Persistent organic pollutant repairing agent as well as preparation method and application thereof

Abstract

The invention provides a persistent organic pollutant repairing agent as well as a preparation method and application of the persistent organic pollutant repairing agent. Nutrient substances required by normal growth of alcaligenes faecalis bacteria (Alcaligenes faecalis) and the Alcaligenes faecalis are packaged in a chitosan-calcium alginate core-shell cross-linked network structure together. According to the present invention, the alcaligenes faecalis is used as the substrate, the biochar is used as the carrier of the alcaligenes faecalis to fix the alcaligenes faecalis, and the calcium alginate is used to package the alcaligenes faecalis, such that the loss of the alcaligenes faecalis can be prevented, the microbial activity of the alcaligenes faecalis can be easily improved, and the mineralization ability of the alcaligenes faecalis on the POPs in the sediment can be improved;

Description

Technical Field

[0001] The invention relates to the technical field of ecological restoration, and in particular to a persistent organic pollutant restoration agent and a preparation method and application thereof. Background Art

[0002] Coastal wetlands are the transitional zone between terrestrial and marine ecosystems, and are an important part of the Earth's ecosystem. With the increasing intensity of human activities, the pollution generated has also migrated and spread. Persistent Organic Pollutants (POPs) in the atmosphere, soil and rivers have flowed into the ocean through atmospheric deposition, surface runoff, sewage discharge and other pathways. Coastal wetlands are located at the junction of land and sea, and are subject to dual pollution from land and sea. In addition, the topography of wetlands leads to weak hydrodynamics. During the deposition process, silt and organic matter will carry POPs with them and be deposited in the sediment, thus becoming the main gathering place for POPs.

[0003] In addition, the litter (waste) of coastal wetland plants has a huge biomass, and due to the influence of seawater and soil salinization, coastal wetland plants are mostly porous structures, and the derived biochar has a good adsorption effect on POPs. The resource utilization of litter of coastal wetland plants not only realizes the high-value utilization of litter, but also can solve the POPs pollution problem in coastal wetlands, thus achieving "waste treatment with waste".

[0004] Microbial remediation technology is to repair POPs in polluted coastal wetland environments through the principle of microbial mineralization. Its advantage is that it uses microorganisms in nature to repair POPs. It is not only inexpensive and effective, but also can be repaired in situ without causing secondary pollution to the environment. It is an important and effective way to repair POPs pollution in coastal wetlands. However, directly applying microorganisms to coastal wetland sediments may cause microbial loss or death, thereby affecting the remediation effect. Therefore, the immobilization of microbial remediation technology on biochar can effectively ensure the activity and adsorption effect of microorganisms, and promote the green and sustainable remediation of POPs pollution in coastal wetlands.

[0005] Phytoremediation technology is a technique in which plant roots extract organic pollutants from the soil and decompose them into non-toxic products through their own metabolism and transpiration. However, phytoremediation often has problems such as insufficient nutrients, damage by organic pollutants, and only being able to degrade organic pollutants near the plant roots. Therefore, combined restoration with biochar and bacteria can effectively solve the above problems.

[0006] Patent CN105080506A discloses a method for preparing sodium alginate microspheres and their applications. After washing, air-drying and crushing the reeds, place them in a muffle furnace at 600°C (an environment filled with N2) for pyrolysis for 2 hours, cool them, pass them through a 100-mesh sieve, and pickle them with hydrochloric acid to obtain reed biochar. At the same time, sodium alginate is dissolved in deionized water to prepare a 4% sodium alginate solution. A 20g / L reed biochar aqueous solution is evenly mixed with a sodium alginate solution in a volume ratio of 1:1, and the mixture is dripped into a CaCl2 solution through a peristaltic pump to obtain a reed biochar-sodium alginate microsphere adsorption material. It has a good adsorption effect on organic pollutants such as pentachlorophenol (PCP) and phenanthrene (Phe).

