CN111410305A - Chromium-polluted water body remediation method and application - Google Patents

Abstract

The invention discloses a restoration method and application of chromium-contaminated water body. The method comprises the following steps: adding biochar-loaded aged nano-zero-valent iron and Shewanella MR-1 bacteria into the chromium-contaminated water body at the same time, and under anaerobic conditions The reaction is carried out for 120-360 min; the preparation method of biochar-loaded aged nano-zero valent iron includes the following steps: adding biochar to ferrous _sulfate solution, adding NaBH4 solution after mixing, collecting the precipitate after continuous stirring, washing, drying Made after drying. Because the nano-zero-valent iron is easily oxidized into aged nano-zero-valent iron in the air, the reaction activity will be significantly reduced after being oxidized. The removal efficiency of hexavalent chromium is improved, and the extra cost of nano-zero-valent iron in the preparation process and preservation process is avoided, and the method of the invention can also be applied to the field of removing chromium-arsenic composite pollutants in water.

Description

A kind of restoration method and application of chromium-polluted water body

technical field

The invention relates to the field of environmental protection, in particular to a method and application for restoring chromium-polluted water bodies.

Background technique

In recent decades, with the rapid development of urbanization and industry in my country, especially the discharge of heavy metals in industrial production has caused great damage to groundwater. Chromium (Cr) is an important chemical raw material, and Cr and its compounds have been widely used in various industrial production (electroplating, alloy materials, printing and dyeing, etc.) Groundwater is seriously polluted by chromium, which eventually enters the food chain and endangers plant growth and human health and safety. Cr mainly exists in water as trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. However, Cr(III) has low toxicity and is easy to form insoluble complexes with organic matter, but Cr(VI) is relatively toxic. Because Cr(III) is highly soluble, highly toxic and carcinogenic, studies have shown that Cr(VI) is 100 times more toxic than Cr(III). Therefore, the remediation of groundwater Cr(VI) pollution has become a major environmental problem to be solved urgently.

Adsorption reduction is considered to be the most convenient and effective method for the removal of Cr(VI) in water. Nano-zero valent iron (nZVI), as a nanomaterial, has shown high performance in reductive removal of various inorganic pollutants (e.g. chromates, perchlorates, nitrates) and organic pollutants (e.g. chlorinated hydrocarbons). and has been used as an effective adsorbent for the removal of Cr(VI) from groundwater. Under anaerobic conditions, nZVI can not only reduce Cr(VI) to Cr(III), but also adsorb Cr(III) with high efficiency. However, due to its high reactivity and nanoscale size, it is easily oxidized in air or water, resulting in the accumulation of iron oxide layers on its surface, resulting in the aging of nZVI. Similar problems will occur even if nZVI is loaded on biochar. (Loading on biochar can solve the problem that nZVI is easy to agglomerate), the reactivity of nZVI after aging is reduced, which reduces the final reduction and removal ability of Cr(VI); this also puts forward higher requirements for the preparation process and preservation of nZVI. Require. Therefore, developing a method to improve the removal of anaerobic Cr(VI) by aged nano-zero valent iron is the key to solve the remediation of chromium pollution in groundwater.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above-mentioned technical problems, specifically through the following technical solutions:

A method for repairing a chromium-contaminated water body, comprising the following steps: adding biochar-loaded aged nano-zero-valent iron and Shewanella MR-1 bacteria to the chromium-contaminated water body at the same time, and reacting under anaerobic conditions for 120-360 minutes;

The preparation method of the biochar-loaded aged nano-zero valent iron includes the following steps: adding biochar to ferrous _sulfate solution, adding NaBH4 solution after mixing, stirring continuously for 50-70min, collecting precipitate, washing, drying, The biochar-loaded aged nano-zero valent iron was prepared.

In some preferred implementations, the pH of the chromium-contaminated water body is 5-9, and the temperature is 20-35°C.

In some preferred implementations, the addition amount of the biochar-supported aged nano-zero-valent iron material is 0.5-2 g/L, and the OD600 of Shewanella MR-1 bacteria is 0.1-0.8.

In some preferred implementations, the mass ratio of biochar to ferrous sulfate is (1～2):1; the mass ratio of biochar to aged zerovalent iron in the biochar-loaded aged nano-zero valent iron is (4～2) 9):1.

In some preferred implementations, the molar ratio of ferrous sulfate to NaBH ₄ is 1:(2-4).

In some preferred implementations, the preparation method of biochar includes the following steps: grinding and drying the biomass, and then heating the biomass to 300-800° C. under a nitrogen atmosphere for 2-5 hours to prepare the biochar.

In some preferred implementations, the biomass is one or more of roots, stems and leaves of woody plants.

In some preferred embodiments, the woody plant is a palm.

