JP2003190976A - Apparatus and method for treating wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating wastewater capable of enhancing contact efficiency of wastewater and ozonated air and realizing a shortening of a retention time of wastewater in a reaction tank and reducing dioxins in treated water by an accelerated oxidation treatment combining O<SB>3</SB>/ oxidating agent/metal element. <P>SOLUTION: The apparatus for treating wastewater is provided with a means for adding an oxidating agent to wastewater and a means for dispersing the wastewater to a gas containing ozone. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment apparatus and method for efficiently decomposing harmful substances contained in wastewater, particularly difficult-to-decompose substances such as dioxins.

[0002]

2. Description of the Related Art In recent years, research and development of water treatment using ozone, which has a strong oxidizing power, has been attracting attention in Japan. The main purposes of using ozone for wastewater treatment are:
1. Removal of odor, 2. Removal of chromaticity, 3. Removal of organics,
4. Removal of iron, manganese, etc., 5. Removal of phenol,
6. Substantial reduction of chloroform extractable substances such as ABS, 7. Examples include sterilization of pathogenic bacteria and inactivation of viruses. However, while recognizing the excellent effect of improving the water quality by ozone treatment, the aggressive introduction plan was stagnant, and the reasons for this were high power consumption and difficulty in operation management.

A conventional wastewater treatment method using ozone is to diffuse the ozonized air into the water in the reaction tank as many fine bubbles to bring the wastewater into contact with the ozonized air. However, since ozone has a low solubility in water, it is extremely difficult to dissolve in water, and since the surface area of bubbles is small if they are diffused as bubbles in water, the contact area of gas-liquid also becomes small, and therefore the utilization efficiency of ozone is reduced. There was a problem such as low.

In order to decompose organic substances in wastewater more effectively, O ₃ / UV treatment, O ₃ / H ₂ O ₂ treatment, O ₃ / UV treatment
/ H ₂ O ₂ treatment has also been developed to promote accelerated oxidation treatment technology by combining ozone treatment with other methods. Even with such a method, ozonized air is converted into many fine bubbles in the water in the reaction tank. It is difficult to say that ozone is effectively used in terms of diffused air, and this is a treatment method that consumes a large amount of energy.

[0005]

In the conventional method of diffusing ozone into wastewater, the contact efficiency of ozone and wastewater is poor, so that dioxins in wastewater are not efficiently decomposed and consume a lot of energy. , The device was not compact either. The present invention is intended to solve the above problems,
It is an object of the present invention to provide an apparatus and method for efficiently decomposing hardly decomposable harmful substances.

[0006]

That is, the present invention is
"Wastewater treatment device equipped with a means for adding an oxidant to wastewater and a means for dispersing the wastewater in a gas containing ozone", "A means for dispersing the wastewater in a gas containing ozone, and irradiating the wastewater with ultraviolet rays "Wastewater treatment apparatus having means", "Wastewater treatment method of dispersing wastewater to which an oxidant is added, or simultaneously disposing wastewater and an oxidant in a gas containing ozone", "Gas containing wastewater containing ozone" Waste water treatment method of irradiating the dispersed waste water with ultraviolet rays.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, waste water is dispersed in a gas containing ozone. There are various forms of dispersion as will be described later, and are not particularly limited, but by dispersing waste water in a gas containing ozone, the contact area of gas-liquid can be increased by a method of dispersing ozone as bubbles in waste water. It is possible to increase the size and efficiently decompose persistent hazardous substances.

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 shows an example of the wastewater treatment apparatus of the present invention.

In the wastewater treatment apparatus shown in FIG. 1, the means for dispersing wastewater in a gas containing ozone (hereinafter referred to as a reaction tower) has a spray nozzle 3 and an ozone gas inlet and outlet.

Waste water containing a hardly decomposable substance such as dioxin is introduced into the reaction tower 2 and dispersed by the spray nozzle 3 to come into gas-liquid contact with a gas containing ozone gas. At this time, an oxidizing agent is added from the oxidizing agent adding means 5, ozone reacts with the oxidizing agent to form an accelerated oxidizing atmosphere, and the hardly decomposable substance is efficiently decomposed.

