A Detection Method for Secondary Pollutants of Chlorinated Hydrocarbons during a Chemical Oxidation Process

Abstract

The present invention relates to the field of environmental remediation. The present invention provides a method for detecting secondary pollutants of chlorinated hydrocarbons in a chemical oxidation process, and the specific steps are as follows: Step 1: Before remediating a contaminated site, a well is constructed in the target area for remediation to collect a certain volume of contaminated groundwater. The pollution of no brominated hydrocarbons in the site and the background value of inorganic bromide ions in the underground environment are determined by GCMS full scan and determination of the background bromide ion concentration in the underground environment; Step 2: brominated inorganic salts are added to the underground environment through injection wells or injection equipment; Step 3: After the injection of the oxidation remediation agent is completed, a GCMS full scan is performed to confirm the types of newly generated brominated hydrocarbons in the site after maintenance; Step 4: Based on the principle that the reaction properties of elements of the same group are similar, it is determined whether there is secondary pollution of chlorinated hydrocarbons with the same structure as the newly generated brominated hydrocarbons on site. The detection method provided by the present invention can overcome the background interference of the polluted site, the results are accurate, the price is low, and it is suitable for polluted sites.

Description

Technical Field

[0001] The present invention relates to the field of environmental remediation, and particularly to a method for detecting secondary pollution during the remediation of chlorinated hydrocarbon-contaminated soil or groundwater. Background Art

[0002] In recent years, with the development of the chemical industry, a large number of chlorinated hydrocarbons have been used as solvents or reaction intermediates in the production process. Typical solvents include chlorobenzene, trichloroethylene, tetrachloroethylene, dichloroethane, etc. These solvent wastewaters are characterized by high toxicity, difficult degradation, and strong stability. They are often listed as typical pollutants during the remediation of contaminated sites.

[0003] In-situ chemical oxidation is a non-selective remediation method. Chemical agents are injected into the ground in-situ and react with chlorinated hydrocarbon pollution in the underground environment to convert harmful chlorinated organic compounds into inorganic substances. A large amount of chemical agents are introduced during the remediation process, and it is inevitable that certain side reactions occur during the remediation process, resulting in the generation of some by-products. Such by-products may pose certain hazards to the human body.

[0004] It is clearly stated in "HJ25.4-2019: Technical Guidelines for Soil Remediation of Construction Land" that secondary pollution prevention and control should be considered during the project implementation process. Identification methods for secondary pollution include direct determination method and isotope tracing method. Due to the existence of a large background value of chlorinated pollutants in chlorinated hydrocarbon-contaminated groundwater or soil, when directly measuring chlorinated pollutants in groundwater, it is often impossible to determine whether the chlorinated substance is secondary pollution generated during the remediation, which has certain limitations; for the isotope tracing method, through radioactive nuclides (or stable nuclides) and their compounds, the chemical properties and biological properties between them and the corresponding ordinary elements and their compounds existing in nature are the same, only with different nuclear physical properties to identify side reactions and secondary pollutants. However, the required isotope agents are expensive and have poor economy. Therefore, it is difficult to detect and distinguish chlorinated hydrocarbons generated by side reactions during the remediation process. Summary of the Invention

[0005] In order to solve the problem that it is not easy to detect and distinguish chlorinated hydrocarbons generated by side reactions during the remediation process in the prior art, the present invention provides a method for detecting chlorinated hydrocarbon secondary pollutants during the chemical oxidation process, and the specific steps are as follows:

[0006] Step 1: Before the remediation of the contaminated site, wells are built in the target area to be remediated to sample and collect a certain volume of contaminated groundwater. Through GCMS full scan and determination of the background bromide ion concentration in the underground environment, it is determined that there is no brominated hydrocarbon pollution in the site and the background value of inorganic bromide ions in the underground environment.

[0007] Step 2: Add brominated inorganic salts into the underground environment through an injection well or an injection device.

[0008] Step 3: After the injection of the oxidative remediation agent is completed, perform curing and then conduct a full-scan by GCMS to confirm the types of newly generated bromohydrocarbons in the site.

[0009] Step 4: According to the principle that the reaction properties of homologous elements are similar, determine whether there is secondary pollution of chlorohydrocarbons with the same structure as the newly generated bromohydrocarbons on-site.

[0010] Specifically, in Step 2 of the method, the brominated inorganic salt is preferably sodium bromide or potassium bromide.

[0011] Preferably, the brominated inorganic salt added in Step 2 of the method is a 5 g / L sodium bromide solution.

[0012] Preferably, the curing time after the injection of the oxidative remediation agent is completed in Step 3 of the method is 3 - 7 days.

[0013] Preferably, the amount of the 5 g / L sodium bromide solution added in Step 2 of the method is 5 / 10000 - 8 / 10000 of the volume of the polluted site.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. By using the detection method of chlorohydrocarbon secondary pollutants in the chemical oxidation process provided by the present invention, background interference in the polluted area can be overcome.

[0016] 2. The detection method of chlorohydrocarbon secondary pollutants in the chemical oxidation process provided by the present invention has accurate results, low cost, and can be applied to polluted sites. Description of the Drawings

[0017] Figure 1 is the reaction formula for determination according to the principle that the reaction properties of homologous elements are similar in a specific embodiment of the present invention;

[0018] Figure 2 is the GCMS scan spectrum in a specific embodiment of the present invention;

[0019] Figure 3 is the structure of the brominated product and the corresponding chlorohydrocarbon secondary pollutants generated after injecting a certain amount of remediation agent in a specific embodiment of the present invention. Detailed Embodiments

[0020] The technical solutions of the present invention will be further described below in conjunction with specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention.

