Water treatment method

Abstract

To provide a water treatment method with superior treatability.SOLUTION: Water to be treated in a treatment tank 1 is degassed to remove dissolved gas, and the water to be treated is circulated and electrolyzed to generate an oxidizing substance in the tank. An ionic substance may be removed by applying an electric field to treated water after treatment. An activated carbon may be allowed to adsorb the water to be treated, and an oxidizing substance may be allowed to decompose the substance adsorbed to the activated carbon. An activated carbon storage tank and an electrolysis mechanism E may be provided, and the water to be treated may be circulated between the treatment tank 1 for the water to be treated, the activated carbon storage tank, and the electrolysis mechanism E.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a water treatment method with better processability.

Background Art

[0002] Conventionally, there has been a proposal regarding a method and apparatus for treating organic wastewater (Patent Document 1). That is, this proposal aims to provide a method for treating organic wastewater that simply controls the amount of powdered activated carbon used in the treatment of organic wastewater containing hardly decomposable organic substances and suppresses the operating cost. For this reason, it has been found that there is a correlation between the electrical conductivity or chloride ion concentration in biologically treated water and the dissolved COD concentration, and the dissolved COD concentration is estimated from the measured value of the electrical conductivity or chloride ion concentration in biologically treated water, and the necessary amount of powdered activated carbon is determined based on the COD equilibrium adsorption amount of the powdered activated carbon corresponding to the COD concentration. On the other hand, there has been a demand for a water treatment method with better processability.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, this invention aims to provide a water treatment method with better processability.

Means for Solving the Problems

[0005] To solve the above problems, this invention takes the following technical means. (1) The water treatment method of this invention is characterized in that it exerts a dissolved gas removal effect by degassing the water to be treated in a treatment tank, and circulates the water to be treated for electrolysis to generate oxidizing substances in the tank.

[0006] This water treatment method exerts a dissolved gas removal effect by degassing the water to be treated in a treatment tank (e.g., made of vinyl chloride as the material) (for example, using a vacuum pump to make the inside of the treatment tank in a vacuum state). Therefore, the fluidity in the tank can be improved by the detachment movement of the dissolved gas bubbles in the water to be treated, and the stirring effect can be promoted.

[0007] Examples of the dissolved gas extracted from the water to be treated by degassing include carbon dioxide (CO2), nitrogen (N2), and volatile organic compounds (the contaminated components of the water to be treated). And by degassing, organic gas (for example, pyrolyzed at about 600 - 1100 °C in a subsequent process) or inorganic gas can be removed from the water to be treated, and the electrolysis efficiency can be improved. In addition, since the water to be treated is circulated for electrolysis to generate oxidizing substances in the tank, combined with the promotion of the stirring effect due to the improvement of the fluidity of the water to be treated in the tank, the continuous encounter rate and reactivity between the contaminated substances and the oxidizing substances in the water to be treated can be increased.

[0008] And since gaseous dissolved gases (such as fine bubbles) such as carbon dioxide (CO2) and nitrogen (N2) are extracted from the water to be treated, the conductivity is improved (fine bubbles inhibit the electrical conductivity in the liquid) when circulating for electrolysis, the electrolysis efficiency is increased, and the production efficiency of oxidizing substances and the electrolysis efficiency of anodic oxidation are high. Thereby, even when the water to be treated contains organic substances (such as alcohols, ethylene glycol, propylene glycol, etc.) or oil components (emulsion oil), its decomposability is high.

[0009] On the water to be treated, a filtering effect by activated carbon can be exerted in the treatment tank or after treatment (together with the electrolysis effect and the electrolysis oxidant effect). Also, the treated water can be treated by a UF membrane. The degassed gas can be thermally decomposed (e.g., at about 600 - 1100 °C) in the heat treatment tank of the next process (e.g., heated by an LNG burner or induction heating), so that the vaporized organic compounds can be reduced to low molecules or rendered harmless.

