METHOD OF WATER TREATMENT TO REMOVE FLUORIDE ION

To provide a water treatment method capable of stably removing fluoride ions from treated water, such as actual wastewater, and avoiding a generation of excessive sludge, while reducing a size of facilities and an amount of chemicals used.SOLUTION: A water treatment method for removing fluoride ions from raw water includes addition of an alkaline agent to raw water containing fluorine and magnesium, separation of the fluorine-impregnated suspended matter in a solid-liquid separation process, modification and volume reduction of sludge derived from a suspended matter by adding acid, removal of solid-liquid separated sludge, and reprocessing of a supernatant returned to an alkaline agent addition process. The method operates under conditions in which an amount of alkaline agent added, COH, is less than 2000 mg/L, a concentration of sludge withdrawn from the solid-liquid separation process, CSS3, is higher than 10,000 but less than 110,000 mg/L, and a residence time t of sludge in an acid addition tank when acid is added to the sludge is not less than 30 minutes and not more than 600 minutes.SELECTED DRAWING: Figure 1 【課題】実際の廃水などの被処理水から、フッ化物イオンの除去が安定して行われ、過剰な汚泥の発生を回避しつつ、設備の小型化や、薬剤の使用量の低減ができる水処理方法の提供。【解決手段】フッ素及びマグネシウムを含む原水にアルカリ剤を添加し、生成されるフッ素を取り込んだ懸濁物質を固液分離工程で分離後、懸濁物質由来のスラッジに酸を添加して改質して減容化した後、固液分離したスラッジを除去し、上澄液をアルカリ剤の添加工程に戻して再処理する際に、アルカリ剤添加量ＣOHを２０００ｍｇ／Ｌ未満にし、固液分離工程からの引抜汚泥濃度ＣSS３を、１００００を超えて１１００００ｍｇ／Ｌ未満と高くし、スラッジに酸を添加した際の酸添加槽でのスラッジの滞留時間ｔが３０分以上６００分以下となる条件で運転する、原水中のフッ化物イオンを除去する水処理方法。【選択図】図１