A method for preparing a deep phosphorus removal and residue base adsorbent applied to sewage sludge

Abstract

This invention belongs to the fields of environmental engineering and solid waste resource utilization technology, specifically relating to a method for preparing a residue-based adsorbent for deep phosphorus extraction from sewage sludge. The preparation method includes the following steps: S1, adjusting the sewage sludge to a moisture content of 90% and performing a first-stage hydrothermal carbonization, after which hydrothermal carbon and aqueous product 1 are separated; S2, leaching the hydrothermal carbon in a mixed acid, after which phosphorus extract and leaching residue are separated; S3, performing MAP precipitation of the phosphorus extract using struvite, after which struvite is obtained to achieve phosphorus recovery, and residual extract is separated; S4, performing a second-stage hydrothermal carbonization on the leaching residue, adding a mixture of aqueous product 1 and residual extract before the reaction, adjusting the solid-liquid ratio to 1:10; after the reaction, solid product and aqueous product 2 are separated; S5, rinsing the solid product and then drying it, after which a high-efficiency residue-based adsorbent is obtained.

Description

Technical Field

[0001] This invention belongs to the fields of environmental engineering and solid waste resource utilization technology, specifically relating to a method for preparing a residue-based adsorbent for deep phosphorus extraction from sewage sludge. Background Technology

[0002] With the acceleration of urbanization, my country's annual municipal sludge production exceeds 60 million tons, and traditional disposal methods mainly include landfill, incineration, and land application. However, landfill leads to the waste of land resources and the risk of leachate pollution, incineration produces toxic gases such as dioxins, and land application is subject to the risk of heavy metal and pathogen pollution. Existing technologies not only pose a risk of secondary pollution but also result in a serious waste of resources such as phosphorus and organic matter in the sludge. Against the backdrop of urgent demand for resource recycling, the value of phosphorus as a non-renewable strategic resource is becoming increasingly prominent—the phosphorus content in sludge can reach 90% of the total phosphorus in the wastewater influent, and global phosphate rock reserves can only last for 50-100 years. Current phosphorus recovery technologies generally suffer from low extraction efficiency (wet chemical extraction rate is less than 60%), poor product purity (phosphate product impurity content >15%), and the residue after extraction still faces the challenge of secondary disposal. Meanwhile, converting sludge into high-value-added products has become a key path to break through the bottleneck of resource utilization: Sludge is rich in carbon-based materials, pore structures and functional groups, and theoretically can be used to prepare residue-based adsorbents with high adsorption capacity. However, existing research focuses on the conversion of single materials, and generally suffers from defects such as large amount of activator, unstable pore structure and large fluctuation of adsorption capacity, resulting in product costs as high as 1.5 times that of commercial activated carbon.

[0003] The existing technology system suffers from a dual disconnect: phosphorus extraction and residue resource utilization are handled independently, leading to process redundancy. Furthermore, the lack of a synergistic mechanism between component regulation and pore construction during the preparation of residue-based adsorbents restricts both the economic feasibility of phosphorus recovery (processing cost > 1500 yuan / ton) and the market competitiveness of residue-based adsorbent products.

[0004] Existing technologies, such as "A Method for Stepwise Recovery and High-Value Conversion of Phosphorus from Sludge," improve phosphorus recovery rates, but do not consider the utilization of sludge residues, failing to achieve deep resource utilization of sludge. "A Method for Phosphorus Recovery from Sludge Pyrolysis Residue, a Method for Flocculant Synthesis and Application" optimizes residue utilization, but the lack of synergy between preceding phosphorus recovery and subsequent flocculant preparation limits resource utilization effectiveness. Sludge-based adsorbent preparation processes, such as "A Method for Preparing Residue-Based Adsorbents from Alumina Industrial Red Mud and Wastewater Treatment Sludge," and "A Method for Preparing Magnetic Biochar and its Preparation and Application, and a Method for Preparing Organic Fertilizer," suffer from problems such as large activator dosages and high costs. Therefore, there is an urgent need to develop integrated technologies for the deep extraction of phosphorus and the synergistic preparation of sludge-based and residue-based adsorbents to achieve efficient phosphorus resource recovery and value-added transformation of solid waste. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the objective of this invention can be achieved through the following technical solutions:

[0006] A method for synergistic preparation of a residue-based adsorbent, the preparation method specifically comprising the following steps:

[0007] S1. Adjust the sewage sludge to a moisture content of 85% to 95%, carry out a first-stage hydrothermal carbonization, and after the hydrothermal carbonization is completed, separate to obtain hydrothermal carbon and aqueous product 1.

