Composite filler and method for synergistically removing nitrate in underground water based on sawdust and zero-valent iron

Abstract

The invention relates to the technical field of adsorption materials, in particular to composite filler and a method for synergistically removing nitrate in underground water based on saw dust and zero-valent iron. Comprising sawdust, nano zero-valent iron, a transforming agent, zero-valent iron, a photocatalyst and a binder, and the transforming agent, the photocatalyst and the zero-valent iron are bonded through the binder; the transforming agent comprises a protein substance, dicyandiamide modified reed biochar and biochar, and the protein substance contains one or more of disulfide bonds and sulfydryl; the photocatalyst is prepared from one or more of a TiO2-based photocatalyst, a Ni-TiO2 bimetallic nano catalyst, g-C3N4, BiVO4, WO3 and boron nitride. The invention aims to provide the preparation method of the composite filler for synergistically removing underground water nitrate based on sawdust and zero-valent iron and the application of the composite filler as an adsorbent to synergistically removing underground water nitrate.

Description

Technical Field

[0001] This invention relates to the field of adsorption materials technology, and more specifically, to a composite filler and method for the synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron. Background Technology

[0002] With the discharge of domestic sewage and nitrogen-containing industrial wastewater, as well as the application of large amounts of nitrogen fertilizer, nitrate pollution in groundwater is becoming increasingly serious. Nitrates can directly or indirectly harm human health, especially infants and young children, and have become one of the most important environmental issues of global concern. Currently, the main methods for removing nitrates from groundwater include ion exchange, reverse osmosis, electrodialysis, chemical reduction, and biological denitrification. Considering operating costs and removal efficiency, the latter two methods are economical and effective in-situ remediation technologies for groundwater pollution. Among them, zero-valent iron (Fe) is used... 0 Permeable reactive barriers (PRBs) for in-situ groundwater remediation, using solid organic carbon sources as fillers, have received widespread attention in Europe and the United States. 0 The main problem with chemical reduction is that the reaction product is ammonia nitrogen, which also needs to be removed. In biological denitrification, heterotrophic denitrification requires the support of organic matter, which can lead to secondary pollution problems. Autotrophic denitrification, on the other hand, requires sufficient electron donors to reduce nitrates.

[0003] In existing technologies, bicarbonate (HCO3) ions in groundwater - ) and sulfate (SO4) 2- These ions significantly inhibit nitrate removal efficiency. In synthetic groundwater tests, the presence of these ions reduced nitrate removal rates, despite an improvement in nitrogen conversion. Furthermore, oxides produced by iron corrosion (such as FeOOH and Fe3O4) may adsorb nitrates, but surface passivation also reduces reactivity. Summary of the Invention

[0004] This invention provides a composite filler and method for the synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron. Zero-valent iron, through its strong reducing properties, can reduce nitrates to nitrites, which are then utilized by microorganisms as electron donors for biological denitrification, ultimately converting nitrates into nitrogen gas. Sawdust, as an organic carbon source, provides the necessary electron donors for microorganisms, thereby promoting the biological denitrification process.

[0005] In a first aspect, the present invention provides a composite filler for the synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron, comprising sawdust, nano-zero-valent iron, a conversion agent, elemental iron, a photocatalyst, and a binder, wherein the binder binds the conversion agent, the photocatalyst, and the elemental iron together. The conversion agent includes proteinaceous substances, dicyandiamide modified reed biochar and biochar, and the proteinaceous substances contain one or more of disulfide bonds and sulfhydryl groups; The photocatalyst includes one or more of TiO2-based photocatalysts, Ni-TiO2 bimetallic nanocatalysts, g-C3N4, BiVO4, WO3 and boron nitride.

[0006] Preferably, the dicyandiamide modified reed biochar is activated by hydrochloric acid, dicyandiamide and magnesium chloride, and after pre-carbonization modification treatment of the reed biochar at 500-600°C for 1-2h, the modified reed biochar is activated at 700-800°C for 2-3h with the activator to obtain the modified reed biochar.

