PURIFICATION OF WASTE WATER

PURPOSE:To perform the removal of S compounds, the other COD components and fluorine in a single apparatus, by treating waste water, which was used for purifying gas generated by dry-distillation or combustion of coal or petroleum, with a Ca compound, and then adding a ferric flocculant to the treated waste water under an alkaline condition. CONSTITUTION:After waste water is mixed with a Ca comound and agitated, the waste water is subjected to solid-liquid separation so that most of fluorine in the waste water is removed as CaF2. To this pretreated water are further added the Ca compound and a ferric flocculant, to remove the remaining fluorine, fluorine complex, S compounds such as polythionic acids and the other COD components, and then adjusted at pH 10 or more by an alkali agent. By this treatment, various components in the pretreated water are let adhere to the ferric flocculant and coprecipitated. In this way, the waste water is effectively purified. As the ferric flocculant may be used a ferric salt such as ferric chloride or ferric sulfate.