JPH07185576A - Method for sterilizing sewage disposal water - Google Patents

Abstract

PURPOSE:To decolor sewage disposal water and to exhance sterilization effect by preventing ultraviolet rays(UV) from being absorbed in colored substance when the UV irradiates by applying ozone treatment to sewage disposal water at a stage before UV irradiation is applied in equipment in the case the sterilization of the sewage disposal water before discharge is performed by the irradiation of the UV. CONSTITUTION:After sludge 3 is sedimented in a sedimentation basin 2, the supernatant liquid of activated sludge 1 is sent to a UV sterilization tank 4, and it is sterilized by applying the UV irradiation by a UV lamp 5. Displosal water is discharged to a river, etc., as discharge water 6. In such a case, an ozone reaction tank 7 is installed at the front stage of the UV sterilization tank 4. The ozone reaction tank 7 performs the ozone treatment of the disposal water by discharging ozonized air generated by an ozone generator 7A to the disposal water by a duffuser pipe 7B and an unreacting ozone is discharged to the air after being decomposed by an exhaust ozone decomposing tower 7C. The following UV sterilization can be effectively performed by performing the decoloring by the ozone treatment in such way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sterilizing sewage treatment water used in sewage treatment facilities and the like.
V) Improvement of the method of sterilizing sewage treatment water before discharge by an irradiation device.

[0002]

2. Description of the Related Art Sewage, which is a wastewater containing a large amount of pollutants with high BOD (biochemical oxygen demand) and COD (chemical oxygen demand), is collected from one home through a sewer and is deposited, After activated sludge and sedimentation, the supernatant water is mixed with a disinfectant and discharged into a river or sea area.

Chlorine is used as a disinfectant,
Due to the excessive use of chlorine, residual chlorine is released into general waters, which disturbs the natural ecosystem. For example, in rivers, it damages aquatic plants that feed on fish such as moss, and directly poisons fish and fry. In addition to direct action of chlorine in the sea, ammonia (NH ₄ ) and chlorine (Cl ₂ ) released as untreated sewage discharge water
It has been clarified that monochloramine reacted with and has a strong toxicity to seaweed, and a physicochemical UV sterilization method has been attracting attention.

The UV sterilization method is well known in many cases such as actual cases overseas and demonstration tests in Japan, but some problems remain. In particular, in Japan, there is a large variation in the amount of treatment per day with time, and it is not possible to stably remove colored components and suspended components.

The UV sterilization method uses a mercury lamp at a wavelength of 25.
It utilizes light of 4 nm. This short-wavelength light can be effectively sterilized by directly hitting bacteria after exiting the glass of the lamp (especially quartz glass that transmits short-wavelength light), but the intensity of the light from the lamp is an index. Those that are far from the lamp are not sterilized because they are logarithmically reduced. In addition, unlike pure water, treated water has a property of absorbing light having a short wavelength, and light having a wavelength of 254 nm, which is effective for sterilization, is absorbed by the coloring component of the treated water.

Further, since the supernatant of the settling basin is discharged as secondary treated water, activated sludge that has not settled out flows out, or it becomes locally anaerobic and the sludge floats up and flows out. There is. In this case, bacteria attached to the suspended matter of the sludge are sterilized by chlorine sterilization, but are not sterilized by UV sterilization because they are not irradiated with light having a short wavelength, and are discharged as they are. Further, if these turbid substances adhere to the surface of the UV lamp, the UV irradiation effect on the discharged water is completely lost, and periodic cleaning of the lamp is required.

FIG. 6 shows an example of a conventional UV sterilization method for treated sewage water. In this figure, after the activated sludge 1 has settled the sludge 3 in the settling tank 2, the supernatant water is sent to the UV sterilization tank 4. In the UV sterilization tank 4, sterilization is performed by irradiating UV with a UV lamp 5. The treated water that has been sterilized is discharged as river 6 into a river or the like. With this configuration, if the colorless and transparent treated water passes near the UV lamp 5, it is sufficiently sterilized, but if the treated water is colored, the 254 nm wavelength light does not hit the bacteria and is sterilized. Can not. Further, even if the surface of the UV lamp 5 is dirty, there is no sterilizing effect, and the treated water is continuously discharged without being sterilized.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and in a method of sterilizing treated sewage water before discharge by UV irradiation, UV irradiation is effectively performed to enhance the sterilization effect. Therefore, the purpose is to solve the problem of environmental pollution caused by treated sewage.

