Method for hydrothermal conversion of sludge whole components into high-quality regenerated soil

Abstract

The present application relates to a kind of methods for hydrothermal conversion of sludge full component into high-quality regenerated soil, belong to sludge resource technology field.The method includes: adding alkali agent in sludge raw material and mixing uniformly to prepare sludge reaction slurry;The sludge reaction slurry is hydrothermally reacted;After reaction, the solid-liquid separation is carried out to reaction product, and the obtained liquid phase product is humic acid enrichment liquid, and the obtained solid phase product is sludge inorganic component;Sludge inorganic component is further hydrothermally converted into inorganic environmental mineral;Humic acid enrichment liquid, inorganic environmental mineral and ordinary soil are mixed, so as to obtain inorganic environmental mineral and high-quality regenerated soil coupled with organic humic acid.The present application is dissolved by hydrothermal method, and the main environmental mineral of soil is restructured to sludge inorganic component, and sludge organic component is dissolved and synthesized into humic acid by hydrothermal method, which constitutes the main organic and inorganic components (humic acid and environmental mineral) of soil, and is expected to realize safe and efficient land use of sludge.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for hydrothermal conversion of sludge into high-quality regenerated soil, belonging to the technical field of sludge resource utilization. BACKGROUND

[0002] With the acceleration of urbanization in China, the scale of urban sewage treatment is expanding year by year. Municipal sludge is the main solid waste generated during sewage treatment, which is large in volume and continuously discharged. Sludge contains heavy metals and other refractory pollutants and a large number of pathogenic microorganisms, and improper disposal can easily lead to environmental secondary pollution and potential resource waste.

[0003] Under the guidance of sludge resource utilization, traditional extensive disposal methods such as landfill and stacking are being gradually abandoned. Incineration can greatly reduce the volume and kill pathogens, but it has the disadvantages of high investment cost, high energy consumption, easy production of volatile toxic substances, and incineration ash still needs to be treated. At present, anaerobic digestion is the most common treatment method, which can digest and degrade the organic matter in sludge into biogas (methane) and other biomass energy. The inorganic residue after sludge digestion is used for land reuse. Land use can realize large-scale absorption and recycling of sludge resources, and has been used as the main sludge disposal method in developed countries in Europe and America in recent years. Although China has also introduced this treatment technology, due to the characteristics of low organic matter and high sand content of sludge in China, the technology is not suitable. In addition, digestion treatment cannot convert the inorganic residue of sludge into effective mineral components of soil, so the inorganic components are not effectively utilized.

[0004] High-quality soil should contain sufficient humus and other components to provide a good fertility environment for plant growth. Sludge contains a lot of organic matter components, such as rich organic carbon elements and nitrogen, phosphorus, potassium and other nutrient elements. However, the existing sludge has a low degree of humification, and the inorganic residue of sludge after digestion has even less organic matter, so direct land use is difficult to meet the needs of plant growth. If the organic components of sludge can be converted into humic acid, the most important organic component of soil, the fertility can be effectively improved, and high-value land use of sludge organic matter can be realized.

[0005] The sludge in China has the characteristics of less organic matter and high sand content. In fact, the organic matter and inorganic matter components in the sludge account for about half of the total components. The inorganic matter of the sludge mainly includes silicon, aluminum, calcium and other components, which are highly similar to the elements of natural soil minerals. Therefore, theoretically, the inorganic matter of the sludge can be converted into the main mineral components of soil (clay minerals, zeolite minerals, etc.). These minerals not only can be the main inorganic mineral components in soil, but also have good self-purification capacity. However, for the digested sludge residue widely used in current land use, the inorganic components cannot be converted into high-quality soil minerals through digestion, thus wasting a large amount of inorganic matter resources of the sludge. In summary, there is an urgent need for a new method that meets the national conditions of China and can realize efficient land use of the total components (organic + inorganic) of the sludge.

[0006] Chinese patent CN102584365B discloses a method for preparing improved soil fertilizer by mixing sludge with straw, feces, fermentation bacteria and the like for aerobic fermentation; Chinese patent CN114538747A discloses a method for preparing ecological soil from sludge by mixing the sludge with carbon-based crushed materials, and then heating, baking and biological fermentation; Chinese patent CN106587572B discloses a sludge soilization treatment process, in which a composite oxidation sterilizing agent and a composite dehydration agent are added to the sludge for chemical treatment, and the sludge is physically dehydrated for multiple times to realize sludge reduction and stabilization treatment.

[0007] The above patents all aim to soilize the sludge, but only use physical or chemical means to treat the sludge in terms of apparent properties, without substantially improving the organic humification degree of the sludge, realizing efficient soil conversion and reuse of the inorganic components of the sludge, or ensuring the harmlessness of the sludge regeneration products. SUMMARY

[0008] In view of the above problems, the present application provides a method for converting the total components of sludge into high-quality regenerated soil by using hydrothermal technology, i.e. the inorganic components of the sludge are dissolved and restructured into the main environmental minerals of soil by hydrothermal method, and the organic components of the sludge are dissolved and synthesized into humic acid by hydrothermal method, which constitutes the main organic and inorganic components of soil (humic acid and environmental minerals), and is expected to realize safe and efficient land use of the sludge.

