JPS62176595A - Method for removing organic substance in waste water - Google Patents

Abstract

PURPOSE:To efficiently decompose an org. substance, by adding hydrogen peroxide, ozone gas and ozonated water to waste water containing the low molecular org. substance while said waste water is irradiated with ultraviolet rays. CONSTITUTION:Waste waater containing an org. substance is guided to a reaction tank 3 from a raw water introducing pipe 1 and hydrogen peroxide water is injected in said waste water on the way of the introducing pipe 1 through a hydrogen peroxide injection pipe 2. An ozone introducing pipe 6 having an air diffusion pipe 5 connected to the leading end thereof is arranged in the vicinity of the bottom part of the reaction tank 3 and ozone gas is introduced into the ozone introducing pipe 6 to diffuse ozone to the reaction tank 3. Further, the waste water is irradiated with ultraviolet rays from an ultraviolet lamp 4 to decompose the org. substance in raw water and treated water is discharged out of the system from a discharge pipe 7. By this method, the org. substance can be oxidized and decomposed within a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a method for decomposing and removing organic substances by ultraviolet wet oxidation when treating industrial wastewater containing relatively low-molecular organic substances. be.

[Prior art]

In recent years, the use of water has diversified, and relatively low concentrations of organic matter have become a problem in terms of water quality.For example, when producing pure water, ion exchange with organic matter in water The resin may be contaminated or organic components may be eluted from the ion exchange resin itself, causing a decrease in the purity of the pure water. Furthermore, blowdown water from fuel cells contains various organic substances, mainly alcohol, brought in from the fuel gas, which poses a problem when this blowdown water is recycled as cooling water for fuel cells. becomes. In addition, it goes without saying that ultrapure water (several μ
Even concentrations of organic matter of g/e are problematic.

Many of the components of these organic substances are relatively low molecular,
Examples include methanol, lower fatty acids, lower aldehydes, and lower amines.

Conventionally, various methods for decomposing organic matter in industrial wastewater have been studied, and can be broadly classified, for example, as follows.

+11 Oxidizing agent addition method Add chlorine oxidizer, hydrogen peroxide, ozone, etc.

(2) Wet oxidation method It decomposes thermally at high temperature and pressure in an oxidizing atmosphere.

(3) Electrolytic oxidation method Oxidative decomposition by electrode reaction (an oxidizing agent may be used in combination).

(4) Catalytic oxidation method Decomposes with an oxidizing agent using a metal salt or metal as a catalyst.

(5) Photocatalytic oxidation method Oxidative decomposition is carried out using a metal salt or a photosemiconductor catalyst under irradiation with ultraviolet rays (hereinafter referred to as rUVJ) or the like.

(610V wet oxidation method Chlorine oxidizer + UV Hydrogen peroxide + UV Ozone + UV Chlorine oxidizer + Hydrogen peroxide + UV Chlorine oxidizer + Ozone + UV Ozone + Ultrasound + UV Among these methods, oxidation by simply adding an oxidant The agent addition method is a technique that is widely used in various fields and is very easy to perform, and may be effective depending on the organic substance.
-a, the reaction rate is slow and the amount of oxidizing agent added is relatively large, which makes it uneconomical.

In addition, although the wet oxidation method can be expected to allow the reaction to proceed completely, it requires a pressure-resistant container and the problem of corrosion cannot be avoided, making operation management difficult and not being put into practical use very often.
On this point, in the electrolytic oxidation method, the progress of the reaction can be arbitrarily controlled by the current and voltage, and although in principle it seems easy to manage the operation, in reality there are problems such as corrosion or wear of the electrodes, resulting in unstable Problems include the fact that it is not easy to control the reaction, and because the reaction is limited to the electrode surface, a large number of electrolytic cells are required, which increases the size of the processing equipment.

Next, for example, catalytic oxidation methods, such as the Fenton treatment method, have been in practical use for a long time and have the advantage of being relatively easy to manage, but they require large amounts of metal salts and metals as catalysts, making them less effective. It cannot be said that it is economical. Also,
Since the photocatalytic oxidation method uses a catalyst such as a metal salt or a photosemiconductor, it has a high reaction rate and usually does not require the addition of an oxidizing agent, so it is economically advantageous, but it is susceptible to deterioration due to corrosion of the catalyst. This is likely to occur and the technology has not yet been developed for practical use.

As described above, since the above-mentioned conventional techniques have advantages and disadvantages, the UV wet oxidation method is said to be the most practical.

That is, the UV wet oxidation method that uses various oxidizing agents in combination is a more effective means than the above-mentioned oxidizing agent addition method, and has the advantage that it requires less amount of oxidizing agent to be added.

[Problem that the invention seeks to solve]

However, even the UV wet oxidation method, which is considered to be the most practical method, has the following problems.

(1) Although the reaction rate is higher than the M other agent addition method, the reaction time is generally required to be 60 minutes or more in many cases.

(2) If a chlorine-based oxidizing agent is used as an oxidizing agent, harmful organic chlorine compounds may be generated and may remain in the treated water.
(above), radical reactions are inhibited and decomposition of organic substances becomes difficult.

