Affiliations: State Key Laboratory of Environmental Aquatic
Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of
Sciences, Beijing 100085, China | School of Environmental Science and Resources, Shanxi
University, Taiyuan 030002, China | School of Water Resources and Environmental Sciences,
China University of Geosciences, Beijing 100083, China
Abstract: 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
ofpre-ozonation on organic 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 process was detected. Changes of aquatic organic matter
(AOM) structure resulted from the influence of pre-ozonation were evaluated.
Results show that dosage of O_3 and characteristics of AOM
are two of the major factors influencing the performance of
O_3 on coagulation. No significant coagulation-aid effect of
O_3 was observed for all experiments using either
AlCl_3 or PACl. On the contrary, with the application of
pre-ozonation, the coagulation efficiency of AlCl_3 was
significantly deteriorated,reflected by the retardation of floc formation, and
the removal decreases of turbidity, DOC, and UV_{254}.
However, if PACl was used instead of AlCl_3, the adverse
effects of pre-ozonation were mitigated obviously, particularly when the
O_3 dosage was less than 0.69 (mg O_3/mg
TOC). The difference between removals of UV_{254} and DOC
indicated that pre-ozonation greatly changed the molecular structure 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 results
showed that the organic products of pre-ozonation exhibited lower molecular
weight and more hydrophilicity, which impaired the removal of DOC in the
following coagulation process.
