CN117361814A

CN117361814A - A method of hydrothermally converting all components of sludge into high-quality regenerated soil

Info

Publication number: CN117361814A
Application number: CN202311305191.8A
Authority: CN
Inventors: 景镇子; 张亚菲
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2023-10-10
Filing date: 2023-10-10
Publication date: 2024-01-09
Anticipated expiration: 2043-10-10
Also published as: CN117361814B

Abstract

The invention relates to a method for hydrothermally converting all components of sludge into high-quality regenerated soil, and belongs to the technical field of sludge resource utilization. The method includes: adding an alkali agent to sludge raw materials and mixing them uniformly to form a sludge reaction slurry; subjecting the sludge reaction slurry to a hydrothermal reaction; and after the reaction is completed, solid-liquid separation of the reaction product is performed, and the resulting liquid The phase product is a humic acid enriched liquid, and the obtained solid phase product is an inorganic component of the sludge; the inorganic components of the sludge are further hydrothermally converted into inorganic environmental minerals; the humic acid enriched liquid, inorganic environmental minerals and ordinary soil are Mixed to obtain high-quality regenerated soil coupled with inorganic environmental minerals and organic humic acids. In the present invention, the inorganic components of the sludge are hydrothermally dissolved and reconstructed into the main environmental minerals of the soil. At the same time, the organic components of the sludge are hydrothermally dissolved and synthesized into humic acid, which constitutes the main organic and inorganic components (humic acid) of the soil. acid and environmental minerals), it is expected to achieve safe and efficient land utilization of sludge.

Description

Method for transforming full-component sludge into high-quality regenerated soil through hydrothermal method

Technical Field

The invention relates to a method for transforming full components of sludge into high-quality regenerated soil by using hydrothermal method, belonging to the technical field of sludge recycling.

Background

With the acceleration of urban process in China, the urban sewage treatment scale is enlarged year by year. Municipal sludge is the main solid waste generated in the sewage treatment process, and is large in volume and continuously discharged. The sludge contains heavy metal and other refractory pollutants and a large number of pathogen microorganisms, and the improper disposal is extremely easy to cause secondary environmental pollution and potential resource waste.

Under the guidance of sludge recycling, the traditional rough disposal modes such as landfill, stacking and the like are gradually abandoned. Although the incineration can greatly reduce the volume and kill pathogens, the method has the defects of high investment cost, high energy consumption, easy generation of volatile toxic substances, treatment of incineration ash and the like. At present, anaerobic digestion is the most common treatment method, which can digest and degrade organic matters of sludge into biomass energy such as methane (methane), and inorganic residues after sludge digestion are recycled. Land utilization can realize large-scale digestion and recycling of sludge resources, and has been used as a main sludge treatment mode in European and American developed countries in recent years. Although the treatment technology is also introduced in China, the sludge in China has the characteristics of less organic matters and high sand content, so that the technology is not suitable for water and soil. In addition, the digestion treatment cannot convert the sludge inorganic residues into the effective mineral components of the soil, so that the inorganic components thereof are not effectively utilized.

The high-quality soil should contain sufficient humus and the like, and provide a good fertility environment for plant growth. The sludge contains more organic components, such as rich organic carbon elements, nitrogen, phosphorus, potassium and other nutrient elements. However, the existing sludge has low humification degree, the organic matters of the digested sludge inorganic residues are less, and the direct land utilization is difficult to meet the plant growth requirement. If the sludge organic component can be converted into the most important organic component humic acid in the soil, the fertilizer efficiency can be effectively improved, and the high-value land utilization of the sludge organic matters can be realized.

The sludge in China has the characteristics of less organic matters and high sand content. In practice, the organic and inorganic components account for approximately half of the total components of the sludge. The inorganic matters of the sludge are mainly silicon, aluminum, calcium and other components, and are similar to natural soil minerals in element composition, so that the inorganic matters of the sludge can be theoretically converted into main mineral compositions (clay minerals, zeolite minerals and the like) of the soil. These minerals not only can be the most important inorganic mineral components in the soil, but also have good self-cleaning ability. However, for digested sludge residues widely used in current land utilization, inorganic components therein cannot be converted into high-quality soil minerals by digestion, and thus a huge volume of sludge inorganic resources are wasted. In summary, a new method which meets the national conditions of China and can realize the efficient land utilization of the full components (organic and inorganic) of the sludge is urgently needed.

Chinese patent CN102584365B discloses a method for preparing soil-improving fertilizer by mixing sludge with straw, manure, fermentation inoculant, etc. and performing aerobic fermentation; chinese patent CN114538747a discloses a method for preparing ecological soil from sludge, which comprises mixing sludge with carbon-based crushed material, heating, baking and biologically fermenting to prepare ecological soil; chinese patent CN106587572B discloses a process for soil treatment of sludge, which comprises adding a composite oxidizing sterilizing agent and a composite dewatering agent to sludge for chemical treatment, and performing physical dewatering for multiple times to realize sludge reduction and stabilization treatment.

The patent aims at the sludge soil, but only adopts physical or chemical means to treat the sludge in apparent properties, so that the organic humification degree of the sludge is not substantially improved, the efficient conversion and reutilization of the soil of inorganic components of the sludge are not realized, and the harmless treatment of a sludge regenerated product is more difficult to ensure.

Disclosure of Invention

Aiming at the problems, the invention provides a method for converting full components of sludge into high-quality regenerated soil by utilizing a hydrothermal technology, namely, inorganic components of the sludge are hydrothermally dissolved and reconstituted into main environmental minerals of the soil, and simultaneously organic components of the sludge are hydrothermally dissolved and synthesized into humic acid, so that the main organic and inorganic components (humic acid and environmental minerals) of the soil are formed, and the safe and efficient land utilization of the sludge is hopefully realized.

