Humic acid removal by electrocoagulation: characterization of aluminum species and humic acid

In this study, the different aluminum (Al) species generated during electrocoagulation (EC), the humic acid (HA) removal, and the change in HA characteristics were evaluated. The results show that the distribution of monomeric Al species (Al-a), medium polymer Al species (Al-b), and colloidal or solid Al species (Al-c) was dependent on initial pH and current density (CD). The higher the fraction of Al-b and Al-c, the faster the HA removal. The fraction of Al-b and HA removal rates were higher at an initial pH of 4.5 than at 6.5. At a CD of 29Am(-2), the fraction of Al-b and Al-c was higher and HA removal was faster than at 5Am(-2). The results of UV/Vis spectroscopy, fluorescence spectroscopy, and size-exclusion chromatography show a decrease in aromaticity, degree of conjugation, and average molecular weight after EC treatment. The decreases were more pronounced at a high CD than at a low CD, indicating that Al-b and Al-c, especially Al-c, contribute much to the preferential removal of highly condensed and high molecular weight structures of HA by adsorption and patch coagulation.