[0007] Preferably, the mass ratio of the sawdust and the nano zero-valent iron is 2-15:1-8, and the particle size of the nano zero-valent iron is 10-60nm.

[0008] Preferably, the binder is one or more of sodium fluoride, sodium sulfate, calcium nitrate, lanthanum nitrate, sodium bicarbonate, sodium nitrate, hydrochloric acid, sodium chloride, sodium citrate, sodium hydroxide and aluminum nitrate.

[0009] Preferably, the proteinaceous substances include one or more of bovine serum albumin, whey protein, thioredoxin, ferredoxin and soybean protein.

[0010] Preferably, the TiO2-based photocatalyst includes one or more of Ag / SiO2@cTiO2, Ag@SrTiO3-TiO2, SrFe x Ti 1−x O3 / TiO2 and Ag2O / BaTiO3@TiO2.

[0011] Preferably, the composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron is a spherical particle with a particle size of 6-8mm.

[0012] Preferably, the mass ratio of the conversion agent, the binder, the photocatalyst and the elemental iron powder is 6-10:12-15:11-16:20-30.

[0013] In a second aspect, the present application provides a preparation method of a composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron, which comprises the following steps: (1) mixing sawdust, nano zero-valent iron, a conversion agent, a binder and elemental iron, adding water and stirring to obtain a composite material paste; (2) adding the photocatalyst to the composite material paste and stirring to obtain a pretreated composite filler; (3) The pre-treatment composite filler is granulated to obtain the composite filler for cooperatively removing nitrate in groundwater by sawdust and zero-valent iron.

[0014] In a third aspect, the application provides a composite filler for cooperatively removing nitrate in groundwater by sawdust and zero-valent iron for removing nitrate in groundwater.

[0015] In a fourth aspect, the application provides a method for removing nitrate in groundwater, comprising the following steps: The composite filler for cooperatively removing nitrate in groundwater by sawdust and zero-valent iron is placed in a packed bed reactor, and a mixed bacteria liquid is inoculated; The mixed bacteria liquid comprises one or more of iron-oxidizing bacteria, pseudomonas, sulfur autotrophic denitrifying bacteria and hydrogen autotrophic denitrifying bacteria; After the surface of the composite filler for cooperatively removing nitrate in groundwater by sawdust and zero-valent iron has biological membrane, the water quality to be treated is introduced into the packed bed reactor to remove nitrate in the groundwater to be treated.

[0016] In summary, the application has the following beneficial effects: 1、The sawdust and zero-valent iron (Fe 0 ) in the application cooperatively remove nitrate by coupling biological denitrification and chemical reduction. The sawdust supports the metabolism of heterotrophic denitrifying bacteria as an organic carbon source, while the zero-valent iron drives hydrogen autotrophic denitrification by producing hydrogen (H2) through corrosion, and its oxidation products (such as Fe²⁺ / Fe³⁺) can adjust the reaction environment. The advantages of their cooperation are: reducing byproduct accumulation: Fe 0 Reduction of nitrate alone is easy to generate ammonia nitrogen (NH4 + ), while the coupling system dominated by biological denitrification can convert nitrate into nitrogen (N2), avoiding secondary pollution. Carbon source and electron donor complement each other: the dissolved organic matter (DOC) released by the sawdust supports heterotrophic bacteria, while the H2 and CO2 (from heterotrophic bacteria metabolism) produced by the corrosion of Fe 0 provide energy and inorganic carbon sources for autotrophic bacteria. pH buffering and reaction promotion: CO2 produced by heterotrophic denitrification can reduce the local pH, promote the corrosion of Fe 0 , and accelerate electron transfer. The research status of the cooperative effect of sawdust and zero-valent iron is mainly focused on the removal of nitrate in groundwater. As a kind of bioremediation material, sawdust has a large specific surface area and porous structure, which can improve the adsorption and reduction performance of zero-valent iron (ZVI), thereby enhancing the removal effect of nitrate.