In a first aspect, the invention provides a method for hydrothermally converting full-component sludge into high-quality regenerated soil. The method comprises the following steps: adding an alkaline agent into a sludge raw material and uniformly mixing to prepare a sludge reaction slurry, wherein the alkaline content of the sludge reaction slurry is 0.1-0.5 mol/L in terms of hydroxide ion concentration; carrying out hydrothermal reaction on the sludge reaction slurry, wherein the hydrothermal reaction temperature is 120-180 ℃, and the hydrothermal reaction time is 0.5-5 hours; after the reaction is finished, carrying out solid-liquid separation on the reaction product, wherein the obtained liquid-phase product is humic acid enrichment liquid, and the obtained solid-phase product is sludge inorganic component; the inorganic components of the sludge are further converted into inorganic environment minerals through hydrothermal conversion; mixing the humic acid enrichment liquid, inorganic environment minerals and common soil, thereby obtaining the high-quality regenerated soil with inorganic environment minerals and organic humic acid coupled.

Preferably, the carbon element of the humic acid is mainly in the form of aromatic carbon.

Preferably, the 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.

Preferably, the humic acid has a loose porous structure with a large number of micron-sized pore canals distributed on the surface and the pore canals are mutually crosslinked and communicated.

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

Preferably, an aluminum source is added into the sludge inorganic component to enable the Al/Si molar ratio of the sludge system to be 0.5-1.5, the hydrothermal reaction is carried out for 6-24 hours under the condition that the hydrothermal reaction temperature is 180-240 ℃, the obtained reaction liquid is subjected to solid-liquid centrifugal separation after the reaction, and the obtained solid product is the clay mineral converted from the sludge inorganic component.

Preferably, the kaolinite contained in the inorganic components of the sludge is used as seed crystal to induce and promote the inorganic components of the sludge to distribute hydrothermal dissolution and be directionally synthesized and converted into clay minerals through reconstruction reaction.

Preferably, a sodium source is added into the sludge inorganic component to enable the Na/Si molar ratio of the sludge system to be 0.3-1.0, an aluminum source is added to enable the Al/Si molar ratio of the reaction system to be 0.5-1.5, the hydrothermal reaction is carried out for 6-24 hours under the condition that the hydrothermal reaction temperature is 160-220 ℃, the obtained reaction liquid is subjected to solid-liquid centrifugal separation after the reaction, and the obtained solid product is the zeolite mineral converted from the sludge inorganic component.

Preferably, the mass ratio of the humic acid enrichment liquid to the inorganic environment minerals added into the soil is regulated and controlled according to the soil fertilizer efficiency requirement and the environment purification requirement.

In a second aspect, the invention provides the use of a method as defined in any one of the preceding claims for soil carbon sequestration and environmental detoxification.

Drawings

FIG. 1 is a microstructure morphology diagram of sludge hydro-thermal humic acid under a scanning electron microscope.

FIG. 2 is a Fourier transform infrared absorption spectrum of humic acid by sludge hydrothermal synthesis.

FIG. 3 is a full spectrum of X-ray photoelectron spectroscopy of sludge hydro-thermal synthesis of humic acid.

FIG. 4 is a fine spectrum of X-ray photoelectron spectroscopy of sludge hydrothermal synthesis of humic acid.

Fig. 5 is an XRD pattern of a clay mineral hydrothermally synthesized from sludge at different reaction times.

Fig. 6 is a microstructure morphology diagram of a clay mineral hydrothermally synthesized from sludge under a scanning electron microscope.

Figure 7 is an XRD pattern of a zeolite mineral hydrothermally synthesized from sludge at different reaction times.

Fig. 8 is a microstructure topography of a sludge hydro-thermal synthesized zeolite mineral under a scanning electron microscope.

Fig. 9 is a microstructure topography of high quality reclaimed soil under a scanning electron microscope.

FIG. 10 shows plant growth in various soil environments.

FIG. 11 shows plant growth in various soil contaminated environments.

FIG. 12 shows heavy metal content at various parts of plants in different soil polluted environments.

Fig. 13 is a process flow diagram of the present invention.

Detailed Description

The invention is further illustrated by the following embodiments, which are to be understood as merely illustrative of the invention and not limiting thereof. The method for hydrothermally converting full components of sludge into high-quality regenerated soil according to the present invention is exemplified as follows.

Adding alkaline agent into the sludge raw material and uniformly mixing to prepare sludge reaction slurry.

The kind of the sludge raw material is not limited. It should be understood that any kind of sludge feedstock may be suitable for use in the present invention. The sludge feedstock may be municipal sludge.

The water content and organic matter content of the sludge raw material are not limited. High water content sludge may also be suitable for use in the present invention. As an example, the water content of the sludge raw material is 80 to 90wt%. Existing sludge treatment techniques typically require deep drying of the sludge to an absolute dry state and crushing and grinding to make it usable. Because the invention takes the state of fluid mud as the raw material of the sludge for reaction, the raw material of the sludge can be directly utilized without any pretreatment before use. Of course, the sludge raw material does not need to be dehydrated or dried.

The alkaline agent includes, but is not limited to, sodium hydroxide, potassium hydroxide, aluminum hydroxide, and the like. The alkali content of the sludge reaction slurry is 0.1-0.5 mol/L based on hydroxide ion concentration. In the hydrothermal reaction environment, the alkali agent is controlled within the concentration range, so that the original macromolecular organic matters in the sludge, such as polysaccharide, lipid, protein and the like, can be effectively decomposed into micromolecular organic matters, such as monosaccharide, fatty acid, amino acid and the like, and sufficient precursors are provided for the final hydrothermal reconstitution-synthesis humic acid product. If the alkali concentration is too low, the concentration is insufficient to completely decompose the original macromolecular organic matters, so that the yield of humic acid is low. If the alkali concentration is too high, the inorganic components of the sludge are further decomposed, namely, the first hydrothermal reaction for generating humic acid by the organic component hydrothermal reaction is carried out, and meanwhile, the second hydrothermal reaction for generating inorganic environment minerals by the inorganic component hydrothermal reaction is started, so that the hydrothermal synthesis of humic acid reaction is interfered. Also, too high an alkali concentration can result in humic acid products that are too alkaline to be useful in land use. Sodium hydroxide is used as the alkaline agent in particular embodiments. Thus, the alkali content of the sludge reaction slurry is 0.1 to 0.5mol/L in terms of sodium hydroxide concentration.