The term "hardly-degradable substance" as used herein means that it is chemically stable and has teratogenicity, carcinogenicity, and immunotoxicity when taken into the living body of an animal, and it is originally used in the living body. Substances that are defined as exogenous substances that affect normal hormonal action, such as dioxins polychlorinated dibenzofuran (PCDF), polychlorinated dibenzo-
Para-dioxane (PCDD), polychlorinated biphenyls, pesticides suspected as endocrine disrupting chemicals, fungicides, dyes, ultraviolet absorbers, surfactants and the like can be mentioned. In particular, it is highly effective against VOC (volatile organic compounds) such as trichloroethylene and tetrachloroethylene, and is suitable for application of the device of the present invention.

The oxidant adding means supplies the oxidant before the waste water is supplied to the reaction tower or at the same time as the waste water is supplied into the reaction tower. The oxidizing agent in the present invention is a substance having an oxidizing ability other than ozone, and a hydroxyl radical when decomposed in water such as hydrogen peroxide, sodium hypochlorite, peracid, persulfuric acid, hydroperoxide, and quinones. An aqueous solution of a substance capable of generating is preferably used. Of these, hydrogen peroxide is the most preferable.

In order to accelerate the reaction, it is also preferable to provide an ultraviolet irradiation means such as a UV lamp 7 in the reaction tower. O ₃ has a large absorption coefficient in the ultraviolet region of wavelength 200 nm to 300 nm, and when it is used in combination with ultraviolet rays in a specific wavelength region, O ₃ can bring out a remarkable oxidizing power as compared with the case where O ₃ is used alone. In particular, since the coefficient of light absorption for O ₃ decomposition becomes maximum at 240 to 260 nm, it is preferable to use a low pressure mercury lamp that emits light having a wavelength of 253.7 nm in the present invention. The position where the UV lamp 7 is installed may be any position where the dispersed wastewater can be irradiated with ultraviolet rays.

The oxidant addition means and the ultraviolet irradiation means are
Only one of them may be installed, but the disassembly effect is higher when both are installed.

The ozone-containing gas in the present invention means ozone of 1000 ppm or more, preferably 5000 ppm.
It means the above gas. At this time, it is preferable that the temperature is 30 ° C. or lower and the pressure is 0.2 MPa or higher. Examples of ozone generation methods include an ultraviolet irradiation method, a water electrolysis method, and a silent discharge method. However, it is preferable to use the silent discharge method, which is excellent in power consumption, generated ozone concentration, and device miniaturization. This is a method in which an insulator is inserted between a pair of electrodes, dry air or oxygen is flown, and an AC voltage of several thousand to ten thousand thousand volts is applied to generate ozone from oxygen in the discharge air. The generated ozone is preferably fed from below the reaction tower and brought into countercurrent contact with the wastewater.

The reaction tower 2 of the present invention is only required to make efficient gas-liquid contact, but a liquid dispersion type gas absorption device is preferable. For example, a spray tower, a wetting wall tower, a packed tower, a scrubber, a disk tower, a liquid injection tower, a continuous ball tower, a disk rotary absorption device, a packed fluidized bed absorption device, a centrifugal absorption device and the like can be adopted. Both devices are in countercurrent contact and have a better contact efficiency between ozone and liquid than in parallel flow. Here, the spray tower has a structure in which the spray nozzles 3 are arranged in a plurality of stages at regular intervals, and is a device for bringing gas into contact with the liquid atomized by the spray nozzles 3. A wet wall tower is a liquid film that flows liquid along the inner wall of a vertical pipe.
It is a device that makes contact with the gas flowing in the center of the tube. Also,
The packed tower is a reaction tower using various packing materials 4, and is a device in which the liquid supplied from above in the packed bed portion and the gas sent from below come into countercurrent contact. Raschig ring for the filler 4,
There are a lessing ring, a berl saddle, an interlocks saddle, a terrarette packing, a pole ring and the like, but any filler may be used in the present invention. However, since ozone is highly corrosive, it is preferable to use a corrosion-resistant material for the filler 4, such as polyvinyl chloride, Teflon (registered trademark), glass, concrete, and stainless steel.

