JPS63218293A - Treatment of waste water containing trichloroethylene - Google Patents

Abstract

PURPOSE:To decompose trichloroethylene to harmless substances, by adding H2O2 to waste water contg. trichloroethylene, irradiating the waste water with ultraviolet rays, and passing the waste water through an adsorption bed contg. active carbon fiber while irradiating the waste water further with ultraviolet rays. CONSTITUTION:H2O2 is added to waste water contg. trichloroethylene in satd. state in a decomposition tank 2 from a tank 4. The trichloroethylene is decomposed by irradiating the waste water with ultraviolet rays using a lamp 3. Then, the waste water treated in the above described stage is further irradiated in a decomposition adsorption apparatus 10 with ultraviolet rays using a lamp 12 in the presence of residual H2O2 from the above described stage. While continuing the irradiation, trichloroethylene is decomposed by passing the waste water through an adsorption pipe 11 contg. active carbon fiber. As the result, waste water contg. trichloroethylene in so high concn. as 1,000ppm (saturation concn.) before treatment is treated in a short time to treated waste water contg. extremely small concn. of residual trichloroethylene so small as expressed in terms of ppm after treatment. No secondary by product requiring trouble some post-treatment is generated.

Description

[Detailed Description of the Invention] [Industrial Application Field] Recently, environmental pollution due to organic chlorine compounds has become a problem, and water quality standards have been established for trichlorethylene and tetrachlorethylene as pollutants. Among them, trichlorethylene is about 1% in water at room temperature.
It is a troublesome pollutant in rivers and underground water, and is discharged in large quantities by machinery and metal industries, electrical equipment-related industries, dry cleaning and recycling industries, etc., but the wastewater standard value There is a strict regulation of 30 ppb or less.

The present invention relates to a method for treating wastewater in which trichlorethylene is dissolved in a severely saturated state, decomposing the trichlorethylene into harmless substances, and reducing the concentration of residual trichlorethylene to an ultra-trace amount, rendering it harmless.

[Conventional technology]

The conventional method for treating trichlorethylene-containing wastewater is to perform a stripping process and release the dissolved trichlorethylene in the water into the atmosphere, but this method simply transfers trichlorethylene into the atmosphere and can cause secondary pollution. However, it has the drawback that the processing time is extremely long, which could be a fundamental solution. Additionally, a method of removing trichlorethylene by adsorption with activated carbon is also commonly used;
Since this is a method of repeated desorption, post-treatment of the trichlorethylene or trichlorethylene-containing condensate obtained is a problem, and the regeneration of activated carbon also requires thermal costs and labor. Another method is to add oxides such as hydrogen peroxide to split the trichlorethylene, but it is not easy to reduce the trichlorethylene after treatment to the order of ppm. Attempts have been made to use an oxidizing agent and irradiate ultraviolet rays, but it is difficult to reduce the trichlorethylene saturation concentration in the wastewater before treatment, which is about 1000 pp-, to the order of ρpb after treatment.

[Problem that the invention seeks to solve]

The purpose of this invention is to solve the problems caused by these conventional methods, and even after treatment with trichlorethylene saturation concentration as high as 1000 pp- in wastewater before treatment (1)
I) It is important to provide a wastewater treatment method that can reduce the amount of residual trichlorethylene to an ultra-trace amount of b order in a short time and does not produce secondary by-products or cause secondary pollution due to the troublesome post-treatment.

[Means to solve the problem]

In order to achieve the above objects, this invention adds hydrogen peroxide to trichlorethylene-containing wastewater and irradiates it with ultraviolet rays, first fractionates the trichlorethylene to a few pp-, and then activates this wastewater. It is characterized by adsorbing residual trichlorethylene with activated carbon fibers.

Hereinafter, in order to easily understand the means of the present invention, examples of embodiments will be described based on the drawings.

