JP2006341229A - Advanced treating method of cyanide compound-containing drain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and economically decompose a cyanide compound-containing drain difficult to decompose containing various cyano-complex compounds. <P>SOLUTION: Treating object water is pretreated with ozone in a pretreatment tank 1. The pretreated treating object water is subjected to the AOP treatment in an ultraviolet ray reactor 3 by ozone and ultraviolet ray irradiation. For an ultraviolet lamp 4, a low pressure mercury lamp and an intermediate-high pressure mercury lamp is selectively used according to the kind of the treating object water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an advanced treatment method for cyanide-containing wastewater used for treating wastewater containing cyanide, such as coke wastewater produced as a by-product in the production process of coke.

  Coke wastewater produced as a by-product in the coke production process contains a large amount of highly toxic cyanide compounds (compounds containing a cyano group), and whether it is discharged outside the system or reused in the system Need purification process.

  Methods for treating cyanide compounds include the alkali chlorine method and the bitumen method, but there are problems such as limitations on treated products and sludge generation. Therefore, there is a method in which the cyanide-containing waste water is irradiated with ultraviolet to visible light, the cyano iron complex is decomposed into free cyan and iron ions that can be easily oxidized, and free cyan is oxidized with an oxidizing agent. However, this method has a problem of ultraviolet ray transmission hindrance due to the precipitate, that is, a precipitate such as fine hydroxide generated by free iron ions obstructs the ultraviolet ray transmission. The processing method described in Patent Document 1 is solved by the above.

Japanese Patent Laid-Open No. 10-57974

  However, according to the studies by the present inventors, the method described in Patent Document 1 cannot efficiently and economically treat cyanide containing wastewater, for example, cyanide in coke wastewater, to a low concentration efficiently. It has been found. The present inventors considered the reason as follows.

  Cyano-iron complexes can be decomposed into free cyanide and iron ions by ultraviolet rays, but they are difficult to decompose into actual cyanide-containing wastewater such as coke wastewater, which cannot be released by irradiation with ultraviolet to visible light. Therefore, it was considered that the cyanide compound in the wastewater could not be treated even by the method described in Patent Document 1.

  Therefore, the present inventors paid attention to AOP treatment (accelerated oxidation treatment). AOP treatment is a combination of ozone and ultraviolet rays to generate OH radicals that have a greater oxidizing power than ozone and have an oxidizing power next to fluorine in nature, thereby decomposing refractory components in the water to be treated. It is a method to do.

  And the present inventors actually performed the AOP process of coke waste water. Surprisingly, the result was that the cyanide in the wastewater could not be completely treated.

  An object of the present invention is to provide an advanced treatment method for cyanide-containing wastewater that can efficiently and economically decompose hardly-decomposable cyanide-containing wastewater containing various cyano complex compounds.

  As described above, the present inventors tried to apply the AOP process in order to achieve the above object, but the object was not achieved. Therefore, the present inventors analyzed and examined problems and solutions when the AOP treatment was performed on coke wastewater. As a result, the following facts were reached.

  OH radicals are very powerful oxidants, but have no reaction selectivity and react with any substance. For this reason, when the raw wastewater is directly AOP-treated, OH radicals are consumed not only by the hardly decomposable cyanide compound but also by other organic substances, and as a result, very large amounts of ozone and ultraviolet rays are required. Therefore, the ozone alone treatment was performed before the AOP treatment, and the AOP treatment was carried out after decomposing the easily decomposable component that can be treated with ozone alone. As a result, the hardly decomposable cyanide was decomposed very efficiently. This is probably because free cyanide and organic substances contained in the wastewater were treated by the ozone treatment alone at the former stage, and the OH radicals produced by the AOP treatment at the latter stage could intensively decompose the hardly decomposable cyanide compound.

  Ultraviolet rays are absorbed by organic substances dissolved in waste water. Since organic substances were decomposed by the preceding ozone treatment, the ultraviolet transmittance in the latter AOP treatment was improved, and the amount of ultraviolet rays that could contribute to the generation of OH radicals was also increased.