[0008] S2. The hydrothermal carbon is placed in a mixed acid for extraction. After the extraction is completed, the phosphorus extract and the extraction residue are separated.

[0009] S3. MAP precipitation is performed on the phosphorus extract. After the recovery is completed, struvite is obtained to achieve phosphorus recovery. At the same time, the residual extract is separated.

[0010] S4. The leaching residue is subjected to two-stage hydrothermal carbonization. Before the reaction, a mixture of aqueous product 1 and residual extract is added to adjust the solid-liquid ratio to 1:10. After the reaction, the solid product and aqueous product 2 are separated.

[0011] S5. The solid product is washed and then dried. After drying, it becomes a residue-based high-efficiency residue-based adsorbent.

[0012] Furthermore, the hydrothermal carbonization in step S1 should have a reaction temperature between 200°C and 240°C, and a reaction time of 4 to 8 hours.

[0013] Further, in step S2, the mixed acid is a mixture of hydrochloric acid and citric acid, wherein the concentration of hydrochloric acid is 0.4M to 0.8M and the concentration of citric acid is 0.1M to 1.0M; the mass fraction of citric acid in the mixed acid is less than 90%.

[0014] Furthermore, in the leaching process of step S2, the liquid-to-solid ratio of the mixed acid and hydrothermal carbon depends on the mixed acid ratio. The liquid-to-solid ratio Y and the hydrochloric acid percentage a should satisfy the relationship Y = 500 - 450a, where 0.1 ≤ a ≤ 1. The leaching time depends on the mixed acid ratio and the hydrochloric acid concentration. The leaching time T1, the hydrochloric acid concentration CHCl, and the citric acid percentage b should satisfy the relationship T1 = 250CHCl + 300b. During the leaching process, the phosphorus extraction rate from the original sewage sludge is greater than 90%.

[0015] Furthermore, during the MAP precipitation process in step S3, the magnesium source is magnesium chloride and / or magnesium sulfate, and the nitrogen source is the reflux aqueous phase product 2.

[0016] Furthermore, in the second-stage hydrothermal carbonization process of step 4, the reaction temperature should be between 200℃ and 240℃, and the reaction time depends on the mixed acid ratio and hydrochloric acid concentration; the reaction time T2, the hydrochloric acid concentration CHCl and the hydrochloric acid percentage a should satisfy the relationship T2=240–140a+100CHCl.

[0017] Furthermore, in step S4, the mixing ratio of aqueous product 1 to residual extract should be between 1:1 and 2:1.

[0018] Further, in step S5, the solid product is washed until the wash water pH = 7, and then dried at 65-70°C.

[0019] A residue-based adsorbent, wherein the residue-based adsorbent is prepared by the aforementioned synergistic preparation method of a residue-based adsorbent.

[0020] The aforementioned residue-based adsorbent is used for the treatment of antibiotics in wastewater.

[0021] The beneficial effects of this invention are:

[0022] 1. Existing technologies suffer from a dual problem of fragmented processes: phosphorus extraction and residue resource utilization are handled separately, and there is a lack of synergistic mechanisms in component regulation and pore construction during residue-based adsorbent preparation. The integrated technology developed in this patent, which combines deep phosphorus extraction with the synergistic preparation of sludge-based and residue-based adsorbents, effectively solves this problem. By combining phosphorus extraction in the sewage and sludge treatment process with residue-based adsorbent preparation, process redundancy is avoided, treatment costs are reduced, the economic feasibility of phosphorus recovery is improved, and the market competitiveness of residue-based adsorbent products is enhanced.

[0023] 2. This patent achieves efficient recovery of phosphorus resources by obtaining struvite with a purity of ≥85% through MAP precipitation, thereby improving the recovery and utilization rate of phosphorus. At the same time, it transforms sewage sludge residue into a residue-based adsorbent with high adsorption performance for the treatment of antibiotics in wastewater, realizing the value-added transformation of solid waste.

[0024] 3. In the process of preparing residue-based adsorbents, this patent has precisely optimized and quantified the process parameters of each step; for example, the temperature and time of the first and second stage hydrothermal carbonization, the ratio of mixed acids, the liquid-solid ratio and the extraction time are all precisely controlled by the relationship formula, which ensures the stability and repeatability of the preparation process and improves product quality and production efficiency.

