Birnessite-oxygen releasing agent composite bottom mud repairing material as well as preparation and application methods of birnessite-oxygen releasing agent composite bottom mud repairing material

Abstract

The invention belongs to the field of environmental governance. The invention provides a birnessite-oxygen-releasing agent composite bottom mud repair material and preparation and application methods thereof, the birnessite-oxygen-releasing agent composite bottom mud repair material comprises a modified oxygen-releasing agent, birnessite, microbial flora and an embedding matrix, the embedding matrix comprises hydrogel formed by crosslinking calcium alginate, polyvinyl alcohol and water, the microbial flora comprises a domesticated aerobic nitrogen and phosphorus removal mixed flora. According to the birnessite-oxygen release agent composite bottom mud remediation material, the photoelectrocatalytic activity of birnessite is utilized to cooperate with the oxygen release capacity of an oxygen release compound, the oxidation-reduction potential of bottom mud is improved, the continuous degradation capacity of the material to organic pollutants is enhanced, nitrogen pollutants in a water environment are removed cooperatively, and the in-situ remediation effect of the bottom mud is enhanced; the method is applied to bottom mud remediation, is more efficient and environment-friendly, and has a long-term effect.

Description

Technical Field

[0001] The present invention belongs to the field of environmental governance, and particularly relates to a sediment remediation agent composed of birnessite and an oxygen releasing agent, its preparation method and application, and especially relates to a technology for removing pollutants through the synergistic effect of the photoelectric effect and oxygen release. Background Art

[0002] The treatment methods for river and lake sediment pollution mainly include ex-situ treatment and in-situ remediation. In-situ remediation can avoid large-scale sediment migration such as dredging and subsequent treatment, and has less interference with the ecosystem. According to the technical principle, the existing in-situ sediment remediation technologies mainly include physical remediation, chemical remediation, and biological remediation methods. Physical remediation methods such as dredging and silt removal require ex-situ remediation, which may cause secondary pollution and also damage the living environment of benthic organisms and microorganisms. Chemical remediation methods such as chemical passivation and oxidation have problems such as high cost and complex operation, and there is also a risk of secondary release. Remediation methods such as adding biological agents have a long cycle and low efficiency.

[0003] Oxygenation is a commonly used means in river and lake sediment treatment. Its main principle is to improve the dissolved oxygen concentration in the overlying water of the sediment, promote the biochemical degradation of various pollutants by aerobic microorganisms, and thus improve water quality. The oxygenation methods mainly include mechanical aeration and adding oxygen releasing agents. Among them, adding oxygen releasing agents is convenient for dosing and has low construction and operation costs. It is more convenient to use this method for river water body restoration. The oxygen releasing agents (ORC) used for water body restoration are mostly peroxides, including calcium peroxide (CaO2), magnesium peroxide (MgO2), hydrogen peroxide (H2O2), and sodium percarbonate (Na2CO3·H2O2), etc. They react with water when put into water to release oxygen and increase the dissolved oxygen value in water. Among them, calcium peroxide has a lower oxygen release rate and a longer continuous release time, and has a high oxygen content and low cost. Therefore, it is the most commonly used oxygen releasing agent material. Adding oxygen releasing agents will have the following positive effects: increasing the dissolved oxygen concentration, raising the oxidation-reduction potential (ORP), promoting the growth of aerobic microorganisms, inhibiting the release of phosphorus in the sediment, enhancing the adsorption performance of the sediment, and having little environmental side effects. However, as a single oxidation matrix, calcium peroxide mainly releases oxygen through chemical processes, which limits its potential in promoting the degradation of organic matter. Moreover, its strong oxidizing property promotes the decomposition of sediment organic matter and the conversion of ammonia nitrogen to nitrate nitrogen. It has a good effect on ammonia nitrogen removal, but has a very limited effect on nitrate nitrogen removal, thus increasing the release of total nitrogen.

[0004] On the other hand, the chemical stability of such ORC decreases under acidic conditions, and the oxygen release and remediation effects are not good. At the same time, a large amount of calcium hydroxide is generated during the oxygen release process of such ORC, resulting in an increase in the pH value of the overlying water, which is not conducive to the survival and growth of submerged plants. Therefore, it is necessary to enhance the environmental adaptability and persistence of the sediment remediation agent.

[0005] Birnessite is widely distributed in nature and can be easily prepared by simple chemical synthesis methods, showing the potential for large-scale applications. It is a layered manganese oxide, a layered two-dimensional metal oxide composed of basic units of MnO6 octahedra. There is a large amount of water and cations (H + , K + , Na + , Ca 2+ , Ba 2+ , etc.) between its layers. It contains Mn with three valence states (+2, +3, +4). Its interlayer spacing is controllable and it has abundant electrochemically active sites, making it widely used in secondary batteries, supercapacitors, water treatment and catalytic fields.