FIG. 1 is a flowchart of a preferred example of the present invention. First, in the first step, raw wastewater containing trichlorethylene in a saturated state, that is, approximately 11,000 pp+, is transferred from the wastewater inflow pipe 1 to the decomposition tank 2. While irradiating ultraviolet rays with the first ultraviolet lamp 3 immersed in this wastewater, hydrogen peroxide solution is added from the hydrogen peroxide tank 4 to 1.0 mole of trichlorethylene contained in the wastewater. ．．
About 2 to 3.5 moles are added and mixed using the stirrer 5 to decompose trichlorethylene. The decomposition at this time is thought to be based on the following reaction formula, and the theoretical equivalent amount of hydrogen peroxide to 1 mole of trichlorethylene is 3 moles, but hydrogen peroxide is added in slight excess to accelerate the reaction and as described below. This contributes to the decomposition of residual trichlorethylene in the second step.

CgHC12+ 311xO□→ 2COg + 3H
As the C+ + 2HtO decomposition reaction progresses, carbon dioxide gas is generated, which is discharged to the outside from the carbon dioxide gas discharge pipe 6, and the pH of the waste water in the decomposition tank 2 is adjusted to pH by the generated hydrochloric acid.
Since the H total 9 gradually decreases, 0 decomposition is usually done by adding an alkaline aqueous solution little by little from the alkali tank 7 via the pH solenoid valve 8 to adjust the pH to around 7.
In ~3 hours, the trichlorethylene count decreases to ppm.

The decomposition reaction of trichlorethylene progresses only slightly with hydrogen peroxide alone even over a long period of time, and the effect is insufficient even with ultraviolet rays alone.
There is almost no industrial meaning when the purpose is to reduce the amount of trichlorethylene to a level on the order of to.

Lichlorethylene concentration can be reduced rapidly.

The ultraviolet lamp used here may be a commonly used one, and may be a mercury lamp with a dominant wavelength of 254 ns. 1~2X1 at the liquid contact part on the outside of the lamp
It may be about 0' μW/cd.

Further, the temperature of the liquid in the decomposition tank 2 may be room temperature, but since this decomposition reaction has a relatively large temperature dependence, it is better to use an appropriate heat source such as waste steam if available.

Next, in the second step, the wastewater with hydrogen peroxide remaining in the trichlorethylene content of several ppm obtained in the first step is removed from the activated carbon fiber adsorption tube of the decomposition and absorption device 10.
1, the second ultraviolet lamp 12 irradiates the ultraviolet rays. This activated carbon fiber adsorption tube 11 has 1500 to 2
Activated carbon fibers having a large adsorption surface area of 0.000 po/g are packed in, for example, a block shape and replaceable to form the activated carbon fiber adsorption layer 13. The irradiation intensity of the ultraviolet lamp and ultraviolet rays may be the same as in the first step, and the ultraviolet lamp is the same in the first step, but it may be divided into multiple units depending on the amount of ultraviolet irradiation. In order to effectively utilize the ultraviolet rays in the decomposition and adsorption device 1O, the distance between the second ultraviolet lamp and the activated carbon fiber adsorption tube 11 should be as small as possible, and the distance between the second ultraviolet lamp and the activated carbon fiber adsorption tube 11 should be kept as small as possible to improve the reflection of the ultraviolet rays. It is desirable to provide a reflective wall 14 to surround the second ultraviolet lamp and the activated carbon fiber adsorption tube 11 so that the entire surface is irradiated with ultraviolet rays. This is a cross-sectional view of the ultraviolet lamp 12 in order to effectively utilize ultraviolet light.
A plurality of activated carbon fiber adsorption tubes 11 are arranged concentrically around the center, and waste water can be passed through these activated carbon fiber adsorption tubes in series or in parallel.

In this way, in the decomposition and adsorption device 10 constructed, trichlorethylene is excited again by ultraviolet rays and at the same time is oxidized and decomposed by hydrogen peroxide on the surface of the activated carbon fiber, and a small amount of undecomposed trichlorethylene is absorbed into the activated carbon. It is adsorbed on fibers, and the concentration of trichlorethylene in wastewater is PI
)b order and is discharged to the outside of the system through the discharge pipe 15. Trichlorethylene adsorbed on activated carbon fibers continues to decompose due to hydrogen peroxide and ultraviolet rays.
The adsorption capacity of the activated carbon fibers is regenerated and the life of the activated carbon fibers is maintained.