[0009] In a first aspect, the present application provides a method for hydrothermal conversion of sludge into high-quality regenerated soil. The method comprises: adding an alkali agent to the sludge raw material and mixing uniformly to form a sludge reaction slurry, wherein the alkali content of the sludge reaction slurry is 0.1-0.5 mol / L in terms of hydroxyl ion concentration; subjecting the sludge reaction slurry to hydrothermal reaction at a temperature of 120-180°C for a time period of 0.5-5 hours; after the reaction, performing solid-liquid separation on the reaction product, wherein the obtained liquid product is a humic acid-rich liquid, and the obtained solid product is a sludge inorganic component; further hydrothermal conversion of the sludge inorganic component into an inorganic environmental mineral; and mixing the humic acid-rich liquid, the inorganic environmental mineral and ordinary soil to obtain a high-quality regenerated soil with the inorganic environmental mineral and organic humic acid coupled.

[0010] Preferably, the carbon element of the humic acid mainly exists in the form of aromatic carbon.

[0011] Preferably, the characteristic molar ratio of the organic elements of the humic acid is H / C<1.30, N / C=0.05-0.11 and O / C>0.30.

[0012] Preferably, the humic acid has a loose porous structure with a large number of micron-sized pores arranged on the surface and interconnected with each other.

[0013] Preferably, the inorganic environmental mineral is a clay mineral and / or a zeolite mineral.

[0014] Preferably, an aluminum source is added to the sludge inorganic component to make the Al / Si molar ratio of the sludge system 0.5-1.5, and the hydrothermal reaction is performed at a temperature of 180-240°C for 6-24 hours, and after the reaction, the obtained reaction liquid is subjected to solid-liquid centrifugal separation, and the obtained solid product is the clay mineral converted from the sludge inorganic component.

[0015] Preferably, the kaolinite contained in the sludge inorganic component acts as a crystal seed to induce and promote the hydrothermal dissolution of the sludge inorganic component and direct synthesis and conversion into the clay mineral through a reconstruction reaction.

[0016] Preferably, a sodium source is added to the sludge inorganic component to make the Na / Si molar ratio of the sludge system 0.3-1.0, and an aluminum source is added to make the Al / Si molar ratio of the reaction system 0.5-1.5, and the hydrothermal reaction is performed at a temperature of 160-220°C for 6-24 hours, and after the reaction, the obtained reaction liquid is subjected to solid-liquid centrifugal separation, and the obtained solid product is the zeolite mineral converted from the sludge inorganic component.

[0017] Preferably, the mass ratio of the humic acid-rich liquid to the inorganic environmental mineral added to the soil is adjusted according to the land fertility requirement and the environmental purification requirement.

[0018] In a second aspect, the present application provides the use of the method of any one of the above in soil carbon sequestration and environmental detoxification. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the microstructure morphology of sludge hydrothermal synthesis humic acid under scanning electron microscope.

[0020] Figure 2 is the Fourier transform infrared absorption spectrum of sludge hydrothermal synthesis humic acid.

[0021] Figure 3 is the X-ray photoelectron spectroscopy full spectrum of sludge hydrothermal synthesis humic acid.

[0022] Figure 4 is the X-ray photoelectron spectroscopy fine spectrum of sludge hydrothermal synthesis humic acid.

[0023] Figure 5 is the XRD spectrum of clay minerals hydrothermally synthesized from sludge under different reaction times.

[0024] Figure 6 is the microstructure morphology of clay minerals hydrothermally synthesized from sludge under scanning electron microscope.

[0025] Figure 7 is the XRD spectrum of zeolite minerals hydrothermally synthesized from sludge under different reaction times.

[0026] Figure 8 is the microstructure morphology of zeolite minerals hydrothermally synthesized from sludge under scanning electron microscope.

[0027] Figure 9 is the microstructure morphology of high-quality regenerated soil under scanning electron microscope.

[0028] Figure 10 is the plant growth under different soil environments.

[0029] Figure 11 is the plant growth under different soil pollution environments.

[0030] Figure 12 is the heavy metal content of each part of the plant under different soil pollution environments.

[0031] Figure 13 is the process flow diagram of the present application. DETAILED DESCRIPTION

[0032] The present application is further illustrated by the following examples, which should be understood as merely illustrative of the present application and not limiting thereof. The following exemplary illustrates the method of the present application for hydrothermal conversion of sludge full components into high-quality regenerated soil.

[0033] The alkali agent is added to the sludge raw material and mixed uniformly to form a sludge reaction slurry.

[0034] The type of sludge raw material is not limited. It should be understood that any type of sludge raw material can be suitable for the present application. The sludge raw material can be municipal sludge.

[0035] The water content and organic matter content of the sludge raw material are also not limited. High water content sludge can also be suitable for the present application. As an example, the water content of the sludge raw material is 80-90 wt%. Existing sludge treatment technologies usually require sludge to be deeply dried to an absolutely dry state and broken and ground before use. Since the present application uses a flow state slurry as the sludge raw material for reaction, the sludge raw material can be directly used without any pretreatment before use. Of course, the sludge raw material does not need to be dewatered or dried.

