A sludge-based biochar for enhanced ozonation sludge dewatering, its preparation method and application

Abstract

This invention discloses a sludge-based biochar for enhancing ozonation sludge dewatering, its preparation method, and its application. Calcium hydroxide and aluminum oxide are uniformly mixed in a specific ratio and calcined to obtain calcium aluminum stone, i.e., Ca... 12 Al 14 O 33 The sludge is ground into powder and passed through a 100-mesh sieve. Sludge, calcium aluminum stone powder, and activator are uniformly mixed in a specific ratio and then treated by hydrothermal carbonization to prepare sludge-based biochar. The method for using this sludge-based biochar to condition sludge includes: adding the sludge-based biochar to a wastewater treatment plant (95% moisture content) and stirring uniformly; while stirring, introducing ozone into the product. The sludge-based biochar prepared by this invention, when added to an ozone oxidation sludge treatment system, can improve ozone utilization and sludge dewatering efficiency.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment and environmental engineering technology, specifically to a sludge-based biochar for enhanced ozonation sludge dewatering, its preparation method, and its application. Background Technology

[0002] Sludge is a major solid waste generated during wastewater treatment. It has high water content and high organic matter content, and direct landfilling poses problems such as secondary pollution and disposal difficulties. Currently, even after dewatering, sludge still has a high water content, typically around 70%-80%, and a high organic matter content, resulting in the emission of toxic and harmful substances and foul odors, seriously affecting the urban environment and the daily lives of surrounding residents. Therefore, reducing, recycling, and rendering harmless the dewatered sludge is of great significance for improving wastewater treatment efficiency and environmental quality.

[0003] Existing methods for treating dewatered sludge mainly include landfill, composting, and incineration. These methods all have limitations. Landfilling requires significant land resources and is prone to secondary pollution; composting requires substantial land resources and time and is prone to producing foul odors; incineration requires large amounts of energy and also causes secondary pollution. In contrast, ozone oxidation is a green, environmentally friendly, and cost-effective treatment method, but it currently suffers from low ozone utilization and poor dewatering performance of ozonated sludge. In recent years, to improve ozone utilization, functional materials have been added to the ozone treatment process to enhance ozone decomposition and generate hydroxyl radicals, thereby breaking down the sludge gel structure and degrading hydrophilic organic matter. However, existing functional materials still suffer from problems such as large dosage requirements, low efficiency, and the potential for secondary pollution. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing sludge-based biochar that enhances the dewatering of ozonated sludge. By using residual sludge from urban wastewater treatment plants as the main component to prepare sludge-based biochar, this method can not only improve the efficiency of catalytic ozone oxidation in degrading organic matter in sludge, but also promote the resource-based reuse of sludge.

[0005] The second objective of this invention is to provide the application of sludge-based biochar for enhanced ozonation sludge dewatering prepared by the above-mentioned preparation method, which can significantly improve sludge dewatering performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing sludge-based biochar for enhanced ozonation sludge dewatering, comprising the following steps:

[0008] Step 1: Mix calcium hydroxide and aluminum oxide in a uniform ratio and calcine to obtain calcium aluminum stone, i.e., Ca... 12 Al 14 O33 Grind into powder and pass through a 100-mesh sieve;

[0009] Step 2: Mix sludge, calcium aluminum stone powder and activator in a uniform ratio, and then process them by hydrothermal carbonization to prepare sludge-based biochar.

[0010] In one embodiment of the first aspect, in step 2, the mass ratio of the sludge, calcium aluminate powder and activator is 65%-80%: 15%-30%: 1%-5% by weight percentage.

[0011] In one embodiment of the first aspect, in step 1, the Ca:Al molar ratio of the calcium hydroxide and aluminum oxide is 1-1.3:1 in molar percentage.

