A method for removing emerging contaminants from groundwater by in-situ reaction zone injection

Abstract

The application discloses a method for removing new pollutants in groundwater by injecting in-situ reaction zone, and belongs to the field of groundwater pollution remediation of contaminated sites. The method comprises the following steps: (1) preparing a solid particle catalyst slurry; (2) preparing an oxidizing agent solution; and (3) synchronously injecting the catalyst slurry obtained in the step (1) and the oxidizing agent solution obtained in the step (2) into an aquifer, respectively, so that the catalyst slurry and the oxidizing agent solution react in a water environment to form an in-situ reaction zone. The method uses a non-dissolved iron-manganese catalyst to prepare the catalyst slurry, avoids the early dissolution of the iron-manganese catalyst in water to generate ferrous ions, avoids the early activation of persulfate to cause the instantaneous generation of a large number of free radicals and cause self-annihilation reaction, and causes the loss of the oxidizing agent, so that the utilization rate of the oxidizing agent is effectively improved, and the cost of the reagent is saved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of contaminated site groundwater pollution remediation, and relates to a method for removing new pollutants in groundwater by injecting an in-situ reaction zone. BACKGROUND

[0002] New pollutants refer to a general term of chemical substances that can be detected in the environment and natural ecosystems, and can bring greater risks and hidden dangers to human health and environmental safety even at low doses. The new pollutants widely concerned at home and abroad mainly include persistent organic pollutants, endocrine disruptors, antibiotics, microplastics and the like controlled by international conventions, and generally have characteristics such as serious harm, relatively hidden risk, environmental persistence, wide source and complex directness. The new pollutants have characteristics such as biological toxicity, environmental persistence and biological accumulation, but have not been included in management or existing management measures are insufficient, and are relatively new compared with traditional pollutants that have been regulated. The new pollutants entering the groundwater pollute the water resources, and the characteristics of low dose and high toxicity pose potential harm to the ecological environment and human health. Therefore, it is of great significance to remove the new pollutants in the groundwater to reduce or eliminate the harm caused by water pollution.

[0003] In-situ chemical oxidation (ISCO) technology is a method for in-situ treatment of soil and groundwater pollution at a contaminated site, which injects oxidants such as permanganate, persulfate, hydrogen peroxide and ozone into the contaminated area to degrade organic pollutants by chemical oxidation reaction and produce harmless substances. This method can avoid the pumping treatment process required for ex-situ remediation, as well as the process of excavating soil to install a remediation reaction wall, thereby effectively reducing the remediation cost and reducing environmental disturbance, and has been considered as a highly potential groundwater new pollutant remediation technology.

[0004] Persulfate is a commonly used oxidant in ISCO technology, but its low oxidation potential and chemical stability limit its oxidation ability for some refractory organic matter, so specific activation technology is needed to generate free radical species with stronger oxidation ability. Iron-manganese catalyst is a catalyst used to promote chemical reactions, which is composed of iron and manganese metals and has high catalytic activity and stability, and can be used for various reaction types, for example, it can be used to catalyze oxidation reaction, so the iron-manganese catalyst is an ideal catalyst in the in-situ chemical oxidation technology. However, since the divalent iron ion formed by dissolving the iron-manganese catalyst in water reacts very quickly with persulfate, when the solution form of the iron-manganese catalyst is injected into the aquifer through the injection well, it will rapidly react with persulfate at the outlet to generate a large amount of free radicals. However, this part of the free radicals has not yet diffused to the pollution plume, i.e. is annihilated, resulting in loss of persulfate. At this time, the demand for oxidants will increase significantly, the remediation cost will increase, and the remediation period will be prolonged.

[0005] Therefore, it is necessary to provide a method for removing new pollutants in groundwater by injecting in-situ reaction zone, which can effectively improve the degradation performance of persulfate on new pollutants, avoid the annihilation of free radical species and the loss of oxidant caused by the rapid activation of oxidant, thereby improving the efficiency of pollution remediation and saving the cost of reagent. SUMMARY

[0006] To overcome the problems in the background art, the present application uses a non-dissolved iron-manganese catalyst to prepare a catalyst slurry, which avoids the premature dissolution of iron-manganese catalyst in water to produce divalent iron ions, avoids the premature activation of persulfate to cause a large number of free radicals to be generated instantaneously, causing self-annihilation reaction and causing the loss of oxidant, so that the persulfate and the catalyst slurry can gradually undergo catalytic activation reaction during the migration of groundwater, slowly release free radicals (such as hydroxyl radicals, sulfate radicals, etc.), and form an in-situ reaction zone to oxidize and degrade the pollutants flowing through the in-situ reaction zone simultaneously. Therefore, the use efficiency of persulfate is improved, the degradation effect of oxidant is more fully exerted, and the cost of reagent is saved.

