An oxygen-doped modified sludge-based biochar and its application in the catalytic degradation of organic pollutants.

Abstract

This invention discloses an oxygen-doped modified sludge-based biochar and its application in the catalytic degradation of organic pollutants. The process involves using municipal sludge powder as raw material, impregnating it with H2SO4, filtering and washing until neutral, dispersing the filter cake in a polysulfide-containing solution for hydrothermal carbonization, filtering, washing, drying, and grinding into powder. This powder is then loaded onto a graphite felt surface and heat-treated at 800℃ under a nitrogen atmosphere to obtain the oxygen-doped modified sludge-based biochar material. Under ambient temperature and pressure, in a three-electrode system, using the oxygen-doped modified sludge-based biochar material as the anode catalyst and Na2SO4 as the electrolyte, air is bubbled into the bottom of the reactor to increase mass transfer and provide O2. The catalytic air oxidation reaction, driven by a weak electric field, can completely remove a certain concentration of organic pollutants from the solution within 2 hours, exhibiting good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to an oxygen-doped modified sludge-based biochar and its application in the catalytic degradation of organic pollutants. Background Technology

[0002] Municipal sewage sludge contains not only organic matter but also heavy metals, microorganisms, and toxic pollutants, which can have serious environmental impacts if not properly treated. Currently, the main technologies for treating and disposing of municipal sewage sludge include landfilling, incineration, agricultural value-added processing, anaerobic digestion to produce biogas, and use as a substitute for building materials. These technologies suffer from drawbacks such as secondary pollution, low product recovery rates, or the generation of harmful gases. Therefore, developing cost-effective and environmentally friendly sludge treatment and disposal methods is of great significance. Converting sludge into high-value-added biochar through high-temperature pyrolysis is a promising approach to solving the sludge treatment and disposal problem.

[0003] Sludge biochar refers to carbon-based materials obtained by high-temperature treatment of sludge precursors under anaerobic conditions. The main preparation methods include hydrothermal carbonization, high-temperature pyrolysis, and microwave pyrolysis. Sludge biochar contains elements such as C, O, H, and N on its surface and possesses advantages such as a large specific surface area, abundant pore structure and functional groups, and elemental self-doping. Therefore, it has been extensively studied for its catalytic oxidation of organic pollutants in water. To improve the catalytic performance of sludge biochar, further process control, activation, or doping modification is usually required. Modification or loading of functional nanoparticles can increase the functional groups on the surface of sludge biochar, thereby increasing the number of active sites participating in the reaction. Summary of the Invention

[0004] This invention aims to provide an oxygen-doped modified sludge-based biochar and its application in the catalytic degradation of organic pollutants. The invention utilizes the hydrothermal reaction of organic matter in sludge with polysulfides in industrial sulfur-containing wastewater to obtain hydrothermally carbonized sludge. This is then subjected to anaerobic high-temperature heat treatment to obtain oxygen-doped sludge-based biochar, which is used as a catalyst in electro-assisted catalytic wet air oxidation for the purification of organic wastewater. This invention prepares sludge-based biochar catalyst materials from municipal sludge, fully leveraging the advantages of abundant non-metallic functional groups, large specific surface area, and ease of doping modification of sludge biochar, significantly enhancing its catalytic activity in electro-assisted catalytic wet air oxidation.

[0005] The present invention discloses a method for preparing oxygen-doped modified sludge-based biochar, which uses municipal sludge dry powder as raw material, impregnates it with H2SO4, filters and washes it until neutral, disperses the filter cake in a solution containing polysulfides for hydrothermal carbonization, filters, washes and dries it and grinds it into powder, then loads it onto the fiber surface of graphite felt, and heat-treats it at 800°C under a nitrogen atmosphere to obtain oxygen-doped modified sludge-based biochar material.

[0006] The municipal sludge dry powder is made from municipal sludge with a water content of 80% from sewage treatment plants. After conditioning with 10% sulfuric acid, it is subjected to thin-layer filtration to obtain a sludge cake with a water content of 40%. After drying, it is ground into sludge dry powder with a particle size of less than 80 mesh.

