Method for synthesizing biological struvite through bacterium induction by taking seawater as magnesium source and application

Abstract

The invention discloses a method for synthesizing biological struvite through bacterium induction by taking seawater as a magnesium source and application of the method. The method comprises the following steps: inoculating immobilized bacillus velezensis into a liquid culture medium prepared by using seawater, and after culture is finished, separating to obtain the biological struvite, the immobilized bacillus velezensis takes activated carbon as a carrier and is loaded with the bacillus velezensis. The specific surface area and Cd < 2 + > maximum unit adsorption capacity of the biological struvite prepared by utilizing the immobilized bacteria are 168.7095 m < 2 > / g and 446.43 mg / g respectively, are far higher than those of struvite synthesized by induction of free bacteria and struvite biologically synthesized by induction of magnesium chloride as a magnesium source, and are obviously higher than those of chemically synthesized struvite. According to the preparation method disclosed by the invention, the required seawater is large in reserves, convenient to obtain and low in cost, the mineralization efficiency of the immobilized bacteria is high, and the biological struvite is simple to prepare and has a relatively good application prospect on cadmium pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the remediation material of heavy metal cadmium, and particularly relates to a method for inducing synthesis of biological struvite by bacteria using seawater as a magnesium source and application. BACKGROUND

[0002] In recent years, with the acceleration of industrialization and urbanization, heavy metal pollution problems have become increasingly serious, and have become one of the important environmental problems of global concern. Heavy metals have high toxicity, are difficult to degrade, and are easily enriched in the environment, and long-term existence in soil, water and organisms poses a serious threat to the stability of the ecological system and human health. Among the many heavy metals, cadmium is of great concern due to its strong toxicity, high biological availability and strong migration. Reducing the migration potential and biological availability of heavy metals has become an effective means to control water and soil pollution, for example, porous solid materials are used to achieve efficient adsorption and fixation of cadmium in water.

[0003] Adsorption is a method of achieving efficient removal of pollutants by physical or chemical interaction between porous solid materials and heavy metals in water. Due to its simple process, low operating cost and strong adaptability, it has been widely used in wastewater treatment practice. Biological struvite has been determined to have good passivation ability for cadmium. However, the induction synthesis of biological struvite in the past often requires expensive commercial magnesium sources such as MgCl2 and MgSO4, which limits its large-scale application. Therefore, there is an urgent need to seek a cheap magnesium source to induce struvite biomineralization. SUMMARY

[0004] The present application provides a method for preparing high-adsorption biological struvite induced by immobilized bacteria using low-cost natural seawater as a magnesium source. The seawater used in the preparation method has large reserves, is easy to obtain and has low cost. The immobilized bacteria have high mineralization efficiency. The prepared biological struvite has a simple preparation method and good application prospects for cadmium pollution treatment.

[0005] The present application also provides a preparation method and application of the biological struvite. The present application uses seawater as a magnesium source and a method for inducing mineral synthesis by Bacillus velezensis to induce synthesis of biological minerals (struvite). The synthesized biological minerals have more pore structure and larger specific surface area than non-biological minerals, and have an advantage in adsorbing heavy metal ions.

[0006] Technical solution: In order to achieve the above-mentioned purpose, the method for inducing synthesis of biological struvite by bacteria using seawater as a magnesium source according to the present application comprises the following steps:

[0007] The immobilized Bacillus velezensis is inoculated into a liquid medium configured with seawater, and biological struvite is obtained after the end of the culture; the immobilized Bacillus velezensis takes activated carbon, attapulgite or bentonite as a carrier and is loaded with Bacillus velezensis.

[0008] The immobilized Bacillus velezensis is immobilized by taking activated carbon as a carrier, polyvinyl alcohol and sodium alginate as embedding agents, and calcium chloride and boric acid as cross-linking agents.

[0009] The Bacillus velezensis with the GeneBank number (accession No. CP037417) or Bacillus velezensis CGMCC 1.12669 or other commercially purchased Bacillus velezensis strains.

[0010] The liquid medium configured with seawater contains 0.5-1.0 g of tryptone, 0.25-0.5 g of yeast extract and 0.088-0.0408 g of potassium dihydrogen phosphate per 1 L of seawater.

[0011] Preferably, the liquid medium configured with seawater contains 1.0 g of tryptone, 0.5 g of yeast extract and 0.0408 g of potassium dihydrogen phosphate per 1 L of seawater.

[0012] The immobilized Bacillus velezensis is inoculated into a liquid medium configured with seawater, and biological struvite is obtained after the end of the culture; the immobilized Bacillus velezensis takes activated carbon, attapulgite or bentonite as a carrier and is loaded with Bacillus velezensis.

