decreasing the internal resistance. (C) 2010 Elsevier B.V. All rights reserved.