Organic removal of anaerobically treated leachate by Fenton coagulation

The leachate from a Hong Kong landfill, containing 15,700 mg/L of chemical oxygen demand (COD) and 2,260 mg/L of ammonia nitrogen (NH3-N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37 degreesC. The process on average removed 90.4% of COD with 6.6 days of hydraulic retention at an organic loading rate of 2.37 g of COD/L day. The UASB effluent was further treated by the Fenton coagulation process using H2O2 and Fe2+. Under the optimal condition of 200 mg of H2O2/L and 300 mg of Fe2+/L and an initial pH of 6.0, 70% of residual COD in the UASB effluent was removed, of which 56% was removed by coagulation/precipitation and only 14% by free radical oxidation. It is obvious that H2O2 and Fe2+ had a strong synergistic effect on coagulation. The average COD in the final effluent was 447 mg/L. Removing each gram of COD required 0.28 g of Fe2+ and 0.18 g of H2O2.