The sludge reaction slurry is subjected to a hydrothermal reaction (which may also be referred to as a first hydrothermal reaction). The first hydrothermal reaction is used for synthesizing humic acid by hydrothermally dissolving the sludge organic components, and simultaneously, the hydrothermal treatment can synchronously and thoroughly kill harmful microorganisms such as original pathogens of the sludge.

In the first hydrothermal reaction, the hydrothermal reaction temperature is 120-180 ℃. Optimally, the hydrothermal reaction temperature is selected to be 150 ℃. The hydrothermal reaction time is 0.5-5 hours. Optimally, the hydrothermal reaction time is chosen to be 1 hour. The temperature and time of the first hydrothermal reaction are controlled in the above range, so that the yield of humic acid can be synergistically improved while the ore-like source humic acid product is generated.

After the reaction is finished, carrying out solid-liquid separation on the reaction product, wherein the obtained liquid-phase product is humic acid enrichment liquid, and the obtained solid-phase product is sludge inorganic component. The humic acid concentrate may be weakly alkaline.

The hydrothermal synthesis humic acid obtained by the first hydrothermal reaction is highly similar to the mineral source humic acid (rich in oxygen-containing groups, aromatic structures and lower H/C ratio) in natural lignite in composition and structure, and is different from the biochemical humic acid produced by traditional fermentation (weak acidification and aromatic degree and high fat degree). This is due to: by providing proper hydrothermal reaction conditions, the reaction process of converting organic matters into mineral source humic acid (for example, the formation process of humic acid in natural lignite) in the natural underground hydrothermal environment can be effectively simulated even highly, macromolecular organic matters in the sludge are promoted to be rapidly dissolved and reconstructed into brand new humic acid products, and a higher humification degree is obtained.

Through analysis and characterization, the hydrothermal synthesis humic acid obtained by the first hydrothermal reaction is mainly in the existence form of aromatic carbon. This indicates that the organic carbon in the sludge has been sufficiently converted to an aromatic carbon structure through the first hydrothermal reaction. Preferably, the main existence form of carbon element of the hydrothermal synthesized humic acid obtained by the first hydrothermal reaction comprises aromatic carbon and aliphatic carbon. Furthermore, the molar ratio of the characteristic organic elements of the humic acid is H/C less than 1.30, N/C=0.05-0.11 and O/C more than 0.30. For example, humic acid has a characteristic organic element molar ratio of H/c=1.24, n/c=0.10, o/c=0.36. This further demonstrates that the humic acid product obtained from sludge hydrothermal has a higher degree of polycondensation (lower H/C ratio) and a higher degree of acidification (higher O/C ratio). "H/C low" means a high degree of unsaturation (or degree of polycondensation or aromatisation). "O/C high" means that the oxygen-containing groups are more, the activity is high, and the acidification degree is high. Namely, the humification degree of the product is remarkable.

From the microstructure, it can be seen that the humic acid has a loose porous structure with a large number of micron-sized pores distributed on the surface and the pores are mutually crosslinked and communicated. The pore canal structures provide effective sites for humic acid to adsorb heavy metals and the like.

In the first hydrothermal reaction of sludge hydro-thermal synthesis humic acid, no conditioner is needed to be added, only sludge is needed to be used as a main reaction raw material, and the treatment process of the reaction system material is simpler and more convenient, the comprehensive cost is lower, and the environment benefit is friendly. Compared with the existing technology for synthesizing humic acid by hydrothermal method, the method has the advantages that the hydrothermal reaction temperature is obviously reduced, and the hydrothermal time is shortened. Through various characterization analysis, the humic acid synthesized by the method has obvious aromaticity degree, acidification degree and polycondensation degree, namely the whole body shows more obvious humification degree, and the characteristic of the humic acid is highly similar to that of natural mineral source humic acid, so that the humic acid has higher humic acid quality.

The inorganic components of the sludge are further converted into inorganic environmental minerals by a hydrothermal reaction (which may also be referred to as a second hydrothermal reaction). The inorganic environment mineral is clay mineral and/or zeolite mineral. Specifically, the target mineral is directionally synthesized by regulating and controlling the element proportion of a sludge system and the hydrothermal reaction condition.

In some technical schemes, an aluminum source is added into the sludge inorganic component to enable the Al/Si molar ratio of a sludge system to be 0.5-1.5, then hydrothermal reaction is carried out for 6-24 hours under the condition that the hydrothermal reaction temperature is 180-240 ℃, the obtained reaction liquid is subjected to solid-liquid centrifugal separation after the reaction, and the obtained solid product is the clay mineral converted from the sludge inorganic component.

The clay mineral may be kaolin Dan Kuangwu. The kaolinite contained in the inorganic components of the sludge is used as seed crystal to induce and promote the inorganic components of the sludge to distribute hydrothermal dissolution and directionally synthesize and convert the clay mineral through a reconstruction reaction.

In some technical schemes, a sodium source is added into the sludge inorganic component to enable the Na/Si molar ratio of a sludge system to be 0.3-1.0 (preferably 0.5), an aluminum source is added to enable the Al/Si molar ratio of a reaction system to be 0.5-1.5, then hydrothermal reaction is carried out for 6-24 hours under the condition of 160-220 ℃ of hydrothermal reaction temperature, after the reaction, solid-liquid centrifugal separation is carried out on the obtained reaction liquid, and the obtained solid product is the zeolite mineral converted from the sludge inorganic component.

