Method for removing hexavalent chromium in water by cooperating indigenous microorganisms with clay mineral material

Abstract

The invention provides a method for removing hexavalent chromium in water through cooperation of indigenous microorganisms and clay mineral materials, which comprises the following steps: (S1) extraction of indigenous microorganisms: uniformly mixing heavy metal Cr (VI) polluted soil with water, centrifuging, and precipitating and suspending in constant volume water to serve as an indigenous microorganism extracting solution; (S2) grinding calcium-based montmorillonite until the particle size of the calcium-based montmorillonite is 200-400 meshes, so as to obtain calcium-based montmorillonite particles; and (S3) putting the indigenous microorganism extracting solution, the calcium-based montmorillonite particles and the electron donor into the water containing the hexavalent chromium, keeping an anaerobic condition, and removing the hexavalent chromium in the water. Compared with a traditional physical and chemical method, the method has the advantages of being easy to operate, low in cost, environmentally friendly, free of secondary pollution and the like, has wide application prospects and can be put into production and use in a large scale.

Description

Technical Field

[0001] The invention relates to the field of pollutant treatment, and in particular to a method for removing hexavalent chromium in water by using indigenous microorganisms in collaboration with clay mineral materials. Background Art

[0002] Due to the rapid development of industry, chromium (Cr) has been widely present in the environment, leading to serious environmental problems and human diseases. The high solubility of hexavalent chromium in the environment and its carcinogenicity to humans make it more toxic than trivalent chromium. At present, the methods for removing Cr(VI) mainly include electrochemical method, photocatalytic reduction method, ion exchange method, chemical precipitation method and microbial method. Among them, compared with the traditional Cr(VI) removal method, the microbial method for remediating Cr(VI) contaminated groundwater is not only efficient and environmentally friendly and will not cause secondary pollution, but also has low operating costs. It is a technology with research and application prospects.

[0003] Natural reductants such as microorganisms, iron-containing minerals (such as pyrite and clay minerals) and organic matter can reduce highly toxic Cr(VI) to less toxic Cr(III) by forming solid or organic composite Cr(III). Iron-containing clay minerals are widely used in the field of heavy metal pollution remediation due to their unique layered structure, large specific surface area, rich pore structure, strong expandability and cation exchangeability, and are a hot topic of research today. Studies have also found that structural Fe(II) in clay minerals and chemically / biologically reduced clay minerals have the ability to reduce Cr(VI) to Cr(III). The formed Cr(III) precipitate will be adsorbed on the surface of clay minerals or exist between clay mineral layers, so that clay minerals play a role in fixation and detoxification. In addition, in the actual natural environment, organic matter is another important factor that participates in and affects the Cr(VI) cycle and geochemical behavior. Organic matter can also achieve the reduction of Cr(VI) by itself or on the mineral surface or under the catalytic action of metal ions.

[0004] CN113816502A discloses a method for continuously removing hexavalent chromium from groundwater by using synthesis gas by microorganisms. The method comprises mixing synthesis gas and hexavalent chromium-contaminated groundwater to obtain hexavalent chromium-contaminated water containing synthesis gas, wherein the synthesis gas is composed of hydrogen, carbon monoxide and carbon dioxide; the hexavalent chromium-contaminated water containing synthesis gas is introduced into a reactor inoculated with microorganisms to carry out a hexavalent chromium reduction reaction; wherein, during the hexavalent chromium reduction reaction, the microorganism uses the synthesis gas as an electron donor to reduce the hexavalent chromium to trivalent chromium.

[0005] Montmorillonite is a mineral material commonly used to treat sewage. It has a wide range of sources, low price, good stability, and is often used for adsorption treatment of heavy metal wastewater. However, its treatment of Cr(VI) is not ideal. There is a prior art report that montmorillonite is inorganically modified with polyhydroxyaluminum chloride ion solution to expand the interlayer spacing and specific surface area of ​​montmorillonite, and then further organically modified with cetylpyridinium chloride as an organic intercalation agent. On the one hand, the interlayer spacing of montmorillonite can be further expanded, and the expanded interlayer spacing creates a spatial environment for the insertion of heavy metal hexavalent chromium ions. On the other hand, the surface of montmorillonite can be made to be constantly positively charged, creating a charge environment where charges attract each other for the removal of heavy metal hexavalent chromium ions. However, this modification method is complicated and actually abandons the advantages of montmorillonite, which is cheap, easy to obtain and low in cost. Although the modified montmorillonite has improved Cr(VI) removal ability, the cost is greatly increased, which is not worth the loss.