Further, it is preferable to use a metal catalyst in order to enhance the accelerated oxidizing atmosphere in the reaction tower. Above all, it is preferable to use a transition metal element such as Fe, Mn, Co, Ni, Cu, or Pt as a catalyst. Although any method may be used using a metal catalyst, for example, a method of using these metals for the packing material 4 of the packed bed, a method of supplying an aqueous solution of a compound containing these metal elements to a reaction tower, etc. are preferably adopted. it can. As a compound containing a metal element,
Examples thereof include oxides, sulfates, acetates, ammonium salts and halides. As a method of supplying the aqueous solution of the compound containing a metal element to the reaction tower, it may be supplied before the waste water is supplied to the reaction tower, or may be supplied into the reaction tower simultaneously with the waste water.

The wastewater to be used in the present invention may be any of industrial wastewater, municipal wastewater, leachate from a waste treatment plant, etc. It is preferable to provide a pretreatment means for removing turbidity because the decomposition efficiency can be increased, the production of by-products can be suppressed, and maintenance such as cleaning of the reaction tower can be reduced. However, in the case of a persistent substance that is adsorbed by turbid components, it is necessary to consider the treatment separately.

Here, the pretreatment includes coagulation sedimentation, sand filtration,
Coagulation filtration, safety filter, membrane filtration and the like can be applied, but filtration using a separation membrane module using a separation membrane having an average pore diameter of 3 nm to 10 μm can be preferably employed. Here, the separation membrane is a membrane capable of removing suspended matter in wastewater, and in the present invention, a membrane having a turbidity of permeated water of 1 degree or less is preferable. Turbidity refers to fine particles floating in water expressed by the degree of turbidity, and 1 g of kaolin suspended in 1 liter of water without turbidity is 1000 degrees.

The pore diameter (Rp: m) of the separation membrane is determined by the equation (1) from the membrane permeation rate (Jv: m ³ / (m ² · s)) and the pressure difference (ΔP: Pa) due to the permeation membrane. Sex (Lp:
m ³ / (m ² · s · Pa)) is obtained, and it can be calculated from the equation (2) using the calculated water permeability of the membrane. Here, H is the water content of the film, L is the thickness of the film (m), and η is the viscosity of water (Pa · s).

Jv = Lp × ΔP (1) Lp = (H / L) × Rp × 2 / (8 × η) (2) Further, the material of the separation membrane is polyacrylonitrile, polysulfone, polyphenylene sulfone, polyphenylene. Sulfide sulfone, polyvinylidene fluoride, cellulose acetate, polyethylene, polypropylene, etc.,
Inorganic materials such as ceramics can be mentioned. Any material can be applied, but hydrophilic polyacrylonitrile,
Cellulose acetate is preferable because it is less likely to become dirty and has high washing recovery property. Further, polyvinylidene fluoride having high chemical resistance can also be preferably adopted.

As the separation membrane module, a hollow fiber membrane or tubular membrane module, a flat membrane made into a plate-and-frame type or a spiral type module, and a rotary disc type flat membrane in which a flat membrane is installed on a rotary disc A module or the like can be used. Above all, a hollow fiber membrane module using a hollow fiber membrane having a large effective membrane area per unit volume of the apparatus, and a plate-and-frame type or rotating disk type flat membrane module having a high cleaning property on the surface of the separation membrane are preferable.

Further, it is also preferable to provide a means for concentrating the waste water in the preceding stage of the reaction tower and to condense the hardly decomposable substance in the waste water before the decomposition treatment, from the viewpoint of enhancing the decomposition efficiency. When the wastewater contains a large amount of turbid components, the means for concentrating the wastewater is preferably provided after the pretreatment means.

As a means for concentrating wastewater, a module using a reverse osmosis membrane is preferably used. Here, the reverse osmosis membrane is a membrane that can separate impurities at the ion level, and in the present invention, it is sufficient if the rejection rate of divalent ions such as Mg ²⁺ is high. The material includes cellulose acetate and polyamide, and any of these membrane materials can be applied. In the present invention, it is preferable that the removal rate of the organic chlorine compound serving as a precursor for dioxin formation is 90% or more, and more preferably 95% or more. The reverse osmosis membrane module may have any form, but a spiral type is generally preferred and preferred.

