Abstract: Water softening device includes water softening tank and neutralizing tank. Water softening tank softens raw water containing a hardness component by weakly acidic cation exchange resin. Water softening tank includes first water softening tank and second water softening tank. Neutralizing tank neutralizes the pH of softened water that has passed through water softening tank by weakly basic anion exchange resin. Neutralizing tank includes first neutralizing tank and second neutralizing tank. Water softening device is configured to cause raw water containing a hardness component to flow through first water softening tank, first neutralizing tank, second water softening tank, and second neutralizing tank in this order.

Abstract: Provided is a water softening device including a water softening tank that softens raw water using a weakly acidic cation exchange resin, a pH adjustment tank, an electrolytic cell that produces acidic electrolyzed water, a conductivity measurement unit S1 that measures conductivity of the raw water, a conductivity measurement unit S2 that measures conductivity of soft water, a water flow amount detecting unit, and a control unit, wherein the control unit calculates a regeneration time for the weakly acidic cation exchange resin based on an amount of the hardness component adsorbed to the weakly acidic cation exchange resin calculated from a difference between the conductivity of the raw water and the conductivity of the soft water and from the accumulated water flow amount of the raw water, and performs a regeneration treatment of the weakly acidic cation exchange resin during the regeneration time.

Abstract: A water softening system includes a water feed channel through which water to be treated flows, and a crystallization unit that causes a metal ion contained in the water to be treated to precipitate. Further, the water softening system includes a separation unit that separates the water to be treated having passed through the crystallization unit into a crystal obtained through precipitation by the crystallization unit and soft water. Further, the water feed channel is configured so that at least a part thereof functions as a feed channel being a pressure application system in a substantially sealed state, and the crystallization unit and the separation unit are connected to parts corresponding to the feed channel being a pressure application system in a substantially sealed state in the water feed channel.

Abstract: A method for controlling a liquid treatment apparatus of the present disclosure includes: (i) providing the liquid treatment apparatus; (ii) treating a polluted liquid in a photocatalytic reaction tank by a photocatalytic reaction to produce a treated liquid; (iii) introducing a liquid mixture into a separation tank from the photocatalytic reaction tank through a feed passage by a circulation pump; (iv) introducing a filtrate to an outside of the separation tank through an extraction passage while filtering the liquid mixture introduced into the separation tank by a filtration membrane, and feeding the liquid mixture to the photocatalytic reaction tank through an overflow passage; and (v) making a flow rate of the liquid mixture measured by a liquid mixture flow meter higher than a flow rate of the filtrate measured by a filtrate flow meter by controlling the circulation pump by a controller.

Abstract: A method for controlling a liquid treatment apparatus of the present disclosure includes: (i) providing the liquid treatment apparatus; (ii) treating a polluted liquid in a photocatalytic reaction tank by a photocatalytic reaction to produce a treated liquid; (iii) introducing a liquid mixture into a separation tank from the photocatalytic reaction tank through a feed passage by a circulation pump; (iv) introducing a filtrate to an outside of the separation tank through an extraction passage while filtering the liquid mixture introduced into the separation tank by a filtration membrane, and feeding the liquid mixture to the photocatalytic reaction tank through an overflow passage; and (v) making a flow rate of the liquid mixture measured by a liquid mixture flow meter higher than a flow rate of the filtrate measured by a filtrate flow meter by controlling the circulation pump by a controller.

Abstract: Provided is a method for treating a hexavalent chromium-containing aqueous solution by water treatment employing a titanium dioxide photocatalyst that is excellent in both photocatalytic activity and solid-liquid separation performance. The method according to the present disclosure includes the steps of: adding catalyst particles to the aqueous solution; reducing hexavalent chromium by irradiating the aqueous solution with light having a wavelength of 200 nanometers or more and 400 nanometers or less while stirring the catalyst particles in the aqueous solution; and stopping the stirring and separating the catalyst particles from the aqueous solution by sedimentation. Each catalyst particle is composed only of a titanium dioxide particle and a zeolite particle, the titanium dioxide particle is adsorbed on the outer surface of the zeolite particle, the zeolite particle has a silica/alumina molar ratio of 10 or more, and the catalyst particles are contained in the aqueous solution at a concentration of 0.