[0006] In the field of water environment, the characteristics of birnessite with many pores and a large specific surface area make it an excellent adsorbent for pollutants. Patent No. CN201910626892.9 provides a modified birnessite and its preparation method and application, using the modified birnessite to enhance the adsorption capacity for heavy metal ions. Birnessite can both act as an electron sink and be "charged" by reducing agents such as organic carbon, reducing the manganese oxidation degree; and can also act as an electron source and "discharge" in an environment where oxidants (such as oxygen, nitrate nitrogen, etc.) exist, showing active "geo-battery" characteristics. Its "charging" rate by reduction with organic carbon is about 0.4–0.8 μM / day, and its oxidation rate by oxygen is about 0.3–0.6 μM / day. In addition, birnessite can remove ammonia nitrogen through chemical oxidation or microbial action (Mnammox), and can oxidize Mn 2+ to resynthesize biogenic manganese oxide through microbial coupling with nitrate reduction, realizing the regeneration of manganese oxide. This indicates that birnessite can drive the processes of a large amount of organic carbon oxidation and nitrogen pollutant transformation and removal through multiple reversible redox cycles and flexible structural adjustment strategies.

[0007] More importantly, the "mineral film" of birnessite has the semiconductor effect of solar photovoltaic conversion, that is, the photovoltaic effect. The band gap of alkaline birnessite is 1.77 eV, which can absorb light with a wavelength range of 300 - 700 nm and can use visible light to excite the generation of photoelectrons and holes. It is reported that birnessite, as a photocatalyst, has strong adaptability to electron donors and high utilization efficiency. When humic acid is used as an electron donor, the amount of manganese reduction is 1.78 - 4.46 times that of methanol. This ability enables birnessite to more effectively catalyze the oxidation of organic pollutants, which is of great significance for the removal of organic pollutants in sediment.

[0008] Aiming at the limitations of existing sediment remediation materials in the prior art, in view of the unique advantages of birnessite, the present invention aims to utilize the composite effect of birnessite and oxygen releasing agent and photocatalytic synergy to repair sediment and enhance the pollutant removal efficiency in river and lake sediment and overlying water. Summary of the Invention

[0009] To solve the problems existing in the prior art, the present invention provides a birnessite-oxygen releasing agent composite sediment remediation material and its preparation and application methods. By utilizing the photoelectric effect of birnessite and the oxygen releasing ability of oxygen releasing compounds, the sediment remediation is enhanced, which is efficient, environmentally friendly and has long-term effects.

[0010] The purpose of the present invention is to provide a birnessite-oxygen releasing agent composite sediment remediation material, which includes a modified oxygen releasing agent, birnessite, a microbial flora and an embedding matrix. The embedding matrix includes a hydrogel formed by cross-linking calcium alginate, polyvinyl alcohol and water. Among them, the microbial flora includes a domesticated aerobic denitrifying and phosphorus removing mixed flora.

[0011] In the present invention, the photoelectric effect of birnessite is combined with the oxygen releasing ability of the oxygen releasing agent. The photoelectric effect of birnessite generates photogenerated electrons and holes. The photogenerated electrons drive denitrification, and the photogenerated holes oxidize ammonia nitrogen and organic matter, promoting the transformation and degradation of pollutants. The oxygen releasing agent in-situ generates dissolved oxygen in the surface sediment, further increasing the dissolved oxygen concentration of the sediment, which is beneficial to the growth and metabolism of aerobic bacteria, promoting the biodegradation of organic matter and the nitrification process. Oxygen can participate in the electron cycle of the photoelectric effect of birnessite, affecting the valence change of Mn in birnessite, thus affecting the Jahn-Teller effect, maintaining the electronic structure of the material, improving the photocatalytic activity of birnessite, and enhancing its continuous degradation ability of organic pollutants. It can synergistically remove pollutants in sediment and water environment under both light and dark conditions, improve the redox potential of sediment, and promote in-situ sediment remediation. In addition, through the reduction reaction of birnessite and photocatalytic production of hydrogen ions, the alkaline substances generated by the oxygen releasing agent are neutralized, maintaining the stability of the water body pH.

[0012] In the present invention, the sum of the masses of the modified oxygen releasing agent and birnessite accounts for 50-80% of the total mass of the composite sediment remediation material, and the mass ratio of the modified oxygen releasing agent to birnessite is 2-5:1.

[0013] Furthermore, the modified oxygen releasing agent is a modified oxygen releasing compound with a silica layer loaded on the surface of a peroxide. The peroxide includes at least one of CaO2, MgO2, Na2CO4, and Na2O2. Calcium peroxide is preferably used, which has a lower oxygen releasing rate and a longer continuous release time, with high oxygen content and low cost.

[0014] The hydrogen peroxide generated by the reaction of the peroxide with water reacts to produce oxygen under the catalysis of birnessite after passing through the silica layer, which can effectively alleviate the problem of too fast oxygen production rate of calcium peroxide in aqueous solution, and at the same time extend the action time of hydroxyl radicals, superoxide radicals, etc. generated during the oxygen releasing process with organic pollutants.

[0015] The preparation method of the above-mentioned modified oxygen-releasing compound includes the following steps:

[0016] (1) Disperse the peroxide powder in a solution composed of absolute ethanol, deionized water, and concentrated ammonia water, and perform ultrasonic dispersion for 15 - 50 min to obtain a suspension;

[0017] (2) Dropwise add tetraethyl orthosilicate (TEOS) into the above-mentioned suspension, and continuously stir for 6 - 8 h under the condition of a water bath at 40 - 60 °C. After the product is washed and dried, the modified oxygen-releasing compound is obtained.