[0007] Patent 202010343977.9 relates to a method for in-situ repair of benzene in soil using plant-microorganism-biochar combined remediation technology. The technical solution adopted is: spreading biochar in the soil containing benzene, and then sowing ryegrass seeds and alfalfa seeds impregnated with alfalfa rhizobium fermentation liquid. Using the method of this application, the degradation rate of toluene in the soil is as high as 83% after 60 days. The method of combined remediation of biochar and plant microorganisms can not only repair and degrade benzene, but also make reasonable reuse of waste in agricultural production, so that abandoned crops can give full play to their value. Summary of the invention

[0008] In view of a series of problems raised in the prior art, such as the inability to control POPs pollution in coastal wetland environments, the direct application of microorganisms in saline-alkali lands such as coastal wetlands easily leading to direct death of microorganisms, and the like, the present application proposes a persistent organic pollutant remediation agent, a preparation method and application thereof, which encapsulates nutrients required for the normal growth of Alcaligenes faecalis (Alcaligenes faecalis) together with Alcaligenes faecalis in a chitosan-calcium alginate core-shell cross-linked network structure, effectively ensuring the survival stability of Alcaligenes faecalis in sediments, and greatly improving the degradation efficiency of Alcaligenes faecalis on POPs in sediments.

[0009] A persistent organic pollutant repair agent, the repair agent is a core-shell structure prepared by a shell layer liquid and a core layer liquid;

[0010] The shell layer liquid includes a bacterial liquid of Alcaligenes faecalis and an aqueous sodium alginate solution, and the mass ratio of the bacterial liquid of Alcaligenes faecalis to the aqueous sodium alginate solution is 5:1;

[0011] The core layer liquid includes nutrients required by alkalinity bacteria, biochar, and acetic acid aqueous solution. The volume ratio of the nutrients required by alkalinity bacteria, the biochar, and the acetic acid aqueous solution is (0.8-1):1:50.

[0012] The core-shell structure is formed by adding the shell layer liquid and the core layer liquid into the calcium chloride solution using a coaxial needle;

[0013] The size of the stainless steel coaxial nozzle is 4 to 8 for the inner needle and 9 to 16 for the outer needle;

[0014] The flow rate ratio of the shell layer liquid to the core layer liquid is (1.5-2):1.

[0015] A method for preparing a persistent organic pollutant remediation agent comprises the following steps: (1) preparing biochar derived from coastal wetland plants; (2) culturing alcaligenes faecalis in LB medium to obtain OD 600 =1.2-1.8 of alcaligenes faecalis bacterial liquid; (3) adding nutrients required by alcaligenes faecalis and the biochar prepared in step (1) to an acetic acid aqueous solution, stirring evenly to obtain a core layer liquid; (4) mixing the alcaligenes faecalis bacterial liquid prepared in step (2) with an aqueous sodium alginate solution evenly to obtain a shell layer liquid; (5) adding the shell layer liquid and the core layer liquid to a calcium chloride solution to prepare a core-shell structure.

[0016] In the above step (1), the coastal wetland plant-derived biochar is made from the coastal wetland plant straw, which is crushed to obtain a powder and passed through a 200-mesh sieve, and then placed in a tubular furnace at a temperature of 300-700° C., nitrogen is passed to an oxygen-free environment, and the powder is obtained by pyrolysis.

[0017] Coastal wetland plants include one of the following: mangrove plants (Avicennia marina, Kandelia candel, Tung tree, Rhizoma mangrovea, Sea lotus, Bruguiera gymnorrhiza, Cercidiphyllum and Sonneratia salsa, etc.), Suaeda salsa, Spartina serrata, Spartina alterniflora, Sedge grass, Scirpus serrata, Water candle, Phragmites australis, etc.

[0018] The culture conditions in step (2) above are to inoculate Alcaligenes faecalis into a sterile culture medium, maintain a certain temperature and shake overnight, and adjust the bacterial solution concentration to OD by centrifugation or by adding physiological saline. 600 =1.2-1.8; the above sterile culture medium is prepared by mixing 20g yeast powder, 15g NH4Cl and 1mmol NiCl2 evenly, adding distilled water to make up to 1L, and then adjusting the sterile culture medium to pH = 9.2-9.3 with NaOH aqueous solution.

[0019] In the above step (3), the mass volume ratio of the nutrients required by alcaligenes faecalis and biochar is (0.8-1):1; the nutrients required by alcaligenes faecalis include chitosan, yeast powder, trypsin, and urea in a mass ratio of 6:2:1:1; the concentration of acetic acid is 0.05 mol / Lwt%.

[0020] In the above step (4), the mass ratio of the alkalinity-producing bacteria liquid to the sodium alginate aqueous solution is 5:1.

