Treatment method of arsenic-containing water body

Abstract

The invention relates to the technical field of water treatment, and discloses a treatment method of an arsenic-containing water body. The treatment method comprises the following steps: dissolving ferric salt in water, adjusting the pH value to 7.0-8.0, carrying out solid-liquid separation, collecting a solid phase to obtain ferrihydrite, and resuspending the ferrihydrite in a sterile culture medium to obtain a ferrihydrite stock solution; under the anaerobic condition, a sterile culture medium, a sodium lactate aqueous solution and the ferrihydrite stock solution are added into an arsenic-containing water body, so that the ferrihydrite adsorbs arsenic, and As-ferrihydrite turbid liquid is obtained; and adding iron reducing bacteria into the As-ferrihydrite turbid liquid, and co-culturing to convert As-ferrihydrite into As-magnetite, thereby finishing the treatment of the arsenic-containing water body. The arsenic-containing water treatment method provided by the invention is simple in steps, wide in raw material source, low in cost and remarkable in As (V) removal effect, the generated magnetite can be magnetically absorbed and recycled, secondary pollution is not generated, drinking water safety and ecological health are guaranteed, and the method has environmental, economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly relates to a method for treating arsenic-containing water bodies. Background Art

[0002] Elemental arsenic (As) has extremely low toxicity, while inorganic As has been recognized as a carcinogen, and long-term exposure can lead to cancer and skin lesions. The As pollution in natural water mainly comes from industrial wastewater (such as pharmaceuticals, metallurgy, and electroplating, etc.), and the enrichment of surface water As caused by geological activities. Arsenides in water bodies are characterized by strong mobility, high toxicity, and strong bioaccumulation, posing a great threat to both the environment and human health.

[0003] Compared with trivalent arsenic (As(III)), pentavalent arsenic (As(V)) has lower toxicity, but still has health risks such as mutagenicity, carcinogenicity, and teratogenicity. As(V) often exists in the form of arsenate (AsO4 3- ) in water, and is more easily removed by chemical precipitation and adsorption than As(III). However, its treatment efficiency is still affected by factors such as pH, coexisting ions, and water quality. The current drinking water standard has strictly restricted its content. Therefore, the efficient removal of As(V) in water is also the core requirement for ensuring drinking water safety and ecological health. Developing an efficient method for removing pentavalent arsenic in water bodies is of great significance.

[0004] The existing treatment technologies for As(V) are mainly chemical precipitation method and adsorption method, supplemented by oxidation pretreatment to improve the removal efficiency. In the chemical precipitation method, ferric salts are favored because they can generate iron hydroxide colloids to adsorb As(V). However, this method requires precise control of pH, and the removal effect on low-concentration As is limited. The adsorption method has become a key means for drinking water treatment due to its high selectivity. Traditional adsorption technologies such as activated carbon and iron oxyhydroxide rely on physical adsorption or surface complexation. Although the cost is relatively low, there are problems such as low adsorption capacity, poor selectivity (easily affected by ions such as phosphate in the environment), and difficulty in solid-liquid separation. In addition, after adsorption saturation, secondary pollution may be caused by desorption. In addition, the coagulation method relies on coagulants such as ferric salts or aluminum salts to remove As by adsorption and coprecipitation. Although it has been widely used in the treatment of industrial arsenic-containing wastewater, this method requires a large amount of chemicals and generates As-containing sludge, posing a risk of secondary pollution. Therefore, developing low-cost, efficient, and environmentally friendly As removal technologies has triple benefits of ecology, society, and economy.

[0005] CN 119390119 A discloses a method for removing arsenic from vanadium-containing solutions. By regulating the pH and recycling the impurity-removing residues, the As concentration in the sewage can be reduced to 0.01 - 10 mg / L. However, this process involves multiple reactions and precise condition control, and is only applicable to specific industrial scenarios, with limited generality. CN 118929736 A discloses a method for removing arsenic from sodium germanate solutions. Using the precipitation method, AsO4 can be efficiently separated under the condition of pH 7.0 - 9.0 3- , but this method requires precise regulation of the types of precipitants and reaction temperature, and the reaction conditions are harsh. CN 104016435 A discloses a method for adsorbing and removing pentavalent inorganic arsenic in water. By combining ferrous salts with carbide materials, the activity of adsorption sites is enhanced through the complexation of ferrous ions with surface groups. The cost is low and there is no secondary pollution. However, if there are high humic acids or competitive anions in the environment, the adsorption of this material to As(V) is also low.

[0006] The above methods are technically mature and have high removal efficiency, especially suitable for the treatment of water bodies polluted by high-concentration As. However, the chemical precipitation method is prone to generating As-containing sludge, which needs to be further disposed of safely to avoid secondary pollution. Although the adsorbent technology can reduce the mobility of As, it is limited by the adsorption capacity and selectivity, and has weak adaptability to the interference of coexisting ions in water quality. Therefore, it is urgent to develop new methods to stably and efficiently immobilize As(V) in water bodies. Summary of the Invention

[0007] The present invention aims to at least solve one of the above technical problems existing in the prior art. For this reason, the object of the present invention is to provide a method for treating arsenic-containing water bodies.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a method for treating arsenic-containing water bodies, comprising the following steps:

[0010] S1. Dissolve ferric salts in water, adjust the pH to 7.0 - 8.0, perform solid-liquid separation to collect the solid phase to obtain ferrihydrite, and resuspend it in a sterile medium to obtain a ferrihydrite stock solution;

[0011] S2. Under anaerobic conditions, add a sterile medium, a sodium lactate aqueous solution, and the ferrihydrite stock solution to the arsenic-containing water body, so that the ferrihydrite adsorbs arsenic to obtain an As-ferrihydrite suspension;

[0012] S3. Add iron-reducing bacteria to the As-ferrihydrite suspension and co-culture to transform the As-ferrihydrite into As-magnetite, thus completing the treatment of the arsenic-containing water body.

