A supported alcaligenes faecalis composite material, its preparation method and application

Abstract

The present application belongs to the technical field of water treatment, and particularly relates to a supported Alcaligenes faecalis composite material, a preparation method thereof and application thereof. The present application forms a composite material by loading Alcaligenes faecalis on phosphate functionalized biochar, utilizes the phosphorus dissolving and accumulating functions of Alcaligenes faecalis to convert the soluble phosphate groups on the surface and inside of the biochar into insoluble metaphosphate minerals and extracellular polymers, and achieves the effect of phosphorus fixation through the adsorption of metal cations in the biological membrane to phosphate; Alcaligenes faecalis can perform microbial phosphorus fixation, thereby improving the adsorption stability of the supported Alcaligenes faecalis composite material to uranium; through the interface synergistic effect of the biochar and Alcaligenes faecalis, the composite material has more excellent U(VI) adsorption performance (wide pH adaptation range, fast adsorption speed, high removal rate, and strong anti-interference ability) and reusability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sewage treatment, and particularly relates to a supported Alcaligenes faecalis composite material and a preparation method and application thereof. BACKGROUND

[0002] Uranium mining and smelting, decommissioned mine sites, and nuclear power plants and other nuclear industrial activities will produce a large amount of U(VI) containing wastewater, which seriously threatens the safety of the ecological environment and restricts the sustainable development of the nuclear industry. The commonly used methods for treating uranium contaminated water bodies include biological remediation, electrochemical method, membrane separation method and adsorption method. In recent years, the adsorption method has attracted widespread attention due to its simple operation and low energy consumption. Biochar is produced by pyrolysis of various waste biomass under anaerobic conditions, and as an adsorbent, it has the advantages of rich raw material and low cost. However, the adsorption capacity of directly prepared biochar for U(VI) is poor, and researchers have developed various biochar modification methods such as physical activation, mineral impregnation, acid / alkali modification, etc. Among them, phosphate functionalized biochar has the advantages of large U(VI) adsorption capacity and strong anti-interference ability due to the specific coordination of phosphate groups to U(VI). Therefore, the modification of biochar with phosphoric acid and other chemical reagents to increase the phosphorus content on the surface of biochar has become a research hotspot.

[0003] Phytic acid, as a natural non-toxic organic acid, widely exists in nature, and one phytic acid molecule contains six phosphate groups. Existing technical research shows that phytic acid modified phosphorus-rich biochar (PBC) has a large specific surface area and excellent U(VI) adsorption capacity, but about 21.43% of the phosphorus on the surface of the PBC remains in the aqueous solution after adsorbing U(VI). Similarly, some documents also point out that the phosphorus on the surface of biochar can indeed be released in the aqueous solution. The release of phosphorus on the surface of PBC in the aqueous solution seriously affects the U(VI) adsorption performance and reusability of the material, and too much phosphorus concentration in the aqueous solution will cause water eutrophication and cause environmental secondary pollution. Therefore, how to reduce the phosphorus desorption rate of PBC material has become a key bottleneck problem for phosphate functionalized biochar to be used for U(VI) contaminated water remediation. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a supported Alcaligenes faecalis composite material and a preparation method and application thereof. The supported Alcaligenes faecalis composite material provided by the present application can not only improve the desorption problem of loaded phosphorus in phosphate functionalized biochar, but also strengthen the biological adsorption and mineralization of U(VI) and improve the removal effect of U(VI).

[0005] In order to achieve the above purpose, the present application provides the following technical solutions:

[0006] The application provides a supported Alcaligenes faecalis composite material, which comprises phosphate functionalized biochar and Alcaligenes faecalis supported on the surface of the phosphate functionalized biochar.

[0007] The loading amount of Alcaligenes faecalis on the phosphate functionalized biochar is 1x10 10 ~ 2x10 10 cells / g.

[0008] Preferably, the specific surface area of the phosphate functionalized biochar is 500~600m 2 / g.

[0009] Preferably, the preparation method of the phosphate functionalized biochar is mixing biomass, a solution of phytic acid and water, and then pyrolyzing to obtain the phosphate functionalized biochar.

[0010] The mass ratio of the biomass to the phytic acid is 1:1~3.

[0011] Preferably, the pyrolysis temperature is 300~700 DEG C, and the holding time is 1~3h.

[0012] The application further provides a preparation method of the supported Alcaligenes faecalis composite material.

[0013] Mixing the phosphate functionalized biochar and a bacterial suspension of Alcaligenes faecalis, and then performing stationary culture to obtain the supported Alcaligenes faecalis composite material.

[0014] Preferably, the mass ratio of the phosphate functionalized biochar to the volume of the bacterial suspension of Alcaligenes faecalis is (0.5~3)g:100mL; and the bacterial number of the bacterial suspension of Alcaligenes faecalis is 1x10 8 ~ 2x10 8 cells / mL.

[0015] Preferably, the stationary culture is performed under oscillation; and the oscillation rate is 130~170r / min.

[0016] Preferably, the stationary culture temperature is 20~35 DEG C, and the time is 10~36h.

[0017] The application further provides application of the supported Alcaligenes faecalis composite material or the supported Alcaligenes faecalis composite material prepared by the preparation method in treatment of uranium-containing wastewater.

[0018] The application further provides a method for treating uranium-containing wastewater.

[0019] The load type Alcaligenes faecalis composite material is mixed with uranium-containing sewage to carry out adsorption.

