Abstract: Provided is a wastewater treatment technology (in particular, pretreatment technology) that, in comparison to existing technologies, can reduce the quantity of sludge generated as a result of processing wastewater that contains fluorine and silicon. Before adding a calcium compound to wastewater that contains fluorine and silicon and performing coagulation-sedimentation treatment on said wastewater, as a pretreatment, sodium hydroxide is added to the wastewater (first reaction tank 1), sodium silicofluoride is precipitated, and the precipitate sodium silicofluoride is removed via solid-liquid separation (first sedimentation tank 2).

Abstract: An object (first object) of the invention is to provide a waste water treatment technology (pretreatment technology in particular) which makes it possible to recover fluorine at a high recovery rate as highly pure calcium fluoride, without diluting waste water containing fluorine and silicon, i.e. to recover fluorine from high-concentration waste water containing fluorine and silicon. Waste water containing fluorine and silicon is supplied to a pH controlling tank 1 and sodium hydroxide (NaOH) is added thereto, with the result that sodium silicate is precipitated. Thereafter, the waste water is supplied to a solid-liquid separator 2 so that solid-liquid separation of sodium silicate is conducted.

Abstract: It is an object of the present invention to provide a membrane separation apparatus and a membrane separation process that are unlikely to cause membrane fouling and plugging, capable of achieving membrane separation even with relatively low flow rate of water, have an excellent membrane packing density, and are unlikely to cause deposition of foreign components in the apparatus. In order to achieve the above object, according to the present invention, vessel-type inner casings are disposed in a pressure vessel along the longitudinal axis thereof, in which the pressure vessel has a water inlet at a first end and a concentrate outlet at a second end. A flow-regulating plate is disposed on the side of the water inlet of the pressure vessel. Stacks of membrane separation units are respectively disposed in the inner casings, and spacers are disposed between the adjacent membrane separation elements. The spacers also serve as sealing members.