[0012] In one embodiment of the first aspect, in step 2, the activator is selected from any one or more of solid potassium hydroxide, sodium hydroxide, hydrochloric acid, zinc chloride, or an aqueous solution of potassium hydroxide, or a combination thereof.

[0013] In one embodiment of the first aspect, in step 1, the calcination temperature is 1000-1500℃ and the time is 0.5-4h.

[0014] In one embodiment of the first aspect, in step 2, the hydrothermal carbonization method is carried out in a closed reactor for a reaction time of 1-4 hours and a reaction temperature of 150-250°C.

[0015] In a second aspect, the present invention provides the application of sludge-based biochar for enhanced ozonation sludge dewatering prepared by the preparation method described in the first aspect, which removes organic matter from sludge and improves dewatering efficiency, wherein the method includes:

[0016] Step a: Add the sludge-based biochar to the sludge (95% moisture content) from the municipal wastewater treatment plant and stir evenly;

[0017] Step b: While stirring, introduce ozone into the product of step a.

[0018] In one embodiment of the second aspect, the amount of sludge-based biochar is 100-500 mg / g TS, preferably 200-500 mg / g TS, and more preferably 300-500 mg / g TS, based on the weight of the sludge, wherein TS represents the dry weight of the sludge.

[0019] In one embodiment of the second aspect, 5-30 mg / L of ozone is introduced into the sludge at a gas flow rate of 1 L / min for 20 min, and the dosage is 10-60 mg / gTS.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This application uses sludge as the main raw material to prepare sludge-based biochar, which is a solid waste resource utilization and meets the national requirements for energy conservation, environmental protection and carbon emission reduction. The surface of the sludge-based biochar is rich in a large number of active groups such as hydroxyl and carbonyl groups, which can effectively catalyze ozone to generate a large number of active oxygen free radicals, greatly improving ozone utilization efficiency and sludge dewatering effect.

[0022] (2) The sludge-based biochar loaded with calcium aluminum stone prepared in this application can adsorb anions in the sludge liquid phase, such as CO3. 2 -、Cl - NO3 - H2PO4 - and HCO3 - This reduces the free radical quencher components in the system and improves the system's oxidation efficiency. Simultaneously, the prepared biochar particles are small, with a loose and porous surface, and are rich in calcium aluminum oxide and the reacted Fred salt (3CaO·Al2O3·CaCl2·10H2O), which can effectively serve as a sludge skeleton building block, constructing drainage channels to promote sludge moisture release.

[0023] (3) As a strong oxidant, ozone does not produce any harmful residues or secondary pollution during sludge treatment. Compared with traditional chemical treatment methods, ozone sludge conditioning is more environmentally friendly and pollution-free. In addition, ozone decomposes into oxygen after reaction and is released, which will not cause harm to environmental safety or human health. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process for preparing and applying sludge-based biochar according to an embodiment of this application.

[0025] Figure 2 This is the XRD pattern of the sludge bio-based char prepared in the embodiments of this application.

[0026] Figure 3 This is a SEM image of the sludge-based biochar prepared in the embodiments of this application.

[0027] Figure 4 This is a diagram showing the elemental content of the sludge-based biochar prepared in the embodiments of this application. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] The "range" disclosed in this document is represented in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive of endpoints and can be combined with each other; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0030] In this application, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0031] In this application, the words "above" or "below" following a number include the number itself. For example, "below 5" means less than or equal to 5, and "above 7" means greater than or equal to 7.

[0032] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0033] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0034] In this application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0035] In this application, unless otherwise specified, the term "comprising" as used herein can be either open-ended or closed-ended. For example, "comprising" may mean that it may also include other components not listed, or it may only include the listed components.

[0036] The above description is also the conventional expression method used in this field. It should be emphasized that the figures shown and the descriptions below are merely some specific embodiments of the present invention, and the scope of protection of the present invention is not limited to these specific embodiments. The scope of protection of the present invention is defined by the claims, and may include any technical means within the scope of the claims, including but not limited to further improvements and substitutions to these specific embodiments.

