A method for treating organic wastewater by ozone catalytic oxidation

Abstract

The present invention relates to the field of water treatment and discloses a method for treating organic wastewater by ozone catalytic oxidation, comprising: 1) precipitating the organic wastewater; 2) passing the organic wastewater and ozone into a reactor filled with a catalyst, and obtaining wastewater with degraded organic pollutants after an ozone catalytic oxidation reaction; the catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the surface of the carrier pores, wherein the catalytically active layer is a magnesium-zinc-nitrogen composite-doped porous carbon layer; the catalytically active layer is formed by in-situ carbonization of magnesium-zinc hydroxide-doped polydopamine on the surface of the carrier pores. The present invention uses a self-developed catalyst in the ozone catalytic oxidation treatment of organic wastewater. This catalyst not only has excellent catalytic effect but also can maintain stable catalytic efficiency for a long time in wastewater environments with complex components.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, and in particular to a method for treating organic wastewater by ozone catalytic oxidation. Background Art

[0002] With the increasing awareness of environmental protection, especially in the field of industrial wastewater treatment, many traditional water treatment methods are difficult to effectively remove refractory organic pollutants in wastewater, or are not green and environmentally friendly. The more mature water treatment processes in the existing technology mainly include: (1) UV / photocatalytic oxidation: UV photocatalysis uses light energy to excite catalysts to generate highly active substances to degrade organic pollutants. However, the efficiency of photocatalytic reactions is low and the requirements for UV light sources are high; (2) Biological treatment technology: Biological treatment technology has the advantages of low cost and sustainability in treating easily degradable organic pollutants, but the treatment effect on refractory organic matter is poor; (3) Fenton oxidation: Fenton oxidation is relatively mature in treating organic pollutants, but its disadvantage is that it consumes a large amount of chemical reagents (such as FeSO4 and H2O2) during the reaction process and produces a large amount of iron-containing sludge, which has a prominent secondary pollution problem.

[0003] Ozone catalytic oxidation is a rapidly developing water treatment technology in recent years. It possesses powerful oxidizing properties and can efficiently remove various difficult-to-degrade organic matter. Compared to traditional treatment methods, this technology not only offers faster reaction times and better treatment results, but also generates no secondary pollution during operation, meeting the needs of sustainable development.

[0004] Currently, the bottleneck limiting the development of ozone catalytic oxidation technology lies primarily in catalyst development. Existing catalysts for ozone catalytic oxidation suffer from poor and persistent water treatment stability. This is primarily due to suboptimal bonding between the active catalytic metal elements and the catalyst support within the reaction system, making it difficult to maintain stable catalytic efficiency in complex wastewater environments.

[0005] In summary, it is necessary to continuously develop ozone catalytic oxidation catalysts with high stability and their suitable water treatment processes. Summary of the Invention

[0006] To address the above technical issues, the present invention provides a method for treating organic wastewater by ozone catalytic oxidation. The present invention utilizes a self-developed catalyst in the ozone catalytic oxidation treatment of organic wastewater. This catalyst not only exhibits excellent catalytic effects but also maintains stable catalytic efficiency over a long period of time in wastewater environments with complex components.

[0007] The specific technical solution of the present invention is: a method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0008] 1) Sedimentation of organic wastewater.

[0009] First, the organic wastewater is precipitated, which not only removes solid impurities in the organic wastewater, but also prevents them from clogging the catalyst filler during the subsequent ozone catalytic oxidation process.

[0010] 2) The organic wastewater and ozone are introduced into a reactor filled with a catalyst, and wastewater with degraded organic pollutants is obtained after ozone catalytic oxidation reaction.

[0011] In step 2), the role of the catalyst is to reduce the activation energy of the reaction and increase the reaction rate. After the catalyst comes into contact with ozone, the free oxygen atoms produced by ozone decomposition can more easily react with water to form hydroxyl radicals, which have extremely strong oxidizing power. This breaks the chemical bonds of the refractory organic matter in the organic wastewater, completely mineralizing it and ultimately achieving degradation.

[0012] Specifically, the catalyst of the present invention includes porous silica microspheres as a carrier and a catalytically active layer attached to the surface of the carrier pores, wherein the catalytically active layer is a magnesium-zinc-nitrogen composite-doped porous carbon layer; the catalytically active layer is formed by in-situ carbonization of magnesium-zinc hydroxide-doped polydopamine on the surface of the carrier pores.