[0018] Among them, the concentration of the concentrated ammonia water is 25 - 28 wt%, and the volume ratio of absolute ethanol, deionized water, and concentrated ammonia water is 20 - 40:5 - 20:0.1 - 5. The dosage ratio of tetraethyl orthosilicate to the peroxide is 2 - 10 ml:1 g.

[0019] Preferably, the preparation method of the above-mentioned birnessite includes the following steps:

[0020] (1) Prepare a manganese hydroxide Mn(OH)₂ solution by mixing a 0.02 - 0.2 M manganese salt solution and a 0.5 - 2.0 M alkali solution;

[0021] (2) Add a 0.05 - 0.5 M potassium permanganate solution to the manganese hydroxide Mn(OH)₂ solution. After reacting for 12 - 24 h, filter the obtained precipitate from the solution, wash and dry it, and grind it to obtain birnessite. The birnessite with the ability of photoelectric effect is prepared by the above chemical synthesis method.

[0022] The manganese salt solution includes at least one of manganese nitrate, manganese chloride, or manganese sulfate solution, and the alkali solution includes at least one of NaOH or KOH.

[0023] Preferably, the aerobic denitrifying and phosphorus-removing mixed bacteria are the aerobic denitrifying and phosphorus-removing mixed bacteria inoculated from activated sludge, the microbial flora that has been domesticated and cultured to adapt to aerobic conditions and the photoelectric effect of birnessite through birnessite and light source irradiation.

[0024] The specific method is to add birnessite to the activated sludge containing nitrate, phosphate, and organic pollutants that has been pretreated by aeration, inoculate the aerobic denitrifying and phosphorus-removing mixed bacteria, and domesticate and culture the microbial flora that adapts to aerobic conditions and the photoelectric effect of birnessite under the irradiation of birnessite and light source.

[0025] Preferably, the aerobic denitrifying and phosphorus-removing mixed bacteria are a mixed flora of aerobic denitrifying bacteria and polyphosphate-accumulating bacteria.

[0026] The object of the present invention also lies in providing a preparation method of the above-mentioned birnessite-oxygen-releasing agent composite sediment remediation material, including the following steps:

[0027] (1) Mix polyvinyl alcohol, sodium alginate and water evenly, and heat at 80 - 110 °C for more than 1 - 2 h to form a hydrogel;

[0028] (2) Add the modified oxygen - releasing agent and birnessite into the above - mentioned hydrogel, and at the same time add the microbial suspension. After stirring evenly, pour it into a mold and freeze - mold it;

[0029] (3) Immerse the material obtained after freeze - molding in step (2) in a saturated H3BO3 solution containing CaCl2 for 24 - 72 h, wash it, air - dry it to obtain a birnessite - oxygen - releasing agent composite sediment remediation material.

[0030] Among them, the dosage ratio of polyvinyl alcohol, sodium alginate and water is 3 - 8 g: 1 g: 50 - 200 mL. The dosage ratio of birnessite and microbial suspension is 1 g: 15 - 25 ml, and the concentration of the microbial suspension is 10 7 -10 9 CFU / mL. The proportion of the microbial suspension in the total mass of the hydrogel is 15% - 25%.

[0031] Polyvinyl alcohol, as a dispersant and embedding agent, on the one hand, improves the dispersibility of birnessite and calcium peroxide, and on the other hand, embeds the domesticated and cultured microbial flora.

[0032] The present invention provides an application method of the above - mentioned birnessite - oxygen - releasing agent composite sediment remediation material, including the steps of laying the birnessite - oxygen - releasing agent composite sediment remediation material on the muddy water interface to be repaired, irradiating with sunlight, solar light source, optical fiber - transmitted light source, LED light source, etc., activating the photoelectric effect of birnessite through light irradiation, and synergistically using the oxygen - releasing function of the oxygen - releasing agent and the metabolic function of microorganisms to repair nitrogen, phosphorus and organic pollutants in the sediment.

[0033] Remove pollutants and repair the surface sediment through the photoelectric effect of birnessite, the synergistic effect of the oxygen - releasing agent and microorganisms.

[0034] Further, the light intensity I at the muddy water interface to be repaired reaches 200 W / m 2 or more.

[0035] The light intensity at the muddy water interface is calculated according to the following formula: I = I0·e -k·d , where I is the light intensity reaching the muddy water interface, I0 is the light intensity at the water surface or the underwater light source, k is the light attenuation coefficient, and d is the propagation distance of light in the water body.