Example 3.0g of trichlorethylene was mixed and dissolved in 3000ml of distilled water, and then saturated trichlorethylene water (1000pp
The sample solution was determined as m concentration). This aqueous solution was placed in a sealed flask and irradiated with an external irradiation type low pressure mercury lamp with an output of 10W at a temperature of 30°C at an intensity of 1.5 x 10'uW/c.
j, 35% while irradiating ultraviolet rays with a main wavelength of 254n-
Hydrogen peroxide solution was added at a ratio of 3.5 moles of hydrogen peroxide to 1 mole of trichlorethylene, and the mixture was stirred with a stirrer. During the course of the reaction, 5% caustic soda was added dropwise from the view left while monitoring with a pFi meter to maintain the pl at approximately pl+7. Sampling was performed every 10 minutes and analyzed by liquid chromatography. The results of the decomposition reaction in this first step are shown in Table 1 below.

Table 1 Next, as a second step, activated carbon fibers were filled in a fluororesin U-shaped tube with an ultra-thin wall thickness of 20 mm in diameter and 400 cm in length and good UV transmission. The aqueous solution containing ittppm of trichlorethylene obtained in the step was heated to SV -5.
A mercury lamp, the same as that used in the first step, was placed between the vertical portions of this U-shaped tube and irradiated with ultraviolet rays.

Trichlorethylene in the aqueous solution discharged from the U-shaped tube was analyzed by gas chromatography using the headspace method and found to be 20 ppb, which was below the wastewater regulation value of 30 pHb.

〔Effect of the invention〕

According to this invention, as explained above, wastewater containing trichlorethylene at a high concentration in the form of a saturated solution is oxidized and decomposed by ultraviolet rays and hydrogen peroxide to reduce the trichlorethylene to ppwr order, and then By oxidatively decomposing the remaining trace amount of trichlorethylene on the surface of the activated carbon fiber using ultraviolet rays and hydrogen peroxide, it is possible to reduce the concentration to an ultra-trace amount on the order of PPb, thereby achieving strict wastewater standard values. Also, according to this method, the processing time is short,
It is convenient because expensive activated carbon fiber adsorbents can be used continuously while being regenerated and activated.Furthermore, the oxidative decomposition products of trichlorethylene are harmless, there is no risk of secondary pollution, and there is no need for post-processing. It is also an excellent method for preventing pollution.

It goes without saying that the present invention is applicable not only to trichlorethylene but also to the oxidative decomposition of similar halogenated hydrocarbon compounds.

[Brief explanation of the drawing]

FIG. 1 shows a flow sheet showing one embodiment of this invention,
Further, FIG. 2 is a plan sectional view of the decomposition and adsorption device shown in FIG. 1. 1... Waste water inflow pipe 2... Decomposition tank 3... First ultraviolet lamp 4... Hydrogen peroxide tank 5... Stirrer 6... Carbon dioxide gas discharge pipe 7... Alkali tank 8... pH solenoid valve 9... pH meter lO... decomposition adsorption device 11... activated carbon fiber adsorption tube 12... second ultraviolet lamp 13... activated carbon fiber adsorption layer 14...・Reflection wall 15...discharge pipe

Claims (1)

[Claims] In the treatment of wastewater containing trichlorethylene in a saturated state, the first step is to add hydrogen peroxide to the wastewater and decompose the trichlorethylene by irradiating it with ultraviolet light, and the wastewater treated in the above step is further processed in the first step. A method for treating trichlorethylene-containing wastewater, characterized in that the second step is to decompose trichlorethylene by passing it through an activated carbon fiber adsorption layer while irradiating ultraviolet rays under residual hydrogen peroxide.