Synergistic remediation method for heavy metal pollution of soil

Abstract

The invention provides a synergistic remediation method for soil heavy metal pollution, and belongs to the technical field of heavy metal soil remediation. The method comprises the following steps: inoculating bacteria with resistance and adsorbability to a plurality of heavy metals into the heavy metal polluted soil; shrub plants with high resistance level to heavy metals are planted in the soil polluted by the heavy metals; crushing a trunk of a shrub plant, performing pyrolysis and carbonization to obtain shrub biochar, mixing the shrub biochar with dispersed nano Fe3O4, and performing crystallization to obtain modified biochar; a product obtained by mixed fermentation of the modified biochar, branches and leaves of shrub plants and bacteria with resistance and adsorbability to various heavy metals is added into the heavy metal polluted soil where the shrub plants are planted, so that remediation of the heavy metal polluted soil is realized. According to the method, microorganisms, plants and biochar are combined, heavy metals in the soil are effectively removed fundamentally through triple remediation cooperation, and the remediation efficiency is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal soil remediation, and in particular relates to a collaborative remediation method for heavy metal contaminated soil. Background Art

[0002] Heavy metals are more prominent among inorganic pollutants in soil, mainly because heavy metals cannot be decomposed by soil microorganisms, but are easily accumulated and converted into more toxic methyl compounds. Some even accumulate in the human body at harmful concentrations through the food chain, seriously endangering human health. The main heavy metal pollutants in soil are mercury, cadmium, lead, copper, chromium, arsenic, nickel, iron, manganese, zinc, etc. In terms of the needs of plants, metal elements can be divided into two categories: ① Elements that are not needed for plant growth and development, but are more harmful to human health, such as cadmium, mercury, lead, etc. ② Elements required for normal growth and development of plants, and have certain physiological functions for the human body, such as copper, zinc, etc., but too much will cause pollution and hinder plant growth and development. The same metal, because they exist in different forms in the soil, their migration and transformation characteristics and pollution properties are also different. Therefore, when studying the hazards of heavy metals in soil, we must not only pay attention to their total content, but also pay attention to the content of various forms.

[0003] There are many bioremediation technologies currently used for heavy metal pollution in soil, mainly including: chemical remediation technology, such as passivation agent remediation, leaching remediation technology, etc.; phytoremediation technology, selecting suitable plant species to absorb heavy metals in the soil; microbial remediation technology, selecting tolerant microorganisms to remove heavy metals; electrochemical remediation technology, under a certain current and voltage, different ions move to the opposite electrode under the action of electroosmosis and electromigration, and metal ions are aggregated and then removed by other methods (electroplating, precipitation / coprecipitation, extraction, ion exchange resin, etc.). In recent years, microbial remediation technology has gradually developed, and it has played an increasingly important role in the remediation of heavy metal-contaminated soil, especially heavy metal-contaminated farmland soil. Among them, phytoremediation and microbial remediation are recommended as green remediation methods. However, at present, artificially added microorganisms with remediation functions have many problems in the environment, such as difficulty in survival, low remediation efficiency, difficulty in competing with indigenous microorganisms, and easy functional degradation.

[0004] Biochar is a solid substance rich in carbon formed by high-temperature pyrolysis and carbonization of biomass under oxygen-limited or oxygen-free conditions. It has hydrophilic groups such as hydroxyl, carboxyl, and fatty double bonds, and an aromatic structure. It contains a large amount of carbon and plant nutrients, has a rich pore structure, a large specific surface area, and contains a large number of oxygen-containing active groups on the surface. It is a multifunctional material. However, biochar also has its shortcomings. It can only achieve physical adsorption for heavy metal ions in the soil, and cannot effectively remove them fundamentally. Therefore, the treatment effect of heavy metal contaminated soil using biochar alone is not ideal.