[0037] The method described in this application will now be explained in detail.

[0038] In the first aspect, a method for preparing sludge-based biochar with enhanced ozone oxidation efficiency is provided, the route being as follows: Figure 1 As shown, the method may include the following steps 1-3.

[0039] Step 1: Mix calcium hydroxide and aluminum oxide in a uniform ratio, calcine to obtain calcium aluminum stone, grind it into powder, and pass it through a 100-mesh sieve;

[0040] In one specific implementation, the mixing is done in a ratio, such as 1:1, 2:1, or 3:1.

[0041] In one specific embodiment, the calcination is carried out at high temperatures, such as 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, or 1500°C.

[0042] Step 2: Mix sludge, calcium aluminum stone powder and activator in a uniform ratio, and then process them by hydrothermal carbonization to prepare sludge-based biochar.

[0043] In one specific embodiment, the sludge comprises 65%-80% of the total amount of sludge, calcium aluminate powder, and activator. For example, the sludge comprises 65%, 70%, 75%, or 80% of the total amount of sludge, calcium aluminate powder, and activator, or any range thereof. This application does not limit the source of the sludge; for example, the sludge may originate from industrial wastewater or domestic sewage treatment.

[0044] In one specific embodiment, the calcium aluminate powder accounts for 15%-30% of the total amount of sludge, calcium aluminate powder, and activator by weight. For example, the calcium aluminate powder accounts for 15%, 20%, 25%, or 30% of the total amount of sludge, calcium aluminate powder, and activator by weight.

[0045] In one specific implementation, the molar ratio of Ca to Al in calcium aluminum stone is Ca:Al = 1-1.3:1.

[0046] In one specific embodiment, the activator accounts for 1%-5% of the total amount of sludge, calcium aluminate powder, and activator by weight. For example, the activator accounts for 1%, 2%, 3%, 4%, and 5% of the total amount of sludge, calcium aluminate powder, and activator by weight.

[0047] In one specific embodiment, the activator is selected from any one or more of solid potassium hydroxide, sodium hydroxide, hydrochloric acid, zinc chloride, or an aqueous solution of potassium hydroxide, or a combination thereof. In one specific embodiment, the activator is solid potassium hydroxide. In another specific embodiment, the activator is sodium hydroxide. In another specific embodiment, the activator is hydrochloric acid. In another specific embodiment, the activator is zinc chloride. In yet another specific embodiment, the activator is an aqueous solution of potassium hydroxide.

[0048] In one specific embodiment, the hydrothermal process is carried out at a temperature of 150-250°C, for example, at 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C. The heating in step 3 causes the mixture to form porous sludge-based biochar.

[0049] In a second aspect of this application, a method is provided for removing organic matter from sludge and improving dewatering efficiency using sludge-based biochar as described in the first aspect of this application, the method comprising:

[0050] Step a: Add the sludge-based biochar to the sludge (95% moisture content) from the municipal wastewater treatment plant and stir evenly.

[0051] In one specific embodiment, the amount of sludge-based biochar is 100-500 mg / g TS, preferably 200-500 mg / g TS, and more preferably 300-500 mg / g TS, based on the weight of the sludge. For example, sludge-based biochar of 300 mg / g TS, 350 mg / g TS, 400 mg / g TS, 450 mg / g TS, and 500 mg / g TS are added.

[0052] Step b: While stirring, introduce ozone into the product of step a.

[0053] In one specific embodiment, the ozone introduction refers to the introduction of ozone at a concentration of 5-30 mg / L, a gas flow rate of 1 L / min, and an aeration time of 20 min. For example, ozone concentrations of 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, and 30 mg / L can be introduced.

[0054] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0055] In the following examples, the sludge was taken from the Changzhou Shenshui Chengbei Wastewater Treatment Plant; calcium hydroxide, aluminum oxide, and potassium hydroxide were all commercially available products.

