Underground water pollution treatment method based on permeable reactive barrier filler capable of being regenerated in situ

Abstract

The invention discloses an underground water pollution treatment method based on an in-situ renewable permeable reactive barrier filler. The method comprises the following steps: an adsorption stage: adsorbing organic pollutants in underground water by using the in-situ renewable permeable reactive barrier filler; and an in-situ regeneration stage: providing persulfate to the permeable reactive barrier filler adsorbed with the organic pollutants, performing catalytic oxidation on the adsorbed organic pollutants, and recovering the adsorption capacity of the permeable reactive barrier filler. The preparation method of the permeable reactive barrier filler capable of being regenerated in situ comprises the following steps: uniformly mixing a crushed biomass material with an active metal salt solution, standing, pre-drying the obtained mixture until the water content is 75-85wt%, grinding and crushing, and continuously drying to obtain a dried product; the active metal salt comprises ferrous sulfate and copper sulfate; and pyrolyzing the dried product under an anoxic or anaerobic condition to obtain active metal iron and copper loaded biochar, namely the permeable reactive barrier filler.

Description

Technical Field

[0001] The invention relates to the technical field of groundwater pollution control, and in particular to a groundwater pollution control method based on in-situ regenerable permeable reaction wall filler. Background Art

[0002] With the continuous advancement of industrialization and urbanization, the problem of groundwater pollution has gradually become prominent. The leakage of sewage in the production process of enterprises in high-pollution industries (such as chemical, coking, printing and dyeing, etc.), illegal landfill of organic solid waste, illegal discharge of industrial wastewater, etc. will lead to the pollution of groundwater with organic pollutants, directly or indirectly endangering the safety of the surrounding environment and human health. The treatment and remediation of organic polluted groundwater requires high costs. Therefore, with limited capital investment, it is the practice of international peers to take risk control of this type of groundwater, which is also the overall idea for the prevention and control of groundwater pollution.

[0003] Permeable reaction wall technology is an emerging engineering technology for groundwater pollution risk control. It has been successfully used in domestic and foreign engineering fields because of its advantages such as continuous in-situ treatment of multiple pollutants, good treatment effect, high cost performance, and easy installation and construction. However, the widespread application of permeable reaction wall technology is still limited by its material properties and long-term stability. According to the reaction mechanism classification, permeable reaction walls can be roughly divided into adsorption type, redox type and biodegradable type according to the different fillers. Adsorption type permeable reaction walls are the most widely used because of their diverse applicable pollution types and significant effects. However, as the treatment time increases, the adsorption filler will gradually become saturated, resulting in a decrease in material treatment efficiency. Therefore, how to improve the adsorption capacity of the adsorption filler of the permeable reaction wall is the key to achieving more long-term and effective control of groundwater pollution.

[0004] The patent specification with publication number CN117049641A discloses a method for preparing a permeable reaction wall slow-release filler and its application. The method for preparing a permeable reaction wall slow-release filler comprises the following steps: mixing an adsorption degradation material, an embedding agent, a nanopore-making material and water, and then subjecting the mixture to freeze-thaw, drying, acid solution treatment and secondary drying to obtain the permeable reaction wall slow-release filler; the adsorption degradation material comprises reduced iron powder, biochar and persulfate. This patented technology fixes reduced iron powder and sodium sulfate on the surface, inside and pores of biochar through an embedding agent, thereby playing the role of a slow-release repair agent. In this patented technology, repair agents such as reduced iron powder and persulfate are still consumables, and the permeable reaction wall slow-release filler cannot be regenerated in situ.

[0005] The patent specification with publication number CN117843117A discloses a composite slow-release material for repairing groundwater contaminated by organic matter, and its preparation method and application. The method includes: pre-treating sludge; mixing sludge powder with RuCl3 solution, passing carbon dioxide into calcination to obtain modified biochar powder; calcining organic nitrogen source to obtain carbon nitride powder; mixing cobalt salt, manganese salt, copper salt, ammonium fluoride, modified biochar powder, urea and water, adding sodium percarbonate to react, and obtaining catalyst biochar material; mixing carbon nitride powder, catalyst biochar material, iron salt and deoxygenation solvent, adding reducing agent to react, and obtaining modified nano zero-valent iron; mixing modified nano zero-valent iron, sodium percarbonate and sodium persulfate, and adding to binder to obtain composite slow-release material. The patent technology also provides a slow-release material, which does not involve regeneration. Summary of the invention

