Sludge-based adsorption material and preparation method thereof

Abstract

The preparation method comprises the following steps: (1) washing residual sludge until the conductivity is lower than 100 [mu] s / cm, removing oxygen, heating to 130-150 DEG C, carrying out a stirring reaction, cooling after the reaction, and carrying out solid-liquid separation; (2) adding water into the separated liquid phase while stirring, then adding 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride, acrylamide and ammonium persulfate, carrying out polymerization reaction, and drying at low temperature after the reaction is completed to obtain a component I; (3) after the solid phase in the step (1) is resuspended, alkali is added for hydrothermal carbonization, acid leaching activation is performed after reaction, and after centrifugation, solid low-temperature drying is performed to obtain a component II; and (4) mixing the component I and the component II in proportion to prepare the adsorption material. The residual sludge is used as the raw material to prepare the adsorbing material, the reaction condition is mild, the preparation process is simple, the adsorbing material has a good adsorption effect on suspended solids, COD and metal ions in sewage, and reduction, harmlessness and recycling treatment of the residual sludge are achieved.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment, specifically relating to a sludge-based adsorbent material and its preparation method. Background Technology

[0002] Currently, sludge treatment in my country is still in its initial stage, with commonly used technologies including anaerobic digestion, drying and incineration, and emergency landfill. Anaerobic digestion produces large amounts of sludge digestate with high ammonia nitrogen and low carbon-to-nitrogen ratio, and the effective treatment of nitrification liquor remains a major challenge. Incineration is energy-intensive and generates high carbon emissions. Landfilling can lead to land waste, geological disasters, and groundwater and air pollution, impacting the environment. Therefore, there is an urgent need to develop economical, efficient, and pollution-free methods for the resource-based treatment of excess sludge.

[0003] CN202010222166.3 discloses a biochar adsorbent material based on sulfate-reduced sludge and its preparation method. First, the sulfate-reduced sludge is sequentially sieved, washed, and dried to obtain dried sludge. Then, under a protective atmosphere, the dried sludge is pyrolyzed to obtain the biochar adsorbent material based on the sulfate-reduced sludge. This patent enables the resource utilization of sulfate-reduced sludge, utilizing the sulfur enriched within the sludge to modify the biochar material, exhibiting good adsorption effects on heavy metals and dyes.

[0004] CN202211347892.3 discloses a sludge-based activated carbon, its preparation method, and its application in the adsorption of organic matter in wastewater. The activated carbon comprises the following raw material components by weight: 40-60 parts sludge particles, 15-30 parts agricultural and forestry waste particles, 10-30 parts binder, and 3-20 parts water. After mixing, the raw materials undergo carbonization, chemical activation, and physical activation treatments, followed by cooling, washing with acid and water sequentially, and drying to obtain the finished sludge-based activated carbon. During the chemical activation process, the composite raw carbon obtained after carbonization is mixed with a 2-5 mol / L activator solution at a mass ratio of 1:(1-4), and impregnated at room temperature for 12-36 hours, followed by drying to constant weight. It exhibits strong adsorption capacity for organic matter in wastewater. The main raw materials used are sludge and agricultural and forestry waste, which not only facilitates the resource utilization of sludge and agricultural and forestry waste but also effectively reduces the production cost of activated carbon.

[0005] The aforementioned patents all involve preparing carbon adsorbent materials from residual sludge, requiring a high-temperature carbonization process. This carbonization process involves relatively high temperatures and energy consumption. Furthermore, the properties of materials prepared using different methods vary significantly, and their overall performance needs improvement.

[0006] Hydrothermal technology is a thermochemical conversion technology that can produce value-added products using wet biomass under relatively mild reaction conditions. Hydrothermal products include solid carbonaceous materials known as hydrothermal carbon, gases mainly composed of carbon dioxide, and hydrothermal liquids containing organic matter.