[0007] To achieve the above-mentioned object, the present application realizes the technical scheme as follows:

[0008] The method comprises the following steps:

[0009] (1) preparing a solid particle catalyst slurry: adding a non-dissolved iron-manganese catalyst into water and performing ultrasonic treatment at room temperature to obtain an iron-manganese catalyst slurry; dissolving xanthan gum powder in water and stirring to form a uniform milky white slurry, adding the milky white slurry into the iron-manganese catalyst slurry, and performing ultrasonic treatment to obtain a catalyst slurry;

[0010] (2) preparing an oxidant solution: dissolving persulfate powder in water to obtain an oxidant solution;

[0011] (3) synchronously injecting the catalyst slurry obtained in the step (1) and the oxidant solution obtained in the step (2) into an aquifer, respectively, and reacting the catalyst slurry and the oxidant solution in the water environment to form an in-situ reaction zone.

[0012] Preferably, the non-dissolved iron-manganese catalyst comprises an iron-manganese oxide catalyst.

[0013] Preferably, in the step (1), the solid-liquid ratio of the non-dissolved iron-manganese catalyst to water is 1.3 g: 1 L.

[0014] Preferably, in the step (1), the solid-liquid ratio of the xanthan gum powder to water is 1 mg: 1 ml.

[0015] As preferred, in the step (1), the volume ratio of the milky white slurry to the iron-manganese catalyst slurry is: milky white slurry: iron-manganese catalyst slurry = 3:10.

[0016] As preferred, in the step (1), the xanthan gum powder is dissolved in water at 60℃, and stirring is kept at 60℃.

[0017] As preferred, in the step (1), the ultrasonic treatment time is 20 min, the ultrasonic treatment power is 200 W, and the ultrasonic frequency is 40 KHz.

[0018] As preferred, in the step (2), the concentration of the oxidant solution is 100-200 times of the target pollutant concentration.

[0019] As preferred, in the step (3), the ratio of the catalyst slurry injection flow rate to the oxidant solution injection flow rate is 17:1.

[0020] As preferred, the specific preparation method of the non-dissolved iron-manganese catalyst is: first, dissolve ferrous sulfate heptahydrate and potassium permanganate in water to obtain an iron-manganese mixed solution, wherein the molar ratio of iron in ferrous sulfate heptahydrate to manganese in potassium permanganate is Fe:Mn=3:1, then add a 2 mol / L NaOH solution to the iron-manganese mixed solution until the liquid pH value reaches 7.0-8.0, stop adding the NaOH solution, then stir the liquid at a speed of 200 rpm for 60 min, then stand for 12 h, filter and wash the liquid, and dry the solid material obtained by filtration at 40℃ for 24 h, grind the dried solid material into powder to obtain the non-dissolved iron-manganese catalyst. During the addition of the NaOH solution, the liquid pH value needs to be detected, so the addition rate of the NaOH solution needs to be slow. At the same time, the amount of water can ensure that the added ferrous sulfate heptahydrate and potassium permanganate are completely dissolved, and the water can be excessive.

[0021] The beneficial effects of the present application are:

[0022] 1. The present application uses a non-dissolved iron-manganese catalyst to prepare a catalyst slurry, which avoids the premature dissolution of the iron-manganese catalyst in water to produce divalent iron ions, avoids the premature activation of persulfate to cause a large number of free radicals to be generated instantaneously, and thus causes self-annihilation reaction, thereby effectively improving the utilization rate of the oxidant, helping to improve the degradation rate of the target pollutant, and saving the cost of reagents.

[0023] 2. Since the non-dissolved iron-manganese catalyst is used to prepare the catalyst slurry in the application, the iron-manganese catalyst enters the aquifer in the form of solid particles during injection, which has a certain impact on the fluidity of the slurry. The application adds xanthan gum to prepare the catalyst slurry, which utilizes the lubricating effect of xanthan gum on the solid particles of the iron-manganese catalyst to reduce the negative impact of the solid particles on the injection of the catalyst slurry, and facilitates the smooth injection of the catalyst slurry into the aquifer and the movement in the aquifer.