[0036] The value of the light attenuation coefficient k:

[0037] In clear fresh - water lakes and rivers, k = 0.1 - 0.3 m -1 ;

[0038] Medium-turbidity water bodies (suspended particle concentration 50 - 200 mg / L, turbidity 20 - 100 NTU), k = 0.3 - 1.0 m -1 ;

[0039] Turbid water bodies (suspended particle concentration > 200 mg / L, turbidity > 100 NTU), k > 1.0 m -1 。

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The synergistic effect enhances the degradation efficiency. In the present invention, the photoelectric effect of birnessite and the oxygen release ability of the oxygen releasing agent are combined. By utilizing the photoelectric effect of birnessite, photo-generated electrons drive denitrification, and photo-generated holes oxidize ammonia nitrogen and organic matter, promoting the transformation and degradation of pollutants. The oxygen releasing agent generates dissolved oxygen in-situ in the surface sediment, and the oxygen can participate in the electron cycle of the photoelectric effect of birnessite, affecting the valence change of Mn in birnessite, thereby affecting the Jahn-Teller effect, maintaining the electronic structure of the material, improving the photocatalytic activity of birnessite, and enhancing its continuous degradation ability of organic pollutants.

[0042] (2) Simultaneous nitrogen and phosphorus removal. In the present invention, the photoelectric effect of birnessite and the oxygen release ability of calcium peroxide are combined. The oxygen releasing material generates dissolved oxygen in-situ in the surface sediment, promoting the enrichment of aerobic denitrifying bacteria and phosphorus-accumulating bacteria. At the same time, calcium ions are used to fix phosphorus through physicochemical actions, achieving simultaneous nitrogen and phosphorus removal and improving the treatment efficiency; the photoelectric effect of birnessite generates photo-generated electrons and holes, the photo-generated electrons drive denitrification, and the photo-generated holes oxidize ammonia nitrogen and organic matter, promoting the transformation and degradation of pollutants.

[0043] (3) Enhanced environmental friendliness. Traditional chemical flocculation and precipitation methods for removing phosphates require the addition of a large amount of chemical agents, which may cause secondary pollution to the environment. The birnessite-oxygen releasing agent composite sediment remediation material of the present invention is environmentally friendly, reducing the use of chemical agents and reducing the negative impact on the environment.

[0044] (4) Strong system stability. By pre-culturing and embedding functional bacteria, the microbial adaptability of the remediation agent is improved, and the start-up time is shortened. At the same time, in an environment with sufficient oxygen, aerobic denitrifying bacteria are likely to become the dominant bacteria, which grow and reproduce quickly, have strong adaptability to environments such as low temperature and high salt, and the aerobic denitrification process has better stability and simpler operation compared to the biological denitrification process under anaerobic or anoxic conditions.

[0045] (5) pH stability. Birnessite can neutralize the alkalinity released by peroxides through two ways: biochemical oxidation and photocatalysis. When the high-valent manganese in birnessite is reduced, hydrogen ions are generated. The photogenerated holes produced during the photocatalysis of birnessite will react with water to generate hydrogen ions (MnO2 + hν → e - + h + ; h + + H2O → H + + OH). Therefore, this composite remediation material can neutralize the alkaline substances released by peroxides in various ways, thereby regulating the pH value of the water body and reducing the negative impact on the aquatic ecosystem.

[0046] (6) The preparation process of the sediment remediation material of the present invention is simple, which can achieve long-term and stable remediation of sediment, avoid the problem of frequent repeated treatment, and is easy for large-scale production and application.

[0047] (7) The present invention can be applied to in-situ sediment remediation and overlying water quality maintenance measures, reducing the total amount of sediment that needs to be dredged, reducing the interference to the surrounding environment, reducing the treatment and disposal costs of dredged sediment, and at the same time being beneficial to the ecological reconstruction after dredging.

[0048] Applied to in-situ remediation of rivers and lakes, the present invention has the following beneficial effects:

[0049] (1) Improve the sediment environment. Increase the dissolved oxygen level in the sediment and create an aerobic environment. This helps to promote the activity of microorganisms in the sediment, enhance their degradation ability of nitrogen, phosphorus and organic matter, and thus improve the overall ecological environment of the sediment. In addition, by improving the oxidation-reduction potential of the sediment, the above materials can promote the growth of plants and benthic animals in the sediment, providing good basic conditions for ecological restoration.

[0050] (2) Improve water quality. Through sediment remediation, the release of harmful substances in the sediment can be effectively reduced, thereby protecting the water quality of the overlying water and reducing secondary pollution. By improving the dissolved oxygen environment on the surface layer of the sediment, it also helps to improve the transparency and oxidation-reduction potential of the water body, thus achieving faster water quality improvement.

[0051] (3) High efficiency and stability. The synergistic effect of multiple elements promotes simultaneous nitrogen and phosphorus removal and in-situ sediment remediation. It can continuously release oxygen for a long time, providing continuous power for aerobic denitrification and phosphate removal, and thus achieving long-term water quality improvement effects.

[0052] (4) Strong adaptability. It can synergistically remove pollutants in the sediment and water environment under both light and dark conditions, is applicable to various water quality conditions, including urban sewage, industrial wastewater, etc., and has good adaptability and broad application prospects.

[0053] (5) Reduce greenhouse gas emissions. Under the long-term influence of the oxygen-releasing agent, the enrichment of aerobic denitrifying bacteria is promoted, the denitrification efficiency is improved, nitrate is completely converted into N2, which helps to reduce greenhouse gas emissions.