[0005] Therefore, there is an urgent need to provide a new method for the remediation of soil heavy metals to achieve rapid and efficient treatment of heavy metal contaminated soil. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a synergistic remediation method for heavy metal pollution in soil, so as to solve the problems of low remediation efficiency and incomplete removal of heavy metals in existing remediation methods.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a collaborative restoration method for soil heavy metal pollution, comprising the following steps:

[0009] 1) Inoculate bacteria that are resistant to and have adsorption capacity for multiple heavy metals into soil contaminated with heavy metals;

[0010] 2) Planting shrubs with high resistance to heavy metals in soils contaminated by heavy metals;

[0011] 3) crushing the trunk of the shrub plant and then pyrolyzing and carbonizing it to obtain shrub biochar, mixing the shrub biochar with the dispersed nano-Fe3O4, and crystallizing it to obtain modified biochar;

[0012] 4) Add the product of mixed fermentation of modified biochar, branches and leaves of shrub plants and bacteria that are resistant to and adsorbent of multiple heavy metals to heavy metal-contaminated soil where shrub plants have been planted to achieve the remediation of soil heavy metal pollution.

[0013] Preferably, in step 1), the bacteria having resistance and adsorption to multiple heavy metals are yeast, lactic acid bacteria, Bacillus polymyxa and Bacillus subtilis, and the mass ratio of the yeast, lactic acid bacteria, Bacillus polymyxa and Bacillus subtilis is 1-3:1-3:2-4:3-5.

[0014] Preferably, the inoculation amount of the bacteria having resistance and adsorption to multiple heavy metals in step 1) is 6.0×10 8 ~8.0×10 8 Bacteria.

[0015] Preferably, the shrub plant with a high resistance level to heavy metals in step 2) is holly.

[0016] Preferably, the temperature of the pyrolysis carbonization in step 3) is 350-550° C., and the time of the pyrolysis carbonization is 3-5 hours.

[0017] Preferably, in step 3), the mass ratio of the shrub biochar to the dispersed nano-Fe3O4 is 12 to 16:1.

[0018] Preferably, the crystallization temperature in step 3) is 130-150° C., and the crystallization time is 2-3 hours.

[0019] Preferably, in step 4), the mass ratio of the modified biochar, the branches and leaves of shrub plants and the bacteria having resistance and adsorption to multiple heavy metals is 5-10:40-50:3-5.

[0020] Preferably, the fermentation temperature in step 4) is 40-50° C., and the fermentation time is 20-30 days.

[0021] Preferably, the amount of the mixed fermentation product added in step 4) is 10-15 kg / mu.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention first inoculates bacteria, and the bacteria can resist the high concentration of heavy metal environment while adsorbing heavy metals in the soil, survive smoothly, and achieve the first level of repair; secondly, plant shrubs with high resistance to heavy metals, and the shrubs have a strong enrichment effect on heavy metals, and are highly adaptable to the growth environment. As ornamental plants, they are used to repair the soil, effectively avoiding pollutants from entering the food chain again, and minimizing the secondary pollution that can be caused in the repaired soil, thereby achieving the second level of repair; finally, the bacteria, modified biochar and shrub branches and leaves are mixed and fermented, and the adsorption effect of bacteria and biochar can be exerted. Under the load of modified biochar, the bacteria can efficiently ferment the shrub branches and leaves to produce humic acid, and the humic acid plays a role as a carrier for transferring metal ions during the adsorption process, which accelerates the adsorption process of metal ions by biochar, thereby improving the adsorption efficiency of heavy metals, and achieving the third level of repair. The combination of microorganisms, plants and biochar can effectively remove heavy metals in the soil through triple repair and coordination, and significantly improve the efficiency of repair.