[0007] Wang Lingzhi et al. (Feasibility Study on the Preparation of Organic Aggregating Media from Sewage Sludge, Industrial Water Treatment, Vol. 42, No. 10, October 2022) found that proteins and polysaccharides in sewage sludge undergo hydrolysis, dehydration, decarboxylation, polymerization, aromatization, and Maillard reactions under hydrothermal conditions. The water-soluble organic polymer (SOP) formed by this repolymerization and recondensation process can be used to prepare aggregation media. Therefore, they proposed that the SOP obtained by hydrothermal treatment of sewage sludge, after modification into an aggregation media with adsorption function, be reintroduced into sewage for the enrichment of organic matter.

[0008] Zhang Yue et al. (Generation Characteristics of Hydrothermal Liquid Phase Products of Sludge under Different Conditions, Journal of Environmental Engineering, Vol. 17, No. 9, September 2023) conducted hydrothermal treatment on urban sewage sludge to obtain water-soluble organic polymers that can be modified into aggregation media. The results showed that the hydrothermal reaction conditions were most suitable at 150℃, 0.5 h, and a NaOH dosage of 10% of the sludge dry weight, yielding SOPs that are more suitable as precursors for aggregation media.

[0009] The above method yields SOPs that can serve as precursors for aggregation media. However, there are currently no specific research and development paths or products for modifying and optimizing reaction conditions to prepare more comprehensive high-performance polymers. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a sludge-based adsorbent material and its preparation method. This invention uses surplus sludge as raw material to prepare the adsorbent material. The reaction conditions are mild, the preparation process is simple, and it exhibits excellent adsorption properties for suspended solids, COD, and metal ions in wastewater, achieving the reduction, harmlessness, and resource-based disposal of surplus sludge.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] The first aspect of this invention provides a method for preparing a sludge-based adsorbent material, comprising the following steps:

[0013] (1) Wash the remaining sludge until the conductivity is below 100 μs / cm, deoxygenate it in the reactor, heat it to 130-150℃ and stir it to react, cool it down after the reaction, and separate the solid and liquid.

[0014] (2) The liquid phase separated in step (1) is mixed with water under stirring, and then 3-chloro-2-hydroxypropyl-trimethylammonium chloride, acrylamide and ammonium persulfate are added to carry out a polymerization reaction. After the reaction is completed, the liquid phase is dried at low temperature to obtain component I.

[0015] (3) After the solid phase is resuspended in step (1), alkali is added for hydrothermal carbonization. After the reaction, acid leaching and activation are performed. After centrifugation, the solid is dried at low temperature to obtain component II.

[0016] (4) Mix component I and component II in a certain proportion to obtain an adsorption material.

[0017] In this invention, the residual sludge in step (1) comes from the residual sludge generated by the aerobic tank, anaerobic tank or secondary sedimentation tank, wherein the sludge moisture content is not less than 90%, and is generally between 90% and 99%.

[0018] In this invention, the washing of the remaining sludge in step (1) is done with deionized water, and the sludge is rinsed until the conductivity is below 100 μs / cm before being placed in the reactor. Deoxygenation can be performed using nitrogen or inert gases such as helium to remove air from the reactor, and the reactor is sealed after deoxygenation.

[0019] In this invention, the heating rate in step (1) is 3-5℃ / min, and the temperature is raised to 130-150℃ for 0.5-1.0h, with a stirring speed of 150-200r / min. After the reaction is completed, the temperature is lowered, which can be done by circulating cooling water to room temperature and atmospheric pressure.

[0020] In this invention, the solid-liquid separation in step (1) can be carried out by centrifugation, preferably by centrifugation at 5000-8000 r / min for 1-10 min to obtain the liquid phase and the solid phase respectively.

[0021] In this invention, the liquid phase separated in step (2) is stirred at 50-80 r / min, and 40-60 times the mass of deionized water is added first, followed by 0.1-0.5 times the mass of 3-chloro-2-hydroxypropyl-trimethylammonium chloride, 1-5 times the mass of acrylamide and 0.01-0.2 times the mass of ammonium persulfate to carry out a polymerization reaction.