  The inventors have also compared a medium to high pressure mercury lamp and a low pressure mercury lamp as ultraviolet lamps. Medium to high pressure mercury lamps and low pressure mercury lamps differ in energy at each wavelength (see Table 1). Specifically, in a medium to high pressure mercury lamp, 30% or more of the power consumption is light energy, and the ratio of the wavelength of 254 nm in the light energy is small. On the other hand, in a low-pressure mercury lamp, about 20% of the power consumption is light energy, and most of it is occupied by a wavelength of 254 nm. In the AOP treatment of ozone and ultraviolet irradiation, ozone is decomposed by ultraviolet light having a wavelength of 254 nm and OH radicals are generated, so that a low-pressure mercury lamp that intensively generates a wavelength of 254 nm is advantageous. On the other hand, ultraviolet to visible light is effective for dissociating cyan and iron in the cyano iron complex, so a medium to high pressure mercury lamp that generates ultraviolet light of a wide wavelength and has a large ratio of total light energy to power consumption is advantageous. It becomes.

  The present inventors compared the case where the above-described two-stage treatment is performed on actual coke wastewater with a medium to high pressure mercury lamp and a low pressure mercury lamp. Met. The reason is considered as follows. Cyanides that cannot be decomposed by ozone treatment in the previous stage are broadly divided into cyano compounds (including cyano iron complexes) that can release cyan ligands and cyano groups with ultraviolet to visible light, and difficult-to-decompose cyan compounds that can be processed only with AOP. Is done. This drainage is mostly the former, and as a result, it is considered that the medium to high pressure mercury lamp capable of treating both the former and the latter at the same time was more advantageous.

  On the other hand, when the same comparative test was performed on another coke wastewater, the low-pressure mercury lamp was better in this test. This is presumably because the waste water contained a large amount of a hardly decomposable cyanide compound that can only be treated with AOP.

  As described above, when performing the above-described two-stage treatment, depending on the type of water to be treated, a medium to high pressure mercury lamp may be effective or a low pressure mercury lamp may be effective, and it is effective to use both separately.

  The cyanide-containing wastewater treatment method according to the present invention is based on the above knowledge, and includes a primary treatment step for treating cyanide-containing wastewater with ozone, and wastewater treated in the primary treatment step with ozone and ultraviolet rays. And a secondary treatment step of performing a composite treatment by irradiation.

  As for the ultraviolet lamp, it is preferable to selectively use a medium to high pressure mercury lamp and a low pressure mercury lamp depending on the type of water to be treated (type of organic matter in the water to be treated).

  In the advanced treatment method for cyanide-containing wastewater of the present invention, among the organic substances in the cyanide-containing wastewater that is the water to be treated, an easily decomposable compound (not containing cyanide) that can be decomposed by ozone is a primary treatment step. Is removed or reduced in advance.

  The remaining organic matter in the wastewater is mainly cyanide, specifically, cyanogen compounds (including cyanoiron complexes) that can liberate cyan ligands and cyano groups with ultraviolet to visible light, and difficult to treat only with AOP. There are two types of decomposable cyan compounds, and these are efficiently decomposed in the secondary treatment step. This is because the readily decomposable organic compounds that cause waste of ozone and ultraviolet rays in the secondary treatment are decomposed and removed in the primary treatment.

  In the case of wastewater containing a large amount of the former cyanide compound (a cyano compound capable of releasing cyan ligand and cyano group with ultraviolet to visible light), it is effective to use a medium to high pressure mercury lamp. As described above, it is effective to use a low-pressure mercury lamp when a relatively large amount of the hardly decomposable cyanide compound that can only be treated.

  The amount of ozone injection is basically determined by the degree of pollution of the wastewater, that is, the type and amount of organic substances in the wastewater. From the viewpoint of suppressing the amount of ozone in the secondary treatment, it is preferable to inject 0.1 to 10 times the amount of ozone injected in the secondary treatment, and particularly preferably 1 to 10 times. This is because ozone is a very strong oxidizer itself, and generally, there are few organic substances in waste water that cannot be decomposed by ozone.

  The advanced treatment method for cyanide-containing wastewater according to the present invention contains various cyano complex compounds such as coke wastewater produced as a by-product in the production process of coke by a combination of ozone treatment and AOP treatment by ozone and ultraviolet irradiation. Refractory cyanide-containing wastewater can be efficiently and economically decomposed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a wastewater treatment apparatus showing an embodiment of the present invention.

  In the present embodiment, cyanide-containing wastewater containing various cyano complex compounds and organic compounds such as coke wastewater produced as a by-product in the coke production process is purified. The waste water is first sent to the pretreatment reaction tank 1. In the pretreatment reaction tank 1, the ozone gas generated by the ozonizer 2 is injected from the bottom of the tank into the water to be treated in the tank through an air diffuser. Thereby, among the organic compounds in the water to be treated, an easily decomposable compound that can be decomposed by ozone is decomposed. The water to be treated treated in the pretreatment reaction tank 1 contains various cyanide compounds that are not treated with ozone, and further contains hardly decomposable organic compounds other than cyanide compounds. 3 is sent.

