A siderite-Shewanella composite system and its preparation method and application

Abstract

The present invention provides a method for preparing a siderite-Shewanella composite system, comprising the following steps: S1. mixing siderite with ferric sulfate and then ball-milling to obtain a siderite composite material; S2. adding activated Shewanella to a new culture medium containing the siderite composite material and incubating the mixture with shaking. The resulting co-culture system is the siderite-Shewanella composite system. The siderite-Shewanella composite system prepared by the present invention can remove chromium (VI) from liquids with a high removal rate and rapid removal rate.

Description

Technical Field

[0001] The present invention relates to the technical field of chromium-containing wastewater treatment, and in particular to a siderite-Shewanella composite system and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid industrialization of cities, chromium and its compounds have been widely used as key raw materials in industries such as metallurgy, electroplating, chemicals, and dyes. Large amounts of chromium-containing wastewater, chromium slag, and chromium-containing dust enter water bodies, causing serious environmental pollution. As a heavy metal, chromium exists primarily in divalent, trivalent, and hexavalent forms in the environment, with trivalent and hexavalent forms predominant in water. Trivalent chromium exists as a hydrated ion, exhibiting low toxicity, low solubility in water, and prone to precipitation. Hexavalent chromium is highly soluble in water, exhibits strong oxidizing properties, is highly mobile, and is potentially carcinogenic and pathogenic. Consequently, countries around the world have established regulations regarding the discharge of hexavalent chromium into wastewater.

[0003] The main treatment methods for wastewater containing hexavalent chromium include reduction precipitation, ion exchange, membrane separation, adsorption, electrolysis and photocatalytic reduction.

[0004] Chemical reduction involves adding a reducing agent to wastewater at a pH of 2-4 to reduce chromium (VI) to the more stable and less toxic chromium (III). While chemical reduction offers advantages such as ease of operation, mature technology, and high efficiency, it requires the addition of large amounts of chemical reagents, which are costly. Therefore, new technologies are needed to address these issues. Ion exchange involves the separation of ions between liquid and solid phases, or between liquid and liquid phases. During this ion exchange process, ion exchange resins with specific properties capable of absorbing metal ions are used. These ions are then desorbed using a corresponding method, exchanging the heavy metals from the water for removal. The advantages of ion exchange for heavy metal removal include simplicity, high efficiency, and excellent chemical stability. However, ion exchange also has certain disadvantages. The chemical resins used must be frequently refreshed to ensure effective removal of pollutants, and complex pretreatment is often required to prevent secondary contamination. Consequently, this method is not suitable for all types of heavy metal ions and requires significant investment. Membrane separation primarily utilizes the selective osmotic properties of membranes. By applying pressure to a fluid, the pressure or concentration difference across the membrane acts as a driving force, forcing it to pass through the membrane or filter, thereby separating pollutants. Membrane separation boasts wide application, requires minimal floor space, and is efficient and convenient to operate. Furthermore, it eliminates the need for chemical reagents, preventing secondary contamination. However, membranes have a short lifespan, require careful maintenance, and have high investment costs. Adsorption is a very common method for removing heavy metals. This process exploits the differences in binding strength between an adsorbent and pollutant components, transferring the substance from a liquid phase to a solid surface. The heavy metals are then removed through filtration or precipitation. Therefore, the performance of the adsorbent material directly determines its adsorption capacity. This process is simple to operate, offers high removal efficiency in a short time, and exhibits excellent recyclability. However, the adsorbent has limited adsorption sites, and some adsorbents are expensive, making them less widely used in water treatment. Electrolysis involves the application of an electric current to different electrode materials to form a galvanic cell, where heavy metals undergo a chemical reaction at the cathode and anode, thereby removing pollutants. The main advantages of the electrolytic method are good operational results, easy maintenance, operating at room temperature, simple operation, and low cost. Photocatalytic reduction, in the absence of an electric current, uses sunlight or artificial light to convert light energy into chemical energy and the catalytic action of semiconductor oxides to convert Cr(VI) to Cr(III). This method offers simple treatment engineering and low investment costs, but its complex removal mechanism and difficulty controlling factors such as light intensity result in relatively low removal rates, hindering widespread adoption.

[0005] It is necessary to develop a simple and efficient material and method for removing hexavalent chromium. Summary of the Invention

[0006] To solve the problems existing in the background technology, the present invention provides a siderite-Shewanella composite system and its preparation method and application. The siderite-Shewanella composite system can quickly and efficiently remove hexavalent chromium from water, is easy to prepare, and has low cost.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] In one aspect, the present invention provides a method for preparing a siderite-Shewanella composite system, comprising the following steps:

[0009] S1. mixing siderite and ferric sulfate and then ball milling to obtain a siderite composite material;

[0010] S2. The activated Shewanella is inoculated into a new culture medium containing the siderite composite material, and cultured with shaking. The resulting co-culture system is the siderite-Shewanella composite system.