[0020] The application provides a load type Alcaligenes faecalis composite material, which comprises phosphate functionalized biochar and Alcaligenes faecalis loaded on the surface of the phosphate functionalized biochar; the loading amount of the Alcaligenes faecalis on the phosphate functionalized biochar is 1x10 10 ~2x10 10 cells / g. The application loads Alcaligenes faecalis on phosphate functionalized biochar to form a composite material, the Alcaligenes faecalis has the functions of dissolving phosphorus and accumulating phosphorus, converts soluble phosphate groups on the surface and in the interior of the biochar into insoluble metaphosphate minerals and extracellular polymers, and achieves the effect of fixing phosphorus through the adsorption of metal cations in the biological membrane to phosphate; the Alcaligenes faecalis can carry out microbial phosphorus fixation, so that the load type Alcaligenes faecalis composite material has high uranium adsorption stability; through the interface synergistic effect of the biochar and the Alcaligenes faecalis, the composite material has more excellent U(VI) adsorption performance (wide pH adaptation range, fast adsorption speed, high removal rate and strong anti-interference ability) and reusability.

[0021] The application further provides a preparation method of the load type Alcaligenes faecalis composite material, which has the advantages of simple process, low cost of raw materials, fast operation, no harsh requirements for equipment and process conditions, easy operation, good repeatability, suitability for mass production and engineering application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM images of PBC and A / PBC prepared in Example 1 of the application;

[0023] Figure 2 EDS image of PBC prepared in Example 1 of the application;

[0024] Figure 3 EDS image of A / PBC prepared in Example 1 of the application;

[0025] Figure 4 XRD images of PBC and A / PBC prepared in Example 1 of the application;

[0026] Figure 5 FTIR images of PBC and A / PBC prepared in Example 1 of the application;

[0027] Figure 6Figure of adsorption effect of PBC, A / PBC and DA / PBC prepared for example 1 of the present application on uranium;

[0028] Figure 7 Figure of adsorption and desorption reuse performance of PBC and A / PBC prepared for example 1 of the present application;

[0029] Figure 8 Figure of XRD of A / PBC prepared for example 1 of the present application before and after adsorbing uranium;

[0030] Figure 9 Figure of TEM of A / PBC prepared for example 1 of the present application before and after adsorbing uranium;

[0031] Figure 10 Figure of TEM-EDS mapping of A / PBC prepared for example 1 of the present application before and after adsorbing uranium;

[0032] Figure 11 Figure of FTIR of A / PBC prepared for example 1 of the present application before and after adsorbing uranium. DETAILED DESCRIPTION

[0033] The present application provides a supported Alcaligenes faecalis composite material, comprising phosphate functionalized biochar and Alcaligenes faecalis supported on the surface of the phosphate functionalized biochar; the loading amount of Alcaligenes faecalis on the phosphate functionalized biochar is 1x10 10 ~2x10 10 cells / g.

[0034] Unless otherwise specified, the present application does not have special requirements for the source of the raw materials used, and commercially available goods known to those skilled in the art can be used.

[0035] The supported Alcaligenes faecalis composite material provided by the present application comprises phosphate functionalized biochar. In the present application, the specific surface area of the phosphate functionalized biochar is preferably 500~600m 2 / g, and more preferably 577.31m 2 / g.

[0036] In the present application, the preparation method of the phosphate functionalized biochar is to mix biomass, a solution of phytic acid and water, and then pyrolyze to obtain the phosphate functionalized biochar.

[0037] In the present application, the biomass is preferably aloe leaf powder; the mass ratio of the biomass to phytic acid is preferably 1:1~3, and more preferably 1:2; the mass concentration of the solution of phytic acid is preferably 30~70%, and more preferably 50%.

[0038] In the present application, the mixing is preferably carried out under oscillation; the oscillation device is preferably a shaking table; the oscillation temperature is preferably 30℃; and the oscillation time is preferably 24h.

[0039] After the mixing, the present application preferably carries out drying of the mixture obtained by the mixing to constant weight. In the present application, the drying temperature is preferably 100-120℃, more preferably 105℃; and the drying time is preferably 12-48h, more preferably 24h.

[0040] In the present application, the pyrolysis temperature is preferably 300-700℃, more preferably 500℃, and the holding time is preferably 1-3h, more preferably 2h; and the heating rate to the pyrolysis temperature is preferably 5-20℃ / min, more preferably 10℃ / min.

[0041] After the pyrolysis, the present application sequentially carries out cooling, crushing, screening, washing and drying of the carbide obtained by the pyrolysis to obtain phosphate functionalized biochar. In the present application, the cooling is preferably natural cooling; the crushing is preferably grinding; the mesh size of the screen used for the screening is preferably 100 mesh; the washing is preferably repeated washing with distilled water until the pH value of the eluate obtained is 7; the drying is preferably oven drying to constant weight; and the drying temperature is preferably 60℃.

[0042] During the pyrolysis, hydrogen protons are separated from phytic acid, attack the C-O bond of alcohol, ether or carboxyl in aloe leaf powder, and promote the rupture of the C-O bond. The phosphate groups in phytic acid are crosslinked with organic matter in biomass through cyclization or dehydration condensation, form phosphate and phosphate bridges, and are combined with biochar in the form of C-O-P bond. At the same time, the phosphate groups produce polyphosphate structures through dehydration at high temperature.

[0043] The supported Alcaligenes faecalis composite material provided by the present application comprises Alcaligenes faecalis supported on the surface of the phosphate functionalized biochar.

[0044] In the present application, the GenBank number of the Alcaligenes faecalis is KU844046.1; the preservation number of the Alcaligenes faecalis in the China General Microbiological Culture Collection Center is CGMCC1.2908, the address of the preservation unit is No.3, Institute of Microbiology, Chinese Academy of Sciences, Beijing City, Chaoyang District, Beichen West Road No.1, the preservation date is January 18, 2002, and the Latin name is Alcaligenes faecalis subsp. faecalis; and the loading amount of the Alcaligenes faecalis on the phosphate functionalized biochar is preferably 1×10 10 ~ 2×10 10 cells / g, more preferably 1.7×10 101.0×108cells / g. The Alcaligenes faecalis used in the present application has been published in Chinese patent document CN106478288A "A soil conditioner for degrading pesticides in soil by microorganisms", and the present application promises to provide the Alcaligenes faecalis to the public for 20 years from the date of filing.

