Removal of organic matters and ammonia in landfill leachate via a UASB and anoxic/aerobic bioreactor process

A combined system consisting of an up-flow anaerobic sludge blanket (UASB) and anoxic /aerobic bioreactor was introduced to treat a mature landfill leachate with a high ammonia concentration and low ratio of COD/TN. After 160 days of stable operation, the results indicated that organic matters were mainly removed by the UASB, while the ammonia was removed by shortcut nitrification in the anoxic /aerobic tank. The COD removal efficiency reached 50%-60% at an organic loading rate (OLR) of 3.0kgCOD/ (m3d). The nitrite accumulation rate and the NH4+-N removal efficiency were above 90% and 85% respectively when the reactor maintained a low dissolved oxygen (DO) concentration (1.0-1.2mgL-1) and pH value (7.8-8.3) and temperature (25-30 degrees C) in the aerobic reactor. Also the results revealed a significant amount of nitrogen was removed by shortcut denitrification in the anoxic tank. The total nitrogen (TN) removal rate reached 60%-70%. The results analyzed by scanning electron microscope (SEM) reflected the shape and variety of the anaerobic and aerobic bacteria in the whole system.