JP3662474B2 - Method and apparatus for treating dioxins in waste water - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention effectively decomposes and removes halogenated organic compounds (hereinafter referred to as dioxins) such as dioxins contained in various industrial effluents, municipal sewage, wastewater from incineration plants, landfill leachate, etc. It relates to a method.
[0002]
[Prior art]
Conventionally, the waste water has been treated with various treatment devices such as biological treatment, coagulation / precipitation, activated carbon treatment, etc., alone or in appropriate combination. By the way, in recent years, it has been found that dioxins whose contamination has caused major social problems in various places have extremely low solubility in water, and many of them are adsorbed on organic substances and suspended solids (SS). ing. Therefore, conventionally, floating substances have been separated and removed from wastewater, and further subjected to high concentration treatment such as activated carbon treatment for removal.
[0003]
[Problems to be solved by the invention]
However, the above-described treatment method removes dioxins by adsorption or the like, and there is a problem that an adsorbent containing concentrated dioxins is generated as waste. An effective means for decomposing and removing dioxins is irradiation decomposition by ultraviolet rays, and more effectively, ultraviolet irradiation and combined use of ozone, hydrogen peroxide, catalyst and the like. However, when wastewater that is hard to transmit ultraviolet rays is treated by executing these means, using a conventional ultraviolet treatment device increases the transmission distance in the wastewater and reduces the irradiation effect, so the ultraviolet rays are uniformly irradiated. In addition, there is a need for a dioxin treatment method and apparatus that can sufficiently reach the dioxins in the waste water and can be efficiently decomposed. The present invention has been completed as a result of research aimed at developing such a dioxin treatment method and treatment apparatus.
[0004]
[Means for Solving the Problems]
[0005]
As a means for solving the above-mentioned problems, the present invention allows wastewater containing dioxins (hereinafter referred to as raw wastewater) to flow down in the form of a film along a falling wall (wetting wall) composed of a plurality of opposing surfaces. In addition, an ultraviolet light source is placed in contact with the drainage film between the falling walls to irradiate the drainage film, and a part of the wastewater irradiated with ultraviolet rays (hereinafter referred to as ultraviolet treatment wastewater) is sent to the ozone dissolution tank. The remainder is returned to the raw waste water, and in the ozone dissolution tank, ozone gas is brought into gas-liquid contact with the ultraviolet treated waste water to decompose and treat the dioxins . And preferably, the outlet effluent of the ozone dissolving tank (hereinafter, referred to as ozone treatment wastewater) a portion of the derived out of the system, and reflux the remainder UV wastewater is recycled to the ozone dissolving tank.
[0006]
In addition, as the ultraviolet irradiation device for irradiating the raw wastewater with ultraviolet rays used in the present invention , a falling wall surface composed of a plurality of faces provided opposite to each other, and a drainage film flowing down between the falling wall surfaces, consists of a UV light source for draining film irradiated attached to a non-contact device are preferred. In the above apparatus, it is preferable to attach a reflector that reflects ultraviolet rays toward the drainage film flowing down. Moreover, the dioxin treatment effect by ultraviolet rays can be promoted by using a falling wall having a groove-like unevenness on the surface, or by adding a catalytic action to the surface of the falling wall.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The ultraviolet irradiation apparatus used in the present invention will be specifically described with reference to an embodiment. FIG. 1 is an apparatus cross-sectional view showing an embodiment of an ultraviolet irradiation apparatus suitable for use in the present invention, and is shown for explaining a basic configuration. In this device , a plurality of flow-down walls (wet walls) 1 with overflow dams 2 at the top are provided facing each other, two surfaces in this example, and the original drainage from each overflow dam 2 to the flow-down wall surface 1 The UV light source 4 is disposed at a position where it does not touch the drainage film 3 to be flowed down, and the drainage film is irradiated to treat dioxins in the raw drainage. 7 is the overflow surface of the raw drainage.
[0008]
By attaching the UV light source 4 including the protective cover 5 in the UV passage to a position where it does not touch the drainage film 3, the UV irradiation efficiency is prevented from being lowered due to dirt, and the film is spread in a film shape. The UV rays are efficiently and uniformly made to reach the dioxins in the raw wastewater 3 with ease. Although there is no restriction | limiting in particular in the kind of ultraviolet light source 4 to be used, A low pressure mercury lamp with a high ultraviolet irradiation efficiency is suitable. The number of UV light sources used, the size per lamp, the arrangement and spacing of the vertical and horizontal positions, etc., may be appropriately designed so as to increase the use efficiency of the UV, and there is no particular limitation. Also, a large number of ultraviolet irradiation devices exemplified in FIG. 1 can be arranged and used. The wastewater can be circulated and irradiated until the dioxin concentration in the wastewater drops to the required level.
