JPS6354992A - Photochemical treatment method for pulp wastewater - Google Patents

Abstract

PURPOSE:To enable quick and substantially perfect decoloration by projecting UV light and/or visible light to pulp waste water in the presence of an oxidizing agent and semiconductor. CONSTITUTION:The pulp waste water is projected with the UV light and/or visible light in the presence of the oxidizing agent such as air and the semiconductor such as TiO2. After the halide of sodium chloride or the like is further added to the pulp waste water in the presence of the above-mentioned oxidizing agent and semiconductor, and is projected with the UV light and/or visible light. As a result, the quick and substantially perfect decoloration treatment is possible. There is also deodorization effect.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for photochemical treatment of pulp wastewater.

(Prior art) Conventional pulp wastewater treatment generally includes: l) untreated discharge;
) coagulation sedimentation treatment, 3) aeration treatment, 4) ion exchange treatment, 5) ultrafiltration membrane treatment, 6) reverse osmosis treatment, 7) electrochemical treatment, or a combination of 1) to 7) above. However, even if such a processing method is used, it is often unsatisfactory.

On the other hand, the method of irradiating pulp wastewater using light is In
d, Eng, Chem, Processl O (4)
509 (1971), but if only ultraviolet light is used as a light source, the quantum yield is low and it is not practical.

A method of using chlorine in combination with light irradiation is described by Amer, Che.
m, soc, Div, Water, Air Waste
e to hem, Gen, Pap, 1 968.
8 (2) 44-50 and Chemical & E
ngineering News p-98 (1969
), and has been found to be highly effective in removing chemical oxygen demand (COD) and total organic carbon (TOC). JP-A-48-73374 and JP-A-48-733
Publication No. 75 is also based on exactly the same principle. There is also a method of using inexpensive oxygen instead of chlorine as an oxidizing agent, which is proposed in Japanese Patent Application Laid-Open No. 48-42101.

For the method of using chlorine or oxygen together during light irradiation, 1
) Strong oxidizing power, chromaticity, biological oxygen demand (BOD)
, COD, and TOC can be reduced to almost zero. 2) Applicable to a wide range of types of wastewater. 3)
No sludge generation.

4) The device is simple and easy to operate. There are advantages such as On the other hand, the drawback is that although the reaction is quick, it takes several hours for complete decolorization. Furthermore, since only ultraviolet light can be used, the light source is limited. This requires expensive lamps and increases the amount of power required for generation.

In the case of electrolytic decolorization, a method is known in which a salt such as sodium chloride is used to oxidize chlorine ions to chlorine on the electrode surface, and wastewater is treated using this as an oxidizing agent. (Pulp &
Paper Can, Dan 0 (4) 68 (1979)
) However, the disadvantages of this method are that it is not economical due to the high power cost and that the electrode surface is heavily contaminated.

As a result of multifaceted studies on light irradiation methods and electrolytic decolorization methods, the present inventors found that it is possible to use only semiconductors in combination with photochemical treatment in which wastewater treatment is performed by irradiating ultraviolet light in the presence of an oxidizing agent. Alternatively, we have learned that when a semiconductor and a water-soluble halogen compound are used together, the processing efficiency increases rapidly. They also discovered that by changing the type of semiconductor, not only ultraviolet light but also visible light can be used as a light source.

(Object of the Invention) The present invention was made to solve the drawbacks of the light irradiation method and the electrolytic decolorization method described above. An object of the present invention is to provide a wastewater treatment method.

Still another purpose is to provide wastewater that does not contain organic chlorine compounds, and yet another purpose is to provide a method for treating not only pulp wastewater but also industrial wastewater that is difficult to treat with normal wastewater treatment methods. Yes, and further objects will become apparent from the description below.

(Structure of the Invention) To summarize the present invention, the first invention relates to a method for photochemical treatment of pulp wastewater, which comprises irradiating the pulp wastewater with ultraviolet light and/or visible light in the presence of an oxidizing agent and a semiconductor. The second invention is an improvement on the first invention, in which a water-soluble halogen compound is further added to the pulp wastewater in the presence of an oxidizing agent and a semiconductor, and then ultraviolet light and/or Alternatively, the present invention relates to a method for photochemical treatment of pulp wastewater, which comprises irradiating visible light.

Next, the elements constituting the present invention will be explained in detail.

Pulp wastewater treated in the present invention includes not only wastewater from so-called chlorine bleach stages such as chlorine stage, alkaline stage, hypo stage, and chlorine dioxide stage, but also wastewater from oxygen stage, ozone stage, hydrogen peroxide stage, etc. It can include wastewater from the pulping process, such as wastewater from so-called non-chlorine bleaching stage or screen wastewater, wastewater from the digestion stage, wastewater from the evaporator, and wastewater from the papermaking process or from the processing process.

The oxidizing agent used in the present invention may be oxygen, air, oxygen-enriched air, ozone, hydrogen peroxide, sodium hypochlorite, nitrogen dioxide, etc.; however, oxygen or air may be used. It is convenient to use. When oxygen or air is used, the supply amount may be sufficient to maintain the state in which the wastewater is saturated with oxygen.