[0013] Preferably, 1% (v / v) of the immobilized bacterial microspheres (about 20 particles) are added per 100 mL of the medium.

[0014] The culture conditions are 25-37℃, 110-180 rpm oscillation culture for 6-10 days; after the end of the culture, the precipitate is collected and dried to obtain biological struvite.

[0015] Preferably, the culture conditions are 30℃, 130 rpm oscillation culture for 8 days.

[0016] The seawater is natural seawater, and the seawater is filtered through a 0.45 μm filter membrane to remove other impurities.

[0017] The struvite organic complex obtained by the method for synthesizing biological struvite induced by bacteria with seawater as a magnesium source.

[0018] The struvite organic complex is used in the removal of cadmium ions or the preparation of a cadmium ion adsorbent.

[0019] The adsorbent for treating heavy metal cadmium ions comprises the struvite organic complex.

[0020] In the preparation method of the application, natural seawater is used as a magnesium source for the first time, and high-purity struvite is formed by using immobilized bacteria, which can be applied to the adsorption of heavy metal cadmium.

[0021] In the application, the seawater is rich in magnesium, has large reserves, and is easy to obtain.

[0022] In the application, the immobilized Bacillus velezensis is inoculated into a culture medium prepared from seawater and then cultured, and biological struvite is obtained after the culture. The biological struvite of the application is a struvite organic complex with porous and mesoporous structures, which is induced and synthesized by the immobilized Bacillus velezensis. 2+ The maximum unit adsorption capacity is 168.7095 mg / g and 446.43 mg / g, which is much higher than that of struvite induced and synthesized by free bacteria (140.9718 mg / g and 386.10 mg / g) and struvite induced and synthesized by using magnesium chloride as a magnesium source (45.4751 mg / g and 182.36 mg / g), and also much higher than that of chemically synthesized struvite (79.4863 mg / g and 216.92 mg / g). 2 2 2 2 In the preparation method of the application, seawater is used, which has large reserves, is easy to obtain, and has low cost.

[0023] The method for synthesizing biological struvite by using microorganisms in the application does not need special pretreatment of seawater and does not need to consider factors such as Ca 2+ , so that high-purity biological struvite crystals can be obtained. The biological mineral synthesized by using the method has more pore structures and a larger specific surface area than non-biological minerals, and has an advantage in adsorbing heavy metal ions.

[0023] Advantages: Compared with the prior art, the application has the following advantages:

[0024] 1. The biological struvite prepared in the application is a struvite organic complex with porous characteristics, which is synthesized by using a common functional microbial fertilizer strain, Bacillus velezensis.

[0025] 2、The biological struvite has a high specific surface area and excellent adsorption capacity for cadmium, and the maximum adsorption capacity for cadmium can reach 446.43 mg / g.

[0026] 3、The magnesium in the biological struvite is derived from seawater, so the material is easy to obtain and has low cost; the seawater does not need to be specially pretreated, and can be directly used after filtering impurities in the water.

[0027] 4、The preparation method of the biological struvite is economical and environmentally friendly, simple and fast to operate, low in cost, and wide in application range; no toxic and harmful substances are added in the synthesis process, so the biological struvite product will not cause secondary pollution, has no potential risk to the environment, and has a good application prospect for heavy metal remediation. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a morphology feature diagram of the immobilized bacillus velezensis in Example 1.

[0029] Figure 2 It is a structure and morphology diagram of struvite induced and synthesized by the immobilized bacteria in Example 2. Figure 2 a is an XRD pattern of the biological struvite; Figure 2 b is an FTIR pattern of the biological struvite; Figure 2 c1-c4 are SEM diagrams of the biological struvite.

[0030] Figure 3 It is a schematic diagram of the process of inducing and synthesizing the biological struvite and the process of removing cadmium.

[0031] Figure 4 It is an XRD and SEM diagram of struvite induced and synthesized by free bacteria in Comparative Example 1.

[0032] Figure 5 It is an XRD and SEM diagram of struvite induced and synthesized by free bacteria with magnesium chloride as a magnesium source in Comparative Example 2.

[0033] Figure 6 It is an XRD and SEM diagram of chemically synthesized struvite with seawater as a magnesium source in Comparative Example 3. DETAILED DESCRIPTION

[0034] The present application will be further illustrated below in combination with examples and drawings.

[0035] The materials, reagents and the like used in the examples can be obtained from commercial channels unless otherwise specified.

