JPH0326119B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method and apparatus for treating wastewater containing an organic chlorine solvent, particularly trichlorethylene or tetrachlorethylene. [Prior Art] Various strict laws and regulations are enforced regarding the treatment of wastewater containing organic chlorine solvents such as trichlorethylene and tetrachlorethylene from the viewpoint of danger and environmental hygiene. Processing technology is required. Common methods for treating wastewater containing such organic chlorine solvents include, for example, aeration methods using an aeration tank;
A diffusion method using a packed column (aeration tower), an adsorption method using activated carbon, and a combination of an adsorption method and an aeration or dispersion method are known. On the other hand, there is also a method of treating wastewater containing oxidizable substances by using Fuenton's reagent.
-136947 etc. is publicly known. [Problems to be solved by the invention] However, the above-mentioned aeration method, diffusion method, adsorption method, etc. are all physical treatments,
It is essential that the organic chlorine solvents and the like removed from the wastewater be subjected to further secondary treatment to render them harmless. On the other hand, the treatment method using Huetone reagent treats a wide variety of oxidizable substances contained in wastewater and reduces the oxygen demand (COD) based on organic matter in wastewater.
The target organic substances in wastewater are not limited to organic chlorine solvents, and the purpose is simply to reduce oxidizable substances in wastewater as much as possible. Therefore, it requires secondary treatment similar to the physical treatment method described above to render it harmless. [Means for Solving the Problems] In view of the current situation, the present invention aims to eliminate trichlorethylene or tetrachlorethylene in the waste water without resorting to complicated means such as secondary treatment when treating waste water containing trichlorethylene or tetrachlorethylene. The purpose is to easily and almost completely render it harmless. That is, the first invention is a method for treating wastewater, which comprises adding hydrogen peroxide to the wastewater containing trichlorethylene or tetrachlorethylene in a molar ratio of 10 or more to the trichlorethylene or tetrachlorethylene contained in the wastewater, and 25 or less;
Molar ratio based on iron atom equivalent to hydrogen peroxide
By adding an iron compound of 0.2 or more, trichlorethylene or tetrachloroethylene contained in wastewater is oxidized and decomposed to render it harmless. Further, the second invention is a wastewater treatment device,
It is equipped with a stirrer inside, has an injection part for hydrogen peroxide and iron compounds, and has an introduction part for wastewater containing trichlorethylene or tetrachlorethylene and a discharge part for wastewater obtained from oxidative decomposition at the bottom. It consists of a nearly closed reaction tank,
A small opening for gas discharge communicating with the outside air is formed in the upper part of the reaction tank, and the generated gas in the upper part of the reaction tank is led out of the reaction tank and is forcibly refluxed into the liquid from the lower part of the reaction tank. It is characterized by: However, the wastewater to be treated by this invention is
This is wastewater generated by washing with water after degreasing, washing, painting, or other processing of articles using trichlorethylene or tetrachlorethylene, or by desorption of water vapor from an exhaust gas adsorption device. Note that even if the wastewater contains oils and fats that have adhered to articles that have been washed or otherwise treated with trichlorethylene or tetrachlorethylene, they can be effectively treated. The molar ratio of hydrogen peroxide used in this method to trichlorethylene or tetrachlorethylene contained in the waste water is 10 or more and 25 or less. In addition, iron compounds to be used include, for example, iron sulfate (,), iron chloride (,), iron nitrate (,
), iron peroxide (,), iron ferrocyanide, hydroxide (,), iron oxide (,), iron rhodan (,), and other inorganic iron compounds. The more these iron compounds are used, the faster the oxidative decomposition rate of trichlorethylene or tetrachlorethylene becomes, but the amount of by-product sludge increases. It is preferable to add an appropriate amount of them. The treatment of wastewater with hydrogen peroxide and iron compounds may be carried out either batchwise or continuously, and the time for which they are brought into contact varies depending on the concentration of the oxidizable substance trichlorethylene or tetrachlorethylene, but is usually A residence time of about 0.2 to 24 hours is suitable. The pH during the reaction is preferably in the range of 2 to 4, preferably around 3. The liquid temperature may be in the range of 0 to 80°C, but it is particularly desirable that the liquid temperature be around 20°C. On the other hand, the second invention is a processing device for carrying out the first invention, and will be specifically explained below based on the attached drawings. FIG. 1 shows a flow sheet including the apparatus used in the present invention, in which 1 is a supply pipe for wastewater containing trichlorethylene or tetrachlorethylene, 2 is a liquid feed pump, and 3 is a valve. Containing wastewater is transferred from supply pipe 1 → liquid feed pump 2 →
It is supplied to the lower part of the reaction tank 5 via the valve 3 and the supply pipe 4. The reaction tank 5 is a vertical tank that is generally closed in its entirety, and has a motor drive shaft extending into the reaction tank 5 through the upper lid, and a stirring fan attached to the tip of the motor drive shaft. In addition to being equipped with a stirrer 6, an oxidative decomposition agent consisting of hydrogen peroxide, an iron compound, and a pH adjustment liquid is supplied to the reaction tank 5 through a pipe 13.