The semiconductors used in the present invention include commercially available TiO2, ZnO, CdS, GaP, Si, and GaA.
Either a P-type semiconductor such as S, SiC, or an N-type conductor may be used. Furthermore, the crystal structure of the semiconductor is, for example, TiO2
In the case of , it may have any crystal structure, such as rutile type or anatase type, and may be doped. Alternatively, a semiconductor may be used after being heated and reduced with hydrogen. Furthermore, other metals, such as platinum, may be supported on the semiconductor. When using a semiconductor, it may be immobilized or suspended in the waste water in the form of granules or powder, and it is preferable to use the method most suitable for each process.

The most economical light source used in the present invention is sunlight, but it is preferable to use a high-pressure mercury lamp when irradiating ultraviolet light, and a cannon lamp when irradiating visible light. Other options include tungsten lamps, halogen lamps, and various lasers, and the light source can be selected by considering the spectral sensitivity of light absorption of the semiconductor performing photochemistry and the type of wastewater.

Rose Bengal, Rhodamine B, Chlorophyll, for drainage.
When performing photochemical treatment by adding a dye sensitizer such as methylene blue or quinomycin, it can be sensitive to light with a wavelength longer than the inherent absorption wavelength of the semiconductor, so in this case more types of light sources are selected. be able to.

The water-soluble halogen compound used in the present invention may be any compound of a halogen element and an alkali metal element and/or an alkali metal element listed in the Peripheral Table as long as it is water-soluble. Considering economic efficiency and ease of handling chemicals, it is preferable to use seawater, sodium chloride, or potassium chloride.

The temperature applied to the pulp wastewater treatment system of the present invention is 10-7
0.C, preferably 30-60.C, the reaction time may be 60 minutes or less because the reaction is fast, but even if the reaction time is extended due to the flow rate of waste water, etc., there will be no interruption between ships. p
H may be in the Iwa area.

In carrying out the present invention, it may be used in the first stage of the pulp wastewater treatment process, or it may be used in the so-called higher-level treatment of wastewater after undergoing coagulation and sedimentation treatment. It may also be a continuous or batch operation, and a number of methods are applicable.

(Examples of the Invention) Next, Examples of the present invention will be described, but the present invention is not limited thereto in any way.

Examples 1 and 2 and Comparative Examples 1.2.3 and 4 Kraft factory alkaline wastewater (COD 1200 ppm,
BOD 470ppm, pHfo, 8) was diluted 10 times to prepare a sample solution.

In the experimental method, 10 cc of a sample solution at room temperature was poured into a quartz container. While stirring with a stirrer, add 50% of the semiconductor powder.
mg container and input 50 while bubbling oxygen.
A 0W high pressure mercury lamp! ! Irradiation was performed from a position of 30cI11, the light was collected by a convex lens, and the reaction was allowed to occur for a predetermined period of time. A supernatant of the solution in contact with the solution for a certain period of time was collected, and its absorbance at 465 nm was measured to determine the degree of color development. Separately, wastewater treated by adding sodium chloride and then irradiating it with light was also measured in the same way.

In Examples 1 and 2, T was added as a semiconductor to the sample solution, respectively.
This is an example in which a treatment experiment was conducted by adding iO□ (Example 1) and ZnO (Example 2). Comparative examples include an example in which the same sample solution was irradiated by bubbling only oxygen (Comparative Example 1), an example in which only sodium chloride was added and irradiated (Comparative Example 2), and an example in which only a ZnO semiconductor was added and irradiated. (Comparative Example 3) and an example in which a combined system of oxygen and sodium chloride was irradiated (Comparative Example 4).The results are shown in Table 1.

In Table 1, the absorbance at 0 minutes of irradiation is taken as 100%, and the absorbance is expressed as a relative value.

In Example 3, reprinted alkali lignin 0.1 was used as the sample solution.
TiO2 as a semiconductor using a solution of g dissolved in water IL.
This is an example of wastewater treatment similar to the above using. Example 4 is an example in which the same alkaline lignin solution was photo-oxidized using ZnO as a semiconductor. The results are shown in Table 2.

Table 2 (Effects of the Invention) As is clear from Tables 1 and 2, if wastewater is treated by light irradiation in the presence of oxygen and semiconductors, it can be completely treated in a very short time. Admitted.

Furthermore, in addition to this effect, a deodorizing effect was also observed for those treated by the method of the present invention.

Another major feature is that the method of the present invention does not produce sludge, which is always produced in ordinary wastewater treatment methods, so there is no problem of sludge disposal.

Claims (1)

[Scope of Claims] 1) A method for photochemical treatment of pulp wastewater, which comprises irradiating the pulp wastewater with ultraviolet light and/or visible light in the presence of an oxidizing agent and a semiconductor. 2) A method for photochemical treatment of pulp wastewater, which comprises adding a water-soluble halogen compound to the pulp wastewater in the presence of an oxidizing agent and a semiconductor, and then irradiating the pulp wastewater with ultraviolet light and/or visible light.