[0011] Furthermore, in step S1, the mass ratio of the siderite to ferric sulfate is 20:1-5.

[0012] Furthermore, the addition ratio of the Shewanella is 1-5 g / L.

[0013] Furthermore, in the siderite-Shewanella composite system, the concentration of siderite is 0.2 g ~ 1 g / L.

[0014] Furthermore, the culture conditions are: 150-180 rpm, 20-30°C, and culture for 20-48 hours.

[0015] Furthermore, the ball milling conditions are: a rotation speed of 300-600 rpm and a time of 1 h.

[0016] Further, the Shewanella is S. oneidensis MR-1 .

[0017] In a second aspect, the present invention provides a siderite-Shewanella composite system prepared by any of the above preparation methods.

[0018] In a third aspect, the present invention provides application of the above-mentioned siderite-Shewanella composite system in treating hexavalent chromium-containing wastewater.

[0019] In a fourth aspect, the present invention provides a method for treating hexavalent chromium-containing wastewater, wherein the siderite-Shewanella composite system is added to the hexavalent chromium-containing wastewater for a certain period of time to reduce the hexavalent chromium in the wastewater to remove the hexavalent chromium.

[0020] Furthermore, the mass of the siderite composite material contained in the siderite-Shewanella composite system added to each liter of wastewater is 1g~5g.

[0021] The mechanism of action and beneficial effects of the siderite-Shewanella composite system prepared by the present invention are:

[0022] Siderite is co-grinded with ferric sulfate to stimulate the dissolution of Fe (II) in siderite. When the prepared siderite-Shewanella composite system is used for hexavalent chromium removal, firstly, Fe (II) can remove a certain amount of Cr (VI) by reduction (pathway I, direct reduction); secondly, S. oneidensis MR-1 It can reduce a small amount of Cr (VI). In addition, in the siderite-Shewanella composite system, a biofilm is formed between the siderite composite material and the bacteria. The presence of the siderite composite material is S. oneidensis MR-1 A carrier is provided to maintain the survival and biological activity of the bacteria and ensure that Cr (VI) is less toxic to the bacteria during the reaction with Cr (VI) (pathway II, direct reduction). S. oneidensis MR-1 It can reduce Fe (III) to generate Fe (II). Fe (II) can act as a strong reducing agent to accelerate the reduction of Cr (VI) to Cr (III) (pathway III, indirect reduction). In this process, Fe (II) and Fe (III) convert into each other and maintain a certain concentration, achieving the role of electron transfer. S. oneidensis MR-1 It is a dissimilatory iron-reducing bacteria. The presence of iron ions can ensure the metabolism of bacteria. In addition, S. oneidensis MR-1 The addition of Cr(VI) can change the surface properties of siderite. Furthermore, the functional groups on the bacterial surface also adsorb and complex Cr(VI). Furthermore, the siderite composite material also has a certain adsorption effect on Cr(VI) (Pathway IV), thus removing hexavalent chromium through multiple pathways.

[0023] The siderite-Shewanella composite system of the present invention requires a low dosage and achieves high efficiency in treating Cr(VI) wastewater. Furthermore, the raw material, siderite, is abundant, widely distributed, and readily available at low cost. A simple preparation method allows for the synthesis of a highly efficient composite system, thereby achieving chromium ion removal and reducing economic costs. Furthermore, the preparation process utilizes mechanical ball milling, resulting in no waste generation and no secondary pollution after the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The removal effect of Cr(VI) in the solution by the siderite-Shewanella direct mixed solution with different Shewanella concentrations prepared in Comparative Example 1 of the present invention;

[0025] Figure 2 The removal effect of the siderite-Shewanella direct mixed solution with different siderite composite material concentrations prepared in Comparative Example 3 of the present invention on Cr (VI) in the solution;

[0026] Figure 3 The removal effects of the siderite-Shewanella composite system prepared in Examples 1 and 2 of the present invention and the siderite-Shewanella direct mixed solution prepared in Comparative Example 1 on Cr(VI) in the solution are shown in Table 1, where 3a is the removal rate of Cr(VI), 3b is the removal rate of Cr(VI), Figure 3 c and 3d are microscopic images of the siderite-Shewanella direct mixed solution, and 3e and 3f are microscopic images of the siderite-Shewanella complex system;

[0027] Figure 4 The figure is a comparison chart of the removal effect, removal rate and pseudo-first-order kinetic model fitting of Cr (VI) reduction of the siderite-Shewanella composite system at different pH values ​​of the present invention, wherein Figure 4 a is the removal rate, Figure 4 b is the removal rate of Cr(VI), Figure 4 c is the pseudo-first-order kinetic model fitting diagram of Cr (VI) reduction;