[0006] The present invention mainly addresses the problem that the adsorption-type permeable reaction wall cannot be regenerated in situ after adsorption saturation, and proposes to use a one-step pyrolysis method to synthesize biochar loaded with transition metals, which can adsorb and remove organic pollutants in groundwater. After adsorption saturation, by adding persulfate to the permeable reaction wall filler area, metals such as iron and copper loaded on the biochar can catalyze the added persulfate, thereby achieving oxidation and removal of organic pollutants on the biochar adsorption site, and restoring the adsorption capacity of the filler. Through the in-situ regeneration of the adsorption filler, long-term and effective risk control of the permeable reaction wall for groundwater pollution can be achieved.

[0007] The present invention provides a method for treating groundwater pollution based on an in-situ regenerable permeable reactive wall filler. The method of the present invention is a risk control method for groundwater contamination by organic matter, and specifically relates to a preparation and in-situ regeneration technology of a permeable reactive wall filler for groundwater contaminated by organic matter.

[0008] The specific technical solutions are as follows:

[0009] A method for treating groundwater pollution based on an in-situ regenerable permeable reactive wall filler, comprising:

[0010] Adsorption stage: using in-situ regenerable permeable reactive wall fillers to adsorb organic pollutants from groundwater;

[0011] In-situ regeneration stage: providing persulfate once or multiple times to the in-situ regenerable permeable reaction wall filler that has adsorbed organic pollutants, catalytically oxidizing the adsorbed organic pollutants, and restoring the adsorption capacity of the permeable reaction wall filler;

[0012] The method for preparing the in-situ regenerable permeable reactive wall filler comprises the steps of:

[0013] (1) mixing the crushed biomass material and the active metal salt solution and letting it stand, pre-drying the obtained mixture to a moisture content of 75 wt% to 85 wt% and then grinding and crushing it, and continuing to dry it to obtain a dry product; the active metal salt includes ferrous sulfate and copper sulfate;

[0014] (2) Pyrolyzing the dried product under anaerobic or anoxic conditions to obtain biochar loaded with active metals iron and copper, i.e., the in-situ regenerable permeable reaction wall filler.

[0015] In order to strengthen the binding force between active metal iron and copper and biochar, prevent the loss of active metal iron and copper in the process of groundwater pollution control, improve the dispersibility of active metal iron and copper on biochar, enhance the metal-carrier interaction between active metal iron and copper and biochar, and improve the in-situ regeneration reaction effect to restore the adsorption capacity of the permeable reaction wall filler as much as possible, the preparation method of the in-situ regenerative permeable reaction wall filler of the present invention adopts the operation of pre-drying-grinding-continuous drying, instead of drying to complete in one step like the existing conventional technology. Although the biomass material has been pre-crushed, it will still cause compaction and agglomeration as the water is lost during the pre-drying process. At this time, if it is directly dried to complete like the existing conventional technology, the binding force between active metal iron and copper and biochar in the filler obtained by subsequent pyrolysis is poor, the active metal iron and copper are easy to lose in the process of groundwater pollution control, the dispersibility of active metal iron and copper on biochar is not good, the metal-carrier interaction between active metal iron and copper and biochar is weak, and the in-situ regeneration reaction effect is not ideal. In order to overcome the above problems, the present invention creatively proposes to add a grinding and crushing operation after pre-drying to a moisture content of 75wt% to 85wt%, so that some of the compacted and agglomerated biomass materials can be re-broken, the dispersion of active metal iron and copper can be enhanced, and the mixing uniformity and binding of biomass materials and active metal salts can be improved, and then the drying can be continued until complete. This can well solve the problems brought about by the above-mentioned conventional technologies, strengthen the binding force of active metal iron, copper and biochar, prevent the loss of active metal iron and copper during groundwater pollution control, improve the dispersion of active metal iron and copper on biochar, enhance the metal-carrier interaction between active metal iron, copper and biochar, and improve the in-situ regeneration reaction effect to restore the adsorption capacity of the permeable reaction wall filler as much as possible.

[0016] The study found that the pre-drying of the obtained mixture to a moisture content of 75wt% to 85wt% is a suitable range that meets the target effect requirements. If the pre-drying is excessive and the moisture content of the mixture used for grinding is too low, the grinding operation will not be able to further evenly disperse the active metal iron and copper on the surface of the biomass material and promote the combination of the active metal iron and copper with the biomass material; if the pre-drying degree is insufficient and the moisture content of the mixture used for grinding is too high, the grinding operation itself will be difficult to carry out and will also fail to work.

