coagulation-electrochemical oxidation of leachate concentrate: A key role of cathodes.

To efficiently remove organic and inorganic pollutants from leachate concentrate, an coagulation-electrochemical oxidation (CO-EO) system was proposed using Ti/TiO anode and Al cathode, coupling the "super-Faradaic" dissolution of Al. The system was evaluated in terms of the removal efficiencies of organics, nutrients, and metals, and the underlying cathodic mechanisms were investigated compared with the Ti/RuO-IrO and graphite cathode systems. After a 3-h treatment, the Al-cathode system removed 89.0% of COD and 36.3% of total nitrogen (TN). The TN removal was primarily ascribed to the oxidation of both ammonia and organic-N to N. In comparison, the Al-cathode system achieved 3-10-fold total phosphorus (TP) (62.6%) and metal removals (>80%) than Ti/RuO-IrO and graphite systems. The increased removals of TP and metals were ascribed to the coagulation of Al(OH), hydroxide precipitation, and electrodeposition. With the reduced scaling on the Al cathode surface, the formation of Al and electrified Al(OH) lessened the requirement for cathode cleaning and increased the bulk conductivity, resulting in increased instantaneous current production (38.9%) and operating cost efficiencies (48.3 kWh kg ). The present study indicated that the CO-EO process could be potentially used for treating persistent wastewater containing high levels of organic and inorganic ions.