[0028] Figure 5 The diffraction spectrum of the residue after the Shewanella-siderite composite material, the siderite-Shewanella composite system, and the siderite-Shewanella composite system treat Cr(III)-containing wastewater;

[0029] Figure 6 This is a comparison diagram of the FT-IR spectra of the products of the Shewanella, the siderite-Shewanella composite system, and the siderite-Shewanella composite system after treating hexavalent chromium-containing wastewater;

[0030] Figure 7 The SEM images of the Shewanella of the present invention, the product after the Shewanella treats the wastewater containing Cr (VI), the siderite-Shewanella composite system, and the product after the siderite-Shewanella composite system treats the wastewater containing Cr (VI), wherein Figure 7 a, 7b, 7c, and 7d are Shewanella, the product after Shewanella treated wastewater containing Cr(VI), the siderite-Shewanella complex system, and the product after the siderite-Shewanella complex system treated wastewater containing Cr(VI), respectively;

[0031] Figure 8 8a is the XPS spectrum of the siderite-Shewanella composite system of the present invention before and after the reaction with Cr (VI), wherein 8b is Cr2p, 8c is Fe2p, and 8d is O1s. DETAILED DESCRIPTION

[0032] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0033] The present invention provides a method for preparing a siderite-Shewanella composite system, comprising the following steps:

[0034] S1. mixing siderite and ferric sulfate and then ball milling to obtain a siderite composite material;

[0035] S2. The activated Shewanella is inoculated into a new culture medium containing the siderite composite material, and cultured with shaking. The resulting co-culture system is the siderite-Shewanella composite system.

[0036] Preferably, in step S1, the mass ratio of the siderite to ferric sulfate is 20:1-5.

[0037] Preferably, the addition ratio of the Shewanella is 1-5 g / L.

[0038] Preferably, in the siderite-Shewanella composite system, the concentration of the siderite composite material is 0.2-1 g / L.

[0039] Preferably, the culture conditions are: 150-180 rpm, room temperature (20-30°C), and culture for 20-48 hours.

[0040] Preferably, the ball milling conditions are: a rotation speed of 300-600 rpm and a time of 1-2 h.

[0041] Preferably, the Shewanella is S. oneidensis MR-1 .

[0042] In a second aspect, the present invention provides a siderite-Shewanella composite system prepared by any of the above preparation methods.

[0043] In a third aspect, the present invention provides application of the above-mentioned siderite-Shewanella composite system in treating hexavalent chromium-containing wastewater.

[0044] In a fourth aspect, the present invention provides a method for treating hexavalent chromium-containing wastewater, wherein the siderite-Shewanella composite system is added to the hexavalent chromium-containing wastewater and shaken or stirred for a certain period of time to reduce the hexavalent chromium in the wastewater to remove the hexavalent chromium.

[0045] Preferably, the mass of the siderite composite material contained in the siderite-Shewanella composite system added to each liter of wastewater is 1 g to 5 g.

[0046] Example 1

[0047] Weigh 2.609g of siderite, Fe2(SO4)3 5H2O 0.391g, after mixing, use Pulverisette7 planetary ball mill to activate the siderite. The specific operation steps are as follows: the mixed siderite and Fe2(SO4)3 5H2O was placed in a ball mill (45 cm 3 ), added 7 zirconium balls (diameter 5 mm), ball milling speed was 500 rpm, time was 1 h, and siderite composite material was obtained. The sample was taken out and put into a ziplock bag for later use.

[0048] Shewanella S. oneidensis MR-1 The activation was carried out, and the specific steps were as follows: the bacteria were inoculated on a sterilized TSA solid culture medium plate, cultured in a constant temperature incubator at 30°C for 24 hours, and then a single colony was picked with an inoculation loop and inoculated into a conical flask containing 200 ml of sterilized TSB liquid culture medium, sealed with a sand core rubber stopper, and placed in a constant temperature shaker, and cultured at 30°C and 150 rpm for 24 hours to obtain a Shewanella suspension.

[0049] 200 mg of the siderite composite material was sterilized and added to 200 ml of sterilized TSB liquid culture medium. 600 mg of Shewanella was added to the TSB liquid culture medium containing the siderite composite material. The medium was sealed with a sand core rubber stopper and placed in a constant temperature shaker for co-culture at 30°C and 150 rpm for 24 hours. The resulting co-culture system was the siderite-Shewanella composite system.

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that the co-culture time is 48 hours, and the other aspects are the same as those in embodiment 1.

[0052] Example 3

[0053] The difference between this embodiment and embodiment 1 is that 200 mg, 400 mg, 800 mg, and 1000 mg of Shewanella were added to the TSB liquid culture medium containing the siderite composite material, respectively.

[0054] Example 4

[0055] The difference between this embodiment and embodiment 1 is that 200 mg of Shewanella was added to 200 ml of TSB liquid culture medium containing 40 mg and 160 mg of the siderite composite material respectively. Other aspects are the same as those in embodiment 1.

