CN112872009B - Method for restoring impoverished soil - Google Patents
Method for restoring impoverished soil Download PDFInfo
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- CN112872009B CN112872009B CN202110354856.9A CN202110354856A CN112872009B CN 112872009 B CN112872009 B CN 112872009B CN 202110354856 A CN202110354856 A CN 202110354856A CN 112872009 B CN112872009 B CN 112872009B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/08—Reclamation of contaminated soil chemically
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/06—Reclamation of contaminated soil thermally
- B09C1/065—Reclamation of contaminated soil thermally by pyrolysis
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Abstract
The invention relates to a impoverished soil restoration method, belongs to the technical field of soil restoration, and solves the problems that the existing treatment method for impoverished soil in greenhouse planting has high economic cost and cannot meet the requirement of greenhouse planting on land. The method for restoring the depleted soil comprises the following steps: step 1, crushing agricultural waste biomass; step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water to obtain solid hydrothermal carbon and hydrothermal carbon liquid; step 3, preparing the nutrient-rich hydrothermal carbon; step 4, preparing porous biochar through microwave carbonization, and step 5, mixing the hydrothermal carbon, the nutrient-rich hydrothermal carbon and the porous biochar in proportion to obtain a depleted soil conditioner; and adding the impoverished soil conditioner into the impoverished soil for soil remediation. According to the invention, the hydrothermal carbon, the nutrient-rich hydrothermal carbon and the porous biochar are added into the impoverished soil according to a certain proportion, so that the effects of soil quality improvement and synergism are achieved.
Description
Technical Field
The invention relates to the technical field of soil remediation, in particular to a method for remediating impoverished soil.
Background
Agriculture is a support for social development and progress, and along with the social development, the agriculture is changed greatly, such as the wide use of chemical fertilizers and pesticides.
In order to meet the requirements of rapid development and diversified development of the society, greenhouse planting of fruits and vegetables is more and more extensive. The greenhouse planting process has no intermittent planting and harvesting of crops, and a large amount of chemical fertilizers and pesticides are used, so that the soil is over utilized and depleted, and the hardening, salinization and fertilizer efficiency reduction of the soil are aggravated.
After the greenhouse is planted for a certain time, the soil is depleted, and the greenhouse crop planting is difficult to continue. At present, the treatment mode is generally to adopt the replacement of foreign soil and cover the high-quality soil of other places on the impoverished soil for continuous planting; and stopping planting the land for a certain time after the greenhouse is planted for a certain time, so that the depleted soil is gradually recovered and then the greenhouse planting is continued. The first mode needs a large amount of high-quality soil, has higher economic cost, does not solve the problem of soil depletion, and the second mode needs longer time and is difficult to meet the requirement of greenhouse planting on the land. How to condition soil for greenhouse planting so that greenhouse planting can be carried out continuously is a problem to be solved at present.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a method for restoring depleted soil, so as to solve the problems that the existing greenhouse planting soil depletion treatment method has high economic cost and cannot meet the requirement of greenhouse planting on land.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides a method for restoring impoverished soil, which comprises the following steps:
step 1, crushing agricultural waste biomass;
step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water, and performing solid-liquid separation on a product of the hydrothermal carbonization to obtain solid hydrothermal carbon and hydrothermal carbon liquid; recycling the hydrothermal carbon liquid;
step 3, preparing part of the solid hydrothermal carbon into nutrient-rich hydrothermal carbon;
step 4, dissolving part of the solid hydrothermal carbon and the activating agent in the step 2 in water to obtain a mixture, stirring and heating the mixture until the water in the mixture is completely volatilized, preparing porous biochar through microwave carbonization, and washing and drying the hydrothermal carbon to obtain the porous biochar;
the microwave power during microwave carbonization is 500-800W, the microwave carbonization time is 4-10min, and the microwave carbonization atmosphere is air, nitrogen or argon isolation;
step 5, mixing the hydrothermal carbon prepared in the step 2, the rich-nutrient hydrothermal carbon prepared in the step 3 and the porous biochar prepared in the step 4 in proportion to obtain a depleted soil conditioner; and adding the impoverished soil conditioner into the impoverished soil for soil remediation.