[0054] In summary, the birnessite-oxygen-releasing agent composite sediment remediation material of the present invention has significant advantages in improving the remediation efficiency, reducing costs, reducing environmental pollution, and enhancing system stability by utilizing the synergistic effect of birnessite and the oxygen-releasing agent and applying it to sediment remediation and overlying water pollutant treatment. Description of the Drawings

[0055] Figure 1 is the band gap width of birnessite;

[0056] Figure 2 is the photocurrent response curve of birnessite;

[0057] Figure 3 is the influence of adding different remediation agents on the ammonia nitrogen concentration in the overlying water;

[0058] Figure 4 is the influence of adding different remediation agents on the nitrate nitrogen concentration in the overlying water;

[0059] Figure 5 is the total organic carbon content in the sediment of each treatment group after 10 days of reaction;

[0060] Figure 6 is the mechanism diagram of the birnessite-oxygen-releasing agent composite sediment remediation material. Detailed Embodiments

[0061] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0062] The embodiments of the present invention have detailedly described the selection and modification of the oxygen-releasing agent, the preparation of birnessite, the cultivation of functional microorganisms, the preparation of the composite sediment remediation material, and its application method, providing a specific technical solution for realizing the efficient purification of river and lake sediments. Through the implementation of the present invention, the remediation efficiency of river and lake sediments can be effectively improved, the cost can be reduced, and secondary pollution can be reduced, realizing the long-term and stable remediation of river and lake water ecosystems.

[0063] The technical principle involved in the present invention is as follows: Birnessite has a photoelectric effect and can generate photoelectron-hole pairs under sunlight or visible light irradiation. Photo-generated holes can oxidize water to produce hydroxyl radicals, superoxide radicals, etc., promoting the oxidative degradation of organic pollutants; photo-generated electrons are transferred to nitrate through the electron transfer chain, promoting the denitrification process. At the same time, calcium peroxide reacts with water to generate hydrogen peroxide, which further decomposes to produce oxygen, increasing the dissolved oxygen concentration in the sediment, facilitating the growth and metabolism of aerobic bacteria, and promoting the biodegradation of organic matter and the nitrification process. Oxygen can act as an electron acceptor and participate in the electron cycle of the birnessite photoelectric effect, which will affect the valence change of Mn in birnessite, thereby affecting the Jahn-Teller effect, maintaining the electronic structure of the material, improving the photoelectrocatalytic activity of birnessite, and enhancing its degradation ability of organic pollutants.

[0064] The birnessite-oxygen releasing agent composite sediment remediation material includes an oxygen-releasing compound, birnessite, and encapsulated functional microorganisms. The mass ratio of the oxygen-releasing compound, birnessite, and the encapsulated functional microorganism flora is 2 - 5:1:0.15 - 0.25.

[0065] Under dark conditions, birnessite chemically oxidizes or oxidizes ammonia nitrogen and organic matter under microbial conditions, and manganese is reduced to divalent manganese. Subsequently, bio-manganese oxide is formed on the surface of birnessite through microbial induction, ensuring the continuous progress of biochemical reactions. Calcium peroxide reacts with water to generate hydrogen peroxide, which further decomposes and releases oxygen. By improving the dissolved oxygen in the water body, the activity of functional microorganisms is stimulated to remove pollutants in the sediment. Under light conditions, this material can release oxygen more effectively under the mediation of the photoelectric effect of birnessite. The released oxygen in turn participates in the discharge process in the "ground battery" effect of birnessite, forming an interactive regulation of the photoelectric effect-oxygen release process, and activating the microorganisms in the sediment with light energy to promote the degradation of organic matter and denitrification, achieving long-term remediation. In addition, this composite remediation agent also has the function of adsorbing and fixing phosphorus, and at the same time realizes microbial phosphorus removal by enriching polyphosphate-accumulating bacteria.

[0066] 1. Selection and modification of the oxygen-releasing agent: The inorganic peroxide is selected from one or more of CaO2, MgO2, Na2CO4, and Na2O2. Calcium peroxide is preferred, which has a relatively low oxygen release rate and a long continuous release time, with high oxygen content and low cost.

[0067] Disperse the inorganic peroxide powder in solution A and ultrasonically disperse for 30 min to obtain suspension B. Dropwise add tetraethyl orthosilicate (TEOS) into suspension B, and continuously stir for 6 - 8 h under a water bath condition of 40 - 60 °C. After the product is washed and dried, calcium peroxide-silica composite is obtained.

[0068] Solution A is composed of 120 mL of absolute ethanol, 40 mL of deionized water, and 4 mL of concentrated ammonia water (mass fraction 25 - 28%). The ratio of the addition amount of TEOS to peroxide in suspension B is 2 - 10 mL / g.

[0069] Loading a silica layer on the surface of the peroxide can enable hydrogen peroxide generated by the reaction of the inorganic peroxide with water to react to produce oxygen under the catalysis of birnessite after passing through the silica layer, effectively alleviating the problem of too fast oxygen production rate of calcium peroxide in aqueous solution, and at the same time extending the action time of hydroxyl radicals, superoxide radicals, etc. generated during the oxygen release process with organic pollutants.

