JPH08141581A - Treatment of waste water - Google Patents

Abstract

PURPOSE: To economically remove a hardly oxidizable substance in waste water. CONSTITUTION: Hydrogen peroxide is mixed with waste water and this waste water is irradiated with light having a spectrum within a wavelength region of below 185nm. Hydrogen peroxide is pref. added within a range of 0.5-50 times the concn. of CPDMn of waste water. A substantial decomposition required average time is usually 30min or less. This method is suitable for reducing COD or BOD of sewage, excretion, industrial waste water or secondary treated water of them, bleading water of a waste landfilling site and secondary treated water thereof or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying sewage, night soil, industrial wastewater and its secondary treated water, waste landfill leachate and its secondary treated water, and more particularly to a method for reducing COD and BOD. .

[0002]

2. Description of the Related Art Conventionally, for advanced treatment of wastewater, ozone treatment, biological treatment, membrane treatment, ultraviolet irradiation treatment, activated carbon treatment,
Chlorine injection treatment, hydrogen peroxide treatment, and various treatment methods combining these treatments are selected and implemented according to the state of treated water and the purpose of purification.

[0003]

However, none of the above-mentioned various wastewater treatment methods has a sufficient effect of reducing COD, and is not suitable for treating a large amount of wastewater.
There were problems such as frequent parts replacement, cleaning and regeneration, the possibility of organic chlorine compounds being generated, and high equipment costs and running costs. Among these, the combination of ultraviolet irradiation and hydrogen peroxide treatment, the combination of ultraviolet irradiation and ozone treatment, and the combination of ozone treatment and hydrogen peroxide treatment generate hydroxy radicals with strong oxidizing power in wastewater. However, it is considered promising as an excellent oxidation treatment method capable of decomposing and removing most organic substances. The present inventor has researched further excellent methods and completed the present invention.

[0004]

The present invention provides a method for treating wastewater, which comprises mixing hydrogen peroxide into the wastewater and irradiating the wastewater with light having a spectrum in a wavelength region of less than 185 nm. . Hydrogen peroxide used in the treatment method of the present invention is usually COD _{Mn of the} wastewater to be treated.
It may be added within the range of 0.5 to 50 times the concentration.

[0005]

The present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic flow sheet showing an embodiment of the present invention. In the present invention, the wastewater to be treated is necessary, for example, directly from the wastewater pipe or after being temporarily stored in the wastewater tank 1 to remove suspended solid particles and the like in the wastewater before the treatment of the present invention. Is sent to the solid-liquid separator 2. In addition to the purpose of removing suspended solid particles in wastewater as pollutants, the ultraviolet rays irradiated in the liquid are absorbed by the suspended solid particles and the irradiation efficiency decreases and the desired result is obtained. This is also to prevent the loss of The solid-liquid separation device 2 may be appropriately selected according to the properties of the substance to be separated, and sedimentation separation such as thickener, centrifugal separation, membrane filtration such as filtration and ultrafiltration may be used alone or in combination. it can.
Flocculants may be used to facilitate separation. When treating wastewater that does not contain suspended solids, the present invention may be carried out without any pretreatment such as solid-liquid separation.

In the present invention, hydrogen peroxide is added to the wastewater to be treated and irradiated with ultraviolet rays. The hydrogen peroxide used in the present invention may be a commercially available hydrogen peroxide solution, or may be produced and supplied by the hydrogen peroxide producing apparatus 3. Hydrogen peroxide
Add before UV irradiation or at the same time as UV irradiation. For example, a stirrer may be attached to a reaction tank that radiates ultraviolet rays, and hydrogen peroxide may be added while stirring. However, in order to increase the irradiation efficiency of ultraviolet rays, it is desirable to add hydrogen peroxide before the irradiation of ultraviolet rays to remove impurities that can be decomposed by hydrogen peroxide alone.
The hydrogen peroxide and the waste water are sufficiently stirred and mixed with each other by using a mixer 4 such as a static mixer, a line mixer, an ejector, and a stirring tank in order to rapidly proceed the reaction. Further, the mixed liquid is irradiated with ultraviolet rays having a spectrum in a predetermined wavelength region. The optimum addition amount of hydrogen peroxide varies depending on the properties of the wastewater, so it cannot be specified unconditionally, but it is usually added within the range of 0.5 to 50 times the COD _Mn concentration of the wastewater. If the amount of hydrogen peroxide added is 0.5 times or less, it is difficult for the treatment to proceed sufficiently,
Further, even if it is added 50 times or more, the ratio of hydrogen peroxide to be self-decomposed and consumed increases, and the processing cost becomes high, which is not preferable.

In the present invention, ultraviolet rays having a spectrum in the wavelength region of 100 to 185 nm are used. Therefore, as the light source 6, an ultraviolet lamp that emits ultraviolet light having a spectrum in the wavelength region of 100 to 185 nm is used. Even if ultraviolet rays having a spectrum in the wavelength region of 100 nm or less are used, light having a wavelength of 100 nm or less is not practically useful for water treatment because there is no suitable window material for transmitting the ultraviolet rays. Therefore, a light source that emits a wavelength of 100 nm or less is not preferable because the efficiency of energy use is reduced accordingly. The light source 6 may generate light with a wavelength longer than 185 nm at the same time, but if the ratio is large, the energy ratio consumed for water treatment will be low, and even if the same energy is consumed, impurities in the wastewater will be lost. Decomposition efficiency decreases. As the light source 6, a low pressure mercury lamp, a deuterium discharge tube, a xenon lamp, a vacuum ultraviolet light source or the like can be used. Among these, the low-pressure mercury lamp is preferable from the viewpoint of efficiency of generating ultraviolet rays and durability. The preferable irradiation amount varies greatly depending on the composition of the waste water and cannot be specified unconditionally, but it is usually in the range of 10 to 10 million μW · s / cm ² .

