Method for increasing the production of hydroxyl radicals in the oxidation of ferrous iron and its use

Abstract

The application belongs to the technical field of soil treatment, and provides a method for increasing the production of hydroxyl radicals in the process of ferrous oxidation and application thereof. The method provided by the application adds biochar into a redox dynamic change reaction system; the redox dynamic change reaction system comprises Fe (III), a driving animal and H + ; the driving animal comprises iron-reducing bacteria and / or sulfide. The method provided by the application promotes the reduction of Fe (III) into Fe (II) under anaerobic conditions and then promotes the oxidation of Fe (II) by oxygen to produce hydroxyl radicals under aerobic conditions by using the redox characteristics of biochar. The application significantly increases the production of hydroxyl radicals by simultaneously increasing the amount of Fe (II) oxidation and the electron utilization efficiency. The method provided by the application is simple to operate and low in cost, and can be used to increase the content of hydroxyl radicals in organic contaminated soil and realize in-situ remediation of soil pollution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil remediation, in particular to a method for improving the production of hydroxyl radicals in the process of ferrous oxidation and application thereof. BACKGROUND

[0002] Iron is the most abundant redox-active metal in soils and sediments, and Fe(II) / Fe(III) cycling plays an important role in the migration and transformation of soil pollutants. In the subsurface environment (i.e. anaerobic conditions), iron-reducing bacteria (e.g. Shewanella and Geobacter) use Fe(III) (hydro)oxides as electron acceptors to reduce Fe(III) to Fe(II). Due to activities such as rainfall, tides and irrigation, soils experience alternating anaerobic and aerobic conditions. When the environment changes from anaerobic to aerobic, Fe(II) is oxidized to Fe(III) under neutral conditions, and hydroxyl radicals are produced, which are the strongest oxidants in the natural environment and can promote the oxidative degradation of various organic pollutants in the soil.

[0003] Aeration of anaerobic soil can promote the production of hydroxyl radicals by Fe(II) oxidation, and achieve in-situ remediation of soil pollution. However, the reaction of Fe(II) with oxygen to produce hydroxyl radicals is a chain electron transfer process, and the complex electron transfer path limits the production of hydroxyl radicals, which restricts its large-scale application in in-situ remediation of soil pollution. There are mainly two ways to improve the production of hydroxyl radicals, one is to increase the content of Fe(II), such as adding additional ferrous reagent or adding reducing agents (bacteria) to promote the reduction of Fe(III) to Fe(II) (CN202210227590.6); the other is to improve the electron utilization efficiency in the process of Fe(II) oxidation, such as adding organic ligands such as ethylenediaminetetraacetic acid or inorganic ligands such as phosphate (CN201911299707.6). However, these methods can only improve the production of hydroxyl radicals through one of the two paths; and the addition of additional chemical reagents not only has high cost, but also may cause secondary pollution to the soil. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a method for improving the production of hydroxyl radicals in the process of ferrous oxidation and application thereof. The method provided by the present application improves the production of hydroxyl radicals through two paths; at the same time, the use of biochar has low cost and does not cause secondary pollution to the soil.

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

[0006] The present application provides a method for improving the production of hydroxyl radicals in the process of ferrous oxidation, comprising the following steps:

[0007] The biochar is added to a redox dynamically changing reaction system;

[0008] The redox dynamically changing reaction system comprises Fe(III), a driving animal and H + ;

[0009] The driving animal comprises iron-reducing bacteria and / or sulfide.

[0010] Preferably, the mass ratio of the biochar and Fe(III) is 5:1-15:1.

[0011] Preferably, the redox dynamically changing reaction system refers to anaerobic-aerobic alternation, wherein the content of O2 in the anaerobic is <0.1 ppm, and the aerobic refers to normal atmospheric oxygen concentration.

[0012] Preferably, the redox dynamically changing reaction system is a buffer system.

[0013] Preferably, the Fe(III) exists in the form of ferrihydrite.

[0014] Preferably, the iron-reducing bacteria is Shewanella oneidensis MR-1.

[0015] Preferably, the sulfide comprises one or more of alkali metal sulfide, H2S and HS - .

[0016] Preferably, the preparation method of the biochar comprises the following steps:

[0017] Pyrolyzing a biomass raw material to obtain the biochar.

[0018] Preferably, the biomass raw material comprises one or more of rice straw, corn straw, wheat straw, wood chips, reed, blue algae, livestock and poultry manure, dead animals and sewage plant sludge.