[0006] The existing technologies have reported the use of microorganisms or iron-containing clay minerals to treat Cr(VI)-contaminated environments, but the interfacial interactions between them, Cr(VI) reduction products, and dominant microorganisms have not been reported and are still unclear. Summary of the invention

[0007] In order to provide an effective, low-cost, simple method for treating hexavalent chromium in water, the present invention provides a method for enhancing the stability of indigenous microorganisms by calcium-based montmorillonite and sodium lactate, and synergistically improving the removal of hexavalent chromium in water, which solves the problems of unsatisfactory hexavalent chromium removal effect in groundwater, high cost and complicated methods in the prior art.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for removing hexavalent chromium from water by using indigenous microorganisms in collaboration with clay mineral materials comprises the following steps:

[0010] (S1) Extraction of indigenous microorganisms: soil contaminated by heavy metal Cr(VI) is mixed with water and centrifuged, and the precipitate is suspended in a constant volume of water to serve as an indigenous microorganism extract;

[0011] (S2) grinding the calcium-based montmorillonite to a particle size of 200-400 mesh to obtain calcium-based montmorillonite particles;

[0012] (S3) placing the indigenous microbial extract, calcium-based montmorillonite particles, and electron donors into water containing hexavalent chromium, maintaining anaerobic conditions, and removing the hexavalent chromium from the water.

[0013] Furthermore, in step (S1), the Cr(VI) content of the soil contaminated with heavy metal Cr(VI) after leaching is tested to be 10-50 mg / Kg; the mass ratio of soil to water is 1:5-20, preferably 1:9-12. There is no particular limitation on the method of uniform mixing, such as stirring, ultrasonic vibration, and glass bead vibration. Centrifugation is divided into two stages, first centrifugation at 2000-3000 rpm for 10-20 min, the supernatant is transferred to a new centrifuge tube, and centrifugation at 4000-10000 rpm for 30-60 min, and the resulting precipitate is suspended in water as an inoculant for later use. The mass ratio of soil to water used to suspend the precipitate is 5-10:1.

[0014] Furthermore, in step (S2), the grinding method is manual grinding, air flow milling, ball milling, etc., without any special limitation, as long as the calcium-based montmorillonite is ground to a suitable particle size.

[0015] Furthermore, in step (S3), the ratio of the indigenous microbial extract, the calcium-based montmorillonite particles, and the electron donor is 10mL: 1-5g: 0.01-0.1g; preferably, the ratio of the indigenous microbial extract, the calcium-based montmorillonite particles, and the electron donor is 10mL: 3-5g: 0.02-0.05g.

[0016] Furthermore, the electron donor is selected from at least one of formate, acetate, lactate, citrate, malate, glucose, and amino acids, and the amino acids are selected from leucine, proline, glycine, cysteine, and methionine; preferably sulfur-containing amino acids (cysteine, methionine), more preferably cysteine; and the cation of the salt is potassium ion or sodium ion.

[0017] Preferably, the electron donor is a compound of lactate and sulfur-containing amino acids in a mass ratio of 1-3: 1-3, and most preferably a compound of lactate and cysteine ​​in a mass ratio of 1-3: 1. The inventors unexpectedly found that the combination of lactate and sulfur-containing amino acids, especially cysteine, as electron donors can play a synergistic role, significantly improving the long-term effectiveness of removing hexavalent chromium from water.

[0018] Furthermore, in step (S3), the content of Cr(VI) in the water containing hexavalent chromium is 10-500 mg / L, preferably 25-100 mg / L.

[0019] Furthermore, in step (S3), the anaerobic condition is to place the treatment equipment in a sealed condition and introduce nitrogen to exclude air.

[0020] Furthermore, in step (S3), hexavalent chromium in water is removed at a temperature of 15-40°C, preferably 20-30°C.

[0021] Through the above technical solutions, the present invention has achieved the following technical advances:

[0022] (1) Compared with the materials used in existing heavy metal wastewater treatment, the clay minerals of the present invention have the characteristics of abundant resources, low cost and no need for secondary processing;

[0023] (2) The clay minerals of the present invention enhance the removal of hexavalent chromium by indigenous microorganisms more quickly and efficiently, and the reduced product Cr 3+ The interlayer Ca2+ is replaced by the excellent interlayer cation exchange property of clay minerals. 2+ It is fixed between the layers, stabilizing the trivalent chromium while reducing the hexavalent chromium.

[0024] (3) The present invention uses a combination of lactate and amino acids, especially lactate and sulfur-containing amino acids as electron donors, which can significantly improve the long-term effectiveness of removing hexavalent chromium from water.