[0036] The alkali agent includes, but is not limited to, sodium hydroxide, potassium hydroxide, aluminum hydroxide, etc. The alkali content of the sludge reaction slurry is 0.1-0.5 mol / L in terms of hydroxyl ion concentration. In the hydrothermal reaction environment, controlling the alkali agent in this concentration range can effectively decompose the original macromolecular organic matter in the sludge, such as polysaccharides, lipids, proteins, etc., into small molecular organic matter, such as monosaccharides, fatty acids, amino acids, etc., thereby providing sufficient precursors for the final hydrothermal restructuring-synthesis of humic acid products. If the alkali concentration is too low, it will not be enough to completely decompose the original macromolecular organic matter, resulting in a low yield of humic acid. If the alkali concentration is too high, it will further decompose the inorganic components of the sludge, i.e., while the first hydrothermal reaction of the organic components to generate humic acid is being carried out, the second hydrothermal reaction of the inorganic components to generate inorganic environmental minerals has already begun, thereby interfering with the progress of the hydrothermal synthesis of humic acid reaction. Moreover, too high an alkali concentration will also result in too high an alkalinity of the humic acid product, making it difficult to use in land. In a specific embodiment, sodium hydroxide is used as the alkali agent. Therefore, the alkali content of the sludge reaction slurry is 0.1-0.5 mol / L in terms of sodium hydroxide concentration.

[0037] The sludge reaction slurry is subjected to a hydrothermal reaction (which can also be referred to as a first hydrothermal reaction). The role of the first hydrothermal reaction is to hydrothermally dissolve and synthesize the organic components of the sludge into humic acid, and at the same time, the hydrothermal treatment can also simultaneously completely kill the original pathogens and other harmful microorganisms in the sludge.

[0038] In the first hydrothermal reaction, the hydrothermal reaction temperature is 120-180°C. Most preferably, the hydrothermal reaction temperature is selected to be 150°C. The hydrothermal reaction time is 0.5-5 hours. Most preferably, the hydrothermal reaction time is selected to be 1 hour. Controlling the temperature and time of the first hydrothermal reaction in the above ranges can simultaneously generate mineral source-like humic acid products and cooperatively improve the yield of humic acid.

[0039] After the reaction, the reaction product is subjected to solid-liquid separation, and the obtained liquid phase product is a humic acid enrichment liquid, and the obtained solid phase product is a sludge inorganic component. The humic acid enrichment liquid can be weakly alkaline.

[0040] The humic acid obtained by the first hydrothermal reaction is highly similar to the source humic acid in natural lignite in composition and structure (containing abundant oxygen-containing groups, aromatic structure and low H / C ratio), and is different from the biochemical humic acid produced by traditional fermentation (weak acidification and aromaticity, and high aliphaticity). This is because: by providing suitable hydrothermal reaction conditions, the reaction process of organic matter conversion into source humic acid in the natural underground hydrothermal environment (for example, the formation process of humic acid in natural lignite) can be effectively simulated and even highly reduced, so that the macromolecular organic matter in the sludge is quickly dissolved and restructured into a new humic acid product, and a high degree of humification is achieved.

[0041] Through analysis and characterization, the humic acid obtained by the first hydrothermal reaction is mainly in the form of aromatic carbon. This shows that the organic carbon in the sludge has been fully converted into aromatic carbon structure after the first hydrothermal reaction. Preferably, the main existing form of carbon element of the humic acid obtained by the first hydrothermal reaction includes aromatic carbon and aliphatic carbon. Furthermore, the characteristic organic element molar ratio of the humic acid is H / C < 1.30, N / C = 0.05-0.11, and O / C > 0.30. For example, the characteristic organic element molar ratio of the humic acid is H / C = 1.24, N / C = 0.10, and O / C = 0.36. This further shows that the humic acid product obtained by the sludge hydrothermal process has a high degree of polycondensation (low H / C ratio) and acidification (high O / C ratio). "Low H / C" means high unsaturation (or high degree of polycondensation or aromaticity). "High O / C" means high oxygen-containing group, high activity and high degree of acidification. That is, the degree of humification of the product is significantly improved.

[0042] As can be seen from the microstructure diagram, the humic acid has a loose porous structure with a large number of micron-sized channels arranged on the surface and interconnected with each other. These channel structures provide effective sites for the humic acid to adsorb heavy metals and the like.

[0043] In the first hydrothermal reaction for synthesizing humic acid from sludge, no additional conditioning agent needs to be added, and only the sludge is used as the main reaction raw material. The treatment process of the reaction system material is more simple, the comprehensive cost is lower, and the environmental benefits are friendly. Moreover, compared with the existing technology for hydrothermal synthesis of humic acid, the hydrothermal reaction temperature of the present application is significantly reduced, and the hydrothermal time is also shortened. Through various characterization analyses, it is found that the humic acid synthesized by the present application has a significantly high degree of aromaticity, acidification and polycondensation, that is, the overall humification degree is significantly improved, and the characteristics are highly similar to the natural source humic acid, and the quality of the humic acid is higher.

[0044] Further hydrothermal reaction of the inorganic component of the sludge to convert into inorganic environmental minerals (may also be referred to as second hydrothermal reaction). The inorganic environmental minerals are clay minerals and / or zeolite minerals. The target minerals are synthesized by regulating the elemental ratio of the sludge system and the hydrothermal reaction conditions.

[0045] In some embodiments, an aluminum source is added to the inorganic component of the sludge to make the Al / Si molar ratio of the sludge system 0.5-1.5, and then the hydrothermal reaction is carried out at a temperature of 180-240°C for 6-24 hours. After the reaction, the obtained reaction liquid is subjected to solid-liquid centrifugal separation, and the obtained solid product is the clay mineral converted from the inorganic component of the sludge.