[0010] Examples of the water to be treated include wastewater (e.g., wastewater containing liquid crystal or resist solution) and waste liquid (e.g., high-concentration waste liquid from factories). Examples of the oxidizing substances generated by the electrolysis include hydroxyl radicals (·OH), electrolytic chlorine (HClO) generated in the coexistence of sodium chloride (NaCl), and oxygen radicals (·O) generated in the coexistence of ozone (O3). Here, the oxidizing power of chlorine (HClO) is highest at pH 6 (the peak of the oxidation percentage is 100%, and it decreases sharply in the alkaline range), but the addition of Br can pull the high oxidizing power up to the pH 7 range.

[0011] (2) An electric field may be applied to the treated water to be treated to remove ionic substances. With such a configuration, the ionic substances in the treated water after treatment due to the oxidizing substances can be electrically repelled, and thus the final treated water with higher purity (e.g., pure water or ultrapure water for semiconductor cleaning) can be obtained.

[0012] Examples of the mode of applying the electric field include passing water (repelling cations) between the positive electrodes at a high voltage and passing water (repelling anions) between the negative electrodes at a high voltage. Examples of the ionic substances include sodium ions (Na + ) as cations and chloride ions (Cl - ) as anions. Here, by returning the Na+ ions and Cl- ions that come out to the raw water tank side, the reuse of NaCl for electrolysis can be achieved. Specifically, HOCl is generated from the Cl- ions by electrolysis, and the Cl- ions generated by the oxidizing agent HOCl decomposing the dirt components can be repeatedly used for water treatment. Thereby, the chemical cost of NaCl to be added can be greatly reduced. When the water to be treated tends to be acidic, HOCl changes to Cl2 gas and escapes. Therefore, it is preferable to maintain and manage the pH in the neutral range while monitoring the water quality (pH and others) of the water to be treated.

[0013] (3) The adsorption action of activated carbon may be exerted on the water to be treated, and a decomposition action by an oxidizing substance may be exerted on the adsorbed substances on the activated carbon. With this configuration, while reducing and purifying the dirt substances in the water to be treated by the adsorption action of activated carbon, the decomposition action (cleaning action of activated carbon) by the oxidizing substances (O3, HOCl, ·O radical, ·OH radical, etc.) generated by electrolysis is continuously exerted on the activated carbon (attack of oxidizing substances on the activated carbon), and the dirt substances adsorbed in the micropores of the activated carbon are oxidized and decomposed to regenerate and recover the original adsorption action of the activated carbon, and its adsorption activity can be maintained in a high state for a long period of time. In addition, the degassing action is also exerted on the activated carbon particles themselves, the unnecessary gases adsorbed on the surface of the activated carbon are removed, and the activated carbon is maintained in a state with excellent activation performance.

[0014] Thereby, the span (interval) until the activated carbon is taken out from the treatment system and subjected to activation treatment at a high temperature (for example, heat treatment at a high temperature for about 1 to 3 hours) can be extended. Or the activation treatment can be omitted. When the activation treatment at a high temperature is used in combination, by washing and regenerating the activated carbon with electrolyzed water, the number of times of activation by heat treatment of the activated carbon can be reduced (the heat treatment at a high temperature involves consumption and depletion due to the CO2 conversion of the carbon itself of the activated carbon), and the life of the activated carbon can be extended.

[0015] Then, small-particle organic compounds can be decomposed by electrolysis treatment (direct anodic oxidation, generation of oxidizing substances), and larger organic compounds can be adsorbed by activated carbon adsorption and reduced and purified from the water to be treated.

[0016] (4) It may have a storage tank for the activated carbon and an electrolysis mechanism, and the water to be treated may be circulated among the treatment tank for the water to be treated, the storage tank for the activated carbon, and the electrolysis mechanism. With such a configuration, by circulating the water to be treated among the treatment tank for the water to be treated, the storage tank for the activated carbon (fixed bed, stationary bed), and the electrolysis mechanism (having electrodes), the water to be treated becomes electrolyzed water in the electrolysis mechanism, and when this electrolyzed water passes through the storage tank for the activated carbon, it exerts a decomposing action on the dirt components.

[0017] The oxidizing substances in the electrolyzed water exert an oxidative decomposition action on the dirt components (such as organic compounds) adsorbed in the micropores of the activated carbon, and continuously attach oxygen around the activated carbon to reduce the decrease in activity and maintain the adsorption reactivity. That is, the activated carbon is in a state of being constantly washed by the electrolyzed water. Also, along with the above chemical action, the storage tank for the activated carbon has a mechanism for physically filtering and removing the dirt components in the water to be treated.