[0009]

Means for Solving the Problems That is, the present invention provides a method for sterilizing sewage treated water by subjecting the sewage treated water before discharge to UV irradiation treatment, in which ozone is applied to the sewage treated water before UV irradiation. It is characterized by doing. Furthermore, in the above-mentioned sterilization method of sewage treatment water, while sewage treatment water is ozone-treated at the stage before UV irradiation,
It is characterized in that sewage-treated water after ozone treatment is stored and suspended matter is separated by floating. In the latter method, the bactericidal effect can be further improved by injecting the coagulant just before the ozone treatment.

[0010]

In the method for sterilizing sewage-treated water of the present invention, the sewage-treated water is treated with ozone before being irradiated with UV.
When irradiated, UV rays are not absorbed by the coloring substance and effectively exhibit a bactericidal effect. In addition, the UV sterilization effect can be further enhanced by removing the suspended matter by floatation separation along with the ozone treatment.

[0011]

Embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 is a constitutional view showing an example of the sterilization method of the present invention. In contrast to the conventional sterilization method shown in FIG. 6, in the method of this embodiment, the ozone reaction tank 7 is provided before the UV sterilization tank 4.
Is provided. The ozone reactor 7 has an ozone generator 7
The ozonized air generated by A is introduced, and the ozonized air is discharged into the treated water through the air diffuser 7B. Here, after the ozone treatment of the treated water is performed, unreacted ozone is decomposed in the exhaust ozone decomposing tower 7C and released into the atmosphere.

4 and 5 are diagrams for explaining the effect of the present invention. First, FIG. 4 shows changes in the ultraviolet absorption spectrum due to ozone treatment. The absorbance of light with a short wavelength of 254 nm was examined for both the sewage-treated water in which ozone was not injected and the sewage-treated water in which ozone was injected at 8 mg / liter. It is a thing. As is clear from this figure, it is understood that the decolorization by ozone treatment improves the light transmittance. In addition, FIG. 5 shows the relationship between the bactericidal effect and the decolorizing effect of the ozone treatment alone. Both effects are improved with the increase of the ozone injection rate, but in the ozone treatment, decolorization occurs before sterilization. It is shown that.

As can be seen from these figures, the sewage-treated water can be decolorized and sterilized only by the ozone treatment. However, it is more effective to decolorize the sewage-treated water at the early stage of the reaction having a high ozone reaction efficiency and then perform the UV sterilization. Therefore, performing ozone treatment and then UV sterilization treatment in this order as in the present invention is more effective than performing these treatments simultaneously. Further, if only ozone treatment is carried out, a large amount of ozone is required and the reaction tank must be enlarged. This is because the ozone reaction oxidizes and decolorizes the coloring substance at the gas-liquid interface, and then dissolves in the liquid to act on bacteria. On the other hand, in the present invention,
Since the treated water is efficiently decolorized in a small ozone reaction tank and then introduced into the UV sterilization tank, it is not necessary to have dissolved ozone present, and the treatment can be easily performed.

(Embodiment 2) FIG. 2 shows a block diagram of this embodiment. In this embodiment, a retention tank 8 is provided downstream of the ozone reaction tank 7, and a water channel 9 for removing the suspended matter component 8A is provided in the retention tank 8. Other than that is the same as that of the first embodiment.

In this embodiment, the phenomena of gas-liquid contact and foam separation caused by ozone treatment are positively utilized. When ozone is injected into the sewage secondary treated water with fine bubbles to perform ozone treatment, and then introduced into the retention tank 8, suspended particles such as sludge mixed in the treated water and fine bubbles due to ozone injection float together. The turbid component 8A can be automatically separated. This suspended matter component 8A is discharged from the drainage channel 9. The treated water subjected to the ozone treatment is drawn out from the lower part of the retention tank 8 and
Sterilization is performed in the V sterilization tank 4. In the present embodiment, the sewage secondary treated water is subjected to UV sterilization in a state where the coloring substances and the suspended substances are removed, so that the sterilization effect is further improved.

(Embodiment 3) FIG. 3 shows a block diagram of this embodiment. In this example, compared with the method of Example 2 shown in FIG. 2, the suspended matter was further completely removed to improve the UV sterilization effect. That is, as shown in FIG. 3, a fixed amount of the coagulant 10 is injected before the ozone reaction tank 7. As the coagulant, for example, polyaluminum chloride, a polymer coagulant or the like is used. When the sewage secondary treated water is sent to the ozone reaction tank 7 after the coagulant is injected in this way, the ozone reaction tank 7
At that time, rapid agitation is performed by the flow of water and ozone injection, and scum that easily floats and separates after ozone treatment is generated.
Further, in this embodiment, unlike the above-described two embodiments, ozone is released by a method of directly stirring water using the underwater aerator 11.