[0017] The present invention adopts two-component active metals of iron and copper, which have higher in-situ catalytic regeneration activity and stability compared with single metal loads of iron or copper, can quickly restore the adsorption capacity of biochar, and have a higher degree of regeneration.

[0018] In some embodiments, in the method for preparing the in-situ regenerable permeable reactive wall filler, the active metal salt can be mixed and added to deionized water and stirred until completely dissolved to obtain the active metal salt solution, wherein the mass ratio of the deionized water to the active metal salt can be 20 to 50:1.

[0019] In some embodiments, in step (1), after the crushed biomass material and the active metal salt solution are mixed, deionized water may be added to adjust the solid-liquid mass ratio of the obtained mixture. After the deionized water is added, mechanical stirring may be performed. The frequency of the mechanical stirring may be 200 to 300 rpm, and the time of the mechanical stirring may be 3 to 5 hours.

[0020] In some preferred examples, in step (1), the mass ratio of the biomass material to the active metal salt is 5 to 10:1, which can take into account both the in-situ regeneration catalytic oxidation activity and the loading firmness of the active metal iron and copper. Within this range, the active metal iron and copper will not be lost, and will not cause secondary pollution of groundwater.

[0021] In some preferred examples, in step (1), the mass ratio of ferrous sulfate to copper sulfate is 5 to 10:1. In the iron-copper bimetallic catalytic oxidation system, iron is the main metal active site, providing catalysis for persulfate, while copper mainly plays a role in changing the surface morphology of the catalyst to increase the number of active sites of iron. Therefore, the addition of copper has an optimal addition ratio, and too much or too little addition may not significantly improve the catalytic performance.

[0022] In step (1), the biomass material may include at least one of wood chips, straw, and bamboo powder.

[0023] In some preferred examples, in step (1), the particle size of the crushed biomass material is less than 5 mm, such as less than 2 mm.

[0024] In step (1), the solid-liquid mass ratio in the mixture can be 1:3 to 8.

[0025] In step (1), the standing time may be 7 to 12 hours.

[0026] In step (1), the pre-drying temperature can be 75-85°C, for example, 80°C. On the one hand, it is easier to control the end point of the pre-drying moisture content to avoid excessive pre-drying. On the other hand, a lower drying temperature can prevent the biomass material from agglomerating first, reducing the specific surface area, and hindering the high dispersion of active metals iron and copper.

[0027] In some preferred embodiments, in step (1), the particles are ground to a particle size of less than 5 mm, such as less than 2 mm.

[0028] In step (1), the temperature for continued drying can be 140-160°C, for example, 150°C. At this time, after the grinding and crushing process, the active metal iron and copper have undergone secondary dispersion and further combined with the biomass material. The drying temperature can be higher, which can improve the production efficiency and further enhance the bonding degree of the active metal iron and copper with the biomass material.

[0029] In some preferred examples, in step (2), the pyrolysis temperature is 800-900° C. This pyrolysis temperature range is conducive to enhancing the degree of aromatization of biochar and increasing the specific surface area, and is also conducive to the reduction of active metals of iron and copper and the binding force between them and biochar, giving full play to the role of copper in increasing the number of active iron sites, that is, it can simultaneously improve the adsorption capacity of the filler and the in-situ regeneration catalytic oxidation performance, and prevent the loss of active metals of iron and copper. On the other hand, it will not cause the destruction of the pore structure of biochar, and maximize the adsorption capacity of the filler without causing excessive energy consumption.

[0030] In step (2), the pyrolysis time may be 1.5 to 2 hours.

[0031] The biochar loaded with active metal iron and copper obtained in step (2) can be used for adsorption-type permeable reaction walls to control groundwater contaminated by organic pollutants. The organic content of the effluent is monitored. When the organic content in the effluent increases significantly, it means that the filler is saturated with adsorption and a persulfate solution can be injected for oxidation treatment. The biochar after oxidation treatment can restore the adsorption function and realize the in-situ regeneration of the biochar.

[0032] In the method for treating groundwater pollution, the persulfate may include at least one of sodium persulfate (Na2S2O8) and potassium persulfate (K2S2O8).