[0046] The clay mineral can be a kaolinite mineral. It is explained that the kaolinite contained in the inorganic component of the sludge acts as a crystal seed to induce and promote the hydrothermal dissolution of the inorganic component of the sludge and direct synthesis of the conversion into a clay mineral through a reconstruction reaction.

[0047] In some embodiments, a sodium source is added to the inorganic component of the sludge to make the Na / Si molar ratio of the sludge system 0.3-1.0 (preferably 0.5), and an aluminum source is added to make the Al / Si molar ratio of the reaction system 0.5-1.5, and then the hydrothermal reaction is carried out at a temperature of 160-220°C for 6-24 hours. After the reaction, the obtained reaction liquid is subjected to solid-liquid centrifugal separation, and the obtained solid product is the zeolite mineral converted from the inorganic component of the sludge.

[0048] The second hydrothermal reaction utilizes the inorganic components of sludge to synthesize multiple types of environmental minerals, including zeolite minerals and clay minerals, etc. Unlike the Chinese patent CN 113426825A which uses pure clay minerals (such as montmorillonite) as raw materials to synthesize other types of minerals, the present invention uses the inorganic residue left after the hydrothermal reaction and the separation of humic acid from sludge to synthesize environmental minerals. In addition, from the perspective of purification principle, the Chinese patent CN 113426825A fixes heavy metals in situ during the synthesis of minerals. That is, the Chinese patent CN 113426825A synchronously fixes heavy metals during the synthesis of minerals. The present invention utilizes the synthesized environmental minerals (such as zeolite) to be put into the real soil environment to adsorb heavy metals and thus purify the environment and promote plant growth and development. That is, the present invention first synthesizes minerals and then fixes heavy metals. Therefore, the present invention and the prior art have significant differences in the mechanism of fixing heavy metals and purifying the environment. Finally, the Chinese patent CN 113426825A synthesizes zeolite minerals according to the types of heavy metals present in the reaction system, that is, the specific type of synthesized minerals changes with the actual types of heavy metals present in the reaction system. The present invention can control the hydrothermal reaction conditions to directionally synthesize multiple types of target minerals, including zeolite minerals and clay minerals, etc., that is, the type of synthesized target minerals can be determined in advance. Therefore, the present invention and the Chinese patent CN 113426825A also have significant differences in the mechanism of synthesizing minerals.

[0049] It is also stated herein that after synthesizing humic acid using the organic components of sludge, the present invention also utilizes the remaining humic residue (inorganic components of sludge). That is, the method of the present invention not only includes the first hydrothermal reaction for synthesizing humic acid, but also includes the second hydrothermal reaction for further synthesizing functional minerals with the function of purifying the environment by further hydrothermal reaction of the reaction residue (inorganic components) obtained from the first hydrothermal reaction, thereby further realizing the efficient reuse of the inorganic components of sludge. This is another important innovation point of the present invention which distinguishes it from the prior art.

[0050] The raw material for the first hydrothermal reaction is sludge (organic components + inorganic components), which is carried out at a relatively short reaction time and a relatively low reaction temperature, with the purpose of hydrothermal dissolution and synthesis of the organic components of sludge into humic acid. The raw material for the second hydrothermal reaction is the sludge residue (inorganic components) remaining after the first step of hydrothermal reaction, which is carried out at a relatively long reaction time and a relatively high reaction temperature, with the purpose of hydrothermal dissolution and synthesis of the inorganic components of sludge into environmental minerals.

[0051] The humic acid-rich solution, inorganic environmental minerals and ordinary soil are mixed to obtain high-quality regenerated soil coupled with inorganic environmental minerals and organic humic acid. After mixing, it can be placed at room temperature for a period of time, the purpose is to promote the full contact of these components so that the inorganic environmental minerals and humic acid are coupled together. The inorganic environmental minerals can be clay minerals, or zeolite minerals, or a mixture of clay minerals and zeolite minerals. The mass ratio of the humic acid-rich solution and the inorganic environmental minerals can be adjusted according to the land fertility demand and environmental purification demand.

[0052] In summary, the prior art cannot realize the efficient and safe transformation of sludge full components (organic matter and inorganic matter) into high-quality regenerated soil, that is, the inorganic and organic components of the sludge are respectively transformed into the most basic components of the soil, clay minerals and humic acid. Unlike the prior art, the present application uses hydrothermal technology to not only hydrothermally dissolve and reconfigure the inorganic components of the sludge into brand new environmental minerals, but also synchronously transforms the organic components of the sludge into high-quality humic acid, substantially improving the degree of soil mineralization and humification. The hydrothermally synthesized environmental minerals and humic acid can in situ stably fix and adsorb heavy metals and other pollutants, which not only improves the self-purification ability of the soil, but also reduces the bioavailability of harmful substances. In addition, the hydrothermal treatment can also synchronously completely kill the original pathogens and other harmful microorganisms in the sludge. Therefore, the present application realizes safe and harmless utilization. Therefore, the present application can provide a new technology for safe, green and efficient transformation of sludge full components into high-quality soil.