If a coagulant is used as in this example, not only ozone decolorization but also a polymeric coloring material is reduced by coagulation, which is more effective for UV sterilization.

As the floating separation tank, not only a simple retention tank is used, but fine bubbles are positively injected into the bottom of the tank, or water obtained by pressurizing and dissolving air is uniformly mixed to form fine bubbles. The effect can be further enhanced by combining the pressure levitation.

Next, a comparison of the sterilization effect between the sterilization method of the present invention and the conventional UV sterilization method will be shown by experiments conducted on a laboratory scale. (1) Conventional UV sterilization treatment ... Length 37 cm, inner diameter 5.7
A 15 W germicidal lamp was attached to the glass tube of cm with a silicon stopper, and test treated water was flowed at a flow rate of about 400 l / min.

(2) Sterilization method of the present invention (ozone treatment and UV
Sterilization treatment ... Test treatment water and ozonized air are contacted for 10 minutes in an ozone oxidation bottle (a certain amount of gas-liquid can be mixed and shaken by hand to react) (Ozone injection rate is 5 mg /
l), after processing, remove a part of it and UV as in (1) above.
Sterilized.

(3) Sterilization method of the present invention (ozone treatment, flotation treatment and UV sterilization treatment) ...
Using a reaction tank having a height of 2 cm and a height of 2 m, the secondary treated water was introduced from the top, and ozonized air was injected from the bottom through the diffuser tube. The ozone injection rate was 5 mg / l. Ozone-treated water was continuously taken out from the lower part of the tank, and a part thereof was subjected to UV sterilization treatment.

(4) Sterilization method of the present invention (addition of coagulant, ozone treatment, flotation treatment and UV sterilization treatment) ... Polyaluminum chloride 30 ppm, polymer coagulant in secondary treated water before introduction into ozone reaction tank After adding 1 ppm and performing ozone treatment on the same conditions as the above-mentioned (3), ozone treated water was left still for 15 minutes, a transparent intermediate layer was taken, and UV sterilization treatment was carried out.

Test water before the experiment in each of the above experiments,
The number of coliform bacteria was examined for each of the test water after pretreatment including ozone treatment and the test water after UV sterilization treatment. The results are shown in the table below.

[0024]

[Table 1]

As is clear from the above table, UV sterilization becomes more effective by performing ozone treatment before the UV treatment. Further, in that case, the effect can be further enhanced by removing the suspended matter after the ozone treatment, and the effect can be further enhanced by adding a coagulant at that time.

[0026]

As described above, according to the present invention, the conventional UV sterilization method of sewage treatment water can be improved to effectively sterilize by UV, so that there is no fear of environmental pollution and hygiene. It is possible to discharge the treated sewage treated water.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing a change in an ultraviolet absorption spectrum by ozone treatment.

FIG. 5 is a diagram showing a relationship between a bactericidal effect and a decolorizing effect by ozone alone treatment.

FIG. 6 is a diagram showing a conventional UV sterilization method.

[Explanation of symbols]

1 ... Activated sludge, 2 ... Sedimentation tank, 3 ... Sludge, 4 ... UV sterilization tank, 5 ... UV lamp, 6 ... Discharge water, 7 ... Ozone reaction tank,
7A ... Ozone generator, 8 ... Retention tank, 8A ... Floating suspended matter component, 9 ... Drainage channel, 10 ... Flocculant, 11 ... Underwater aerator.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C02F 9/00 R 503 C 504 B

Claims (3)

[Claims] 1. A method of sterilizing sewage treated water by subjecting the sewage treated water before discharge to ultraviolet irradiation treatment, wherein the sewage treated water is ozone-treated at a stage before ultraviolet irradiation. Sterilization method. 2. A method for sterilizing sewage treated water by subjecting the sewage treated water before discharge to ultraviolet irradiation treatment, wherein the sewage treated water is ozone-treated at a stage before ultraviolet irradiation, and the sewage treated water after ozone treatment is treated. A method for sterilizing sewage-treated water, characterized in that the suspended solids are stored and the suspended matter is floated and removed. 3. The method for sterilizing sewage treated water according to claim 2, wherein a coagulant is added to the sewage treated water immediately before the ozone treatment.