[0025] (4) The preparation and application of the functional mineral material for strengthening the stabilization of heavy metals by indigenous microorganisms of the present invention are simple and easy to control, green and environmentally friendly, and have no secondary pollution. It can achieve a heavy metal stabilization rate of more than 95%, has broad application prospects, and can be put into large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The time variation of Cr(VI) removal efficiency in the first cycle of different groups in Example 1.

[0027] Figure 2 This is a diagram of the final removal efficiency of Cr(VI) in the first cycle of different groups in Example 1.

[0028] Figure 3 The time course of Cr(VI) concentration in four consecutive operation cycles of the biological group in Example 1.

[0029] Figure 4 The XRD diagrams of the montmorillonite in Example 1 and the reactor products after the first, second and third cycles are shown.

[0030] Figure 5 The composition and abundance of the microbial community in the initial inoculum and bioreactor at the class level in Example 1.

[0031] Figure 6 Heat map analysis of the microbial community in the initial inoculum and bioreactor at the genus level in Example 1. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0033] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0034] The simulated groundwater used in the embodiment of the present invention contains the following components: 1L of groundwater contains 0.2464gCaCl2, 1.0572g MgCl2·6H2O, 0.4459g NaCl, 0.0283g KCl, 0.1557g NH4Cl, 0.0299gKH2PO4, and 0.8082gNaHCO3, Cr(VI) is added to the simulated groundwater in the form of K2CrO4, and the initial concentration of Cr(VI) is 50mg / L.

[0035] Example 1 (Biological Group)

[0036] (1) Weigh 50 g of soil from a chromium slag contaminated site in Jinan, Shandong Province (the original soil was mainly composed of Actinobacteria and Acidimicrobiia at the order level, and the Cr(VI) content was 20.58 mg / Kg after soil leaching), 450 mL of deionized water and an appropriate amount of glass beads into a 500 mL conical flask, and shake it in a shaking incubator at 180 rpm and 37 °C for 2 h. After taking it out, centrifuge it at 2530 rpm for 12 min to take the upper clear liquid, then centrifuge it at 8000 rpm for 30 min to take the lower precipitate, and suspend the precipitate in 10 mL of deionized water to use as a reserve inoculum.

[0037] (2) A 250 mL serum bottle was used as an intermittent reactor and then sealed with a butyl rubber stopper and an aluminum gland to maintain strict anaerobic conditions. 5 g of montmorillonite, 10 mL of inoculum, 200 mL of simulated groundwater, and 0.02334 g of electron donor sodium lactate as a carbon source were added to the bioreactor, and the COD was 100 mg / L.

[0038] (3) The serum bottles were aerated with N2 for 15 min to remove oxygen from the bottles, and then the bottles were incubated at 22 ± 2 °C to conduct an experiment on clay mineral-enhanced microbial removal of Cr(VI) from simulated groundwater.

[0039] (4) After that, samples were taken at regular intervals. After the first cycle (10 days), the Cr(VI) in the solution was tested using the diphenylcarbohydrazide spectrophotometric method. First, diphenylcarbohydrazide colorimetric agent was prepared, i.e., 2 g of diphenylcarbohydrazide was weighed, dissolved in 100 mL of acetone, 0.2 mL of sulfuric acid was added, and shaken well. Then, the solution Cr(VI) was tested, i.e., 0.5 mL of the sample to be tested was taken, water was added to about 40 mL of the 50 mL colorimetric dish, and then 0.5 mL of sulfuric acid solution (volume ratio of sulfuric acid: water = 1:1), 0.5 mL of phosphoric acid solution (volume ratio of phosphoric acid: water = 1:1) and 2 mL of diphenylcarbohydrazide were added, and the volume was fixed to 50 mL. Shake well, let stand for 5 min-10 min, and measure the absorbance at 540 nm.

[0040] Comparative Example 1 (endogenous group)

[0041] The method is basically the same as that of Example 1, except that no montmorillonite is added to the serum bottle reactor.

[0042] Comparative Example 2 (Sterilization Group)

[0043] The method was basically the same as in Example 1, except that no montmorillonite was added to the serum bottle reactor and the inoculum was sterilized.

[0044] Comparative Example 3 (non-biological group)

[0045] The method is basically the same as that of Example 1, except that no microbial extract is added to the serum bottle reactor.

[0046] Comparative Example 4 (no sodium lactate group)

[0047] The method is basically the same as that of Example 1, except that sodium lactate is not added to the serum bottle reactor.