[0009]
Further, an ultraviolet reflector 6 can be provided in order to increase the utilization efficiency of ultraviolet rays. The reflector 6 is intended to reflect the ultraviolet rays lost without directly irradiating the drainage film 3 in the direction of the drainage film 3 to effectively use the ultraviolet rays. Although there are no special restrictions on the mounting position or shape, it is desirable to use a reflective surface that is not soiled and has high reflection efficiency in order to enhance the irradiation efficiency, and to design and arrange the drainage film surface evenly. . FIG. 1 shows an example in which a plurality of ultraviolet lamps 4 and reflecting mirrors 6 are alternately arranged side by side.
[0010]
Moreover, the flow-down wall 1 is not restricted to a perpendicular | vertical and plane. For example, the opposing surface may be a slope or a curved surface, or the cross-section of the opposing falling wall may be set to a rectangle, a rhombus, a polygon, or the like. Alternatively, grooves and bank-like irregularities are appropriately provided on the surface of the flow-down wall to prevent uneven flow, and the drainage film 3 is disturbed to update the surface, to enlarge the surface area and increase the irradiation efficiency of ultraviolet rays. it can. Furthermore, the surface 1 of the falling wall can be coated with a substance having a catalytic action such as titanium oxide to promote the decomposition of dioxins.
[0011]
In the present invention, it is possible to use ultraviolet batch circulation irradiation, the continuous flow is irradiated, or the irradiated effluent a continuous supply and circulation-part continuous withdrawal irradiation. It can also be used in combination with hydrogen peroxide treatment in addition to ozone treatment to efficiently decompose dioxins. When hydrogen peroxide is used in combination, the required amount of hydrogen peroxide may be injected into the wastewater at once, or an appropriate amount of hydrogen peroxide may be divided or continuously injected in parallel with ultraviolet irradiation as the treatment progresses. it can.
[0012]
In order to specifically explain the present invention, FIG. 2 schematically shows an example of a batch-type waste water treatment apparatus in which an ultraviolet irradiation tank 11 and an ozone dissolution tank 12 are combined. In this example, two facing downflow walls 13 and an ultraviolet lamp 14 arranged in the horizontal direction between the downflow walls 13 are provided. The wastewater stored in the drainage circulation tank 15 is fed into the overflow dam reservoir 17 by the ultraviolet irradiation tank pump 16, forms a drainage film across the overflow dam 18, and flows down along the falling wall 13 to drainage circulation tank. 15 is circulated and stored.
[0013]
In this example, a part of the wastewater stored in the wastewater circulation tank 15 is sent into the ozone dissolution tank 12 by the ozone dissolution tank pump 19, and the ultraviolet irradiation and the ozone treatment are simultaneously performed. Ozone gas is blown from the ozone generator 20 into the bottom of the ozone dissolution tank 12 and is in countercurrent gas-liquid contact with the waste water in the tank. 21 is an ozone gas concentration meter. The ultraviolet irradiation / ozone treatment time of the wastewater is generally about 0.1 to 4 hours although it varies depending on the kind and concentration of dioxins in the wastewater.
[0014]
【Example】
In order to confirm the effect of the present invention, an implementation experiment was performed using the apparatus having the same flow as that illustrated in FIG. 2 described above, and the details thereof will be described below. In addition, the flow-down wall of the ultraviolet irradiation tank was composed of two opposing surfaces having a width of 2000 × height of 1500 mm, and three 500 W low-pressure mercury lamps were horizontally arranged as the ultraviolet light source. Dioxins were analyzed in accordance with the dioxin standard measurement manual (Ministry of Health and Welfare), and the toxicity equivalent coefficient of WHO / IPCS was applied.
[0015]
Example 1
After extracting dioxins in fly ash with toluene, the methanol-substituted extract was added to the raw water of BOD 90 mg / l, COD 210 mg / l leachate to prepare test effluent with a dioxin concentration of 4000 pg / L. It used for the implementation test of this invention. Using 150 liters of the above test wastewater, the circulation amount of the test wastewater by the ultraviolet irradiation tank pump is adjusted to 1000 liters per hour, and ozone gas whose ozone concentration is adjusted to 5 g / Nm3 or more is blown into the ozone dissolution tank. The operation was performed for 60 minutes at a circulation rate of 5400 liters per hour using an ozone dissolution tank circulation pump. After the operation, the concentration of dioxins in the test waste water was measured. As a result, the removal rate of all dioxins in the test waste water was 88%, and 75% or more of each homolog was removed.