It is configured to be supplied from the top of the Furthermore, a gas consisting of trichlorethylene or tetrachlorethylene vapor that remains in the upper part of the reaction tank 5 during treatment of waste water is supplied to the upper part of the reaction tank 5 through a blower 9, a check valve 10, and a supply pipe 4 to the lower part of the reaction tank 5. One end of a reflux pipe 8 is connected to the reflux pipe 8 for forcibly refluxing the water, and a small opening 7 is provided to reduce the vapor pressure generated during the oxidative decomposition reaction. One end of a discharge pipe 11 is connected to the discharge pipe 11 for sending it out via a pump 12 to a neutralization treatment facility (not shown). The size of the micro opening 7 is set to a size that allows steam to escape easily depending on the amount of wastewater introduced. [Function] In the present invention, waste water is treated by oxidative decomposition while maintaining the molar ratio of hydrogen peroxide to waste water containing trichlorethylene or tetrachlorethylene and the molar ratio of iron compounds to hydrogen peroxide at the above-mentioned predetermined ratios. The trichlorethylene or tetrachlorethylene contained in the water is oxidatively decomposed, and the carbon content contained in the trichlorethylene or tetrachlorethylene becomes carbon dioxide, and the chlorine content becomes hydrochloric acid. This hydrochloric acid is contained in the oxidatively decomposed wastewater. If necessary, it can be easily rendered harmless by subsequent neutralization means. Furthermore, when treating wastewater containing trichlorethylene or tetrachlorethylene, the vapor pressure of the trichlorethylene or tetrachlorethylene contained therein is high, so there is a risk that it will be released into the atmosphere during the treatment process. Taking these points into consideration, the apparatus of the present invention has a reaction tank 5.
