Water treatment device

Abstract

Provided is a water treatment device that suppresses the degradation of electrodes in a capacitive de-ionization treatment section and is capable of maintaining high water treatment capability. The water treatment device includes an activated carbon treatment section that receives an inflow of water having a total organic carbon concentration of 100 mg/l or less and adsorbs and removes organic matters contained in the water; and, on the downstream side of the activated carbon treatment section, a capacitive de-ionization treatment section including a pair of electrodes to which voltages having polarities opposite to each other are applied, a flow path, and ion exchange membranes. Ions contained in the water are adsorbed to the electrodes with voltages applied thereto, and voltages reverse to the voltages at the time of ions adsorption are applied to the electrodes to release the ions from the electrodes.

Claims

1. A water treatment device comprising: an activated carbon treatment section that receives an inflow of water having a total organic carbon concentration of 100 mg/l or less and adsorbs and removes organic matters contained in the water; on a downstream side of the activated carbon treatment section, a capacitive de-ionization treatment section including a pair of electrodes to which voltages having polarities opposite to each other are applied, a flow path that is located between the electrodes and allows the water to flow therethrough, and an ion exchange membrane that is installed on a flow path side of each of the electrodes, wherein when the water flows between the electrodes with voltages applied thereto, ions contained in the water are adsorbed to the electrodes and removed from the water, and voltages reverse to the voltages at a time of adsorption of the ions are applied to the electrodes to release the ions from the electrodes, whereby the electrodes are regenerated; organic matter content measurement sections that are installed on an upstream side of the activated carbon treatment section and between the activated carbon treatment section and the capacitive de-ionization treatment section, and that measure the total organic carbon concentration in the water; and a biological treatment section, installed on the upstream side of the activated carbon treatment section, where the organic matters in the water are decomposed and removed by microorganisms.

2. The water treatment device according to claim 1, wherein water having a total organic carbon concentration of 20 mg/l or less is discharged from the activated carbon treatment section.

3. The water treatment device according to claim 1, further comprising, on the upstream side of the activated carbon treatment section, an oxidization treatment section where the organic matters in the water are subjected to an oxidization treatment.

4. The water treatment device according to claim 2, further comprising, on the upstream side of the activated carbon treatment section, an oxidization treatment section where the organic matters in the water are subjected to an oxidization treatment.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a block diagram of an example of a water treatment device.

(2) FIG. 2 is a schematic diagram explaining an example of a demineralization section of a water treatment device.

(3) FIG. 3 is a graph showing time-dependent changes in the effective capacity of an electrode when waters having different organic matter contents are subjected to a capacitive de-ionization treatment.

(4) FIGS. 4(a) to 4(c) are schematic diagrams of a capacitive de-ionization treatment device.

DESCRIPTION OF EMBODIMENTS

(5) FIG. 1 is a block diagram of an example of a water treatment device. The water treatment device 1 includes, from the upstream side, a pretreatment section 2 and a demineralization section 3. The pretreatment section 2 is a biological treatment section that decomposes organic matters by a biological treatment, an oxidization treatment section that decomposes organic matters by an oxidation treatment, or a combination thereof.

(6) In the case where waste water from a plant or domestic waste water is treated, the pretreatment section 2 includes an oil separator that separates oils from waste water and a separation section that causes the aggregation and sedimentation of heavy metals or suspended particles. The oil separator and the separation section are installed on the upstream side of the biological treatment section. In the case where water taken from nature, such as a river, is treated, the oil separator and the separation section may be omitted.

(7) The biological treatment section subjects organic matters in water to a decomposition treatment by microorganisms. The biological treatment section is configured as a combination of a treatment device using a membrane-separation activated sludge process (MBR: Membrane Bio-Reactor), a treatment device using a biofilm process (BFR: Bio-Film Reactor), an aeration tank, and a sedimentation tank. The biological treatment section may also be configured as a combination of MBR and BFR. In the case of configuration having a combination of an aeration tank and an sedimentation tank, in order to prevent clogging in a demineralizer in the demineralization section 3, a filtration device, such as a filter, is provided downstream of the sedimentation tank.

(8) In the case of MBR, a membrane having pores of about 0.1 μm is immersed in water in the biological reactor. Microorganisms are present in water in the biological reactor, and the microorganisms decompose organic matters in water. The size of microorganisms useful for the sludge treatment in the biological reactor is about 0.25 μm at the minimum. Accordingly, water in the biological reactor is solid-liquid separated through the membrane into water and microorganisms, and only water is discharged from MBR.