[0013] The carrier of the above-mentioned catalyst of the present invention is a porous silica microsphere with a porous structure inside, which can effectively adsorb ozone and organic wastewater, thereby extending the stay of ozone and organic wastewater in the catalyst filler and realizing, and enhancing the catalytic oxidation effect. In addition, it is also more critical that the catalytic active material of the catalyst of the present invention is a magnesium-zinc-nitrogen composite doped porous carbon layer, which not only has an excellent catalytic effect under the coordination of each element, but also can be stably attached to the carrier pore surface, the active element is embedded and doped in the carbon layer, and the binding property with the carrier is good, even in a wastewater environment with complex components, long-term and stable catalytic efficiency can be maintained. And the carbon layer also has a porous structure, thereby effectively increasing the specific surface area of ​​the catalytic active layer, further enhancing the catalytic effect.

[0014] Preferably, in step 1), the COD value of the organic wastewater is 100-600 mg / L.

[0015] Preferably, step 1) specifically comprises: passing the organic wastewater into a sedimentation tank for precipitation, with a residence time of 5-20 hours.

[0016] Preferably, in step 2), the flow rate of the organic wastewater is 50-200 L / h.

[0017] Preferably, in step 2), the flow rate of ozone is 40-100 mL / min.

[0018] Preferably, in step 2), the temperature of the ozone catalytic oxidation reaction is 10-40° C., and the time is 20-200 min.

[0019] The ozone catalytic oxidation reaction of the present invention can be carried out at room temperature without the need for additional heating, thus effectively saving energy.

[0020] Preferably, in step 2), the specific surface area of ​​the porous silica microspheres is 200-500 m 2 / g, particle size is 1-10mm.

[0021] Preferably, in step 2), the method for preparing the catalyst comprises:

[0022] A) Dopamine, magnesium salt, and zinc salt are added to water under anaerobic conditions and stirred evenly, and the carrier is dispersed in the resulting precursor solution.

[0023] B) adding alkaline solution dropwise to the precursor liquid under oxygen-containing conditions and stirring the reaction, filtering, and obtaining a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0024] Under alkaline conditions, since the surface of the porous silica microspheres serving as the carrier is negatively charged, the positively charged magnesium ions and zinc ions are enriched on the pore surface of the porous silica microspheres under electrostatic action to form a positively charged adsorption layer; as the alkalinity of the system increases, dopamine self-polymerizes with the pore surface under alkaline and oxygen-containing conditions to form polydopamine. At the same time, magnesium ions and zinc ions are also converted into magnesium zinc hydroxide on the surface of the carrier pores. In the above two reaction processes, a magnesium zinc hydroxide-doped polydopamine layer is formed in which magnesium zinc hydroxide is doped in the polydopamine polymerization network. Polydopamine has high adhesion and can be firmly attached to the carrier pore surface.

[0025] C) calcining the product support of step B) in an oxygen-free atmosphere to carbonize the magnesium zinc hydroxide-doped polydopamine layer into a magnesium zinc nitrogen composite-doped porous carbon layer, washing and drying to obtain a catalyst.

[0026] During the above-mentioned high-temperature anaerobic calcination treatment, on the one hand, polydopamine is carbonized, and hydrogen and oxygen elements are gradually burned away to form a nitrogen-doped carbon layer; on the other hand, magnesium zinc hydroxide is dehydrated at high temperature to produce water molecules, which form pores in the carbon layer during the escape process, thereby making the carbon layer have a porous structure, greatly increasing the specific surface area of ​​the catalytic active layer, and thus enhancing the catalytic effect.

[0027] Preferably, in step A), the concentrations of dopamine, magnesium ions, and zinc ions in the precursor liquid are (0.4-0.8) mol / L, (0.2-0.4) mol / L, and (0.1-0.2) mol / L, respectively.

[0028] The present invention has found that the content of magnesium ions and zinc ions has a significant impact on the catalytic performance of the catalyst, and therefore requires optimization. Dopamine content is also important. If the dopamine content is too low, it may be difficult to form a sufficient polydopamine layer on the surface of the carrier pores, and the nitrogen content of the carbonized carbon layer may be low, thus affecting the catalytic performance. If the dopamine content is too high, it may easily lead to an excessively thick polydopamine layer, thereby blocking the carrier pore space.