[0033] In the method for treating groundwater pollution, the persulfate can be provided in the form of a solution. The concentration of the provided persulfate solution can be 2 to 3 mM. The persulfate solution can be provided for 2 to 3 hours at a time.

[0034] In the method for treating groundwater pollution, the organic pollutants may include one or more of benzene series, polycyclic aromatic hydrocarbons, etc., and specifically may include at least one of chlorobenzene and naphthalene.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention proposes a preparation and application method of a permeable reaction wall filler for organically contaminated groundwater. A one-step pyrolysis method is used to synthesize a biochar material loaded with active metal iron and copper, which can produce a good adsorption and removal effect on organic pollutants in groundwater. When the filler is saturated with adsorption, sodium persulfate or the like can be added to form catalytic oxidation with the active metal iron and copper on the biochar, and the adsorbed organic matter can be oxidized and removed, and the adsorption sites on the biochar are released to achieve the regeneration of the biochar. Since the active metal iron and copper are loaded on the biochar, the heterogeneous catalytic process will not lead to the loss of active metal iron and copper, and will not cause secondary pollution of groundwater. The one-step pyrolysis method used combines the burning of biochar and the loading of metal into one step, and the preparation method is simple, which is conducive to the industrial mass production of materials. Compared with the traditional adsorption-type permeable reaction wall, the present invention combines the in-situ chemical oxidation method to improve the service life and load impact resistance of the biochar adsorption material. Compared with single in-situ chemical oxidation technology, the combination of permeable reaction wall technology can achieve long-term pollutant removal without high-frequency agent injection, improve the utilization efficiency of oxidizing agents, and is a more economical and efficient technical means for risk control of organic contaminated groundwater. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples where no specific conditions are indicated are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0038] Embodiment 1:

[0039] Take 10g of ferrous sulfate and 2g of copper sulfate and add 100mL of water to completely dissolve. Crush 100g of sawdust to less than 5mm, mix with the above solution, add 250mL of deionized water, set the frequency of the magnetic stirrer to 300rpm and stir for 5h and then let it stand for 8h. Put the mixed material into an oven and set the temperature to 80℃ for pre-drying. The moisture content is 78wt% after drying for 6 hours. Grind and crush the above materials, pass through a 5mm sieve, and put them into an oven preheated to 150℃ again to dry until completely dry. The dried mixed material is placed in a muffle furnace at 800℃ for pyrolysis for 2h to obtain 43.68g of iron-copper loaded biochar.

[0040] A permeable reaction wall simulation column test was carried out. The total length of the simulated column was 30 cm and the inner diameter was 2.62 cm. The upper and lower parts of the simulated column were filled with quartz sand with a thickness of 12 cm, which played a role in water distribution. The middle layer was filled with a mixture of quartz sand and 0.2 g iron-copper loaded biochar, with a filling thickness of 6 cm. A simulated contaminated groundwater with a chlorobenzene concentration of 6 mg / L was prepared. The water flow direction was from bottom to top and the flow rate was 2 mL / min. After the operation started, sodium persulfate was added to the test group at 8 h and 16 h respectively. The addition method was to replace the influent with simulated groundwater containing 6 mg / L chlorobenzene and 3 mM sodium persulfate, and then replace it with groundwater containing only chlorobenzene after 2 hours. In addition, a control group was set up in the experiment, in which only groundwater containing chlorobenzene was passed, and no sodium persulfate was added. The chlorobenzene concentration of the effluent is shown in Table 1. From the change of chlorobenzene concentration in the effluent, the concentration of the control group gradually increased with time, and the removal rate was maintained at more than 90% in the first 2 hours, but at 24 hours, the removal rate was only 18.17%. In the case of the experimental group using sodium persulfate for in-situ regeneration, the removal rate of chlorobenzene was more than 70% within 24 hours.

[0041] Table 1 Simulation column test effluent chlorobenzene concentration (mg / L)

[0042]

[0043] Embodiment 2:

[0044] Take 10g of ferrous sulfate and 1g of copper sulfate and add 100mL of water to completely dissolve. Crush 100g of straw to less than 2mm, mix with the above solution, add 550mL of deionized water, set the frequency of the magnetic stirrer to 200rpm and stir for 3h, then let it stand for 12h. Put the mixed material into an oven and set the temperature to 80℃ for pre-drying. The moisture content is 85wt% after drying for 12 hours. Grind and crush the above materials, pass through a 2mm sieve, and put them into an oven preheated to 150℃ again to dry until completely dry. The dried mixed material is placed in a muffle furnace at 900℃ for pyrolysis for 1.5h to obtain 41.79g of iron-copper loaded biochar.