[0070] 2. Preparation of birnessite: Birnessite is prepared by a chemical synthesis method, which has the ability of photoelectric effect. Birnessite is prepared by a chemical synthesis method. Manganese hydroxide Mn(OH)2 is formed from a solution containing a manganese salt (0.02 - 0.2 M, such as manganese nitrate, manganese chloride or manganese sulfate) and a base (0.5 - 2.0 M, such as NaOH or KOH). Potassium permanganate (0.05 - 0.5 M) is introduced into the solution to oxidize Mn(OH)2. After reacting for 12 - 24 h, the obtained precipitate is filtered out from the solution, washed and dried, and ground to obtain birnessite.

[0071] 3. Cultivation of functional microorganisms: Birnessite is added to the activated sludge containing nitrate, phosphate, and organic pollutants that has been pretreated by aeration. Aerobic denitrifying bacteria and polyphosphate-accumulating bacteria are inoculated, and the microbial flora adapted to aerobic conditions and the photoelectric effect of manganese ore is domesticated and cultured under the irradiation of visible light. The microbial flora is a mixed flora for aerobic denitrification and phosphorus removal.

[0072] 4. Polyvinyl alcohol, sodium alginate, and water are mixed evenly at a mass ratio of 3 - 8 g:1 g:100 mL, and heated at 95 °C for more than 2 h to form a hydrogel. The peroxide-silica composite material and the pre-prepared birnessite are added to the hydrogel at a mass ratio of 2 - 5:1, and at the same time, the domesticated and cultured microbial cell suspension is added. After stirring evenly, it is poured into a mold and frozen and formed into block-shaped or spherical particles. The formed particles are soaked in a saturated H3BO3 solution containing CaCl2 for crosslinking for 24 - 72 h, washed and air-dried to obtain the birnessite-oxygen releasing agent composite sediment remediation agent.

[0073] The proportion of the embedded cell suspension in the total mass of the hydrogel is 15% - 25%. The modified oxygen releasing agent and birnessite account for 20% - 30% of the total mass of the composite material.

[0074] Using polyvinyl alcohol as a dispersant and embedding agent can, on the one hand, improve the dispersibility of birnessite and calcium peroxide, and on the other hand, embed the domesticated and cultured microbial flora.

[0075] 5. Application of birnessite-oxygen releasing agent composite sediment remediation agent: Spread the birnessite-oxygen releasing agent composite sediment remediation agent on the sediment-water interface, and irradiate it with sunlight, solar light source, light guide fiber transmission light source, LED light source, etc. Remove pollutants and repair the surface sediment through the photoelectric effect of birnessite and the synergistic effect of oxygen releasing agent and microorganisms.

[0076] To ensure the repair efficiency, the light intensity I at the sediment-water interface of the water body to be repaired needs to reach 200 W / m 2 or above.

[0077] The light intensity at the sediment-water interface is calculated according to the following formula, I = I0·e -k·d , where I is the light intensity reaching the sediment-water interface, I0 is the light intensity at the water surface or underwater light source, k is the light attenuation coefficient, and d is the propagation distance of light in the water body. The value of the light attenuation coefficient k: In clear fresh water lakes and rivers, k = 0.1 - 0.3 m -1 ; In moderately turbid water bodies (suspended particle concentration 50 - 200 mg / L, turbidity 20 - 100 NTU), k = 0.3 - 1.0 m -1 ; In turbid water bodies (suspended particle concentration > 200 mg / L, turbidity > 100 NTU), k > 1.0 - 1 m.

[0079] Example 1 Preparation of birnessite-oxygen releasing agent composite sediment remediation material

[0080] (1) Disperse 2 g of calcium peroxide powder in a solution composed of 120 mL of absolute ethanol, 40 mL of deionized water, and 4 mL of concentrated ammonia water (mass fraction 25 - 28%) and ultrasonically disperse for 30 min to obtain a suspension. Dropwise add 10 mL of tetraethyl orthosilicate (TEOS) to the above suspension, and continuously stir at 60 °C in a water bath for 8 h. After the product is washed and dried, the modified oxygen releasing agent calcium peroxide-silica composite material is obtained.

[0081] (2) Prepare birnessite by chemical synthesis method, which has special photoelectric effect ability. Prepare birnessite by chemical synthesis method. Mn(OH)2 is formed from a solution containing 0.2 M manganese sulfate and 0.5 M NaOH, and 0.1 M potassium permanganate is added to oxidize Mn(OH)2. After reacting for 24 h, the obtained precipitate is filtered out from the solution, washed and dried, and ground to obtain birnessite. As Figure 1 shown, the band gap of birnessite is 1.77 eV, corresponding to the visible light absorption ability; Figure 2 The photocurrent response curve shows its significant photocatalytic activity.

[0082] (3) Cultivation of microbial flora: Birnessite was added to the activated sludge containing nitrate, phosphate, and organic pollutants that had been pretreated by aeration. Aerobic denitrifying bacteria and polyphosphate-accumulating bacteria were inoculated, and the microbial flora adapted to aerobic conditions and the photoelectric effect of manganese ore was domesticated and cultured under visible light irradiation.