[0029] Preferably, in step A), the ratio of the carrier to the precursor liquid is 50-150 g / L.

[0030] Preferably, in step A), the magnesium salt is magnesium chloride; and the zinc salt is zinc chloride.

[0031] Preferably, in step A), the stirring and dispersing is performed at a rotation speed of 100-500 rpm and for a time of 10-30 min.

[0032] Preferably, in step B), the alkali solution is aqueous ammonia, and the target pH is 8-10.

[0033] Preferably, in step B), the stirring reaction is carried out at a temperature of 35-60° C. and for a time of 1-5 h.

[0034] Preferably, in step C), the calcination temperature is 700-1100° C. and the calcination time is 4-8 hours.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The catalytically active substance of the catalyst of the present invention is a magnesium-zinc-nitrogen composite-doped porous carbon layer, which has an excellent catalytic effect under the cooperation of various elements. At the same time, the magnesium-zinc-nitrogen composite-doped porous carbon layer can be stably attached to the surface of the carrier pores, and the active elements are embedded and doped in the carbon layer, and have good binding properties with the carrier, and can maintain stable catalytic efficiency even in a wastewater environment with complex components.

[0037] (2) The present invention cleverly utilizes the principles of electrostatic adsorption and dopamine self-polymerization in the catalyst preparation process, thereby forming a magnesium-zinc-nitrogen composite-doped porous carbon layer on the surface of the carrier pores as a catalytically active layer. The catalytically active layer has a porous structure and a large specific surface area, which can further enhance the catalytic effect. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the embodiments.

[0039] Overall embodiment

[0040] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0041] 1) Sedimentation of organic wastewater.

[0042] In some preferred implementation cases, step 1) specifically includes: passing the organic wastewater into a sedimentation tank for precipitation, with a residence time of 5-20 hours.

[0043] In some preferred implementation cases, in step 1), the COD value of the organic wastewater is 100-600 mg / L.

[0044] 2) Passing the organic wastewater and ozone into a reactor filled with a catalyst, and subjecting the wastewater to an ozone-catalyzed oxidation reaction, yielding wastewater containing degraded organic pollutants. Specifically, the catalyst of the present invention comprises porous silica microspheres as a carrier and a catalytically active layer attached to the surface of the carrier pores. The catalytically active layer is a magnesium-zinc-nitrogen composite-doped porous carbon layer; the catalytically active layer is formed by in-situ carbonization of magnesium-zinc hydroxide-doped polydopamine on the surface of the carrier pores.

[0045] In some preferred implementation cases, in step 2), the flow rate of the organic wastewater is 50-200 L / h.

[0046] In some preferred implementation cases, in step 2), the flow rate of ozone is 40-100 mL / min.

[0047] In some preferred implementation cases, in step 2), the temperature of the ozone catalytic oxidation reaction is 10-40° C., and the time is 20-200 min.

[0048] In some preferred embodiments, in step 2), the specific surface area of ​​the porous silica microspheres is 200-500 m 2 / g, particle size is 1-10mm.

[0049] In some preferred implementation cases, in step 2), the method for preparing the catalyst comprises:

[0050] A) Dopamine, magnesium salt, and zinc salt are added to water under anaerobic conditions and stirred evenly, and the carrier is dispersed in the resulting precursor solution.

[0051] In some more preferred embodiments, in step A), the concentrations of dopamine, magnesium ions, and zinc ions in the precursor liquid are (0.4-0.8) mol / L, (0.2-0.4) mol / L, and (0.1-0.2) mol / L, respectively; in some more preferred embodiments, in step A), the ratio of the carrier to the precursor liquid is 50-150 g / L; in some more preferred embodiments, in step A), the magnesium salt is magnesium chloride; the zinc salt is zinc chloride; in some more preferred embodiments, in step A), the stirring and dispersing speed is 100-500 rpm, and the time is 10-30 min.

[0052] B) adding alkaline solution dropwise to the precursor liquid under oxygen-containing conditions and stirring the reaction, filtering, and obtaining a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0053] In some more preferred embodiments, in step B), the alkaline solution is aqueous ammonia, and the target pH is 8-10. In some more preferred embodiments, in step B), the stirring reaction temperature is 35-60° C., and the time is 1-5 hours.

