Effects of pre-ozonation on organic matter removal by coagulation with IPF-PACl

摘要

Ozone plays an important role as a disinfectant and oxidant in potable water treatment practice and is increasingly being used as a pre-oxidant before coagulation. The purpose of this study is to obtain insight into the mechanisms that are operative in pre-ozonized coagulation. Effects of pre-ozonation on org anic matter removal during coagulation with IPF-PACl were investigated by using PDA (photometric disperse analysis), apparent molecular weight distribution and chemical fractionation. The dynamic formation of flocs during coagulation proces s was detected. Changes of aquatic organic matter(AOM) structure resulted from t he influence of pre-ozonation were evaluated. Results show that dosage of O3 and characteristics of AOM are two of the major factors influencing the performance of O3 on coagulation. No significant coagulation-aid effect of O3 was observed for all experiments using either AlCl3 or PACl. On the contrary, with the applic ation of pre-ozonation, the coagulation efficiency of AlCl3 was significantly de teriorated, reflected by the retardation of floc formation, and the removal decr eases of turbidity, DOC, and UV254. However, if PACl was used instead of AlCl3, the adverse effects of pre-ozonation were mitigated obviously, particularly when the O3 dosage was less than 0.69 (mg O3/mg TOC). The difference between removal s of UV254 and DOC indicated that pre-ozonation greatly changed the molecular st ructure of AOM, but its capability of mineralization was not remarkable. Only 5% or so DOC was removed by pre-ozonation at 0.6—0.8 mg/L alone. Fractionation re sults showed that the organic products of pre-ozonation exhibited lower molecula r weight and more hydrophilicity, which impaired the removal of DOC in the follo wing coagulation process.