[0018] When activating the activated carbon at a high temperature, it is considered that the moisture in the water-retaining activated carbon particles after treatment evaporates to become high-temperature water vapor, and new micropores are drilled in the activated carbon. However, with the above configuration, the activated carbon can be constantly washed and regenerated at room temperature with electrolyzed water. Here, if the activated carbon particles are in a fine powder form (particle size of about 30 - 50 μm), compared with the case of a larger powder form (particle size of about 0.6 mm), the adsorption capacity is high, but the treatment water permeable membrane used is likely to be clogged and easily lost due to carry-over, etc. Therefore, mixing powdered activated carbon and granular activated carbon and setting the proportion of the granular activated carbon to about 20 - 40% can perform the treatment in a well-balanced manner.

[0019] As a source of the powdered activated carbon, when the activated carbon is regenerated by activation, there is a case where the organic matter adsorbed on the surface of the activated carbon is carbonized. In this case, since the powdered activated carbon (minute) is generated from the dirt components (organic components) of the water to be treated itself, the additional supply amount of the activated carbon (which is a consumable) can be reduced. The powdered activated carbon having a small particle size (relatively large specific surface area) has an advantage of excellent cleaning and regenerating property by electrolyzed water. On the other hand, in the case of activation regeneration at a high temperature, since the particles are fine, the constituent carbon (C) of the activated carbon (which is minute) is likely to be converted into CO2 and disappear.

Effects of the Invention

[0020] This invention has the following configuration and effects. Since the electrolysis efficiency is increased and the production efficiency of the oxidizing substance and the electrolysis efficiency of anodic oxidation are large, a water treatment method having more excellent treatability can be provided.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

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Figure 5

Modes for Carrying Out the Invention

[0022] Hereinafter, embodiments of this invention will be described with reference to the drawings. (Embodiment 1) As shown in FIG. 1, in the water treatment method (treatment apparatus) of this embodiment, the water to be treated in the treatment tank 1 is degassed (using a vacuum pump VP) to exert a dissolved gas removal effect. As the water to be treated, simulated wastewater (salt concentration of about 3%, COD of 19,800 ppm) containing ethylene glycol, which is an organic compound (contaminant component), was prepared. Also, the water to be treated is circulated and electrolyzed (using an electrolysis mechanism E, current value 5 A / dm 2 ) to generate an oxidizing substance (HOCl) in the tank.

[0023] That is, in the water to be treated, a filtration effect by activated carbon was exerted in the activated carbon storage tank C, together with the electrolysis effect (direct anodic oxidation) and the action of the electrolytic oxidant (HOCl). Furthermore, the adsorbing effect of activated carbon was exerted on the water to be treated, and at the same time, a decomposition effect by the electrolytic oxidizing substance (HOCl) was exerted on the adsorbed substances (contaminant components) on the activated carbon.

[0024] The water to be treated was circulated between the treatment tank 1 of the water to be treated, the activated carbon storage tank C, and the electrolysis mechanism E. The water to be treated flows from the upper treatment tank 1 to the lower tank. In this way, by circulating the water to be treated between the treatment tank 1 of the water to be treated, the storage tank of activated carbon, and the electrolysis mechanism E, the water to be treated becomes electrolyzed water in the electrolysis mechanism E, and this electrolyzed water exerts a decomposition effect when passing through the activated carbon storage tank C. Here, a degassing effect may be exerted separately on the electrolysis mechanism E.

[0025] The treated water to be treated (COD 4 ppm) can be reduced to COD 1 ppm by feeding back this treated water and passing it through the activated carbon storage tank C again. An electric field effect was exerted by the electric field mechanism EIS to remove ionic substances. In the electric field mechanism EIS, water was passed between the high-voltage positive electrodes and between the high-voltage negative electrodes. As a result, finally treated water was obtained in which the ionic substances (sodium ions, chloride ions) in the treated water to be treated due to the oxidizing substance were electrically repelled. The gas that has been degassed in the treatment tank 1 is subjected to pyrolysis treatment (at about 600 - 1100 °C) in the heat treatment tank 2 (where hot air is generated by the induction heating mechanism IH) so as to reduce the molecular weight or render harmless the vaporized organic compounds.