[0083] (4) Polyvinyl alcohol and sodium alginate were mixed at a mass ratio of 3 g:1 g, added to 100 mL of deionized water, stirred evenly, and heated at 95 °C for more than 2 h to form a hydrogel. The peroxide-silica composite material and the pre-prepared birnessite were added to the hydrogel at a mass ratio of 5:1. Subsequently, 20 mL of the pre-cultured microbial suspension (bacterial content 10 7 -10 9 CFU / mL), accounting for 20% of the total mass of the hydrogel, was added. After stirring evenly, it was poured into a mold and frozen to form block-shaped or spherical particles.

[0084] (5) The formed particles were soaked in a saturated H3BO3 solution containing CaCl2 for crosslinking for 24 h, washed, air-dried, and the birnessite-oxygen releasing agent composite sediment remediation material BORC was obtained.

[0085] Application Example 1 Sediment Oxygenation Remediation Simulation Experiment

[0086] The experimental sediment was taken from Jiaxing South Lake. After testing, the water content of the used sediment was 82%, the pH value was 7.13, the DO concentration was 2.34 mg / L, and the oxidation-reduction potential (ORP) was -58 mV.

[0087] 100 mL of sediment was taken and placed in 6 500-mL covered beakers, which were respectively labeled as CK, CaO2, BIR, BIR + CaO2, BIR + ORC, and BORC. Among them, ORC was an oxygen releasing composite material prepared by the same method as in Example 1 without birnessite.

[0088] The CK group was an untreated blank control group.

[0089] The CaO2 group added 1 g of the oxygen releasing agent CaO2 at the sediment-water interface.

[0090] The BIR group added 1 g of birnessite.

[0091] The BIR + CaO2 group added 1 g of the oxygen releasing agent CaO2 and 1 g of birnessite simultaneously.

[0092] The BIR + ORC group added 5 g of the oxygen releasing composite material and 1 g of birnessite simultaneously.

[0093] The BORC group added 5 g of the birnessite-oxygen releasing agent composite sediment remediation material prepared in Example 1.

[0094] Subsequently, 300 mL of synthetic wastewater (10 mg / L NH4 + -N, 10 mg / L NO3 - -N, 6 mg / L PO4 3- -P) was poured into a beaker. The beaker was covered with a transparent lid to reduce the influence of atmospheric reoxygenation and simulate the low dissolved oxygen state at the mud-water interface.

[0095] An LED light strip (800 μmol·m 2 ·s -1 ) was fixed at a height of 20 cm above the liquid surface as the light source, and the ambient temperature was about 20 °C. The changes in the concentrations of ammonia nitrogen, nitrate nitrogen, and phosphate were continuously detected during the reaction time of 0 - 120 h. After 48 h of reaction, the physical and chemical properties of the overlying water were monitored, and the total organic carbon (TOC) concentration of the sediment was detected after 10 d.

[0096] After 48 h of reaction, the physical and chemical indexes of the overlying water are shown in Table 1.

[0097] Table 1 Physical and chemical indexes of the overlying water after 48 h of reaction

[0098]

[0099] As can be seen from the data in Table 1, the introduction of CaO2 or birnessite BIR can both increase the oxidation-reduction potential of the aqueous solution, enhance the oxidation of reducing substances, and reduce the consumption of DO. The addition of CaO2 causes a significant increase in the solution pH. While promoting the oxygen release utilization rate through the photoelectric effect, BIR effectively neutralizes the alkalinity released by CaO2 and enhances the pH stability. The oxygen-releasing agent ORC can slow down the alkalinity release process by slowly releasing oxygen and improve the microbial environment of the surface sediment. The preparation of the birnessite-oxygen-releasing agent composite sediment remediation material BORC in Example 1 has a significant effect on reducing the turbidity of the overlying water, increasing the dissolved oxygen level, stabilizing the water environment pH, and increasing the oxidation-reduction potential. After adding the BORC remediation agent, the turbidity of the overlying water decreased from 27.28 NTU to 3.378 NTU, and the DO increased to 4.91 mg / L.

[0100] Figure 3 、 Figure 4 The effects of adding different remediation agents on the ammonia nitrogen concentration and nitrate nitrogen concentration of the overlying water are shown in Figure 3 、 4 . As shown, the addition of the composite sediment remediation material BORC significantly accelerates the removal process of ammonia nitrogen and nitrate nitrogen in the overlying water, and the removal rates reach 97% and 82% respectively after 72 h of reaction.

[0101] At 120 h of reaction, adding BIR and CaO2 simultaneously to the sediment or directly adding BORC makes the NO3 in the overlying water -The -N removal rate was significantly increased to over 95%, compared with less than 40% in the blank control group. Figure 5 For the total organic carbon (TOC) content in the sediment of each treatment group after 10 days of reaction, the TOC content in the sediment of the BORC group decreased to about 1 / 2 of the initial value.

[0102] The BIR photoelectric effect enriched the electron transfer pathway of the system, improved the oxygen release efficiency of CaO2, accelerated the nitrification and denitrification processes, and promoted the degradation and transformation of refractory organic compounds. Figure 6 It is a diagram of the action mechanism of the birnessite-oxygen releasing agent composite sediment remediation material, which includes the photoelectric effect of birnessite and its process of synergistically strengthening the degradation of organic matter in polluted sediment, ammonia nitrogen removal and denitrification.