[0007] The concentration of the H2SO4 solution used during impregnation is 0.1~3 mol•L. -1 The soaking time is 12~24h.

[0008] The polysulfide-containing solution comes from the reddish-brown industrial wastewater of the dicyclohexyl disulfide synthesis section in the production of CTP rubber anti-scorching agent. The sulfur content is 2-2.2%, the solution pH is 14, and it can be diluted 1-10 times before use.

[0009] The hydrothermal carbonization reaction temperature is 120~180℃, and the reaction time is 6~18h.

[0010] The particle size of the ground hydrothermal carbonized sludge is below 200 mesh.

[0011] The method for loading hydrothermally carbonized sludge onto graphite felt is to first disperse the hydrothermally carbonized sludge powder into a 2% polyethylene glycol-6000 aqueous solution, then draw the well-stirred solution into the graphite felt and hang it in a 60℃ oven to dry.

[0012] The mass ratio of polyethylene glycol, hydrothermal carbonized sludge, and graphite felt is 1~2: 1~5: 5.

[0013] The application of the oxygen-doped modified sludge-based biochar of this invention involves using the oxygen-doped modified biochar as an anode catalyst to catalyze the oxidation and degradation of organic pollutants by air under a weak electric field.

[0014] Specifically, under normal temperature and pressure, in a three-electrode system, oxygen-doped modified sludge-based biochar is used as the anode catalyst and Na2SO4 is used as the electrolyte. By blowing air into the bottom of the reactor to increase mass transfer and provide O2, the air oxidation reaction is catalyzed under a weak electric field, which can completely remove organic pollutants within 2 hours and has good cycle stability.

[0015] The current intensity of the weak electric field is constant at 10mA.

[0016] The concentration of the organic pollutant is 30~100 mg•L. -1 The air velocity is 2 L•min -1 .

[0017] The organic pollutants include methylene blue, neutral red, sulfamethoxazole, and p-nitrophenol.

[0018] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0019] 1. This invention prepares sludge-based biochar catalyst materials from municipal sludge, giving full play to the advantages of abundant organic functional groups, large specific surface area, and easy doping modification of sludge biochar, and significantly enhancing its catalytic activity in electro-assisted catalytic wet air oxidation reaction.

[0020] 2. This invention uses municipal sludge solid waste as a biochar precursor and polysulfide-containing industrial wastewater as a modifier, which not only reduces the preparation cost of catalyst materials, but also provides ideas for the resource-based disposal of these two types of waste.

[0021] 3. This invention uses non-metallic element-doped modified sludge-based biochar material. The catalyst prepared does not leach metal ions during the weak electric field process, and the material has good stability in use. Attached Figure Description

[0022] Figure 1 The images show the XPS spectra of the hydrothermally doped and undoped sludge products used in Example 1, as well as the biochar materials after high-temperature heat treatment. It can be seen that the undoped hydrothermally treated sludge contains non-metallic elements such as C, S, O, and N. After heat treatment at 800℃ under anaerobic conditions, the contents of O and N decreased significantly, while the contents of S and C increased. In the sludge hydrothermally treated in a sulfide solution, the contents of S and O increased significantly, while the contents of C and N decreased. After further anaerobic carbonization at 800℃, compared with the undoped sludge biochar, only the O content increased significantly; the other three elements were lower than in the undoped material. This indicates that the sludge after hydrothermal reaction with polysulfides and high-temperature carbonization mainly underwent an oxygen doping reaction.

[0023] Figure 2 High-resolution XPS spectra of C1s of the hydrothermally doped and undoped sludge products used in Example 1, and the biochar materials after high-temperature heat treatment. It can be seen that the undoped hydrothermal sludge and carbonized sludge contain CC / C=C, COC, and C-COOH groups on their surfaces, while the doped hydrothermal sludge and carbonized sludge show increased C=O and OC=O functional groups. This indicates that the active sites of the catalyst are mainly C=O and OC=O functional groups.