The second hydrothermal reaction utilizes inorganic components of the sludge to synthesize various types of environmental minerals including zeolite minerals, clay minerals, and the like. Unlike Chinese patent CN 113426825A, which synthesizes other kinds of minerals with pure clay mineral, such as montmorillonite, as material, the present invention synthesizes environment mineral with inorganic sludge residue produced through synthesizing sludge via hydrothermal reaction and separating humic acid. In addition, chinese patent CN 113426825a is to fix heavy metals in situ during the synthesis of minerals from the purification principle. That is, chinese patent CN 113426825a is to fix heavy metals simultaneously during the process of synthesizing minerals. The invention utilizes synthesized environmental minerals (such as zeolite) to be put into a real soil environment for absorbing heavy metals, thereby purifying the environment and promoting the growth and development of plants. Namely, the invention targets the synthetic mineral and post-fixes the heavy metal. Thus, the present invention is significantly different from the prior art in the mechanism of fixing heavy metals and purifying the environment. Finally, chinese patent CN 113426825a adapts to the synthetic zeolite minerals according to the type of heavy metals present in the reaction system, i.e. the specific type of synthetic minerals varies with the actual presence of heavy metals in the reaction system. The invention can regulate the hydrothermal reaction condition to directionally synthesize various target minerals including zeolite minerals, clay minerals and the like, i.e. the type of the synthesized target minerals can be determined in advance. Thus, the present invention also differs significantly from chinese patent CN 113426825a in the mechanism of the synthetic minerals.

In the present invention, it is also described that the remaining humic acid (sludge inorganic component) is used after the humic acid is synthesized by using the sludge organic component. That is, the method of the present invention further comprises a second hydrothermal reaction of further subjecting the reaction residue (inorganic component) obtained by the first hydrothermal reaction to a hydrothermal reaction to synthesize a functional mineral having a clean environment, in addition to the first hydrothermal reaction of synthesizing humic acid by the hydrothermal reaction, thereby further achieving efficient reuse of the inorganic component of the sludge. This is yet another important innovation of the present invention that distinguishes over the prior art.

The raw material used for the first hydrothermal reaction is sludge (organic component + inorganic component) which is carried out at a lower reaction temperature for a shorter reaction time, with the aim of hydrothermally dissolving the organic component of the sludge to synthesize humic acid. The raw materials used in the second hydrothermal reaction are sludge residues (inorganic components) remained after the first step of hydrothermal reaction, which are carried out at a higher reaction temperature for a longer reaction time, and the purpose of hydrothermally dissolving the inorganic components of the sludge to synthesize environmental minerals.

Mixing the humic acid enrichment liquid, inorganic environment minerals and common soil, thereby obtaining the high-quality regenerated soil with inorganic environment minerals and organic humic acid coupled. The mixture may be left at ambient temperature for a period of time to facilitate sufficient contact of the components to allow the inorganic environmental minerals and humic acid to couple together. The inorganic environmental mineral may be a clay mineral, a zeolite mineral, or a mixture of clay mineral and zeolite mineral. The mass ratio of the humic acid enrichment liquid to inorganic environment minerals can be regulated and controlled according to the soil fertilizer efficiency requirement and the environment purification requirement.

In summary, the prior art cannot realize the efficient and safe conversion from the full components (organic matters and inorganic matters) of the sludge to the high-quality regenerated soil, namely, the inorganic and organic components of the sludge are respectively the most basic components of the soil, namely, clay minerals and humic acid. Compared with the prior art, the invention not only can hydrothermally dissolve and reconstruct the inorganic components of the sludge into brand new environmental minerals by utilizing the hydrothermal technology, but also can synchronously convert the organic components of the sludge into high-quality humic acid, thereby substantially improving the mineralization and humification degree of the soil. The environmental minerals and humic acid synthesized by hydrothermal orientation can be used for in-situ stable fixation and adsorption of pollutants such as heavy metals, so that the self-purification capability of soil can be improved, the bioavailability of harmful substances can be reduced, and in addition, the original harmful microorganisms such as pathogens of the sludge can be synchronously and thoroughly killed by the hydrothermal treatment. Therefore, the technology realizes safe and harmless utilization. Therefore, the invention can provide a novel technology for safely, environmentally-friendly and efficient full-component high-quality soil formation of the sludge.

As a specific example, the method for synthesizing high-quality regenerated soil by using the hydro-thermal conversion sludge comprises the following specific steps:

[ step 1 ] sludge raw material selection: the surplus sludge discharged from the sewage plant is selected as a raw material (the water content is 80% -90%), and the surplus sludge can be directly utilized without re-dehydration or drying treatment.

[ step 2 ] the organic components of the sludge are hydrothermally converted to synthesize humic acid. Adding alkaline agent sodium hydroxide into the sludge raw material to prepare sludge reaction slurry. The alkali content of the sludge reaction slurry is regulated to be 0.1 to 0.5mol/L (optimally, 0.1mol/L is selected) based on the concentration of sodium hydroxide. The hydrothermal reaction is carried out in an autoclave of a homogeneous reactor. The hydrothermal reaction temperature is 120-180 ℃, and the hydrothermal reaction time is 0.5-5 hours. The liquid phase product obtained by solid-liquid separation after the reaction is the humic acid enrichment liquid obtained by converting the sludge organic component, and the solid phase product obtained is the sludge inorganic component.

The inorganic components of the sludge are synthesized into environmental minerals by hydro-thermal conversion. Adding a small amount of sodium source reagent and/or aluminum source reagent into the sludge inorganic residue obtained in the step 2, so that the inorganic system element ratio is: (1) the Na/Si molar ratio of the sodium source reagent (sodium hydroxide, sodium chloride, etc.) is 0.3 to 1.0 (preferably 0.5 to 1.0); and/or (2) an Al/Si molar ratio of 0.5 to 1.5 (preferably 0.5 to 1.0, more preferably 0.8 to 1.2, still more preferably 0.6 to 1.0, most preferably 1.0) to which an aluminum source reagent (aluminum nitrate, aluminum chloride, aluminum hydroxide, etc.) is added. Preferably, the sodium source reagent and the aluminum source reagent are separate distinct reagents.

Specifically, the target mineral is directionally synthesized by regulating and controlling the element proportion of a sludge system and the hydrothermal reaction condition.

