Method for preparing vegetation material by cooperatively treating sludge with building gypsum

Abstract

The invention relates to the technical field of synergistic comprehensive utilization of ardealite and multi-source solid waste, and discloses a method for preparing a plant-growing material by synergistic treatment of sludge with building gypsum, which effectively solves the problems of high energy consumption and long period of sludge dewatering and drying by utilizing the strong water absorption characteristic of the building gypsum and mixing with the sludge, and reduces the drying energy consumption by more than 40%; through co-calcination, the content of fluoride in the phosphogypsum can be reduced to 80%, and organic matters, nitrogen, phosphorus, potassium and other nutrient elements in the sludge are effectively reserved and become a nutrient source for plant growth in the gypsum-based plant growing material; according to the method, equipment investment does not need to be increased, synergistic utilization of multi-source solid waste is achieved, the gypsum-based plant-growing material which is excellent in plant-growing performance, qualified in hygiene index and standard in environmental protection can be obtained in one step, and remarkable environmental, ecological and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of synergistic utilization of phosphogypsum and multi-source solid waste, and in particular to a method for preparing vegetation materials by using building gypsum to co-treat sludge. Background Technology

[0002] Phosphogypsum is a byproduct of wet-process phosphoric acid production; approximately 5 tons of phosphogypsum are produced for every ton of phosphoric acid produced. Currently, my country's annual phosphogypsum production is close to 80 million tons, with a comprehensive utilization rate of only about 45%. As the amount of phosphogypsum stockpiled continues to increase, the required land area for slag storage is also growing, increasing environmental risks.

[0003] Phosphogypsum closely resembles natural soil in terms of mineral composition, particle size distribution, aggregate formation process, and soil-forming structure. Its colloidal surface potential, bonding, and electrostatic properties are well-matched with most organic and inorganic minerals, forming various stable composite aggregate structures. Phosphogypsum is rich in calcium ions, which can increase soil base saturation and cation exchange capacity, automatically regulate soil pH, promote soil aggregate formation, and facilitate rapid plant adaptation and growth. Due to the characteristics of phosphate chemical industry, phosphogypsum contains a certain amount of fluorine, including insoluble and soluble fluorides. Soluble fluoride, in particular, can have adverse effects on plants, animals, and humans; therefore, fluorine is a crucial control factor in the land use of phosphogypsum. Most existing technologies do not effectively treat fluorides in phosphogypsum soil materials, posing potential environmental risks during application; others use simple water washing processes, which significantly increase costs (and can generate new water pollution in scenarios where the washing water cannot be balanced), and also wash away other beneficial components such as phosphorus, resulting in resource waste.

[0004] With rapid socio-economic development, the amount of urban sewage generated is increasing year by year. Municipal sludge, as a major byproduct of sewage treatment, is also experiencing rapid growth in production along with the increase in sewage treatment volume. Therefore, sludge reduction, harmless treatment, and resource utilization have become key priorities for government work and the environmental technology and engineering fields.

[0005] Meanwhile, unreasonable emissions from agricultural and industrial production activities have led to increasingly severe eutrophication problems in surrounding lakes. Dredging, using dredgers to remove lakebed sediments, is an effective measure to continuously reduce the load of endogenous pollutants throughout the entire lake basin and has proven to be an important means of improving the eutrophication status of lakes. However, how to rationally and effectively treat the large amounts of lakebed sediment generated by dredging is a crucial link in the entire process of lake eutrophication control.

[0006] Municipal sludge and lake sediment (hereinafter collectively referred to as "sludge") are essentially sediments produced by physical, chemical, and biological processes in water bodies related to human life and production. Their main components include organic matter, inorganic minerals, and microorganisms. They are rich in nutrients such as nitrogen, phosphorus, potassium, calcium, and magnesium, essential for plant growth, but also contain heavy metals, pathogens, parasite eggs, and toxic and harmful substances such as persistent organic matter. If properly treated, sludge can be transformed into a valuable agricultural or ecological restoration resource. Currently, the main treatment methods include sanitary landfill, thermal drying and incineration, pyrolysis carbonization, and aerobic fermentation. Aerobic fermentation technology is relatively widely used. Under aerobic conditions, this technology utilizes naturally occurring bacteria, actinomycetes, fungi, and other microorganisms in the sludge to promote the transformation of organic matter into humic substances. The high temperatures generated during the process (reaching above 55°C) can kill parasite eggs and pathogens. However, this technology involves complex procedures, numerous control factors, a long fermentation cycle (usually 30-45 days), requires a large site, and has high project investment and operating costs. Furthermore, although fermentation treatment mainly solves the hygienic indicators of sludge, its stabilization effect on other pollutants is limited, and the cost-effectiveness ratio needs to be improved.