By making the whole almost closed type, the reaction tank 5
By restricting the opening ratio of the upper part of the reaction tank 5 to the necessary minimum, and allowing the gas remaining in the upper part of the reaction tank 5 to flow back to the lower part of the reaction tank 5 and contact with the liquid in the reaction tank 5 again, the gas can be removed. Oxidatively decompose the trichlorethylene or tetrachlorethylene as much as possible,
It renders it harmless. In addition, in the apparatus of the present invention, the trichlorethylene or tetrachlorethylene-containing wastewater to be treated is supplied from the lower part of the reaction tank 5, and as a result, trichlorethylene or tetrachlorethylene in the wastewater, which is naturally prone to evaporation, is directly supplied to the liquid in the reaction tank 5. The evaporation of trichlorethylene or tetrachloroethene can be suppressed as much as possible, and the decomposition rate of trichlorethylene or tetrachloroethene can be improved. In this invention, wastewater containing trichlorethylene or tetrachlorethylene is rendered harmless by setting the molar ratio of hydrogen peroxide to trichlorethylene or tetrachlorethylene to 10 or more and 25 or less, as well as by adjusting the iron compound to hydrogen peroxide in terms of iron atoms. This is achieved by maintaining the molar ratio at 0.2 or higher. Trichlorethylene or tetrachlorethylene is a solvent with a chemically unsaturated bond structure, and if oxidation is insufficient, intermediate compounds such as dichloroacetic acid and trichloroacetic acid will be produced as shown in the reaction formula below, and complete oxidation will occur. Detoxification cannot be achieved. Although these intermediate compounds are not subject to wastewater regulations, they are still organic chlorine compounds, and the production of intermediate compounds is not suitable for the purpose of the present invention. This invention is intended to prove and provide conditions for a reaction formula that results in complete detoxification through examples. The reason why the molar ratio of hydrogen peroxide to trichlorethylene or tetrachlorethylene was limited to 10 or more and 25 or less is that this is the minimum necessary level for making trichlorethylene and tetrachlorethylene harmless, and that hydrogen peroxide is not used in excess. This is to avoid the waste of having to add a new reduction treatment in order to eliminate the adverse effect of an increase in COD due to hydrogen peroxide remaining when added. [Oxidation reaction of trichlorethylene] [Oxidation reaction of tetrachlorethylene] [Example] Hereinafter, this invention will be described in detail based on an example. The test results in each example were confirmed by the following analysis. (1) Analysis of carbon dioxide gas in exhaust gas Exhaust gas was sampled and analyzed using TCD gas chromatography. (2) Analysis of hydrochloric acid in wastewater This was carried out using the Mohr method and PH. (3) Analysis of trichlorethylene or tetrachlorethylene in wastewater According to Annex ``Testing methods for total trihalomethane, trichlorethylene, tetrachlorethylene, and 1,1,1-trichloroethane'' of Kansui No. 15 of the Ministry of Health and Welfare dated February 18, 1980. Headspace gas chromatography (ECD) method Example of solvent extraction and gas chromatography (ECD) method 1 In a transparent glass flask equipped with a stirrer, waste water containing trichlorethylene and a FeSO ₄ 7H ₂ O solution as an iron compound were placed. and turn the stirrer to the rotation speed.
While stirring at 150 rpm, hydrogen peroxide was added to perform oxidative decomposition. Note that an inert gas was introduced into the flask to collect the generated gas. The reaction was carried out at a liquid temperature of 25±3°C and a reaction time of 2 hours. In this oxidative decomposition, the relationship between the molar ratios of hydrogen peroxide/trichlorethylene and iron compound (FeSO ₄ 7H ₂ O)/hydrogen peroxide and the removal rate of trichlorethylene during treatment was measured and the results shown in Figure 2 were obtained. Got the results. In addition, in the figure, A of each curve is the molar ratio of hydrogen peroxide/trichlorethylene. From the results shown in Figure 2, it can be seen that 100% of the iron was removed when the hydrogen peroxide/trichlorethylene molar ratio was 10 and the iron/hydrogen peroxide molar ratio was 0.2. Example 2 In the same manner as in Example 1, wastewater containing trichlorethylene was oxidized and decomposed. Through this oxidative decomposition, carbon becomes carbon dioxide gas and chlorine becomes chlorine, but the decomposition rate of carbon relative to the hydrogen peroxide/trichlorethylene molar ratio (in the reaction exhaust gas)
The amount of C in CO ₂ and CO/the amount of C in the stock solution×100) was measured, and the results shown in FIG. 3 were obtained. Similarly, the decomposition rate of chlorine (amount of chlorine ions in the solution after reaction/amount of Cl in the stock solution x 100) was measured, and the results shown in FIG. 4 were obtained. Note that the molar ratio of iron compound (FeSO ₄ .7H ₂ O)/hydrogen peroxide was kept constant at 0.2. This result shows that when the molar ratio of hydrogen peroxide/trichlorethylene is 10 or more, both carbon and chlorine are 100% decomposed. Furthermore, when we further investigated the presence of dichloroacetic acid and trichloroacetic acid in the oxidatively decomposed liquid, we found that the decomposition rate was
These exist in conditions less than 100%, and 100%
These were not observed in the area. Example 3 Tetrachlorethylene was subjected to oxidative decomposition in the same manner as in Examples 1 and 2, and the removal and decomposition rates of tetrachlorethylene were measured. The hydrogen/tetrachloroethylene molar ratio was 20, and the iron/hydrogen peroxide molar ratio was 0.2. An overview is shown in Table 1.