[0036] The bacillus velezensis in the embodiments of the present application is isolated from bio-organic fertilizer, and its whole genome sequence has been stored in GeneBank (accession No. CP037417) and provided by the School of Life Sciences, Nanjing Normal University. Other bacillus velezensis strains can also be used to achieve the effect of the present application, for example, bacillus velezensis CGMCC 1.12669 of China General Microbiological Culture Collection Center or other strains purchased through commercial channels.

[0037] The seawater in the embodiments is selected from the Yellow Sea waters in Yancheng, Jiangsu (E120.86°, N33.12°), and the seawater is filtered through a 0.45 μm filter membrane to remove other impurities.

[0038] The activated carbon is commercially available and is fully ground through a 100 mesh sieve.

[0039] Embodiment 1

[0040] The preparation method of the immobilized bacillus velezensis is as follows:

[0041] 1. Seed liquid preparation: inoculate 2 loops of bacillus velezensis (GeneBank accession No. CP037417) into 100 mL of sterilized (115°C, 30 min) LB liquid medium, and place it in a shaking incubator at 30°C and 130 rpm for 12 h to prepare the bacterial seed liquid (bacterial liquid concentration is about 4.7×10 9 cfu / mL).

[0042] 2. Activated carbon pretreatment: grind the activated carbon and pass it through a 100 mesh sieve, and take 0.1 g and place it in a 50 mL beaker for standby.

[0043] 3. Preparation of polyvinyl alcohol and sodium alginate solution: weigh 0.5 g of polyvinyl alcohol (44.05 MW) and 2 g of sodium alginate into 80 mL of double distilled water, stir in a 95°C water bath until the solution is thick, and then sterilize at 115°C for 30 min, and cool for standby.

[0044] 4. Preparation of 2% calcium chloride and 1% boric acid mixed solution: weigh 2 g of calcium chloride and 1 g of boric acid into 100 mL of double distilled water, and then sterilize at 115°C for 30 min, and cool for standby.

[0045] 5. Preparation of immobilized Bacillus velezensis: 100 ml of bacterial seed solution in step 1 was centrifuged to remove the supernatant, and the bacterial cells were washed with sterile water three times and resuspended in 20 mL of sterile water, and mixed with activated carbon in step 2, and shaken gently for 20 min to promote adsorption. Then, the mixture was slowly added to the cooled polyvinyl alcohol-sodium alginate solution in step 3, and stirred evenly; using a 10 mL sterile syringe, the mixture was dropped into the sterilized cross-linking solution containing 2% calcium chloride and 1% boric acid in step 4, and cross-linked at 4°C for 8 h to form calcium alginate microspheres, i.e. immobilized Bacillus velezensis Figure 1 ).

[0046] Example 2

[0047] The preparation method of biological struvite with seawater as magnesium source is as follows:

[0048] 1. Biological struvite induced synthesis with seawater as magnesium source: add 1.0 g of tryptone, 0.5 g of yeast extract, 0.0408 g of potassium dihydrogen phosphate and 100 mL of seawater in a clean 250 mL conical flask, sterilize at 115°C for 30 min, then inoculate 1% (v / v) volume of immobilized bacterial microspheres (about 20 pieces), set 30 parallels, cultivate at 30°C with 130 rpm shaking for 8 days to induce the formation of biological struvite.

[0049] 2. Collection of biological struvite: after incubation for 8 days, the conical flask was naturally precipitated for 1 h, and then washed with double distilled water and anhydrous ethanol, then dried in a 40°C oven and ground through a 100 mesh sieve for use.

[0050] 3. The structure and morphology of the precipitate obtained by the above preparation were identified by XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), SEM (scanning electron microscope) and BET (specific surface area and pore size analyzer). The BET result shows that the specific surface area of biological struvite is 168.7095 m 2 / g, and the XRD and FTIR results show that the precipitate is mainly a composite of struvite and organic matter combined Figure 2 a,b). SEM can observe long strip-shaped struvite crystals with porous surface, and also bacterial cells aggregated together Figure 2 c1-c4).