[0024] The present invention mixes shrub biochar with ferroferric oxide and crystallizes them to obtain Fe3O4@biochar magnetic functional adsorption material. The heavy metal ions in the soil are physically adsorbed by the shrub biochar, and the heavy metal ions in the soil are chemically adsorbed by Fe3O4. The heavy metals in the soil are modified into an extractable state that can be absorbed by bacteria and plants by combining physical adsorption and chemical adsorption, thereby further improving the remediation efficiency of heavy metal soil. DETAILED DESCRIPTION

[0025] The present invention provides a collaborative restoration method for soil heavy metal pollution, comprising the following steps:

[0026] 1) Inoculate bacteria that are resistant to and have adsorption capacity for multiple heavy metals into soil contaminated with heavy metals;

[0027] 2) Planting shrubs with high resistance to heavy metals in soils contaminated by heavy metals;

[0028] 3) crushing the trunk of the shrub plant and then pyrolyzing and carbonizing it to obtain shrub biochar, mixing the shrub biochar with the dispersed nano-Fe3O4, and crystallizing it to obtain modified biochar;

[0029] 4) Add the product of mixed fermentation of modified biochar, branches and leaves of shrub plants and bacteria that are resistant to and adsorbent of multiple heavy metals to heavy metal-contaminated soil where shrub plants have been planted to achieve the remediation of soil heavy metal pollution.

[0030] In the present invention, bacteria that are resistant to and adsorb to multiple heavy metals are inoculated into soil contaminated by heavy metals. The bacteria that are resistant to and adsorb to multiple heavy metals are yeast, lactic acid bacteria, polymyxa bacillus and bacillus subtilis. The mass ratio of the yeast, lactic acid bacteria, polymyxa bacillus and bacillus subtilis is preferably 1-3:1-3:2-4:3-5, and more preferably 1.5-2.5:1.5-2.5:2.5-3.5:3.5-4.5; the inoculation amount of the bacteria that are resistant to and adsorb to multiple heavy metals is preferably 6.0×10 per square meter of soil contaminated by heavy metals. 8 ~8.0×10 8 bacteria, preferably 6.5×10 bacteria per square meter of heavy metal contaminated soil. 8 ~7.5×10 8 Bacteria.

[0031] In the present invention, shrubs with high resistance to heavy metals are planted in soil contaminated by heavy metals. The shrubs with high resistance to heavy metals are hollies.

[0032] In the present invention, the trunks of shrub plants are crushed and then pyrolyzed and carbonized to obtain shrub biochar, and the shrub biochar is mixed with dispersed nano-Fe3O4 and crystallized to obtain modified biochar; the crushing is to 80-100 mesh, and further to 85-95 mesh; the temperature of the pyrolysis carbonization is preferably 350-550°C, and more preferably 400-500°C; the time of the pyrolysis carbonization is preferably 3-5h, and more preferably 3.5-4.5h; the mass ratio of the shrub biochar and the dispersed nano-Fe3O4 is preferably 12-16:1, and more preferably 13-15:1; the crystallization temperature is preferably 130-150°C, and more preferably 135-145°C; the crystallization time is preferably 2-3h, and more preferably 2.5h.

[0033] In the present invention, the product of the mixed fermentation of modified biochar, branches and leaves of shrub plants and bacteria with resistance and adsorption to multiple heavy metals is added to the heavy metal-contaminated soil where shrub plants have been planted to achieve the remediation of soil heavy metal pollution. The mass ratio of the modified biochar, branches and leaves of shrub plants and bacteria with resistance and adsorption to multiple heavy metals is preferably 5-10:40-50:3-5, more preferably 6-9:42-48:4; the fermentation temperature is preferably 40-50°C, more preferably 42-48°C; the fermentation time is preferably 20-30 days, more preferably 22-28 days; the addition amount of the mixed fermentation product is preferably 10-15 kg / mu, more preferably 12-14 kg / mu.

[0034] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0035] Yeast: Angel Yeast was purchased from Nanning Saihua Fermentation Products Co., Ltd.; lactic acid bacteria: purchased from Shaanxi Hehua Beikang Biotechnology Co., Ltd.; Bacillus polymyxa was purchased from Shandong Ops Biotechnology Co., Ltd.; Bacillus subtilis was purchased from Shandong Dehe Supply Chain Management Co., Ltd.