[0054] C) calcining the product support of step B) in an oxygen-free atmosphere to carbonize the magnesium zinc hydroxide-doped polydopamine layer into a magnesium zinc nitrogen composite-doped porous carbon layer, washing and drying to obtain a catalyst.

[0055] In some more preferred embodiments, in step C), the calcination temperature is 700-1100° C. and the calcination time is 4-8 h.

[0056] Specific Examples and Comparative Examples

[0057] Example 1

[0058] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0059] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0060] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0061] The catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the pore surface of the carrier. The preparation method thereof specifically comprises the following steps:

[0062] A) Dopamine, magnesium chloride, and zinc chloride were added to water and stirred evenly under anaerobic conditions (rotation speed of 300 rpm, time of 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) was dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of dopamine, magnesium ions, and zinc ions in the precursor solution were 0.4 mol / L, 0.3 mol / L, and 0.15 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0063] B) adding aqueous ammonia to the precursor liquid under air conditions and stirring the reaction until the pH reaches 9±0.2; the stirring reaction temperature is 50° C. and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0064] C) The product support obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the magnesium zinc hydroxide-doped polydopamine layer was carbonized into a magnesium zinc nitrogen composite-doped porous carbon layer, which was repeatedly washed with water and vacuum-dried to obtain a catalyst.

[0065] Example 2

[0066] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0067] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0068] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0069] The catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the pore surface of the carrier. The preparation method thereof specifically comprises the following steps:

[0070] A) Dopamine, magnesium chloride, and zinc chloride were added to water and stirred evenly under anaerobic conditions (rotation speed of 300 rpm, time of 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) was dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of dopamine, magnesium ions, and zinc ions in the precursor solution were 0.6 mol / L, 0.3 mol / L, and 0.15 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0071] B) adding aqueous ammonia to the precursor liquid under air conditions and stirring the reaction until the pH reaches 9±0.2; the stirring reaction temperature is 50° C. and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0072] C) The product support obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the magnesium zinc hydroxide-doped polydopamine layer was carbonized into a magnesium zinc nitrogen composite-doped porous carbon layer, which was repeatedly washed with water and vacuum-dried to obtain a catalyst.

[0073] Example 3

[0074] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0075] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0076] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0077] The catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the pore surface of the carrier. The preparation method thereof specifically comprises the following steps:

[0078] A) Dopamine, magnesium chloride, and zinc chloride were added to water and stirred evenly under anaerobic conditions (rotation speed of 300 rpm, time of 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) was dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of dopamine, magnesium ions, and zinc ions in the precursor solution were 0.8 mol / L, 0.3 mol / L, and 0.15 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0079] B) adding aqueous ammonia to the precursor liquid under air conditions and stirring the reaction until the pH reaches 9±0.2; the stirring reaction temperature is 50° C. and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0080] C) The product support obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the magnesium zinc hydroxide-doped polydopamine layer was carbonized into a magnesium zinc nitrogen composite-doped porous carbon layer, which was repeatedly washed with water and vacuum-dried to obtain a catalyst.

[0081] Comparative Example 1

[0082] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0083] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0084] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0085] The catalyst comprises porous silica microspheres as a carrier and catalytically active components loaded on the surface of the carrier pores. The preparation method thereof specifically comprises the following steps:

[0086] A) Magnesium chloride and zinc chloride were added to water and stirred evenly (rotating speed of 300 rpm for 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) were dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of magnesium ions and zinc ions in the precursor solution were 0.3 mol / L and 0.15 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0087] B) adding ammonia water dropwise to the precursor liquid and stirring the reaction until the pH reaches 9±0.2, the stirring reaction temperature is 50° C., and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier with magnesium zinc hydroxide loaded on the pore surface.

[0088] C) The product support obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the magnesium zinc hydroxide was dehydrated, and the catalyst was repeatedly washed with water and dried in vacuum to obtain a catalyst.

[0089] Comparative Example 2

[0090] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0091] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0092] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0093] The catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the pore surface of the carrier. The preparation method thereof specifically comprises the following steps:

[0094] A) Dopamine, magnesium chloride, and zinc chloride were added to water and stirred evenly under anaerobic conditions (rotation speed of 300 rpm, time of 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) was dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of dopamine, magnesium ions, and zinc ions in the precursor solution were 1.0 mol / L, 0.3 mol / L, and 0.15 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0095] B) adding aqueous ammonia to the precursor liquid under air conditions and stirring the reaction until the pH reaches 9±0.2; the stirring reaction temperature is 50° C. and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0096] C) The product support obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the magnesium zinc hydroxide-doped polydopamine layer was carbonized into a magnesium zinc nitrogen composite-doped porous carbon layer, which was repeatedly washed with water and vacuum-dried to obtain a catalyst.