(1) Synthetic clay mineral (kaolinite): adding an aluminum source reagent (aluminum nitrate) to enable the Al/Si molar ratio of a sludge system to be 1, and carrying out hydrothermal reaction in a high-pressure reaction kettle: the hydrothermal reaction temperature is 180-240 ℃ (optimally 220 ℃), and the hydrothermal reaction time is 6-24 hours. After the reaction, the solid and the liquid are centrifugally separated, and the obtained solid product is the clay mineral converted from inorganic components of the sludge.

(2) Synthetic zeolite mineral (analcite): sodium source reagent (sodium hydroxide) is added to adjust the Na/Si molar ratio of the reaction system to 0.5, aluminum source reagent (aluminum nitrate) is added to adjust the Al/Si molar ratio of the reaction system to 0.5, and hydrothermal reaction is carried out in a reaction kettle. The hydrothermal reaction temperature is 160-220 ℃ (optimally, 200 ℃) and the hydrothermal reaction time is 6-24 hours. And (3) carrying out solid-liquid centrifugal separation after the reaction, wherein the obtained solid product is the zeolite mineral converted from the inorganic components of the sludge.

Step 4, preparing high-quality regenerated soil by coupling inorganic environment minerals and organic humic acid: uniformly mixing the humic acid enrichment solution obtained in the step 2, the environmental minerals obtained in the step 3 and the common soil according to a certain proportion (the mixing ratio of the humic acid component and the environmental mineral component can be regulated and controlled according to the soil fertilizer efficiency requirement and the environmental purification requirement), and standing for 1 day at normal temperature, wherein the final mixture is the high-quality regenerated soil synthesized by full-component conversion of the sludge.

The present invention will be described in more detail by way of examples. It is also to be understood that the following examples are given solely for the purpose of illustration and are not to be construed as limitations upon the scope of the invention, since numerous insubstantial modifications and variations will now occur to those skilled in the art in light of the foregoing disclosure. The specific process parameters and the like described below are also merely examples of suitable ranges, i.e., one skilled in the art can make a suitable selection from the description herein and are not intended to be limited to the specific values described below.

Example 1: hydro-thermal synthesis of humic acid from organic sludge component

Selecting a sludge raw material: the surplus sludge discharged from the sewage plant is selected as a raw material (the water content is 90 wt%) and can be directly utilized without re-dehydration or drying treatment.

[ step 2 ] the organic components of the sludge are hydrothermally converted to synthesize humic acid. And adding sodium hydroxide into the sludge raw material to prepare sludge reaction slurry. The alkali content of the sludge reaction slurry is 0.1mol/L based on the concentration of sodium hydroxide. The hydrothermal reaction is carried out in an autoclave of a homogeneous reactor. The hydrothermal reaction temperature was 150℃and the hydrothermal reaction time was 1 hour. The liquid phase product obtained by solid-liquid separation after the reaction is the humic acid enrichment liquid obtained by converting the sludge organic component, and the solid phase product obtained is the sludge inorganic component.

In the embodiment, the sludge obtained in the step 1 is taken as a main raw material, and sludge organic components are synthesized into an enrichment liquid rich in humic acid by regulating hydrothermal reaction conditions according to the method in the step 2. The pH of the humic acid enrichment solution is measured to be 7.6, and the humic acid enrichment solution is slightly alkaline and has better environment affinity for land utilization. In order to effectively characterize the characteristics of the humic acid product, the humic acid product is extracted from the humic acid enrichment liquid according to the humic acid extraction and purification method of the International Humic Substance Society (IHSS), and the detailed characterization and analysis are carried out.

FIG. 1 shows the microstructure of sludge hydro-thermal humic acid by Scanning Electron Microscopy (SEM). In a high-resolution visual field (under the hundred-micrometer scale), the whole humic acid product is observed to be in a typical loose porous structure, a large number of micron-sized pore canals are distributed on the surface of the humic acid product, and all the pore canals are mutually crosslinked and communicated, so that the humic acid product synthesized by the sludge organic components after hydrothermal reaction has good structural development, can provide larger specific surface area and more adsorption sites, and has stronger adsorption potential for pollutants such as heavy metals. From the figure it can be seen that the size of the micro-scale channels is from a few microns to tens of microns. In addition, the micro-structure of the sludge hydro-thermal humic acid also has smaller mesopores. The mesoporous is nano-sized, and the size of the mesoporous can be found to be about 50nm through nitrogen adsorption test.

FIG. 2 is a Fourier transform infrared absorption spectrum (FTIR) characterization of characteristic functional groups of sludge hydro-thermal synthesis humic acid. Humic acid synthesized in hydrothermal environment is 3400-3200 cm ^-1 There are obvious characteristic peaks, tableThe stretching vibration of phenolic hydroxyl groups (-OH) in the humic acid is remarkable; 2930cm ^-1 And 2850cm ^-1 The absorption peak at this point represents methyl (-CH) ₃ ) And methylene (-CH) ₂ ) Stretching vibration indicates that the humic acid product has a certain amount of aliphatic structures; 1040cm ^-1 Stretching vibration of the C-O-C-bond and 1630-1450 cm ^-1 The absorption peak intensity corresponding to the vibration of the aromatic ring C=C skeleton is obvious, which indicates that humic acid obtained by hydro-thermal synthesis of sludge organic matters has a plurality of carboxyl and aromatic ring structures and has higher humification degree.

Fig. 3 and 4 are elemental compositions and chemical states of sludge hydro-thermal humic acid products analyzed by X-ray photoelectron spectroscopy (XPS). As shown in the full spectrum of fig. 3, the humic acid product mainly consists of C, O, N, S and other typical organic elements, which are highly similar to the organic matter elements of the sludge, and the humic acid elements are mainly derived from the organic matter components of the sludge.