[0022] In this invention, step (2) adjusts the pH to 5.0-6.0, and any one or more inorganic acids can be used, preferably 0.1-0.5M dilute hydrochloric acid.

[0023] In this invention, the conditions for the polymerization reaction in step (2) are: under anaerobic conditions, the reaction temperature is 60-75℃ and the reaction time is 2.0-3.0h.

[0024] In this invention, after the polymerization reaction in step (2), the material is dried at a low temperature of 50-70°C until the moisture content is less than 2%.

[0025] In this invention, the solid phase in step (3) is resuspended in an equal mass of deionized water. The alkali is an inorganic alkali, preferably one or more of KOH, NaOH, etc.; the amount of alkali added is 1%-2% of the mass of the mixture.

[0026] In this invention, the hydrothermal carbonization conditions in step (3) are: heating rate of 3-6℃ / min, temperature of 160-260℃, reaction time of 1-2h, and stirring speed of 150-300rpm.

[0027] In this invention, the acid leaching in step (3) uses one or more of sulfuric acid, phosphoric acid or nitric acid, and the mass concentration of the acid solution is 10%-20%.

[0028] In this invention, after the solid hydrothermal carbonization in step (3) is completed, it is mixed at a dosage of 5-10 g / L in the acid solution and reacted at room temperature for 1-2 hours.

[0029] In this invention, after the acid leaching reaction in step (3), the material is centrifuged and the solid is dried at a low temperature of 50-70°C until the moisture content is less than 3%.

[0030] In this invention, step (4) involves mixing component I and component II at a mass ratio of 1-5:100, preferably 1-3:100, to obtain an adsorbent material.

[0031] A second aspect of the present invention provides a sludge-based adsorbent material prepared using the method described above.

[0032] A third aspect of this invention provides an application of a sludge-based adsorbent material, used as a wastewater adsorbent for adsorbing suspended solids, dissolved organic matter, and Cu in water. 2+ Ions have good adsorption properties.

[0033] In the application of this invention, the concentration of suspended solids in the water is 100-300 mg / L.

[0034] In the application of this invention, the COD content in the water body is 60-1000 mg / L.

[0035] In the application of this invention, Cu in water 2+ The ion content is 1-50 mg / L.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) This invention uses residual sludge as raw material, and modifies the liquid and solid phases generated by hydrothermal treatment. The liquid phase is used to obtain a modified water-soluble organic polymer, i.e., component I, and the solid phase is used to obtain carbonized powder, i.e., component II. The two are then mixed in a certain proportion to obtain an adsorbent material, which is effective against suspended solids, COD, and Cu in water. 2+ It has a good adsorption and removal effect.

[0038] (2) This invention utilizes the liquid phase generated by hydrothermal treatment to prepare modified water-soluble organic polymers. Compared with directly using SOP, it has more suitable properties such as charge neutralization and adsorption bridging, and is effective in controlling COD and Cu in water. 2+ It exhibits better adsorption and improves removal efficiency.

[0039] (3) The preparation of adsorbent materials using residual sludge is carried out under mild reaction conditions and simple preparation process, which realizes the reduction, harmlessness and resource utilization of residual sludge. Detailed Implementation

[0040] The technical solution and its effects of the present invention will be further described in detail below through embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples can be purchased from biochemical reagent stores.

[0042] In this embodiment of the invention, Cu 2+ The detection method adopted was GB / T 17141-1997 "Determination of Copper in Water - Atomic Absorption Spectrometry"; COD concentration was determined by GB11914-89 "Determination of Chemical Oxygen Demand in Water - Potassium Dichromate Method"; suspended solids were determined by gravimetric method.

[0043] Example 1

[0044] The residual sludge from the secondary sedimentation tank of a sewage treatment plant in Dalian City had a moisture content of 91%.