[0051] Example 3

[0052] Adsorption characteristics of biological struvite on heavy metal cadmium:

[0053] Example 3: Adsorption of cadmium by the biostruvite prepared in Example 2: The biostruvite prepared above was used to adsorb cadmium. The biostruvite was added to simulated wastewater containing cadmium at different concentrations (50-400 mg / L) at a dosage of 0.5 g / L. The adsorption was carried out at 25°C and 100 rpm for 24 hours. After the adsorption, the solution was centrifuged (9000 rpm, 5 min) and the concentration of cadmium was determined by atomic absorption spectrometry. The removal rate A (%) of cadmium by the biostruvite was calculated (see Equation (1)) and the adsorption capacity q e (mg / g) was calculated (see Equation (2)). The adsorption data was analyzed using the Langmuir adsorption model (see Equation (3)) to obtain the maximum adsorption capacity q max (mg / g) of cadmium by the biostruvite. The results are shown in Table 1, and the synthesis of the biostruvite and the removal of cadmium are shown in Figure 3

[0054] Removal rate

[0055] Adsorption capacity

[0056]

[0057] C0and C e are the concentrations of Cd 2+ in the initial solution and the supernatant after adsorption equilibrium, respectively (mg / L); V is the volume of the solution in the adsorption system (L); M is the mass of the adsorbent (g); K L is the parameter of the Langmuir adsorption isotherm model; q max is the maximum adsorption capacity of Cd 2+ by the adsorbent (mg / g).

[0058] Table 1 Langmuir adsorption isotherm model for the adsorption of Cd 2+ by the biostruvite

[0059]

[0060] Example 4

[0061] Calculation of the amount of biostruvite required to treat 1 t of wastewater containing cadmium: According to the results calculated in Example 3, the maximum removal capacity of Cd 2+ by the biostruvite was 446.43 mg / g, and the amount of biostruvite required to treat 1 t of wastewater containing cadmium was calculated to be 2.24 g.

[0062] The biostruvite was prepared according to the method of Example 3, and 2.5 g of the biostruvite was added to 1 t of wastewater and stirred thoroughly. The concentration of Cd 2+ ​The ion concentration, the removal rate is calculated by the formula in Example 3, and the results show that the removal rate of the biological struvite to cadmium is above 95%. The heavy metal cadmium ion holding material prepared by the present application has large adsorption capacity and good performance of removing cadmium ions, and has wide application prospect.

[0063] Comparative Example 1

[0064] Adsorption characteristics of free bacteria-induced biological struvite to heavy metal cadmium:

[0065] 1. Synthesis of free bacteria-induced struvite with seawater as magnesium source: ① The seed liquid is the same as that in Example 1; ② The culture medium is the same as that described in Example 2. After the culture medium is sterilized at 115℃ for 30 min, 1% (v / v) of the seed liquid is inoculated, 30 parallels are set, and the culture is shaken at 130 rpm at 30℃ for 8 days to induce the formation of biological struvite; the collection method of the biological struvite is the same as that described in Example 2, and the XRD and SEM thereof are shown in Figure 4 .

[0066] 2. Specific surface area of the free bacteria-induced biological struvite: the specific surface area is 140.9718 m 2 / g, which is significantly lower than that of the struvite induced and synthesized by the immobilized bacteria in the present application.

[0067] 3. Adsorption characteristics to heavy metal cadmium: the specific steps are the same as those described in Example 3. The maximum adsorption capacity of the free bacteria-induced biological struvite to cadmium is 386.10 mg / g, which is significantly lower than that of the struvite induced and synthesized by the immobilized bacteria in the present application.

[0068] Comparative Example 2

[0069] Adsorption characteristics of free bacteria-induced biological struvite with magnesium chloride as magnesium source to heavy metal cadmium:

[0070] 1. Synthesis of free bacteria-induced struvite with magnesium chloride as magnesium source: ① The seed liquid is the same as that in Example 1; ② The culture medium is LB culture medium prepared by double distilled water. After the culture medium is sterilized at 115℃ for 30 min, 1% (v / v) of the seed liquid and 2 mL of sterilized magnesium chloride solution (0.4 g / mL) are inoculated, 30 parallels are set, and the culture is shaken at 130 rpm at 30℃ for 8 days to induce the formation of biological struvite; the collection method of the biological struvite is the same as that described in Example 2, and the XRD and SEM thereof are shown in Figure 5 .

[0071] 2. Specific surface area of the free bacteria-induced struvite with magnesium chloride as magnesium source: the specific surface area is 45.4751 m 2 / g, which is significantly lower than that of the struvite induced and synthesized by the immobilized bacteria in the present application and in Comparative Example 1.

[0072] 3. Adsorption characteristics of heavy metal cadmium: The specific steps are the same as described in Example 3. The maximum adsorption capacity of the biological struvite induced by free bacteria with magnesium chloride as magnesium source for cadmium is 182.36 mg / g, which is significantly lower than that of the struvite induced by the immobilized bacteria of the present application.