[0025] 4. The experimental data from the verification experiment show that the prepared residue-based adsorbent has a good adsorption effect on tetracycline, with a maximum equilibrium adsorption capacity of 189.1 mg / g and a maximum methylene blue removal rate of 94.6%, indicating that the adsorbent has broad application prospects in the field of wastewater treatment. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0027] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] like Figure 1 As shown, a method for deep phosphorus extraction from sewage sludge and synergistic preparation of a high-efficiency residue-based adsorbent includes the following steps:

[0031] 1. First-stage hydrothermal carbonization: Take sewage sludge with a moisture content of 90% (total phosphorus content of 1.8% dry basis), place it in a reactor, heat it to 220℃, react for 5 hours, and separate hydrothermal carbon (yield of 45%) and aqueous product 1 (pH=3.2).

[0032] 2. Mixed Acid Extraction: Hydrothermal charcoal and mixed acids (0.6M hydrochloric acid and 0.5M citric acid, mass ratio 1:1) are mixed at a liquid-to-solid ratio Y = 275 (calculated from Y = 500 - 450a, a = 0.5). The extraction time T1 = 300 minutes (calculated from T1 = 250 × 0.6 + 300 × 0.5 = 300), achieving a phosphorus extraction rate of 92.5%. The phosphorus extract is then separated from the extraction residue.

[0033] 3. MAP precipitation: Add MgCl2 and reflux aqueous phase product 2 to the phosphorus extract, adjust the pH to 9.0, precipitate struvite (purity ≥85%), and separate the residual extract (pH=8.5).

[0034] 4. Two-stage hydrothermal carbonization: The leaching residue, aqueous product 1, and residual extract are mixed at a ratio of 1.5:1 (W / W), with a solid-liquid ratio of 1:10. The reaction temperature is 220℃, and the time T2 = 240 - 140 × 0.5 + 100 × 0.6 = 250 minutes to generate a solid product.

[0035] 5. Preparation of residue-based adsorbent: The solid product was washed until pH=7 and dried at 65℃ to obtain the residue-based adsorbent.

[0036] Example 2

[0037] like Figure 1 As shown, a method for deep phosphorus extraction from sewage sludge and synergistic preparation of a high-efficiency residue-based adsorbent includes the following steps:

[0038] 1. First-stage hydrothermal carbonization: Take sewage sludge with a moisture content of 90% (total phosphorus content of 1.8% dry basis), place it in a reactor, heat it to 220℃, react for 5 hours, and separate hydrothermal carbon (yield of 45%) and aqueous product 1 (pH=3.2).

[0039] 2. Mixed Acid Extraction: Hydrothermal charcoal and mixed acids (0.6M hydrochloric acid and 0.5M citric acid, mass ratio 1:9) were mixed at a liquid-to-solid ratio of Y = 455 (calculated from Y = 500 - 450a, a = 0.1). The extraction time was T1 = 300 minutes (calculated from T1 = 250 × 0.6 + 300 × 0.9 = 420 minutes), and the phosphorus extraction rate reached 89.1%. The phosphorus extract was then separated from the extraction residue.

[0040] 3. MAP precipitation: Add MgCl2 and reflux aqueous phase product 2 to the phosphorus extract, adjust the pH to 9.0, precipitate struvite (purity ≥85%), and separate the residual extract (pH=8.5).

[0041] 4. Two-stage hydrothermal carbonization: The leaching residue, aqueous product 1, and residual extract are mixed at a ratio of 1.5:1 (W / W), with a solid-liquid ratio of 1:10. The reaction temperature is 220℃, and the time T2 = 240 - 140 × 0.1 + 100 × 0.6 = 286 minutes to generate a solid product.

[0042] 5. Preparation of residue-based adsorbent: The solid product was washed until pH=7 and dried at 65℃ to obtain the residue-based adsorbent.

[0043] Example 3

[0044] like Figure 1 As shown, a method for deep phosphorus extraction from sewage sludge and synergistic preparation of a high-efficiency residue-based adsorbent includes the following steps:

[0045] 1. First-stage hydrothermal carbonization: Take sewage sludge with a moisture content of 90% (total phosphorus content of 1.8% dry basis), place it in a reactor, heat it to 220℃, react for 5 hours, and separate hydrothermal carbon (yield of 45%) and aqueous product 1 (pH=3.2).

[0046] 2. Mixed Acid Extraction: Hydrothermal charcoal and mixed acids (0.6M hydrochloric acid and 0.5M citric acid, mass ratio 9:1) are mixed at a liquid-to-solid ratio Y = 95 (calculated from Y = 500 - 450a, a = 0.9). The extraction time T1 = 300 minutes (calculated from T1 = 250 × 0.6 + 300 × 0.1 = 180 minutes), achieving a phosphorus extraction rate of 94.4%. The phosphorus extract and extraction residue are then separated.