Table 1 shows the content of the characteristic organic elements in the sludge hydrothermal humic acid by using an organic element analyzer, and the atomic molar ratio of the characteristic organic elements was calculated. The results show that the H/C=1.24 of the sludge hydro-thermal humic acid (the H/C of the natural humic acid is less than 1.30), which shows that the aromatic polycondensation degree (unsaturation degree) is higher; n/c=0.10 for hydrothermal humic acid, indicating that it contains more nitrogen-carbon condensed ring structure; the O/c=0.36 of the hydrothermal humic acid showed that it contained more oxygen-containing functional groups, consistent with the results of the previous characterization.

TABLE 1 molar ratio of organic elements characteristic of sludge hydrothermal humic acid

In order to characterize the chemical state of key elements of humic acid, further fine spectrum analysis is performed on carbon elements. As can be seen from the fine spectrum peak-splitting results of fig. 4, the existence form of carbon elements in the humic acid product comprises aromatic carbon (35.9%) and aliphatic carbon (30.5%), which indicates that the humic acid synthesized by hydrothermal method has higher aromaticity; in addition, a larger part of carbon elements exist in forms of carbonyl carbon, carboxyl carbon, alcohol ether carbon (carbon connected with alcohol and ether) and amino carbon (carbon connected with amino), which indicate that humic acid products have rich oxygen-containing groups and also show higher activity and acidification degree, and are consistent with the analysis of infrared absorption spectrum results shown in figure 2.

The above results are summarized: the humic acid synthesized by sludge hydrothermal synthesis in the embodiment is highly similar to the mineral source humic acid in natural lignite in composition and structure, namely, the humic acid contains rich oxygen-containing functional groups and aromatic structures and has a lower H/C ratio, obvious condensation degree, acidification degree and aromatic degree, and has stronger water-retaining and fertilizer-supplying capability and metal ion exchange/adsorption/complexation effect; meanwhile, the hydrothermal humic acid is obviously different from biochemical humic acid (which has weaker acidification and aromatization degree and higher aliphatic degree) generated by traditional composting fermentation.

Therefore, compared with the traditional composting humic acid, the humic acid obtained by sludge hydro-thermal synthesis in the embodiment has more remarkable advantages in the aspects of soil fertility, soil carbon fixation, environmental detoxification and the like.

Example 2: hydrothermal synthesis of clay mineral from inorganic components of sludge

In the embodiment, the sludge inorganic residue obtained in the step 2 is taken as a main raw material, and the target clay mineral (kaolinite) is synthesized by regulating and controlling the hydrothermal reaction condition according to the method in the step 3.

Synthesis of clay mineral (kaolinite): adding an aluminum source reagent (aluminum nitrate) to enable the Al/Si molar ratio of a sludge system to be 1, and carrying out hydrothermal reaction in a high-pressure reaction kettle: the hydrothermal reaction temperature is 220 ℃, and the hydrothermal reaction time is 0-24 hours. After the reaction, the solid and the liquid are centrifugally separated, and the obtained solid product is the clay mineral converted from inorganic components of the sludge.

Fig. 5 is a graph showing the analysis of the crystalline phase composition of the clay mineral by sludge hydrothermal synthesis at various reaction times by X-ray diffractometer (XRD). The results show that: as the hydrothermal reaction time was prolonged to 24h, the quartz characteristic peak intensity gradually decreased, while the kaolin Dan Tezheng peak appeared and gradually increased, which suggests that as the hydrothermal reaction continued, the quartz mineral structure gradually dissolved and reformed into a completely new clay mineral structure; when the reaction time reached 24h, the peak intensity of the kaolin Dan Tezheng peak was quite significant, indicating that the kaolinite synthesized under this condition developed well. Notably, a small amount of kaolinite is already present in the sludge raw material before the reaction (0 h), and just because of the presence of these seeds (kaolinite), the thermodynamic barrier of the nucleation of kaolinite crystals is reduced, the rapid nucleation crystallization of the inorganic components of the sludge is induced and promoted after the hydrothermal dissolution/precipitation, and thus the yield of kaolinite increases rapidly with the increase of the hydrothermal reaction time.

Fig. 6 is a Scanning Electron Microscope (SEM) characterization of the microstructure of kaolinite synthesized by 24-hour hydrothermal reaction of sludge. The results show that: at the micrometer scale, a dense distribution of a large number of lamellar morphology minerals can be observed, which exhibit the typical lamellar aluminosilicate characteristics of soil clay minerals. Meanwhile, EDS point scan data indicate that: the atomic ratio of main elements of the kaolinite product is as follows: si=0.98:1, approaching the ideal atomic ratio of natural kaolinite. This example shows that under suitable hydrothermal conditions, the sludge inorganic component can undergo a hydrothermal dissolution-reconstitution reaction to be directionally synthesized and converted into clay mineral, which becomes an important mineral component of soil.

Example 3: hydrothermal synthesis of zeolite mineral from inorganic components of sludge

In the embodiment, the sludge inorganic residue obtained in the step 2 is taken as a main raw material, and target zeolite mineral (analcite) is synthesized by regulating hydrothermal reaction conditions according to the method in the step 3.

Synthesis of zeolite minerals (analcite) [ step 3 ]: sodium source reagent (sodium hydroxide) is added to adjust the Na/Si molar ratio of the reaction system to 0.5, aluminum source reagent (aluminum nitrate) is added to adjust the Al/Si molar ratio of the reaction system to 0.5, and hydrothermal reaction is carried out in a reaction kettle. The hydrothermal reaction temperature is 200 ℃, and the hydrothermal reaction time is 0-24 hours. And (3) carrying out solid-liquid centrifugal separation after the reaction, wherein the obtained solid product is the zeolite mineral converted from the inorganic components of the sludge.

Fig. 7 shows the crystalline phase composition of the sludge hydrothermal synthesis zeolite minerals at various reaction times analyzed by X-ray diffractometer (XRD). The results show that: the quartz characteristic peak intensity gradually weakens along with the prolongation of the hydrothermal reaction time from 0h to 24h, and meanwhile, the analcite characteristic peak appears and gradually strengthens, which shows that along with the progress of the hydrothermal reaction, the quartz mineral structure gradually dissolves and is converted into a brand new analcite mineral; when the reaction time was extended to 24 hours, the quartz characteristic peak had almost completely disappeared, and instead, the widely distributed and prominent intensity of the analcite characteristic peak was obtained.