[0045] (1) The remaining sludge was washed with deionized water until its conductivity was 80 μS / cm, placed in a reactor, and the air inside the reactor was replaced with nitrogen to remove oxygen. After deoxygenation, the reactor was sealed. The temperature was increased to 135℃ at a rate of 5℃ / min and reacted for 1.0 h with a stirring speed of 180 r / min. After the reaction, the temperature was lowered to room temperature and atmospheric pressure using circulating cooling water. The material in the reactor was centrifuged at 8000 r / min for 5 min to achieve solid-liquid separation, obtaining the liquid phase and solid phase respectively.

[0046] (2) The liquid phase separated in step (1) was stirred at 80 r / min and then mixed with 50 times its mass of deionized water, followed by 0.5 times its mass of 3-chloro-2-hydroxypropyl-trimethylammonium chloride, 2 times its mass of acrylamide, and 0.1 times its mass of ammonium persulfate. The pH was adjusted to 5.5 with 0.2 M hydrochloric acid, and the temperature was raised to 65 °C. The mixture was reacted under anaerobic conditions for 2.5 h. After the reaction, the mixture was dried at 70 °C until the moisture content was less than 2% to obtain component I.

[0047] (3) After resuspending the solid phase in step (1) with an equal mass of deionized water, 2% NaOH powder by mass of the mixture was added, and the temperature was increased to 200℃ at 5℃ / min, and the reaction was carried out for 2 hours with a stirring speed of 300 rpm. After the reaction was completed, 5 g / L of the solid phase was added to a 15% sulfuric acid solution and the reaction was carried out at room temperature for 1-2 hours. After centrifugation, the solid was dried at 70℃ until the moisture content was less than 3% to obtain component II.

[0048] (4) Mix component I and component II at a mass ratio of 1:100 to obtain the adsorption material.

[0049] Example 2

[0050] The residual sludge from the secondary sedimentation tank of a sewage treatment plant in Dalian City had a moisture content of 91%.

[0051] (1) The remaining sludge was washed with deionized water until its conductivity was 84 μS / cm, placed in a reactor, and the air inside the reactor was replaced with nitrogen to remove oxygen. After deoxygenation, the reactor was sealed. The temperature was increased to 150℃ at a rate of 5℃ / min and reacted for 0.5 h with a stirring speed of 200 r / min. After the reaction was completed, the temperature was lowered to room temperature and atmospheric pressure using circulating cooling water. The material in the reactor was centrifuged at 8000 r / min for 3 min to achieve solid-liquid separation, obtaining the liquid phase and solid phase respectively.

[0052] (2) The liquid phase separated in step (1) was mixed with 60 times its mass of deionized water under stirring at 80 r / min, followed by 0.5 times its mass of 3-chloro-2-hydroxypropyl-trimethylammonium chloride, 5 times its mass of acrylamide, and 0.2 times its mass of ammonium persulfate. The pH was adjusted to 6.0 with 0.2 M hydrochloric acid, and the temperature was raised to 65 °C. The mixture was reacted for 3 h under anaerobic conditions. After the reaction, the mixture was dried at 70 °C until the moisture content was less than 2%, to obtain component I.

[0053] (3) After resuspending the solid phase in step (1) with an equal mass of deionized water, 1% NaOH powder by mass of the mixture was added, and the temperature was increased to 260℃ at 6℃ / min, and the reaction was carried out for 2 hours with a stirring speed of 150 rpm. After the reaction was completed, it was added to a 20% sulfuric acid solution at a dosage of 10 g / L, and the reaction was carried out at room temperature for 2 hours. After centrifugation, the solid was dried at 70℃ until the water content was less than 3% to obtain component II;

[0054] (4) Mix component I and component II at a mass ratio of 3:100 to obtain the adsorption material.

[0055] Example 3

[0056] The residual sludge from the secondary sedimentation tank of a sewage treatment plant in Dalian City had a moisture content of 91%.

[0057] (1) The remaining sludge was washed with deionized water until its conductivity was 92 μS / cm, placed in a reactor, and the air inside the reactor was replaced with nitrogen to remove oxygen. After deoxygenation, the reactor was sealed. The temperature was increased to 140℃ at a rate of 3℃ / min and reacted for 0.8 h with a stirring speed of 150 r / min. After the reaction was completed, the temperature was lowered to room temperature and atmospheric pressure using circulating cooling water. The material in the reactor was centrifuged at 5000 r / min for 10 min to achieve solid-liquid separation, obtaining the liquid phase and solid phase respectively.

