A method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III)

Abstract

The application discloses a method for repairing chlorobenzene contaminated groundwater in-situ by using soluble Mn(III), and belongs to the technical field of environmental pollution repair, and comprises the following steps: construction of an in-situ injection system, preparation of a repair reagent, rapid removal of chlorobenzene, and continuous mineralization of degradation products. The soluble Mn(III) generated by a permanganate / bisulfite (PM / BS) process is selected as the repair reagent, the chlorobenzene pollutants are rapidly and efficiently degraded through an electrophilic substitution mechanism, the PM process is coupled, the continuous mineralization of intermediate products is realized, and the complete elimination of the chlorobenzene pollutants in the groundwater is achieved. The technical method is simple and practical, the process is green, the treatment effect is complete and not prone to rebound, the cost is relatively low, the method is beneficial to large-scale promotion, and the method has remarkable economic, environmental and social effects.

Description

TECHNICAL FIELD

[0001] The application relates to a method for in-situ remediation of chlorobenzene contaminated groundwater by using soluble Mn (III), and belongs to the technical field of groundwater pollution remediation. BACKGROUND

[0002] Chlorobenzenes (CBs) include 12 homologues, namely chlorobenzene, dichlorobenzene, trichlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene, which are widely used as important chemical raw materials in the production of dyes, medicines, pesticides, rubber, paint, cleaning supplies, building materials and the like. China is the largest chlorobenzene producer in the world, and the production capacity and output of chlorobenzene series products rank first in the world. Due to the "leakage" in the production, use, transportation and storage process and the unreasonable discharge of waste, chlorobenzenes enter the environment, polluting the soil and groundwater. Chlorobenzenes have a wide pollution range, high toxicity, are easy to accumulate in organisms and have "three effects" (teratogenic, carcinogenic and mutagenic), and have been listed as priority controlled pollutants in many countries and regions including the United States, China and the European Union. Chlorobenzenes are frequently detected in the soil and groundwater environment in China, especially in chemical contaminated sites, and the concentration of chlorobenzenes can reach several hundred or even several thousand mg / kg or mg / L.

[0003] Due to the strong electronegativity of chlorine atoms, the electron cloud density on the large pi bond of the benzene ring is reduced, so that the chemical properties of chlorobenzenes are extremely stable and difficult to degrade. With the increase of chlorine substituents, the stability is enhanced and the reactivity is decreased. Chlorobenzenes have strong resistance to photodegradation and chemical decomposition under natural environmental conditions. Chlorobenzenes are difficult to be oxidized and reduced, and only a small amount of photolysis and microbial degradation exists in the natural environment. The special oligotrophic and lightless environment of the underground environment leads to the fact that it is extremely difficult to complete ecological restoration through natural attenuation once the groundwater is contaminated.

[0004] At present, a variety of methods have been developed for in-situ treatment of chlorobenzene in groundwater. However, due to the structure and characteristics of chlorobenzene, physical remediation methods cannot completely remove chlorobenzene, and chlorobenzene is not degraded, which requires high energy consumption equipment, high cost and high operation difficulty. The biological remediation period is long, and chlorobenzene is toxic to microorganisms, so it is very difficult to cultivate and select strains. In-situ advanced oxidation technology is a technology that uses HO· and SO4 -· For the main active group degradation of organic matter, while the traditional Fenton and persulfate process can not be effectively degraded, the cost of using palladium as catalyst is high. The Fenton-like reaction system has many defects in the in-situ remediation of groundwater, such as small pH range, easy introduction of other pollutants, low H2O2 utilization rate, low in-situ generation rate, and insufficient degradation of pollutants under natural conditions of groundwater. Persulfate process needs to be activated, and heat activation needs to heat the water temperature to a high temperature (such as above 50℃), and alkali activation needs to adjust the pH to above 12, and the sulfuric acid produced after the oxidation of persulfate is decomposed, which causes the acidification of groundwater, the release of metals in minerals, and the secondary pollution. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a simple and practical method for in-situ remediation of chlorobenzene contaminated groundwater, which is green in process, complete in treatment effect, and relatively low in cost. The soluble Mn(III) generated by PM / BS process is used as a strong electrophile to rapidly and effectively degrade chlorobenzene through electrophilic substitution mechanism, and then PM and PM / BS process are coupled to further mineralize the degradation products into H2O and CO2, achieving effective degradation of chlorobenzene.