[0024] 3. The application activates persulfate by using the iron-manganese catalyst to efficiently generate free radicals, thereby improving the oxidative degradation effect of persulfate on target pollutants.

[0025] 4. The application uses non-dissolved iron-manganese catalyst to catalytically activate persulfate. The iron-manganese catalyst can maintain stability in the form of solid particles in the groundwater seepage for a long period of time, and the iron-manganese ion leaching amount is kept at a low level, reducing or even avoiding the problem of secondary pollution of water body caused by the addition of iron-manganese catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The figure is a schematic diagram of the method of the application;

[0027] Figure 2 The figure is a schematic diagram of the sand column simulation experiment of the application;

[0028] Figure 3 The figure is a real photo of the sand column simulation experiment of the application;

[0029] Figure 4 The figure is an electron spin resonance magnetic spectrum of the application of the iron-manganese catalyst to activate persulfate to generate free radicals. DETAILED DESCRIPTION

[0030] The application will be further described in detail below in combination with specific embodiments.

[0031] In the embodiments and comparative examples of the application, the chemical reagents not specifically described are all commercially available analytical pure reagents for experiments.

[0032] In the embodiments and comparative examples of the application, the new pollutant is bisphenol A (BPA), which is an important chemical organic raw material. It has been confirmed to have an endocrine disrupting effect and belongs to a typical new pollutant, and has been frequently detected in the groundwater environment. Its low-dose high-toxicity characteristics pose a potential threat to the ecological environment and human health.

[0033] Example 1

[0034] In this embodiment, the following method is used to remove pollutants from groundwater:

[0035] (1) FeSO4.7H2O and KMnO4 were weighed according to the molar ratio of Fe:Mn = 3:1, and then dissolved in water. The dissolution process was observed to determine when the FeSO4.7H2O and KMnO4 were completely dissolved. Then, NaOH solution with a concentration of 2 mol / L was slowly added to the mixed Fe-Mn solution until the pH value of the liquid reached 7.0-8.0. The liquid was stirred at a speed of 200 rpm for 60 min, and then left to stand for 12 h. The liquid was filtered and washed, and the solid obtained by filtration was dried at 40°C for 24 h. The dried solid was ground into powder to obtain the non-dissolved Fe-Mn catalyst.

[0036] (2) 1.95 g of the Fe-Mn catalyst powder obtained in step (1) was added to 1.5 L of ultrapure water, and ultrasonic treatment was performed at room temperature for 20 min. 450 mg of xanthan gum was dissolved in 450 ml of ultrapure water at 60°C, and stirred at 800 r / min for 20 min to form a uniform milky white slurry. The dissolved xanthan gum solution was poured into the beaker containing the Fe-Mn catalyst slurry, and ultrasonic treatment was performed for another 20 min to form a catalyst slurry. A 35.0 mM potassium monopersulfate solution was prepared using ultrapure water. The catalyst slurry and the potassium monopersulfate solution were injected into the simulated groundwater prepared in this embodiment at pump rates of 0.8 ml / min and 0.047 ml / min, respectively, to form an in-situ reaction zone.

[0037] This embodiment used a sand column simulation method (as shown in Figure 2 , 3 ). The sand column was composed of a quartz sand with a fixed particle size and was filled in a plexiglass column. The column was divided into a water distribution zone, a reaction zone, and a water outlet zone from bottom to top. The inner diameter of the plexiglass column was 5 cm, and the total length was 50 cm. The heights of the water distribution zone, the reaction zone, and the water outlet zone were 3 cm, 44 cm, and 3 cm, respectively. The main pollutant in the simulated groundwater was bisphenol A, and the content of bisphenol A was 0.175 mM. In addition, the simulated groundwater also contained 5 mM HCO3 - , 2 mM Ca 2+ , 0.3 mM Mg 2 + , 0.2 mM Cl - . During the experiment, the simulated groundwater was injected from the lower end of the sand column (as shown in Figure 2 ) through a peristaltic pump (set flow rate), passed through the water distribution zone, the reaction zone, and the water outlet zone in sequence, and finally flowed out from the upper end of the sand column. The hydraulic retention time in the sand column was set to 4 hours, and the seepage rate of the simulated groundwater was 3 m / day. The content of bisphenol A in the simulated groundwater flowing out of the plexiglass column was detected, and the results showed that the removal rate of bisphenol A reached 100%.

