Electrochemical oxidation of leachate pretreated in an upflow anaerobic sludge blanket reactor

Abstract

This study was conducted to develop a two-stage process for the treatment of Hong Kong leachate. The leachate, containing 4750 mg l-1 of chemical oxygen demand (COD) and 1310 mg l-1 of ammoniacal nitrogen (NH3-N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37°C. The process removed on average 66.1% of COD with 6.1 days of hydraulic retention time (HRT), corresponding to an organic loading rate of 0.78 g-COD (1-day)-1. The UASB effluent, which had an average pH of 8.9, COD of 1610 mg l-1 and NH3-N of 1480 mg 1-1, was then further treated by electrochemical oxidation in a batch reactor with recirculation. With the addition of 2000 mg l-1 of chloride (in the form of sodium chloride) and at a current density of 32.3 mA cm-2, 87% of COD and 100% of NH3-N were removed from the UASB effluent in six hours. The energy consumption was <55 kWh kg-COD-1. The final effluent contained no residual NH3-N and only 209 mg l-1 of COD.