(3) The selectivity of the decomposition reaction varies depending on the type of organic matter (,
Optimal reaction conditions are different.

Furthermore, in the current situation where the organic matter in industrial wastewater is becoming more and more diverse, including trace components, it is becoming more and more difficult to carry out a fully satisfactory treatment using the conventional UV wet oxidation method.

One of the causes of the above problem is that the oxidizing power to decompose organic substances is insufficient.If sufficient oxidation could be carried out in a short time, the reaction would stop at the by-product stage. It becomes possible to decompose organic matter into CO and gas without causing problems with selectivity due to the type of organic matter.

[Means for solving problems]

In order to solve the above problems, the present inventors investigated a method for removing organic matter from industrial wastewater that is easy to operate, highly economical, and has high efficiency in decomposing organic matter. It has been found that a UV wet oxidation method in which UV irradiation is performed in the coexistence of hydrogen and ozone is the most practical.

An object of the present invention is to provide a method for removing organic matter from wastewater that can efficiently and easily decompose organic matter, particularly organic matter with relatively fine molecules.

A feature of the present invention is that hydrogen peroxide and ozone gas or ozonized water are added to wastewater containing relatively low-molecular organic substances, and UV irradiation is applied. Here, most of the above-mentioned substances are volatile substances of relatively low molecular weight, and more specifically, lower fatty acids, lower aldehydes, lower amines, lower alcohols, etc. In addition, the pH during treatment is
By setting it preferably to 8 or less, the decomposition efficiency of organic matter can be further improved.

[Effect]

The present invention will be explained based on FIG. 1 showing embodiment B. Waste water containing organic matter (hereinafter referred to as "raw water") is introduced into the reaction tank 3 from the raw water introduction pipe 1, A hydrogen peroxide solution is injected through the hydrogen peroxide injection pipe 2. Near the bottom of the reaction tank 3, an ozone introduction pipe 6 with an aeration pipe 5 connected to the tip is arranged, and by introducing ozone gas into the ozone introduction pipe 6, ozone is diffused into the reaction tank 3, and ultraviolet rays are also emitted. The organic matter in the raw water is decomposed by UV irradiation with the lamp 4, and the treated water is discharged from the system through the discharge pipe 7.

The operation of the present invention will be further explained in detail below.

Conventional ozone + UV treatment without the addition of hydrogen peroxide has been extensively studied; for example, regarding pH, which is one of the reaction conditions, alkaline pH is better for decomposing phenol, and neutral pH is more effective for polyethylene glycol decomposition. It is. In addition, sodium acetate has a pH of 8 or less, and the alkaline side is preferable for methanol decomposition. As described above, since the reaction conditions differ depending on the type of organic matter, with conventional ozone + UV treatment, it is usually difficult to determine the optimal reaction conditions for treating wastewater containing many types of organic matter, and the treatment effect is unstable. Furthermore, it is well known that organic substances are not primarily decomposed to carbon dioxide gas, but produce intermediate products. Therefore, if the intermediate product is a substance that exists fairly stably, it is not expected that the concentration of organic matter in the treated water will decrease much, and the total organic carbon (TOC) or chemical oxygen demand (CO [l '') will decrease. This is a problem not only with conventional ozone + UV treatment but also with conventional UV wet oxidation methods.

The present invention was achieved as a result of thorough study of this reaction. That is, when UV irradiation and an oxidizing agent are used together, the decomposition of Ia compounds in water proceeds by a radical reaction, and in particular, HO and radicals make a large contribution. For example, when ozone is used, UV o,l −→ Oz”0・0・+Hg0−2IO・ When hydrogen peroxide is used, HO・radical is Generate.Of course, IO・
Various other radicals are generated in addition to radicals, but in general, when the above-mentioned oxidizing agent is used, the 0.radical is primarily generated.

Generation of HO radicals requires that ozone be dissolved in water. Ozone that was not dissolved in water was produced by self-decomposition. It is uneconomical because it becomes waste gas including 2 and dissipates into the atmosphere. That is, in order to increase the amount of HO radicals produced, it is clear that it is more advantageous to directly generate HO radicals from a water-soluble substance. However, for example, if only hydrogen peroxide, which is a water-soluble substance, is irradiated with UV light, the self-decomposition rate of hydrogen peroxide is slower than that of ozone, so the rate of decomposition of organic matter is also slow and the organic matter is decomposed into carbon dioxide in a short time. It is not possible. Particularly, the self-decomposition rate of hydrogen peroxide is slow, partly because commercially available hydrogen peroxide usually contains various stabilizers.

Therefore, the present inventors discovered that by using ozone and hydrogen peroxide in combination, the amount of HO radicals produced can be dramatically increased, and organic substances can be decomposed in a short time, leading to the present invention. In other words, the self-decomposition of hydrogen peroxide is promoted by the 0-radicals generated from ozone by UV irradiation or the nascent oxygen (0), and HO-radicals are generated in large quantities compared to conventional methods. It has characteristics,
For example, the following reactions are thought to occur in a chain sequence.

