[Landfill leachate treatment by anaerobic process and electrochemical oxidation]

This study was conducted to develop a two-stage process of UASB and electrochemical oxidation for the treatment of Hong Kong leachate. The leachate, containing 4750 mg/L of chemical oxygen demand (COD) and 1310 mg/L of ammoniacal nitrogen (NH3-N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37 degrees C. The process removed on average 66% of COD with 6.1 days of hydraulic retention time (HRT), corresponding to an organic loading rate COD of 0.78 g/(L.d). The UASB effluent, which had an average pH of 8.9, COD of 1610 mg/L and NH3-N of 1480 mg/L, was then further treated by electrochemical oxidation in a batch reactor with recirculation. With the addition of 2000 mg/L of chloride (in the form of sodium chloride) and at a current density of 32.3 mA/cm2, 87% of COD and 100% of NH3-N were removed from the UASB effluent in six hours. The energy consumption was < 55 kW.h/kg COD. The final effluent contained no residual NH3-N and only 209 mg/L of COD. In this paper, some basic problems in electrochemical oxidation, such as the effects of the operation parameters, the mechanism of the process, and assessment of the energy requirements were discussed in detail.