A two-stage membrane bioreactor system was applied to the treatment of partially stabilized leachate from solid waste landfill in Thailand. In the system, an anoxic tank with incline tube for biomass separation from re-circulated sludge is followed by a second-stage aerobic tank in which a direct submerged hollow-fiber membrane module is used for solid–liquid separation. During steady operation of 200 days, BOD, COD, NH3 and TKN removals were found to be 99.6, 68, 89 and 86% respectively. Determination of nitrogen transforming bacteria by fluorescent in-situ hybridization technique revealed a slightly higher percentage of nitrifying bacteria in the aerobic tank and a higher percentage of denitrifying bacteria in the anoxic tank respectively. Anammox-like bacteria were also detected at relatively high percentage.