[0026] Next, the usage state of the water treatment method of this embodiment will be described. In this water treatment method, the dissolved gas removal action is exerted by degassing the water to be treated in the treatment tank 1. Therefore, the fluidity in the tank is improved by the detachment movement of the dissolved gas bubbles in the water to be treated, and the stirring action can be promoted.

[0027] Also, since the water to be treated is circulated and electrolyzed to generate oxidizing substances in the tank, the continuous encounter rate and reactivity between the dirt substances and the oxidizing substances in the water to be treated can be increased in combination with the promotion of the stirring action due to the improvement of the fluidity of the water to be treated in the tank. And since the gaseous dissolved gas is extracted from the water to be treated, the conductivity is improved when circulating and electrolyzing, the electrolysis efficiency is increased, and it has excellent treatability.

[0028] (Embodiment 2) Next, Embodiment 2 will be described centering on the differences from the above Embodiment 1. As shown in FIGS. 2, 3 (partially shown in block flow), 4, and 5, in the water treatment method (treatment apparatus) of this embodiment, the dissolved gas removal action is exerted by degassing the water to be treated in the treatment tank 1. As the water to be treated, simulated wastewater (salt concentration of about 2.5%, COD 20,300 ppm) containing propylene glycol as an organic compound (dirt component) was prepared. To degas the water to be treated, a vacuum pump VP was used. The water to be treated sequentially moves from the treatment tank 1 on the right side to the treatment tank 1 on the left side.

[0029] An activated carbon storage tank C and an electrolysis mechanism E are provided above the treatment tank 1, and the water to be treated is circulated among the treatment tank 1 for the water to be treated, the activated carbon storage tank C, and the electrolysis mechanism E. By circulating the water to be treated in this way, electrolysis is carried out by the electrolysis mechanism E to generate an oxidizing substance in the tank. That is, the adsorption action of activated carbon is exerted on the water to be treated in the activated carbon storage tank C, and a decomposition action by an oxidizing substance (generated by the electrolysis mechanism E) is exerted on the adsorbed substance on the activated carbon.

[0030] Finally, the treated water to be treated (COD 6 ppm) is filtered by a UF membrane treatment device, and then an electric field action is exerted by the electric field mechanism EIS to remove ionic substances (sodium ions, chloride ions). On the other hand, the gas degassed in the treatment tank 1 is thermally decomposed (at about 600 - 1100 °C) in the heat treatment tank 2 (where hot air is generated by the induction heating mechanism IH) to reduce the vaporized organic compound to a lower molecular weight or render it harmless.

[0031] Also, the activated carbon in the activated carbon storage tank C is gradually withdrawn and stored in a storage tank for regenerated activated carbon (the tank at the lower right of Fig. 3), and is sequentially transferred from here to the heat treatment tank 2 by the impeller pump IP for activation and regeneration treatment. The regenerated portion is temporarily stored in the storage tank C-tank for activated regenerated carbon and then supplied again to the activated carbon storage tank C.

Industrial Applicability

[0032] Since it is more excellent in treatability, it can be applied to various water treatment method applications.

Explanation of Reference Numerals

[0033] 1 Treatment tank E Electrolysis mechanism

Claims

1. A water treatment method characterized in that it exerts a dissolved gas removal effect by degassing the water to be treated in the treatment tank (1), and circulates the water to be treated to electrolyze it to generate an oxidizing substance in the tank.

2. The water treatment method according to claim 1, wherein an electric field is applied to the treated water to remove ionic substances.

3. The water treatment method according to claim 1 or 2, wherein the water to be treated is subjected to the adsorption action of activated carbon, and the adsorbed substance on the activated carbon is decomposed by an oxidizing substance.

4. The water treatment method according to claim 3, which has a storage tank for activated carbon and an electrolysis mechanism (E), and circulates the water to be treated between the treatment tank (1) for the water to be treated, the storage tank for activated carbon, and the electrolysis mechanism (E).

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