The aim of this study was to investigate the effectiveness of ozonation on the removal of organic matter with low coagulability from municipal secondary effluent. The results revealed that the removal efficiency of coagulation generally remained quite low. The residual organic matter belonged to low coagulability organic matter. The presence of the ozone increased the removal efficiency of color and UV254 gradually for low coagulability organic matter, whereas DOC had no noticeable change; the efficiencies were 45%, 34%, and 20%, respectively, at a dosage (denoted as O3/DOC) of 1.5 mg·mg-1. It could be concluded that ozone easily reacted with unsaturated organic matter, and the mineralization of organic matter was less effective. In order to further define the variation in organic matter of the secondary effluent, the differences between the relative molecular weight distribution and fluorescence characteristics of coagulation and ozonation with different zone dosages were monitored in this study. The findings showed that coagulation had little effect on organic content. Nonetheless, ozone might have preferentially reacted with high-molecular-weight substances of organic matter with low coagulability and reduced the fluorescence intensity in the humic-like regions significantly. The shift of fluorescence peak was not changed by ozonation. In addition, via X-ray photoelectron spectroscopy (XPS) analysis, it was identified that coagulation could remove carboxylic organic matter. On the other hand, with the increasing ozone dosage (from 0 to 1.5 mg·mg-1), ozone could preferentially react with low coagulability organic matter with aromatic structure, thus the amount of aliphatics increased gradually.
Keywords: X-ray photoelectron spectroscopy; coagulation; organic matters with low coagulability; ozonation; three-dimensional fluorescence.