[0013] In some embodiments of the present invention, the arsenic in the arsenic-containing water is mainly As(V); the concentration of As(V) is 100 - 300 mg / L.

[0014] In some specific embodiments of the present invention, the arsenic in the arsenic-containing water is mainly As(V); the concentration of As(V) is 150 - 250 mg / L.

[0015] In some embodiments of the present invention, the pH of the arsenic-containing water is 6 - 10.

[0016] In some specific embodiments of the present invention, the pH of the arsenic-containing water is 7 - 9.

[0017] In some embodiments of the present invention, the arsenic-containing water also contains Cu 2+ , Pb 2+ , Cl - and SO4 2- ; wherein, the concentrations of Cu 2+ and Pb 2+ are lower than 0.5 mg / L, and the concentrations of Cl - and SO4 2- are lower than 1.2 mg / L.

[0018] In some specific embodiments of the present invention, the arsenic-containing water includes chemical oxidation process wastewater.

[0019] In some specific embodiments of the present invention, the arsenic-containing water includes chemical oxidation process wastewater filtered by a 0.2 - 0.25 μm polyethersulfone membrane.

[0020] In some embodiments of the present invention, the iron salt in step S1 is selected from at least one of ferric chloride, ferric sulfate, ferric acetate, ferric nitrate, and ferric nitrate nonahydrate (Fe(NO3)3·9H2O).

[0021] In some embodiments of the present invention, in step S1, the solid-liquid ratio of the iron salt to water is 1 g:(40 - 60) mL.

[0022] In some specific embodiments of the present invention, in step S1, the solid-liquid ratio of the iron salt to water is 1 g:(45 - 55) mL.

[0023] In some embodiments of the present invention, the process of dissolving the iron salt in step S1 is assisted by stirring; the stirring time is 25 - 35 min.

[0024] In some embodiments of the present invention, in step S1, an alkali solution is added dropwise to adjust the pH, the concentration of the alkali solution is 0.5 - 1.5 mol / L, and the dropping rate is 1.5 - 2 mL / min.

[0025] In some specific embodiments of the present invention, in step S1, an alkali solution is added dropwise to adjust the pH. The concentration of the alkali solution is 0.8 - 1.2 mol / L, and the dropping rate is 1.7 - 2 mL / min.

[0026] In some embodiments of the present invention, the alkali source of the alkali solution in step S1 includes alkali metal hydroxides.

[0027] In some specific embodiments of the present invention, the alkali source of the alkali solution in step S1 is selected from at least one of sodium hydroxide and potassium hydroxide.

[0028] In some embodiments of the present invention, the process of adding the alkali solution dropwise to adjust the pH is assisted by stirring; the rotation speed of the stirring is 200 - 240 rpm.

[0029] In some embodiments of the present invention, after adjusting the pH to 7.0 - 8.0 in step S1, stirring is continued for 40 - 50 h, and solid - liquid separation is carried out to collect the solid phase, obtaining ferrihydrite.

[0030] In some embodiments of the present invention, in step S1, an operation of washing the ferrihydrite is further included.

[0031] In some embodiments of the present invention, the sterile culture medium in step S1 or S2 includes the following components: 8 - 12 mmol / L 4 - (2 - hydroxyethyl)piperazine - 1 - ethanesulfonic acid (HEPES), 0.3 - 0.7 mmol / L magnesium chloride, 0.3 - 0.7 mmol / L calcium chloride, and 4 - 6 mmol / L sodium chloride.

[0032] In some specific embodiments of the present invention, the sterile culture medium in step S1 or S2 includes the following components: 9 - 11 mmol / L 4 - (2 - hydroxyethyl)piperazine - 1 - ethanesulfonic acid, 0.4 - 0.6 mmol / L magnesium chloride, 0.4 - 0.6 mmol / L calcium chloride, and 4.3 - 4.8 mmol / L sodium chloride.

[0033] In some embodiments of the present invention, the concentration of the ferrihydrite stock solution in step S1 is 40 - 60 mmol / L.

[0034] In some specific embodiments of the present invention, the concentration of the ferrihydrite stock solution in step S1 is 45 - 55 mmol / L.

[0035] In some embodiments of the present invention, the concentration of the sodium lactate aqueous solution in step S2 is 230 - 270 mmol / L.

[0036] In some specific embodiments of the present invention, the concentration of the sodium lactate aqueous solution in step S2 is 240 - 260 mmol / L.

[0037] In some embodiments of the present invention, the volume ratio of the arsenic-containing water body, the sterile culture medium, the sodium lactate solution, and the ferrihydrite stock solution in step S2 is (3 - 5):(35 - 45):1:(3 - 7).

[0038] In some specific embodiments of the present invention, the volume ratio of the arsenic-containing water body, the sterile culture medium, the sodium lactate solution, and the ferrihydrite stock solution in step S2 is (3 - 4):(38 - 42):1:(4 - 6).

[0039] In some embodiments of the present invention, in step S2, an operation of adjusting the pH of the system to 7 - 8 using an acid or a base is further included.

[0040] In some specific embodiments of the present invention, the concentration of the acid or the base is 0.8 - 1.2 mol / L; the acid includes hydrochloric acid; the base includes sodium hydroxide.