[0045] A permeable reaction wall simulation column test was carried out, with a total length of 30 cm and an inner diameter of 2.62 cm. The upper and lower parts of the simulation column were filled with quartz sand with a thickness of 12 cm, which played a role in water distribution. The middle layer was filled with a mixture of quartz sand and 0.4 g iron-copper loaded biochar, with a filling thickness of 6 cm. A simulated contaminated groundwater with a naphthalene concentration of 4 mg / L was prepared, and the water flow direction was from bottom to top at a flow rate of 2 mL / min. After the start of operation, sodium persulfate was added to the test group at 8 h and 16 h, respectively. The addition method was to replace the influent with simulated groundwater containing 4 mg / L naphthalene and 2 mM potassium persulfate, and then replace it with groundwater containing only naphthalene after 3 hours of passage. In addition, a control group was set up in the experiment, in which only groundwater containing naphthalene was passed, and potassium persulfate was not added. The naphthalene concentration of the effluent is shown in Table 2.

[0046] From the change of naphthalene concentration in the effluent, the concentration of the control group gradually increased with time, and the removal rate was maintained at more than 95% in the first 2 hours, but it was only 35.75% at 24 hours. In the case of sodium persulfate in situ regeneration in the experimental group, the removal rate of naphthalene was above 85% within 24 hours.

[0047] Table 2 Naphthalene concentration in simulated column test (mg / L)

[0048]

[0049] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for treating groundwater pollution based on in-situ regenerable permeable reactive wall filler, characterized in that: include: Adsorption stage: using in-situ regenerable permeable reactive wall fillers to adsorb organic pollutants from groundwater; In-situ regeneration stage: providing persulfate once or multiple times to the in-situ regenerable permeable reaction wall filler that has adsorbed organic pollutants, catalytically oxidizing the adsorbed organic pollutants, and restoring the adsorption capacity of the permeable reaction wall filler; The method for preparing the in-situ regenerable permeable reactive wall filler comprises the steps of: (1) mixing the crushed biomass material and the active metal salt solution and letting it stand, pre-drying the obtained mixture to a moisture content of 75 wt% to 85 wt% and then grinding and crushing it, and continuing to dry it to obtain a dry product; the active metal salt includes ferrous sulfate and copper sulfate; (2) Pyrolyzing the dried product under anaerobic or anoxic conditions to obtain biochar loaded with active metals iron and copper, i.e., the in-situ regenerable permeable reaction wall filler.

2. The method for treating groundwater pollution according to claim 1, characterized in that: In step (1): The mass ratio of the biomass material to the active metal salt is 5 to 10:1; The mass ratio of ferrous sulfate to copper sulfate is 5 to 10:

1.

3. The method for treating groundwater pollution according to claim 1, characterized in that: In step (1), the biomass material includes at least one of wood chips, straw, and bamboo powder.

4. The method for treating groundwater pollution according to claim 1, characterized in that: In step (1), the particle size of the crushed biomass material is less than 5 mm.

5. The method for treating groundwater pollution according to claim 1, characterized in that: In step (1), the solid-liquid mass ratio in the mixture is 1:3-8.

6. The method for treating groundwater pollution according to claim 1, characterized in that: In step (1), the standing time is 7 to 12 hours.

7. The method for treating groundwater pollution according to claim 1, characterized in that: In step (1): The pre-drying temperature is 75-85°C; Grind to a particle size of less than 5 mm; The temperature of the continued drying is 140-160°C.

8. The method for treating groundwater pollution according to claim 1, characterized in that: In step (2): The pyrolysis temperature is 800-900°C; The pyrolysis time is 1.5 to 2 hours.

9. The method for treating groundwater pollution according to claim 1, characterized in that: The persulfate includes at least one of sodium persulfate and potassium persulfate; The persulfate is provided in the form of a solution; the concentration of the provided persulfate solution is 2 to 3 mM; The persulfate solution is provided for 2 to 3 hours at a time.

10. The method for treating groundwater pollution according to claim 1, characterized in that: The organic pollutants include at least one of chlorobenzene and naphthalene.

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