Method for treating acid mine wastewater by nanofiber material reinforced sulfate reducing bacteria

Abstract

The invention discloses a method for treating acid mine wastewater by using nanofiber material reinforced sulfate reducing bacteria, which comprises the following steps: immobilizing the sulfate reducing bacteria by using the nanofiber material as a carrier to obtain immobilized sulfate reducing bacteria, and treating the immobilized sulfate reducing bacteria in the acid mine wastewater. According to the method, the nanofiber material and the sulfate reducing bacteria are combined to efficiently treat the acid mine wastewater, graphene oxide (GO) in the nanofiber material can be reduced into reduced graphene oxide (rGO) by the sulfate reducing bacteria, growth and metabolism of the sulfate reducing bacteria and removal of pollutants in the wastewater are promoted, the maximum Pb < 2 + > adsorption capacity reaches 260.94 mg / g, and the acid mine wastewater can be efficiently treated. The maximum Cr < 6 + > adsorption capacity reaches 130.25 mg / g, and the Pb < 2 + > removal rate of the nanofiber material immobilized sulfate reducing bacteria reaches up to 96%.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a method for treating acid mine wastewater by using nanofiber materials to enhance sulfate-reducing bacteria. Background Art

[0002] With the development of human society, the demand for mineral resources is increasing. Mining and non-ferrous metal smelting processes generate acidic mine wastewater rich in heavy metal ions and sulfates. This wastewater primarily originates from surface seepage water, groundwater, rock pore water, pit water, and mineral production and processing wastewater generated during the mining process. Untreated wastewater can severely damage surrounding waters, soil, and microorganisms. The heavy metal ions present in this wastewater can enter the human body through the food chain, causing significant harm to human health. Heavy metal pollution is a serious problem facing my country's water environment, and there is an urgent need to develop efficient and cost-effective methods for treating heavy metal wastewater.

[0003] Currently, the commonly used methods for treating heavy metal wastewater include chemical, physical, and biological methods. The chemical method involves adding reagents to the wastewater to remove pollutants through precipitation or redox reactions. The physical adsorption method uses porous solid materials as adsorbents to absorb heavy metal ions in the wastewater through intermolecular forces and chemical bonds. Traditional treatment methods have problems such as large amounts of treatment agents, high energy consumption, and secondary pollution. The biological method utilizes the physiological and biochemical characteristics of microorganisms to precipitate metal ions in the wastewater while reducing the sulfate concentration in the wastewater. Among them, the most common microorganism is sulfate-reducing bacteria (SBR). Sulfate-reducing bacteria can convert sulfate into sulfide, which is then converted into biosulfur by sulfur-oxidizing bacteria. Using sulfate-reducing bacteria to treat acidic mine drainage has the advantages of low cost, high efficiency, and no secondary pollution. It is currently a treatment method with great potential and development prospects.

[0004] Electrospinning nanotechnology primarily utilizes high electrical forces to stretch a polymer solution into a Taylor cone. When the electric field overcomes surface tension, a charged jet of fluid is ejected from the cone's tip. The solvent evaporation and unstable motion of the charged jet cause the solid nanofibers to randomly deposit onto a collector, forming a nonwoven nanofiber membrane. Electrospun nanofiber membranes offer numerous advantages, including high surface area, distinct interconnected structures, and high porosity. They have been widely used in many fields, particularly in water treatment, where they offer significant advantages.

[0005] In recent years, numerous studies and patent applications have been filed domestically and internationally on the use of immobilized sulfate-reducing bacteria for wastewater treatment, such as those published under CN 118652880 A and CN 103952390 B. However, these approaches are limited in how to combine the materials and sulfate-reducing bacteria. Furthermore, the immobilization process often involves the use of chemical reagents such as glutaraldehyde and boric acid, which can affect the activity of sulfate-reducing bacteria and, consequently, their degradation efficiency. Summary of the Invention

[0006] The present invention aims to address the low treatment efficiency of existing biological treatment technologies using sulfate-reducing bacteria to treat acidic mine drainage (AMD). By providing a method for using nanofiber materials to enhance the use of sulfate-reducing bacteria to treat AMD, the present invention addresses the problem of low treatment efficiency when using sulfate-reducing bacteria to treat AMD. The nanofiber materials prepared by the present invention can immobilize sulfate-reducing bacteria through electrostatic adsorption and pore adsorption, and are harmless to the bacteria. Furthermore, the graphene oxide (GO) in the nanofiber materials can be reduced to reduced graphene oxide (rGO) by the sulfate-reducing bacteria. rGO not only promotes the growth of the sulfate-reducing bacteria but also enhances electron transfer during sulfate reduction by the bacteria, thereby increasing the ability of the bacteria to reduce sulfate to sulfide ions, which then form a precipitate with heavy metal ions, achieving the dual purpose of removing sulfate and heavy metals from wastewater. Furthermore, the polyethyleneimine (PEI) in the nanofiber materials contains abundant amino and imino groups, which can chelate heavy metal ions, further removing heavy metal ions from the AMD.