[0047] 3. MAP precipitation: Add MgCl2 and reflux aqueous phase product 2 to the phosphorus extract, adjust the pH to 9.0, precipitate struvite (purity ≥85%), and separate the residual extract (pH=8.5).

[0048] 4. Two-stage hydrothermal carbonization: The leaching residue, aqueous product 1, and residual extract are mixed at a ratio of 1.5:1 (W / W), with a solid-liquid ratio of 1:10. The reaction temperature is 220℃, and the time T2 = 240 - 140 × 0.9 + 100 × 0.6 = 174 minutes to generate a solid product.

[0049] 5. Preparation of residue-based adsorbent: The solid product was washed until pH=7 and dried at 65℃ to obtain the residue-based adsorbent.

[0050] Example 4

[0051] like Figure 1 As shown, a method for deep phosphorus extraction from sewage sludge and synergistic preparation of a high-efficiency residue-based adsorbent includes the following steps:

[0052] 1. First-stage hydrothermal carbonization: Take another sewage sludge with a water content of 90% (total phosphorus content 2.1% dry basis), place it in a reactor, heat it to 220℃, react for 5 hours, and separate hydrothermal carbon (yield 45%) and aqueous product 1 (pH=3.2).

[0053] 2. Mixed Acid Extraction: Hydrothermal charcoal and mixed acids (0.6M hydrochloric acid and 0.5M citric acid, mass ratio 9:1) are mixed at a liquid-to-solid ratio Y = 95 (calculated from Y = 500 - 450a, a = 0.9). The extraction time T1 = 300 minutes (calculated from T1 = 250 × 0.6 + 300 × 0.1 = 180 minutes), achieving a phosphorus extraction rate of 93.5%. The phosphorus extract and extraction residue are then separated.

[0054] 3. MAP precipitation: Add MgCl2 and reflux aqueous phase product 2 to the phosphorus extract, adjust the pH to 9.0, precipitate struvite (purity ≥85%), and separate the residual extract (pH=8.5).

[0055] 4. Two-stage hydrothermal carbonization: The leaching residue, aqueous product 1, and residual extract are mixed at a ratio of 1.5:1 (W / W), with a solid-liquid ratio of 1:10. The reaction temperature is 220℃, and the time T2 = 240 - 140 × 0.9 + 100 × 0.6 = 174 minutes to generate a solid product.

[0056] 5. Preparation of residue-based adsorbent: The solid product was washed until pH=7 and dried at 65℃ to obtain the residue-based adsorbent.

[0057] Verification experiment:

[0058] In this embodiment, the residue-based high-efficiency residue-based adsorbents prepared in Examples 1, 2, 3, and 4 were applied to the adsorption treatment of typical antibiotics, and the dye concentrations before and after adsorption were measured. The specific process was as follows: 0.025 g of the dyeing sludge-based high-efficiency residue-based adsorbents prepared in Examples 1, 2, 3, and 4 were weighed into a 250 mL stoppered conical flask containing 100 mL of tetracycline, oxytetracycline, and erythromycin solutions with an initial concentration of 50 mg / L. The conical flask was placed in a constant-temperature shaker and shaken under sealed conditions at 25℃ and 180 r·min⁻¹ until adsorption equilibrium was reached. After adsorption, the mixture was filtered through a 0.45 μm aqueous filter membrane. The remaining concentration of methylene blue was measured using a UV-Vis spectrophotometer. The results are shown in Tables 1 and 2.

[0059] Table 1. Adsorption results of tetracycline in Examples 1-4

[0060]

[0061] Table 2 Adsorption results of oxytetracycline in Examples 1-4

[0062]

[0063] According to the data in Tables 1 and 2 above,

[0064] 1. Analysis of tetracycline adsorption results

[0065] Example 2 showed the highest equilibrium adsorption capacity at 189.1 mg / g, while Example 3 showed the lowest at 165.4 mg / g. This indicates that the adsorption capacity of the residue-based adsorbent obtained under different preparation conditions for tetracycline varies. Example 2 achieved the highest removal rate of 94.6%, while Example 3 had the lowest at 82.7%. Overall, the preparation method of Example 2 performed best in terms of tetracycline adsorption, mainly due to the combined effect of factors such as the mixed acid ratio, liquid-solid ratio, and reaction time, which gave the adsorbent better tetracycline adsorption performance.