〔Effect of the invention〕

The method for treating wastewater according to the present invention includes hydrogen peroxide having a molar ratio of 10 or more and 25 or less relative to trichlorethylene or tetrachlorethylene contained in the wastewater, and 0.2 or more in terms of iron atom molar ratio to the hydrogen peroxide. This method oxidizes and decomposes trichlorethylene or tetrachlorethylene in wastewater by adding an iron compound of It can be decomposed into the substances that exist in the world and rendered harmless. In addition, the wastewater treatment device is equipped with an internal agitator, an introduction part for wastewater containing trichlorethylene or tetrachlorethylene at the bottom, and a discharge part for wastewater obtained by oxidative decomposition, and also contains hydrogen peroxide and iron compounds. A nearly closed reaction tank is constructed with an injection port, and a small opening for gas discharge is formed in the upper part of the reaction tank, minimizing the opening ratio of the reaction tank to the necessary minimum. The structure is such that the generated gas at the top is led out of the reaction tank and is forced to flow back into the liquid from the bottom of the reaction tank. Therefore, it is possible to easily oxidize and decompose all trichlorethylene or tetrachlorethylene in waste water, which originally has a high vapor pressure, to render it harmless.

[Brief explanation of the drawing]

Figure 1 is a flow sheet including the equipment used in this invention, and Figure 2 is a flow sheet containing hydrogen peroxide/trichlorethylene, iron compound/
A graph showing the relationship between each molar ratio of hydrogen peroxide and the trichlorethylene removal rate, FIG. 3 is a graph showing the carbon decomposition rate with respect to the molar ratio of hydrogen peroxide/trichlorethylene in the wastewater treatment of Example 2,
FIG. 4 is a graph showing the decomposition rate of chlorine with respect to the molar ratio of hydrogen peroxide/trichlorethylene in the wastewater treatment of Example 2. 1, 4... Supply pipe, 2... Liquid feed pump, 5...
Reaction tank, 6... Stirrer, 7... Micro opening, 8...
...Recirculation piping, 9...Blower, 11...Discharge pipe, 1
2...Liquid pump, 13...Piping.

Claims (1)

[Scope of Claims] 1. In wastewater containing trichlorethylene or tetrachlorethylene, hydrogen peroxide in a molar ratio of 10 to 25 with respect to trichlorethylene or tetrachlorethylene contained in the wastewater,
In terms of molar ratio in terms of iron atoms to the hydrogen peroxide
A method for treating wastewater, which comprises adding an iron compound of 0.2 or more to oxidize and decompose trichlorethylene or tetrachlorethylene contained in the wastewater to render it harmless. 2. The method for treating wastewater according to claim 1, wherein the oxidative decomposition involves capturing trichlorethylene or tetrachlorethylene that is vaporized during the oxidative decomposition and forcibly refluxing it into the oxidative decomposition liquid. 3.In addition to being equipped with a stirrer inside, it has an injection part for hydrogen peroxide and iron compounds, and an introduction part for wastewater containing trichlorethylene or tetrachlorethylene and a discharge part for wastewater obtained from oxidative decomposition are provided at the bottom. A nearly closed type reaction tank is constructed, and a small opening for gas discharge that communicates with the outside air is formed in the upper part of the reaction tank, and the generated gas in the upper part of the reaction tank is led out to the outside of the reaction tank. A wastewater treatment device configured to forcibly flow back into the liquid from the bottom.