[0058] (2) The liquid phase separated in step (1) was mixed with 40 times its mass of deionized water under stirring at 50 r / min, followed by 0.1 times its mass of 3-chloro-2-hydroxypropyl-trimethylammonium chloride, 1 times its mass of acrylamide, and 0.1 times its mass of ammonium persulfate. The pH was adjusted to 6.0 with 0.5 M hydrochloric acid, and the temperature was raised to 75 °C. The mixture was reacted for 2 h under anaerobic conditions. After the reaction, the mixture was dried at 70 °C until the moisture content was less than 2%, to obtain component I.

[0059] (3) After resuspending the solid phase in step (1) with an equal mass of deionized water, 2% NaOH powder by mass of the mixture was added. The temperature was increased to 160℃ at 3℃ / min, and the reaction was carried out for 1 hour with a stirring speed of 300 rpm. After the reaction was completed, 5 g / L of the solid phase was added to a 10% sulfuric acid solution and the reaction was carried out at room temperature for 1 hour. After centrifugation, the solid was dried at 70℃ until the moisture content was less than 3% to obtain component II.

[0060] (4) Mix component I and component II at a mass ratio of 4:100 to obtain the adsorption material.

[0061] Example 4

[0062] Same as Example 1, except that: in step (3), the alkali used is KOH, and the acid leaching uses a 20% phosphoric acid solution. The final adsorbent material is thus prepared.

[0063] Comparative Example 1

[0064] Same as Example 1, except that steps (1) and (2) are omitted, and the remaining sludge is directly treated with alkali according to step (3) at 150°C for 0.5 h with NaOH added at 10% of the dry weight of the sludge. The adsorbent material is finally prepared.

[0065] Comparative Example 2

[0066] Same as Example 1, except that in step (2), octadecyltrimethylammonium chloride is used instead of 3-chloro-2-hydroxypropyl-trimethylammonium chloride to finally prepare the adsorbent material.

[0067] Comparative Example 3

[0068] Same as Example 1, except that: acrylamide was not used in step (2), and the final adsorbent material was prepared.

[0069] Comparative Example 4

[0070] Same as Example 1, except that the temperature of low-temperature drying in steps (2) and (3) is 85°C, and the adsorbent material is finally prepared.

[0071] Test Example 1

[0072] Wastewater from an electro-desalination plant with a COD concentration of 540 mg / L and a suspended solids concentration of 150 mg / L was collected. Different adsorbent materials prepared according to the embodiments and comparative examples of this invention were added to the wastewater at a concentration of 0.5 g / L. After stirring for 0.5 h, the COD and suspended solids in the effluent were measured. The results are shown in Table 1.

[0073] Table 1. Removal rates of COD and suspended solids in effluent

[0074]

[0075] Test Example 2

[0076] Simulated wastewater was used, with a COD concentration of 310 mg / L and a Cu concentration of... 2+ The ion concentration was 20 mg / L. The adsorbent material prepared according to the embodiments and comparative examples of this invention was added at a concentration of 0.5 g / L, and after stirring for 0.5 h, the COD and Cu in the effluent were detected. 2+ The test results are shown in Table 2.

[0077] Table 2. Effluent COD Removal Rate and Cu 2+ concentration

[0078]

Claims

1. A method for preparing a sludge-based adsorbent material, characterized in that... Includes the following steps: (1) Wash the remaining sludge until the conductivity is below 100 μs / cm, deoxygenate it in the reactor, heat it to 130-150℃ and stir it to react. After the reaction, cool it down and separate the solid and liquid. (2) In step (1), the liquid phase is separated and water is added under stirring, followed by 3-chloro-2-hydroxypropyl-trimethylammonium chloride, acrylamide, and ammonium persulfate to carry out a polymerization reaction. After the reaction is completed, the mixture is dried at low temperature to obtain component I. (3) After the solid phase is resuspended in step (1), alkali is added for hydrothermal carbonization. After the reaction, acid leaching and activation are carried out. After centrifugation, the solid is dried at low temperature to obtain component II. Component I and component II are mixed in proportion to obtain the adsorbent material.