[0048] The results are as follows Figure 1 and 2 As shown in the figure, after the first cycle (10 days), the biological group (mineral + microorganism + sodium lactate) had the highest removal rate of hexavalent chromium, which was 100%. However, the endogenous group (bacteria + sodium lactate), the group without sodium lactate (mineral + bacteria), the sterilized group (sterilized + sodium lactate) and the non-biological group (mineral + sodium lactate) were only 38.72%, 16.57%, 7.33% and 1.41% respectively.

[0049] Comparison between the above Example 1 and Comparative Examples 1-4 shows that clay mineral-enhanced microorganisms can significantly promote the removal of Cr(VI) in groundwater based on the presence of minerals+microorganisms+electron donors of the present invention.

[0050] Example 2

[0051] The other conditions were the same as those in Example 1, except that the electron donor was replaced by sodium citrate.

[0052] Example 3

[0053] The other conditions were the same as those in Example 1, except that the electron donor was replaced by a mixture of sodium citrate and cysteine ​​in a mass ratio of 1:1.

[0054] Example 4

[0055] The other conditions were the same as those in Example 1, except that the electron donor was replaced by cysteine.

[0056] Example 5

[0057] The other conditions were the same as those in Example 1, except that the electron donor was replaced by a mixture of sodium lactate and cysteine ​​in a mass ratio of 1:1.

[0058] Example 6

[0059] The other conditions were the same as those in Example 1, except that the electron donor was replaced by a mixture of sodium lactate and methionine in a mass ratio of 1:1.

[0060] Example 7

[0061] The other conditions were the same as those in Example 1, except that the electron donor was replaced by a mixture of sodium lactate and cysteine ​​in a mass ratio of 3:1.

[0062] Example 8

[0063] The other conditions were the same as those in Example 1, except that the electron donor was replaced by a mixture of sodium lactate and glycine in a mass ratio of 1:1.

[0064] Example 9

[0065] The other conditions were the same as those in Example 1, except that the electron donor was replaced by a mixture of sodium lactate and leucine in a mass ratio of 1:1.

[0066] Application Examples

[0067] The effect of the above embodiment on removing hexavalent chromium from water was tested for long-term effectiveness, and samples were taken at regular intervals. After four consecutive cycles (10 days for the first cycle, 4 days for the second cycle, 4 days for the third cycle, and 8 days for the fourth cycle), the Cr(VI) in the solution was tested using diphenylcarbazide spectrophotometry. The results are shown in Table 1 below.

[0068] Table 1 Test on the effect of removing hexavalent chromium from water

[0069] project Cr(VI) removal rate in the first cycle Cr(VI) removal rate in the fourth cycle Example 1 100％ 95.3％ Example 2 100％ 93.7％ Example 3 100％ 95.2％ Example 4 98.5％ 92.8％ Example 5 100％ 99.4％ Example 6 100％ 97.2％ Example 7 100％ 99.1％ Example 8 100％ 94.6％ Example 9 100％ 96.5％

[0070] The long-term effectiveness results of removing hexavalent chromium from water in Example 1 are as follows: Figure 3As shown in the figure, with the increase of the number of cycles (from the first cycle to the third cycle), the removal effect of the bioreactor on Cr(VI) gradually improves and the reaction rate accelerates. As the number of cycles continues to increase, the removal effect of Cr(VI) deteriorates after the fourth cycle.

[0071] In Example 1, montmorillonite and the product of the bioreactor after three cycles were taken for XRD testing and analysis. The results are as follows: Figure 4 As shown in the figure, compared with the original montmorillonite, the 001 diffraction value of the product of the bioreactor after the three cycles, that is, the montmorillonite after microbial reduction, is slightly increased, indicating that the spacing between the TOT structure layers is gradually increasing, which may be due to the Cr 3+ It enters the interlayer of montmorillonite through cation exchange and is fixed in the interlayer, thereby increasing the interlayer distance of montmorillonite.