UV Ol-10? +0・o −+H,O→2HO− 0・+HzO1=HO−Hot V H bah −→2HO・ Therefore, ozone is used to promote the self-decomposition of hydrogen peroxide rather than contributing to the decomposition of organic matter. , ozone can be said to be a kind of radical generation initiator.

As described above, the rate of decomposition of organic matter in the present invention is much higher than that of the conventional method, but of course the molecular weight of the organic matter also influences the decomposition of organic matter into carbon dioxide in a short time. That is, when the organic substance has a high molecular weight, various intermediate products are produced, and the reaction time until carbon dioxide gas is finally produced tends to be long. However, since pretreatments such as coagulation and sedimentation and sand filtration are usually performed before UV wet oxidation treatment, the target organic substances are relatively low molecular weight organic substances that could not be removed by these pretreatments. The effects of the present invention can be fully exhibited.

As described above, the present invention uses hydrogen peroxide and ozone in combination to
V irradiation has the effect of generating HO radicals, which are necessary to oxidize and decompose organic substances in a short time.
This effect is much greater than the conventional UV wet oxidation method.

〔Example〕

Next, examples of the method of the present invention and the conventional method will be shown.

Example-1 Approximately 80μ/I of methyl alcohol in tap water of 500mA
1 was added as raw water, and methyl alcohol was decomposed under the conditions shown in Table 1. Note that a low-pressure mercury lamp (power consumption: 32 W) was used as the UV light source.

In addition, to adjust the po level, an appropriate amount of sodium hydroxide solution or sulfuric acid was added to adjust the pH to the desired level.

Margin below This example is an example of the conventional method of ozone + UV irradiation.
The results are shown in FIG. As can be seen from Figure 2, the decomposition of methyl alcohol is affected by the pH of the raw water, and pt
There is almost no reaction when + is on the alkali side. Also, 1
Even when 1000 pp of ozone was used, the TOC removal rate in Example B was about 50% in a reaction time of 60 minutes.

On the other hand, for an example of the present invention in which hydrogen peroxide and ozone were used in combination and UV irradiation was performed, the decomposition conditions are shown in Table 2, and the results are shown in FIG.

As can be seen from Figure 2 in the margin below, C of the present invention reacts much faster than the conventional method and has a higher TOC removal rate; TOC in 5 minutes
The removal rate was 90% or more, and methyl alcohol was decomposed to carbon dioxide gas in a short time.

Example 2 After conditioning a strongly basic anion exchange resin, it was regenerated and immersed in pure water for about 72 hours, and the supernatant liquid was subjected to TOC decomposition under the conditions shown in Table 3.
As shown in the figure.

Note that the pH was adjusted as in Example 1 by adding sodium hydroxide or sulfuric acid at appropriate times.

Margins below In this case, E is the conventional method, and G of the present invention, which uses hydrogen peroxide in combination, has a much higher TOC removal rate than the conventional method, and under pH conditions like F of the present invention, the reaction time is 15 minutes. T
The OC removal rate was over 90%.

Example 3 Using the raw water shown in Example 2, the reaction conditions were the same as those in F and G in Table 3, but only the pH was adjusted to various conditions. FIG. 4 shows the relationship between the TOC removal rate of the treated water at a reaction time of 15 minutes and the pH of the raw water before the start of the reaction.

As shown in FIG. 4, when the pH is 8 or less, the TOC removal rate is almost constant at 90% or more, but when the pH is 8 or more, the TOC removal rate clearly decreases. However, if the reaction time is 60 minutes or more, the influence of pH will not be seen much.

However, in order to carry out the reaction in a short time, pi conditions are an important factor, and it can be said that pu is preferably 8 or less.

〔Effect of the invention〕

As is clear from the above description, the present invention achieves the following by performing tJV irradiation in the coexistence of hydrogen peroxide and ozone.
Organic matter can be decomposed extremely efficiently and in a much shorter time than conventional methods.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the relationship between reaction time and treated water Toe in each example, and FIG. 4 is a diagram showing the raw water of the present invention. FIG. 3 is a diagram showing the relationship between pn and TOC removal rate. l...Raw water introduction pipe, 2...Hydrogen peroxide injection pipe, 3.
...Reaction tank, 4...Ultraviolet lamp, 5...Diffuser pipe,
6...Ozone introduction pipe, 7...Drainage pipe. Patent applicant: Ebara Infilco Corporation
Takashi, Patent Attorney, Ebara Research Institute, Inc.
Ki Tadashi Apothecary between the lines
Twisting 1) Takashibe Figure 2 Reaction time (min) Figure 4

Claims (1)

[Scope of Claims] 1. A waste water containing relatively low-molecular-weight organic matter is treated by adding hydrogen peroxide and ozone and irradiating it with ultraviolet rays to decompose and remove the organic matter. Method for removing organic matter from wastewater. 2. The method for removing organic matter from commercial wastewater according to claim 1, wherein the pH of the commercial wastewater is adjusted to 8 or less.