(9) In the case of BFR, a support having a film of microorganisms formed on the surface thereof is installed inside. When microorganisms on the support surface come into contact with water containing organic matters, the microorganisms decompose the organic matters in water.

(10) In the case of configuration having a combination of MBR and BFR, the operation of MBR and BFR is controlled according to the amount of organic matters in water (COD). For example, in the case where COD in water is low, only MBR is operated. In the case where COD greatly varies, BFR is operated in parallel with MBR.

(11) The oxidization treatment section removes organic matters from water by oxidation and decomposition. In the water treatment device of this embodiment, an ozone treatment, an ultraviolet treatment, a sodium hypochlorite treatment, and a hydrogen peroxide treatment are employed as oxidation treatment methods. The above treatment may be performed alone, or it is also possible to perform a plurality of treatments in combination.

(12) The oxidization treatment section is installed on the upstream side of the activated carbon treatment section 10.

(13) In the case of an ozone treatment, ozone generated by an ozone generator is supplied to the oxidization treatment section. Organic matters in water passing through the oxidization treatment section are oxidized and decomposed by ozone.

(14) In the case of an ultraviolet treatment, an ultraviolet lamp is installed in the oxidization treatment section. Water passing through the oxidization treatment section is irradiated with ultraviolet light, and organic matters are oxidized and decomposed by ultraviolet light.

(15) In the case of a sodium hypochlorite treatment, sodium hypochlorite is supplied to the oxidization treatment section. Organic matters in water passing through the oxidization treatment section are oxidized and decomposed by sodium hypochlorite.

(16) In the case of a hydrogen peroxide treatment, hydrogen peroxide is supplied to the oxidization treatment section. Organic matters passing through the oxidization treatment section are oxidized and decomposed by hydrogen peroxide.

(17) FIG. 2 is a schematic diagram explaining an embodiment of the demineralization section 3 of the water treatment device.

(18) The demineralization section 3 includes an activated carbon treatment section 10 and a capacitive de-ionization treatment section 100. The demineralization section 3 may further have a reverse osmosis membrane demineralizer.

(19) The activated carbon treatment section 10 houses a filled tank 11 that is filled with activated carbon inside. The activated carbon used in this embodiment is activated carbon for water treatment. Water fed from the biological treatment section is supplied into the activated carbon treatment section 10 from the top, permeates through the filled tank 11, and is discharged from the bottom of the activated carbon treatment section 10.

(20) In this embodiment, the capacitive de-ionization treatment section 100 has the same configuration as the capacitive de-ionization treatment device of FIG. 4. One or more capacitive de-ionization treatment sections 100 are installed downstream of the activated carbon treatment section 10. As shown in FIG. 2, in many cases, a plurality of capacitive de-ionization treatment sections 100 are arranged parallel to the flow of water. However, it is also possible that a plurality of capacitive de-ionization treatment sections 100 are disposed in series. Alternatively, a combination of series and parallel arrangements is also possible.

(21) The demineralization section 3 may also have, on the upstream side of the activated carbon treatment section 10, a tank (not shown) that temporarily stores water from the biological treatment section and feeds a predetermined amount of water to the capacitive de-ionization treatment section 100.

(22) On the upstream side of the activated carbon treatment section 10 in the demineralization section 3 and between the activated carbon treatment section 10 and the capacitive de-ionization treatment section 100, organic matter content measurement sections 12 and 13 for measuring the total organic carbon concentration (TOC) in water are installed, respectively.

(23) The process of a water treatment using the above water treatment device will be described hereinafter. The following will describe, as an example, the case where the water treatment device includes an oil separator and a separation section and treats industrial waste water.

(24) The pretreatment section 2 receives raw water (waste water). In the case of waste water from a plant or domestic waste water, the water contains, as organic components, oils in the form of oil droplets or an emulsion, as well as organic matters that are present in water in the form of molecules or ions (acetic acid, formic acid, phenol, etc.).

(25) The oil separator removes oils form the raw water. The separation section adds a chelating agent to waste water to chelate heavy metals and insolubilize them. The separation section adds an aggregating agent to waste water to cause the aggregation of heavy metal chelates, suspended particles, etc., followed by sedimentation, thereby removing heavy metals and suspended particles from the waste water.