[0045] The Alcaligenes faecalis converts the unstable phosphates on the surface of phosphate functionalized biochar (PBC) into extracellular polymeric substances (EPS) and metaphosphate minerals and greatly reduces the release of PBC surface phosphorus by adsorption of metal cations in the biofilm. The polysaccharides, DNA, proteins, etc. in the extracellular polymeric substances (EPS) can be bridged by metal ions such as Ca 2+ , Mg 2+ , etc. to form a cross-linked network, thereby enhancing the structural stability of the biofilm, so that the Alcaligenes faecalis has greater tolerance to environmental stress. At the same time, the metal cations in the biofilm can provide adsorption sites for phosphate groups. When the supported Alcaligenes faecalis composite material (A / PBC) is added to an aqueous solution, the phosphate groups on the surface of PBC are first released into the biofilm, and these metal ions can fix the phosphate groups in the biofilm. Metaphosphate is a substrate for bacterial phosphorylation or polypeptide synthesis. When the Alcaligenes faecalis synthesizes EPS, the orthophosphate on the surface of PBC is converted into metaphosphate, and metaphosphate, Ca, Na and Mg gradually form two minerals Ca(PO3)2 and NaMg(PO3)3 in the biofilm, reducing the release of A / PBC surface phosphorus in water.

[0046] The loading of Alcaligenes faecalis and the formation of biofilm make the content of active groups (such as hydroxyl, carboxyl, amide and phosphate groups) on the surface of A / PBC more abundant, which can further promote A / PBC to capture U(VI) from aqueous solution.

[0047] The presence of PBC is conducive to the formation of biofilm by Alcaligenes faecalis in the attached state, which provides nucleation sites for mineralization and enriches phosphate and U(VI). The high concentration of phosphate and uranium ions in the microenvironment of the biofilm promotes the formation of uranyl phosphate minerals by biomineralization.

[0048] The oxygen-containing functional groups on PBC and EPS can quickly complex with U(VI) in water. At the same time, the diffusion of U(VI) into the bacteria around the biological membrane activates the detoxification mechanism of the bacteria: Alcaligenes faecalis takes up the nutrient elements from PBC and transfers these elements to the surface of A / PBC in the form of EPS and metaphosphate minerals to fix U(VI) in water. In this way, not only the contact distance between microorganisms and nutrients is shortened, but also the mass transfer resistance of U(VI) in water to the inside of A / PBC is avoided, thereby improving the U(VI) adsorption rate of A / PBC. With the metabolic transformation of Alcaligenes faecalis, the abundance of acidic functional groups on the surface of A / PBC increases, which promotes the electrostatic attraction of U(VI) in water and enhances the Lewis acid-base interaction. Therefore, the synergistic effect of Alcaligenes faecalis and PBC improves the uranium immobilization effect.

[0049] The present application loads Alcaligenes faecalis on phosphate functionalized biochar to form a composite material. The soluble phosphate groups on the surface and inside of the biochar are converted into insoluble metaphosphate minerals and extracellular polymers by the phosphorus-dissolving and phosphorus-polymerizing functions of Alcaligenes faecalis, and the adsorption of metal cations in the biological membrane to phosphate ions achieves the effect of phosphorus fixation. Alcaligenes faecalis can perform microbial phosphorus fixation, thereby improving the uranium adsorption stability of the supported Alcaligenes faecalis composite material. Through the interfacial synergistic effect of biochar and Alcaligenes faecalis, the composite material has more excellent U(VI) adsorption performance (wide pH adaptation range, fast adsorption speed, high removal rate, and strong anti-interference ability) and reusability.

[0050] The present application also provides a preparation method of the supported Alcaligenes faecalis composite material.

[0051] The phosphate functionalized biochar and the bacterial suspension of Alcaligenes faecalis are mixed and fixedly cultured to obtain the supported Alcaligenes faecalis composite material.

[0052] In the present application, the number of bacteria in the bacterial suspension of Alcaligenes faecalis is preferably 1×10 8 ~ 2×10 8 cells / mL, and more preferably 1.8×10 8 cells / mL.

[0053] In the present application, the preparation method of the bacterial suspension of Alcaligenes faecalis is preferably as follows: Alcaligenes faecalis is inoculated into a culture medium, and after being cultured to the logarithmic phase, centrifuged and resuspended to obtain the bacterial suspension of Alcaligenes faecalis.

[0054] In the present application, the culture medium is preferably LB medium; the logarithmic phase is preferably OD600 = 1.0; the rate of centrifugation is preferably 6000-12000 rpm, more preferably 8000 rpm; the temperature of centrifugation is preferably 4-30℃, more preferably 25℃; the time of centrifugation is preferably 3-10 min, more preferably 5 min; and the resuspension is preferably re-dispersing the Alcaligenes faecalis concentrate obtained by centrifugation with deionized water to obtain a bacterial suspension of Alcaligenes faecalis.

[0055] In the present application, the stationary culture is preferably carried out under shaking conditions; the rate of shaking is preferably 130-170 r / min, more preferably 150 r / min; and the device used for shaking is preferably a constant temperature shaker.

[0056] In the present application, the temperature of stationary culture is preferably 20-35℃, more preferably 30℃, and the time is preferably 10-36 h, more preferably 24 h.