[0073] Comparative Example 3

[0074] Adsorption characteristics of heavy metal cadmium of the struvite chemically synthesized with seawater as magnesium source:

[0075] 1. Chemical struvite synthesis with seawater as magnesium source: KH2PO4 (0.3295 g) and NH4Cl (1.4087 g) were dissolved in 500 mL of double distilled water and placed in a 1 L beaker, 1 mol / L NaOH solution was used to adjust the pH value to 9.2, and a magnetic stirrer was used for continuous stirring at 150 rpm, 65 mL of seawater (Mg 2+ concentration is 1.108 g / L, which is consistent with the magnesium precipitation amount in Example 2) was slowly added to the beaker, and stirred at room temperature for 30 min. Then the mixture was filtered through a 0.45 μm pore size filter to separate the precipitate. The obtained solid was washed with double distilled water for 3 times to remove any impurities. The precipitate was air-dried overnight at room temperature for subsequent experiments. Its XRD and SEM are shown in Figure 6 .

[0076] 2. Specific surface area of the chemical struvite with seawater as magnesium source: The specific surface area is 79.4863 m 2 / g, which is significantly lower than that of the struvite induced by the immobilized bacteria of the present application.

[0077] 3. Adsorption characteristics of heavy metal cadmium: The specific steps are the same as described in Example 3. The maximum adsorption capacity of the chemical struvite for cadmium is 216.92 mg / g, which is significantly lower than that of the struvite induced by the immobilized bacteria of the present application.

[0078] In addition, it is found in the present application that the biological struvite induced by the immobilized Bacillus vallismortis in seawater medium has high heavy metal cadmium removal capacity. If the conventional free bacteria induced biological struvite is directly used, its crystal performance, specific surface area and heavy metal cadmium adsorption capacity are obviously inferior to those of the present application. In addition, the heavy metal cadmium removal capacity of the struvite synthesized by the chemical method with seawater as magnesium source is obviously inferior to that of the present application. The effect of the biological struvite induced by free bacteria with magnesium chloride as magnesium source on heavy metal adsorption is also far inferior to that of the present application.

Claims

1. A method for synthesizing biogenic struvite by bacteria induction using seawater as magnesium source, characterized in that, It comprises the following steps: The immobilized Bacillus velezensis is inoculated into a liquid medium configured with seawater, and after the culture is finished, biological struvite is separated; the immobilized Bacillus velezensis takes activated carbon, attapulgite or bentonite as a carrier and is loaded with Bacillus velezensis.

2. The method for synthesizing struvite induced by bacteria using seawater as magnesium source according to claim 1, characterized in that, The immobilized Bacillus velezensis takes activated carbon as a carrier, polyvinyl alcohol and sodium alginate as embedding agents, and calcium chloride and boric acid as cross-linking agents.

3. The method for synthesizing struvite induced by bacteria using seawater as magnesium source according to claim 1, characterized in that, The Bacillus velezensis is Bacillus velezensis with GeneBank accession No. (CP037417) or Bacillus velezensis CGMCC 1.12669 or other commercially available Bacillus velezensis strains.

4. The method for synthesizing struvite induced by bacteria using seawater as magnesium source according to claim 1, characterized in that, The liquid medium configured with seawater contains 0.5-1.0 g of tryptone, 0.25-0.5 g of yeast extract and 0.0088-0.0408 g of potassium dihydrogen phosphate per 1 L of seawater.

5. The method for synthesizing struvite induced by bacteria using seawater as magnesium source according to claim 1, characterized in that, The immobilized Bacillus velezensis is inoculated into a liquid medium configured with seawater, and after the culture is finished, biological struvite is separated; the immobilized Bacillus velezensis takes activated carbon, attapulgite or bentonite as a carrier and is loaded with Bacillus velezensis.

6. The method for synthesizing struvite induced by bacteria using seawater as magnesium source according to claim 1, characterized in that, The culture conditions are 25-37℃, 120-180 rpm oscillation culture for 6-10 days; after the culture is finished, the precipitate is collected and dried to obtain biological struvite.

7. The method for synthesizing struvite induced by bacteria using seawater as magnesium source according to claim 1, characterized in that, The seawater is natural seawater, and other impurities are filtered out of the seawater.

8. A struvite organic complex obtained by the method of claim 1-7 for synthesizing biological struvite induced by bacteria with seawater as a magnesium source.

9. The struvite organic complex of claim 8 is used for removing cadmium ions or preparing a cadmium ion adsorbent.

10. An adsorbent for treating heavy metal cadmium ions, characterized by, The struvite organic complex of claim 8 is included.

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