[0053] As a specific example, the specific steps of the present application for hydrothermal transformation of sludge to synthesize high-quality regenerated soil are as follows:

[0054]

Step 1

[0055]

Step 2

[0056]

Step 3

[0057] Specifically, by adjusting the sludge system element ratio and the hydrothermal reaction conditions, the target mineral is synthesized in a targeted manner.

[0058] (1) Synthesis of clay mineral (kaolinite): aluminum source reagent (aluminum nitrate) is added to make the Al / Si molar ratio of the sludge system 1, and a hydrothermal reaction is carried out in a high-pressure reaction kettle: the hydrothermal reaction temperature is 180-240°C (most preferably 220°C), and the hydrothermal reaction time is 6-24 hours. After the reaction, the solid-liquid centrifugal separation is carried out, and the obtained solid product is the clay mineral transformed from the inorganic components of sludge.

[0059] (2) Synthesis of zeolite mineral (analcite): sodium source reagent (sodium hydroxide) is added to adjust the Na / Si molar ratio of the reaction system to 0.5, and aluminum source reagent (aluminum nitrate) is added to adjust the Al / Si molar ratio of the reaction system to 0.5, and a hydrothermal reaction is carried out in a reaction kettle. The hydrothermal reaction temperature is 160-220°C (most preferably 200°C), and the hydrothermal reaction time is 6-24 hours. After the reaction, the solid-liquid centrifugal separation is carried out, and the obtained solid product is the zeolite mineral transformed from the inorganic components of sludge.

[0060]

Step 4

[0061] The following examples are further listed to illustrate the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application all belong to the protection scope of the present application. The specific process parameters in the following examples are only one example in the appropriate range, i.e. those skilled in the art can make appropriate selection within the range through the description herein, and are not limited to the specific values in the following examples.

[0062] Example 1: Hydrothermal synthesis of humic acid from sludge organic components

[0063] [Step 1] Selecting sludge raw material: The excess sludge discharged from a sewage treatment plant was selected as the raw material (water content of 90wt%). The raw material was directly used without further dewatering or drying treatment.

[0064] [Step 2] Hydrothermal conversion of sludge organic components to synthesize humic acid. Sodium hydroxide was added to the above sludge raw material to form a sludge reaction slurry. The alkali content of the sludge reaction slurry was 0.1 mol / L in terms of sodium hydroxide concentration. The hydrothermal reaction was carried out in a high-pressure reactor of a homogeneous reactor. The hydrothermal reaction temperature was 150°C, and the hydrothermal reaction time was 1 hour. The liquid phase product obtained after solid-liquid separation after the reaction was the humic acid-rich liquid converted from the sludge organic components, and the solid product obtained was the sludge inorganic components.

[0065] In this example, the sludge obtained in [Step 1] was used as the main raw material, and the method described in [Step 2] was used to synthesize a humic acid-rich liquid by adjusting the hydrothermal reaction conditions. The pH of the humic acid-rich liquid was 7.6, which was weakly alkaline and had good environmental affinity for land use. In order to effectively characterize the properties of the humic acid product, the humic acid product was extracted from the humic acid-rich liquid according to the humic acid extraction and purification method of the International Humic Substances Society (IHSS), and was characterized and analyzed in detail.

[0066] Figure 1 is the microstructure of the humic acid synthesized by the hydrothermal reaction of sludge. In the high-resolution field of view (under the scale of hundreds of microns), it is observed that the overall humic acid product presents a typical loose porous structure, with a large number of micron-sized pores arranged on the surface, and the pores are interconnected and penetrating, indicating that the humic acid product synthesized by the hydrothermal reaction of sludge organic components has well-developed structure, can provide a larger specific surface area and more adsorption sites, and has strong adsorption potential for heavy metals and other pollutants. As can be seen from the figure, the size of the micron-sized pores is several microns to tens of microns. In addition, the microstructure of the humic acid synthesized by the hydrothermal reaction of sludge also has smaller mesopores inside. The mesopores are nanoscale, and through nitrogen adsorption testing, it can be found that the size of the mesopores is about 50 nm.

[0067] Figure 2 is the characterization of the functional groups of the humic acid synthesized by the hydrothermal reaction of sludge. The humic acid synthesized under hydrothermal conditions has obvious characteristic peaks at 3400-3200 cm -1 , indicating that the phenolic hydroxyl group (-OH) in the humic acid has significant stretching vibration; 2930 cm -1 and 2850 cm -1The absorption peaks at 2920 and 2850 cm"1 represent the stretching vibration of methyl (-CH3) and methylene (-CH2), indicating that the humic acid product has a certain amount of aliphatic structure; the absorption peaks at 1040 cm -1 -C-O-C bond stretching vibration and 1630-1450 cm -1 The absorption peaks corresponding to the aromatic ring C=C skeleton vibration are significantly strong, indicating that the humic acid synthesized by hydrothermal synthesis of sludge organic matter has a large number of carboxyl and aromatic ring structures, and presents a high degree of humification.

[0068] Figure 3 and Figure 4 The elemental composition and chemical state of the humic acid product synthesized by hydrothermal synthesis of sludge were analyzed by X-ray photoelectron spectroscopy (XPS). As shown in the full spectrum, Figure 3 As shown in the full spectrum, the humic acid product is mainly composed of C, O, N, S and other typical organic elements, which is highly similar to the elements of sludge organic matter, indicating that the elements of humic acid are mainly derived from the sludge organic matter components.