[0057] After the stationary culture, the present application preferably sequentially carries out solid-liquid separation, washing and drying on the system obtained by stationary culture to obtain a supported Alcaligenes faecalis composite material. In the present application, the solid-liquid separation is preferably centrifugation; the time of centrifugation is preferably 2-10 min, more preferably 5 min; the washing is preferably carried out with sterile distilled water; the number of washing is preferably 1-5 times, more preferably 3 times; the drying is preferably freeze-drying; the temperature of freeze-drying is preferably -10--60℃, more preferably -50℃; and the time of freeze-drying is preferably 5-10 h, more preferably 6 h.

[0058] The present application preferably stores the supported Alcaligenes faecalis composite material in a 4℃ refrigerator for standby use.

[0059] The present application also provides the use of the supported Alcaligenes faecalis composite material in the above technical solution or the supported Alcaligenes faecalis composite material prepared by the preparation method in the above technical solution in the treatment of uranium-containing wastewater.

[0060] The present application also provides a method for treating uranium-containing wastewater, comprising the following steps:

[0061] Mixing the supported Alcaligenes faecalis composite material with uranium-containing wastewater for adsorption; the supported Alcaligenes faecalis composite material is the supported Alcaligenes faecalis composite material in the above technical solution or the supported Alcaligenes faecalis composite material prepared by the preparation method in the above technical solution.

[0062] In the present application, the mass concentration of uranium in the uranium-containing wastewater is preferably 10-80 mg / L, more preferably 10-20 mg / L; the pH value of the uranium-containing wastewater is preferably 2-7, more preferably 4-7; the ratio of the mass of the loaded Alcaligenes faecalis composite material to the volume of the uranium-containing wastewater is preferably (0.05-0.3) g:1 L, more preferably (0.2-0.3) g:1 L; and the adsorption temperature is preferably 20-40℃, more preferably 20-40℃.

[0063] After the adsorption is completed, the adsorbed loaded Alcaligenes faecalis composite material is preferably sequentially subjected to desorption and washing, and then repeated adsorption.

[0064] In the present application, the number of times of repeated adsorption is preferably 2-5, more preferably 5; the desorption is preferably placing the adsorbed loaded Alcaligenes faecalis composite material in an acid solution; the desorption time is preferably 60-2160 min, more preferably 1440 min; the acid solution is preferably a hydrochloric acid solution; the concentration of the hydrochloric acid solution is preferably 0.1 mol / L; the washing liquid used for washing is preferably distilled water; and the number of times of washing is preferably 3-5, more preferably 3.

[0065] The technical solutions in the present application will be clearly and completely described below in combination with the examples in the present application, but they should not be understood as limitations to the protection scope of the present application.

[0066] Example 1

[0067] 10 g of aloe vera leaf powder was added to a conical flask, 20 g (50 wt.%) of a phytic acid (PA) solution was added according to the mass ratio of aloe vera leaf powder to phytic acid of 1:2, and 150 mL of distilled water was added. The conical flask was placed in a shaking bed for oscillation at 30℃ for 24 h, and then the mixture was collected and placed in a ceramic evaporating dish. The pretreated aloe powder was placed in an oven at 105℃ for 24 h to dry to constant weight. The phytic acid-pretreated aloe leaf powder was placed in a ceramic crucible and put into a muffle furnace at 500℃ for pyrolysis for 2 h, with a heating rate of the muffle furnace of 10℃ / min. After the muffle furnace was naturally cooled, the charred product was taken out, ground, and then sieved through a 100-mesh sieve. Then the sieved product was repeatedly washed with distilled water until the pH value of the washing liquid reached 7. Finally, the product was dried to constant weight at 60℃ to obtain a phosphate functionalized biochar (counted as PBC). The C content in the phosphate functionalized biochar was 62.49 wt.%, the O content was 20.75 wt.%, the P content was 10.39 wt.%, the Ca content was 4.67 wt.%, the Na content was 0.57 wt.%, and the Mg content was 0.79 wt.% (see Table 1). Figure 2

[0068] ​After the Alcaligenes faecalis (GenBank accession number: KU844046.1) was cultured in 100 mL LB medium to logarithmic phase (OD600=1.0) and centrifuged at 8000 rpm for 5 min at 25°C, a bacterial suspension was prepared by resuspending with 100 mL distilled water, and the bacterial count of the obtained bacterial suspension was 1.8×10 8 cells / mL. 1.0 g of PBC prepared in Example 1 was weighed and placed in 100 mL of the bacterial suspension, and fixed culture was performed in a constant temperature shaker at 30°C and 150 r / min for 12 h. Then, it was separated by centrifugation at 1000 rpm for 5 min, and finally, it was repeatedly washed three times with sterile distilled water. After freeze-drying at -50°C for 6 h, the composite material was stored in a 4°C refrigerator for standby, and a loaded Alcaligenes faecalis composite material (counted as A / PBC-12) was obtained. When A / PBC-12 reached the adsorption saturation state in the U(VI) solution, the U(VI) removal rate was 97.70%, which was lower than the U(VI) removal rate (99.98%) of A / PBC. 7 10 cells / g, and finally, it was repeatedly washed three times with sterile distilled water. After freeze-drying at -50°C for 6 h, the composite material was stored in a 4°C refrigerator for standby, and a loaded Alcaligenes faecalis composite material (counted as A / PBC) was obtained. When A / PBC reached the adsorption saturation state in the U(VI) solution, the U(VI) removal rate was 99.98%.

