Electro-oxidation of landfill leachate using boron-doped diamond: role of current density, pH and ions.

Electro-oxidation using a boron-doped diamond (BDD) anode can be used as an alternative to leachate treatment. Aside from the hydroxyl radical, BDDs are capable of generating chloride and sulfate radical species that play significant roles in the oxidation of pollutants. This research investigated the role of Cl:SO ions at molar ratios of 237:1, 4:1 and 18:1, and the influence of applied current density (i.e. 50, 75 and 100 mA cm) on the removal of organic and ammonium contaminants. The results show that current density had considerable effects on chemical oxygen demand (COD) and colour removal, while ion composition of Cl:SO at pH 3, 5 and 8.5 (original pH) gave different effects on COD and ammonium removal. The pH had a significant effect on the COD removal at the ratio of 237:1, but showed no dramatic effect at the ratio of 18:1, giving ∼40% of COD removal at all pHs tested. This indicates that electro-oxidation at the ratio of 18:1 could be effectively conducted at a wide range of pH. Furthermore, the optimum ammonium removal was obtained at pH 8.5 with the ratio of 237:1. This process was found to be ineffective in increasing the biodegradability index of the leachate; instead, it exhibited mineralization of organic content.