[0069] Table 1 shows the content of characteristic organic elements in the humic acid synthesized by hydrothermal synthesis of sludge, and the atomic molar ratio of the characteristic organic elements is calculated. The results show that the H / C of the humic acid synthesized by hydrothermal synthesis of sludge is 1.24 (the H / C of natural humic acid is less than 1.30), indicating that the degree of aromatic condensation (unsaturation) is high; the N / C of the humic acid synthesized by hydrothermal synthesis of sludge is 0.10, indicating that it contains more nitrogen-carbon condensation ring structures; the O / C of the humic acid synthesized by hydrothermal synthesis of sludge is 0.36, indicating that it contains more oxygen-containing functional groups, which is consistent with the previous characterization results.

[0070] Table 1 Molar ratio of characteristic organic elements of humic acid synthesized by hydrothermal synthesis of sludge

[0071]

[0072] In order to characterize the chemical state of the key elements of humic acid, the carbon element was further analyzed by fine spectrum. As shown in the fine spectrum, Figure 4 As shown in the fine spectrum peak separation results, the forms of carbon elements in the humic acid product include aromatic carbon (35.9%) and aliphatic carbon (30.5%), indicating that the humic acid synthesized by hydrothermal synthesis has a high degree of aromaticity; a large part of the carbon elements include carbonyl carbon, carboxyl carbon, alcohol ether carbon (carbon connected to alcohol and ether), and amino carbon (carbon connected to amino), indicating that the humic acid product has rich oxygen-containing groups and also shows a high degree of activity and acidification, which is consistent with the analysis of the infrared absorption spectrum results described in Figure 2

[0073] ​In summary, the humic acid synthesized from sludge by hydrothermal method in this example is highly similar to the original humic acid in natural lignite in both composition and structure, i.e. both of them contain abundant oxygen-containing functional groups and aromatic structure and low H / C ratio, and show high condensation degree, acidification degree and aromatic degree, and have strong water-holding and fertilizer-providing capacity and metal ion exchange / adsorption / complexation capacity. Meanwhile, the hydrothermal humic acid is obviously different from the biochemical humic acid produced by traditional compost fermentation (which has weak acidification and aromatic degree, but high aliphatic degree).

[0074] Therefore, compared with the traditional compost humic acid, the humic acid synthesized from sludge by hydrothermal method in this example has more significant advantages in soil fertility, soil carbon sequestration and environmental detoxification, etc.

[0075] Example 2: Synthesis of clay mineral from sludge inorganic components by hydrothermal method

[0076] In this example, the sludge inorganic residue obtained in

step 2

step 3

[0077]

step 3

[0078] Figure 5 The crystalline phase composition of the clay mineral synthesized from sludge by hydrothermal method under different reaction times was analyzed by X-ray diffractometer (XRD). The results show that with the extension of hydrothermal reaction time to 24h, the intensity of quartz characteristic peak gradually decreases, while the intensity of kaolinite characteristic peak gradually increases, which indicates that with the continuous hydrothermal reaction, the quartz mineral structure gradually dissolves and restructures into a new clay mineral structure; when the reaction time reaches 24h, the intensity of kaolinite characteristic peak is quite significant, indicating that the kaolinite synthesized under this condition develops well. It is worth noting that a small amount of kaolinite exists in the sludge raw material before reaction (0h), and due to the presence of these seeds (kaolinite), the thermal kinetic hindrance of kaolinite nucleation is reduced, which induces and promotes the rapid nucleation and crystallization of sludge inorganic components after hydrothermal dissolution / precipitation, so the amount of kaolinite increases rapidly with the extension of hydrothermal reaction time.

[0079] Figure 6The microstructure of the kaolinite synthesized by the sludge under the hydrothermal reaction for 24 hours was characterized by a scanning electron microscope (SEM). The results show that a large number of sheet-like mineral structures are densely distributed under the micron scale, which presents the typical sheet-like silicate features of the soil clay mineral. Meanwhile, the EDS point scanning data show that the main element atomic ratio of the kaolinite product is Al:Si = 0.98:1, which is close to the ideal atomic ratio of the natural kaolinite. This embodiment shows that under the suitable hydrothermal conditions, the hydrothermal dissolution-reconstruction reaction of the inorganic components of the sludge can be used to direct synthesis and conversion into the clay mineral, which becomes an important mineral component of the soil.

[0080] Example 3: Hydrothermal synthesis of zeolite mineral from the inorganic components of sludge

[0081] In this embodiment, the inorganic residue of sludge obtained in

Step 2

Step 3

[0082]

Step 3

[0083] Figure 7 The crystal phase composition of the zeolite mineral synthesized by the sludge under different reaction times was analyzed by an X-ray diffractometer (XRD). The results show that with the extension of the hydrothermal reaction time from 0h to 24h, the intensity of the quartz characteristic peak gradually weakens, and the characteristic peak of the analcite appears and gradually strengthens, which indicates that with the progress of the hydrothermal reaction, the quartz mineral structure gradually dissolves and is converted into a new analcite mineral; when the reaction time is extended to 24h, the quartz characteristic peak has almost completely disappeared, and instead, there are widely distributed and significantly strong analcite characteristic peaks.