[0036] Example 1

[0037] (1) Bacteria with resistance and adsorption to multiple heavy metals (yeast: lactic acid bacteria: Bacillus polymyxa: Bacillus subtilis = 2:2:3:4) were inoculated into the soil contaminated with heavy metals at a rate of 7.0×10 per square meter. 8 The inoculum of bacteria was inoculated into the soil contaminated with heavy metals;

[0038] (2) Planting holly, a shrub with high resistance to heavy metals, in soil contaminated by heavy metals;

[0039] (3) The trunks of shrub plants were crushed into 90 meshes. In a nitrogen atmosphere, the crushed trunks of shrub plants were heated from room temperature to 450°C in a tubular furnace at a heating rate of 15°C / min, kept warm for 4 hours, cooled to room temperature, ball-milled and sieved through a 200-mesh sieve to obtain shrub biochar; nano-Fe3O4 was added to chloroform and ultrasonicated until a transparent and clear solution A was obtained; shrub biochar was added to chloroform and ultrasonicated until a stable solution B was formed; solution A was added to solution B, mixed evenly, and crystallized at 140°C for 2.5 hours, and then filtered, washed, and dried to obtain modified biochar, wherein the modified biochar is Fe3O4@biochar; the mass ratio of the shrub biochar to the dispersed nano-Fe3O4 is 14:1;

[0040] (4) The modified biochar, branches and leaves of shrub plants and bacteria that are resistant to and adsorbent of multiple heavy metals (8:45:4) were mixed, and the product was added to the heavy metal-contaminated soil where shrub plants were planted after fermentation at 45°C for 25 days to achieve the remediation of soil heavy metal pollution. The amount of the mixed fermentation product added was 13 kg / mu.

[0041] Example 2

[0042] (1) Bacteria with resistance and adsorption to multiple heavy metals (yeast: lactic acid bacteria: polymyxa: Bacillus subtilis = 1:1:2:3) were inoculated into the soil contaminated with heavy metals at a rate of 6.0×10 8 The inoculum of bacteria was inoculated into the soil contaminated with heavy metals;

[0043] (2) Planting holly, a shrub with high resistance to heavy metals, in soil contaminated by heavy metals;

[0044] (3) The trunks of shrub plants were crushed into 80 meshes. In a nitrogen atmosphere, the crushed trunks of shrub plants were heated from room temperature to 350°C in a tubular furnace at a heating rate of 15°C / min, kept warm for 3 hours, cooled to room temperature, ball-milled and sieved through a 200-mesh sieve to obtain shrub biochar; nano-Fe3O4 was added to chloroform and ultrasonicated until a transparent and clear solution A was obtained; shrub biochar was added to chloroform and ultrasonicated until a stable solution B was formed; solution A was added to solution B, mixed evenly, and crystallized at 130°C for 2 hours, and then filtered, washed, and dried to obtain modified biochar, wherein the modified biochar is Fe3O4@biochar; the mass ratio of the shrub biochar to the dispersed nano-Fe3O4 is 12:1;

[0045] (4) The modified biochar, branches and leaves of shrub plants and bacteria with resistance and adsorption to multiple heavy metals (5:40:3) were mixed, and the product was added to the heavy metal-contaminated soil where shrub plants were planted after fermentation at 40°C for 20 days to achieve the remediation of soil heavy metal pollution. The amount of the mixed fermentation product added was 10 kg / mu.