[0041] In some embodiments of the present invention, in step S2, after adding the sterile culture medium, the sodium lactate aqueous solution, and the ferrihydrite stock solution to the arsenic-containing water body, the content of As(V) in the system is less than or equal to 1.8% of the total mass of As(V) and ferrihydrite.

[0042] In some embodiments of the present invention, the adsorption of arsenic by ferrihydrite in step S2 is carried out under light-shielded conditions.

[0043] In some embodiments of the present invention, the process of arsenic adsorption by ferrihydrite in step S2 is assisted by oscillation; the rotation speed of the oscillation is 200 - 240 rpm, and the temperature is 20 - 30 °C.

[0044] In some embodiments of the present invention, the adsorption time in step S2 is 45 - 55 h.

[0045] In some specific embodiments of the present invention, the adsorption time in step S2 is 45 - 50 h.

[0046] In some embodiments of the present invention, the iron-reducing bacteria in step S3 are selected from at least one of Shewanella putrefaciens MR-1, Shewanella putrefaciens CN-32, Tetrasphaera sediminicola DH10, Comamonas ferrooxidans CY01, Geobacter sulfurreducens SG198, and Geobacter sulfurreducens.

[0047] In some specific embodiments of the present invention, the iron-reducing bacteria in step S3 are Shewanella putrefaciens MR-1, purchased from the China Center for Industrial Culture Collection, and the preservation number is CICC 25104.

[0048] In the present invention, in the process of using iron-reducing bacteria to regulate the transformation of ferrihydrite into magnetite, in addition to the above selection, other common iron-reducing bacteria in the soil can also be used to promote the occurrence of this process.

[0049] In some embodiments of the present invention, the activation culture of the iron-reducing bacteria in step S3 includes the following steps:

[0050] 1) Inoculate the strain into a lysogeny broth medium (the main components are: 3 - 7 g / L yeast extract, 8 - 12 g / L tryptone, and 8 - 12 g / L sodium chloride), and perform constant-temperature oscillation (160 - 200 rpm, 28 - 32 °C) in the dark for 16 - 20 h;

[0051] 2) Collect the bacteria in the late logarithmic growth phase, place them in a sterile centrifuge tube, and centrifuge at a centrifugal force of 7000 - 9000 g and a temperature of 3 - 5 °C for 8 - 12 min; remove the supernatant, add a sterile medium (containing 8 - 12 mmol / L HEPES, 0.3 - 0.7 mmol / L magnesium chloride, 0.3 - 0.7 mmol / L calcium chloride, and 0.8 - 1.2 mmol / L sodium chloride), and repeat multiple times until the lysogeny broth is removed;

[0052] 3) Resuspend the clean bacteria in a sterile medium, and purge the enriched bacterial suspension with N2 for 0.8 - 1.2 h to obtain the iron-reducing bacteria liquid, and store it sealed.

[0053] In some embodiments of the present invention, the OD of the iron-reducing bacteria liquid 600 = 0.5×10 9 cells / mL - 1.5×10 9 cells / mL.

[0054] In some embodiments of the present invention, in the co-culture system in step S3, the concentration of the iron-reducing bacteria is 0.5×10 8 cells / mL - 1.5×10 8 cells / mL.

[0055] In some specific embodiments of the present invention, in the co-culture system in step S3, the concentration of the iron-reducing bacteria is 0.8×10 8 cells / mL - 1.2×10 8 cells / mL.

[0056] In some embodiments of the present invention, the pH of the co-culture system in step S3 is 6.5 - 8.5, and the temperature is 25 - 35 °C.

[0057] In some embodiments of the present invention, the co-culture time in step S3 is 5 - 7 d.

[0058] In some specific embodiments of the present invention, the co-culture time in step S3 is 5 - 6 d.

[0059] In some embodiments of the present invention, the solid-phase mineral composition of the As-magnetite described in step S3 includes 2 wt% - 4 wt% ferrihydrite, 1 wt% - 3 wt% lepidocrocite, and 95 wt% - 97 wt% magnetite.

[0060] The basic principle of the present invention is described as follows:

[0061] 1) Using ferric ions as raw materials, by regulating the hydrolysis rate of ferric ions, ferrihydrite with a loose porous structure and a large specific surface area is formed. Due to its special structure, ferrihydrite can fix free As(V) in water on its surface through adsorption and coprecipitation, forming As-ferrihydrite, thereby improving the removal rate of As(V) in water;

[0062] 2) Utilizing common iron-reducing bacteria in soil to catalyze the mineral phase transformation of ferrihydrite adsorbed with As(V) into magnetite nanoparticles. During this transformation process, the originally unstable adsorbed As(V) on the surface of ferrihydrite will be transformed into a stable doped As(V) incorporated into the magnetite lattice. This transformation from As-ferrihydrite to As-magnetite not only enhances the fixation of As(V) but also reduces the mobility of As(V), enabling As(V) to be fixed in the mineral lattice for a longer time. Even when As-magnetite is long-term in water bodies with different pH values, the content of doped As(V) released back into the water is extremely low, which can achieve long-term and lasting fixation of As(V) in water and avoid secondary pollution.