[0007] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0008] A method for treating acidic mine wastewater by using nanofiber materials to strengthen sulfate-reducing bacteria comprises immobilizing the sulfate-reducing bacteria using the nanofiber materials as carriers to obtain immobilized sulfate-reducing bacteria, which are then placed in the acidic mine wastewater for treatment.

[0009] The immobilization method is to mix the bacterial solution of the sulfate-reducing bacteria with the nanofiber material and shake them.

[0010] The preparation method of the nanofiber material is as follows: polyacrylonitrile (PAN) and polyethyleneimine (PEI) are added to N,N-dimethylformamide (DMF), stirred, graphene oxide (GO) is added, ultrasonicated to obtain an electrospinning solution, and electrospinning is performed to obtain the nanofiber material.

[0011] In the electrospinning solution, the concentrations of polyacrylonitrile, polyethyleneimine and graphene oxide are 10-15wt%, 25-30wt% and 1-6wt%, respectively, preferably 10-12wt%, 27-29wt% and 1-3wt%, and most preferably 10wt%, 28wt% and 2wt%.

[0012] Among them, the conditions for the electrospinning are: voltage of 12-18 kV, injection speed of 0.5-1.0 mL / h, distance between the needle tip and the rotating axis of 10-15 cm, inner diameter of the needle of 0.5-0.8 mm, and the spinning time is adjusted according to the required thickness of the nanofiber material.

[0013] Preferably, the electrospinning conditions are: voltage of 16 kV, injection speed of 0.6 mL / h, distance between needle tip and rotating axis of 10 cm, inner diameter of needle of 0.7 mm, and spinning time of 5 h.

[0014] After obtaining the nanofiber material, it is dried at a temperature of 60 to 70° C. for 4 to 6 hours and cut into suitable sizes for later use.

[0015] The stirring time is 10 to 16 hours; the ultrasonic power is 300 to 500 W, and the time is 15 to 30 minutes.

[0016] The oscillation speed is 120-160 rpm and the oscillation time is 3-6 hours.

[0017] Wherein, the sulfate-reducing bacteria are subjected to acid-resistance acclimation before immobilization; preferably, the method for acid-resistance acclimation is: inoculating the sulfate-reducing bacteria into a sulfate-reducing bacteria culture medium with a pH of 4-6, and culturing under anaerobic conditions at 30-35°C until the sulfate-reducing bacteria culture medium changes from clear and transparent to turbid and black and produces a rotten egg smell, indicating that sulfate-reducing bacteria are growing, thereby completing the acid-resistance acclimation of the sulfate-reducing bacteria.

[0018] The sulfate-reducing bacteria culture medium comprises the following components: 0.1-0.5 g / L of dipotassium hydrogen phosphate, 0.5-1 g / L of ammonium chloride, 1-2 g / L of anhydrous sodium sulfate, 0.1-0.5 g / L of anhydrous magnesium sulfate, 0.1-0.5 g / L of anhydrous calcium chloride, 5-6 g / L of 70 wt% sodium lactate, 1-2 g / L of yeast powder, 0.1-0.5 g / L of ferrous sulfate heptahydrate, and 0.1-0.5 g / L of ascorbic acid.

[0019] The sulfate-reducing bacteria are preferably Desulfovibrio, Desulfovibrio enterobacter, Desulfomonas, or Desulfobacter, and are commercially available.

[0020] The acid mine wastewater has a pH of 3 to 5 and contains heavy metal ions including Pb 2+ Cr 6+ , where the sulfate concentration is 1 to 2 g / L.

[0021] Beneficial effects:

[0022] (1) The nanofiber material prepared by the present invention can promote the growth and metabolism of sulfate-reducing bacteria and absorb a large amount of heavy metals. 2+ The maximum adsorption capacity reached 260.94 mg / g for Cr 6+ The maximum adsorption capacity reached 130.25 mg / g, which was significantly higher than that of the nanofiber material without graphene oxide (GO). 2+ The adsorption capacity of Cr 6+ The adsorption capacity increased by 30%.