[0017] 2、The photocatalyst in the application is to utilize the photoactive material to generate photo-electrochemical interaction by charge separation and transfer under light, so as to realize photo-electric conversion. Generally, a semiconductor is used as the photoactive material to form an electron-hole pair at the interface under light, thereby causing the oxidation-reduction reaction of the molecular ground state or the excited state. According to different ways of photoelectron transfer to nitrate, the nitrate removal technology based on photoelectrochemical reduction is divided into three kinds of photocatalytic nitrate reduction, photoelectrocatalytic nitrate reduction and microbial photoelectric nutrient nitrate reduction. The resourceization of nitrate in water bodies (such as conversion into ammonia) can also be realized, so as to realize the recycling use of nitrogen resources, and a green and efficient new technical means for treating nitrate pollution is expected to be brought.

[0018] 3、The photocatalyst in the application can further improve the efficiency of removing pollutants by combining the reduction ability of zero-valent iron with the photocatalytic technology. The photocatalytic system can promote the generation of Fe(III) and CO2· - radicals to generate Fe 2+ , thereby enhancing the reduction ability of zero-valent iron. The light-induced Fe-C-H selective catalytic reaction also shows that zero-valent iron can effectively catalyze the reduction reaction under light. The photocatalysis and zero-valent iron synergistically regulate the reaction path, reduce the accumulation of ammonium ions, and efficiently remove nitrate through the multi-path mechanism of photocatalysis-chemical reduction-biology, which has high activity, stability and environmental friendliness.

[0019] 4、The catalytic hydrogenation denitrification reaction condition of the application is mild and fast, and will not cause secondary pollution to the environment. The application mainly uses transition metal as a catalyst and hydrogen as a reducing agent to reduce nitrate. The composite filler prepared by the application based on sawdust and zero-valent iron improves the adsorption selectivity of nitrate. The selectivity of the product is regulated, and the nitrogen selectivity continues to improve in the scene of nitrate pollution treatment such as sewage treatment and groundwater remediation. The stability, regenerability and safety of the material are improved, the anti-pollution property of the membrane material is improved while ensuring good permeability, the regenerability of the adsorption material such as biochar is improved, and the activity and stability of various catalysts are enhanced.

[0020] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the protection scope of the application. DETAILED DESCRIPTION

[0021] The application will be further described in detail below in combination with examples, and it is particularly pointed out that: in the following examples, the specific conditions not specified are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the raw materials used in the following examples can be sourced from ordinary market sales unless otherwise specified.

[0022] EMBODIMENT EMBODIMENT 1 A composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron in cooperation comprises sawdust, nano zero-valent iron, a conversion agent, elemental iron, a photocatalyst and a binder, the mass ratio of the sawdust and the nano zero-valent iron being 2:1, the particle size of the nano zero-valent iron being 60 nm; the conversion agent, the photocatalyst and the elemental iron are bonded by the binder, the mass ratio of the conversion agent, the binder, the photocatalyst and the elemental iron powder being 6:13:11:20. The conversion agent comprises proteinaceous substances, dicyandiamide-modified reed biochar, biochar and nano zero-valent iron. The photocatalyst is a Ni-TiO2 bimetallic nano catalyst;

[0023] The dicyandiamide-modified reed biochar is prepared by using hydrochloric acid, dicyandiamide and magnesium chloride as activators, modifying the reed biochar at 500 DEG C for 2 hours, and then activating the modified reed biochar at 700 DEG C for 2 hours. The binder is sodium fluoride and sodium sulfate. The proteinaceous substances are bovine serum albumin. The composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron in cooperation is a spherical particle with a particle size of 6 mm.

[0024] A preparation method of a composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron in cooperation comprises the following steps: (1) mixing the sawdust, the nano zero-valent iron, the conversion agent, the binder and the elemental iron, adding water and stirring to prepare a composite material paste; (2) adding the photocatalyst to the composite material paste and stirring to prepare a pretreated composite filler; (3) granulating the pretreated composite filler to prepare the composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron in cooperation.