  The ultraviolet reaction tank 3 is equipped with an ultraviolet lamp 4 in the center. The ultraviolet lamp 4 is a high-pressure mercury lamp that emits a large amount of ultraviolet to visible light having a wavelength of 254 nm and beyond, or a low-pressure mercury lamp that intensively generates ultraviolet light having a wavelength of 254 nm, and their spectral characteristics are shown in Table 1.

  In the ultraviolet reaction tank 3, predetermined ultraviolet light is irradiated from the ultraviolet lamp 4 to the water to be treated in the tank, and ozone gas generated by the ozonizer 5 is injected from the bottom of the tank through a diffuser tube. Further, the treated water circulates to the filter 6. As a result, the next reaction proceeds in the ultraviolet reaction tank 3.

  As described above, cyanide compounds are classified into those that cause liberation upon irradiation with ultraviolet to visible light and those that do not. For example, ultraviolet light to visible light contribute to liberation of a cyan ligand from a cyano iron complex and liberation of a cyano group from an organic substance containing a part of the cyano group. The injected ozone generates OH radicals by irradiation with ultraviolet rays. Ultraviolet rays having a wavelength of 254 nm mainly contribute to the generation of radicals. The generated OH radical liberates a cyano group from a hardly decomposable cyanide compound that is difficult to be liberated by irradiation with ultraviolet to visible light. Both free cyano groups (cyan ions) are efficiently decomposed by ozone or OH radicals.

  In addition, the solid substance which arises with a process is sequentially removed with the filter 6. FIG. The treated water after the treatment is sequentially discharged from the upper part of the tank to the outside of the tank.

  In the reaction in the ultraviolet reaction tank 3, organic compounds that can be treated only with ozone are removed in advance. For this reason, waste of ozone in the reaction tank 3 is suppressed. That is, in the reaction tank 3, the input ozone is intensively used for decomposition of cyanide compounds, generation of OH radicals, and deoxidization of cyanide ions. Moreover, as a result of restraining waste of ozone, the amount of ozone gas injected can be minimized and the amount of bubbles can be reduced. For these reasons, the transmittance of ultraviolet rays in the tank is increased, and the ultraviolet rays in the reaction tank 3 are also effectively used from this point. As a result, in the ultraviolet reaction tank 3, an effective decomposition treatment of the cyano complex is performed without particularly increasing the ultraviolet output and the ozone injection amount, and even when combined with the ozone injection amount in the pretreatment reaction tank 1, The amount used can be suppressed to an appropriate level.

  FIG. 2 is a configuration diagram of a wastewater treatment apparatus showing another embodiment of the present invention. In the present embodiment, ozone gas from the ozonizer 5 is injected into the water to be treated treated in the pretreatment reaction tank 1 in the diffuser-type ozone injection tank 7 provided on the upstream side of the ultraviolet reaction tank 3. Part of the water to be treated that has been treated in the ultraviolet reaction tank 3 is discharged out of the system as treated water. The remaining water to be treated is sent to the filter 6 and returned to the diffuser tube type ozone injection tank 7.

  FIG. 3 is a configuration diagram of a wastewater treatment apparatus showing still another embodiment of the present invention. In the present embodiment, ozone gas from the ozonizer 5 is injected into the water to be treated treated in the pretreatment reaction tank 1 by the ejector 8 provided on the upstream side of the ultraviolet reaction tank 3. A gas-liquid separation tower 9 is provided between the ejector 8 and the ultraviolet reaction tank 3. Part of the water to be treated that has been treated in the ultraviolet reaction tank 3 is discharged out of the system as treated water. The remaining treated water is sent to the filter 6 and returned to the upstream side of the ejector 8.

  FIG. 4 is a configuration diagram of a wastewater treatment apparatus showing still another embodiment of the present invention. In the present embodiment, an ejector 8 is provided on the upstream side of the ultraviolet reaction tank 3. A gas-liquid separation tower 9 is not provided between the ejector 8 and the ultraviolet reaction tank 3. The treated water treated in the pretreatment reaction tank 1 is sent to the ultraviolet reaction tank 3. Ozone gas from the ozonizer 5 is injected into the ultraviolet reaction tank 3 by the ejector 8 and sent. Part of the water to be treated that has been treated in the ultraviolet reaction tank 3 is discharged out of the system as treated water. The remaining treated water is sent to the filter 6 and returned to the upstream side of the ejector 8.

