Landfill leachate treatment with combined UASB and Fenton coagulation

A two-stage process was developed for the treatment of landfill leachate in Hong Kong. The leachate contained 15700 mg/L of chemical oxygen demand (COD) and 2300 mg/L of ammonia-nitrogen (NH3-N). In the first stage, it was treated in a UASB (upflow anaerobic sludge blanket) reactor at 37 degreesC. The process removed 89%-91% COD on average within a 6.6 days hydraulic retention period. The UASB effluent, containing 1500 mg/L GOD, was then treated in the second stage using a Fenton coagulation process with H2O2 and excess Fe2+. In this process, organic substances were oxidized and precipitated through the Fenton reaction and coagulation. 70% COD of the UASB effluent was further removed. The optimal parameters of the Fenton coagulation process were determined as an initial pH between 4 and 6, mixing for 5-10 min, a Fe2+ concentration of 300 mg/L, and a H2O2 concentration of 200 mg/L. The final effluent contained a 447 mg/L GOD, which was acceptable sewer system level according to the present Hong Kong regulations.