[0103] Therefore, the birnessite-oxygen releasing agent composite sediment remediation material of the present invention combines the photoelectric effect of birnessite and the oxygen releasing ability of the oxygen releasing agent to improve the photoelectrocatalytic activity of birnessite, enhance its continuous degradation ability of organic pollutants, promote synchronous nitrogen and phosphorus removal and in-situ sediment remediation through the synergistic effect of multiple components, improve the redox potential of the sediment, synergistically remove pollutants in the sediment and water environment, and improve the ammonia removal efficiency of the sediment.

[0104] The above embodiments are only for illustrating the present invention, rather than limiting the present invention. Those skilled in the relevant technical fields can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also belong to the scope of the present invention and should be defined by each claim.

Claims

1. A birnessite-oxygen release agent composite sediment remediation material, characterized in that: The invention comprises a modified oxygen-releasing agent, birnessite, microbial flora and an embedding matrix, wherein the embedding matrix comprises a hydrogel formed by cross-linking calcium alginate, polyvinyl alcohol and water, and the microbial flora comprises a domesticated aerobic denitrification and dephosphorization mixed flora.

2. The birnessite-oxygen-release agent composite sediment repair material according to claim 1, characterized in that: The sum of the mass of the modified oxygen-releasing agent and birnessite accounts for 50-80% of the total mass of the composite sediment repair material, and the mass ratio of the modified oxygen-releasing agent to birnessite is 2-5:

1.

3. The birnessite-oxygen-release agent composite sediment repair material according to claim 1, characterized in that: The modified oxygen-releasing agent is a modified oxygen-releasing compound with a silicon dioxide layer loaded on the surface of the peroxide.

4. The birnessite-oxygen-release agent composite sediment repair material according to claim 3, characterized in that: The peroxide includes at least one of CaO2, MgO2, Na2CO4, and Na2O2.

5. The composite sediment repair material according to claim 3, characterized in that: The preparation method of the modified oxygen-releasing agent, The following steps are included: (1) dispersing peroxide powder in a solution consisting of anhydrous ethanol, deionized water and concentrated ammonia water, and ultrasonically dispersing for 15-50 minutes to obtain a suspension; (2) Tetraethyl orthosilicate (TEOS) is added dropwise into the suspension, and stirred continuously for 6-8 hours in a water bath at 40-60° C. The product is washed and dried to obtain a modified oxygen-releasing compound.

6. The composite sediment repair material according to claim 5, characterized in that: The concentration of the concentrated ammonia water is 25-28wt%, the volume ratio of anhydrous ethanol, deionized water and concentrated ammonia water is 20-40:5-20:0.1-5, and the dosage ratio of tetraethyl orthosilicate to peroxide is 2-10ml:1g.

7. The birnessite-oxygen-release agent composite sediment repair material according to claim 1, characterized in that: The preparation method of birnessite, The following steps are included: (1) mixing a 0.02-0.2M manganese salt solution and a 0.5-2.0M alkali solution to obtain a manganese hydroxide Mn(OH)2 solution; (2) Add 0.05-0.5M potassium permanganate solution to a manganese hydroxide Mn(OH)2 solution, react for 12-24 hours, filter the resulting precipitate from the solution, wash and dry, and grind to obtain birnessite.

8. The birnessite-oxygen-release agent composite sediment repair material according to claim 1, characterized in that: The aerobic denitrification and phosphorus removal mixed bacterial community is a microbial community inoculated from activated sludge, which is acclimated and cultivated through irradiation with birnessite and light source to adapt to aerobic conditions and birnessite photoelectric effect.

9. A method for preparing the birnessite-oxygen-release agent composite sediment repair material according to claim 1, characterized in that: The following steps are included: (1) mixing polyvinyl alcohol, sodium alginate and water evenly, and heating at 80-110° C. for more than 1-2 hours to form a hydrogel; (2) adding the modified oxygen-releasing agent and birnessite to the hydrogel, stirring evenly, pouring into a mold, and freezing to form; (3) Soaking the frozen molded material obtained in step (2) in a saturated H3BO3 solution containing CaCl2 for 24-72 hours, washing and air-drying to obtain a birnessite-oxygen release agent composite sediment remediation material.

10. The preparation method according to claim 9, characterized in that: The dosage ratio of the polyvinyl alcohol, sodium alginate and water is 3-8g:1g:50-200mL; The dosage ratio of birnessite and microbial suspension is 1g:15-25ml. The concentration of microbial suspension was 10 7 -10 9 CFU / mL, the mass of the microbial suspension accounts for 15%-25% of the total mass of the hydrogel.

11. A method for using the birnessite-oxygen-releaser composite sediment remediation material prepared by the preparation method according to claim 1 or claim 9, characterized in that: The birnessite-oxygen-releaser composite sediment repair material is laid on the mud-water interface to be repaired, and irradiated with at least one light source including sunlight, solar light source, optical fiber transmission light source, and LED light source. The photoelectric effect of the birnessite is activated by light, and the oxygen-releasing function of the oxygen-releasing agent and the metabolic action of microorganisms are coordinated to repair nitrogen, phosphorus and organic matter in the sediment.

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