[0021] The preparation method of the core-shell structure in the above step (5) is as follows: the shell layer liquid and the core layer liquid are respectively injected into the outer layer and the inner layer of a stainless steel coaxial needle, and the shell layer liquid and the core layer liquid are sprayed into a calcium chloride solution with a concentration of 2-20% under high-voltage electrostatic spraying conditions using a high-voltage electrospinning device, stirred at 200-300 r / min for 24-32 hours, filtered, and dried at 40-50° C. for 6-8 hours to obtain the core-shell structure; the size of the above stainless steel coaxial nozzle is 4 to 8 for the inner needle and 9 to 16 for the outer needle.

[0022] The above-mentioned high-voltage electrostatic spraying conditions are as follows: an ambient temperature of 0 to 40°C, an output voltage of the high-voltage power supply of 1 to 5 kV, a distance between the receiving device and the stainless steel coaxial needle spinneret of 7 to 15 cm, a flow rate of 5 to 20 mL / h, and a flow rate ratio of the shell liquid to the core liquid of (1.5-2):1.

[0023] The persistent organic pollutant remediation agent obtained by the above preparation method can be used for the treatment of persistent organic pollutants in saline-alkali lands such as coastal wetlands, and can be specifically applied to the mineralization precipitation of persistent organic pollutants (POPs) in coastal wetland sediments. The POPs in the above coastal wetland sediments include at least one of organochlorine pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, etc.

[0024] Specific applications include a method for in situ remediation of POPs in soil by a combination of plant-microorganism-biochar, the method being as follows: applying a persistent organic pollutant remediation agent to soil in sediments of a coastal wetland planted with plants.

[0025] Compared with the prior art, this application has the following advantages:

[0026] (1) The Alcaligenes faecalis used in the present invention can tolerate high concentrations of salt stress while degrading POPs, thereby ensuring degradation efficiency. Moreover, when Alcaligenes faecalis is applied to sediments, it can fix nitrogen, secrete indoleacetic acid, gibberellins and other plant hormones, promote plant growth and development, and accelerate the degradation of POPs.

[0027] (2) Using biochar as a carrier of Alcaligenes faecalis to fix it, and then encapsulating it with calcium alginate, which can not only prevent the loss of Alcaligenes faecalis, but also help to improve the microbial activity of Alcaligenes faecalis;

[0028] (3) Experiments have shown that combining the nutrients required for the normal growth and metabolism of Alcaligenes faecalis with biochar and then encapsulating them together with Alcaligenes faecalis in a calcium alginate cross-linked network can improve the mineralization capacity of Alcaligenes faecalis for POPs in sediments more than directly combining Alcaligenes faecalis with the nutrients required by Alcaligenes faecalis and biochar and then encapsulating them in a calcium alginate cross-linked network. When the nutrients required by Alcaligenes faecalis are fixed on biochar, the bacteria will go to places where they can be supplied with nutrients due to their favorable tendency.

[0029] (4) The present invention adds biochar-immobilized Alcaligenes faecalis to sediments, which can serve as a nutrient source for microorganisms and plants, improve soil aeration, pH, water and carbon content, promote the growth and interaction of plants and microorganisms; reduce the POPs concentration in the sediments, ensure that the toxic effects on the early growth and development of plants are reduced; enrich POPs, and greatly increase the degradation efficiency of plants.

[0030] The coastal wetland plant biochar produced by the above method provided by the present invention is more valuable than biochar from agricultural sources (corn straw, barley straw). The coastal wetland plant biochar not only protects the coastal wetland ecosystem, but also improves resource utilization, providing a feasibility analysis for the resource utilization of a large number of coastal wetland plants and agricultural and forestry waste biomass in my country. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] (1) The coastal wetland plant Spartina alterniflora was used as raw material, and the straw powder was obtained after crushing and sieving. The powder was placed in a tubular furnace and pyrolyzed at a temperature of 400°C to obtain Spartina alterniflora-derived biochar.

[0034] (2) Cultivating Alcaligenes faecalis in LB medium, specifically, inoculating Alcaligenes faecalis in sterilized LB medium, culturing at 30° C. with shaking at 200 rpm for 24 h, and adding physiological saline to adjust the bacterial solution concentration to OD600=1.2 to obtain an Alcaligenes faecalis bacterial solution.

[0035] The sterilized LB medium is prepared by uniformly mixing 20 g yeast powder, 15 g NH4Cl, and 1 mmol NiCl2, adding distilled water to make up to 1 L, and then dropping 1 mol / L NaOH aqueous solution to adjust the pH of the medium to 9.2.

[0036] (3) 30 g of chitosan, 10 g of yeast powder, 5 g of tryptone, 5 g of urea, and 50 g of biochar were added to 500 ml of 0.05 mol / L acetic acid aqueous solution and stirred evenly to obtain a core layer liquid.