[0019] The pyrolysis temperature is 500-900℃, the heating rate to the pyrolysis temperature is 5℃ / min, the atmosphere is nitrogen, and the holding time is 4h.

[0020] The application further provides an application of the method in soil treatment.

[0021] The method comprises the following steps:

[0022] The application provides a method for increasing the production of hydroxyl radicals in ferrous oxidation, comprising the following steps: adding biochar into a redox dynamically changing reaction system; the redox dynamically changing reaction system comprises Fe(III), a driving animal and H + ; the driving animal comprises iron-reducing bacteria and / or sulfide.

[0023] The method provided by the application promotes the reduction of Fe(III) into Fe(II) under anaerobic conditions and then promotes the oxidation of Fe(II) to generate hydroxyl radicals under aerobic conditions by using the redox characteristics of biochar. The application significantly increases the production of hydroxyl radicals by simultaneously increasing the amount of Fe(II) oxidation and the electron utilization efficiency. The method of the application is simple to operate and has low cost of adding biochar, and can be used to increase the content of hydroxyl radicals in organic contaminated soil, realize in-situ remediation of soil pollution, and will not cause secondary pollution. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Effect diagram of biochar on Fe(II) (left) and the production of hydroxyl radicals (right) under anaerobic-aerobic alternating conditions;

[0025] Figure 2 Effect diagram of biochar on Fe(II) (a), the production of hydroxyl radicals (b) and the electron utilization efficiency (c) under aerobic conditions. DETAILED DESCRIPTION

[0026] The application provides a method for increasing the production of hydroxyl radicals in ferrous oxidation, comprising the following steps:

[0027] adding biochar into a redox dynamically changing reaction system;

[0028] the redox dynamically changing reaction system comprises Fe(III), a driving animal and H + ;

[0029] the driving animal comprises iron-reducing bacteria and / or sulfide.

[0030] In the application, the raw materials used in the application are preferably commercially available products unless otherwise specified.

[0031] In the application, the content of Fe(III) in the redox dynamically changing reaction system is preferably 5-100 mmol / L. In the application, the Fe(III) preferably exists in the form of ferrihydrite.

[0032] In the present application, the iron-reducing bacteria is preferably Shewanella oneidensis MR-1. In the present application, the quantity of the iron-reducing bacteria in the redox dynamically changing reaction system is preferably 10 8 ~10 9 mL -1 .

[0033] In the present application, the sulfide preferably includes one or more of alkali metal sulfide, H2S and HS - , further preferably alkali metal sulfide; the alkali metal sulfide is preferably sodium sulfide. In the present application, the content of the sulfide in the redox dynamically changing reaction system is preferably 1~10 mmol / L.

[0034] In the present application, the redox dynamically changing reaction system preferably refers to anaerobic-aerobic alternation, the content of O2 in the anaerobic is preferably <0.1 ppm, and the aerobic preferably refers to normal atmospheric oxygen concentration. In the present application, the redox dynamically changing reaction system is preferably a buffer system, which can ensure that the redox dynamically changing reaction system contains H + . In the present application, the redox dynamically changing reaction system is preferably neutral. In the present application, the redox dynamically changing reaction system is particularly preferably present in a rice field, an irrigated wheat field, and a rainfall wheat field.

[0035] In the present application, the mass ratio of the biochar and Fe(III) is preferably 5:1~15:1, further preferably 9:1.

[0036] In the present application, the preparation method of the biochar preferably includes the following steps:

[0037] pyrolyzing the biomass raw material to obtain the biochar.

[0038] In the present application, the biomass raw material preferably includes one or more of rice straw, corn straw, wheat straw, wood chips, reed, blue-green algae, livestock and poultry manure, dead animals, and sewage plant sludge. In the present application, the pyrolysis temperature is preferably 500~900℃, further preferably 600~800℃, and more preferably 700℃; the rate of temperature rise to the pyrolysis temperature is preferably 5℃ / min, the atmosphere is preferably nitrogen, and the holding time is preferably 4h. After the pyrolysis, the present application preferably further includes grinding, and the present application does not specifically limit the parameters of the grinding, which can be ground to the desired particle size.

[0039] In the present application, the biochar is preferably used in the form of solid powder or suspension. In the present application, the content of biochar in the suspension is preferably 1-5 g / L. In the present application, the particle size of the biochar is preferably 100-300 mesh.

