Effect of ozonation and hydrogen peroxide oxidation on the structure of humic acids and their removal

Using pyrolysis-GC-MS and HPLC techniques, a series of studies were conducted on the effect of pre-oxidation on the structure of natural humic acids (HA) by ozone and hydrogen peroxide (H2O2). Both ozone and H₂O₂ could more or less result in direct removal of organic matter, but the removal of UV₂₅₄ was much higher than that of TOC, implying that an important function of the oxidants is to change the structure of the organic molecules rather than to decompose them into inorganic matters. The result of pyrolysis-GC-MS analysis showed that in the process of oxidation, the organic functional groups on the HA molecules underwent a significant change in their structure, mostly from cyclic to chain hydrocarbons and/or from aromatics to aliphatics. This process was also accompanied by a decrease in the molecular weight of the HA. With an apparent change in the structure and molecular weight of the HA molecules after preoxidation, a great improvement was seen on the overall removal of TOC as coagulation or GAC adsorption was subsequently applied. Additionally, in the case of H₂O₂, a small dose of O₃ showed much better catalysing effect than Mn²⁺, Cu²⁺ or Fe²⁺ ions.