A water treatment system includes a first demineralizing section that separates water to be treated including Ca ions, SO.sub.4 ions, and carbonate ions into concentrated water and treated water; a crystallizing section including a first crystallizing tank 21 that crystallizes gypsum from the concentrated water and a first seed crystal supplying section 22 that supplies seed crystals of gypsum to the first crystallizing tank 21; a first pH measuring section 543 that measures the pH of the first concentrated water in the first crystallizing tank 21; and a first controlling section that reduces the amount of the seed crystals of the gypsum to be supplied when the measured pH falls within a pH range in which a scale inhibition function of the calcium scale inhibitor is reduced, and increases the amount of the seed crystals of the gypsum to be supplied when the measured pH is beyond the pH range.

Provided are a water treatment system and a water treatment process, which are capable of reproducing water containing salts with high water recovery. In the water treatment system (200) and the water treatment process of the present invention, after a calcium scale inhibitor and a silica scale inhibitor are supplied to water to be treated containing Ca ions, SO.sub.4 ions, carbonate ions, and silica, and the water to be treated is separated in a second demineralizing section (210) into second concentrated water in which the Ca ions, the SO.sub.4 ions, the carbonate ions, and the silica are concentrated and treated water. In a second crystallizing section (220), seed crystals of gypsum are supplied to the second concentrated water, whereby gypsum is crystallized and removed from the second concentrated water.

Provided are a water treatment system and a water treatment process, which are capable of reproducing water containing salts with high water recovery. In the water treatment system (200) and the water treatment process of the present invention, after a calcium scale inhibitor and a silica scale inhibitor are supplied to water to be treated containing Ca ions, SO.sub.4 ions, carbonate ions, and silica, and the water to be treated is separated in a second demineralizing section (210) into second concentrated water in which the Ca ions, the SO.sub.4 ions, the carbonate ions, and the silica are concentrated and treated water. In a second crystallizing section (220), seed crystals of gypsum are supplied to the second concentrated water, whereby gypsum is crystallized and removed from the second concentrated water.

A method for degassing a cross-flow diafiltration unit, a cross-flow diafiltration method and a cross-flow diafiltration unit. The degassing method includes (i) providing a cross-flow diafiltration unit having a diafiltration channel, a retentate channel and a permeate channel, a first filter material that delimits the diafiltration channel from the retentate channel, and a second filter material that delimits the retentate channel from the permeate channel; and thereafter (ii) feeding a liquid into the retentate channel so that the liquid flows in a flow direction through the retentate channel and penetrates through the first filter material into the diafiltration channel, whereby the retentate channel and the diafiltration channel are filled with and degassed by the liquid.

Provided are a water treatment system and a water treatment process, which are capable of reproducing water containing salts with high water recovery. A water treatment system 100 comprises a second demineralizing section 210a, 210b that separates water to be treated containing Ca ions, SO.sub.4 ions and carbonate ions into concentrated water in which the Ca ions and the SO.sub.4 ions are concentrated and treated water; a crystallizing section which is positioned on a downstream side of the second demineralizing section 210a, 210b and which includes a second crystallizing tank 221a, 221b that crystallizes gypsum from the concentrated water and a seed crystal supplying section that supplies seed crystals of gypsum to the second crystallizing tank 221a, 221b; and a separating section that is positioned on a downstream side of the crystallizing section and separates the gypsum from the concentrated water.

Provided are a water treatment system and a water treatment process, which are capable of reproducing water containing salts with high water recovery. A water treatment system 100 comprises a second demineralizing section 210a, 210b that separates water to be treated containing Ca ions, SO.sub.4 ions and carbonate ions into concentrated water in which the Ca ions and the SO.sub.4 ions are concentrated and treated water; a crystallizing section which is positioned on a downstream side of the second demineralizing section 210a, 210b and which includes a second crystallizing tank 221a, 221b that crystallizes gypsum from the concentrated water and a seed crystal supplying section that supplies seed crystals of gypsum to the second crystallizing tank 221a, 221b; and a separating section that is positioned on a downstream side of the crystallizing section and separates the gypsum from the concentrated water.

In a water treatment system (1) and a water treatment process, a scale inhibitor is supplied to water to be treated containing Ca ions, SO.sub.4 ions, carbonate ions, and silica, and the water to be treated is adjusted to a pH at which silica is soluble. The pH-adjusted water to be treated containing the calcium scale inhibitor is separated in a demineralizing section (10) into concentrated water and treated water. In a crystallizing section (20), seed crystals of gypsum are supplied to the concentrated water, whereby gypsum is crystallized and removed. Silica in the water to be treated is removed from the concentrated water on the downstream side of the crystallizing section (20). Calcium carbonate in the water to be treated is removed from the concentrated water on the upstream side of the demineralizing section (10) or the downstream side of the crystallizing section (20).

In a water treatment system (1) and a water treatment process, a scale inhibitor is supplied to water to be treated containing Ca ions, SO.sub.4 ions, carbonate ions, and silica, and the water to be treated is adjusted to a pH at which silica is soluble. The pH-adjusted water to be treated containing the calcium scale inhibitor is separated in a demineralizing section (10) into concentrated water and treated water. In a crystallizing section (20), seed crystals of gypsum are supplied to the concentrated water, whereby gypsum is crystallized and removed. Silica in the water to be treated is removed from the concentrated water on the downstream side of the crystallizing section (20). Calcium carbonate in the water to be treated is removed from the concentrated water on the upstream side of the demineralizing section (10) or the downstream side of the crystallizing section (20).

Provided are a water treatment system and a water treatment process, which are capable of reproducing water containing salts with high water recovery. In the water treatment system (400) and the water treatment process of the present invention, after a calcium scale inhibitor and a silica scale inhibitor are supplied to water to be treated containing Ca ions, SO.sub.4 ions, carbonate ions, and silica, and the water to be treated is separated in a second demineralizing section (210) into second concentrated water in which the Ca ions, the SO.sub.4 ions, the carbonate ions, and the silica are concentrated and treated water. In a second crystallizing section (220), seed crystals of gypsum are supplied to the second concentrated water, whereby gypsum is crystallized and removed from the second concentrated water.

Provided are a water treatment system and a water treatment process, which are capable of reproducing water containing salts with high water recovery. In the water treatment system (400) and the water treatment process of the present invention, after a calcium scale inhibitor and a silica scale inhibitor are supplied to water to be treated containing Ca ions, SO.sub.4 ions, carbonate ions, and silica, and the water to be treated is separated in a second demineralizing section (210) into second concentrated water in which the Ca ions, the SO.sub.4 ions, the carbonate ions, and the silica are concentrated and treated water. In a second crystallizing section (220), seed crystals of gypsum are supplied to the second concentrated water, whereby gypsum is crystallized and removed from the second concentrated water.