[0097] Comparative Example 3

[0098] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0099] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0100] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0101] The catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the pore surface of the carrier. The preparation method thereof specifically comprises the following steps:

[0102] A) Dopamine and zinc chloride were added to water under anaerobic conditions and stirred evenly (rotating speed of 300 rpm for 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) was dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of dopamine and zinc ions in the precursor solution were 0.6 mol / L and 0.45 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0103] B) adding ammonia water dropwise to the precursor liquid under air conditions and stirring the reaction until the pH reaches 9±0.2; the stirring reaction temperature is 50° C. and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier having a zinc hydroxide-doped polydopamine layer attached to the pore surface.

[0104] C) The product carrier obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the zinc hydroxide-doped polydopamine layer was carbonized into a zinc-nitrogen composite-doped porous carbon layer, which was repeatedly washed with water and vacuum-dried to obtain a catalyst.

[0105] Comparative Example 4

[0106] A method for treating organic wastewater by ozone catalytic oxidation, which specifically comprises the following steps:

[0107] 1) Organic wastewater precipitation: The purification object is organic wastewater with a COD value of 210±15 mg / L from an enterprise in Ningbo City, Zhejiang Province. The organic wastewater is passed into a sedimentation tank for precipitation. The residence time of the organic wastewater in the sedimentation tank is 10 hours. Solid impurities are precipitated during the slow flow of the organic wastewater.

[0108] 2) Ozone catalytic oxidation: The precipitated organic wastewater is passed from the top outlet weir of the sedimentation tank into the reactor at a flow rate of 100L / h. The reactor is equipped with a catalyst bed and filled with catalyst; and ozone is also passed into the reactor at a flow rate of 70mL / min. In the process of passing through the catalyst bed, the organic wastewater comes into contact with the catalyst and ozone, undergoing an ozone catalytic oxidation reaction to achieve the degradation of organic pollutants. The temperature of the ozone catalytic oxidation reaction in the reactor is set at 25°C, the residence time of the organic wastewater in the catalyst bed is 60 minutes, and the organic wastewater flows out from the outlet of the reactor and is collected to obtain wastewater with degraded organic pollutants.

[0109] The catalyst comprises porous silica microspheres as a carrier and a catalytically active layer attached to the pore surface of the carrier. The preparation method thereof specifically comprises the following steps:

[0110] A) Dopamine and magnesium chloride were added to water under anaerobic conditions and stirred evenly (rotating speed of 300 rpm for 20 min). Porous silica microspheres (specific surface area of ​​350 ± 20 m 2 / g, with an average particle size of approximately 3 mm) was dispersed (at a speed of 300 rpm for 20 minutes) in the resulting precursor solution. The concentrations of dopamine and magnesium ions in the precursor solution were 0.6 mol / L and 0.3 mol / L, respectively; the solid-to-liquid ratio of the carrier to the precursor solution was 100 g / L.

[0111] B) adding aqueous ammonia to the precursor liquid under air conditions and stirring the reaction until the pH reaches 9±0.2; the stirring reaction temperature is 50° C. and the time is 3 hours; after the reaction is completed, filtering is performed to obtain a carrier having a magnesium hydroxide-doped polydopamine layer attached to the pore surface.

[0112] C) The product carrier obtained in step B) was calcined in an argon protective atmosphere at a temperature of 900° C. for 6 hours. During the calcination process, the magnesium hydroxide-doped polydopamine layer was carbonized into a magnesium-nitrogen composite-doped porous carbon layer, which was repeatedly washed with water and vacuum-dried to obtain a catalyst.

[0113] Performance Testing

[0114] The total organic carbon test was performed on the organic wastewater after treatment in the above embodiments and comparative examples, and the results are shown in the following table:

[0115]

[0116] Note: The calculation method of COD reduction rate maintenance rate after 30 days of continuous operation is: COD reduction rate after 30 days of continuous operation / effluent COD reduction rate after the first operation * 100%.

