A method for rapidly converting sludge into nutrient soil and the nutrient soil produced thereby

Abstract

The application discloses a method for rapidly converting sludge into nutrient soil and the prepared nutrient soil, and belongs to the fields of sludge treatment and agronomy technology. Steps of the method for rapidly converting sludge into nutrient soil include: stirring and mixing hydrogen peroxide solution and ammonium sulfate, filtering after stirring and reacting under an acidic condition, washing, and drying to obtain ammonium persulfate; mixing calcium hydroxide and citric acid gypsum and then placing the mixture in a tube furnace to perform pyrolysis, so as to obtain a composite catalyst; adding the composite catalyst and the ammonium persulfate solution into sludge, stirring and reacting, and then the nutrient soil can be obtained. The macromolecules in the sludge are converted into small-molecule structures such as fulvic acid by the advanced oxidation technology, and the heavy metals in the sludge are passivated, so that the value of the nutrient soil is improved.

Description

Technical Field

[0001] This invention belongs to the fields of sludge treatment and agronomy, specifically relating to a method for rapidly converting sludge into nutrient soil and the resulting nutrient soil. Background Technology

[0002] With the acceleration of global urbanization and the improvement of wastewater treatment rates, the production of sludge (a byproduct of wastewater treatment) has increased dramatically. Sludge contains a large amount of organic matter, nitrogen, phosphorus, potassium and other nutrients, but it may also accumulate heavy metals, pathogens and persistent organic pollutants. If not properly disposed of, it will lead to environmental risks such as soil pollution, groundwater infiltration and greenhouse gas emissions (such as methane).

[0003] Currently, the mainstream methods for sludge treatment worldwide include landfill, incineration, land application, and resource utilization. However, landfill occupies land and easily pollutes groundwater; incineration is costly (approximately 400-800 yuan / ton) and produces harmful gases such as dioxins; land application (such as composting) is controversial due to the potential introduction of pollutants, but after strict treatment, land application remains the internationally recommended approach (e.g., in Germany and Denmark, the agricultural utilization rate of sludge exceeds 60%).

[0004] Therefore, how to transform sludge into usable resources (such as nutrient soil) under safe and controllable conditions, and achieve sludge reduction, stabilization, harmlessness and resource utilization, is a key issue in environmental governance and circular economy.

[0005] Citric acid gypsum is an industrial waste residue produced during the acidolysis of citric acid using sulfuric acid. Its main component is calcium sulfate dihydrate. Most citric acid gypsum is stored in stockpiles. This gypsum contains high levels of free water, a certain amount of residual acid and organic matter, making its comprehensive utilization difficult. Therefore, seeking resource-based utilization methods for citric acid gypsum is currently a hot topic. Summary of the Invention

[0006] The purpose of this invention is to provide a method for rapidly converting sludge into nutrient soil and the resulting nutrient soil. Advanced oxidation technology is used to convert macromolecules in the sludge into smaller molecules such as fulvic acid and passivate heavy metals in the sludge, thereby increasing the value of the nutrient soil.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] One of the technical solutions of this invention is to provide a method for rapidly converting sludge into nutrient soil, comprising the following steps:

[0009] Hydrogen peroxide solution and ammonium sulfate are mixed and stirred under acidic conditions. After stirring, the mixture is filtered, washed, and dried to obtain ammonium persulfate. Calcium hydroxide and citric acid gypsum are mixed and pyrolyzed to obtain a composite catalyst. The composite catalyst and ammonium persulfate solution are added to sludge and stirred to obtain nutrient soil rich in humic acid.

[0010] This invention utilizes a composite catalyst derived from the pyrolysis of calcium hydroxide and citric acid gypsum to synergistically activate persulfate through advanced oxidation technology, transforming the macromolecular structure in sludge into small molecules such as fulvic acid that are easily absorbed and utilized by plants. Simultaneously, the alkaline environment created by the catalyst can effectively passivate heavy metals. This process achieves the resource utilization of sludge while passivating heavy metals in the sludge, further enhancing the safety and value of the nutrient soil.

[0011] Preferably, after the hydrogen peroxide solution is mixed with the ammonium sulfate, the concentrations of both hydrogen peroxide and ammonium sulfate are 0.3~1.0 mol / L; the acidic conditions are provided by sulfuric acid; the stirring speed of the mixture of hydrogen peroxide solution and ammonium sulfate is 200~400 rpm and the stirring time is 2~4 h.

