Characteristics of the bioreactor landfill system using an anaerobic–aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic–aerobic process might remove above 90% of COD and near to 100% of from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8–7.7 g/l d, but the effluent COD concentration increased to 2.9–4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic–aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.