Abstract: Provided is a method for treating an arsenic-containing aqueous solution by water treatment employing a titanium dioxide photocatalyst that is excellent in both photocatalytic activity and solid-liquid separation performance. The method according to the present disclosure includes the steps: of adding catalyst particles to the aqueous solution; oxidizing trivalent arsenic by irradiating the aqueous solution with light having a wavelength of 200 nanometers or more and 400 nanometers or less while stirring the catalyst particles in the aqueous solution; and stopping the stirring and separating the catalyst particles from the aqueous solution by sedimentation. Each catalyst particle is composed only of a titanium dioxide particle and a zeolite particle, the titanium dioxide particle is adsorbed on the outer surface of the zeolite particle, the zeolite particle has a silica/alumina molar ratio of 10 or more, and the catalyst particles are contained in the aqueous solution at a concentration of 0.

Abstract: Provided is a method for decomposing at least one of organic compound contained in an aqueous solution by using a titanium dioxide photocatalyst that is excellent in both photocatalytic activity and solid-liquid separation performance for water treatment. The method includes: a step of adding catalyst particles into the aqueous solution; a step of decomposing the organic compound by irradiating the aqueous solution with light having a wavelength of 200 nanometers or more and 400 nanometers or less while stirring the catalyst particles in the aqueous solution; and a step of stopping the stirring, and separating the catalyst particles from the aqueous solution by sedimentation.

Abstract: Provided is a method for treating an arsenic-containing aqueous solution by water treatment employing a titanium dioxide photocatalyst that is excellent in both photocatalytic activity and solid-liquid separation performance. The method according to the present disclosure includes the steps of adding catalyst particles to the aqueous solution; oxidizing trivalent arsenic by irradiating the aqueous solution with light having a wavelength of 200 nanometers or more and 400 nanometers or less while stirring the catalyst particles in the aqueous solution; and stopping the stirring and separating the catalyst particles from the aqueous solution by sedimentation. Each catalyst particle is composed only of a titanium dioxide particle and a zeolite particle, the titanium dioxide particle is adsorbed on the outer surface of the zeolite particle, the zeolite particle has a silica/alumina molar ratio of 10 or more, and the catalyst particles are contained in the aqueous solution at a concentration of 0.

Abstract: Provided is a method for treating a hexavalent chromium-containing aqueous solution by water treatment employing a titanium dioxide photocatalyst that is excellent in both photocatalytic activity and solid-liquid separation performance. The method according to the present disclosure includes the steps of: adding catalyst particles to the aqueous solution; reducing hexavalent chromium by irradiating the aqueous solution with light having a wavelength of 200 nanometers or more and 400 nanometers or less while stirring the catalyst particles in the aqueous solution; and stopping the stirring and separating the catalyst particles from the aqueous solution by sedimentation. Each catalyst particle is composed only of a titanium dioxide particle and a zeolite particle, the titanium dioxide particle is adsorbed on the outer surface of the zeolite particle, the zeolite particle has a silica/alumina molar ratio of 10 or more, and the catalyst particles are contained in the aqueous solution at a concentration of 0.

Abstract: Provided is a method for decomposing at least one of organic compound contained in an aqueous solution by using a titanium dioxide photocatalyst that is excellent in both photocatalytic activity and solid-liquid separation performance for water treatment. The method includes: a step of adding catalyst particles into the aqueous solution; a step of decomposing the organic compound by irradiating the aqueous solution with light having a wavelength of 200 nanometers or more and 400 nanometers or less while stirring the catalyst particles in the aqueous solution; and a step of stopping the stirring, and separating the catalyst particles from the aqueous solution by sedimentation.