[0084] Figure 8 The microstructure of the zeolite synthesized by the inorganic residue of sludge under the hydrothermal reaction for 24 hours was characterized by a scanning electron microscope (SEM). The results show that a large number of multi-ribbed spherical particles (analcite) are densely distributed in the large-scale field of view, and in the higher resolution field of view, the analcite particles present the typical three-eighths pyramidal structure, indicating that the analcite crystals have been synthesized and fully developed under this condition. Meanwhile, the EDS point scanning data show that the main element atomic ratio of the analcite product is Na:Al:Si = 1.07:1:2, which is close to the ideal atomic ratio of the analcite Na:Al:Si = 1:1:2. The nitrogen adsorption test results show that the BET specific surface area of the analcite product is 62.97m2 / g, which is significantly increased compared with the unreacted sludge raw material (0.3 m 2 / g) and has good adsorption performance and purification potential. This embodiment shows that under suitable hydrothermal conditions, the inorganic components of sludge can undergo complete hydrothermal dissolution-reconstruction reactions and ultimately be converted into high-quality zeolite minerals.

[0085] Example 4: Preparation of high-quality regenerated soil by coupling inorganic environmental minerals with organic humic acid

[0086] To verify the land use effect of the inorganic environmental minerals and organic humic acid synthesized from sludge, in this embodiment, the humic acid-rich liquid obtained in the foregoing Example 1, the zeolite environmental mineral obtained in Example 3, and ordinary soil are mixed in a certain proportion according to the method described in

Step 4

[0087]

Step 4

Step 2

Step 3

[0088] To specifically explore the fertility and environmental purification capacity of the high-quality regenerated soil, in this embodiment, the high-quality regenerated soil is prepared by selecting a specific component mass ratio (i.e., 20% of humic acid-rich liquid, 30% of zeolite mineral, and 50% of ordinary soil), which is used as an example to explore its fertility.

[0089] The above examples are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the proportion of humic acid (0-100%) and the proportion of environmental mineral (0-100%) can be adjusted within a reasonable range according to the specific land use requirements to prepare high-quality regenerated soil that meets their own needs.

[0090] In this embodiment, the high-quality regenerated soil (the above example) is subjected to microscopic morphology analysis. Figure 9 The microstructure of the regenerated soil is characterized by a scanning electron microscope (SEM). At a scale of 100 microns, it can be clearly observed that a large amount of loose and porous structure of humic acid is attached to the surface of the larger particles of inorganic minerals, and the humic acid is densely distributed and has basically completely coated the surface of the minerals. This indicates that the humic acid and the inorganic mineral structure have been fully combined after being mixed and regenerated, and together constitute the two main components of the high-quality regenerated soil.

[0091] Example 5: Evaluation of the fertility effect of the regenerated soil

[0092]

Regenerated soil group

[0093]

Sludge soil group

[0094]

Ordinary soil group

[0095] After planting the seeds and cultivating for 30 days, several whole plants are picked from each of the three groups when the plants are mature, and the plant length is measured and recorded to comprehensively compare and evaluate the fertility effects of the regenerated soil, ordinary soil, and sludge soil.

[0096] Figure 10 The plant length statistics of the plants harvested from the ordinary soil group, the regenerated soil group, and the sludge soil group are recorded, and the measurement of the plant length includes the roots, stems, and leaves. The average plant length of the ordinary soil group is 7.0 cm, the average plant length of the sludge soil group is 3.8 cm, and the average plant length of the regenerated soil group is 11.8 cm. The plant growth effect of the regenerated soil group is significantly better than that of the ordinary soil group and the sludge soil group, indicating that the regenerated soil group has a higher degree of humification after hydrothermal treatment, exhibits higher soil fertility, and is more conducive to plant growth.

[0097] In addition, the plant growth of the sludge soil group is not as good as that of the ordinary soil group, indicating that the sludge raw material without treatment has a low degree of humification, which is not conducive to plant growth. Moreover, sludge often contains heavy metals and other pollutants, and direct land use without decomposition and removal will inhibit plant growth. This embodiment also shows that the fertility effect of direct land use of sludge is poor; the sludge can be converted into regenerated soil through hydrothermal treatment, which has higher soil fertility and effectively promotes plant growth, and ultimately realizes high-quality land use.

[0098] Example 6: Evaluation of the pollution remediation effect of regenerated soil

[0099] The high-quality regenerated soil obtained in Step 4 is used as a soil base for plant cultivation (100 g per group), and green leaf plants (Brassica chinensis) are planted to investigate the remediation and purification effect of the regenerated soil on heavy metal pollution, which is the regenerated soil group. At the same time, ordinary soil (100 g per group) is also selected to plant green leaf plants as a control, which is the ordinary soil group. The ordinary soil described in this example is natural soil that has not been fertilized and is far away from pollution sources and other human disturbances, and is collected from common land types such as grasslands, forest lands, or undeveloped wastelands.

[0100] To simulate heavy metal pollution, heavy metal Cu (in the form of copper nitrate solution) is added to one group of each of the two types of soil as a pollution group, and the Cu concentration of the pollution soil group is controlled at 500 ppm, which is the regenerated soil (pollution) group and the ordinary soil (pollution) group. After planting the seeds and cultivating for 30 days, several complete plants are picked from each of the four groups when they are mature, and the plant length is measured and recorded to evaluate the pollution remediation effect of the regenerated soil.