[0007] The core challenge in treating sludge lies in effectively reducing its high water content. Sludge typically has a water content exceeding 80%, sometimes even reaching 90%. Due to its high organic matter content and the resulting colloidal substances, most of the water is trapped within cells or colloidal structures, making it difficult to remove effectively using conventional mechanical dewatering methods. Therefore, approximately 60% or more of the sludge requires thermal drying, i.e., high-temperature drying and calcination. Temperatures typically need to reach 750–800℃, with a residence time of 30–60 minutes, to reduce the water content to below 10%. Afterward, it is often mixed with coal for use as fuel. This treatment method is extremely energy-intensive, and the direct incineration of the rich organic matter in the sludge increases carbon emissions and wastes valuable organic resources and nutrients.

[0008] Therefore, how to achieve large-scale synergistic resource utilization of phosphogypsum with domestic sewage sludge and lake sediment at low cost and high efficiency is a key technical problem that urgently needs to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing vegetative materials by co-processing sludge with building gypsum.

[0010] The solution of the present invention is: A method for preparing vegetation materials by co-processing sludge with building gypsum includes the following steps: S1. Mix sludge and building gypsum at a mass ratio of 1-2:1-5, stir until uniform, and then age for 12-24 hours. The moisture content of the aged mixture should be <60%. S2. The mixture is fed into a drying oven for drying treatment at a temperature of 500-750°C. The mixture stays in the drying oven for 5-30 minutes. The moisture content of the dried mixture is <10%, thus obtaining the vegetation material.

[0011] As a preferred technical solution, the mixing and stirring in step S1 is carried out by either rotary tillage or spiral mixing.

[0012] In a further optimized scheme, the mixing method involves using a hoisted rotary tiller to operate directly on the sludge stockpile. The gypsum powder is sprinkled onto the sludge surface in multiple batches, and the rotary tiller is turned on to mix and stir until the two materials can no longer be clearly distinguished, at which point the mixture is considered to be uniform.

[0013] As a preferred technical solution, the sludge in step S1 is one or both of domestic sewage sludge and lake bottom sediment.

[0014] As a preferred technical solution, the drying oven in step S2 is a rotary drying oven.

[0015] As a preferred technical solution, the ratio of sludge to building plaster is 1:1.

[0016] As a preferred technical solution, the ratio of sludge to building plaster is 1:2.

[0017] As a preferred technical solution, the aging time is 12 hours.

[0018] As a preferred technical solution, the moisture content of the mixture in step S1 is 55-60%; As a preferred technical solution, the drying process in step S2 should be temperature-adjusted according to the moisture content of the mixture before it enters the drying furnace. The drying temperature for a mixture with a moisture content of 55% is 600℃, and the drying temperature for a mixture with a moisture content of 60% is 700℃.

[0019] As a preferred technical solution, the residence time of the mixture in the drying furnace is also adjusted according to the moisture content of the mixture before entering the drying furnace. The residence time for materials with 55% moisture content is 10 to 15 minutes, and the residence time for materials with 60% moisture content is 15 to 20 minutes. As a preferred technical solution, the hygienic indicators of the dried mixture meet the national standard requirements: fecal coliform count > 0.01, and ascarid egg mortality rate > 95% (refer to standards GB7959~2012, GB4284~2018, GB / T23486~2009).

[0020] As a preferred technical solution, the leachate prepared from the plant material using the HJ 557 standard method has a fluoride content lower than the land use standard requirement (5 mg / L) in HJ 1415.

[0021] This invention also discloses the application of a vegetation material, which is suitable for ecological restoration of slopes, engineering damage surfaces, and rocky desertification land, as well as for soil improvement materials for landscaping. The organic matter content in the vegetation material can reach 5-20% depending on the ratio of the front-end mixture, which is far higher than the relevant standards for greening soil and land reclamation soil.