[0063] Among them, the process of iron-reducing bacteria catalyzing the mineral phase transformation of ferrihydrite adsorbed with As(V) mainly involves several aspects such as electron transfer, the impact of microbial metabolic activities on the environment, the interaction between As(V) and iron minerals, and the transformation of crystal structures. Specifically:

[0064] ① Electron transfer: During the metabolism of iron-reducing bacteria, electrons inside the cells are transferred to extracellular electron acceptors through the respiratory chain. Fe(III) in ferrihydrite acts as an electron acceptor and is reduced to Fe(II) after accepting the electrons transferred by iron-reducing bacteria. This electron transfer process is the core step of iron-reducing bacteria catalyzing the transformation of ferrihydrite and provides the chemical driving force for subsequent mineral phase transformation;

[0065] ② The impact of microbial metabolic activities on the environment: Iron-reducing bacteria consume organic substances (such as sodium lactate) in the surrounding environment during growth and metabolism, produce metabolic products, and change the acidity, alkalinity, and redox potential of the environment. These changes have an important impact on the stability and reactivity of ferrihydrite. The metabolic products produced by consuming organic substances may interact with the surface of ferrihydrite, affecting the dissolution and reprecipitation processes of iron ions. The changes in environmental acidity, alkalinity, and redox potential create favorable conditions for the transformation of ferrihydrite into magnetite;

[0066] ③Interaction between As(V) and iron minerals: After arsenate (As(V)) is adsorbed by ferrihydrite, chemical bonds or complexes are formed between As(V) and iron ions on the surface of ferrihydrite. When iron-reducing bacteria catalyze the phase transformation of ferrihydrite, As(V) is incorporated into the lattice structure of magnetite along with the reduction and rearrangement of iron ions. This process transforms As(V) from the adsorbed state to the doped state, enhancing the stability of As(V) in the mineral. The presence of As(V) may also affect the metabolic activity of iron-reducing bacteria and the rate of mineral phase transformation. Its complex interaction with iron ions jointly promotes the entire mineral phase transformation process;

[0067] ④Crystal structure transformation: Ferrihydrite and magnetite have different crystal structures. Ferrihydrite is a weakly crystalline iron mineral with a relatively loose structure, while magnetite has a more regular crystal structure. Under the action of iron-reducing bacteria, iron ions in ferrihydrite are gradually reduced, and its structure gradually changes, eventually transforming into the crystal structure of magnetite. During this process, the coordination environment and crystal symmetry of iron ions change. As(V) enters the magnetite lattice by isomorphous substitution, occupying specific lattice positions, further stabilizing the structure of magnetite and effectively immobilizing As(V).

[0068] Compared with the prior art, the beneficial effects of the present invention are:

[0069] The method for treating arsenic-containing water provided by the present invention adsorbs As(V) in water by preparing ferrihydrite, and uses common iron-reducing bacteria to regulate the transformation of ferrihydrite adsorbed with As(V) into magnetite nanoparticles. The mineral phase transformation process is utilized to convert the originally unstable adsorbed As(V) on the surface of ferrihydrite into the stable doped As(V) doped into the magnetite lattice, thereby realizing the in-situ synthesis of magnetite nanoparticle materials and long-term and stable immobilization of As(V) in water. Compared with traditional methods, the method for treating As-containing water provided by the present invention has simple steps, wide sources of raw materials, low cost, significant removal effect of As(V), and the generated magnetite can also be magnetically recovered without producing secondary pollution, which is beneficial to ensuring drinking water safety and ecological health, and has environmental, economic and social benefits. Description of the Drawings

[0070] Figure 1 It is the transmission electron microscope images of As-ferrihydrite and As-magnetite in Example 1;

[0071] Figure 2 It is the transmission electron microscope images of ferrihydrite and magnetite in Comparative Example 1;

[0072] Figure 3 It is the X-ray diffraction comparison chart before and after the synthesis of magnetite nanoparticles in Example 1 and Comparative Example 1;

[0073] Figure 4 It is a comparison chart of the mineral component changes before and after the synthesis of magnetite nanoparticles in Example 1 and Comparative Example 1;

[0074] Figure 5 It is a comparison chart of the specific surface areas before and after the synthesis of magnetite nanoparticles in Example 1 and Comparative Example 1;

[0075] Figure 6 It is a diagram of the morphological changes of As(V) before and after the synthesis of magnetite nanoparticles in Example 1;

[0076] Figure 7 It is the stability test result of As-magnetite nanoparticles in surface water with pH = 5.5;

[0077] Figure 8 It is the stability test result of As-magnetite nanoparticles in surface water with pH = 7.0;

[0078] Figure 9 It is the stability test result of As-magnetite nanoparticles in surface water with pH = 8.5. Detailed implementation manners

[0079] The content of the present invention will be further described in detail through specific examples below. The raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial channels or by existing technical methods without special instructions. Unless otherwise specified, the test or measurement methods are conventional methods in the art.

[0080] 1. The composition of the sterile culture medium used in the examples is: 10 mmol / L 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 0.5 mmol / L magnesium chloride, 0.5 mmol / L calcium chloride, and 5 mmol / L sodium chloride;

[0081] 2. The arsenic-containing water body in the examples is taken from chemical oxidation process wastewater. The key water quality parameters are: pH is 8.0, the As(V) concentration is 200 mg / L, and it contains a small amount of Cu 2+ , Pb 2+ , Cl - and SO4 2- . Before use, it is filtered through a 0.25 μm polyethersulfone filter membrane and stored in a brown glass bottle, and stored in a 4 °C refrigerator;

[0082] 3. The Shewanella putrefaciens MR-1 used in the examples was purchased from the China Center for Industrial Culture Collection, and the preservation number is CICC 25104. Before use, it was frozen in an -80 °C refrigerator. When used, it was activated and prepared into a bacterial solution. The steps are as follows:

[0083] 1) Take Shewanella putrefaciens MR-1 out of the frozen stock solution at -80 °C, inoculate it into a glass conical flask containing 200 mL of lysogeny broth (main components: 5 g / L yeast extract, 10 g / L tryptone, and 10 g / L sodium chloride), and place the conical flask in a constant temperature shaking incubator. Incubate it for 18 h under dark conditions, set the rotation speed of the shaking incubator to 180 rpm, and the temperature to 30 °C;