[0056] Comparative Example 1

[0057] Weigh 2.609g of siderite, Fe2(SO4)3 5H2O 0.391g, after mixing, use Pulverisette7 planetary ball mill to activate the siderite. The specific operation steps are as follows: the mixed siderite and Fe2(SO4)3 5H2O was placed in a ball mill (45 cm 3), added 7 zirconium balls (diameter 5 mm), ball milling speed was 500 rpm, time was 1 h, and siderite composite material was obtained. The sample was taken out and put into a ziplock bag for later use.

[0058] Shewanella S. oneidensis MR-1 The activation was carried out, and the specific steps were as follows: the bacteria were inoculated on a sterilized TSA solid culture medium plate, cultured in a constant temperature incubator at 30°C for 24 hours, and then a single colony was picked with an inoculation loop and inoculated into a conical flask containing 200 ml of sterilized TSB liquid culture medium, sealed with a sand core rubber stopper, and placed in a constant temperature shaker, and cultured at 30°C and 150 rpm for 24 hours to obtain a Shewanella suspension.

[0059] The Shewanella suspension was centrifuged, the supernatant was discarded, and the bacteria were resuspended in 200 ml of 100 mM Tris-HCl buffer. 200 mg of sterilized siderite composite material was added, and the suspension was sealed with a sand core rubber stopper and placed in a constant temperature shaker. It was cultured at 30°C and 150 rpm for 24 hours to prepare a siderite-Shewanella direct mixed solution.

[0060] Comparative Example 2

[0061] Weigh 2.609g of siderite, Fe2(SO4)3 5H2O 0.391g, after mixing, use Pulverisette7 planetary ball mill to activate the siderite. The specific operation steps are as follows: the mixed siderite and Fe2(SO4)3 5H2O was placed in a ball mill (45 cm 3 ), added 7 zirconium balls (diameter 5 mm), ball milling speed was 500 rpm, time was 1 h, and siderite composite material was obtained. The sample was taken out and put into a ziplock bag for later use.

[0062] Shewanella S. oneidensis MR-1 The activation was carried out, and the specific steps were as follows: the bacteria were inoculated on a sterilized TSA solid culture medium plate, cultured in a constant temperature incubator at 30°C for 24 hours, and then a single colony was picked with an inoculation loop and inoculated into a conical flask containing sterilized TSB liquid culture medium, which was sealed with a sand core rubber stopper and placed in a constant temperature shaker, and cultured at 30°C and 150 rpm for 24 hours to obtain a Shewanella suspension.

[0063] The Shewanella suspension was centrifuged and the supernatant was discarded. Six groups of 200 ml 100 mM Tris-HCl buffer were prepared and sterilized. 0.2 g of sterilized siderite composite material was added to each buffer, and bacterial precipitates were added respectively so that the bacterial concentrations in the buffer were 0 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L and 5 g / L, respectively. The buffers were sealed with sand core rubber stoppers and placed in a constant temperature shaker. They were cultured at 30°C and 150 rpm for 24 hours to prepare siderite-Shewanella direct mixed solutions with different Shewanella concentrations.

[0064] Comparative Example 3

[0065] Weigh 2.609g of siderite, Fe2(SO4)3 5H2O 0.391g, after mixing, use Pulverisette7 planetary ball mill to activate the siderite. The specific operation steps are as follows: the mixed siderite and Fe2(SO4)3 5H2O was placed in a ball mill (45 cm 3 ), added 7 zirconium balls (diameter 5 mm), ball milling speed was 500 rpm, time was 1 h, and siderite composite material was obtained. The sample was taken out and put into a ziplock bag for later use.

[0066] Shewanella S. oneidensis MR-1 The activation was carried out, and the specific steps were as follows: the bacteria were inoculated on a sterilized TSA solid culture medium plate, cultured in a constant temperature incubator at 30°C for 24 hours, and then a single colony was picked with an inoculation loop and inoculated into a conical flask containing sterilized TSB liquid culture medium, which was sealed with a sand core rubber stopper and placed in a constant temperature shaker, and cultured at 30°C and 150 rpm for 24 hours to obtain a Shewanella suspension.

[0067] The Shewanella suspension was centrifuged and the supernatant discarded. Five 200 ml 100 mM Tris-HCl buffers were prepared and sterilized. 0.2 g of sterilized bacterial precipitate was added to each buffer. The siderite composite material was then added to each buffer, such that the concentrations of the siderite composite material in the buffer were 0.2 g / L, 0.8 g / L, and 1 g / L, respectively. The buffers were sealed with sand-core rubber stoppers and placed in a constant temperature shaker for incubation at 30°C and 150 rpm for 24 hours to prepare siderite-Shewanella direct mixed solutions with different siderite composite material concentrations.