The beneficial effects of the present invention are as follows: since the nano-zero valent iron is easily oxidized in the air to become aged nano-zero-valent iron, the reaction activity will be significantly reduced after being oxidized, and the present invention couples Siva by loading the aged nano-zero-valent iron on biochar. The MR-1 bacteria can obviously improve the removal efficiency of hexavalent chromium, and at the same time avoid the extra cost required in the preparation process and storage process of nano zero-valent iron, and the method of the invention can also be applied to the removal of chromium and arsenic complexes in water bodies. Contaminant field.

Description of drawings

Fig. 1 is the SEM image (A) of biochar-loaded aged nano-zero-valent iron, the SEM image of Shewanella MR-1 bacteria (B), and the XRD image of bio-char and bio-char-loaded aged nano-zero-valent iron (C);

Figure 2 is a graph showing the removal effect of biochar-loaded aging nano-zero-valent coupled Shewanella MR-1 bacteria on Cr(VI) in water under anaerobic conditions under different pH conditions;

Figure 3 shows the removal effect of Cr(VI) in water by biochar-loaded aging nano-zero-valent coupled Shewanella MR-1 bacteria under anaerobic conditions under the condition of different bacteria dosage (A), Shewanella MR- The removal effect of 1 bacteria on Cr(VI) in water (B) and the effect of biochar-loaded aging nano zero-valent iron coupled with Shewanella MR-1 bacteria and the combination of single aging nZVI/500B and Shewanella MR-1 bacteria Cr(VI) removal rate vs. histogram (C).

Detailed ways

The concept of the present invention and the resulting technical effects will be clearly and completely described below with reference to the embodiments, so as to fully understand the purpose, solution and effect of the present invention. It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict.

Example 1: Preparation of a biochar-loaded aged nano-zero valent iron and culture of Shewanella MR-1 bacteria

1. Preparation of biochar:

Step 1): washing the fresh palm biomass with distilled water, drying at 80°C, and breaking into pieces to obtain biomass fragments;

Step 2): place the biomass fragments in a vacuum tube furnace, heat up to 500°C in a nitrogen atmosphere, and the heating rate is 10°C/min, stop heating after holding for 2 hours, and take out at room temperature to obtain biochar;

Step 3): Then soak the prepared biochar in 1 mol/L HCl solution, shake at 200 rpm for 5 hours to remove excess impurities, and finally rinse with deionized water until the pH of the solution remains unchanged, and dry at 80 ° C to obtain the final product The biochar (abbreviated as BC, XRD is shown in C in Figure 1).

2. Preparation of biochar-loaded and aged nano-zero valent iron:

Step 1): add the final product biochar (0.9g) and FeSO4·7H2O (0.5g) prepared by the above method into 100mL deionized water, and stir for 1h (200rpm);

Step ₂ ): in the continuous stirring process, the NaBH of 0.3g is prepared into 100mL solution with deionized water and added, and the stirring is continued for 1h (200rpm), and the reaction is carried out in the there-necked flask, and the whole process is carried out in the air;

Step 3): centrifugal washing after the reaction, washing with alcohol for 3 times, then collecting the precipitate, drying at 60° C. to obtain the biochar-loaded aged nano-zero-valent iron material for use (the bio-char-loaded aged nano-zero-valent iron material is abbreviated as nZVI for short) /500B, its SEM image is shown in A in Figure 1, and XRD is shown in Figure 1 in C).

3. Culture of Shewanella MR-1 bacteria:

Step 1): Configuration of LB medium: 10 g of tryptone, 5 g of yeast extract, and 10 g of NaCl were added to 950 mL of deionized water, stirred with a glass rod until fully dissolved, and then adjusted to pH 7 with 5 M NaOH solution, Use deionized water to dilute to 1L, and finally sterilize by high pressure steam at 120°C for 21min;

Step 2): Cultivation of Shewanella MR-1: Inoculate the MR-1 strain into the sterilized LB medium, and culture at 25°C for 10 hours. The SEM image of Shewanella MR-1 is shown in the figure B of 1.

Example 2: Anaerobic removal of Cr(VI) from water by biochar-loaded and aged nano-zero-valent coupled Shewanella MR-1 bacteria under different pH conditions

Step 1): configure a Cr(VI) solution with a concentration of 12 mg/L, and the solvent is oxygen-free deionized water;

Step 2): take the biochar-loaded aging nano-zero-valent iron and Shewanella MR-1 bacteria prepared in Example 1 for Cr(VI) adsorption kinetic experiment, the dosage of nZVI/500B is 1g/L, The OD600 of MR-1 bacteria was set to 0.2 and no addition, and the sodium lactate concentration was 20mmol/L. The initial pH of the chromium solution was adjusted to 5, 7, and 9 with 0.1M HCl solution and 0.1M NaOH solution, respectively. It is 40mL, and the reaction is carried out in a 100mL vial, and the whole reaction process is carried out in an anaerobic box;

Step 3): start timing after feeding, and take samples at specified time points, and the sampling times are respectively 0, 5, 30, 60, 120, and 240min;

Step 4): after the reaction, pass the reaction mixture through a 0.22 μm water film, measure the concentration of Cr(VI) in the filtrate, and calculate C/C ₀ , where C ₀ is the initial Cr(VI) concentration, and C at different sampling time points Cr(VI) concentration in solution.