[0084] 2) Collect the bacteria in the late logarithmic growth phase, aliquot the bacterial solution into 50 mL sterile centrifuge tubes and place them in a centrifuge. Centrifuge at 8000 g centrifugal force and 4 °C for 10 min, remove the supernatant, continue to add sterile medium, repeat the above operation three times, then resuspend the clean bacteria without lysogeny broth in sterile medium, purge the enriched bacterial suspension with N2 for 1 h, and store it in a sterile serum bottle sealed with a butyl rubber stopper;

[0085] 3) Use a UV-visible double-beam spectrophotometer (UV-1700, Shimadzu) to measure the absorbance value (OD 600 ) of the bacteria at 600 nm to quantify the number of bacteria. After conversion, it can be known that the concentration of Shewanella putrefaciens MR-1 is 10 9 cells / mL;

[0086] 4. The sodium lactate aqueous solution used in the examples was prepared by the following steps: Weigh 2.80 g of solid sodium lactate into a 150 mL glass beaker, add 100 mL of deionized water, place the resulting solution on a magnetic stirrer and stir for 0.5 h at a rotation speed of 220 rpm to obtain a sodium lactate aqueous solution with a concentration of 250 mmol / L, and store it in a 4 °C refrigerator;

[0087] 5. Reagents used in the examples, comparative examples, and test examples such as ferric nitrate nonahydrate, potassium dihydrogen phosphate, sodium lactate, and sodium hydroxide were all purchased from Sinopharm Reagents and were all of analytical grade.

[0088] Example 1

[0089] This example provides a method for treating arsenic-containing water bodies, and the steps are as follows:

[0090] S11. Weigh 2.02 g of ferric nitrate nonahydrate solid into a 150 mL glass beaker, add 100 mL of deionized water, and place the resulting solution on a magnetic stirrer and stir for 30 min to fully dissolve the solid. Adjust the pH of the above solution to 7.5 with 1 mol / L sodium hydroxide solution, and set the dropping rate of the sodium hydroxide solution to 1.8 mL / min. During the pH adjustment, place the glass beaker on the magnetic stirrer and continuously stir at a stirring speed of 220 rpm. After continuous stirring for 48 h, the color of the solution gradually turns red and turbid. Centrifuge to remove the supernatant, and wash the obtained wet solid 3 times with deionized water to obtain ferrihydrite. Then resuspend the obtained ferrihydrite in 100 mL of sterile medium to obtain a ferrihydrite stock solution with a concentration of 50 mmol / L.

[0091] S21. Add 3.9 mL of arsenic-containing water body, 40.1 mL of anaerobic sterile medium, 1 mL of sodium lactate aqueous solution, and 5 mL of ferrihydrite stock solution to a 100 mL serum bottle, so that the concentration of sodium lactate in the system is 5 mmol / L, the concentration of ferrihydrite is 10 mmol / L, and the content of As(V) is 1.8 wt% (mass of As(V) / (mass of As(V)+mass of ferrihydrite)*100%). Then seal the serum bottle with a butyl rubber stopper and an aluminum cap, place the bottle in a dark shaking incubator and shake at a speed of 220 rpm, and set the temperature to 25 °C to allow ferrihydrite to adsorb As(V). After 48 h, obtain an As-ferrihydrite suspension for the transformation experiment.

[0092] S31. Add 1 mL of Shewanella putrefaciens MR-1 bacterial solution with a concentration of 10 9 cells / mL to the serum bottle containing the As-ferrihydrite suspension to make the system pH = 8.5 and the bacterial concentration in the system is 10 8 cells / mL. After shaking well, place the serum bottle in an incubator at 30 °C and cultivate for 6 days to convert As-ferrihydrite into As-magnetite, completing the treatment of the arsenic-containing water body.

[0093] Comparative Example 1

[0094] This comparative example provides a method for treating arsenic-containing water body, and the steps are as follows:

[0095] S11. Weigh 2.02 g of ferric nitrate nonahydrate solid into a 150 mL glass beaker, add 100 mL of deionized water, and place the resulting solution on a magnetic stirrer and stir for 30 min to fully dissolve the solid. Adjust the pH of the above solution to 7.5 with 1 mol / L sodium hydroxide solution, and set the dropping rate of the sodium hydroxide solution to 1.8 mL / min. During the pH adjustment, place the glass beaker on the magnetic stirrer and continuously stir, set the stirring speed to 220 rpm, and continue stirring for 48 h. Then, the color of the solution gradually turns red and becomes turbid. Centrifuge to remove the supernatant, wash the obtained wet solid 3 times with deionized water to obtain ferrihydrite, and then redisperse the obtained ferrihydrite in 100 mL of sterile medium to obtain a ferrihydrite stock solution with a concentration of 50 mmol / L.

[0096] S21. Add 44 mL of anaerobic sterile medium, 1 mL of sodium lactate aqueous solution, and 5 mL of ferrihydrite stock solution into a 100 mL serum bottle, so that the concentration of sodium lactate in the system is 5 mmol / L, the concentration of ferrihydrite is 10 mmol / L, and the content of As(V) is 0. Then seal the serum bottle with a butyl rubber stopper and an aluminum cap, place the bottle in a dark shaker and shake at a speed of 220 rpm, set the temperature to 25 °C, and after 48 h, obtain a ferrihydrite suspension for the transformation experiment.