[0024] Figure 3This section evaluates the catalytic oxidation degradation performance of different catalysts for methylene blue under the conditions of Example 1. It can be seen that oxygen-doped sludge-based biochar, as the anode catalyst for the electro-catalyzed wet air oxidation reaction, achieves a 100% removal efficiency of methylene blue within 2 hours. Undoped sludge biochar, lacking catalytically active sites, has a removal rate for methylene blue only slightly higher than that of graphite felt support, possibly due to the high specific surface area of ​​sludge-based biochar enhancing its electroadsorption. Although hydrothermally doped sludge possesses catalytically active sites, the material has not undergone high-temperature carbonization, resulting in poor conductivity and insufficient electric field activation of the catalytically active sites; therefore, it exhibits the lowest removal efficiency for methylene blue.

[0025] Figure 4 Under the conditions of Example 1, the cycling stability of oxygen-doped sludge biochar for the electro-catalyzed wet air oxidation degradation of methylene blue was evaluated. It can be seen that, because the active sites of the oxygen-doped sludge-based biochar catalyst are carbonyl or ester functional groups, there is no problem with metal ion leaching, thus its cycling stability is excellent.

[0026] Figure 5 Under the conditions of Example 1, the effect of soaking municipal sludge dry powder in H2SO4 solutions of different concentrations for 12 h on the catalytic oxidation of methylene blue by the prepared oxygen-doped sludge biochar was investigated. It can be seen that the sulfuric acid concentration is lower than 1 mol•L... -1 Subsequently, the catalytic performance of the prepared sludge biochar gradually decreased. This is mainly because municipal sludge contains metal ions such as iron and aluminum, which easily form hydroxide or sulfide precipitates in alkaline polysulfide solutions. These metal ions hinder the doping and modification of organic functional groups and, after high-temperature heat treatment, form non-catalytically active metals and their compounds, thereby reducing the catalytic active sites of the catalyst.

[0027] Figure 6 Under the conditions of Example 1, and under the same hydrothermal pH conditions (pH adjusted with NaOH), the effect of the dilution factor of the polysulfide solution on the catalytic oxidation performance of the prepared oxygen-doped sludge biochar was investigated. It can be seen that a lower mass ratio of polysulfides to sludge is detrimental to the oxygen doping reaction, especially when the polysulfide concentration is diluted by more than 2 times, at which point the catalytic performance of the sludge biochar begins to decrease. Detailed Implementation

[0028] The embodiments of the present invention are described in detail below with reference to some technical solutions.

[0029] The municipal sludge used in the following examples is municipal sludge with a water content of 80% from a sewage treatment plant. After being conditioned with 10% sulfuric acid, it is subjected to thin-layer filtration to obtain a sludge cake with a water content of 40%. After drying, it is ground into sludge dry powder with a particle size of less than 80 mesh.

[0030] The polysulfide solution used in the following examples is a reddish-brown industrial wastewater from the dicyclohexyl disulfide synthesis section in the production of CTP rubber anti-scorching agent. The sulfur content is 2-2.2%, the solution pH is 14, and it can be diluted 1-10 times before use.

[0031] Example 1:

[0032] Take 5.0g of municipal sludge powder in 1 mol•L -1 The mixture was stirred and impregnated in H2SO4 solution for 12 hours, filtered and washed until neutral, and the filter cake was placed in a polysulfide solution diluted 1:1, dispersed evenly, and then hydrothermally carbonized at 180℃ for 12 hours. After cooling, it was filtered, washed, and dried at 60℃ for 24 hours. After grinding, powder with a mesh size of less than 200 was obtained. The hydrothermal carbonized sludge powder was dispersed in a 2% polyethylene glycol-6000 aqueous solution at a weight ratio of 2:5:5 (polyethylene glycol, hydrothermal carbonized sludge, and graphite felt). After thorough stirring, the graphite felt was placed in the solution until the solution was completely absorbed into the graphite felt. The graphite felt was then suspended in a 60℃ oven and dried for 12 hours. Finally, the graphite felt loaded with hydrothermal sludge was placed in a tube furnace and heat-treated at 800℃ for 2 hours under a nitrogen atmosphere to obtain oxygen-doped modified sludge-based biochar material.