FIG. 8 shows the zeolite microstructure synthesized by 24-hour hydrothermal reaction of sludge inorganic residues, characterized by Scanning Electron Microscopy (SEM). The results show that: a large number of polygonal-surface spherical particles (analcite) are densely distributed in a large-scale view, and the analcite particles are clearly observed to exhibit a typical trioctahedral prismatic structure in a higher resolution view, indicating that the analcite crystals have been synthesized and fully developed under such conditions. Meanwhile, EDS point scan data indicate that: the atomic ratio of main elements of the analcite product is Na: al: si=1.07: 1:2, ideal atomic ratio Na close to analcite: al: si=1: 1:2. the nitrogen adsorption test result shows that the BET specific surface area of the analcite product is 62.97m ² Per gram, ratio of unreacted sludge raw material (0.3 m ² And/g) is remarkably increased compared with the method, and has good adsorption performance and purification potential. This example shows that under suitable hydrothermal conditions, the sludge inorganic components can undergo a thorough hydrothermal dissolution-reconstitution reaction, ultimately converting to high quality zeolite minerals.

Example 4: preparation of high-quality regenerated soil by coupling inorganic environment minerals and organic humic acid

In order to verify the land utilization effect of inorganic environmental minerals and organic humic acid synthesized by sludge, the embodiment mixes the humic acid enrichment solution obtained in the previous embodiment 1, the zeolite environmental minerals obtained in the previous embodiment 3 and common soil uniformly according to a certain proportion according to the method described in the step 4, prepares high-quality regenerated soil by coupling, and plants green plants.

Step 4, preparing high-quality regenerated soil by coupling inorganic environment minerals and organic humic acid: uniformly mixing the humic acid enrichment solution obtained in the step 2, the environmental minerals obtained in the step 3 and the common soil according to a certain proportion, standing for 1 day at normal temperature, and finally obtaining the mixture which is the high-quality regenerated soil synthesized by full-component conversion of the sludge.

In order to specifically explore the fertilizer efficiency and the environmental purification capability of the high-quality regenerated soil, the embodiment selects specific component mass proportions (namely 20% of humic acid enrichment liquid, 30% of zeolite minerals and 50% of common soil) to prepare the high-quality regenerated soil, and takes the high-quality regenerated soil as an example to explore the fertilizer efficiency.

The above examples are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, according to specific land utilization requirements, the humic acid ratio (0-100%) and the environmental mineral ratio (0-100%) can be regulated and controlled in a reasonable range, so as to prepare the high-quality regenerated soil meeting the self requirements.

This example performed microscopic morphological analysis on high quality reclaimed soil (example above). Fig. 9 is a graph of the microstructure of the regenerated soil characterized by Scanning Electron Microscopy (SEM), which is clearly observable on the hundred micron scale: the surface of the inorganic mineral with larger particles is adhered with a large amount of humic acid with loose porous structure, and the humic acid is densely distributed and completely coats the surface of the mineral, which indicates that the humic acid and the inorganic mineral structure are fully combined after being regenerated and mixed, thus forming two main components of the high-quality regenerated soil together.

Example 5: evaluation of fertility Effect of regenerated soil

In this example, the high quality regenerated soil obtained in example 4 was used as a soil base for plant cultivation, a regenerated soil group (100 g each) was set up to plant green leaf plants (select chicken hair seeds), and the fertility effect of the regenerated soil was investigated.

Selecting the sludge raw material (without hydrothermal treatment) obtained in the step 1 and common soil according to the mass ratio of 1:1, planting green leaf plants as sludge soil groups (100 g each) so as to simulate a sludge direct land utilization path and explore the soil fertility effect.

Normal soil was selected for planting green leaf plants as a blank (100 g per group). The common soil in this embodiment is natural soil which is not fertilized and is far away from artificial interference of pollution sources, and is collected from common land type areas such as grasslands, woodlands or undeveloped barren lands.

And (3) cultivating the plant seeds for 30 days after sowing, respectively picking a plurality of complete plants from the three groups after the plants are mature, measuring and recording the lengths of the plants, and comprehensively comparing and evaluating the fertility effects of the regenerated soil, the common soil and the sludge soil.

Fig. 10 records statistical results of plant lengths planted and harvested in a normal soil group, a regenerated soil group and a sludge soil group, respectively, and the measured parts of the plant lengths include three parts of roots, stems and leaves. The average length of plants of the common soil group is 7.0 cm, the average length of plants of the sludge soil group is 3.8 cm, and the average length of plants of the regenerated soil group is 11.8 cm, so that the plant growth effect is obviously better than that of the common soil group and the sludge soil group, and the regenerated soil group shows higher soil fertility due to higher humification degree after hydrothermal treatment, and is more beneficial to plant growth.

In addition, the plant growth vigor of the sludge soil group is rather inferior to that of the common soil group, which shows that the untreated sludge raw material has lower humification degree and is not beneficial to plant growth; in addition, the sludge often contains pollutants such as heavy metals, and the plant growth can be inhibited by directly utilizing the soil without being decomposed and removed. The embodiment also shows that the fertility effect of directly utilizing the sludge to the land is poor; the sludge can be converted into regenerated soil through hydrothermal treatment, the soil fertility is higher, the plant growth is effectively promoted, and finally, the high-quality land utilization is realized.

Example 6: pollution remediation effect evaluation of regenerated soil

In the embodiment, the high-quality regenerated soil obtained in the step 4 is taken as a soil substrate (100 g of each group) for plant cultivation, green leaf plants (chicken feather cocks) are planted, and the repair and purification effects of the regenerated soil on heavy metal pollution are explored, namely the regenerated soil group. Meanwhile, the green leaf plants planted in the common soil (100 g in each group) are also selected as a control, namely the common soil group. The common soil in this embodiment is natural soil which is not fertilized and is far away from artificial interference of pollution sources, and is collected from common land type areas such as grasslands, woodlands or undeveloped barren lands.

