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

To efficiently remove organic and inorganic pollutants from leachate concentrate,an in situ coagulation-electrochemical oxidation(CO-EO)system was proposed using Ti/Ti_(4)O_(7)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_(2)-IrO_(2)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_(2).In comparison,the Al-cathode system achieved 3-10-fold total phosphorus(TP)(62.6%)and metal removals(>80%)than Ti/RuO_(2)-IrO_(2)and graphite systems.The increased removals of TP and metals were ascribed to the in situ coagulation of Al(OH)_(3),hydroxide precipitation,and electrodeposition.With the reduced scaling on the Al cathode surface,the formation of Al^(3+)and electrified Al(OH)_(3)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_(COD)^(−1)).The present study indicated that the in situ CO-EO process could be potentially used for treating persistent wastewater containing high levels of organic and inorganic ions.