[0023] (2) The nanofiber material prepared by the present invention can immobilize sulfate-reducing bacteria through electrostatic adsorption and pore adsorption, and is harmless to the bacteria. In addition, the graphene oxide (GO) in the nanofiber material can be reduced to reduced graphene oxide (rGO) by sulfate-reducing bacteria. rGO can not only promote the growth of sulfate-reducing bacteria, but also enhance the electron transfer in the process of sulfate-reducing bacteria reducing sulfate, thereby enhancing the sulfate-reducing bacteria to reduce sulfate to sulfide ions, and then form precipitation with heavy metal ions, achieving the dual purpose of removing sulfate and heavy metals from sewage. In addition, the polyethyleneimine (PEI) in the nanofiber material contains rich amino and imino groups, which can produce chelation with heavy metal ions, further removing heavy metal ions in acidic mine wastewater, and the nanofiber material immobilized sulfate-reducing bacteria has a strong effect on Pb 2+ The removal rate is as high as 96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0025] Figure 1 This is a line graph showing the growth curve of the sulfate-reducing bacteria after acid-resistance acclimation in Example 1 and their sulfate degradation efficiency.

[0026] Figure 2 This is the SEM image of the nanofiber material PAN+PEI+GO prepared in Example 2.

[0027] Figure 3 The effect of nanofiber material PAN+PEI on Pb under different pH conditions in Example 4 2+ and Cr 6+ Line graph of adsorption amount.

[0028] Figure 4 The effect of nanofiber material PAN+PEI+GO on Pb under different pH conditions in Example 4 2+ and Cr 6+ Line graph of adsorption amount.

[0029] Figure 5 The free SBR, PAN+PEI+GO, PAN+PEI immobilized SBR, PAN+PEI+GO immobilized SBR containing Pb in Example 5 2+ Statistical chart of wastewater treatment effects. DETAILED DESCRIPTION

[0030] The present invention is further described below with reference to the following examples. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0031] Specific techniques or conditions not specified in the examples were carried out according to those described in the literature in the field or according to the product instructions. Reagents or instruments used without manufacturer specified were all conventional products available through regular channels.

[0032] The components of the culture medium described in the following examples are: 0.5 g / L dipotassium hydrogen phosphate, 1 g / L ammonium chloride, 2 g / L anhydrous sodium sulfate, 0.2 g / L anhydrous magnesium sulfate, 0.1 g / L anhydrous calcium chloride, 5 g / L 70 wt % sodium lactate, 1 g / L yeast extract, 0.1 g / L ferrous sulfate heptahydrate, and 0.1 g / L ascorbic acid.

[0033] Example 1 Acclimation of sulfate-reducing bacteria

[0034] First, the Desulfurization Vibrio (purchased from Wuhan Huizao Biotechnology Co., Ltd., item number: HZB417988) stored in the refrigerator was activated, and the strain in the storage tube was inoculated into an anaerobic bottle filled with culture medium after sterilization, and then sealed with a butyl rubber stopper and an aluminum cap. Nitrogen was then flushed into it for 15 minutes to eliminate the oxygen therein, and finally sealed again with a sealing film, transferred to an anaerobic operating table and cultured at 35°C until the culture medium turned from clear and transparent to turbid and black and produced a rotten egg smell, indicating that sulfate-reducing bacteria grew and the culture was completed. The bacterial liquid was then subjected to acid-resistant acclimation culture: the bacterial liquid was inoculated into a culture medium with a pH of 7 for culture. After the culture was completed, the obtained bacterial liquid was inoculated again into a culture medium with a pH of 6 for culture. After the culture was completed, the obtained bacterial liquid was inoculated again into a culture medium with a pH of 5 for culture. The inoculum size, culture method and culture end time of each round of culture were the same as those of the above-mentioned activation method.

[0035] The culture medium of sulfate-reducing bacteria that had been acclimated to acid resistance was inoculated at an inoculum rate of 10% v / v into a sterilized anaerobic bottle containing sulfate-reducing bacteria culture medium, and then sealed with a butyl rubber stopper and an aluminum cap. Nitrogen was then flushed into the bottle for 15 minutes to eliminate oxygen. Finally, the bottle was sealed again with a sealing film and transferred to an anaerobic operating table for incubation at 35°C for 120 hours. During this period, the growth density of sulfate-reducing bacteria and the sulfate degradation rate in the culture medium were measured at regular intervals.

[0036] The results are as follows Figure 1 As shown in Figure 2, sulfate-reducing bacteria reached the stable phase of their growth cycle at 48 h, and OD 600 It reached 0.512, and the sulfate degradation rate tended to stabilize at around 88.05% after 48 hours.

