Next, fluorine in the waste water i

Next, fluorine in the waste water is primarily treated, and the waste water the organic matters of which have been primarily and secondarily treated is filtrated by the submerged membrane 9 set at the reaction-tank upper part 3-1. The filtrated waste water is transferred to the slaked lime reaction tank 14 by the submerged membrane pump 7 connected to the submerged membrane 9 with piping. A rapid agitator 15 is set at this slaked lime reaction tank 14, where new slaked lime is added and agitated so as to react with fluorine in the waste water that has not completely reacted in the reaction tank 3, thus making the fluorine secondarily treated. That is, with respect to fluorine in the waste water, the reaction at the reaction-tank lower part 3-3 is primary coarse treatment and the reaction at the slaked lime reaction tank 14 is reliable secondary treatment of fluorine.In this slaked lime reaction tank 14, fluorine remaining in the waste water is formed into granular calcium fluoride by the addition of slaked lime and the agitation with the rapid agitator 15. Subsequently, the waste water is introduced into the polychlorinated aluminum flocculation tank 16, where polychlorinated aluminum as an inorganic flocculant is added, forming larger flocs. Then, the waste water containing the flocs is subsequently introduced into the polymer-flocculant flocculation tank 17, where a slow agitator 18 is set, and where the large flocs are formed into more stable, easy-to-settle even larger flocs by the addition of polymer flocculants. These more stable, easy-to-settle even larger flocs subsequently flow into the settling tank 19 having a settling-tank collector 20, where the flocs are settled to lower part of the settling tank 19. The resulting supernatant in this settling tank 19 is treated water.The flocs, or sludge, settled in the settling tank 19 contains unreacted slaked lime, unreacted polychlorinated aluminum and unreacted polymer flocculants, due to the fact that slaked lime is added, polychlorinated aluminum is excessively added and polymer flocculants are added in the slaked lime reaction tank 14, the polychlorinated aluminum flocculation tank 16 and the polymer-flocculant flocculation tank 17. All the sludge settled in this settling tank 19 is returned to upper part of the reaction-tank lower part 3-3 by a sludge return pump 21.As a result, the unreacted chemicals 29 are fully recycled for the treatment of organic matter-containing fluorine waste water, so that the sludge of the reaction-tank lower part 3-3 is settled, passing through the upper part of the inclined wall 27 and moving to the settling part 6. This sludge of the settling part 6 is transferred to the concentration tank 22 by the settling part pump 8, concentrated there, and then transferred to the filter press 25 by a filter press pump 24 and then dehydrated there.According to this embodiment, since the biological sludge 31 and the calcium-containing chemical sludge 28 are introduced to one reaction tank 3, organic matters in the waste water can be treated by microorganisms contained in the biological sludge 31 and fluorine can be treated by the calcium-containing chemical sludge 28.Also according to this embodiment, since the reaction tank 3 has the submerged membrane 9 as a membrane separation unit, the biological sludge 31 and the chemical sludge 28 can be prevented from flowing out of the reaction tank 3 so that the biological sludge 31 and the chemical sludge 28 can be effectively used for waste water treatment. Also, microorganisms contained in the biological sludge 31 do not flow out of the reaction tank 3 and therefore can be effectively used for waste water treatment. Further, since neither the biological sludge 31 nor the chemical sludge 28 flow out of the reaction tank 3, continuously introducing the biological sludge 31 and the chemical sludge 28 to the reaction tank 3 allows biological sludge concentration and chemical sludge concentration to be markedly increased, thus allowing the waste water treatment efficiency to be enhanced.Also according to this embodiment, the reaction tank 3 comprises the aeration zone 3-1 having the membrane separation unit 9, the biological sludge zone 3-2 and the chemical sludge zone 3-3, and organic matter-containing fluorine waste water showing acidity is introduced from the reaction-tank lower part. Therefore, first, fluorine in the organic matter-containing fluorine waste water can be treated (primary treatment of fluorine) and, simultaneously therewith, the waste water can be neutralized. Then, the organic matter-containing fluorine waste water that has been neutralized by the chemical sludge 28 goes up from the lower chemical sludge zone 3-3 so as to be introduced to the biological sludge zone 3-2. In this biological sludge zone 3-2, the organic matters in the waste water are biologically treated by the microorganisms contained in the biological sludge 31. Next, the waste water i