Ozone-enhanced photocatalytic degradation of macromolecular natural organic matter (NOM) in drinking water source was investigated. The influences of ozone dosage, retention time and bicarbonate concentration on the NOM degradation rate were studied. The change of molecular weight distribution of NOM caused by ozone-enhanced photocatalysis was analysed, as well as the degradation rate of NOM with different molecular weight (MW). It was shown that ozone-enhanced photocatalysis was much better for NOM degradation than sole ozonation or photocatalysis. Increase of both ozone dosage and retention time could effectively increase the TOC removal rate, while biodegradability could be improved solely by an increase in ozone dosage. The existence of bicarbonate significantly reduced the photocatalytic degradation rate of NOM; however, its impact was effectively offset by the addition of ozone into the photocatalytic process. Macromolecular NOM was transformed into smaller molecules, and the larger NOM was mineralized by ozone-enhanced photocatalysis much faster than the smaller NOM.

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