[0037] (4) The Alcaligenes faecalis bacterial solution obtained in step (2) and a sodium alginate aqueous solution with a mass concentration of 1.0% are mixed in a mass ratio of 830:170 to obtain a shell liquid.

[0038] Using a coaxial needle tube with a No. 6 inner needle and a No. 12 outer needle, the shell layer liquid and the core layer liquid were continuously dripped into a 5% calcium chloride aqueous solution at a flow rate ratio of 2:1 to obtain a core-shell structured biochar-immobilized Alcaligenes faecalis composite sediment POPs remediation agent.

[0039] Example 2

[0040] The difference between Example 2 and Example 1 is that in Example 2, the mass ratio of the alcaligenes faecalis liquid to the sodium alginate aqueous solution is 4:1.

[0041] Example 3

[0042] The difference between Example 3 and Example 1 is that in Example 3, the mass ratio of the alcaligenes faecalis liquid to the sodium alginate aqueous solution is 6:1.

[0043] Example 4

[0044] The difference between Example 4 and Example 1 is that in Example 4, the mass ratio of nutrients required by Alcaligenes faecalis to biochar is 0.8:1.

[0045] Comparative Example 1

[0046] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses corn stalks as biochar raw material to prepare biochar.

[0047] Comparative Example 2

[0048] The difference between Comparative Example 2 and Example 1 is that, in Comparative Example 2, Alcaligenes faecalis, nutrients required for the normal growth and metabolism of Alcaligenes faecalis, and biochar are directly encapsulated in the calcium alginate cross-linked network.

[0049] Comparative Example 3

[0050] The difference between Comparative Example 4 and Example 1 is that the flow rate ratio of the shell layer liquid to the core layer liquid in Comparative Example 4 is 1:1.

[0051] Comparative Example 4

[0052] The difference between Comparative Example 5 and Example 1 is that the flow rate ratio of the shell layer liquid to the core layer liquid in Comparative Example 5 is 3:1.

[0053] Comparative Example 5

[0054] The difference between Comparative Example 5 and Example 1 is that the mass ratio of nutrients and biochar required by the alkalinity-producing bacteria in Comparative Example 5 is 0.7:1.

[0055] Comparative Example 6

[0056] The difference between Comparative Example 6 and Example 1 is that the mass ratio of nutrients and biochar required by the alkalinity-producing bacteria in Comparative Example 6 is 1.2:1.

[0057] Test Example 1: PAHs sediment removal ability test:

[0058] Preparation of PAHs-contaminated (phenanthrene as an example) sediment samples: Mix the phenanthrene aqueous solution with the ground and sieved coastal wetland sediments to make the phenanthrene concentration in the sediment reach 40 mg / kg. The repair agents prepared in each embodiment and comparative example are mixed with the phenanthrene-contaminated sediment samples, and the addition amount is 5% of the total weight of the sediment. The 1 kg of treated sediment is placed in a dark place indoors. Samples are taken on the 1st, 3rd, and 7th days respectively, and the phenanthrene content in the extract is detected by high performance liquid chromatography-fluorescence detection. The specific test results are shown in Table 1:

[0059] Table 1

[0060]

[0061] As can be seen from the results in the above table, in Comparative Example 1, corn stalks are used as biochar raw materials to prepare biochar for application in the preparation of repair agents. The obtained repair agent also has a good ability to remove phenanthrene, but it is slightly inferior to the embodiment. In Comparative Example 2, the nutrients required for the normal growth and metabolism of Alcaligenes faecalis and biochar are directly encapsulated in the calcium alginate cross-linked network, which cannot ensure that the biochar is loaded with sufficient nutrients, resulting in a decrease in bacterial activity, and therefore, the ability to remove phenanthrene is poor. Comparative Examples 3 and 4 have reduced phenanthrene removal capabilities due to changes in the shell layer flow rate and the core layer flow rate, which affect the shell thickness of the core-shell structure. In Comparative Example 5, the nutrient loading is too little, which affects the bacterial activity, while in Comparative Example 6, the nutrient loading is too much, which affects the bacterial load, so the phenanthrene removal capability is not as good as that of the embodiments.

[0062] Test Example 2: Cyclic performance.

[0063] In order to verify the recyclability of the repair agent, the repair agent was placed in 1 kg of sediment, and the removal effect of the repair agent was evaluated by adding 40 mg / kg phenanthrene solution every other week.