[0056] Example 1: Preparation of sludge-based biochar

[0057] (1) Prepare calcium aluminum stone by uniformly mixing calcium hydroxide and aluminum oxide in a certain proportion.

[0058] Weigh out 7.4g of calcium hydroxide and 5.1g of aluminum oxide at room temperature. Mix the two powders thoroughly and add them to a tube furnace, then heat at 1200℃ for 3 hours. After heating is complete and cooling to room temperature, weigh out 8.743g of the mixture. Grind the coarse calcium aluminum oxide into fine particles and pass them through a 100-mesh sieve.

[0059] (2) Preparation of sludge-based biochar loaded with calcium aluminum stone

[0060] At room temperature, 30g of sludge, 8.7g of calcium aluminum stone, and 1.3g of sodium hydroxide were weighed out. After the above substances were thoroughly mixed, they were added to a hydrothermal reactor. Under sealed conditions, the temperature was maintained at 200℃ and heated for 3 hours. After the heating was completed and the reactor was cooled to room temperature, the product was taken out and vacuum filtered. The product was dried in an oven at 80℃ and then ground to 100 mesh to obtain 20.48g of the final product.

[0061] Example 2: Preparation of sludge-based biochar

[0062] (1) Prepare calcium aluminum stone by uniformly mixing calcium hydroxide and aluminum oxide in a certain proportion.

[0063] Weigh out 9.62g of calcium hydroxide and 5.1g of aluminum oxide at room temperature. Mix the two powders thoroughly and add them to a tube furnace, then heat at 1500℃ for 2 hours. After heating is complete and cooling to room temperature, weigh out 9.7184g. Grind the coarse calcium aluminum oxide into fine particles and pass them through a 100-mesh sieve.

[0064] (2) Preparation of sludge-based biochar loaded with calcium aluminum stone

[0065] At room temperature, 20g of sludge, 9.7g of calcium aluminum stone, and 1.2g of potassium hydroxide were weighed out. After the above substances were thoroughly mixed, they were added to a hydrothermal reactor. Under sealed conditions, the temperature was maintained at 250℃ and heated for 4 hours. After the heating was completed and the reactor was cooled to room temperature, the product was taken out and vacuum filtered. The product was dried in an oven at 80℃ and then ground to 100 mesh to obtain 14.81g of the final product.

[0066] Example 3: Preparation of sludge-based biochar

[0067] (1) Prepare calcium aluminum stone by uniformly mixing calcium hydroxide and aluminum oxide in a certain proportion.

[0068] Weigh out 8.88g of calcium hydroxide and 5.1g of aluminum oxide at room temperature. Mix the two powders thoroughly and add them to a tube furnace, then heat at 1000℃ for 1 hour. After heating is complete and cooling to room temperature, weigh out 8.6428g of the mixture. Grind the coarse calcium aluminum oxide into fine particles and pass them through a 100-mesh sieve.

[0069] (2) Preparation of sludge-based biochar loaded with calcium aluminum stone

[0070] At room temperature, 20g of sludge, 8.6g of calcium aluminum stone, and 1.1g of zinc chloride were weighed out. After the above substances were thoroughly mixed, they were added to a hydrothermal reactor. Under sealed conditions, the temperature was maintained at 150℃ and heated for 3 hours. After the heating was completed and the reactor was cooled to room temperature, the product was taken out and vacuum filtered. It was then dried in an oven at 80℃ and ground to 100 mesh to obtain 13.96g of the final product.

[0071] Depend on Figure 2 The XRD pattern shown and Figure 4 The elemental composition diagram shown indicates that the biochar prepared in this invention contains a large amount of metal oxides (such as Al2O3, CaO, and Ca). 12 Al 14 O 33 This process (e.g., hydroxyl, carbonyl groups) enriches the surface of biochar with numerous active groups. When ozone is introduced, it effectively catalyzes the generation of large amounts of reactive oxygen species, efficiently oxidizing and degrading hydrophilic organic matter, thus significantly improving sludge dewatering. The calcium aluminum ore in biochar can adsorb anions in the sludge, such as CO32-. 2 The presence of free radical quencher components such as Cl-, NO3-, H2PO4-, and HCO3- can reduce the free radical quencher components in the system and improve the oxidation efficiency of the system.