[0072] The initial inoculum in Example 1 and the inoculum of the bioreactor after three cycles were taken for 16S metagenomic sequencing to analyze the community structure composition at the microbial class level and the genus level, as well as the bacterial richness and diversity index of the community. The results are shown in Table 2. The number of OUTs is an important indicator for measuring microbial diversity. The more OTUs there are, the richer the microbial species in the sample. Through OTU analysis, the microbial diversity and richness in the sample can be understood. The Ace index and Chao index are used to evaluate the microbial richness index in the sample. The larger the Ace value, the richer the species in the environment and the more evenly the species are distributed. The larger the Chao value, the higher the species richness of the sample. The Simpson index and Shannon index are used to evaluate the microbial diversity index in the sample. The larger the Simpson value, the lower the community diversity. The larger the Shannon value, the higher the community diversity. It can be seen that after the reaction, the diversity of the microbial community has changed significantly. Compared with the initial inoculum, the number of OTUs in the bioreactor decreased after three cycles. In the three bioreactors, the number of OTUs after the third cycle was higher than that after the remaining two cycles, indicating that more organisms in the bioreactors after the third cycle were able to tolerate and detoxify Cr(VI). The microbial richness reflected by the Ace and Chao indices after the three cycles showed a significant downward trend relative to the initial inoculum. In addition, the Shannon index of the microbial community after the third cycle was the lowest and the Simpson index was the highest in the initial inoculum and the three bioreactors, indicating that microbial diversity may actually decrease after Cr(VI) incubation. Figure 5 The composition and abundance of the microbial community in the initial inoculum and bioreactor at the class level. Compared with the initial inoculum, the inoculum of the bioreactor after three cycles was mainly dominated by Gammaproteobacteria, reaching more than 90%. Figure 6 Heat map analysis of the microbial communities in the initial inoculum and bioreactor at the genus level. With the extension of acclimatization time, the bioreactor mainly included microorganisms related to heavy metal reduction, such as Burkholderiales and Pseudomonadales.

[0073] Table 2 Community structure composition at the class and genus levels and bacterial richness and diversity index of the community

[0074] system OTU Ace Chao Shannon Simpson Inoculum 429 429 429 5.16 0.015 Loop 1 55 55 55 1.62 0.253 Loop 2 86 91 88 1.77 0.258 Loop 3 120 123 121 1.50 0.342

Claims

1. A method for removing hexavalent chromium from water by using indigenous microorganisms in collaboration with clay mineral materials, characterized in that: The following steps are involved: (S1) Extraction of indigenous microorganisms: soil contaminated with heavy metal Cr(VI) is mixed evenly with water, centrifuged, and the precipitate is suspended in a constant volume of water to serve as an indigenous microorganism extract; (S2) grinding the calcium-based montmorillonite to a particle size of 200-400 mesh to obtain calcium-based montmorillonite particles; (S3) placing the indigenous microbial extract, calcium-based montmorillonite particles, and electron donors into water containing hexavalent chromium, maintaining anaerobic conditions, and removing the hexavalent chromium from the water.

2. The method according to claim 1, characterized in that In step (S1), after leaching, the soil contaminated with heavy metal Cr(VI) has a Cr(VI) content of 10-50 mg / kg; the mass ratio of soil to water is 1:5-20, preferably 1:9-12.

3. The method according to claim 1, characterized in that In step (S1), the centrifugation is divided into two stages. First, the centrifugation is performed at a speed of 2000-3000 rpm for 10-20 min, and the supernatant is transferred to a new centrifuge tube and centrifuged at a speed of 4000-10000 rpm for 30-60 min.

4. The method according to claim 1, characterized in that: In step (S1), the mass ratio of soil to water for suspending sediment is 5-10:

1.

5. The method according to claim 1, characterized in that In step (S3), the ratio of the indigenous microbial extract, calcium-based montmorillonite particles, and the electron donor is 10 mL: 1-5 g: 0.01-0.1 g.

6. The method according to claim 1, characterized in that In step (S3), the ratio of the indigenous microbial extract, calcium-based montmorillonite particles, and the electron donor is 10 mL: 3-5 g: 0.02-0.05 g.

7. The method according to claim 1, characterized in that The electron donor is selected from at least one of formate, acetate, lactate, citrate, malate, glucose and amino acids; and the amino acids are selected from leucine, proline, glycine, cysteine ​​and methionine.

8. The method according to claim 7, characterized in that The electron donor is a compound of lactate and amino acids, and the amino acids are preferably sulfur-containing amino acids (cysteine, methionine); in lactate, the cation is a potassium ion or a sodium ion.

9. The method according to claim 8, characterized in that The electron donor is a compound of lactate and sulfur-containing amino acid in a mass ratio of 1-3:1-3, preferably a compound of lactate and cysteine ​​in a mass ratio of 1-3:

1.

10. The method according to claim 1, characterized in that In step (S3), the content of Cr(VI) in the water containing hexavalent chromium is 10-500 mg / L, preferably 25-100 mg / L; the anaerobic condition is to make the treatment equipment in a sealed condition, introduce nitrogen and exclude air; the hexavalent chromium in the water is removed at a temperature of 15-40°C, preferably 20-30°C.

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