[0037] Example 2 Preparation of functional nanofiber materials

[0038] The specific preparation method of nanofiber material is as follows:

[0039] (a) Polyacrylonitrile and polyethyleneimine were dissolved in DMF and stirred overnight. Graphene oxide was then added and ultrasonicated at 300 W for 30 min to prepare an electrospinning solution. The amounts of polyacrylonitrile, polyethyleneimine, and graphene oxide were 10 wt%, 28 wt%, and 2 wt%, respectively, based on the mass of the electrospinning solution.

[0040] (b) electrospinning the electrospinning solution obtained in step (a) to obtain a nanofiber material PAN+PEI+GO; wherein the electrospinning conditions are: voltage of 16 kV, injection speed of 0.6 mL / h, distance between needle tip and rotating axis of 10 cm, inner diameter of needle of 0.7 mm, and spinning time of 5 h.

[0041] (c) The obtained nanofiber material was dried at 60° C. for 6 h and cut into pieces of 2 cm×2 cm for later use.

[0042] The nanofiber material obtained in this example was observed using a scanning electron microscope. Figure 2 As shown, the diameter distribution of the nanofibers is uniform, with an average diameter of 791 nm, exhibiting a porous structure with random fiber orientation.

[0043] Comparative Example 3 Preparation of Nanofiber Material PAN+PEI

[0044] (a) Polyacrylonitrile and polyethyleneimine were dissolved in DMF, stirred overnight, and ultrasonicated at 300 W for 30 min to prepare an electrospinning solution; wherein the amounts of polyacrylonitrile and polyethyleneimine used were 10 wt% and 28 wt% of the mass of the electrospinning solution, respectively.

[0045] (b) electrospinning the electrospinning solution obtained in step (a) to obtain a nanofiber material; wherein the electrospinning conditions are: voltage of 16 kV, injection speed of 0.6 mL / h, distance between the needle tip and the rotating axis of 10 cm, inner diameter of the needle tip of 0.7 mm, and spinning time of 5 h.

[0046] (c) The obtained nanofiber material was dried at 60° C. for 6 h and cut into pieces of 2 cm×2 cm for later use.

[0047] Example 4 Effect of pH on Pb content in nanofiber materials 2+ and Cr 6+ Effect of adsorption amount

[0048] The nanofiber material PAN+PEI+GO prepared in Example 2 was placed in different pH (3, 4, 5, 6 and 7) containing 100 mg / L Pb 2+ 50mL aqueous solution and 100mg / L Cr at different pH 6+ The residual Pb in the aqueous solution was determined by treating it at 25℃ and 120r / min for 6h. 2+ and Cr 6+ The concentration of nanofiber materials was calculated to determine the effect of Pb 2+ and Cr 6+ The adsorption amount, Where M is Pb 2+ or Cr 6+ .

[0049] The nanofiber material PAN+PEI prepared in Comparative Example 3 was subjected to the same Pb 2+ and Cr 6+ adsorption experiments.

[0050] The experimental results of nanofiber materials PAN+PEI and PAN+PEI+GO are shown as follows: Figure 3 and 4 As shown, the nanofiber PAN+PEI has a great influence on the Pb 2+ The adsorption capacity of Cr increases with the increase of pH, and the maximum adsorption capacity reaches 95.36 mg / g. 6+ The adsorption capacity of the product decreased with the increase of pH, and reached the maximum adsorption capacity of 91.74 mg / g at pH = 4 ( Figure 3 ). Nanofiber PAN+PEI+GO on Pb 2+ The adsorption capacity of Cr increases with the increase of pH, the minimum adsorption capacity is 115.58 mg / g (pH = 3), and the maximum adsorption capacity is as high as 260.94 mg / g (pH = 7). 6+ The adsorption capacity of the adsorbent decreases with the increase of pH, and reaches a maximum adsorption capacity of 130.25 mg / g at pH = 4 ( Figure 4 ).

[0051] The above results show that the nanofiber material PAN+PEI+GO prepared in the present invention has a strong effect on the absorption of heavy metal ions Pb in liquid under acidic conditions. 2+ and Cr 6+ It has excellent adsorption capacity, and the graphene oxide (GO) in it has excellent adsorption capacity for Pb 2+ and Cr6+ Adsorption capacity plays an important role.