[0072] from Figure 3The SEM images show that the prepared biochar particles are small, with a loose and porous surface, and are rich in calcium aluminum stone and the reactant salt (3CaO·Al2O3·CaCl2·10H2O), which can effectively serve as a sludge skeleton building block and construct drainage channels to promote the release of sludge moisture.

[0073] Example 4: Sludge-based biochar enhances ozone oxidation dewatering effect

[0074] At room temperature, 200 mL of sludge with a moisture content of 95% was weighed and added at the amounts shown in Table 1 below. Ozone at the concentrations shown in Table 1 was introduced while stirring, with a gas flow rate of 1 L / min and an aeration time of 20 min. The sludge was then filtered using a plate and frame filter press at a pressure of 1 MPa for 30 min. The moisture content of the sludge cake was measured and is shown in Table 1 below.

[0075] Table 1

[0076]

[0077] As can be seen from the above examples, adding 10 mg of the product from Example 1 to 200 mL of sludge with a moisture content of 95%, and then introducing ozone at a flow rate of 1 L / min for 20 min yielded the best results. The sludge was then filtered using a plate and frame filter press at a pressure of 1 MPa for 30 min. The moisture content of the sludge cake was measured to be 58.13%.

[0078] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing sludge-based biochar for enhanced ozonation sludge dewatering, characterized in that, Includes the following steps: Step 1: Mix calcium hydroxide and aluminum oxide in a uniform ratio and calcine to obtain calcium aluminum stone, i.e., Ca... 12 Al 14 O 33 The calcium hydroxide and aluminum oxide are ground into powder and passed through a 100-mesh sieve; wherein, by molar percentage, the Ca:Al molar ratio in the calcium hydroxide and aluminum oxide is 1-1.3:

1. Step 2: Sludge, calcium aluminate powder, and activator are mixed evenly in a certain proportion and then treated by hydrothermal carbonization to prepare sludge-based biochar rich in calcium aluminate and the reactant salt 3CaO·Al2O3·CaCl2·10H2O; wherein, by weight percentage, the mass ratio of sludge, calcium aluminate powder, and activator is 65%-80%: 15%-30%: 1%-5%; the hydrothermal carbonization is carried out in a closed reactor for 1-4 hours at a temperature of 150-250℃.

2. The method for preparing sludge-based biochar for enhanced ozonation sludge dewatering according to claim 1, characterized in that, In step 2, the activator is selected from any one or more of potassium hydroxide, sodium hydroxide, hydrochloric acid, and zinc chloride, or a combination thereof.

3. The method for preparing sludge-based biochar for enhanced ozonation sludge dewatering according to claim 1, characterized in that, In step 1, the calcination temperature is 1000-1500℃ and the time is 0.5-4 h.

4. The application of the sludge-based biochar for enhanced ozonation sludge dewatering prepared by the method described in claim 1 in sludge dewatering.

5. The application according to claim 4, characterized in that, The specific steps include: Step a: Add the sludge-based biochar to the sludge from the urban wastewater treatment plant with a moisture content of 95% and stir evenly; Step b: While stirring, introduce ozone into the product of step a.

6. The application according to claim 5, characterized in that, The amount of sludge-based biochar is 100-500 mg / g TS based on the weight of the sludge, where TS represents the dry weight of the sludge.

7. The application according to claim 5, characterized in that, Introduce 5-30 mg / L ozone into the sludge at a flow rate of 1 L / min for 20 min, with a dosage of 10-60 mg / g TS.

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