[0069] Example 2

[0070] After the Alcaligenes faecalis (GenBank accession number: KU844046.1) was cultured in 100 mL LB medium to logarithmic phase (OD600=1.0) and centrifuged at 8000 rpm for 5 min at 25°C, a bacterial suspension was prepared by resuspending with 100 mL distilled water, and the bacterial count of the obtained bacterial suspension was 1.8×10 8 cells / mL. 1.0 g of PBC prepared in Example 1 was weighed and placed in 100 mL of the bacterial suspension, and fixed culture was performed in a constant temperature shaker at 30°C and 150 r / min for 12 h. Then, it was separated by centrifugation at 1000 rpm for 5 min, and finally, it was repeatedly washed three times with sterile distilled water. After freeze-drying at -50°C for 6 h, the composite material was stored in a 4°C refrigerator for standby, and a loaded Alcaligenes faecalis composite material (counted as A / PBC-12) was obtained. When A / PBC-12 reached the adsorption saturation state in the U(VI) solution, the U(VI) removal rate was 97.70%, which was lower than the U(VI) removal rate (99.98%) of A / PBC.

[0071] Example 3

[0072] ​The Alcaligenes faecalis (GenBank accession number: KU844046.1) was cultured in 100 mL LB medium to logarithmic phase (OD600 = 1.0), then centrifuged at 8000 rpm for 5 min at 25℃, and resuspended with 100 mL distilled water to prepare a bacterial suspension, and the bacterial number of the obtained bacterial suspension was 1.8 x 10 8 cells / mL, 1.0 g of PBC prepared in Example 1 was weighed and placed in 100 mL of the bacterial suspension, and incubated in a constant temperature shaker at 30℃ and 150 r / min for 36 h, then centrifuged at 1000 rpm for 5 min, finally washed repeatedly 3 times with sterile distilled water, and the composite material was placed in a 4℃ refrigerator after being freeze-dried at -50℃ for 6 h, to obtain the loaded Alcaligenes faecalis composite material (counted as A / PBC-36). When A / PBC-36 reached the adsorption saturation state in the U(VI) solution, the U(VI) removal rate was 98.23%, which was lower than the U(VI) removal rate of A / PBC (99.98%).

[0073] Comparative Example 1

[0074] The corn cob phosphorus-rich biochar was prepared according to the scheme in Example 1, and the mass fractions of C, O, N, P and Na were 80.78%, 14.78%, 4.00%, 0.22% and 0.22%, respectively. After loading Alcaligenes faecalis according to the method in Example 1, the uranium removal rate reached 92.94%, which was lower than the uranium removal effect of the loaded Alcaligenes faecalis composite material obtained in Example 1, indicating that the greater the phosphate loading, the better the uranium removal effect.

[0075] Application Example 1

[0076] The effect of the loaded Alcaligenes faecalis composite material prepared in Example 1 on treating actual uranium-contaminated groundwater was tested. The uranium-contaminated groundwater sample was collected from a geological monitoring well near a tailings dam reservoir, and the water level was about 10 m underground. The physicochemical composition of the groundwater is shown in Table 1. The results showed that the A / PBC material prepared in Example 1 could well treat the uranium-contaminated water body, and could reduce the uranium concentration of 0.52 mg / L in the uranium-contaminated water body to 23 μg / L, reaching the drinking water standard (<50 μg / L).

[0077] Table 1 Composition analysis of groundwater samples

[0078]

[0079] Performance test

[0080] (1) The microstructure of the phosphate functionalized biochar (PBC) and A / PBC prepared in Example 1 was analyzed by scanning electron microscopy (SEM, JSM-7500F, JPN), and the results are shown inFigure 1 (a-c) are PBC and (d-f) are A / PBC.

[0081] From Figure 1 As can be seen from (a-c), the PBC surface is very smooth with a developed and irregular pore structure.

[0082] From Figure 1 As can be seen from (d), a large number of Alcaligenes faecalis successfully loaded onto the PBC surface leads to a significant reduction in the number of surface pores, and the biofilm structure composed of Alcaligenes faecalis and its produced extracellular polymeric substances (EPS) can be clearly seen. The loading amount of Alcaligenes faecalis in the A / PBC prepared in Example 1 is 1.7 x 10 10 cells / g.

[0083] From Figure 1 As can be seen from (e), some colonies are fixed in the form of embedding on the PBC surface, which may be because Alcaligenes faecalis forms corrosion pits on the PBC surface through degradation.

[0084] From Figure 1 As can be seen from (f), some small granular substances are also doped in the biofilm on the surface of A / PBC, which may be a biological mineralization reaction of Alcaligenes faecalis using metal ions on the surface of biochar.

[0085] (2) The surface morphology and element composition of the PBC and A / PBC prepared in Example 1 were analyzed by X-ray energy spectrum (EDS, X-Max, UK), and the results are shown in Figure 2 and Figure 3 .

[0086] As can be seen from Figure 2 , the C content of the PBC prepared in Example 1 is 62.49 wt.%, the O content is 20.75 wt.%, the P content is 10.39 wt.%, the Ca content is 4.67 wt.%, the Na content is 0.57 wt.%, and the Mg content is 0.79 wt.%. The PBC surface not only contains a large amount of C, O, and P, but also a small amount of Ca, Na, Mg, and other metal elements due to the aloe leaf powder. The polysaccharides, DNA, proteins, and other substances in the EPS can be bridged with Ca 2+ , Mg 2+ metal ions to form a cross-linked network, thereby enhancing the structural stability of the biofilm and enabling Alcaligenes faecalis to have greater tolerance to environmental stress.

[0087] As can be seen from Figure 3It can be seen that the atomic percentage of Ca on the surface of A / PBC is increased by 1.46 At% compared with PBC, indicating that Ca ions are enriched in the biofilm. At the same time, metal cations in the biofilm can provide adsorption sites for phosphate groups. When A / PBC is added to the aqueous solution, the phosphate groups on the surface of PBC will be released into the biofilm first, and these metal ions can fix the phosphate groups in the biofilm.