[0040] In the present application, the redox dynamic reaction system preferably undergoes the following reactions:

[0041] Under anaerobic conditions, driven by the driving force:

[0042] Fe 3+ →Fe 2+ ;

[0043] Under aerobic conditions:

[0044] Fe 2+ +O2→Fe 3+ +·O2 - ;

[0045] Fe 2+ +·O2 - +2H + →Fe 3+ +H2O2 or 2Fe 2+ +O2+2H + →2Fe 3+ +H2O2;

[0046] Fe 2+ +H2O2+H + →Fe 3+ +H2O+·OH.

[0047] The present application utilizes biochar to promote the oxidation of Fe(II) to generate hydroxyl radicals, without the need for additional addition of oxidizing agent hydrogen peroxide (H2O2), which can significantly reduce the remediation cost.

[0048] The present application also provides an application of the above technical solution in soil remediation, comprising the following steps:

[0049] The redox dynamic reaction system is used in the soil to be treated, and biochar is added to the soil to be treated to realize the migration and conversion of organic matter in the soil to be treated.

[0050] In the present application, the soil to be treated can meet the conditions of the redox dynamic reaction system.

[0051] The present application applies the above method to soil remediation, which can increase the yield of hydroxyl radicals and improve the migration and conversion of organic matter in the soil; and does not need to add hydrogen peroxide, which can significantly reduce the remediation cost.

[0052] The method for increasing the production of hydroxyl radicals in ferrous oxidation and its application provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the protection scope of the present application.

[0053] Example 1: Biochar improves the production of hydroxyl radicals under anaerobic-aerobic alternating conditions

[0054] The preparation method of the biochar is as follows: rice straw is pyrolyzed at 700℃ (the heating rate is 5℃ / min) for 4h under a nitrogen atmosphere, and then ground to 300 meshes.

[0055] The reaction system with dynamic redox change is built: first, in the anaerobic box (O2<0.1ppm), the neutral environment of the soil solution is simulated by using HEPES buffer (4-hydroxyethyl piperazine ethanesulfonic acid, 10mM, pH 7.0), and then 10mM ferrihydrite suspension and 30mM L-sodium lactate are sequentially added, and then 5g / L biochar is added, and the reaction is carried out for 12h to make the biochar and ferrihydrite fully react, and finally Shewanella oneidensis MR-1 (the number of bacteria is about 1×10 9 mL -1 ) is added. After 3 days of reaction in the anaerobic box, part of the sample is taken out from the reactor and added to another reactor containing 10mM sodium benzoate (sodium benzoate is used as a probe molecule of hydroxyl radicals, and this operation is because sodium benzoate is toxic to Shewanella oneidensis MR-1), then a 0.22μm membrane is covered on the reactor bottle mouth (to isolate miscellaneous bacteria and carry out gas exchange), and the reactor is removed from the anaerobic box, and aerobic reaction is carried out for 1 day, and finally the reactor without sodium benzoate is moved into the anaerobic box, and the next round of anaerobic-aerobic cycle is carried out according to the above steps.

[0056] The experiment is carried out in the dark at 30℃ and 150rpm. The Fe(II) and hydroxyl radicals are detected by using o-phenanthroline method and high performance liquid chromatography respectively. The experimental results are shown in Figure 1 , Figure 1 Figure of the effect of biochar on the production of Fe(II) (left) and hydroxyl radicals (right) under anaerobic-aerobic alternating conditions; it can be seen from Figure 1 that the biochar not only promotes the production of Fe(II) by microbial reduction of ferrihydrite under anaerobic conditions, but also promotes the oxidation of Fe(II) by oxygen under aerobic conditions, and the production of hydroxyl radicals is increased by nearly 2 times.

[0057] Example 2: Biochar with different pyrolysis temperatures improves the production of hydroxyl radicals under aerobic conditions

[0058] In this example, no microorganism and ferrihydrite are added, and the influence of biochar on the production of hydroxyl radicals by Fe(II) oxidation is directly explored.

[0059] In HEPES buffer (10 mM, pH 7.0) with 5 mM FeSO4, 5 g / L biochar (pyrolysis temperature 500, 700 and 900 ℃) and 10 mM sodium benzoate, first equilibrated in anaerobic chamber for 3 h, then removed from the anaerobic chamber, aerobic reaction in constant temperature shaker (light shielding, 30 ℃ and 150 rpm) for 5 h. The detection of Fe(II) and hydroxyl radical is the same as Example 1.