[0097] S31. Add 1 mL of Shewanella putrefaciens MR-1 bacterial solution with a concentration of 10 9 cells / mL to the serum bottle containing the ferrihydrite suspension, so that the system pH = 8.5, the bacterial concentration in the system is 10 8 cells / mL. After shaking well, place the serum bottle in an incubator at 30 °C for 6 days to transform ferrihydrite into magnetite and complete the treatment of arsenic-containing water.

[0098] Test Example 1

[0099] For the treatment of arsenic-containing water in Example 1 and Comparative Example 1, three parallel groups are set respectively. On the 0th day, 1st day, 2nd day, and 6th day after co-culturing with Shewanella putrefaciens MR-1, take part of the suspension, centrifuge at 8000 rpm for 15 min to separate the solid and liquid, wash the solid three times with deionized water to wash away other impurities remaining on the surface of magnetite particles. After freeze-drying the wet solid for 48 h, obtain magnetite particle powder samples and conduct characterization and analysis respectively. The characterization methods and results are as follows:

[0100] 1. Transmission electron microscopy characterization:

[0101] Take 20 μL of the suspension of different treatment groups before and after transformation and drop it into ethanol. Ultrasonic for 2 min at room temperature of 25 °C to evenly disperse the suspension in the ethanol solution. The obtained evenly dispersed liquid is used for mineral morphology characterization. Use a 100 μL pipette to drop the ultrasonicated suspension onto an ultra-thin C film supported by a 200-mesh copper mesh grid, and then place it at room temperature to dry naturally. Analyze the mineral morphology using a transmission electron microscope (JEM 2100). To ensure reliable results, select different regions of the analyzed samples for characterization.

[0102] Figure 1 Figures for transmission electron microscopy of As-ferrihydrite and As-magnetite in Example 1, where, Figure 1 (a) in Figure 1 and (b) in Figure 1 (c) in Figure 1 and (d) in Figure 2 are transmission electron microscopy images of As-ferrihydrite at different magnifications, Figure 2 (a) in Figure 2 and (b) in Figure 2 (c) in Figure 2 and (d) in Figure 1 are transmission electron microscopy images of magnetite at different magnifications; it can be seen from Figure 2 that both As-ferrihydrite in Example 1 and ferrihydrite in Comparative Example 1 have a loose porous structure and show a cloud-like shape, indicating that the addition of As(V) does not affect the formation of ferrihydrite; after the mineral phase transformation of ferrihydrite promoted by iron-reducing bacteria, both As-magnetite in Example 1 and magnetite in Comparative Example 1 show an ellipsoidal shape, and the synthesized magnetite particles have a particle size of less than 100 nm, indicating that the generated magnetite is a nano-mineral.

[0103] 2. X-ray diffraction characterization and mineral component quantification:

[0104] Place the freeze-dried powder sample in an agate mortar and grind it. Collect the ground powder sample and put it in a 1.8 mL polyethylene centrifuge tube. Use an X-ray diffractometer (XRD, D8 ADVANCE) to characterize the collected powder sample. During the process of collecting the diffraction patterns of all samples, set the tube current and tube voltage of the instrument to 40 mA and 40 kV respectively, the step size to 0.02°, the step speed to 1° / min, and the diffraction spectrum collection range of all powder samples to 10° - 80°;

[0105] To determine the mineral composition during the formation of magnetite nanoparticles, the Jade 6.0 software was used in combination with the standard cards of ferrihydrite (ICSD#46-1315), lepidocrocite (ICSD#93948), and magnetite (ICSD#26410) for qualitative analysis of the mixed phases in the samples. To quantify the composition of each phase in the samples, TOPAS 5.0 was used to perform Rietveld refinement on the XRD diffraction patterns of the samples. This calculation mainly uses the crystal structure and the integrated intensity of the diffraction peaks to calculate the relative mass of each phase in the sample.

[0106] Figure 3 Figure 4 shows the X-ray diffraction comparison diagrams before and after the synthesis of magnetite nanoparticles in Example 1 and Comparative Example 1. Figure 3 It can be seen that both the As-ferrihydrite in Example 1 and the ferrihydrite in Comparative Example 1 are weakly crystalline iron minerals. The As-magnetite and magnetite generated after transformation both have relatively high crystallinity, and no other minerals were found before and after the transformation, indicating that the synthesized As-ferrihydrite / ferrihydrite and As-magnetite / magnetite nanoparticles both have high purity.

[0107] Figure 4 Figure 5 shows the comparison diagram of the changes in mineral components before and after the synthesis of magnetite nanoparticles in Example 1 and Comparative Example 1. Figure 4 It can be seen that for the As-ferrihydrite in Example 1 and the ferrihydrite in Comparative Example 1, almost 100% of the solid-phase product is ferrihydrite, and no other minerals were found. After the mineral phase transformation of ferrihydrite promoted by iron-reducing bacteria, the solid phase of As-magnetite in Example 1 contains 2.7% ferrihydrite, 1.5% lepidocrocite, and 95.8% magnetite; the solid phase of magnetite in Comparative Example 1 contains 1.6% ferrihydrite, 1.3% lepidocrocite, and 97.1% magnetite. This indicates that co-culturing with iron-reducing bacteria for 6 days can promote the transformation of ferrihydrite into magnetite nanoparticles, and the addition of As(V) has almost no effect on the formation of magnetite nanoparticles, indicating that using iron-reducing bacteria to regulate the mineral phase transformation of ferrihydrite to immobilize arsenic has strong applicability for the removal of As(V) in water.