[0006] Mn(VII)+4HSO3 - →Mn(III)+4SO3 - +4H + (1)

[0007] Mn(VII)+4SO3 2- →Mn(III)+4SO3 - (2)

[0008] To achieve the above purpose, the present application adopts the following technical solutions:

[0009] A. Construction of in-situ injection system

[0010] According to the source characteristics of chlorobenzene pollutants in groundwater and the hydrogeological conditions of the site, a waterproof curtain is laid around the pollution area to the depth of the underground aquifer. Injection wells are laid in the pollution source and pollution plume area, and pumping wells are laid downstream of the pollution area.

[0011] B. Preparation of remediation agent

[0012] High manganate PM and bisulfite BS are dissolved in water according to the molar concentration ratio of 1:2-10 to react to generate a soluble Mn(III) remediation agent. High manganate PM is dissolved in water to prepare a mineralization remediation agent, and they are prepared in the agent tank respectively.

[0013] C. Rapid removal of chlorobenzene

[0014] The soluble Mn(III) remediation agent prepared in step B is injected under pressure into the chlorobenzene-contaminated groundwater area through injection wells. An intermittent injection method is used, with the injection volume and frequency determined based on the chlorobenzene pollution load in the groundwater of the injection well area. Each injection volume is 0.5–3.0% of the contaminated groundwater volume, and the injection time is 60–180 minutes. Downstream, groundwater is pumped out through pumping wells and reinjected upstream to create water circulation and enhance the mixing reaction effect. Soluble Mn(III) reacts with chlorobenzene to generate easily mineralized degradation intermediates. The soluble Mn(III) remediation agent is circulated and injected multiple times until the chlorobenzene concentration in the groundwater reaches the standard. Afterward, pumping operations are stopped, and the groundwater is allowed to mature for 2–10 days.

[0015] D. Continuous mineralization of degradation products

[0016] The mineralization remediation agent prepared in step B is injected under pressure into the groundwater area treated in step C through injection wells. An intermittent injection method is used, with the injection volume and frequency determined based on the concentration load of degradation products in the groundwater of the injection well area. The single injection volume is 1.0–4.0% of the contaminated groundwater volume, and the injection time is 60–180 minutes. Pumping wells are activated to maintain groundwater flow and enhance the mixing reaction. PM further oxidizes and degrades the products, achieving mineralization removal of pollutants. The mineralization agent is circulated and injected multiple times until the concentration of intermediate degradation products in the groundwater reaches the target. Afterward, pumping operations are stopped, and the groundwater is treated for 1–5 days.

[0017] Furthermore, regarding the layout of the injection wells, within the pollution source area, the spacing between the injection wells is set at 3–10 m, and the locations are arranged in an equilateral triangle pattern; within the pollution plume area, every 100–400 m 2 An injection well is installed inside, with a well diameter of 100–300 mm.

[0018] Furthermore, the pH value of the polluted groundwater is 4 to 8.

[0019] Furthermore, the total molar concentration of the permanganate PM and bisulfite BS in the soluble Mn(III) remediation agent in water is 4 to 20 times, preferably 5 to 12 times, the total molar concentration of chlorobenzene pollutants in groundwater; the molar ratio of permanganate PM to bisulfite BS in the soluble Mn(III) remediation agent is 1:4 to 6, preferably 1:5.

[0020] Further, the chlorobenzene includes one or more of chlorobenzene (CB), dichlorobenzene (DCB) isomers (1,2-DCB, 1,3-DCB and 1,4-DCB), trichlorobenzene (TCB) isomers (1,2,3-TCB, 1,2,4-TCB and 1,3,5-TCB), tetrachlorobenzene (TeCB) isomers (1,2,3,4-TeCB, 1,2,3,5-TeCB and 1,2,4,5-TeCB) and pentachlorobenzene (PeCB), without hexachlorobenzene (HCB), and the total concentration of which is less than 250 μmol / L.

[0021] Further, the multiple injections in step C are selected to be 2 to 4 injections.

[0022] Further, the degradation intermediates in step C include one or more of p-chlorophenol, o-chlorophenol, p-dihydroxybenzene and p-benzoquinone, and the total concentration of which is 20 to 150 μmol / L.

[0023] Further, the molar concentration of permanganate PM in the mineralization repair agent prepared in step B is 1.5 to 10 times, preferably 2.5 to 5 times, the total molar concentration of the degradation intermediates generated in step C.

[0024] Further, the multiple injections in step D are selected to be 2 to 4 injections.

[0025] Compared with the prior art, the present application has the following advantages and effects:

[0026] 1. Compared with the physical repair method, the present application does not need to invest high-energy-consuming equipment and can directly degrade chlorobenzene; compared with biological repair, the degradation efficiency is higher. And the degradation product is chlorophenol which is easy to be oxidized by active substances, facilitating further mineralization treatment, and the complete degradation of chlorobenzene can be completed.