[0088] (3) The surface crystal structure of the phosphate functionalized biochar (PBC) and A / PBC prepared in Example 1 was determined by X-ray diffractometer (XRD, Bruker D8, USA), and the results are shown in Figure 4 .

[0089] It can be seen from Figure 4 that the broad peak near 25° in the XRD spectrum of PBC is the amorphous diffraction peak of the (002) crystal plane of graphite structure. It is found from the spectrum of A / PBC that Ca (PO3)2 (PDF #97-006-0117) and NaMg (PO3)3 (PDF #97-009-0483) exist on the surface of A / PBC, and the two minerals are not found on the surface of PBC. Metaphosphate is a substrate for bacteria to phosphorylate or polypeptide synthesis. When A / PBC is used to synthesize EPS of Alcaligenes faecalis, orthophosphate on the surface of PBC is converted into metaphosphate, and metaphosphate, Ca, Na and Mg gradually form the above two minerals in the biofilm, reducing the release of phosphorus on the surface of A / PBC in water.

[0090] (4) The A / PBC prepared in Example 1 was characterized by potassium bromide tabletting method for Fourier transform infrared spectroscopy (FTIR, Nicolet-460, USA), and the results are shown in Figure 5 .

[0091] It can be seen from Figure 5 that the loading of Alcaligenes faecalis and the formation of biofilm make the content of the above active groups (hydroxyl, carboxyl, amide and phosphate groups) on the surface of A / PBC more abundant, which can further promote A / PBC to capture U(VI) from aqueous solution.

[0092] (5) Adsorption experiment

[0093] 1) Changes of solution parameters in the process of A / PBC adsorbing uranium

[0094] 0.2 g / L of A / PBC prepared in Example 1 was added to a conical flask containing 50 mL of 10 mg / L U(VI) solution. First, 3.5 × 10 6cells / mL of free Alcaligenes faecalis (FAF), 0.2 g / L of PBC and DA / PBC were used as controls. The initial pH was adjusted with 0.1 mol / L NaOH and HC1, and the adsorption effect of A / PBC on U(VI) was evaluated at an initial pH ranging from 2 to 7. The supernatant was obtained by filtration using a 0.22 μm filter membrane. The amount of phosphorus released in the solution was determined using the ammonium molybdate spectrophotometric method. The concentration of U(VI) in the filtrate was determined using inductively coupled plasma mass spectrometry (ICP-MS), and the removal rate and adsorption capacity of U(VI) were calculated. The results are shown in Figures 1 and 2, where (a) is a system without U(VI) and (b) is a system with U(VI), the change in phosphorus concentration over time; (c) is a system without U(VI) and (d) is a system with U(VI), the change in pH over time; (e) is a system with U(VI), the change in U(VI) concentration over time; and (f) is a system with U(VI), the change in the (UO2)3(PO4)2saturation index over time. Figure 6

[0095] 1. Phosphorus release pattern

[0096] The release of surface phosphorus of PBC and DA / PBC can be divided into three stages: rapid release (0-15 min), slow release (15-720 min), and release equilibrium (720-2160 min). When the adsorption of PBC was completed (t = 2160 min), the phosphorus concentration of the U(VI) solution was 2.32 mg / L. After the adsorption of A / PBC was saturated (t = 720 min), the phosphorus concentration in the solution was 0.34 mg / L, which was 82.47% less than that of PBC. Within 0-2160 min, the amount of phosphorus released by A / PBC was significantly lower than that of PBC, and the amount of phosphorus release slowly increased and gradually reached equilibrium. Therefore, Alcaligenes faecalis converts the unstable phosphorus on the surface of PBC into EPS and metaphosphate minerals and greatly reduces the release of surface phosphorus of PBC through the adsorption of metal cations in the biofilm. The amount of phosphorus released by DA / PBC is higher than that of A / PBC, which may be because the structure of the biofilm on the surface of DA / PBC is destroyed after high-temperature treatment, and the ability to fix phosphorus is lost. Within the entire reaction time, the amount of phosphorus released by PBC and DA / PBC in the system containing U(VI) is lower than that in the system without U(VI), indicating that the phosphate in the water reacts with U(VI) to form a coprecipitate. No phosphorus was detected in the FAF system with and without U(VI) Figure 6 a,b).

[0097] 2. Change in solution pH over time

[0098] ​The pH values of the two systems were quite different. In the U(VI)-free system, the pH value decreased to 5.55 with the release of phosphate. However, in the U(VI) solution, the pH value decreased to 6.23 (5 min) and then gradually increased to 7.26. This phenomenon might be due to the low metabolic activity of PBC in the U(VI)-free system, which was not enough to resist the impact of deprotonation of phosphate groups. When PBC was stressed by U(VI), its detoxification mechanism was activated, and the metabolic activity of PBC was enhanced. In addition, compared with free PBC, A / PBC had a more significant effect on the increase of the solution pH value, which also illustrated the promotion of PBC on the metabolic activity of PBC Figure 6 c,d).

[0099] 3) Changes in U(VI) concentration during adsorption

[0100] The removal rate of U(VI) by A / PBC was significantly faster than that by PBC, DA / PBC, and FAF. In the system with A / PBC, the (UO2)3(PO4)2 precipitate was formed within 120 min, and then the solution was in an undersaturated state. A / PBC reached the adsorption saturation state at 720 min, and the removal rate of U(VI) was as high as 99.98%. At this time, the residual concentration of U(VI) in the solution was about 2 μg / L, which was much lower than the standard limit value of the World Health Organization (less than 30 μg / L) Figure 6 e).