[0108] 3. Specific surface area characterization:

[0109] To characterize the specific surface area of minerals in different treatment groups before and after transformation, 50 mg of the powder sample was weighed and placed in a sample loading glass tube. All samples were degassed under vacuum conditions at 298 K for 48 h to remove the moisture, gas, and impurities adsorbed on the surface of the solid powder. Then, under the protection of nitrogen at 77 K, all samples were measured using a specific surface area analyzer (Micromeritics ASAP2020). The adsorption-desorption isotherms of the samples were collected in the partial pressure region of 0.995 to 0.01 (P / P0), and the BET equation was used to analyze the desorption and adsorption curves to obtain the specific surface area of the samples.

[0110] Figure 5 The specific surface area comparison diagram before and after the synthesis of magnetite nanoparticles in Example 1 and Comparative Example 1 shows that Figure 5 limonite in Comparative Example 1 has a larger surface area, indicating that limonite can provide sufficient adsorption sites for the fixation of As(V), which helps limonite adsorb and fix As(V) from water in the initial stage. The specific surface area of As-limonite in Example 1 is lower than that of pure limonite in Comparative Example 1, indicating that As(V) has been adsorbed and fixed on the surface of limonite. After the mineral phase transformation of limonite promoted by iron-reducing bacteria, the specific surface areas of As-magnetite in Example 1 and magnetite in Comparative Example 1 are significantly reduced, but their crystallinity is higher and stability is stronger.

[0111] Test Example 2

[0112] Determine the concentration of As(V) adsorbed on the mineral surface in As-limonite in Example 1 (defined as adsorbed As), and calculate the concentration of As(V) doped into the magnetite lattice in As-magnetite (defined as doped As). The specific steps are as follows:

[0113] 1) Take 1.0 mL of the As-limonite suspension and add it to a polypropylene centrifuge tube. Centrifuge and filter to remove the supernatant. Then add 10 mL of anaerobic KH2PO4 with a concentration of 1 mol / L to the centrifuge tube. Keep the system pH = 5.0 by adding HCl or NaOH. Wrap the centrifuge tube with aluminum foil and place it in an oscillation box to extract for 24 h at a rotation speed of 220 rpm. (Among them, KH2PO4 is selected as the extractant because under this condition, phosphate ions can desorb As(V) from the mineral surface through competitive action)

[0114] 2) Centrifuge the suspension after the above oscillation for 20 min at a centrifuge speed of 8000 rpm. Then filter the supernatant with a 0.22 μm nylon filter membrane, collect the filtrate, acidify it, and measure the As(V) concentration by inductively coupled plasma. Calculate the actual As(V) concentration in the filtrate according to the dilution factor. Based on the total As(V) concentration added (total As concentration) and the As(V) (solution-state As) and surface-adsorbed As(V) (adsorbed As) concentrations measured by the instrument in the supernatant, calculate the concentration of As(V) (doped As) doped into the magnetite lattice through mass conservation. The calculation formula is:

[0115] Percentage content of doped As (%) = (total As concentration - solution-state As concentration - adsorbed As concentration) / total As concentration * 100%.

[0116] Figure 6 The morphological change diagram of As(V) before and after the synthesis of magnetite nanoparticles in Example 1 shows that Figure 6It can be seen that with the occurrence of the microbial-mediated biomineralization reaction, magnetite nanoparticles are gradually generated in the system. After 6 days of the reaction, the content of dissolved As(V) in the solution decreases from the initial 3.39% to 0.34%, the content of adsorbed As(V) decreases from the initial 93.58% to 4.70%, while the content of doped As(V) increases from the initial 3.02% to 94.95%. The above results indicate that with the gradual formation of As-magnetite nanoparticles, more adsorbed As(V) is transformed into doped As(V), suggesting that As(V) is gradually doped into the lattice of magnetite nanoparticles, significantly reducing the mobility of As(V) and promoting the effective and stable fixation of As(V).

[0117] In addition, through experiments, the present invention further verifies the optimal content of As(V) in the system during the formation of As-ferrihydrite, as well as the optimal conditions for iron-reducing bacteria to promote the transformation of As-ferrihydrite into As-magnetite. It is found that after adding a sterile medium, a sodium lactate aqueous solution, and a ferrihydrite stock solution to the arsenic-containing water body, the content of As(V) in the system is 0-1.8% (not zero) of the total mass of As(V) and ferrihydrite. When the process of iron-reducing bacteria promoting the transformation of As-ferrihydrite into As-magnetite is carried out at pH = 6.5-8.5 and 25-35 °C, the treatment effect of the arsenic-containing water body is the best. If the content of As(V) is higher than 1.8%, the transformation pH is lower than 6.5 or higher than 8.5, and the transformation temperature is lower than 25 °C or higher than 35 °C, it will reduce the microbial activity, resulting in insufficient transformation of ferrihydrite and the generation of other secondary iron minerals (such as lepidocrocite and goethite), causing low purity of the synthesized magnetite nanoparticles and ultimately reducing the content of As(V) doped inside the lattice of magnetite nanoparticles, affecting the fixation effect of As(V) and its subsequent stability.

[0118] Test Example 3

[0119] Surface waters with three different pH values were collected, located in the Pearl River Delta of Guangdong Province, the Lijiang River Basin of Guangxi Zhuang Autonomous Region, and the North China Plain of Shandong Province respectively. The pH values of the three surface waters are 5.5, 7.0, and 8.5 respectively.

[0120] 1) Pipette 50 mL of each of the above three surface waters with different pH values into a 250 mL glass beaker, and respectively add 0.12 g of the dried As-magnetite nanoparticles in Example 1, and then place them on a magnetic stirrer and continuously stir. The rotation speed of the stirrer is set at 280 rpm;

[0121] 2) Samples were taken from different treatment groups on the 0th day, 15th day, 30th day, and 60th day respectively. The suspension was sucked and centrifuged and filtered, and the supernatant was collected to measure the content of As(V) in the solution (dissolved As).

