Oxidation and coagulation removal of humic acid using Fenton process

The treatment of humic acid (HA) in water with Fenton reagents was carried out and the roles of oxidation and coagulation in removing HA during treatment were investigated. The removal efficiencies of HA by oxidation and coagulation were tested under various operating conditions: reaction time, initial pH, dosages of Fenton reagents, [H2O2]/[Fe2+] molar ratio, initial HA concentration and reaction temperature. It is demonstrated that Fenton process can effectively remove HA. The values of 27.6% mineralization of HA and 78.9% reduction of UV absorbance at 254 nm (UV254) by oxidation after 120 min reaction time indicated that HA was not completely oxidized to carbon dioxide but rather transformed to some organic intermediates. Moreover, the oxidation occurred mainly at the first 60 min and predominated the HA removal efficiency. Under the most favorable conditions (initial pH 4.0, H2O2 160 mM, Fe2+ 40 mM, reaction time 120 min, reaction temperature 30 °C), 93.3% of UV254 was reduced, the reduction of UV254 by oxidation and coagulation were 78.9% and 14.4%, respectively. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of HA.