[0022] Reaction Mechanism: After calcination, phosphogypsum forms hemihydrate gypsum (also known as building gypsum), with an average attached water content typically below 1% and a crystal structure containing 0.5 water molecules, giving it strong water absorption and the ability to hydrate and transform into dihydrate gypsum. Building gypsum is mixed with sewage sludge or lake sediment (collectively referred to as sludge) in a certain proportion, utilizing the strong water absorption of building gypsum to rapidly reduce the moisture content of the sludge. The resulting mixture is then subjected to high-temperature, short-process drying to obtain a gypsum-based vegetation material rich in organic matter. This material can be directly used as a substitute for natural soil in various engineering projects requiring soil covering and greening.

[0023] This invention cleverly utilizes the strong water absorption properties of building gypsum to efficiently adsorb or absorb moisture present inside cells and colloids in sludge, thereby rapidly reducing the sludge's moisture content. Subsequently, the mixture, with its moisture content reduced to a certain level, undergoes high-temperature short-time drying treatment. Firstly, this ensures that the hygienic indicators of pathogenic microorganisms and insect eggs in the sludge meet standards. Secondly, during the high-temperature treatment, most of the fluoride in the gypsum volatilizes or sublimates, significantly reducing its content and thus meeting environmental standards for land use. This invention creatively and effectively couples the treatment processes of phosphogypsum and sludge, two major categories of solid waste. Combining the characteristics of both, it leverages their strengths and avoids their weaknesses, achieving direct synergistic treatment of the two through a simplified process. This one-step method produces land-use vegetation materials that meet multiple standards, achieving significant synergistic utilization effects of multi-source solid waste.

[0024] Compared with the prior art, the advantages of the present invention are: 1. Based on the high level of synergistic utilization of multi-source solid waste, this invention comprehensively considers the difficulties in the utilization and disposal of two major categories of solid waste: phosphogypsum and municipal sludge and river and lake sediment. It systematically explores the potential for high-value and large-scale application of these two types of solid waste and cleverly combines their advantages. First, it solves the problems of high energy consumption and unnecessary waste of organic matter in the sludge drying process. Second, it solves the pain point of difficulty in controlling the fluoride content in the preparation of land use materials from phosphogypsum.

[0025] 2. This invention utilizes the property of building gypsum to strongly absorb water and undergo hydration to transform into dihydrate gypsum. By mixing it with sludge, the problems of high energy consumption and long cycle of sludge dewatering and drying are solved in one fell swoop. The drying temperature and calcination time are significantly reduced and shortened, and energy consumption is reduced by more than 40%. At the same time, after co-calcination at a temperature of more than 500°C, the fluoride content in phosphogypsum can be reduced by up to 80%, achieving an effect that cannot be achieved by traditional water washing and chemical modification methods. Finally, the organic matter and nutrients such as nitrogen, phosphorus and potassium in the sludge are effectively retained, becoming an essential source of nutrients for plant growth in gypsum-based vegetation materials.

[0026] 3. This invention requires no additional equipment investment. Utilizing existing technical conditions, the method of this invention enables the synergistic utilization of multi-source solid waste. It can obtain gypsum-based vegetation materials, or artificial soil, with excellent vegetation performance, qualified hygiene indicators, and environmental protection indicators in one step, thus achieving good environmental, ecological, and social benefits.

[0027] 4. The present invention employs a method combined with sludge drying process, which allows phosphogypsum to undergo short-time, high-temperature calcination treatment, significantly reducing the fluoride content. This simultaneously reduces the fluoride content in phosphogypsum during the preparation of gypsum-based vegetation materials in the present invention.

[0028] 5. Traditional methods such as water washing, flotation, or reagent modification require the construction of large-scale specialized equipment, the consumption of large amounts of water resources, or the investment of large amounts of reagent costs. In contrast, this invention does not require new equipment or other investments, which greatly reduces the treatment cost of the two types of solid waste. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 This is a photograph of ryegrass two weeks after it was planted, as an application example. Figure 2 This is a photograph of ryegrass after five weeks of growth, as an application example. Detailed Implementation

[0031] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0032] Example 1: Raw materials: Sludge from a municipal wastewater treatment plant with a moisture content of 85% was tested and found to have a fecal coliform count of <0.01 and a mortality rate of <50% for Ascaris eggs; phosphogypsum produced by a phosphate chemical plant was calcined at low temperature to become a building gypsum product with a moisture content of less than 2%. The leachate prepared using the HJ 557 method had a fluoride content of 25 mg / L.