[0038] Example 2

[0039] The simulation experiment of this embodiment was carried out by using the same method as that of Embodiment 1, except that the concentration of the potassium peroxymonosulfate solution was 17.5 mM in this embodiment.

[0040] In this embodiment, the removal effect on bisphenol A was about 70%.

[0041] Embodiment 3

[0042] The simulation experiment of this embodiment was carried out by using the same method as that of Embodiment 1, except that the concentration of the potassium peroxymonosulfate solution was 26.2 mM in this embodiment.

[0043] In this embodiment, the removal effect on bisphenol A was about 90%.

[0044] Embodiment 4

[0045] The new pollutant removal experiment of this embodiment was carried out by using the same method as that of Embodiment 1, except that the catalyst slurry and oxidant solution were injected into the actual aquifer in this embodiment, and the background chemical components of the groundwater in the aquifer included: 2.982 mM HCO3 - , 2.525 mM Ca 2+ , 1.607 mM Mg 2+ , and 1.004 mM Cl - .

[0046] In this embodiment, the removal rate of bisphenol A was 78%.

[0047] Comparative Example 1

[0048] The simulation experiment of this comparative example was carried out by using the same method as that of Embodiment 1, except that the catalyst was a ferrous sulfate solution in this embodiment.

[0049] In this comparative example, the removal rate of bisphenol A was about 43%.

[0050] Comparative Example 2

[0051] The simulation experiment of this comparative example was carried out by using the same method as that of Embodiment 1, except that xanthan gum was not added to the catalyst slurry in this comparative example.

[0052] It can be seen from the comparison of Example 1 and Comparative Example 1 that the removal rate of bisphenol A in Comparative Example 1 is significantly reduced, and the reason is that when ferrous sulfate is dissolved in water, divalent iron ions are formed, and thus, after the ferrous sulfate solution contacts with the persulfate oxidant, the reaction to generate free radicals occurs very quickly, and since the simulated groundwater is introduced from the bottom end of the sand column at a slow flow rate, it first needs to pass through the water distribution area, and during this period, the simulated groundwater does not enter the reaction zone and thus does not contact with the oxidant, but after a certain period of time, the simulated groundwater enters the reaction zone and contacts with the oxidant, but after a certain period of time, the free radicals generated in Comparative Example 1 undergo self-annihilation reaction, resulting in a large reduction of free radicals under the same amount of oxidant, which affects the degradation effect of bisphenol A.

[0053] It can be seen from the comparison of Example 1 and Comparative Example 1 that the removal rate of bisphenol A in Comparative Example 1 is significantly reduced, and the reason is that when ferrous sulfate is dissolved in water, divalent iron ions are formed, and thus, after the ferrous sulfate solution contacts with the persulfate oxidant, the reaction to generate free radicals occurs very quickly, and since the simulated groundwater is introduced from the bottom end of the sand column at a slow flow rate, it first needs to pass through the water distribution area, and during this period, the simulated groundwater does not enter the reaction zone and thus does not contact with the oxidant, but after a certain period of time, the simulated groundwater enters the reaction zone and contacts with the oxidant, but after a certain period of time, the free radicals generated in Comparative Example 1 undergo self-annihilation reaction, resulting in a large reduction of free radicals under the same amount of oxidant, which affects the degradation effect of bisphenol A. Figure 3 It can be seen (Example 1 and Comparative Example 2) that the iron-manganese catalyst prepared in the present application is not dissolved in water, and it can be clearly seen from the figure that after the catalyst slurry without xanthan gum (Comparative Example 2) is introduced into the sand column, the number of iron-manganese catalyst particles accumulated at the bottom of the sand column is larger, and after the catalyst slurry with xanthan gum is introduced into the sand column, the number of iron-manganese catalyst particles accumulated at the bottom of the sand column is smaller, which shows that the addition of xanthan gum is beneficial to the movement of iron-manganese catalyst particles in the sand column, i.e., it proves that the catalyst slurry prepared in the present application has good performance of moving with liquid flow after being injected into the aquifer, thereby reducing the negative impact of solid particle catalyst slurry on fluidity.

