Biological nitrogen removal using nitrite as a shortcut has recently been proposed for the treatment of high strength landfill leachate. The aim of this study was to assess the application of the SHARON (Single reactor High activity Ammonium Removal Over Nitrite) process for the partial nitrification of leachate generated in old landfills. Particular attention was given to the start-up phase of the process. This study demonstrated that partial nitrification can be obtained when treating raw leachate after biomass acclimation. Only a fraction (50-70%) of the ammonia present in the leachate can be oxidised due to a limited amount of alkalinity available. Stable nitritation was obtained by applying a hydraulic retention time (HRT) of 4-5 d, which is higher than the values proposed for the effluent of anaerobic digesters. This higher HRT could probably be allowed by the high concentration of free ammonia present in the leachate, which could severely inhibit the growth of nitrite-oxidising bacteria.
Keywords: SHARON process; acclimation; inhibition; nitrification; nitrite; start-up.