[0068] Experimental example

[0069] 1. Removal of Cr(VI) using the siderite-Shewanella direct mixed solution with different Shewanella concentrations prepared in Comparative Example 2

[0070] The siderite-Shewanella direct mixed solution with different Shewanella concentrations prepared in Comparative Example 2 was used to remove Cr(VI). The specific method was as follows: at room temperature of 20°C, 100 ml of deionized water was taken, hexavalent chromium was added to make the concentration of hexavalent chromium ions in the water 100 mg / L, and the siderite-Shewanella direct mixed solution with different Shewanella concentrations was added to the prepared water containing hexavalent chromium ions so that the mass of the siderite composite material contained was 0.1 g. The reaction was shaken at room temperature for 48 hours, and the Cr(VI) concentration was measured by spectrophotometer at 6 hours, 8 hours, 12 hours, 24 hours, and 48 hours of reaction, respectively, and the Cr(VI) removal effect was calculated.

[0071] The results are as follows Figure 1 As shown in the figure, with the increase of Shewanella concentration, the removal rate of Cr (VI) by the direct mixed solution of siderite-Shewanella increased significantly. In the first 4 hours of the reaction, the removal rate of Cr (VI) by the solution without Shewanella was higher than that by the solution with the bacterial concentration of 1 g / L and 2 g / L, indicating that in this process, the reduction effect of the siderite composite material was the main factor. As the reaction time increased, the reduction effect of the siderite composite material reached its highest level, and in the later stage, the main factor was Shewanella ( S. oneidensis MR-1 ) reduction effect. When the concentration of Shewanella was 3g / L, 4g / L, and 5g / L, the removal rate reached a good effect with the increase of Shewanella concentration, and the time of Cr(VI) removal shortened with the increase of bacterial concentration, indicating that Shewanella played a major role in the reaction process. However, the synergistic effect of Shewanella and siderite composite material was not reflected, and the main effect was Shewanella.

[0072] 2. Cr(VI) removal using the siderite-Shewanella direct mixed solution with different siderite composite material concentrations prepared in Comparative Example 3

[0073] The siderite-Shewanella direct mixed solution with different siderite composite material concentrations prepared in Comparative Example 3 was used to remove Cr(VI). The specific method was as follows: at room temperature of 20°C, 100 ml of deionized water was taken, hexavalent chromium was added to make the concentration of hexavalent chromium ions in the water 100 mg / L, and the siderite-Shewanella direct mixed solution with different siderite composite material concentrations was added to the prepared water containing hexavalent chromium ions so that the mass of the siderite composite material contained was 0.1 g. The reaction was shaken at room temperature for 48 hours, and the Cr(VI) concentration was measured by spectrophotometer at 6 hours, 8 hours, 12 hours, 24 hours and 48 hours of the reaction, respectively, and the Cr(VI) removal effect was calculated.

[0074] The results are as follows Figure 2As shown in the figure, with the increase of siderite composite material, the removal rate of Cr (VI) by the direct mixed solution of siderite-Shewanella increases, and the removal rate of Cr (VI) is higher than that of Shewanella alone acting on Cr (VI)-containing wastewater. The high removal rate is due to the Fe (III) and Fe (II) in the siderite composite material: a part of Fe (II) can directly reduce Cr (VI) in the solution, while the existing Fe (III) is S. oneidensis MR-1 Reduced to Fe (II), Fe (II) indirectly reduces Cr (VI), S. oneidensis MR-1 Indirectly affects the removal rate of Cr (VI). In this process, Fe (II) and Fe (III) as transfer electrons are circulated.

[0075] 3. Removal of Cr(VI) by siderite-Shewanella direct mixed solution and siderite-Shewanella composite system

[0076] The siderite-Shewanella composite systems prepared in Examples 1 and 2 and the siderite-Shewanella direct mixed solution prepared in Comparative Example 1 were used to treat Cr(VI)-containing wastewater, respectively. Only Shewanella was added to the control group. The specific method was as follows: at room temperature of 20° C., 100 ml of deionized water was taken, hexavalent chromium was added to make the concentration of hexavalent chromium ions in the water 100 mg / L, and the siderite-Shewanella composite systems prepared in Examples 1 and 2, the siderite-Shewanella direct mixed solution prepared in Comparative Example 1, and Shewanella were added to the prepared water containing hexavalent chromium ions so that the mass of the siderite composite material was 0.1 g. The mixture was shaken at room temperature and reacted for 48 hours. The Cr(VI) concentration was measured by spectrophotometer at 6 hours, 8 hours, 12 hours, 24 hours, and 48 hours of reaction, respectively, and the Cr(VI) removal effect was calculated.