[0027] 2. Compared with the Fenton-like and persulfate processes, the present application can effectively treat chlorobenzene pollutants under a wide range of pH conditions, at room temperature, and has a wide range of applications. And it does not need to invest catalysts, does not produce secondary pollution, has a simple process, is easy to control, has low cost, and is conducive to large-scale promotion.

[0028] 3. In the PM / BS process of the present application, chlorobenzene with 5 or fewer chlorine atoms can be quickly removed, and after multiple PM / BS process treatments, the degradation rate of chlorobenzene is more than 95%. The process is green, the treatment effect is complete and is not easy to rebound. DETAILED DESCRIPTION

[0029] The present application will be further described below in conjunction with specific embodiments, which are only used to illustrate the present application and not to limit the scope of the present application.

[0030] Example 1

[0031] Taking a certain chemical plant in East China as an example, the main pollutants exceeding the standard in the groundwater are volatile organic pollutants, including benzene, chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB), and 1,4-dichlorobenzene (1,4-DCB). The chlorobenzene pollution source involves an area of 128 m 2 , and the pollution plume involves the entire plant area, involving an area of up to 926 m 2 . The pH value of the groundwater is 5.67-7.81, the underground saturated water layer is 5-10 m, the amount of groundwater to be treated is about 4630 m 3 , and the total organic carbon content ranges from 6.4 to 7.6 mg / L. The detected concentrations of groundwater pollutants are shown in Table 1.

[0032] Table 1: Detected concentrations of selected groundwater pollutants

[0033]

[0034]

[0035] A. Construction of in-situ injection system

[0036] According to the characteristics of the chlorobenzene pollutants in the groundwater and the hydrogeological conditions of the site, a waterproof curtain was arranged around the pollution area to a depth of the underground aquifer. In the pollution source area, the injection wells were arranged in the form of equilateral triangles with a spacing of 5 m, a total of 9 wells; the setting density in the pollution plume area was 200 m 2 , a total of 6 wells, 6 monitoring wells were arranged around the plant, and 4 pumping wells were arranged downstream of the pollution area, with a well diameter of 200 mm. In this case, the Geoprobe drilling equipment was used to inject the reagent into the underground saturated layer, the injection pump pressure was 20 MPa, and the injection flow rate was 18.0 L / min.

[0037] B. Preparation of remediation reagent

[0038] According to the chlorobenzene pollution load, soluble Mn(III) remediation reagent was prepared by reacting permanganate PM and bisulfite BS dissolved in water. The concentrations of permanganate PM and bisulfite BS prepared in water were 100 μmol / L and 500 μmol / L, respectively. Permanganate PM was dissolved in water to prepare a mineralization remediation reagent with a PM concentration of 100 μmol / L, and they were respectively prepared in the reagent tank.

[0039] C. Rapid removal of chlorobenzene

[0040] The soluble Mn(III) remediation agent prepared in step B was injected into the chlorobenzene-contaminated groundwater area through injection wells under pressure, and the intermittent agent injection mode was adopted. The injection amount and injection frequency were determined according to the chlorobenzene pollution load of the groundwater in the area where the injection well was located. The single injection amount was 46.3 m 3 , and the time was 140 min. Downstream, groundwater was extracted by pumping wells and was recharged to the upstream to form water flow circulation to enhance the mixing reaction effect. Four extraction pumps were arranged, and the total amount of water extraction per day was 140-160 m 3 . The soluble Mn(III) reacted with chlorobenzenes to generate degradation intermediates that were easy to mineralize. The soluble Mn(III) remediation agent was injected into the groundwater for 3 cycles, and the chlorobenzene concentration reached the standard, and the degradation rate reached more than 95%. Then, the pumping well extraction operation was stopped, and the groundwater was maintained for 10 days. The concentration of phenolic compounds was measured to be in the range of 21.86-36.34 μmol / L.

[0041] D. Continuous mineralization of degradation products

[0042] The mineralization remediation agent prepared in step B was injected into the groundwater area after maintenance in step C through injection wells under pressure, and the intermittent agent injection mode was adopted. The injection amount and injection frequency were determined according to the concentration load of the degradation products of the groundwater in the area where the injection well was located. The single injection amount was 64.82 m 3 , and the time was 180 min. Downstream, groundwater was extracted by pumping wells and was recharged to the upstream to form water flow circulation to enhance the mixing reaction effect. Four extraction pumps were arranged, and the total amount of water extraction per day was 120-140 m 3 . PM further oxidized the degradation products to achieve the mineralization removal of pollutants. The mineralization agent was injected into the groundwater for 3 cycles, and the degradation intermediate concentration reached the standard, and the phenol was not detected. Then, the pumping well extraction operation was stopped, and the groundwater was maintained for 5 days, and the TOC concentration range was 2.4-2.8 mg / L. The detected concentration of the groundwater pollutants after remediation is shown in Table 2.