As the ultraviolet irradiation device 5, for example, a reaction tank or a tubular reactor in which an ultraviolet lamp is inserted, or an external irradiation type tubular reactor in which a tube made of an ultraviolet transmitting material is wrapped with an ultraviolet lamp can be used. On the light source 6 side of the ultraviolet irradiation device 5 used in the present invention, it is preferable to select and design the device material so that the transmittance of ultraviolet light having a wavelength of 185 nm or less can be secured at 50% or more. Further, as a device material, durability is required for waste water and hydrogen peroxide. Specifically, for example, fused quartz, lithium fluoride, or magnesium fluoride can be used. The treated wastewater is taken out of the system through the treated water pipe 7.

The decomposition reaction time from the addition of hydrogen peroxide to wastewater to the discharge thereof, that is, the average time required for the substantial decomposition of impurities in the wastewater by hydrogen peroxide, varies greatly depending on the properties of the wastewater. 30 minutes or less. However, if the decomposition reaction time is too short, even the substances that can be decomposed with hydrogen peroxide alone will be oxidized by the hydroxy radicals generated by UV irradiation in order to reach the prescribed processing level, which will increase the running cost. There is a case to let. Further, if the decomposition reaction time is made longer than necessary, the rate of self-decomposition of hydrogen peroxide increases, and the amount of hydrogen peroxide used increases, which causes a high cost. The decomposition reaction time can be shortened by adding hydrogen peroxide or by keeping the wastewater in the decomposition reaction in a turbulent state.

There is no particular reason to limit the temperature of waste water when the present invention is carried out, as long as the waste water keeps the liquid tank. However, although the reaction speed increases as the wastewater temperature increases,
Since the rate of hydrogen peroxide self-decomposition also increases, and the ultraviolet lamp also has the optimum irradiation temperature, an appropriate treatment temperature is selected in consideration of these conditions.

[0011]

EXAMPLES The present invention will be specifically described with reference to examples. The COD treatment efficiency (%) is based on JIS K010
It is a value calculated by the following equation using the COD _Mn concentrations of the water to be treated and the treated water measured according to the method specified in 2.

COD treatment efficiency (%) = {1-treated water CO
D _Mn concentration (mg / l) / treated water COD _Mn concentration (mg / l)} × 10
0 Example 1 A treatment test of secondary treated human waste water having a COD _Mn concentration of 120 mg / l was carried out using the present invention. Hydrogen peroxide was added at a ratio of 100 mg per 1 liter of human waste secondary treated water, and the average residence time from the addition of hydrogen peroxide to the ultraviolet irradiation tank was 10 minutes, and the average residence time in the ultraviolet irradiation tank was 10 minutes. did. The hydrogen peroxide mixer had an upright cylindrical shape, and the water to be treated was passed through the inside of the cylinder in a descending flow after adding hydrogen peroxide. A cylindrical reaction tank in which an ultraviolet lamp was inserted by inserting it in the axial direction was also used for the ultraviolet irradiation device, and the treated water was allowed to pass through the periphery of the ultraviolet lamp in an upward flow while uniformly absorbing the ultraviolet light. The light source of ultraviolet rays is 253.
A 30 W low-pressure mercury lamp having main wavelengths of 7 nm and 184.9 nm was used. The COD _Mn concentration after the treatment was measured. The obtained COD treatment efficiency is shown in Table 1.

Comparative Example 1 The same wastewater was treated in the same manner as in Example 1 except that hydrogen peroxide was not added, and the COD _Mn concentration after the treatment was measured. The obtained COD treatment efficiency is shown in Table 1.

Comparative Example 2 The same wastewater was treated in the same manner as in Example 1 except that the low-pressure mercury lamp of the light source was not turned on, and the treated COD _Mn was treated.
The concentration was measured. The obtained treated COD efficiency is shown in Table 1.

Comparative Example 3 A light source having a main wavelength of 253.7 nm and a wavelength of 184.9 nm
The same wastewater was treated in the same manner as in Example 1 except that a 30 W low-pressure mercury lamp that did not emit light of the above wavelength was used, and the COD _Mn concentration of the treated wastewater was measured. The obtained COD treatment efficiency is shown in Table 1.

[0016]

Table 1 Example 1 Comparative example 1 Comparative example 2 Comparative example 3 COD treatment efficiency (%) 76 52 2 23

[0017]

EFFECTS OF THE INVENTION By utilizing the present invention, it is possible to decompose hardly oxidizable substances which cannot be treated by conventional treatment methods such as ultraviolet irradiation, ozone oxidation and oxidation treatment with hydrogen peroxide alone. In particular, the use of light having a wavelength of 185 nm or more has an extremely excellent effect that the efficiency is dramatically increased as compared with the conventional treatment method using hydrogen peroxide and light having a wavelength of 185 nm or more. Further, unlike the ozone treatment, it does not require an exhaust gas treatment device and is an economical and safe treatment means. It is suitable for reducing COD and BOD of sewage, night soil, industrial wastewater and its secondary treated water, waste landfill leachate and its secondary treated water.

[Brief description of drawings]

FIG. 1 is a schematic flow sheet showing an exemplary embodiment of an apparatus for carrying out the present invention.

[Explanation of symbols]

1: Waste water tank 2: Solid-liquid separation device 3: Hydrogen peroxide production device 4: Mixer 5: Ultraviolet irradiation device 6: Light source (ultraviolet lamp) 7: Treated water pipe

Claims (1)

[Claims] 1. A method in which hydrogen peroxide is mixed with waste water, and 185
A wastewater treatment method, which comprises irradiating the wastewater with light having a spectrum in a wavelength region of less than nm.