[0077] The results are as follows Figure 3 As shown in Figure a, in the early stage of the reaction, the removal rate of Cr (VI) by the siderite-Shewanella composite system is higher than that by the siderite-Shewanella direct mixed solution. As the reaction proceeds, the removal rates of Cr (VI) by the two systems tend to be the same. However, as Figure 3 As shown in b, the removal rate of Cr (VI) by the siderite-Shewanella composite system is significantly higher than that by the siderite-Shewanella direct mixed solution, indicating that in the siderite-Shewanella composite system, S. oneidensis MR-1 The siderite composite material synergizes with each other, couples chemical and biological reduction, and promotes the removal of Cr(VI), which may be related to the growth of bacteria and siderite composite material during the co-culture stage.

[0078] The siderite-Shewanella direct mixed solution and the siderite-Shewanella complex system were observed under a microscope. The results were as follows: Figure 3As shown in c, d and 3e, f, in the direct mixed solution, some bacteria exist in the fluid, and only some exist in the water bag formed by the siderite composite material and bacteria. In the middle of the composite system, it can be seen that a biofilm is formed between the bacteria and the siderite composite material, and the bacteria are coated on the surface of the siderite composite material. The black solid in the figure is a complex of bacteria and the siderite composite material. The microscopic examination results show that in the process of co-cultivation to form the siderite-Shewanella composite system, the siderite composite material can serve as S. oneidensis MR-1 The co-culture system provides a living environment for the bacteria, maintaining their normal metabolism and growth. The resulting biofilm can promote the removal of Cr(VI), indicating that the co-culture system does not affect bacterial growth and can promote the increase of bacterial concentration, thereby effectively improving the removal rate of Cr(VI). A comparison of co-culture time shows that extending the co-culture time to 48 hours can improve the removal rate of Cr(VI) to a certain extent. This may be due to the increase in the concentration of bacteria that act on Cr(VI), thereby improving the removal rate of Cr(VI).

[0079] 4. Removal effect of the siderite-Shewanella composite system prepared in Example 1 on Cr(VI) under different pH conditions

[0080] The room temperature was 20°C, and the pH values ​​of the Cr(VI)-containing wastewater were adjusted to 5, 7, and 9 with hydrochloric acid buffer. The removal effect of the siderite-Shewanella composite system prepared in Example 1 on Cr(VI) was determined. The experimental method was the same as that in Experimental Example 3. The removal rate and removal rate of Cr(VI) were determined, and a pseudo-first-order kinetic model fitting diagram of Cr(VI) reduction was drawn. The results are shown in FIG. Figure 4 As shown in the results, changes in pH value can affect the functional groups on the surface of microbial cells, such as amino, hydroxyl, and carboxyl groups, and thus have a certain impact on the metabolic activity and adsorption effect of Cr (VI). In addition, in the process of exploring the effect of pH on the removal of hexavalent chromium by the composite system, acidic conditions are conducive to the reduction reaction, that is, the initial pH has a significant effect on the removal rate and removal efficiency of Cr (VI), and the pseudo-first-order kinetic model fits well (R 2 >0.9), when the pH value is 5, the composite system has a better removal effect on Cr (VI), but the removal rate is lower than that of pH=7 within a certain period of time, and the rate constant K is the largest. The possible reason is that acidity is conducive to the reduction reaction. When the pH value is 7, the composite system has a smaller removal effect on Cr (VI) than that of pH 5, but it also has a good effect. The removal rate within 8h is the highest among several pH systems. When the pH is 9, S. oneidensis MR-1The activity of the chromium (VI)-containing compound may have been slightly affected, as it failed to synergize well with the siderite composite, resulting in a decrease in its Cr (VI) reduction capacity. However, in the later stages of the experiment, all three pH conditions achieved good removal results. Although pH 5 or 9 are both within the optimal range for bacterial growth, they did affect the biochemical activity of S. oneidensis MR-1 to some extent.

[0081] Table 1 Rate constants K and R of reactions at three pH values 2

[0082]

[0083] 5. XRD analysis of siderite composite materials, siderite-Shewanella composite system, products after treatment of hexavalent chromium-containing wastewater by siderite-Shewanella composite system, and dried Shewanella samples

[0084] The siderite-Shewanella composite system prepared in Example 1 was used. The sample containing bacteria was naturally air-dried in a clean bench at room temperature of 20° C., and the sample without bacteria was naturally dried in the shade in a drying dish. XRD analysis was performed on each sample.