[0060] The results are shown in Figure 2 Figure 2 The effect diagram of biochar with different pyrolysis temperatures on Fe(II) (a), hydroxyl radical production (b) and electron utilization efficiency (c) under aerobic conditions; from Figure 2 It can be seen that: with the increase of pyrolysis temperature of biochar, the oxidation amount of Fe(II) increased by 33-86%, and the production of hydroxyl radical increased by 3.6-6.5 times. After calculation, the electron utilization efficiency of Fe(II) oxidation to produce hydroxyl radical increased by 2.9-3.3 times.

[0061] The results of the examples show that biochar can promote the production of Fe(II) from Fe(III) under anaerobic conditions and the production of hydroxyl radical from Fe(II) under aerobic conditions. The increase of Fe(II) oxidation amount and the increase of electron utilization efficiency synergistically improve the production of hydroxyl radical.

[0062] Example 3: Biochar increases the production of hydroxyl radical in paddy soil

[0063] Paddy soil was collected for pot experiment. According to the content of Fe(III) in the soil, appropriate biochar was added (the mass ratio of biochar to Fe(III) was 5:1-15:1), and mixed evenly with the soil. Deionized water was added, and the liquid level was higher than the soil by 3-5 cm, so that the soil was in a flooded state, and was anaerobically cultured for one month, during which appropriate water was added to maintain the anaerobic state of the soil; then 10 mM sodium benzoate was added, and the soil was allowed to enter an aerobic state by natural evaporation of water, so as to produce hydroxyl radical. The surface layer and pore water of the soil were collected, and the production of hydroxyl radical was measured.

[0064] Example 4: Biochar promotes the transformation and degradation of pollutants in paddy soil

[0065] 100 mg / kg As(III) (NaAsO2) was added to the paddy soil, and the rest was the same as Example 3. The contents of As(III) and As(V) were detected to investigate the effect of hydroxyl radical on the transformation of pollutants.

[0066] Example 5: Application of biochar in paddy soil and evaluation of pollution remediation

[0067] ​The biochar powder is sprinkled into the arsenic contaminated paddy field soil (100-500 kg / acre) and mixed with the soil evenly by ploughing and the like.

[0068] Then rice is planted, and in the drainage stage of the later growth stage of the rice, the generation of hydroxyl radicals is detected, and after the rice is harvested, the content of arsenic in the grains is detected, so as to evaluate the remediation effect of the biochar on the contaminated farmland.

[0069] The above merely describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for increasing the yield of hydroxyl radicals during ferrous oxidation, characterized in that, Includes the following steps: Biochar is added to a reaction system with dynamic redox changes; The redox dynamic reaction system includes Fe(III), a driving factor, and H. + ; The driving force includes iron-reducing bacteria and / or sulfides; The mass ratio of biochar to Fe(III) is 5:1 to 15:1; The redox dynamic reaction system refers to the alternating anaerobic-aerobic process, where the O2 content in the anaerobic environment is <0.1ppm, and the aerobic environment refers to the normal atmospheric oxygen concentration. The method for preparing the biochar includes the following steps: The biochar is obtained by pyrolyzing the biomass raw material.

2. The method according to claim 1, characterized in that, The reaction system with dynamic redox changes is a buffer system.

3. The method according to claim 1, characterized in that, The Fe(Ⅲ) exists in the form of ferrohydrate.

4. The method according to claim 1, characterized in that, The iron-reducing bacteria are Shewanella oneidensis MR-1.

5. The method according to claim 1, characterized in that, The sulfides include alkali metal sulfides, H2S, and HS. - One or more of them.

6. The method according to claim 1, characterized in that, The biomass raw materials include one or more of the following: rice straw, corn straw, wheat straw, sawdust, reeds, cyanobacteria, livestock and poultry manure, dead animals, and sewage sludge from wastewater treatment plants. The pyrolysis temperature is 500~900℃, the rate of heating to the pyrolysis temperature is 5℃ / min, the atmosphere is nitrogen, and the holding time is 4h.

7. The application of the method according to any one of claims 1 to 6 in soil remediation, characterized in that, Includes the following steps: Using the soil to be treated as a reaction system with dynamic redox changes, biochar is added to the soil to achieve the migration and transformation of organic matter in the soil.

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