[0066] 2. Analysis of oxytetracycline adsorption results

[0067] Example 2 showed the highest equilibrium adsorption capacity at 167.9 mg / g, while Example 1 showed the lowest at 156.7 mg / g. Example 2 also exhibited the highest removal rate at 84.0%, compared to the lowest at 78.4% in Example 1. This indicates that the adsorbent in Example 2 demonstrated relatively good adsorption performance for oxytetracycline under the preparation conditions described in Example 2.

[0068] Therefore, it is evident that the adsorption capacity and removal rate of the residue-based adsorbents obtained under different preparation conditions vary significantly for tetracycline and oxytetracycline. In Example 2, the equilibrium adsorption capacity and removal rate for both tetracycline and oxytetracycline were relatively high, indicating that this preparation method is most effective in treating these two antibiotics. This is likely due to the combination of parameters such as the mixed acid ratio, liquid-solid ratio, and reaction time, which are more conducive to the formation of suitable pore structures and surface functional groups in the adsorbent, thereby enhancing its adsorption performance for tetracycline and oxytetracycline. Thus, this adsorbent has broad application prospects in the field of wastewater treatment.

[0069] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0071] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a residue-based adsorbent for deep phosphorus extraction from sewage sludge, characterized in that, The preparation method specifically includes the following steps: S1. Adjust the sewage sludge to a moisture content of 85% to 95%, carry out a first-stage hydrothermal carbonization, and after the hydrothermal carbonization is completed, separate to obtain hydrothermal carbon and aqueous product 1. S2. The hydrothermal carbon is placed in a mixed acid for extraction. After the extraction is completed, the phosphorus extract and the extraction residue are separated. S3. MAP precipitation is performed on the phosphorus extract. After the recovery is completed, struvite is obtained to achieve phosphorus recovery. At the same time, the residual extract is separated. S4. The leaching residue is subjected to two-stage hydrothermal carbonization. Before the reaction, a mixture of aqueous product 1 and residual extract is added to adjust the solid-liquid ratio to 1:

10. After the reaction, the solid product and aqueous product 2 are separated. S5. The solid product is washed and then dried. The dried product is a residue-based adsorbent. In step S2, the mixed acid is a mixture of hydrochloric acid and citric acid, wherein the concentration of hydrochloric acid is 0.4M to 0.8M and the concentration of citric acid is 0.1M to 1.0M; the mass fraction of citric acid in the mixed acid is less than 90%. The two-stage hydrothermal carbonization process in step S4 should have a reaction temperature between 200℃ and 240℃, and the reaction time depends on the mixed acid ratio and hydrochloric acid concentration. The reaction time T2, the hydrochloric acid concentration CHCl and the hydrochloric acid percentage a should satisfy the relationship T2=240–140a+100CHCl. In step S4, the mixing ratio of aqueous product 1 to residual extract is between 1:1 and 2:

1.

2. The method for preparing a synergistic residual-based adsorbent for deep phosphorus extraction from sewage sludge according to claim 1, characterized in that, The first-stage hydrothermal carbonization in step S1 should have a reaction temperature between 200℃ and 240℃, and a reaction time of 4 to 8 hours.

3. The method for preparing a synergistic residual-based adsorbent for deep phosphorus extraction from sewage sludge according to claim 1, characterized in that, In step S2, the liquid-to-solid ratio of the mixed acid to the hydrothermal carbon depends on the ratio of the mixed acid. The liquid-to-solid ratio Y and the proportion of hydrochloric acid a should satisfy the relationship Y = 500 - 450a, where 0.1 ≤ a ≤ 1. The leaching time depends on the ratio of the mixed acid and the concentration of hydrochloric acid. The leaching time T1, the concentration of hydrochloric acid CHCl, and the proportion of citric acid b should satisfy the relationship T1 = 250CHCl + 300b. During the leaching process, the leaching rate of phosphorus in the original sewage sludge is greater than 90%.

4. The method for preparing a synergistic residual-based adsorbent for deep phosphorus extraction from sewage sludge according to claim 1, characterized in that, In step S3, during the MAP precipitation process, the magnesium source is magnesium chloride and / or magnesium sulfate, and the nitrogen source is the reflux aqueous phase product 2.

5. The method for preparing a synergistic residual-based adsorbent for deep phosphorus extraction from sewage sludge according to claim 1, characterized in that, In step S5, the solid product is washed until the wash water pH = 7, and then dried at 65-70°C.

6. A residue-based adsorbent, characterized in that, The residue-based adsorbent is prepared by the method described in any one of claims 1 to 5 for preparing a residue-based adsorbent for deep phosphorus extraction in sewage sludge.

7. The residue-based adsorbent as described in claim 6, characterized in that, The residue-based adsorbent is used for antibiotic treatment in wastewater.

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