[0085] The results are as follows Figure 5 As shown, Fe3(SO4)2 is added 5H2O co-grinding did not change the crystal phase of siderite, and the crystal phase shifted towards the amorphous phase. After co-grinding, needle vitriol (Fe3(SO4)2 9H2O or Fe3(SO4) 2OH. After co-culture of the siderite composite with Shewanella, a new crystalline phase appeared in the chromatogram, which can be determined to be a crystalline phase of the bacteria itself. The Fe2O3 crystalline phase that appeared is consistent with the crystalline phase that appears after high-temperature sterilization. Furthermore, in the presence of bacteria, the insoluble Fe2O3 formed can be utilized by specific chelating agents secreted by the bacteria to convert insoluble Fe(III) oxides into soluble chelated ions, which participate in redox reactions under anaerobic conditions. The crystalline phase in the residue after reaction with Cr(VI) is more unstable, and no new crystalline phase appears, indicating that the functional groups may react with Cr(VI). A chromatogram analysis reveals the presence of Cr2O3 and FeCr2O4 crystalline phases in the residue. However, due to the low chromium content in the residue, no crystalline phases formed, indicating that redox reactions occurred.

[0086] 6. FT-IR analysis of the products after treatment of hexavalent chromium-containing wastewater by Shewanella, siderite-Shewanella complex system, and siderite-Shewanella complex system

[0087] The siderite-Shewanella composite system prepared in Example 1 was used. The samples containing bacteria were naturally air-dried in a clean bench at room temperature of 20°C, and the samples without bacteria were naturally dried in a drying dish. FT-IR analysis was performed on each of them. The results are as follows: Figure 6 As shown, S. oneidensis MR-1 It shows abundant surface functional groups, such as hydroxyl groups at 3447 cm -1 stretching vibration at 1657 cm -1 , NH bending vibration and CN stretching vibration (amide II band) at 1543 cm -1 , HCH, COH symmetric deformation at 1454 cm -1 , HCC at 1398 cm -1 Bending vibration of P=O at 1240 cm -1 Asymmetric stretching vibration of COC at 1083 cm -1 The glycosidic bond at the . S. oneidensis MR-1 After co-culture with siderite composites, most of the bands showed blue-shift or red-shift, indicating S. oneidensis MR-1 The presence of bacteria did not affect the loss of characteristic functional groups in the siderite composites, but increased the types of functional groups. -1 , 740 cm -1 A characteristic peak was observed at 2- and Fe-O stretching of Fe2O3. After reaction with Cr (VI), most of the peaks shifted and a new peak appeared at 1385 cm -1 , which is attributed to the stretching vibration of Cr-O in Cr2O3; 740 cm -1 The Fe-O peak at 737 cm -1 This is mainly due to the formation of new stable Cr x Fe 1-x (OH)3. Inevitably, S. oneidensis MR-1 The main characteristic absorption peaks are C=O (amide І) and NH / CN (amide II). The trend of peak intensity weakening suggests that Cr(VI) grows on the siderite composite material. S. oneidensis MR-1 Reaction, confirmation S. oneidensis MR-1 The surface carboxyl and amide groups play a key role in the reaction process.

[0088] 7. SEM analysis of Shewanella, the products after Shewanella treated Cr(VI)-containing wastewater, the siderite-Shewanella complex system, and the products after the siderite-Shewanella complex system treated Cr(VI)-containing wastewater

[0089] The siderite-Shewanella composite system prepared in Example 1 was used.

[0090] Shewanella treatment method: Centrifuge the bacterial suspension at 4°C for 15 minutes, discard the supernatant, and wash the pellet three times with 0.1 M Tris-HCl buffer for 15 minutes each time. Centrifuge the pellet and fix it with 2.5% glutaraldehyde in the buffer. Refrigerate and fix it at 4°C for 24 hours, then centrifuge. Wash the pellet with 0.1 M Tris-HCl buffer and dehydrate it using a gradient of ethanol concentrations: 15%, 30%, 50%, 70%, 80%, 90%, and 100%, with each dehydration lasting 15 minutes. Finally, wash the pellet twice with tert-butyl alcohol. After centrifugation, freeze-dry the pellet for SEM analysis.

[0091] SEM results are as follows Figure 7 As shown in a, the cultured bacteria are regular rod-shaped with a smooth surface. After reacting with Cr (VI), the SEM results are as follows Figure 7 As shown in b, the bacterial cells became shrunken and flat with wrinkles on the surface. Obvious cracks and depressions can be observed on the bacterial surface. The observed phenomenon indicates that Cr (VI) stress changes S. oneidensis MR-1 The morphology of cells and has a certain toxic effect on bacteria. Figure 7 c is S. oneidensis MR-1 The morphology of bacteria after co-cultivation with siderite composite materials. The bright part is siderite. The photo shows that the morphology of bacteria has not changed significantly, and the bacteria can grow well on the surface of the siderite composite material. Figure 7 d is the SEM image of the product after the siderite-Shewanella composite system treated the wastewater containing Cr (VI). The picture shows that after the reaction with Cr (VI), the cells are wretched and the surface is wrinkled. Cracks and depressions can be observed on the surface of the bacteria. However, compared with the single S. oneidensis MR-1 When cells were exposed to Cr(VI), it was observed that the toxicity of Cr(VI) to bacteria was reduced, which proved that the siderite composite material was used as a carrier. S. oneidensis MR-1 Cells provide a good living environment.