2. The method according to claim 1, characterized in that: The residual sludge in step (1) comes from the residual sludge generated in the aerobic tank, anaerobic tank or secondary sedimentation tank, wherein the sludge moisture content is not less than 90%, preferably 90%-99%.

3. The method according to claim 1 or 2, characterized in that: Step (1) The remaining sludge is washed with deionized water; nitrogen and inert gases such as helium are used to remove air from the reactor for deoxygenation, and the reactor is sealed after deoxygenation.

4. The method according to claim 1, characterized in that: Step (1) The heating rate is 3-5℃ / min, and the temperature is raised to 130-150℃ for 0.5-1.0h. The stirring speed is 150-200r / min.

5. The method according to claim 1, characterized in that: Step (1) Solid-liquid separation is carried out by centrifugation. The liquid phase and solid phase are obtained by centrifugation at 5000-8000 r / min for 1-10 min.

6. The method according to claim 1, characterized in that: In step (2), the separated liquid phase is stirred at 50-80 r / min, and 40-60 times the mass of deionized water is added, followed by 0.1-0.5 times the mass of 3-chloro-2-hydroxypropyl-trimethylammonium chloride, 1-5 times the mass of acrylamide, and 0.01-0.2 times the mass of ammonium persulfate.

7. The method according to claim 1, characterized in that: Step (2) Adjust the pH to 5.0-6.0 using any one or more inorganic acids, preferably 0.1-0.5M dilute hydrochloric acid.

8. The method according to claim 1, characterized in that: The conditions for the polymerization reaction in step (2) are: under anaerobic conditions, the reaction temperature is 60-75℃ and the reaction time is 2.0-3.0h.

9. The method according to claim 1, characterized in that: After the polymerization reaction in step (2), the material is dried at a low temperature of 50-70℃ until the moisture content is less than 2%.

10. The method according to claim 1, characterized in that: The solid phase in step (3) is resuspended in an equal mass of deionized water; the alkali is an inorganic alkali, preferably one or more of KOH and NaOH; the amount of alkali added is 1%-2% of the mass of the mixture.

11. The method according to claim 1, characterized in that: The hydrothermal carbonization conditions in step (3) are: heating rate of 3-6℃ / min, temperature of 160-260℃, reaction time of 1-2h, and stirring speed of 150-300rpm.

12. The method according to claim 1, characterized in that: The acid leaching in step (3) uses one or more of sulfuric acid, phosphoric acid, and nitric acid, and the mass concentration of the acid solution is 10%-20%.

13. The method according to claim 1, characterized in that: After the solid hydrothermal carbonization in step (3) is completed, mix according to the addition amount of 5-10 g / L in the acid solution and react at room temperature for 1-2 hours.

14. The method according to claim 1, characterized in that: Step (3) After acid leaching, the material is centrifuged and the solid is dried at a temperature of 50-70℃ until the moisture content is less than 3%.

15. The method according to claim 1, characterized in that: Step (4) Mix component I and component II at a mass ratio of 1-5:100, preferably 1-3:100, to obtain the adsorbent material.

16. A sludge-based adsorbent material, characterized in that... It is prepared using the method of the present invention described above.

17. The application of a sludge-based adsorbent material prepared by the method according to any one of claims 1-15 or the sludge-based adsorbent material according to claim 16, characterized in that: Suspended solids, dissolved organic matter and Cu in water bodies 2+ Ions have good adsorption properties.

18. The application according to claim 17, characterized in that: The concentration of suspended solids in the water is 100-300 mg / L.

19. The application according to claim 17, characterized in that: The COD content in the water body is 60-1000 mg / L.

20. The application according to claim 17, characterized in that: Cu in water 2+ The ion content is 1-50 mg / L.

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