[0046] Example 3

[0047] (1) Bacteria with resistance and adsorption to multiple heavy metals (yeast: lactic acid bacteria: polymyxa: Bacillus subtilis = 3:3:4:5) were inoculated into the soil contaminated with heavy metals at a rate of 8.0 × 10 8 The inoculum of bacteria was inoculated into the soil contaminated with heavy metals;

[0048] (2) Planting holly, a shrub with high resistance to heavy metals, in soil contaminated by heavy metals;

[0049] (3) The trunks of shrub plants were crushed into 100 meshes. Under nitrogen atmosphere, the crushed trunks of shrub plants were heated from room temperature to 550°C at a heating rate of 15°C / min in a tube furnace, kept warm for 5 hours, cooled to room temperature, ball-milled and sieved through a 200-mesh sieve to obtain shrub biochar; nano-Fe3O4 was added to chloroform and ultrasonicated until a transparent and clear solution A was obtained; shrub biochar was added to chloroform and ultrasonicated until a stable solution B was formed; solution A was added to solution B, mixed evenly, and crystallized at 150°C for 3 hours, and then filtered, washed, and dried to obtain modified biochar, wherein the modified biochar is Fe3O4@biochar; the mass ratio of the shrub biochar to the dispersed nano-Fe3O4 is 16:1;

[0050] (4) The modified biochar, branches and leaves of shrub plants and bacteria with resistance and adsorption to multiple heavy metals (10:50:5) were mixed, and the product was added to the heavy metal-contaminated soil where shrub plants were planted after fermentation at 50°C for 30 days to achieve the remediation of soil heavy metal pollution. The amount of the mixed fermentation product added was 15 kg / mu.

[0051] Comparative Example 1

[0052] Compared with Example 1, the difference is that the modified biochar and bacteria that are resistant and adsorbent to multiple heavy metals (5:3) are mixed and directly added to the heavy metal-contaminated soil where shrubs have been planted without fermentation.

[0053] Comparative Example 2

[0054] Compared with Example 1, the difference is that the mass ratio of the modified biochar, the branches and leaves of shrub plants and the bacteria with resistance and adsorption to multiple heavy metals is 4:35:2.

[0055] Comparative Example 3

[0056] Compared with Example 1, the difference is that the mass ratio of the modified biochar, the branches and leaves of shrub plants and the bacteria with resistance and adsorption to multiple heavy metals is 15:55:10.

[0057] Comparative Example 4

[0058] Compared with Example 1, the difference is that the fermentation temperature is 35°C.

[0059] Comparative Example 5

[0060] Compared with Example 1, the difference is that the fermentation temperature is 55°C.

[0061] Comparative Example 6

[0062] Compared with Example 1, the difference is that the fermentation time is 15 days.

[0063] Comparative Example 7

[0064] Compared with Example 1, the difference is that the fermentation time is 35 days.

[0065] Comparative Example 8

[0066] Compared with Example 1, the difference is that yeast: lactic acid bacteria: Bacillus polymyxa: Bacillus subtilis = 4:4:1:2.

[0067] Comparative Example 9

[0068] Compared with Example 1, the difference is that the crystallization temperature is 120° C. and the crystallization time is 4 hours.

[0069] Experimental Example 1

[0070] A field in Zhengzhou City, Henan Province was selected as the test field. The soil in the test field was contaminated by heavy metals due to industrial emissions. The soil from the surface layer of 0 to 25 cm in the test field was taken and dried in a cool and ventilated place to remove impurities. The soil pH was 7.8, and the concentrations of heavy metals Zn, Pb, Cd, Cu, Hg and As were 495.5, 248.1, 87.4, 486.7, 30.8 and 121.1 mg / kg, respectively.

[0071] The soil of the experimental field was repaired by the methods of Examples 1 to 3 and Comparative Examples 1 to 9, and then the heavy metal content of the soil was determined. After the soil was digested with HCl-HNO3, the total content of Pb and Cd in the soil was determined by ICP-MS (Thermo Fisher Scientific, Inc., iCAPQ, USA). The concentrations of Cu and Zn were determined by flame atomic absorption spectrometry, and the concentrations of As and Hg were determined by atomic fluorescence spectrometry.

[0072] Experimental results: as shown in Table 1.