[0101] Figure 11 The plant length statistics of the regenerated soil group and the ordinary soil group planted and harvested in the polluted and non-polluted environments are recorded, and the measurement of the plant length includes the root, stem, and leaf parts. The average length of the plants in the ordinary pollution soil group is 5.5 cm, while the average length of the plants in the regenerated pollution soil group is 10.1 cm, which is significantly better than that of the ordinary pollution soil, and is similar to that of the non-polluted regenerated soil group, indicating that the plants in the regenerated soil group are less disturbed in the polluted environment.

[0102] Further leaching experiments were conducted on the above-mentioned polluted plants, and the heavy metal content of the root, stem, and leaf parts of the plants was measured by ICP-OES (inductively coupled plasma optical emission spectrometer), and the results are shown in Table 2. Figure 12 For the same group of plants, the heavy metal concentration in the body decreases in the order of root, stem, and leaf, which is consistent with the migration and distribution rule of heavy metals from the soil environment along the plant root into the plant body. Compared with the ordinary soil pollution group, the heavy metal content of each part of the regenerated soil pollution group is significantly reduced, which indicates that the migration of heavy metals is effectively controlled in the regenerated soil, and the bioavailability is reduced.

[0103] The results showed that compared with ordinary soil, the sludge hydrothermal regenerated soil contained more humic acid and environmental minerals, and the two had stronger ability to synergistically adsorb / complex heavy metal ions through physical and chemical coupling, effectively reducing the bioavailability of heavy metal ions and making it more difficult to migrate to the plant body, which was conducive to the growth and development of plants under heavy metal stress, achieved in-situ remediation and purification of heavy metal pollution, and achieved safe and harmless land use of high-quality regenerated soil. Among them, humic acid and environmental minerals acted as organic and inorganic purifiers, respectively, and played a complexing, ion exchange and adsorption role in the soil environment, effectively reducing the bioavailability of heavy metal pollutants; while purifying the environment, it also enhanced the diversity of soil microbial community structure, promoted the benign circulation of soil nutrients, and promoted plant growth.

Claims

1. A method for hydrothermally converting all components of sludge into high-quality regenerated soil, characterized in that: The method comprises: An alkali agent is added to the sludge raw material and mixed uniformly to prepare a sludge reaction slurry, wherein the alkali content of the sludge reaction slurry is 0.1-0.5 mol / L in terms of hydroxide ion concentration; The sludge reaction slurry is subjected to a first hydrothermal reaction, wherein the temperature of the first hydrothermal reaction is 120-180° C. and the time of the first hydrothermal reaction is 0.5-5 hours; After the reaction is completed, the reaction product is subjected to solid-liquid separation. The resulting liquid phase product is a humic acid-enriched liquid, and the resulting solid phase product is an inorganic component of the sludge. The humic acid has a loose porous structure with a large number of micron-sized pores arranged on the surface, and the pores are interconnected. The inorganic components of the sludge are further subjected to a second hydrothermal reaction, and converted into the main inorganic environmental minerals of the soil through hydrothermal dissolution and reconstruction; the inorganic environmental minerals are clay minerals and / or zeolite minerals; and the target minerals are synthesized by regulating the element ratio of the sludge system and the hydrothermal reaction conditions; The humic acid enriched liquid, the inorganic environmental minerals and ordinary soil are mixed to obtain high-quality regenerated soil in which the inorganic environmental minerals and organic humic acid are coupled.

2. The method according to claim 1, characterized in that The carbon element of the humic acid is mainly in the form of aromatic carbon.

3. The method according to claim 1, characterized in that The characteristic organic element molar ratios of the humic acid are H / C < 1.30, N / C = 0.05-0.11, and O / C > 0.

30.

4. The method according to claim 1, wherein An aluminum source is added to the inorganic components of the sludge so that the Al / Si molar ratio of the sludge system is 0.5-1.

5. The hydrothermal reaction is carried out at a hydrothermal reaction temperature of 180-240°C for 6-24 hours. After the reaction, the obtained reaction liquid is subjected to solid-liquid centrifugation to obtain a solid product, which is the clay mineral converted from the inorganic components of the sludge.

5. The method according to claim 4, characterized in that The kaolinite contained in the inorganic components of the sludge acts as a crystal seed to induce and promote the hydrothermal dissolution of the inorganic components of the sludge and to convert them into clay minerals through a reconstructive reaction and directional synthesis.

6. The method according to claim 1, characterized in that A sodium source is added to the inorganic components of the sludge so that the Na / Si molar ratio of the sludge system is 0.3-1.0, and an aluminum source is added so that the Al / Si molar ratio of the reaction system is 0.5-1.

5. The hydrothermal reaction is carried out at a hydrothermal reaction temperature of 160-220° C. for 6-24 hours. After the reaction, the obtained reaction liquid is subjected to solid-liquid centrifugation separation, and the obtained solid product is the zeolite mineral converted from the inorganic components of the sludge.

7. The method according to claim 1, characterized in that The mass ratio of humic acid enriched liquid and inorganic environmental minerals added to ordinary soil is regulated according to the requirements of land fertilizer efficiency and environmental purification.

8. Application of the method for hydrothermal conversion of all components of sludge into high-quality regenerated soil according to any one of claims 1 to 7 in soil carbon sequestration and environmental detoxification.

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