[0064]

[0065]

[0066] It can be seen from the long-term test data in the above table that the efficiency of removing phenanthrene in each stage of the repair agent obtained by the present application is almost 90% as the time of being placed in the sediment increases.

[0067] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A persistent organic pollutant remediation agent, characterized in that: The repair agent is a core-shell structure prepared by a shell layer liquid and a core layer liquid; The shell layer liquid includes a bacterial liquid of Alcaligenes faecalis and a sodium alginate aqueous solution, and the mass ratio of the bacterial liquid of Alcaligenes faecalis to the sodium alginate aqueous solution is (4-6):1; The core layer liquid includes nutrients required by alcaligenes faecalis, biochar, and acetic acid aqueous solution, and the volume ratio of the nutrients required by alcaligenes faecalis, the biochar, and the acetic acid aqueous solution is (0.8-1):1:50; The core-shell structure is formed by adding the shell layer liquid and the core layer liquid into the calcium chloride solution using a coaxial needle; The outer and inner needles of the stainless steel coaxial nozzle have diameters of 1.2 mm and 0.6 mm respectively; The flow rate ratio of the shell layer liquid to the core layer liquid is (1.5-2):1, and the flow rate is 5 to 20 mL / h.

2. The method for preparing a persistent organic pollutant remediation agent according to claim 1, characterized in that: The following steps are involved: (1) Preparation of biochar derived from coastal wetland plants; (2) Cultivation of Alcaligenes faecalis in LB medium to obtain OD 600 = 1.2-1.8 Alcaligenes faecalis bacterial liquid; (3) adding the nutrients required by Alcaligenes faecalis and the biochar from step (1) to the acetic acid aqueous solution, stirring evenly, to obtain a core layer liquid; (4) mixing the alcaligenes faecalis liquid obtained in step (2) with the sodium alginate aqueous solution to obtain a shell liquid; (5) Adding the shell layer liquid and the core layer liquid into a calcium chloride solution with a concentration of 2-20% to prepare a core-shell structure.

3. The method for preparing a persistent organic pollutant remediation agent according to claim 2, characterized in that: In the step (1), the coastal wetland plant-derived biochar is made from the coastal wetland plant straw as raw material, which is crushed to obtain powder and passed through a 200-mesh sieve, and then placed in a tubular furnace for pyrolysis to obtain the powder.

4. The method for preparing a persistent organic pollutant remediation agent according to claim 2, characterized in that: The culture conditions of step (2) are to inoculate Alcaligenes faecalis into a sterile culture medium, maintain a certain temperature and shake overnight, and adjust the bacterial solution concentration to OD by centrifugation or by adding physiological saline. 600 =1.2-1.8; the sterile culture medium is prepared by mixing 20g yeast powder, 15g NH4Cl, and 1mmol NiCl2 evenly, adding distilled water to make up to 1L, and then adjusting the sterile culture medium to pH = 9.2-9.3 with a NaOH aqueous solution.

5. The method for preparing a persistent organic pollutant remediation agent according to claim 2, characterized in that: The nutrients required by the alkalinityogenic bacteria include chitosan, yeast powder, trypsin, and urea in a mass ratio of 6:2:1:1; the concentration of the acetic acid aqueous solution is 0.05 mol / Lwt%.

6. The method for preparing a persistent organic pollutant remediation agent according to claim 2, characterized in that: The preparation method of the core-shell structure in step (5) is as follows: the shell layer liquid and the core layer liquid are respectively injected into the outer layer and the inner layer of a stainless steel coaxial needle, and the shell layer liquid and the core layer liquid are sprayed into a calcium chloride solution with a concentration of 2-20% under high-voltage electrostatic spraying conditions using a high-voltage electrospinning device.

7. The method for preparing a persistent organic pollutant remediation agent according to claim 6, characterized in that: The high-voltage electrostatic spraying conditions are as follows: the ambient temperature is 0-50° C., the output voltage of the high-voltage power supply is 5-10 kV, and the distance between the receiving device and the stainless steel coaxial needle spinneret is 10-15 cm.

8. Use of the persistent organic pollutant remediation agent according to claim 1 in the treatment of persistent organic pollutants in saline-alkali land.

9. The use according to claim 8, characterized in that: The invention comprises a method for in-situ restoration of POPs in soil by combining plant-microorganism-biochar. The method is as follows: a persistent organic pollutant restoration agent is spread in the soil in the sediment of a coastal wetland planted with plants.

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