Biological treatment of municipal landfill leachate

A two-stage UASB-A/O system was introduced to treat a leachate containing high organics and ammonia from an immature landfill site. The simultaneous denitrification and methanogenesis were successfully carried out in UASB1 and the effluent COD was further removed in UASB2. The biodegradation of residual organic substance and nitrification took place in the A/O reactor. The maximum organic removal rates in UASB1 and UASB2 were 12.5 and 8.5 kg/(m3 &middot d), respectively. The subsequent nitrification was improved significantly due to the lower influent COD from the two-stage UASB. The gas production rate in UASB1 was 0.28 m/kg COD at 30°C. The composition of biogas CH4, N2 and CO2 was relatively constant, accounting for 63%-73%, 25%-35%, and about 2%, respectively. The gas production rate in UASB2 was 0.40 mVkg at 35°C and the composition of boigas CH4 and CO2 was also relatively constant at 98% and 2%, respectively. The maximum NH+4-N removal rate was 0.68 kg/ (m &middot d) and NH-4-N removal efficiency was nearly 100% by complete short-cut nitrification in the aerobic reactor. Biological nitrogen removal for leachate with high-strength ammonia was realized economically and effectively.