[0016]
Example 2
Example except that four aluminum reflectors having the same arrangement as shown in FIG. 1 and having a length of 2000 mm and a cross-sectional shape of a diamond having a side of 50 mm are attached to the same apparatus as used in Example 1. Under the same conditions as in No. 1, a wastewater treatment experiment was conducted. After the experiment, the concentration of dioxins in the test effluent was measured. As a result, the removal rate of all dioxins in the test waste water was 92%, and 78% or more of each homologue was removed.
[0017]
Example 3
The same apparatus as used in Example 1 was used under the same conditions as in Example 1 except that equilateral triangular serrated irregularities having a length of 2000 mm and a side length of 5 mm were attached to the flow wall at intervals of 30 mm on the surface. A test treatment of waste water for testing was conducted. After the experiment, the concentration of dioxins in the test waste water was measured. As a result, the removal rate of the entire dioxins in the test wastewater was 91%, and 76% or more of each homolog was removed.
[0018]
Example 4
A test wastewater treatment experiment was conducted under the same conditions as in Example 1 using the same apparatus as used in Example 1, except that the falling wall coated with titanium oxide having photocatalytic action on the surface was used. After the experiment, the concentration of dioxins in the test waste water was measured. As a result, the removal rate of all dioxins in the test wastewater was 95%, and 80% or more of each homolog was removed.
[0019]
Comparative Example 1
The same apparatus as used in Example 1 was used under the same conditions as in Example 1 except that a conventional immersion type apparatus equipped with the same ultraviolet light source as in Example 1 was used instead of the ultraviolet irradiation tank of the present invention. An irradiation treatment experiment was performed on the same amount of test wastewater for the same time. After the experiment, the concentration of dioxins in the test waste water was measured. As a result, the removal rate of the whole dioxins in the test waste water was 81%, and the removal rate of each homolog was 60 to 90%.
[0020]
As shown in the above-mentioned examples, the present invention makes the wastewater containing dioxins into a thin film shape and irradiates with ultraviolet rays, and then sends a part of the wastewater to an ozone treatment tank to perform ozone treatment, and the rest is ultraviolet rays. By returning to the treatment device and continuing the ultraviolet treatment, it is possible to uniformly irradiate the wastewater that does not transmit ultraviolet rays, and to reach the decomposition target efficiently. Accordingly, halogenated organic substances including dioxins are effectively dechlorinated. In addition, the size and number of faces of the flow-down wall can be appropriately changed according to the installation conditions and processing conditions.
[0021]
In the ultraviolet treatment apparatus , a reflector, a groove on the surface of the falling wall, a falling wall having a catalytic action, and the like can be provided as necessary. The reflector increases the utilization efficiency of the ultraviolet rays, such as grooves falling wall surface increases the radiation area, increasing the efficiency of decomposing dioxins by generating turbulence drainage layer, also the flow down the wall surface by substances having a catalytic action Can promote the decomposition of dioxins.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an apparatus showing an embodiment of an ultraviolet irradiation apparatus suitable for carrying out the present invention. FIG. 2 is a schematic diagram showing an example of a batch-type wastewater treatment apparatus in which the ultraviolet irradiation tank and an ozone dissolution tank are combined. Figure [Explanation of symbols]
1: Downflow wall (surface) 2: Overflow weir 3: Drain film 4: UV light source 5: Light source cover 6: Reflector 7: Drain overflow surface 11: Ultraviolet irradiation tank 12: Ozone dissolution tank 13: Downflow wall 14: Ultraviolet lamp 15: Waste water circulation tank 16: Ultraviolet irradiation tank pump 17: Overflow weir 18: Overflow weir 19: Ozone dissolution tank pump 20: Ozone generator 21: Ozone gas concentration meter

Claims (2)

      A method for treating dioxins in wastewater by irradiating wastewater containing dioxins with ultraviolet light, followed by oxidation treatment with ozone, wherein the wastewater is formed into a film along a falling wall composed of a plurality of opposing surfaces. The UV light source is placed in contact with the drainage film in contact with the drainage film, and the drainage film is irradiated. A method for treating dioxins in wastewater, characterized in that water is fed back to the original wastewater, and ozone gas is brought into gas-liquid contact with ultraviolet treatment wastewater to decompose and treat dioxins in the ozone dissolution tank. Outlet drainage of the ozone dissolving tank (hereinafter, referred to as ozone treatment wastewater) a portion of the derived out of the system, the waste water according to claim 1, wherein the circulating by refluxing the remainder UV wastewater ozone dissolving tank Dioxins treatment method in the inside.

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