(26) In the case of configuration having a biological treatment section, the waste water from which oils, heavy metals, and suspended particles have been removed is fed to the biological treatment section. In the biological treatment section, organic matters, such as acetic acid, formic acid, humic acid, and phenol as mentioned above, are decomposed.

(27) In the case of configuration having an oxidization treatment section, the waste water is irradiated with ultraviolet light. Alternatively, ozone-containing water, a sodium hypochlorite solution, and a hydrogen peroxide solution are supplied into the waste water. As a result, organic matters, such as acetic acid, formic acid, humic acid, and phenol as mentioned above, are oxidized and decomposed.

(28) The organic matter content measurement section 12 measures the TOC of waste water before the treatment in the activated carbon treatment section 10. TOC may be measured by an online meter or may also be sampled and analyzed. In this embodiment, as a result of pretreatments such as the biological treatment, water before flowing into the activated carbon treatment section 10 has a TOC of 100 mg/l or less.

(29) The waste water having a TOC of 100 mg/l or less flows into the activated carbon treatment section 10 in the demineralization section 3. While the waste water passes through the filled tank 11 of the activated carbon treatment section 10, organic matters remaining in the waste water, such as acetic acid, formic acid, humic acid, and phenol as mentioned above, are adsorbed to the activated carbon surface and thus removed. The TOC of the water after the treatment in the activated carbon treatment section 10 is reduced to about ⅓ to ⅕ of the TOC before the treatment.

(30) The organic matter content measurement section 13 measures the total organic carbon concentration of the waste water after the treatment in the activated carbon treatment section 10. In this embodiment, the TOC of water after the treatment in the activated carbon treatment section 10 is 20 mg/l or less, more preferably 10 mg/l or less.

(31) The waste water discharged from the activated carbon treatment section 10 is fed to the capacitive de-ionization treatment section 100. In the capacitive de-ionization treatment section 100, the demineralization treatment described in FIG. 4 is performed. By the demineralization treatment, the water stored in the flow path 103 is discharged from the capacitive de-ionization treatment section 100 and recovered as a concentrated water having a high concentration of ions. The positive electrode 101 and the negative electrode 102 are regenerated to the state where no ions are adsorbed.

(32) FIG. 3 is a graph showing time-dependent changes in the effective capacity of an electrode when waters having different organic matter contents were subjected to capacitive de-ionization treatments under the same conditions. In the figure, the abscissa is the number of elapsed days and the ordinate is effective capacity. Effective capacity is defined by the proportion of ions that can be adsorbed to the electrode, taking the effective capacity of the electrode before use as 100%.

(33) In FIG. 3, the organic matter amount A represents the case where the TOC of water flowing into the capacitive de-ionization treatment section is 10 mg/l, and the organic matter amount B represents the case where TOC is 20 mg/l. The organic matter amounts C and D each represent the case where TOC exceeds 20 mg/l, and TOC is higher in the organic matter amount D than in the organic matter amount C.

(34) As shown in FIG. 3, the effective capacity rapidly decreases in the case of the organic matter amount C or D, and it can be understood that the demineralization treatment capability is reduced within a short period of time. That is, in the case where water flowing into the capacitive de-ionization treatment section contains a large amount of organic matters, short-cycle electrode maintenance, for example, is required to maintain high treatment performance, resulting in a decrease in treatment efficiency.

(35) Meanwhile, in the case of the organic matter amount A or B, the effective capacity decreases slowly. From these results, it can be understood that when an activated carbon treatment section is provided on the upstream side of the capacitive de-ionization treatment section, and the TOC of water is reduced to 20 mg/l or less by a treatment in the activated carbon treatment section prior to performing a capacitive de-ionization treatment, a decrease in the effective ion adsorption areas of electrodes in the capacitive de-ionization treatment section is suppressed, and high water treatment capability can be maintained for a long period of time.

REFERENCE SIGNS LIST

(36) 1 Water treatment device 2 Pretreatment section 3 Demineralization section 10 Activated carbon treatment section 11 Filled tank 12, 13 Organic matter content measurement section 100 Capacitive de-ionization treatment section 101 Positive electrode 102 Negative electrode 103 Flow path 104 Anion exchange membrane 105 Cation exchange membrane