[0043] Table 2: Detected concentration of selected groundwater pollutants after remediation

[0044]

Claims

1. A method for in-situ remediation of chlorobenzenes contaminated groundwater by soluble Mn(III), characterized in that: A. Construction of the system for in-situ injection According to the characteristics of the source of groundwater chlorobenzenes pollution and the hydrogeological conditions of the site, a waterproof curtain is laid around the contaminated area to the depth of the underground aquiclude; injection wells are laid in the pollution source and pollution plume area, and pumping wells are laid downstream of the pollution area; B. Preparation of the remediation agent The permanganate PM and bisulfite BS are dissolved in water according to the molar concentration ratio of 1:2-10 to generate the soluble Mn(III) remediation agent, the permanganate PM is dissolved in water to generate the mineralized remediation agent, and they are prepared in the agent tank respectively; C. Rapid removal of chlorobenzenes The soluble Mn(III) remediation agent prepared in step B is injected into the chlorobenzenes contaminated groundwater area through the injection well under pressure, an intermittent agent injection method is adopted, and the agent injection amount and injection frequency are determined according to the chlorobenzenes pollution load of the groundwater in the area where the injection well is located; the single injection amount is 0.5-3.0% of the volume of the contaminated groundwater, and the time is 60-180 min; the downstream pumping well is used to extract groundwater for recharging to the upstream to form a water flow circulation to enhance the mixing reaction effect; the soluble Mn(III) reacts with chlorobenzenes to generate degradation intermediates that are easy to mineralize, and the soluble Mn(III) remediation agent is injected into the groundwater for multiple cycles until the concentration of chlorobenzenes in the groundwater meets the standard; then, the pumping well extraction operation is stopped, and the groundwater is maintained for 2-10 days; the chlorobenzenes pollutants include one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, tetrachlorobenzene, and pentachlorobenzene, and the total concentration is less than 250 μmol / L; the total molar concentration of the permanganate PM and bisulfite BS of the soluble Mn(III) remediation agent prepared in water is 4-20 times that of the total molar concentration of chlorobenzenes pollutants in the groundwater; the molar concentration ratio of the permanganate PM to the bisulfite BS in the soluble Mn(III) remediation agent is 1:4-6; the degradation intermediates in step C include one or more of p-chlorophenol, o-chlorophenol, p-benzene diol, and p-benzene quinone, and the total concentration is 20-150 μmol / L; D. Continuous mineralization of the degradation products The mineralized remediation agent prepared in step B is injected into the groundwater area after maintenance in step C through the injection well under pressure, an intermittent agent injection method is adopted, and the agent injection amount and injection frequency are determined according to the concentration load of the degradation products of the groundwater in the area where the injection well is located; the single injection amount is 1.0-4.0% of the volume of the contaminated groundwater, and the time is 60-180 min; the pumping well is opened to extract to keep the groundwater flowing to enhance the mixing reaction effect; the PM further oxidizes the degradation products to achieve the mineralization removal of the pollutants; the mineralized agent is injected into the groundwater for multiple cycles until the concentration of the degradation intermediates meets the standard; then, the pumping well extraction operation is stopped, and the groundwater is maintained for 1-5 days. The pH value of the contaminated groundwater is 4-8. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 1, characterized in that, The injection well is arranged at a distance of 3-10 m in the pollution source area and arranged in the form of equilateral triangle; and in the pollution plume area, one injection well is arranged every 100-400 m 2 with a well diameter of 100-300 mm.

3. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 1, characterized in that, ​ 4. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 1, characterized in that, The total molar concentration of permanganate PM and bisulfite BS of the soluble Mn(III) remediation agent prepared in water is 5-12 times of the total molar concentration of chlorobenzene pollutants in the groundwater; the molar concentration ratio of permanganate PM to bisulfite BS in the soluble Mn(III) remediation agent is 1:

5.

5. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 1, characterized in that, The multiple injections in step C are selected to be 2-4 injections.

6. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 1, characterized in that, The molar concentration of permanganate PM in the mineralization remediation agent prepared in step B is 1.5-10 times of the total molar concentration of degradation intermediates generated in step C.

7. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 6, characterized in that, The molar concentration of permanganate PM in the mineralization remediation agent prepared in step B is 2.5-5 times of the total molar concentration of degradation intermediates generated in step C.

8. The method for in-situ remediation of chlorobenzene contaminated groundwater using soluble Mn(III) according to claim 1, characterized in that, The multiple injections in step D are selected to be 2-4 injections.

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