[0012] Preferably, both the calcium hydroxide and the citric acid gypsum are powders that have passed through a 100-mesh sieve; the mixing ratio of the calcium hydroxide and the citric acid gypsum is 1:1; and the pyrolysis temperature is 500~600℃ and the time is 1~3h.

[0013] Preferably, the amount of the composite catalyst added is 4-8% of the sludge mass; the concentration of the ammonium persulfate solution is 0.3-1.5 mol / L; and the amount of ammonium persulfate solution added is 0.1-0.3 mL / g sludge.

[0014] Preferably, when the composite catalyst and ammonium persulfate solution are added to the sludge and stirred, the stirring rate is 200-400 rpm and the time is 10-60 min.

[0015] The second technical solution of the present invention provides a nutrient soil obtained by the above-described method for rapidly converting sludge into nutrient soil.

[0016] The beneficial technical effects of the present invention are as follows:

[0017] 1. The advanced oxidation process used in this invention can quickly prepare sludge nutrient soil within one hour. The raw materials are simple and readily available, making it suitable for industrial applications.

[0018] 2. This invention achieves effective passivation of heavy metals in sludge while preparing nutrient soil, thus reducing environmental risks.

[0019] 3. This invention achieves the resource utilization of citric acid gypsum while preparing harmless nutrient soil, reducing the environmental risks caused by the stockpiling of citric acid gypsum. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This shows the changes in fulvic acid content in the sludge before and after treatment in Example 1 of the present invention.

[0022] Figure 2 This shows the changes in humic acid content in the sludge before and after treatment in Example 1 of the present invention.

[0023] Figure 3 This shows the changes in the concentration of available heavy metals in the sludge before and after treatment in Example 1 of the present invention.

[0024] Figure 4 The content of fulvic acid in the sludge after treatment in Examples 1, 2, 3, 4, and 5 of this invention.

[0025] Figure 5 The content of fulvic acid in the sludge after treatment in Examples 1, 6, 7, and 8 of this invention. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0027] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0028] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] Unless otherwise specified, "room temperature" in this invention refers to a temperature of 20±10℃.

[0032] The sludge used in the examples was taken from Jinan City, Shandong Province, and other raw materials were all commercially available products.

[0033] Example 1

[0034] The steps to quickly convert sewage sludge into nutrient soil are as follows:

[0035] (1) Hydrogen peroxide solution and ammonium sulfate were mixed in a 500 mL flask to make their concentrations 1.0 mol / L. Sulfuric acid was added to adjust the pH to 2. After stirring the reaction at 300 rpm for 3 hours, the mixture was filtered, washed three times with ice water, and dried in a vacuum drying oven at 60℃ to obtain pure white crystalline ammonium persulfate.

[0036] (2) Calcium hydroxide and citric acid gypsum were mixed in a 1:1 ratio and placed in a tube furnace. The mixture was then pyrolyzed at 600°C for 2 hours to obtain a composite catalyst.

[0037] (3) Dissolve the pure ammonium persulfate obtained in step (1) in water to prepare a 0.5 M ammonium persulfate solution;

[0038] (4) Add 0.8 g of the composite catalyst obtained in step (2) and 2 mL of the ammonium persulfate solution obtained in step (3) to 10 g of sludge, stir at 200 rpm for 60 min at room temperature to prepare nutrient soil, and passivate the heavy metals in the sludge.

[0039] The contents of fulvic acid and humic acid in the sludge before and after treatment in Example 1 were measured, and the results are as follows: Figure 1 and Figure 2 As shown. Figure 1 and Figure 2 The results showed that the fulvic acid and humic acid content in the treated sludge were 3.95 times and 3.23 times that of the original sludge, respectively, indicating that the technology can achieve rapid treatment of sludge and transform it into nutrient soil rich in fulvic acid.

[0040] The effective concentrations of heavy metals (Zn and Cu) in the sludge before and after treatment in Example 1 were determined, and the results are as follows: Figure 3 As shown. Figure 3 The results showed that after treatment, more than 90% of the available heavy metals in the sludge were passivated, indicating that the technology can not only prepare sludge into nutrient soil with high humic acid content, but also effectively passivate heavy metals and improve the safety of the nutrient soil.