The liquid dropped to the lower part of the reaction tower may be directly discharged to the natural world as treated water, or may be reused for cooling water for air conditioning, sprinkling water and the like. There is no problem because ozone remaining in the treated water is easily decomposed into oxygen by light, water and the like.

Further, it is preferable that the ozone in the discharged exhaust gas is decomposed by the exhaust ozone treatment device 8. The exhaust ozone treatment includes an activated carbon adsorption decomposition method, a thermal decomposition method, a chemical cleaning method, a catalyst contact method, a soil contact method, and the like, but any treatment method may be used in the present invention.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0028]

EXAMPLES Example 1 FIG. 2 shows a wastewater decomposition apparatus apparatus which has been operated. As pretreatment, the wastewater was supplied under pressure to the polyacrylonitrile-made separation membrane 11 having an average pore diameter of 10 nm, and after removing the suspended matter, it was allowed to flow into the reaction column 2. In addition to waste water, an oxidizing agent was introduced into the reaction tower 2 from an oxidizing agent inlet 5, and a metal catalyst aqueous solution for promoting the reaction was introduced from a catalyst inlet 6. A UV lamp 7 (λ = 253.7 nm) was installed in the reaction tower.
This time, hydrogen peroxide was used as the oxidant and ferrous sulfate was used as the metal catalyst. The oxidizing agent was added so that the molar ratio of hydrogen peroxide / tetrachloroethylene was 1: 1 and the metal catalyst was added so as to be 1/100 equivalent to the oxidizing agent.

In the experiment, the average turbidity was 5.2 degrees and the average TOC.
An artificial wastewater prepared by adding tetrachlorethylene to a concentration of 1.5 mg / l in 2.9 mg / l Lake Biwa water was used. The amount of treated water in the reaction tower 2 was 4 m ³ / day. The membrane-treated water was dispersed by the spray nozzle 3 in the reaction tower and brought into contact with ozone gas in the reaction tower. Reaction tower 2
Was operated at an ozone injection rate of 3.6 mg / l. Ozone injection rate (Applied Ozone Dosag
e: D) was calculated by the following formula.

D (mgO₃/ L) = C_i× (Q_G/ Q_L) here,: C_i: Injection gas ozone concentration (mg / l) Q_G: Gas flow rate (l / min) Q_L: Liquid flow rate (l / min) Injection gas ozone concentration C_i= 5 (mg / l) Gas flow rate Q_G= 2 (l / min) Liquid flow rate Q_L= 2.78 (l / min) D = 5 × (2 / 2.78) = 3.6 (mg / l).

Further, the humidity in the air introduced into the generator has an effect on the generated ozone concentration, so that the humidity was sufficiently removed with a desiccant. Since the voltage also affects the generated ozone concentration, a ballast was installed to stabilize the voltage and adjust the generated ozone concentration to a constant value.

The concentration of tetrachloroethylene recovered from the lower part of the reaction tower is about 0.03 mg / l, which is less than the allowable limit of 0.1 mg / l specified in the Water Pollution Control Law and can be discharged into natural water. Met. Moreover, the decomposition rate of tetrachlorethylene by this wastewater treatment device is about 9
It was 8%.

Comparative Example 1 A conventional wastewater decomposition apparatus is shown in FIG. As a pretreatment, the wastewater was supplied under pressure to a separation membrane 11 made of polyacrylonitrile having an average pore diameter of 10 nm to remove turbid components and then flowed into the reaction tank 9. The waste water and the ozone gas were brought into contact with each other by a diffuser system in which ozone was injected into the waste water that had flowed in by the diffuser pipe 10. In addition to waste water, an oxidizing agent was introduced into the reaction tank 9 through the oxidizing agent inlet 5, and an aqueous metal catalyst solution for promoting the reaction was introduced through the catalyst inlet 6. An experiment was conducted under the same conditions as in Example 1 regarding the treatment amount of wastewater, the membrane treatment conditions, the ozone injection rate, the UV lamp, the type of substance containing an oxidizing agent and a metal element, and the addition amount.