[0025] The concentration of nitrate in raw water is 33 mgN / L, the concentration of sulfate is 200 mg / L, the median particle size of sulfur granules is 0.3 mm, the residence time of raw water in the mixed culture denitrification column is 0.75 h, the effluent nitrate is 10.2 mgN / L, the effluent sulfate is 135 mg / L, the electro-dialysis is started, the voltage is 5 V, the mixing ratio of the effluent from the sulfur autotrophic denitrification section to the electro-dialysis section is 1:1, the final effluent nitrate is 9.5 mgN / L, and the final effluent sulfate is 120 mg / L.

[0026] Example 2 A composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron in cooperation comprises sawdust, nano zero-valent iron, a conversion agent, elemental iron, a photocatalyst and a binder, the mass ratio of the sawdust and the nano zero-valent iron being 10:1, the particle size of the nano zero-valent iron being 10 nm; the mass ratio of the conversion agent, the binder, the photocatalyst and the elemental iron powder being 7:12:15:28. The conversion agent comprises proteinaceous substances, dicyandiamide-modified reed biochar, biochar and nano zero-valent iron. The photocatalyst is a Ni-TiO2 bimetallic nano catalyst;

[0027] The dicyandiamide modified reed biochar is prepared by using hydrochloric acid, dicyandiamide and magnesium chloride as activators, and by modifying the reed biochar at 600 DEG C for 1 h, then mixing the modified reed biochar with the activators at 700 DEG C for 2 h; the binder is sodium fluoride and sodium sulfate; the protein substance is bovine serum albumin; and the composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron is a spherical particle with a particle size of 8 mm.

[0028] A preparation method of a composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron, comprising the following steps: (1) mixing sawdust, nano zero-valent iron, a conversion agent, a binder and elemental iron, adding water and stirring to prepare a composite material paste; (2) adding a photocatalyst to the composite material paste and stirring to prepare a pretreated composite filler; (3) granulating the pretreated composite filler to prepare the composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron.

[0029] The concentration of nitrate in raw water is 52 mgN / L, the concentration of sulfate is 150 mg / L, the median particle size of sulfur particles is 10 mm, the residence time of raw water in the mixed culture denitrification column is 0.75 h, the effluent nitrate reaches 22.3 mgN / L, the effluent sulfate reaches 92 mg / L, the electro-dialysis is started, the voltage is 5 V, the mixing ratio of effluents from the sulfur autotrophic denitrification section and the electro-dialysis section is 1:1, the final effluent nitrate reaches 20.5 mgN / L, and the final effluent sulfate reaches 85 mg / L.

[0030] Example 3 A composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron, comprising sawdust, nano zero-valent iron, a conversion agent, elemental iron, a photocatalyst and a binder, the mass ratio of sawdust and nano zero-valent iron is 15:8, the particle size of nano zero-valent iron is 30 nm; the mass ratio of the conversion agent, the binder, the photocatalyst and elemental iron powder is 10:14:15:29. The conversion agent comprises a protein substance, dicyandiamide modified reed biochar, biochar and nano zero-valent iron. The photocatalyst is a Ni-TiO2 bimetallic nano catalyst.

[0031] The dicyandiamide modified reed biochar is prepared by using hydrochloric acid, dicyandiamide and magnesium chloride as activators, and by modifying the reed biochar at 600 DEG C for 2 h, then mixing the modified reed biochar with the activators at 700 DEG C for 2 h; the binder is sodium fluoride and sodium sulfate; the protein substance is bovine serum albumin; and the composite filler for removing nitrate in groundwater based on sawdust and zero-valent iron is a spherical particle with a particle size of 7 mm.