[0092] 8. XPS analysis of the siderite-Shewanella complex system before and after the reaction with Cr (VI)

[0093] The siderite-Shewanella composite system prepared in Example 1 was used to measure the XPS of the siderite-Shewanella composite system and the siderite-Shewanella composite system after reacting with Cr (VI). The results are as follows: Figure 8 As shown, Figure 8 a The full spectrum shows that the atomic percentages of C1s, O1s and Fe2p of the composite material are 41.55%, 49.69% and 8.76%, respectively, while the atomic percentage of Fe2p decreases significantly after reaction with Cr (VI), indicating that iron plays a vital role in the reduction of Cr (VI). Figure 8 As shown in b, two characteristic peaks of Cr2p were observed. Compared with chemical reduction, the Cr2p peak in the co-culture system shifted to a lower angle, confirming that redox reduction and adsorption reactions occurred simultaneously. Figure 8 In the spectrum of c, the contents of Fe (II) and Fe (III) were 52.72% and 47.28% before reaction with Cr (VI) solution, and 58.66% and 41.34% after reaction with Cr (VI) solution. S. oneidensis MR-1 It can maintain the content of Fe (III) and Fe (II) in the co-culture system, promote the formation of Fe (II), and promote the reduction of Cr (VI) by Fe (II). Figure 8 d, for the composite system, OH - The peaks may be attributed to Fe(OH)3, O 2- The peaks may be attributed to Fe2O3 or FeO. After reacting with Cr (VI), most of the binding energy is transferred, indicating that the sample in the composite system reacts with Cr (VI) and is likely to generate Cr2O3 or Cr x Fe 1-x (OH)3.

[0094] In summary, the mechanism of action of the siderite-Shewanella complex system was proposed. First, Fe (II) can remove a certain amount of Cr (VI) by reduction (pathway I, direct reduction); secondly, S. oneidensis MR-1 It can reduce a small amount of Cr (VI). In addition, in the siderite-Shewanella composite system, a biofilm is formed between the siderite composite material and the bacteria. The presence of the siderite composite material is S. oneidensis MR-1 A carrier is provided to maintain the survival and biological activity of the bacteria and ensure that the bacteria are less toxic to Cr (VI) during the reaction with Cr (VI) (pathway II, direct reduction). S. oneidensis MR-1It can reduce Fe (II) generated by Fe (III). Fe (II) can act as a strong reducing agent to accelerate the reduction of Cr (VI) to Cr (III) (pathway III, indirect reduction). In this process, Fe (II) and Fe (III) convert into each other and maintain a certain concentration, achieving the role of electron transfer; S. oneidensis MR-1 It is a dissimilatory iron-reducing bacteria. The presence of iron ions can ensure the metabolism of bacteria. In addition, S. oneidensis MR-1 The addition of can change the surface properties of siderite. At the same time, the functional groups on the bacterial surface also adsorb and complex Cr (VI). In addition, the siderite composite material also has a certain adsorption effect on Cr (VI) (pathway IV).

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a siderite-Shewanella composite system, characterized in that: The steps include: S1. mixing siderite and ferric sulfate and then ball milling to obtain a siderite composite material; S2. Adding the activated Shewanella to a new culture medium containing the siderite composite material, and culturing with shaking, the resulting co-culture system is the siderite-Shewanella composite system.

2. The method for preparing the siderite-Shewanella composite system according to claim 1, characterized in that: In step S1, the mass ratio of the siderite to ferric sulfate is 20:1-5.

3. The method for preparing the siderite-Shewanella composite system according to claim 1, characterized in that: The addition ratio of the Shewanella is 1-5 g / L.

4. The method for preparing the siderite-Shewanella composite system according to claim 2, characterized in that: In the siderite-Shewanella composite system, the concentration of the siderite composite material is 0.2g~1g / L.

5. The method for preparing the siderite-Shewanella composite system according to claim 4, characterized in that: The culture conditions are: 150~180rpm, 20~30℃, and culture for 20~48h.

6. The method for preparing the siderite-Shewanella composite system according to claim 1, characterized in that: The ball milling conditions are: rotation speed of 300~600rpm, time of 1~2h.

7. The method for preparing the siderite-Shewanella composite system according to claim 1, characterized in that: The Shewanella S. oneidensis MR-1 .

8. A siderite-Shewanella composite system, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the siderite-Shewanella composite system according to claim 8 in treating hexavalent chromium-containing wastewater.

10. A method for treating hexavalent chromium-containing wastewater, characterized in that: The siderite-Shewanella composite system according to claim 8 is added into the wastewater containing hexavalent chromium and treated for a certain period of time to reduce the hexavalent chromium in the wastewater to remove the hexavalent chromium.

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