[0073] Table 1 Heavy metal contents in soil of different treatment groups

[0074]

[0075] As can be seen from Table 1, the remediation efficiency of heavy metal soil in Examples 1 to 3 is much higher than that in Comparative Examples 1 to 9. According to Comparative Example 1 and Example 1, the adsorption efficiency of heavy metals by simply using modified shrub biochar loaded strains is not high. According to Comparative Examples 2 to 3 and Example 1, too much or too little mixing ratio of modified biochar, branches and leaves of shrub plants, and bacteria with resistance and adsorption to multiple heavy metals is not conducive to the fermentation process. Only when the ratio of the three is controlled within a reasonable range can the physical and chemical dual adsorption and modification of heavy metals by biochar be fully exerted. According to Comparative Examples 4 to 7 and Example 1, too high or too low fermentation temperature and too long or too short fermentation time are not conducive to the production of humic acid, thereby affecting the transfer of heavy metal ions by humic acid during the adsorption process. According to Comparative Example 8 and Example 1, the unreasonable ratio of microbial strains will not only affect the adsorption and tolerance of soil heavy metals by the strains, but also affect the fermentation rate of the branches and leaves of shrub plants. According to Comparative Example 9 and Example 1, inappropriate crystallization temperature and time will affect the binding strength of Fe3O4 and biochar, and further affect the adsorption performance of the modified biochar.

[0076] It can be seen from the above embodiments and experimental examples that the present invention combines microorganisms, plants and biochar to effectively remove heavy metals in the soil through triple repair synergy, thereby significantly improving the efficiency of repair.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A collaborative remediation method for heavy metal pollution in soil, characterized in that: The following steps are involved: 1) Inoculate bacteria that are resistant to and have adsorption capacity for multiple heavy metals into soil contaminated with heavy metals; 2) Planting shrubs with high resistance to heavy metals in soils contaminated by heavy metals; 3) crushing the trunk of the shrub plant and then pyrolyzing and carbonizing it to obtain shrub biochar, and mixing the shrub biochar with the dispersed nano-Fe3O4 and crystallizing it to obtain modified biochar; 4) Add the product of mixed fermentation of modified biochar, branches and leaves of shrub plants and bacteria that are resistant to and adsorbent of multiple heavy metals to heavy metal-contaminated soil where shrub plants have been planted to achieve the remediation of soil heavy metal pollution.

2. The collaborative repair method according to claim 1, characterized in that: In step 1), the bacteria having resistance and adsorption to multiple heavy metals are yeast, lactic acid bacteria, Bacillus polymyxa and Bacillus subtilis, and the mass ratio of the yeast, lactic acid bacteria, Bacillus polymyxa and Bacillus subtilis is 1-3:1-3:2-4:3-5.

3. The collaborative repair method according to claim 1, characterized in that: Step 1) The inoculation amount of the bacteria having resistance and adsorption to multiple heavy metals is 6.0×10 8 ~8.0×10 8 Bacteria.

4. The collaborative repair method according to claim 1, characterized in that: In step 2), the shrub plant with a high resistance level to heavy metals is holly.

5. The collaborative repair method according to claim 1, characterized in that: Step 3) The temperature of the pyrolysis carbonization is 350-550° C., and the time of the pyrolysis carbonization is 3-5 hours.

6. The collaborative repair method according to claim 1, characterized in that: Step 3) The mass ratio of the shrub biochar to the dispersed nano-Fe3O4 is 12 to 16:

1.

7. The collaborative repair method according to claim 1, characterized in that: Step 3) The crystallization temperature is 130-150° C. and the crystallization time is 2-3 hours.

8. The collaborative repair method according to claim 1, characterized in that: Step 4) The modified biochar, the branches and leaves of shrub plants and the bacteria having resistance and adsorption to a variety of heavy metals are mixed in a mass ratio of 5-10:40-50:3-5.

9. The collaborative repair method according to claim 1, characterized in that: Step 4) The fermentation temperature is 40-50° C. and the fermentation time is 20-30 days.

10. The collaborative repair method according to claim 1, characterized in that: Step 4) The amount of the mixed fermentation product added is 10-15 kg / mu.

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