[0033] Process 1: Mix sludge and building gypsum at a mass ratio of 1:1. Use a hoisting rotary tiller to add gypsum powder multiple times on the sludge pile and mix until the two materials are indistinguishable. This is considered a uniform mixture. Let it stand for 12 hours to allow for full hydration reaction. Process 2: The mixed and aged materials are conveyed by belt into a rotary drying oven, the oven temperature is adjusted to 650℃, and the residence time is 25 minutes; After treatment, the hygienic indicators of the materials were tested, and the fecal coliform count was >5.3, with a 100% mortality rate of Ascaris eggs. The fluoride content of the leachate was tested using the HJ557 method and found to be 0.97 mg / L. The fertility indicators of the materials were tested, and the organic matter content was 166 g / kg, the hydrolyzable nitrogen content was 691 mg / kg, the available phosphorus content was 227 mg / kg, and the available potassium content was 339 mg / kg, reaching the level of fertile soil.

[0034] Example 2: Raw materials: Sludge from a municipal wastewater treatment plant with a moisture content of 89% was tested and found to have a fecal coliform count of <0.01 and a roundworm egg mortality rate of <40%; phosphogypsum produced by a phosphate chemical plant was calcined at low temperature to become a building gypsum product with a moisture content of less than 1%. The leachate prepared using the HJ 557 method had a fluoride content of 31 mg / L.

[0035] Process 1: Mix sludge and building gypsum at a mass ratio of 1:3. Use a hoisting rotary tiller to add gypsum powder multiple times on the sludge pile and mix until the two materials can no longer be distinguished, which is considered to be a uniform mixture. Let it stand for 16 hours to allow it to fully hydrate and react. Process 2: The mixed and aged materials are conveyed by belt into a rotary drying oven, the oven temperature is adjusted to 550℃, and the residence time is 20 minutes; After treatment, the hygienic indicators of the materials were tested, and the fecal coliform count was >5.7, with a 100% mortality rate of Ascaris eggs. The fluoride content of the leachate was tested using the HJ557 method and found to be 2.12 mg / L. The fertility indicators of the materials were tested, and the organic matter content was 89 g / kg, the hydrolyzable nitrogen content was 477 mg / kg, the available phosphorus content was 321 mg / kg, and the available potassium content was 549 mg / kg, reaching the level of fertile soil.

[0036] Example 3: Raw materials: dredged sludge from a river, after being piled up and dried, had a moisture content of 80%. The fecal coliform count was <0.01 and the mortality rate of roundworm eggs was <80%. Phosphogypsum produced by a phosphate chemical plant was calcined at low temperature to become building gypsum products with a moisture content of about 1.7%. The leachate prepared using the HJ 557 method had a fluoride content of 29 mg / L.

[0037] Process 1: Mix sludge and building gypsum at a mass ratio of 2:3. Use a hoisting rotary tiller to add gypsum powder multiple times on the sludge drying yard until the two materials are indistinguishable, which is considered a uniform mixture. Let it stand for 24 hours to allow it to fully hydrate and react. Process 2: The mixed and aged materials are conveyed by belt into a rotary drying oven, the oven temperature is adjusted to 600℃, and the residence time is 30 minutes; After treatment, the hygienic indicators of the materials were tested, and the fecal coliform count was >2.2, with a 100% mortality rate of Ascaris eggs. The fluoride content of the leachate was tested using the HJ557 method and found to be 2.01 mg / L. The fertility indicators of the materials were tested, and the organic matter content was 128 g / kg, the hydrolyzable nitrogen content was 517 mg / kg, the available phosphorus content was 291 mg / kg, and the available potassium content was 449 mg / kg, reaching the level of fertile soil.

[0038] Application examples To systematically evaluate the comprehensive performance of gypsum-based vegetation materials with different proportions prepared using the method of this invention, three samples with sludge-to-building gypsum mass ratios of 25:75, 40:60, and 50:50 (i.e., prepared in Examples 2, 3, and 1) were selected. The three samples underwent comprehensive testing for physicochemical properties, plant growth effects, environmental safety, and hygiene indicators. All samples were prepared according to the method described in this invention (mixing, aging, and drying).

[0039] 1. Basic physicochemical properties and fertility indicators, the test results are shown in Table 1 below.

[0040] Table 1 All samples had a near-neutral pH, suitable for plant growth. Nutrient indicators (nitrogen, phosphorus, potassium) and organic matter content were all at high levels. Furthermore, with the increase of sludge proportion, the organic matter and nitrogen content significantly increased, proving that this invention can effectively retain and transform nutrients and organic matter in sludge. The product's fertility is far superior to that of ordinary soil, meeting the requirements for fertile soil or improved substrate in standards such as TD / T 1036.