[0032] A preparation method of a composite filler for cooperatively removing nitrate in groundwater based on sawdust and zero-valent iron, comprising the following steps: (1) mixing sawdust, nano zero-valent iron, a conversion agent, a binder and elemental iron, adding water and stirring to prepare a composite material paste; (2) adding a photocatalyst to the composite material paste and stirring to prepare a pretreated composite filler; (3) performing granulation treatment on the pretreated composite filler to prepare the composite filler for cooperatively removing nitrate in groundwater based on sawdust and zero-valent iron.

[0033] The nitrate concentration of raw water is 68 mgN / L, the sulfate concentration is 200 mg / L, the median particle size of sulfur granules is 10 mm, the residence time of raw water in the mixed culture denitrification column is 0.75 h, the effluent nitrate reaches 30.6 mgN / L, and the effluent sulfate reaches 152.2 mg / L; the electro-dialysis is started, the voltage is 5 V, the mixing ratio of effluent from the sulfur autotrophic denitrification section and the electro-dialysis section is 1:1, the final effluent nitrate reaches 28.5 mgN / L, and the final effluent sulfate reaches 150 mg / L.

[0034] Comparative Example 1 The main difference between Comparative Example 1 and Example 1 is that no conversion agent is added.

[0035] The nitrate concentration of raw water is 33 mgN / L, the sulfate concentration is 200 mg / L, the median particle size of sulfur granules is 0.3 mm, the residence time of raw water in the mixed culture denitrification column is 0.75 h, the effluent nitrate reaches 28.9 mgN / L, and the effluent sulfate reaches 150 mg / L; the electro-dialysis is started, the voltage is 5 V, the mixing ratio of effluent from the sulfur autotrophic denitrification section and the electro-dialysis section is 1:1, the final effluent nitrate reaches 25.4 mgN / L, and the final effluent sulfate reaches 180 mg / L.

[0036] Comparative Example 2 The main difference between Comparative Example 2 and Example 1 is that no photocatalyst is added.

[0037] The nitrate concentration of raw water is 33 mgN / L, the sulfate concentration is 200 mg / L, the median particle size of sulfur granules is 0.3 mm, the residence time of raw water in the mixed culture denitrification column is 0.75 h, the effluent nitrate reaches 28.9 mgN / L, and the effluent sulfate reaches 150 mg / L; the electro-dialysis is started, the voltage is 5 V, the mixing ratio of effluent from the sulfur autotrophic denitrification section and the electro-dialysis section is 1:1, the final effluent nitrate reaches 25.4 mgN / L, and the final effluent sulfate reaches 180 mg / L.

[0038] Comparative Example 3 The main difference between Comparative Example 3 and Example 1 is that the photocatalyst is replaced by a Pd-based catalyst PdNi(OH)2Cu / C.

[0039] The raw water has a nitrate concentration of 33 mgN / L and a sulfate concentration of 200 mg / L, the sulfur granules have a median particle size of 0.3 mm, the raw water has a residence time of 0.75 h in the mixed culture denitrification column, the effluent nitrate reaches 31.5 mgN / L, the effluent sulfate reaches 155 mg / L, the electrodialysis is started, the voltage is 5 V, the effluent mixing ratio of the sulfur autotrophic denitrification section and the electrodialysis section is 1:1, the final effluent nitrate reaches 25.4 mgN / L, and the final effluent sulfate reaches 168 mg / L.

[0040] Comparative Example 4 The main difference between Comparative Example 4 and Example 1 is that the conversion agent does not contain dicyandiamide modified reed biochar.

[0041] The raw water has a nitrate concentration of 33 mgN / L and a sulfate concentration of 200 mg / L, the sulfur granules have a median particle size of 0.3 mm, the raw water has a residence time of 0.75 h in the mixed culture denitrification column, the effluent nitrate reaches 27.5 mgN / L, the effluent sulfate reaches 160 mg / L, the electrodialysis is started, the voltage is 5 V, the effluent mixing ratio of the sulfur autotrophic denitrification section and the electrodialysis section is 1:1, the final effluent nitrate reaches 22.7 mgN / L, and the final effluent sulfate reaches 180 mg / L.

