Electrocoagulation treatment of compost leachate using aluminium alloy, carbon steel and zinc anode

Abstract

Analysis of surface changes and corrosion occurrence at the electrode surface, electro-generated sludge analysis, and electrocoagulation (EC) treatment efficiency using aluminium alloy, low carbon steel, and zinc sacrificial anode as electrodes for the treatment of compost leachate with the medium organic load were compared for the first time. Different operating conditions (initial pH values in the range of 4–8, stirring rates in the range 70–270 rpm, and contact times in the range of 10–30 min) were used to study the EC process. Light microscopy analysis show the significant corrosion of anodes, while minor corrosion damage was also observed on the cathodes. Pitting was found on carbon steel and aluminium electrodes, and general corrosion on the zinc electrodes, which increase with the duration of EC (10 to 30 min). Weight loss analysis of electrodes shows a decrease in anode mass in all experiments and aluminium cathode mass, while steel cathode mass increases. Zinc cathode mass increases in initially acid and decreases in an alkaline environment. The highest anode consumption was obtained in the experiment with the Zn electrode (in the range of 0.3300–0.6469 g). SEM/EDS analysis of the electro-generated sludge confirmed the presence of aluminium, zinc, and iron, with oxygen as the main elements, while carbon indicated collected organic matter from the compost leachate. PXRD analysis of sludge shows a mixture of amorphous phase with the a semicrystalline phase of AlO(OH) and the crystalline phase of AlPO4 obtained with Al electrodes, an amorphous structure of the sludge obtained with Fe electrodes, and structurally well-ordered phases of Zn7Cu(OH)13((SiO(OH)3)0.7(O4H7)0.3(SO4)) and (Zn0.9Cu0.1)O obtained with Zn electrodes. In addition, the treatment efficiency was analysed and Taguchi's L9 orthogonal array design was performed.