[0052] Example 5: Nanofiber materials and sulfate-reducing bacteria collaborate to treat heavy metal ions and sulfate

[0053] 20 mL of the bacterial solution obtained after acid acclimation in Example 1 was taken into two centrifuge tubes, and then 2 cm × 2 cm nanofiber materials PAN + PEI + GO and PAN + PEI prepared in Example 2 and Comparative Example 3 were added to the centrifuge tubes respectively. The centrifuge tubes were placed in a shaker at 120 rpm for 3 h to fix the bacteria on the nanofiber materials by electrostatic adsorption and pore adsorption. Subsequently, the two nanofiber materials immobilized sulfate-reducing bacteria were transferred to the 50 mg / L PB 2+ The culture medium was sterilized in 100 mL of a pH 5 medium and treated in an anaerobic incubator for 48 h. The Pb content in the culture medium was measured every 4 h. 2+ concentration.

[0054] As a control experiment, 20 mL of the bacterial solution obtained after acid acclimation in Example 1 was transferred to a solution containing 50 mg / L Pb 2+ The 2cm×2cm nanofiber material PAN+PEI+GO prepared in Example 2 was placed in a 100mL sterilized medium with a pH of 5 for 48h, and other conditions were the same as those of the experimental group. 2+ The cells were treated in 100 mL of sterilized culture medium with a pH of 5 for 48 h. Other conditions were the same as those of the above experimental group.

[0055] The results are as follows Figure 5 As shown, after 8 hours of treatment, the lead ion removal rate of sulfate-reducing bacteria immobilized on nanofiber material PAN+PEI+GO was 90.99%, the lead ion removal rate of sulfate-reducing bacteria immobilized on nanofiber material PAN+PEI+GO was 82.60%, the removal rate of free sulfate-reducing bacteria was 72.60%, and the lead ion removal rate of nanofiber PAN+PEI+GO was 31.2%. After 48 hours of treatment, the lead ion removal rates of sulfate-reducing bacteria immobilized on PAN+PEI+GO reached 92.67%, the lead ion removal rates of sulfate-reducing bacteria immobilized on PAN+PEI+GO reached 96.00%, the removal rate of free sulfate-reducing bacteria was approximately 90%, and the lead ion removal rate of nanofiber PAN+PEI+GO remained around 30%. This indicates that immobilizing sulfate-reducing bacteria on nanofiber materials can improve the lead ion removal rate and efficiency in the culture medium compared to sulfate-reducing bacteria acting alone. In addition, the addition of graphene oxide to the nanofiber material can enhance the removal efficiency of heavy metal ions.

[0056] The present invention provides a concept and method for treating acidic mine drainage using nanofiber materials to enhance sulfate-reducing bacteria. While there are numerous methods and approaches for implementing this technical solution, the aforementioned are merely preferred embodiments of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria, characterized in that: The nanofiber material is used as a carrier to immobilize sulfate-reducing bacteria to obtain immobilized sulfate-reducing bacteria, which are then placed in the acidic mine wastewater for treatment.

2. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 1, characterized in that: The preparation method of the nanofiber material comprises the following steps: adding polyacrylonitrile and polyethyleneimine to N,N-dimethylformamide, stirring, adding graphene oxide, ultrasonicating to obtain an electrospinning solution, and electrospinning the solution.

3. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 2, characterized in that: The usage amounts of polyacrylonitrile, polyethyleneimine and graphene oxide are 10-15 wt%, 25-30 wt% and 1-6 wt% of the mass of the electrospinning solution respectively.

4. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 2, characterized in that: The electrospinning conditions are as follows: voltage of 12-18 kV, injection speed of 0.5-1.0 mL / h, distance between needle tip and rotating axis of 10-15 cm, and inner diameter of needle of 0.5-0.8 mm.

5. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 2, characterized in that: The stirring time is 10 to 16 hours; the ultrasonic power is 300 to 500W, and the time is 15 to 30 minutes.

6. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 1, characterized in that: The sulfate-reducing bacteria are any one or more combinations of Desulfovibrio, Desulfuricans, Desulfuromicrobium and Desulfobacterium.

7. The method for treating acid mine drainage using sulfate-reducing bacteria enhanced by nanofiber materials according to claim 1 or 6, characterized in that: The sulfate-reducing bacteria are acclimated to acid resistance before being immobilized.

8. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 1, characterized in that: The immobilization method is to mix the bacterial solution of the sulfate-reducing bacteria with the nanofiber material and shake them.

9. The method for treating acid mine drainage using nanofiber materials to enhance sulfate-reducing bacteria according to claim 8, characterized in that: The shaking speed is 120-160 rpm, and the shaking time is 3-6 hours.

10. The method for treating acid mine drainage using sulfate-reducing bacteria enhanced by nanofiber materials according to claim 1, characterized in that: The acid mine wastewater has a pH of 3 to 5 and contains heavy metal ions including Pb 2+ and Cr 6+ .

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