[0033] At ambient temperature and pressure, in a three-electrode system, an oxygen-doped modified sludge-based biochar electrode was used as the anode catalyst, and Na2SO4 was used as the electrolyte. The solution was applied at the bottom of the reactor at a rate of 2 L / min. -1 Air is bubbled in at a flow rate to increase mass transfer and provide O2. Catalytic air oxidation at a current intensity of 10 mA can achieve a concentration of 50 mg•L. -1 The removal rate of methylene blue solution reached 100% within 2 hours.

[0034] Example 2:

[0035] Take 1.0 g of municipal sludge powder in 0.1 mol•L -1 The sludge was stirred and impregnated in H2SO4 solution for 24 hours, filtered and washed until neutral, and then the filter cake was placed in a polysulfide solution diluted 10 times. After being dispersed evenly, it was hydrothermally carbonized at 120℃ for 18 hours. After cooling, it was filtered, washed, and dried at 60℃ for 24 hours. After grinding, powder with a mesh size of less than 200 was obtained. The hydrothermal carbonized sludge powder was dispersed in a 2% polyethylene glycol-6000 aqueous solution at a weight ratio of 1:1:5 (polyethylene glycol, hydrothermal carbonized sludge, and graphite felt). After thorough stirring, the graphite felt was placed in the solution until the solution was completely absorbed into the graphite felt. The graphite felt was then suspended in a 60℃ oven and dried for 12 hours. Finally, the graphite felt loaded with hydrothermal sludge was placed in a tube furnace and heat-treated at 800℃ for 2 hours under a nitrogen atmosphere to obtain oxygen-doped modified sludge-based biochar material.

[0036] At ambient temperature and pressure, in a three-electrode system, an oxygen-doped modified sludge-based biochar electrode was used as the anode catalyst, and Na2SO4 was used as the electrolyte. The solution was applied at the bottom of the reactor at a rate of 2 L / min. -1 Air is bubbled in at a flow rate to increase reaction mass transfer and provide O2. Catalytic air oxidation reaction is performed at a current intensity of 10 mA, resulting in a concentration of 80 mg•L. -1 The removal rate of neutral red reached 100% within 2 hours.

[0037] Example 3:

[0038] Take 3.0g of municipal sludge powder in 1 mol•L -1 The sludge was stirred and impregnated in H2SO4 solution for 18 hours, filtered and washed until neutral, and the filter cake was placed in a polysulfide solution diluted 2 times. After being dispersed evenly, it was hydrothermally carbonized at 150℃ for 10 hours. After cooling, it was filtered, washed, and dried at 60℃ for 24 hours. After grinding, powder with a mesh size of less than 200 was obtained. The hydrothermal carbonized sludge powder was dispersed in a 2% polyethylene glycol-6000 aqueous solution at a weight ratio of 2:3:5 (polyethylene glycol, hydrothermal carbonized sludge, and graphite felt). After thorough stirring, the graphite felt was placed in the solution until the solution was completely absorbed into the graphite felt. The graphite felt was then suspended in a 60℃ oven and dried for 12 hours. Finally, the graphite felt loaded with hydrothermal sludge was placed in a tube furnace and heat-treated at 800℃ for 2 hours under a nitrogen atmosphere to obtain oxygen-doped modified sludge-based biochar material.

[0039] Under normal temperature and pressure, in a three-electrode system, an oxygen-doped modified sludge-based biochar electrode is used as the anode, and Na2SO4 is used as the electrolyte. The electrolyte is added at the bottom of the reactor at a rate of 2 L / min. -1 Air is bubbled in at a flow rate to increase mass transfer and provide O2. Catalytic air oxidation at a current intensity of 10 mA can achieve a concentration of 30 mg•L. -1 The removal rate of sulfamethoxazole solution reached 100% within 2 hours.

