Advanced nitrogen removal using bio-refractory organics as carbon source for biological treatment of landfill leachate

•A combined system with different kinds of anaerobic and anoxic/aerobic reactors was developed.•The system accomplished improvements in nitrogen removal rate from landfill leachate.•Nitrite and nitrate nitrogen were efficiently removed through denitrification.•Refractory organics served as the carbon source and were also degraded. A combined system was developed to enhance the chemical oxygen demand (COD) and total nitrogen (TN) removal from landfill leachate. The system consists of an up-flow anaerobic sludge blanket (UASB), anoxic/aerobic (A/O) reactor, and the denitrifying UASB (DUASB). The influent used in our study was a mixture of 1:2 raw leachate and domestic wastewater. Because of the inhibitory effect of free ammonia (FA) on the nitrite-oxidizing bacteria (NOB), stable partial nitrification occurred, with a consistent nitrite accumulation ratio in the A/O reactor. In the DUASB, the nitrite and nitrate nitrogen (NOX−-N) were removed efficiently by denitrification by utilizing the carbon source of refractory organics under anoxic condition, which were likewise degraded. The organic matter, total nitrogen and ammonia nitrogen in the final effluent were 80–90, 39, and 14mg/L, respectively, with respective removal efficiencies of 95, 98, and 95%. The respective COD removal efficiencies in the UASB, A/O and denitrifying-UASB were 76.8, 2.8, and 16.3%. The proposed process is an advanced technique that accomplishes the removal of organic matter and nitrogen in a single step.