To provide a waste water treatment method where harmful waste water containing heavy metals and organic matters is subjected to purification treatment, and the waste water is made harmless to a dischargeable state.

Floatation waste water W3 or the like generated by subjecting slurry S1 containing chlorine bypass dust to floatation is admixed with an alkaline agent such as slaked lime slurry, so as to adjust the pH of the slurry S2 to 10 to 12. Next, the pH adjusted slurry S2 is subjected to solid-liquid separation by a filter press 12, and heavy metals remaining in the waste water W3 are removed. Then, a filtrate W4 in the filter press 12 is subjected to secondary filtration by a sand filter 14, and a filtrate W5 from which heavy metals are adsorbed away by a chelate resin tower 15 is admixed with an oxidizer in an organic matter treatment tank 16, so as to decompose organic compounds in the filtrate W5. By the waste water treatment method, waste water generated when the slurry of soot and dust is subjected to floatation, waste water generated when the slurry of contaminated soil is subjected to floatation or the like can be made harmless.

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