In order to simulate heavy metal pollution, heavy metal Cu (in the form of copper nitrate solution) is doped into one of the two types of soil respectively to serve as a pollution group, and the Cu concentration of the pollution soil group is controlled to be 500ppm, namely a regenerated soil (pollution) group and a common soil (pollution) group. And (3) cultivating the plant seeds for 30 days after sowing, respectively picking a plurality of complete plants from the four groups after the plant seeds are ripe, measuring and recording the lengths of the plants, and evaluating the pollution restoration effect of the regenerated soil.

Fig. 11 records statistical results of plant lengths obtained by planting in a contaminated and a non-contaminated environment, respectively, of a regenerated soil group and a normal soil group, and the measured part of the plant length includes three parts of root, stem and leaf. The average length of the plants of the common polluted soil group is 5.5 cm, the average length of the plants of the regenerated polluted soil group is 10.1 cm, the growth effect of the plant is obviously better than that of the common polluted soil, and the plant lengths of the plant of the non-polluted regenerated soil group are similar, which shows that the plant of the regenerated soil group is less disturbed in the polluted environment.

Further, leaching experiments were performed on the contaminated plants, and the heavy metal contents of the roots, stems, leaves and other parts of the plants were measured by ICP-OES (inductively coupled plasma emission spectrometry) respectively, and the results are shown in fig. 12. For the same group of plants, the concentration of heavy metals in the body is gradually decreased according to the sequence of roots, stems and leaves, and the migration distribution rule of the heavy metals entering the plant body from the soil environment along the plant root system is met. Compared with the common soil pollution group, the heavy metal content corresponding to each part of the regenerated soil pollution group plant is obviously reduced, which indicates that the migration of the heavy metal is effectively controlled in the regenerated soil, and the bioavailability is reduced.

Taken together, the above results indicate that: compared with common soil, the sludge hydro-thermal regeneration soil contains more humic acid and environmental minerals, the capacity of the sludge hydro-thermal regeneration soil for cooperatively adsorbing/complexing heavy metal ions by means of the physical-chemical coupling effect is stronger, the bioavailability of the heavy metal ions is effectively reduced, the heavy metal ions are more difficult to migrate into plants, the growth and development of the plants under the stress of the heavy metals are facilitated, the in-situ restoration and purification of heavy metal pollution are realized, and the safe and harmless land utilization of the high-quality regeneration soil is achieved. Wherein humic acid and environmental minerals are respectively used as organic and inorganic purifying agents, and perform complexation, ion exchange and adsorption in the soil environment together, so that the bioavailability of pollutants such as heavy metals is effectively reduced; the environment is purified, meanwhile, the structural diversity of soil microbial communities can be enhanced, the virtuous circle of nutrient elements in the soil environment is promoted, and the plant growth is promoted.

Claims

1. A method for hydrothermally converting full-component sludge into high-quality regenerated soil, the method comprising:

adding an alkaline agent into a sludge raw material and uniformly mixing to prepare a sludge reaction slurry, wherein the alkaline content of the sludge reaction slurry is 0.1-0.5 mol/L in terms of hydroxide ion concentration;

carrying out hydrothermal reaction on the sludge reaction slurry, wherein the hydrothermal reaction temperature is 120-180 ℃, and the hydrothermal reaction time is 0.5-5 hours;

after the reaction is finished, carrying out solid-liquid separation on the reaction product, wherein the obtained liquid-phase product is humic acid enrichment liquid, and the obtained solid-phase product is sludge inorganic component;

the inorganic components of the sludge are further converted into inorganic environment minerals through hydrothermal conversion;

mixing the humic acid enrichment liquid, inorganic environment minerals and common soil, thereby obtaining the high-quality regenerated soil with inorganic environment minerals and organic humic acid coupled.

2. The method according to claim 1, wherein the carbon element of humic acid is predominantly in the form of aromatic carbon.

3. The method according to claim 1 or 2, characterized in that the humic acid has a characteristic organic element molar ratio of H/C < 1.30, n/c=0.05-0.11, o/C > 0.30.

4. A method according to any one of claims 1 to 3, wherein the humic acid has a loose porous structure with a surface on which a plurality of micro-scale cells are arranged and each cell is cross-linked to each other.

5. The method according to any one of claims 1 to 4, wherein the inorganic environmental mineral is a clay mineral and/or a zeolite mineral.

6. The method according to any one of claims 1 to 5, 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 to 1.5, the hydrothermal reaction is carried out for 6 to 24 hours at a hydrothermal reaction temperature of 180 to 240 ℃, and the obtained reaction solution is subjected to solid-liquid centrifugal separation after the reaction, so that the obtained solid product is the clay mineral converted from the inorganic components of the sludge.

7. The method according to claim 6, wherein the kaolinite contained in the inorganic components of the sludge is used as seed to induce and promote the hydrothermal dissolution of the inorganic components of the sludge and the directional synthesis and conversion into clay minerals by the reconstitution reaction.

8. The method according to any one of claims 1 to 7, wherein a sodium source is added to the sludge inorganic component so that the Na/Si molar ratio of the sludge system is 0.3 to 1.0 and an aluminum source is added so that the Al/Si molar ratio of the reaction system is 0.5 to 1.5, the reaction is performed for 6 to 24 hours under the condition of a hydrothermal reaction temperature of 160 to 220 ℃, and the obtained reaction solution is subjected to solid-liquid centrifugal separation after the reaction, and the obtained solid product is the zeolite mineral converted from the sludge inorganic component.

9. The method according to any one of claims 1 to 8, wherein the mass ratio of the humic acid rich liquid to the inorganic environment minerals to be added into the common soil is regulated according to the soil fertilizer efficiency requirement and the environment purification requirement.

10. Use of the method according to any one of claims 1 to 9 for soil carbon sequestration and environmental detoxification.