[0117] By comparing the data in the above table, we can see that:

[0118] After the first operation of Examples 1-3, the effluent COD reduction rate can reach more than 80%, especially the COD reduction rate of Example 2 is the highest; at the same time, the COD reduction rate retention rate of the catalysts of Examples 1-3 can reach more than 90% after continuous operation for 30 days, indicating that the catalysts have excellent stability.

[0119] The difference between Comparative Example 1 and Example 2 is that the precursor liquid does not contain dopamine during the catalyst preparation process, so the catalytic active layer of the catalyst finally obtained does not contain a carbon layer and is not doped with nitrogen, which affects the catalytic activity and thus reduces the COD reduction rate. More importantly, due to the lack of the combination of the carbon layer and the carrier, the binding between the metal ions and the carrier is poor, which is ultimately reflected in the poor COD reduction rate retention rate of only 73.3% after 30 days of continuous operation.

[0120] The difference between Comparative Example 2 and Example 2 is that the dopamine content in the precursor liquid during the catalyst preparation process is relatively high, resulting in a COD reduction rate that is not as good as that of Examples 1-3. Analysis shows that the reason may be that excessive polydopamine production has blocked the carrier pore space to a certain extent, resulting in the metal elements being unable to fully contact with ozone and organic wastewater, resulting in a decrease in catalytic efficiency.

[0121] The difference between Comparative Examples 3 and 4 and Example 2 is that the catalyst does not contain magnesium or zinc, respectively. By comparing the results, it can be seen that the catalytic effect of single zinc or magnesium is significantly inferior to that of magnesium + zinc, indicating that there is a synergistic effect between magnesium and zinc.

[0122] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0123] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for treating organic wastewater by ozone catalytic oxidation, characterized in that The following steps are involved: 1) Sedimentation of organic wastewater; 2) The organic wastewater and ozone are introduced into a reactor filled with a catalyst, and wastewater with degraded organic pollutants is obtained after ozone catalytic oxidation reaction; The catalyst includes porous silica microspheres as a carrier and a catalytically active layer attached to the surface of the carrier pores. The catalytically active layer is a magnesium-zinc-nitrogen composite-doped porous carbon layer. The catalytically active layer is formed by in-situ carbonization of magnesium-zinc hydroxide-doped polydopamine on the surface of the carrier pores.

2. The method according to claim 1, wherein: In step 1), the COD value of the organic wastewater is 100-600 mg / L.

3. The method according to claim 1, wherein: Step 1) specifically includes: passing the organic wastewater into a sedimentation tank for sedimentation, with a residence time of 5-20 hours.

4. The method according to claim 1, wherein: In step 2), The flow rate of the organic wastewater is 50-200 L / h; The ozone flow rate is 40-100 mL / min.

5. The method according to claim 1, wherein: In step 2), the temperature of the ozone catalytic oxidation reaction is 10-40° C., and the time is 20-200 min.

6. The method according to claim 1, wherein: In step 2), the specific surface area of ​​the porous silica microspheres is 200-500m 2 / g, particle size is 1-10mm.

7. The method according to claim 1, wherein: In step 2), the preparation method of the catalyst comprises: A) adding dopamine, magnesium salt, and zinc salt to water under anaerobic conditions and stirring uniformly to disperse the carrier in the resulting precursor solution; B) adding alkaline solution dropwise to the precursor solution under oxygen-containing conditions and stirring the reaction, followed by filtering to obtain a carrier having a magnesium zinc hydroxide-doped polydopamine layer attached to the pore surface; C) calcining the product of step B) in the absence of oxygen, so that the magnesium zinc hydroxide-doped polydopamine layer is carbonized into a magnesium zinc nitrogen composite-doped porous carbon layer, thereby obtaining a catalyst.

8. The method according to claim 7, wherein: In step A), The concentrations of dopamine, magnesium ions, and zinc ions in the precursor fluid are (0.4-0.8) mol / L, (0.2-0.4) mol / L, and (0.1-0.2) mol / L, respectively; The ratio of the carrier to the precursor liquid is 50-150 g / L.

9. The method according to claim 7, wherein: In step B), the alkali solution is aqueous ammonia, and the target pH is 8-10.

10. The method according to claim 7, wherein: In step C), the calcination temperature is 700-1100° C. and the calcination time is 4-8 hours.

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