[0042] The performance test results of the composite fillers based on sawdust and zero-valent iron for cooperatively removing nitrate in groundwater prepared in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1.

[0043] Table 1 The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, and should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A composite filler for the synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron, characterized in that, It includes sawdust, nano-zero-valent iron, a conversion agent, elemental iron, a photocatalyst, and a binder, wherein the binder binds the conversion agent, the photocatalyst, and the elemental iron together; The conversion agent includes protein-based substances, dicyandiamide-modified reed biochar, and biochar, wherein the protein-based substances contain one or more of disulfide bonds and thiol groups; The photocatalyst includes one or more of TiO2-based photocatalysts, Ni-TiO2 bimetallic nanocatalysts, g-C3N4, BiVO4, WO3, and boron nitride.

2. The composite filler for synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron according to claim 1, characterized in that, The dicyandiamide-modified reed biochar is prepared by using hydrochloric acid, dicyandiamide, and magnesium chloride as activators. The reed biochar is pre-carbonized and modified at 500-600℃ for 1-2 hours. The modified reed biochar is then activated with the activator at 700-800℃ for 2-3 hours.

3. The composite filler for synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron according to claim 1, characterized in that, The mass ratio of sawdust to nano-zero valent iron is 2-15:1-8, and the particle size of the nano-zero valent iron is 10-60 nm; the binder is one or more of sodium fluoride, sodium sulfate, calcium nitrate, lanthanum nitrate, sodium bicarbonate, sodium nitrate, hydrochloric acid, sodium chloride, sodium citrate, sodium hydroxide, and aluminum nitrate.

4. The composite filler for synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron according to claim 1, characterized in that, The protein substances include one or more of bovine serum albumin, whey protein, thioredoxin, ferricyanide, and soy protein.

5. The composite filler for synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron according to claim 1, characterized in that, The TiO2-based photocatalyst includes Ag / SiO2@cTiO2, Ag@SrTiO3-TiO2, and SrFe. x Ti 1−x One or more of O3 / TiO2 and Ag2O / BaTiO3@TiO2.

6. The composite filler for synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron according to claim 1, characterized in that, The biochar has a particle size of 0.5-1 mm.

7. The composite filler for synergistic removal of nitrates from groundwater based on sawdust and zero-valent iron according to claim 1, characterized in that, The mass ratio of the converter, the binder, the photocatalyst, and the elemental iron powder is 6-10:12-15:11-16:20-30.

8. The method for preparing the composite filler based on the synergistic removal of nitrates from groundwater using sawdust and zero-valent iron according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Mix sawdust, nano-zero valent iron, conversion agent, binder and elemental iron, add water and stir to obtain a composite material viscous substance; (2) The photocatalyst is added to the composite material viscous material and stirred to obtain a pretreated composite filler; (3) The pretreated composite filler is granulated to obtain a composite filler that uses sawdust and zero-valent iron to synergistically remove nitrates from groundwater.

9. The composite filler based on sawdust and zero-valent iron for synergistic removal of nitrates in groundwater as described in any one of claims 1 to 7 is used to remove nitrates from groundwater.

10. A method for removing nitrates from groundwater, characterized in that, Includes the following steps: The composite packing material based on the synergistic removal of nitrates from groundwater by sawdust and zero-valent iron as described in any one of claims 1 to 7 is placed in a packed bed reactor, and mixed culture solution is added for inoculation; The mixed culture solution includes one or more of the following: iron-oxidizing bacteria, pseudomonads, sulfur-autotrophic denitrifying bacteria, and hydrogen-autotrophic denitrifying bacteria. After the composite packing material based on sawdust and zero-valent iron synergistically removes nitrates from groundwater has a biofilm on its surface, the water to be treated is introduced into the packed bed reactor to remove nitrates from the groundwater.

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