[0040] Example 4:

[0041] Take 5.0g of municipal sludge powder in 1 mol•L -1The mixture was stirred and impregnated in H2SO4 solution for 12 hours, filtered and washed until neutral, and the filter cake was placed in a polysulfide solution diluted 1:1, dispersed evenly, and then hydrothermally carbonized at 180℃ for 6 hours. After cooling, it was filtered, washed, and dried at 60℃ for 24 hours. After grinding, powder with a mesh size of less than 200 was obtained. The hydrothermal carbonized sludge powder was dispersed in a 2% polyethylene glycol-6000 aqueous solution at a weight ratio of 2:5:5 (polyethylene glycol, hydrothermal carbonized sludge, and graphite felt). After thorough stirring, the graphite felt was placed in the solution until the solution was completely absorbed into the graphite felt. The graphite felt was then suspended in a 60℃ oven and dried for 12 hours. Finally, the graphite felt loaded with hydrothermal sludge was placed in a tube furnace and heat-treated at 800℃ for 2 hours under a nitrogen atmosphere to obtain oxygen-doped modified sludge-based biochar material.

[0042] At ambient temperature and pressure, in a three-electrode system, an oxygen-doped modified sludge-based biochar electrode was used as the anode catalyst, and Na2SO4 was used as the electrolyte. The solution was applied at the bottom of the reactor at a rate of 2 L / min. -1 Air is bubbled in at a flow rate to increase mass transfer and provide O2. Catalytic air oxidation at a current intensity of 10 mA can achieve a concentration of 100 mg•L. -1 The removal rate of p-nitrophenol reached 100% within 2 hours.

Claims

1. A method for preparing oxygen-doped modified sludge-based biochar, characterized in that: Municipal sludge dry powder is used as raw material. After being impregnated with H2SO4 solution, it is filtered and washed until neutral. The filter cake is dispersed in a solution containing polysulfides for hydrothermal carbonization. After filtration, washing and drying, it is ground into powder. The obtained hydrothermally carbonized sludge powder is loaded onto the surface of graphite felt fiber and heat-treated under nitrogen atmosphere to obtain oxygen-doped modified sludge-based biochar material. The concentration of the H2SO4 solution used during impregnation is 0.1~3 mol•L. -1 The soaking time is 12-24 hours; The polysulfide-containing solution is derived from the reddish-brown industrial wastewater from the dicyclohexyl disulfide synthesis section in the production of CTP (a rubber anti-scorching agent). The sulfur content is 2.0-2.2%, the solution pH is 14, and it is diluted 1-10 times before use.

2. The preparation method according to claim 1, characterized in that: The municipal sludge dry powder is made from municipal sludge with a water content of 80% from sewage treatment plants. After conditioning with 10% sulfuric acid, it is subjected to thin-layer filtration to obtain a sludge cake with a water content of 40%. After drying, it is ground into sludge dry powder with a particle size of less than 80 mesh.

3. The preparation method according to claim 1, characterized in that: The hydrothermal carbonization reaction temperature is 120~180℃, and the reaction time is 6~18h.

4. The preparation method according to claim 1, characterized in that: The particle size of the hydrothermal carbonized sludge powder obtained after grinding is less than 200 mesh.

5. The preparation method according to claim 1, characterized in that: The hydrothermal carbonized sludge powder is loaded onto the surface of graphite felt fiber by the following method: first, the hydrothermal carbonized sludge powder is dispersed in a 2% aqueous solution of polyethylene glycol-6000, and then the solution after stirring is drawn into the graphite felt and hung to dry at 60°C.

6. The preparation method according to claim 5, characterized in that: The mass ratio of polyethylene glycol-6000, hydrothermal carbonized sludge powder, and graphite felt is 1~2: 1~5:

5.

7. The application of oxygen-doped biochar prepared according to any one of claims 1-6 in the catalytic degradation of organic pollutants, characterized in that: Using the oxygen-doped biochar as an anode catalyst, organic pollutants are catalyzed by air oxidation.

8. The application according to claim 7, characterized in that: At ambient temperature and pressure, in a three-electrode system, oxygen-doped modified sludge-based biochar material is used as the anode catalyst, and Na2SO4 is used as the electrolyte. Air is blown into the bottom of the reactor to increase mass transfer and provide O2. The air oxidation reaction is catalyzed under a weak electric field to degrade organic pollutants. The current intensity of the weak electric field is constant at 10mA.

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