[0101] 4) Calculation of the saturation index

[0102] As shown in Figure 6 f, the increase in the stability of the phosphate groups on the surface of A / PBC not only did not reduce its surface electrostatic attraction and complexing ability but also avoided the formation of electrically neutral uranyl phosphate molecules in water. At the same time, the biological adsorption mediated by microbial metabolism further improved the adsorption rate and performance of U(VI). Within 720 to 2160 min, U(VI) fixed on A / PBC did not exhibit the desorption phenomenon as free bacteria. The main reasons might include that PBC and the biofilm in A / PBC were rich in active functional groups that could complex with U(VI) to reduce the toxicity of U(VI) to the activity of bacteria; the structure of the biofilm on the surface of A / PBC was stable enough; and P. alcaliphilus could generate more stable uranyl minerals through biomineralization.

[0103] 2) Adsorption model

[0104] 1) Kinetic analysis

[0105] The U(VI) adsorption and desorption behaviors of A / PBC were investigated at different reaction times (t = 0-2160 min). The pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models were used to study the U(VI) adsorption kinetics of A / PBC. The PSO correlation coefficient (0.982) was slightly higher than that of PFO (0.891), and the theoretical adsorption capacity (50.43 mg / g) obtained by PSO was closer to the experimental value (49.99 mg / g). The U(VI) removal process of A / PBC was more consistent with the PSO model, and the removal rate was mainly controlled by chemical action (Table 2).

[0106] Table 2 Pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models for U(VI) adsorption by A / PBC

[0107]

[0108]

[0109] 2. Adsorption isotherm model

[0110] The isotherm (Langmuir, Freundlich) and thermodynamic studies were carried out at different initial concentrations (10-80 mg / L) and different experimental temperatures (20, 30 and 40 ℃), and the results are shown in Table 3.

[0111] As shown in Table 3, the Freundlich fitting correlation coefficient (R 2 0.975, 0.988, 0.919) was higher than that of Langmuir (R 2 0.916, 0.781, 0.848), indicating that the Freundlich model was more suitable for describing the U(VI) adsorption behavior of A / PBC. This also indicated that the U(VI) binding sites on A / PBC were heterogeneous (heterogeneous), and chemical adsorption was responsible for the uptake of U(VI) in water. The Freundlich fitting results n were all greater than 1, indicating that A / PBC had good adsorption performance and the adsorption process was easy to proceed.

[0112] Table 3 Isotherm model fitting for U(VI) adsorption by A / PBC

[0113]

[0114] 3. Thermodynamic analysis

[0115] Table 3 shows the thermodynamic parameters of the adsorption process of U(VI) on A / PBC. ΔG was less than 0 at temperatures of 293, 303, and 313 K, indicating that the adsorption reaction proceeded spontaneously. ΔG increased with increasing temperature, indicating that the spontaneity of the reaction is positively correlated with temperature. ΔH = 13.41, a positive value, indicates that the adsorption reaction is endothermic and that increasing temperature favors its progress, consistent with experimental results. ΔS > 0 indicates that the reaction proceeds in an entropy-increasing direction. In summary, the thermodynamic analysis results indicate that the adsorption of U(VI) on A / PBC is a spontaneous reaction at high temperatures, and increasing temperature promotes the reaction and enhances the adsorption efficiency (Table 4).

[0116] Table 4 Adsorption thermodynamic parameters of U(VI) on A / PBC

[0117]

[0118]

[0119] (6) Reusability

[0120] 0.2 g / L of A / PBC and PBC prepared in Example 1 were added to a 10 mg / LU(VI) solution and reacted for 1440 min to ensure that the adsorption reaction was complete. A desorption experiment was performed using 0.1 M HCl, and the desorption time was 1440 min. After the desorption reaction was completed, the mixture was washed three times with distilled water. After A / PBC and PBC were dried, the next set of adsorption experiments was performed. After repeating the adsorption-desorption experiment 5 times, the U(VI) removal rates of A / PBC and PBC were as follows: Figure 7 shown.

[0121] Depend on Figure 7 It can be seen that the U(VI) removal rate of PBC decreased from 84.24% to 67.44%, while the U(VI) removal rate of A / PBC remained above 98%. Therefore, A / PBC has better recycling performance.

[0122] (7) Analysis of uranium fixation mechanism

[0123] The U(VI) removal mechanism of A / PBC was preliminarily analyzed by comparing the FTIR and XRD results before and after U(VI) adsorption. The interface morphology and element distribution between A. faecalis and PBC in A / PBC before and after U(VI) adsorption were observed by transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS, FEI Talos F200X, USA) to analyze the microscopic interfacial reaction mechanism.

[0124] 1) Figure 8 XRD patterns of A / PBC (a) and DA / PBC (b) before and after uranium adsorption.

[0125] Figure 8 The figure shows the changes in the crystal structure of A / PBC and DA / PBC after loading U(VI). Figure 8 In (b), after U(VI) adsorption by DA / PBC, the diffraction peak intensities of Ca(PO3)2 and NaMg(PO3)3 decreased significantly, indicating the involvement of these two substances in the U(VI) adsorption process. The peak intensities of NaMg(PO3)3 and Ca(PO3)2 on the A / PBC surface remained unchanged, likely due to the generation of new Ca(PO3)2 and NaMg(PO3)3 by A. faecalis during the reaction with U(VI). A. faecalis utilizes PBC to generate metaphosphate minerals, which can act as a buffer against acidic environments and a U(VI) adsorbent, potentially representing a synergistic mechanism between the two. No characteristic peaks associated with crystal structure were observed in the XRD patterns of free A. faecalis (FAF) and after U(VI) removal by PBC. The presence of PBC facilitates biofilm formation by attached A. faecalis. This structure provides nucleation sites for mineralization and enriches phosphate and U(VI). The high ion concentration in the biofilm microenvironment promotes biomineralization and the formation of uranyl phosphate minerals. However, FAF and PBC do not have these nucleation conditions and cannot undergo mineralization reactions.