The tetrachloroethylene concentration of the treated water recovered from the reaction tank was 0.13 mg / l, and it was impossible to discharge it to natural water. The decomposition rate of tetrachloroethylene by this wastewater treatment device was about 91%.

[0035]

EFFECTS OF THE INVENTION In the treatment of wastewater, by installing a reaction tower in which the wastewater is dispersed and brought into contact with a gas containing ozone, the production of by-products in the reaction tower is suppressed more than before, and the reaction of the wastewater is suppressed. The residence time in the tower can be shortened and the concentration of the hardly decomposable substance in the treated water can be lowered to a concentration at which it can be released. Further, if the persistent substance in the wastewater is removed in the preceding stage of the reaction tower and then the hardly-decomposable harmful substance is concentrated, the harmful substance can be decomposed more efficiently.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of a wastewater decomposition apparatus of the present invention.

FIG. 2 is a flow chart showing an example of a wastewater decomposition apparatus of Example 1.

FIG. 3 is a flow chart showing an example of a wastewater decomposition apparatus of Comparative Example 1.

[Explanation of symbols]

1: Pretreatment or reverse osmosis membrane module 2: Reaction tower 3: Spray nozzle 4: Filling material 5: Oxidizing agent inlet 6: Catalyst injection port 7: UV lamp 8: Waste ozone treatment device 9: Reaction tank 10: Air diffuser 11: Separation membrane

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 1/72 C02F 1/72 Z 101 101 1/76 1/76 A (72) Inventor Takao Sasaki Shiga Prefecture 1-1 1-1 Sonoyama, Otsu-shi Toray Co., Ltd. Shiga Plant F-term (reference) 4D006 GA03 HA01 HA21 HA41 HA61 HA83 KA72 KB30 MA01 MA02 MA03 MA04 MB09 MB11 MC03 MC18 MC22 MC23 MC29 MC39 MC54 MC62 MC63 PA02 PB08 PB70 4D037 AA11 AB11 AB14 BA18 CA03 CA11 4D050 AA12 AB13 AB19 BB02 BB06 BB07 BB09 BB10 BB12 BB13 BC04 BC09 BD02 CA09 4G069 BB04A BB08A BB10A BB10B BC29A BC31A BC62A BC66A BC66B BC67A BC68A CA75A BD01A BD01A

Claims (11)

[Claims] 1. A wastewater treatment apparatus comprising means for adding an oxidizing agent to wastewater and means for dispersing the wastewater in a gas containing ozone. 2. A wastewater treatment apparatus comprising means for dispersing the wastewater in a gas containing ozone and means for irradiating the wastewater with ultraviolet rays. 3. The wastewater treatment apparatus according to claim 1, wherein a metal catalyst that enhances the accelerated oxidizing atmosphere is used. 4. The wastewater treatment apparatus according to claim 3, wherein the metal catalyst for enhancing the accelerated oxidizing atmosphere is a compound containing a metal element, and a means for supplying an aqueous solution of the compound is provided. 5. The liquid dispersion type gas absorption device as the means for dispersing the wastewater in a gas containing ozone.
The wastewater treatment device according to any one of 1. 6. The wastewater treatment apparatus according to claim 1, wherein the ozone-containing gas and the dispersed wastewater come into contact in countercurrent. 7. The oxidizing agent is one or more compounds selected from the group consisting of hydrogen peroxide, sodium hypochlorite, peracids, persulfates, hydroperoxides and quinones. The wastewater treatment device described in Crab. 8. A pretreatment means is provided in front of a means for dispersing wastewater in a gas containing ozone.
The wastewater treatment device according to any one of 1. 9. A means for concentrating the waste water is provided before the means for dispersing the waste water in a gas containing ozone.
9. The wastewater treatment device according to any one of 8 to 8. 10. A method for treating wastewater, which comprises dispersing wastewater containing an oxidizing agent, or simultaneously dispersing the wastewater and the oxidizing agent in a gas containing ozone. 11. A method for treating wastewater, which comprises dispersing the wastewater in a gas containing ozone and irradiating the dispersed wastewater with ultraviolet rays.