The results are shown in Figure 2. It can be seen from Figure 2 that under different pH conditions, the biochar-loaded and aged nano-zero-valent iron coupled with Shewanella MR-1 significantly improved the removal rate of Cr(VI) in the solution. The effect is best when it is 7.

Example 3: Anaerobic removal of Cr(VI) from water by biochar-loaded aging nano-zero-valent coupled Shewanella MR-1 bacteria with different dosages of bacteria

Step 1): configure a Cr(VI) solution with a concentration of 12 mg/L, and the solvent is oxygen-free deionized water;

Step 2): take the biochar-loaded aging nano-zero-valent iron and Shewanella MR-1 bacteria prepared in Example 1 for Cr(VI) adsorption kinetic experiment, the dosage of nZVI/500B is 1g/L, The OD600 of MR-1 bacteria was set to 0.2, 0.4 and 0.6 respectively, referred to as MR-11.25%, MR-12.5%, MR-13.75%, where the sodium lactate concentration was 20mmol/L, and 0.1M HCl solution and 0.1M NaOH solution were used to make the The initial pH value of the chromium solution was adjusted to 7 for the experiment, the reaction system was 40 mL, and the reaction was carried out in a 100 mL vial, and the entire reaction process was carried out in an anaerobic box;

Step 3): start timing after feeding, and take samples at specified time points, and the sampling times are respectively 0, 5, 30, 60, 120, and 240min;

Step 4): after the reaction, pass the reaction mixture through a 0.22 μm water film, measure the concentration of Cr(VI) in the filtrate, and calculate C/C ₀ , where C ₀ is the initial Cr(VI) concentration, and C is the different sampling times The Cr(VI) concentration in the solution was spotted, and the results are shown in Figure 3.

It can be seen from A in Figure 3 that the effect of biochar-loaded and aged nano-zero-valent iron alone to remove Cr(VI) is obviously not as good as that of bio-char-loaded and aged nano-zero-valent coupled Shewanella MR-1 bacteria. From C in Figure 3, it is obvious that the removal rate of Cr(VI) by the biochar-loaded aged nano-zero-valent iron material coupled with Shewanella MR-1 bacteria is significantly greater than that of nZVI/500B alone for Cr(VI) and the Shewan. The sum of the removal rates of Cr(VI) by bacteria MR-1 (as can be seen from B in Figure 3).

Claims (9)

1. The method for restoring the chromium-polluted water body is characterized by comprising the following steps of: adding the biochar-loaded aged nano zero-valent iron and the Shewanella MR-1 bacteria into a chromium-polluted water body at the same time, and reacting for 120-360 min under an anaerobic condition;

the preparation method of the biochar loaded aged nano zero-valent iron comprises the following steps: adding biochar into ferrous sulfate solution, uniformly mixing, and adding NaBH₄And stirring the solution for 50-70 min, collecting the precipitate, washing and drying to prepare the biochar-loaded aged nano zero-valent iron.

2. The remediation method of claim 1, wherein the chromium-contaminated water has a pH of 5 to 9 and a temperature of 20 to 35 ℃.

3. The repair method according to claim 1, wherein the addition amount of the biochar-loaded aged nano zero-valent iron is 0.5-2 g/L, and the OD600 of the Shewanella MR-1 strain is 0.1-0.8.

4. The restoration method according to claim 1, wherein the mass ratio of biochar to ferrous sulfate is (1-2): 1; the mass ratio of the biochar in the biochar-loaded aged nano zero-valent iron to the aged zero-valent iron is (4-9): 1.

5. The method of remediation of claim 1 wherein the ferrous sulfate and NaBH₄The molar ratio of (1) to (2-4).

6. The repair method according to claim 1, wherein the preparation method of the biochar comprises the steps of: and grinding and drying the biomass, then heating to 300-800 ℃ in a nitrogen atmosphere, and keeping for 2-5 h to obtain the biochar.

7. The repair method according to claim 6, wherein the biomass is one or more of roots, stems, leaves of woody plants.

8. The method of repairing according to claim 7, wherein said woody plant is palm.

9. Use of the remediation method of any one of claims 1 to 8 in the field of removal of chromium arsenic complex contaminants from a body of water.

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