[0021] Example 1

[0022] In a 2000 m 2 chlorobenzene-contaminated site, monitoring wells were established. After sampling and analysis, it was found that the background value of bromide ion concentration in the on-site groundwater was 0 mg / L. Through full-scan GCMS, it was found that the main pollutants on-site were chlorobenzene and dichloromethane. 1 m 3 of sodium bromide solution with a concentration of 5 g / L was added by in-situ injection through injection wells. Subsequently, the site was repaired by chemical oxidation. The groundwater of the site was sampled and tested 3 to 7 days after maintenance.

[0023] Through full-scan GCMS determination of the repaired groundwater, it was found that the contents of the main pollutants chlorobenzene and dichloromethane were significantly reduced and dibromodichloromethane (as shown on the left) was produced. During the chemical oxidation repair process, a large amount of organic chloride ions were converted into inorganic chloride ions, and the chemical reaction properties of elements in the same group are similar. The above GCMS identification results can help us determine that the main secondary pollutant is chloroform (as shown on the right) among many side reactions. Figure 3 The derivation process of chloroform as the secondary pollutant based on the GCMS results is as shown in Figure 3 the right: During the process of site repair by chemical oxidation, chloroform radicals are produced from chloroform under the action of free radicals. In the second reaction, due to the instability of the free radicals, dibromodichloromethane radicals are generated under the action of sodium bromide, and disproportionation reactions occur under the action of hydroxyl radicals or other free radicals to form dibromodichloromethane. Based on this reaction process, it can be concluded that since chloroform is not among the initial pollutant types, there is a certain concentration of chloroform by-products in the background when dibromodichloromethane is produced.

[0024] Example 2 Figure 1 In a 1000 m

[0025] chlorobenzene-contaminated site, the bromide ion concentration in the site was 0. 0.8 m

[0026] of sodium bromide solution with a concentration of 5 g / L was added through injection wells. Subsequently, the site was repaired by chemical oxidation. After 3 to 7 days of maintenance, trace amounts of dibromodichloromethane were detected in the site groundwater by full-scan GCMS. It can be concluded that chloroform is the secondary pollution produced by side reactions during the site repair process. 2 The GCMS scanning spectrum is as shown in 3 where the lower spectral line is the site pollutant before repair and the upper spectral line is the site pollutant after repair. It was found in the figure that dibromodichloromethane exists in the reaction products (as shown in

[0027] the figure, and Figure 2 as shown on the left). Figure 3As shown on the left side), according to the same judgment idea as in Example 1, it is determined that chloroform (such as Figure 3 as shown on the right side) is a by-product of the site.

[0028] The above descriptions of the embodiments of the present invention are for better understanding of the present invention, which are merely exemplary and not intended to limit the present invention. It should be noted that in the above descriptions, the features shown for one embodiment can be used in the same or similar manner in other embodiments, combined with the features in other embodiments, or replace the features in other embodiments. Those skilled in the art can understand that, without departing from the concept of the present invention, various changes and modifications made to the above-described embodiments all fall within the scope of protection of the invention.

Claims

1. A method for detecting secondary pollutants of chlorinated hydrocarbons during a chemical oxidation process, characterized in that, It includes the following steps: Step 1: Before the remediation of the contaminated site, wells are built in the target area to be remediated to sample a certain volume of contaminated groundwater. Through GCMS full scan and determination of the background bromide ion concentration in the underground environment, it is determined that there is no pollution of brominated hydrocarbons in the site and the background value of inorganic bromide ions in the underground environment; Step 2: Add brominated inorganic salts into the underground environment through injection wells or injection equipment; Step 3: After the injection of the oxidation remediation agent is completed, conduct a GCMS full scan after curing to confirm the types of newly generated brominated hydrocarbons in the site; Step 4: According to the principle that the reaction properties of homologous elements are similar, determine whether there is secondary pollution of chlorinated hydrocarbons with the same structure as the newly generated brominated hydrocarbons on site.

2. The detection method of chlorinated hydrocarbon secondary pollutants in the chemical oxidation process according to claim 1, wherein: The brominated inorganic salt in step 2 of the method is sodium bromide or potassium bromide.

3. The detection method of chlorinated hydrocarbon secondary pollutants in the chemical oxidation process according to claim 1 or 2, characterized in that: The brominated inorganic salt added in step 2 of the method is a 5 g / L sodium bromide solution.

4. The detection method of chlorinated hydrocarbon secondary pollutants in the chemical oxidation process according to claim 3, characterized in that: The amount of the 5 g / L sodium bromide solution added in step 2 of the method is 5 / 10000 - 8 / 10000 of the volume of the contaminated site.

5. The detection method of chlorinated hydrocarbon secondary pollutants in the chemical oxidation process according to claim 1 or 2, characterized in that: The curing time after the injection of the oxidation remediation agent is completed in step 3 of the method is 3 - 7 days.

6. The detection method of chlorinated hydrocarbon secondary pollutants in the chemical oxidation process according to claim 3, characterized in that: The curing time after the injection of the oxidation remediation agent is completed in step 3 of the method is 3 - 7 days.

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