[0122] 3) Conduct chemical extraction experiments on the wet solids remaining in the centrifuge tube. Continue to add 10 mL of anaerobic potassium dihydrogen phosphate with a concentration of 1 mol / L to the centrifuge tube, and maintain the pH of the mixed suspension at 5.0 by adding 0.1 mol / L HCl or NaOH. Wrap the centrifuge tube with aluminum foil and place it in an oscillator to extract for 24 h at a rotation speed of 220 rpm. Centrifuge the suspension after the above oscillation for 20 min, set the centrifuge speed to 8000 rpm. After centrifugation, filter through a 0.22 μm nylon filter membrane, collect the filtrate, measure the content of As(V) (adsorbed As) adsorbed on the mineral, and calculate the percentage content of doped As(V) (doped As) by mass conservation. The calculation method is the same as that in Test Example 2.

[0123] Figure 7 Figure shows the stability test results of As-magnetite nanoparticles in surface water with pH = 5.5. Figure 7 It can be seen that in the slightly acidic surface water of the Pearl River Delta in Guangdong Province, after 60 days of cultivation, 94.15% of As(V) is still fixed in the magnetite nanoparticle lattice in the form of doped state, 3.73% of As(V) exists in the form of adsorbed state, and only 2.86% of dissolved As(V) is released into the solution.

[0124] Figure 8 Figure shows the stability test results of As-magnetite nanoparticles in surface water with pH = 7.0. Figure 8 It can be seen that in the slightly neutral surface water of the Lijiang River Basin in Guangxi Zhuang Autonomous Region, after 60 days of cultivation, the content of As(V) doped into the magnetite lattice accounts for 93.70% of the total fixed amount, 3.43% of As(V) exists in the form of adsorbed state, and only 2.86% of dissolved As(V) is released into the solution.

[0125] Figure 9 Figure shows the stability test results of As-magnetite nanoparticles in surface water with pH = 8.5. Figure 9 It can be seen that in the slightly alkaline surface water of the North China Plain in Shandong Province, after 60 days of cultivation, the content of As(V) fixed in As-magnetite accounts for 93.20% of the total fixed amount, 2.67% of As(V) exists in the form of adsorbed state, and only 4.13% of dissolved As(V) is released into the solution.

[0126] The stability test in Test Example 3 shows that for the method for treating arsenic-containing water provided by the present invention, after As(V) is fixed inside the magnetite lattice, the formed As-magnetite nanoparticles have good stability in water bodies with different pH values. In weakly acidic, neutral, and weakly alkaline water bodies, the content of As(V) originally combined with the magnetite nanoparticles released back into the water is less than 5%, and it is basically released into the solution in an adsorbed state desorbed, and the doped state concentration remains basically unchanged, indicating that the method provided by the present invention can achieve efficient and stable removal of As(V) in water bodies.

Claims

1. A method for treating arsenic-containing water body, characterized in that, It includes the following steps: S1. Dissolve iron salt in water, adjust the pH to 7.0 - 8.0, perform solid-liquid separation to collect the solid phase to obtain ferrihydrite, and resuspend it in a sterile medium to obtain a ferrihydrite stock solution; S2. Under anaerobic conditions, add a sterile medium, a sodium lactate aqueous solution, and the ferrihydrite stock solution to an arsenic-containing water body, and allow ferrihydrite to adsorb arsenic to obtain an As-ferrihydrite suspension; S3. Add iron-reducing bacteria to the As-ferrihydrite suspension and co-culture to convert As-ferrihydrite into As-magnetite, thus completing the treatment of the arsenic-containing water body.

2. The processing method according to claim 1, wherein The arsenic in the arsenic-containing water body is mainly As(V); the concentration of As(V) is 100 - 300 mg / L.

3. The processing method according to claim 1, characterized in that In step S1, a base solution is added dropwise to adjust the pH. The concentration of the base solution is 0.5 - 1.5 mol / L, and the dropping rate is 1.5 - 2 mL / min.

4. The processing method according to claim 1, characterized in that, The sterile medium described in step S1 or S2 includes the following components: 8 - 12 mmol / L 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 0.3 - 0.7 mmol / L magnesium chloride, 0.3 - 0.7 mmol / L calcium chloride, and 4 - 6 mmol / L sodium chloride.

5. The processing method according to claim 4, wherein The concentration of the ferrihydrite stock solution in step S1 is 40 - 60 mmol / L.

6. The processing method according to claim 1, characterized in that The concentration of the sodium lactate aqueous solution in step S2 is 230 - 270 mmol / L.

7. The processing method according to any one of claims 2-6, characterized in that, The volume ratio of the arsenic-containing water body, the sterile medium, the sodium lactate solution, and the ferrihydrite stock solution in step S2 is (3 - 5):(35 - 45):1:(3 - 7); and / or, the adsorption time is 45 - 55 h.

8. The processing method according to claim 1, wherein The iron-reducing bacteria described in step S3 are selected from at least one of Shewanella putrefaciens MR-1, Shewanella putrefaciens CN-32, Tetrasphaera sediminis DH10, Comamonas ferrireducens CY01, Geobacter subterraneus SG198, and Geobacter sulfurreducens.

9. The processing method according to claim 8, characterized in that In the co-culture system described in step S3, the concentration of iron-reducing bacteria is 0.5×10 8 cells / mL - 1.5×10 8 cells / mL.

10. The processing method according to claim 9, wherein The pH of the co-culture system in step S3 is 6.5 - 8.5, and the temperature is 25 - 35 °C; and / or, the co-culture time is 5 - 7 d.

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