Anaerobic and sequential anaerobic-aerobic treatments of municipal landfill leachate at low temperatures

Anaerobic treatment of municipal landfill leachate (COD 1–4 g l−1, NH4-N c. 0.16 g l−1) was studied at 11 and 24°C by using laboratory-scale UASB and hybrid reactors. Aerobic post-treatment of the anaerobically treated leachate was also studied at 24°C using an activated-sludge process. In the 11°C reactors, a COD removal of up to 60–65% was obtained with 1.5-2 day HRT and 0.7-1.5 kg COD m−3 day−1 organic loading rates. At 24°C, a COD removal of up to 75% was achieved with a 10 h HRT. The highest organic loading rate applied was 10 kg COD m−3 day−1 at 24°C. Inorganic material accumulated in the reactor sludges at both temperatures. However, the specific methanogenic activity of the 24°C reactor sludge did not decrease during the 282 days of operation. After 196 days of operation, the specific methanogenic activity of the 11°C reactor sludge was one-third of that of the 24°C sludge. The aerobic post-treatment removed 45–75% of the COD left after the anaerobic treatment and produced effluent with a BOD7 of less than 22 mg l−1 and a COD of less than 380 mg l−1. The COD removal in the sequential process was 80–90%. An ammonium removal of up to 80% and a total nitrogen removal of 40% were achievable in the aerobic stage. The results showed that the anaerobic treatment of medium-strength leachate was feasible even at 11°C. The sequential process produced effluent quality close to the requirements set for municipal wastewater treatment plants.