[0041] 2. Plant growth effect experiment (using ryegrass as an indicator plant) A five-week potted ryegrass experiment was conducted, with a sample layer thickness of 15cm. Ryegrass was sprinkled on the sample, and the results are shown in Table 2 below.

[0042] Table 2 All three materials supported good growth of ryegrass with normal germination rates. In particular, plant height increased significantly with the increase of sludge addition ratio, indicating that the materials of this invention are not only safe for plants, but also effectively promote plant growth and have excellent vegetative properties.

[0043] 3. Environmental safety and pollutant control indicators Potential contaminants in the materials were tested, and the results all met the relevant standard limits, as shown in Table 3 below. Table 3 Heavy metals: The heavy metal content in all samples was far below the risk screening value (based on similar pH conditions) in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control (Trial)" (GB 15618~2018), indicating that the product has extremely low environmental risk and can be used for safe land use.

[0044] Fluoride: The fluoride content in the leachate was significantly lower than the limit (5 mg / L) specified in the "Technical Specification for Land Use of Sludge Disposal from Urban Wastewater Treatment Plants" (HJ 1415~2025), especially in the 50% sludge ratio sample where the content was less than 1 mg / L. This directly verifies the high-temperature synergistic treatment process of this invention for the efficient removal of fluoride from phosphogypsum (removal rate >95%), solving a key environmental bottleneck in the land use of phosphogypsum.

[0045] 4. Hygiene indicators Table 4 The hygienic indicators of the samples fully meet and significantly exceed the relevant national standards such as "Hygienic Requirements for Harmless Treatment of Feces" (GB 7959~2012), proving that the high-temperature short-time drying process of this invention can completely kill pathogenic microorganisms and parasite eggs, and achieve the harmless treatment of sludge.

[0046] in conclusion: This application example fully demonstrates the effectiveness of gypsum-based vegetation materials prepared using the method of this invention: Abundant nutrients: Rich in organic matter and nitrogen, phosphorus and potassium, which can effectively promote plant growth.

[0047] Environmental safety: Low heavy metal content, fluoride leaching concentration meets standards, and environmental risks are controllable.

[0048] Hygienic and harmless: Pathogens and insect eggs are completely inactivated.

[0049] Adjustable performance: By adjusting the ratio of sludge to gypsum, products with different fertility levels can be flexibly obtained to meet the needs of different scenarios such as slope restoration and landscaping.

[0050] The above description further verifies the significant advantages and reliability of the present invention in realizing the synergistic utilization of multi-source solid waste and high-value resource utilization.

[0051] 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 present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing vegetation materials by co-processing sludge with building gypsum, characterized in that, Includes the following steps: S1. Mix sludge and building gypsum at a mass ratio of 1-2:1-5, stir until uniform, and then age for 12-24 hours. The moisture content of the aged mixture should be <60%. S2. The mixture is fed into a drying oven for drying treatment at a temperature of 500-750°C. The mixture stays in the drying oven for 5-30 minutes. The moisture content of the dried mixture is <10%, thus obtaining the vegetation material.

2. The method for preparing vegetation materials by co-processing sludge with building gypsum as described in claim 1, characterized in that: In step S1, the mixing and stirring are carried out using either rotary tillage or spiral mixing.

3. The method for preparing vegetation materials by co-processing sludge with building gypsum as described in claim 1, characterized in that: In step S1, the sludge is one or both of the following: domestic sewage sludge and lake bottom sediment.

4. The method for preparing vegetation materials by co-processing sludge with building gypsum as described in claim 1, characterized in that: The drying oven in step S2 is a rotary drying oven.

5. The method for preparing vegetation materials by co-processing sludge with building gypsum as described in claim 1, characterized in that: The fecal coliform count in the plant material was >0.01, and the mortality rate of Ascaris eggs was >95%.

6. The method for preparing vegetation materials by co-processing sludge with building gypsum as described in claim 1, characterized in that: The fluoride content of the leachate from the plant material was <5 mg / L during testing.

7. An application of the method for preparing vegetation materials as described in any one of claims 1 to 6, characterized in that: The aforementioned vegetation material is suitable for ecological restoration of slopes, engineering damage surfaces, and rocky desertification land, as well as for soil improvement materials used in landscaping.

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