[0041] Example 2

[0042] The only difference from Example 1 is that:

[0043] The concentration of the ammonium persulfate solution in step (3) is 0 mol / L, and the other dosages and operations are exactly the same as in Example 1.

[0044] Example 3

[0045] The only difference from Example 1 is that:

[0046] The concentration of ammonium persulfate solution in step (3) is 0.3 mol / L, and the other dosages and operations are exactly the same as in Example 1.

[0047] Example 4

[0048] The only difference from Example 1 is that:

[0049] The concentration of ammonium persulfate solution in step (3) is 0.75 mol / L, and the other dosages and operations are exactly the same as in Example 1.

[0050] Example 5

[0051] The only difference from Example 1 is that:

[0052] The concentration of ammonium persulfate solution in step (3) is 1.5 mol / L, and the other dosages and operations are exactly the same as in Example 1.

[0053] The fulvic acid content in the sludge treated in Examples 1, 2, 3, 4, and 5 was determined, and the results are as follows: Figure 4 As shown. Figure 4 The results showed that the fulvic acid content in sludge first increased and then decreased with the increase of ammonium persulfate concentration. This is because a lower ammonium persulfate concentration cannot completely decompose macromolecules, while an excessively high ammonium persulfate concentration may further decompose humic products.

[0054] Example 6

[0055] The only difference from Example 1 is that:

[0056] In step (4), the amount of composite catalyst added is 0 g, and the remaining amounts and operations are exactly the same as in Example 1.

[0057] Example 7

[0058] The only difference from Example 1 is that:

[0059] In step (4), the amount of composite catalyst added is 0.4 g, and the remaining amounts and operations are exactly the same as in Example 1.

[0060] Example 8

[0061] The only difference from Example 1 is that:

[0062] In step (4), the amount of composite catalyst added is 0.6 g, and the remaining amounts and operations are exactly the same as in Example 1.

[0063] The fulvic acid content in the sludge treated in Examples 1, 6, 7, and 8 was determined, and the results are as follows: Figure 5 As shown. Figure 5 The results showed that the fulvic acid content in the sludge increased with the increase of the concentration of the composite catalyst. This is because more catalyst can better activate ammonium persulfate, and the heat generated can further activate ammonium persulfate, making the decomposition of macromolecules in the sludge more thorough and producing more fulvic acid.

[0064] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for rapidly converting sewage sludge into nutrient soil, characterized in that, Includes the following steps: Hydrogen peroxide solution and ammonium sulfate are stirred and mixed, reacted under acidic conditions, filtered, washed, and dried to obtain ammonium persulfate; calcium hydroxide and citric acid gypsum are mixed and pyrolyzed to obtain a composite catalyst; the composite catalyst and ammonium persulfate solution are added to sludge and stirred to obtain nutrient soil rich in fulvic acid, which effectively passivates heavy metals in the sludge. Both the calcium hydroxide and the citric acid gypsum are powders that have passed through a 100-mesh sieve; the mass ratio of calcium hydroxide to citric acid gypsum is 1:1; the pyrolysis temperature is 500~600℃ and the time is 1~3h. The amount of the composite catalyst added is 4-8% of the sludge mass; the concentration of the ammonium persulfate solution is 0.3-1.5 mol / L; and the amount of ammonium persulfate solution added is 0.1-0.3 mL / g sludge.

2. The method for rapidly converting sludge into nutrient soil according to claim 1, characterized in that, After the hydrogen peroxide solution is mixed with the ammonium sulfate, the concentrations of both hydrogen peroxide and ammonium sulfate are 0.3~1.0 mol / L; the acidic conditions are provided by sulfuric acid; the stirring speed of the mixture of hydrogen peroxide solution and ammonium sulfate is 200~400 rpm and the stirring time is 2~4 h.

3. The method for rapidly converting sludge into nutrient soil according to claim 1, characterized in that, The composite catalyst and ammonium persulfate solution were added to the sludge and then stirred at a rate of 200-400 rpm for 10-60 min.

4. A nutrient soil obtained by a method for rapidly converting sludge into nutrient soil according to any one of claims 1 to 3.

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