Improvement of biodegradability of dissolved organic carbon (DOC) by ozonation does not always induce improvement of DOC removal and extension of activated carbon service time, because most of biodegradable DOC increased by ozonation is adsorbable on activated carbon. The objective of this study is to clarify the fate of the biodegradable DOC increased by preozonation on biological activated carbon (BAC) and to evaluate effects of preozonation on BAC performance for the removal of DOC and extension of activated carbon service time. DOC breakthrough curve for BAC process obviously shifted to the right by combination with ozonation, indicating that preozonation extended BAC service time. Higher removal of DOC was noted in the ozone-BAC process than the BAC process after saturation with DOC. Ozonation increased biodegradable DOC by 2.89 mg·l−1 (31%). Although the increased biodegradable DOC had possibilities to be removed both by adsorption and biodegradation, most of it was removed by biodegradation on BAC which resulted in longer BAC service time. Biodegradation of the increased biodegradable DOC was responsible for the higher removal of DOC after saturation with DOC in the ozone-BAC process.

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