[0126] 2) Figure 9 Transmission electron microscopy (TEM) images of A / PBC before and after uranium adsorption, where (a) and (b) are before adsorption, and (c) and (d) are after adsorption.

[0127] Depend on Figure 9 (a-b) shows that before the adsorption reaction, Alcaligenes faecalis was tightly attached to the PBC surface. At the same time, there was a certain gap between the bacteria, which provided a mass transfer channel for nutrients and dissolved oxygen. The cross section of PBC showed a dense and regular layered graphite structure. Figure 9 In (c-d), after reaction with U(VI), a corrosion area appears at the interface between A. faecalis and PBC, where the dense graphite layer structure of PBC becomes dispersed due to the erosion of A. faecalis.

[0128] 3) Figure 10 TEM-EDS mapping images of A / PBC before and after uranium adsorption, where (a) is before adsorption and (b) is after adsorption.

[0129] Depend on Figure 10 It can be seen that the relative contents of O, P and Ca in Alcaligenes faecalis on the surface of A / PBC after the reaction were significantly increased compared with those before the reaction.

[0130] 4) Figure 11 FTIR spectra of A / PBC before and after uranium adsorption.

[0131] fromFigure 11 It can be seen from the figure that the characteristic peak intensity of -OH (NH), carboxyl and phosphate groups on the surface of A / PBC increases significantly after loading U(VI). These functional groups are consistent with the functional groups corresponding to the EPS components. Figure 11 After the reaction between A / PBC and U(VI), the -OH(NH) peak on its surface changes from 3421cm -1 Move to 3396cm -1 The infrared characteristic peaks of C=O are from 1600cm -1 Move to 1583cm -1 Moreover, the peaks belonging to CO and phosphate groups also shift slightly to the left. The above phenomenon can prove that these active functional groups participate in the complexation reaction with U(VI).

[0132] During the U(VI) adsorption process on A / PBC, oxygen-containing functional groups on PBC and EPS first rapidly (within 5 minutes) complex with U(VI) in the water. Simultaneously, U(VI) diffuses into the biofilm surrounding the bacteria, activating the bacterial detoxification mechanism: Alcaligenes faecalis absorbs nutrients from PBC and transfers these nutrients to the A / PBC surface in the form of EPS and metaphosphate minerals, thereby immobilizing U(VI) in the water. This not only shortens the contact distance between the microorganism and the nutrients but also eliminates the mass transfer resistance of U(VI) in the water diffusing into the A / PBC interior, thereby increasing the U(VI) adsorption rate on A / PBC. As A. faecalis metabolizes U(VI), the abundance of acidic functional groups on the A / PBC surface increases, promoting its electrostatic attraction to U(VI) in the water and enhancing Lewis acid-base interactions. Consequently, the synergistic effect of A. faecalis and PBC enhances the uranium fixation efficiency, achieving a U(VI) removal rate of nearly 100%.

[0133] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for treating uranium-containing wastewater, characterized in that: The following steps are involved: 10 g of aloe leaf powder was added to a conical flask, 20 g of a phytic acid solution with a concentration of 50 wt.% was added, and 150 mL of distilled water was added; the conical flask was placed in a shaker and shaken at 30°C for 24 hours, and then the mixed substance was collected and placed in a ceramic evaporating dish, and the pretreated aloe vera powder was placed in a 105°C oven for 24 hours to dry to constant weight; the aloe vera leaf powder pretreated with phytic acid was placed in a ceramic crucible and placed in a muffle furnace at 500°C for pyrolysis for 2 hours, and the heating rate of the muffle furnace was 10°C / min. After the muffle furnace was naturally cooled, the carbonized product was taken out, ground and passed through a 100-mesh sieve, and then repeatedly rinsed with distilled water until the pH value of the eluate reached 7, and finally dried at 60°C to constant weight to obtain phosphate-functionalized biochar; Alcaligenes faecalis, GenBank accession number: KU844046.1, was cultured in 100 mL of LB medium until the logarithmic phase (OD600 = 1.0), centrifuged at 8000 rpm for 5 min at 25°C, and resuspended in 100 mL of distilled water to prepare a bacterial suspension. The bacterial count of the resulting suspension was 1.8 × 10 8 cells / mL, 1.0 g of phosphate-functionalized biochar was weighed and placed in 100 mL of bacterial suspension, and cultured in a constant temperature shaker at 30 °C and 150 rpm for 24 h. Then, the suspension was separated by centrifugation at 1000 rpm for 5 min, and the residual concentration of Alcaligenes faecalis was measured by hemocytometer to be 1.2 × 10 7 cells / mL, and the bacterial loading of phosphate-functionalized biochar was calculated to be 1.7×10 10 cells / g, and finally washed repeatedly with sterile distilled water for 3 times, freeze-dried at -50°C for 6 hours, and then stored in a 4°C refrigerator for later use to obtain a loaded Alcaligenes faecalis composite material, which was inactivated at 121°C for 20 minutes to obtain an inactivated loaded Alcaligenes faecalis composite material; Mixing a loaded Alcaligenes faecalis composite material with uranium-containing wastewater for adsorption; the loaded Alcaligenes faecalis composite material comprises phosphate-functionalized biochar and Alcaligenes faecalis loaded on the surface of the phosphate-functionalized biochar; The mass concentration of uranium in the uranium-containing wastewater is 10-80 mg / L; the pH value of the uranium-containing wastewater is 2-7; and the ratio of the mass of the supported Alcaligenes faecalis composite material to the volume of the uranium-containing wastewater is (0.05-0.3) g:1L.

2. The method according to claim 1, characterized in that The specific surface area of ​​the phosphate functionalized biochar is 500-600 m 2 / g.

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