  As can be seen from these embodiments, the injection of ozone gas into the water to be treated may be performed in an ultraviolet reaction tank or may be performed using another independent injection means. It may be performed with an air diffuser or an ejector. Gas-liquid separation means may be provided between the ultraviolet reaction tank and the upstream ejector as necessary. Moreover, the water to be treated treated in the pretreatment reaction tank may be directly introduced into the ultraviolet reaction tank or may be introduced through an ozone gas injection means. In actual equipment, it is necessary to appropriately take out and treat exhaust ozone.

  Moreover, although these embodiment is a continuous type which introduces to-be-processed water and drains treated water continuously, the batch type which introduces and circulates a predetermined amount of to-be-processed water in a system may be sufficient.

  In order to demonstrate the effect of the present invention, the following comparative test was conducted. As the processing apparatus, the processing apparatus shown in FIG. 2 was used in batch mode. Two kinds of coke wastewater were used as the water to be treated, and the treatment amount was 15L.

  For the first treated water, conventional method 1 (alkali chlorine method), conventional method 2 (ozone + ultraviolet light to visible light irradiation + filtration described in Patent Document 1), comparative method 1 (AOP method), this Invention method 1 (primary ozone + secondary AOP + filtration, UV lamp uses 120 W low-pressure mercury lamp) and invention method 2 (primary ozone + secondary AOP + filtration, UV lamp uses 100 W high-pressure mercury lamp) were carried out. The ozone injection amount was 200 mg / L in all cases. Table 1 shows the light emission characteristics of the low-pressure mercury lamp and high-pressure mercury lamp used.

  Table 2 shows the cyan concentration (mg / L) before and after treatment for each treatment method. In the conventional method and the comparative method, the total cyan concentration before treatment of 9.7 mg / L did not decrease to 2 mg / L or less. However, by carrying out the method of the present invention, the total cyan density decreased from 9.7 mg / L to 1 mg / L or less. The treatment effect was higher when the high-pressure mercury lamp was used. This is presumably because the wastewater contained a large amount of cyanide compounds (including cyanoiron complexes) capable of releasing cyan ligands and cyano groups with ultraviolet to visible light.

  For the second treated water, the present invention method 1 (primary ozone + secondary AOP + filtration, UV lamp uses a 120 W low-pressure mercury lamp), the present invention method 2 (primary ozone + secondary AOP + filtration, UV lamp uses 100 W) High pressure mercury lamp was used. The ozone injection amount was 200 mg / L in all cases. Table 2 shows the cyan concentration (mg / L) before and after treatment for each treatment method. By carrying out the method of the present invention, the total cyan concentration decreased from 1.4 mg / L to 1 mg / L or less, and the effect was higher when a low-pressure mercury lamp was used. This is presumably because this waste water contains a large amount of a hardly decomposable cyanide compound that can be treated only with AOP.

  In the above-described embodiment, the pretreatment reaction tank is used for the primary treatment, but it is also possible to inject ozone gas with an ejector. Moreover, although ozone used for the primary treatment and the secondary treatment was produced by separate ozonizers, ozone gas produced by the same ozonizer can be used for both treatments.

It is a block diagram of the waste water treatment equipment which shows one Embodiment of this invention. It is a block diagram of the waste water treatment equipment which shows another embodiment of this invention. It is a block diagram of the waste water treatment equipment which shows another embodiment of this invention. It is a block diagram of the waste water treatment equipment which shows another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pretreatment reaction tank 2,5 Ozonizer 3 Ultraviolet reaction tank 4 Ultraviolet lamp 6 Filter 7 Diffuser tube type ozone injection tank 8 Ejector 9 Gas-liquid separation tower

Claims (4)

  Advanced treatment of cyanide-containing wastewater, comprising a primary treatment step of treating cyanide-containing wastewater with ozone, and a secondary treatment step of treating wastewater treated in the primary treatment step with ozone and ultraviolet irradiation. Processing method.   The advanced treatment method for cyanide-containing wastewater according to claim 1, wherein a low-pressure mercury lamp or a medium to high-pressure mercury lamp is used for ultraviolet irradiation in the secondary treatment.   The advanced treatment method of the cyanide containing waste water of Claim 1 which makes the ozone injection amount in the said primary treatment 0.1 to 10 times the ozone injection amount in the said secondary treatment.   The advanced processing method of the cyanide containing waste water of Claim 1 which performs a circulation filtration process by the said secondary treatment.

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