[0054] It can be seen from the comparison of Example 1 and Comparative Example 1 that the removal rate of bisphenol A in Comparative Example 1 is significantly reduced, and the reason is that when ferrous sulfate is dissolved in water, divalent iron ions are formed, and thus, after the ferrous sulfate solution contacts with the persulfate oxidant, the reaction to generate free radicals occurs very quickly, and since the simulated groundwater is introduced from the bottom end of the sand column at a slow flow rate, it first needs to pass through the water distribution area, and during this period, the simulated groundwater does not enter the reaction zone and thus does not contact with the oxidant, but after a certain period of time, the simulated groundwater enters the reaction zone and contacts with the oxidant, but after a certain period of time, the free radicals generated in Comparative Example 1 undergo self-annihilation reaction, resulting in a large reduction of free radicals under the same amount of oxidant, which affects the degradation effect of bisphenol A. Figure 4 It can be seen that the non-dissolved catalyst prepared in the present application can effectively activate persulfate to generate free radicals.

[0055] In summary, the present application uses non-dissolved iron-manganese catalyst to prepare catalyst slurry, avoids the premature and rapid catalytic activation of oxidant, and thus effectively improves the utilization rate of oxidant and the removal rate of pollutants, and saves the cost of reagents.

[0056] Finally, it should be pointed out that the above preferred embodiments are only used to illustrate the technical solutions of the present application and are not limiting, and although the present application has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present application.

Claims

1. A method for removing emerging contaminants from groundwater by in-situ reaction zone injection, characterized by: The method comprises the following steps: (1) preparing a solid particle catalyst slurry: adding a non-dissolved iron-manganese catalyst into water and performing ultrasonic treatment at room temperature to obtain an iron-manganese catalyst slurry; dissolving xanthan gum powder in water, stirring to form a uniform milky white slurry, adding the milky white slurry into the iron-manganese catalyst slurry, and performing ultrasonic treatment to obtain a catalyst slurry; The specific preparation method of the non-dissolved iron-manganese catalyst is as follows: first, dissolving ferrous sulfate heptahydrate and potassium permanganate in water to obtain an iron-manganese mixed solution, wherein the molar ratio of iron in the ferrous sulfate heptahydrate to manganese in the potassium permanganate is Fe:Mn=3:1, then adding a 2 mol / L NaOH solution to the iron-manganese mixed solution until the pH value of the liquid reaches 7.0-8.0, stopping adding the NaOH solution, then stirring the liquid at a speed of 200 rpm for 60 min, then standing for 12 h, filtering and washing the liquid, and drying the solid material obtained by filtration at 40°C for 24 h, grinding the dried solid material into powder to obtain the non-dissolved iron-manganese catalyst; (2) preparing an oxidant solution: dissolving a persulfate powder in water to obtain an oxidant solution; (3) synchronously injecting the catalyst slurry obtained in step (1) and the oxidant solution obtained in step (2) into an aquifer, respectively, and allowing the catalyst slurry and the oxidant solution to react in the water environment to form an in-situ reaction zone.

2. The method for removing emerging contaminants from groundwater by in-situ reaction with injection according to claim 1, characterized in that: The non-dissolved iron-manganese catalyst comprises an iron-manganese oxide catalyst.

3. The method of claim 1, wherein the injection-type in-situ reaction zone is configured to remove a new contaminant from the groundwater. In step (1), the solid-liquid ratio of the non-dissolved iron-manganese catalyst to water is 1.3 g:1 L.

4. The method of claim 1, wherein the injection-type in-situ reaction zone is configured to remove a new contaminant from the groundwater. In step (1), the solid-liquid ratio of the xanthan gum powder to water is 1 mg:1 ml.

5. The method of claim 1, wherein the method is characterized by: In step (1), the volume ratio of the milky white slurry to the iron-manganese catalyst slurry is milky white slurry:iron-manganese catalyst slurry=3:

10.

6. The method of claim 1, wherein the method is characterized by: In step (1), the xanthan gum powder is dissolved in 60°C water and stirred at 60°C.

7. The method of removing emerging contaminants from groundwater by in-situ reaction zone injection according to any one of claims 1-6, characterized in that: In step (1), the ultrasonic treatment time is 20 min, the ultrasonic treatment power is 200 W, and the ultrasonic frequency is 40 KHz.

8. The method of claim 1, wherein the injection-type in-situ reaction zone is configured to remove a new contaminant from the groundwater. In step (2), the concentration of the oxidant solution is 100-200 times that of the target pollutant.

9. The method of claim 1, wherein the method is characterized by: In step (3), the ratio of the injection flow rate of the catalyst slurry to the injection flow rate of the oxidant solution is 17:1.

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