Further, in step 1, the agricultural waste biomass comprises straw, wood chips, fallen leaves, crop wastes and livestock manure, and the particle size of the crushed agricultural waste biomass is less than 0.18 mm.
Further, in the step 2, the mass ratio of the biomass to the water in the hydrothermal carbonization process is 1:1-1:4, the hydrothermal carbonization temperature is 180-.
Further, in the step 4, the drying temperature of the hydrothermal carbon is 60-100 ℃, and the water content of the hydrothermal carbon after drying is less than 5%.
Further, in step 4, the activator solution is one of sodium hydroxide, potassium hydroxide and phosphoric acid;
the temperature was heated to less than 100 c while stirring in the activator solution.
Further, in step 4, the biochar washing medium is water, the pH of the washed biochar is 6.5-7.5, the drying temperature is 80-120 ℃, and the drying time is 300-600 min.
Further, in the step 5, the proportion of the hydrothermal carbon, the nutrient-rich hydrothermal carbon and the porous biochar is 1:0.5-1:0.4-0.8, and the addition amount of the porous biochar in the impoverished soil is 3% -10%.
Further, in step 3, the preparation method of the nutrient-rich hydrothermal carbon comprises the following steps:
step i, adding hydrothermal carbon into a nutrient solution with the concentration of 500-1500mg/L, fully stirring, separating out the hydrothermal carbon, and drying at the temperature lower than 70 ℃ to obtain dry hydrothermal carbon;
step ii, adding urea into a granulator, spraying a binder, and then adding dry hydrothermal carbon for granulation and forming;
and iii, continuously spraying a binder to the granulator, adding dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size requirement to obtain the nutrient-rich hydrothermal carbon with the particle diameter of 0.5-1.0 mm.
Further, in the step ii, the particle size of the urea is 0.074-0.1mm, and the binder adopts 3.0-10.0% by mass of polyvinyl alcohol aqueous solution; the mass ratio of the hydrothermal carbon to the urea is 1:4-10, and the diameter of the formed particles is 0.2-0.4 mm.
Further, in step i, the nutrient solution is one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, magnesium phosphate and calcium superphosphate.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
(1) in the aspect of raw materials, the agricultural waste biomass raw materials adopted by the invention are cheap, have wide sources, are renewable and are environment-friendly, and the waste biomass is subjected to hydrothermal carbonization treatment, so that wet waste biomass can be directly treated by the hydrothermal carbonization, and the drying process of the waste biomass is avoided.
(2) In the hydrothermal carbonization process, partial components of the agricultural waste biomass are subjected to thermal decomposition, ash (namely mineral substances) in the biomass can enter the hydrothermal carbon solution, and further, the increase of saline-alkali components when the hydrothermal carbon is added into soil can be avoided.
Most of the biomass is organic carbon hydrate (more than 90 percent) and also contains a small amount of mineral components (generally less than 5 percent) such as silicon, calcium, magnesium salts and the like, minerals or ash in the biomass enter a liquid phase in the hydrothermal carbonization process, and the organic carbon hydrate is converted into hydrothermal carbon.
(3) The surface of the solid hydrothermal carbon prepared by the method contains a large number of functional groups, and the surface functional groups are beneficial to fixing nutrients such as nitrogen, phosphorus, potassium, magnesium and the like in the solid hydrothermal carbon through chemical action when the nutrient-rich hydrothermal carbon is prepared, so that the slow release effect of the nutrients is improved; the prepared nutrient-rich hydrothermal carbon has a multilayer structure, and urea serving as a nitrogen fertilizer is wrapped at the core of the nutrient-rich hydrothermal carbon particles, so that the slow release effect of the fertilizer efficiency can be obviously improved.
(4) According to the invention, hydrothermal carbon is used as a raw material to carry out microwave carbonization, the hydrothermal carbon reacts with an activating agent, the preparation of the porous biochar with a large specific surface area is facilitated, the rapid preparation of the porous biochar can be realized through the microwave carbonization, the porous biochar is added into the impoverished soil, the soil gap and the air permeability can be effectively increased, and the hardening property of the impoverished soil is improved.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a schematic flow diagram of a method of remediation of depleted soil;
FIG. 2 is a scanning electron microscope image of porous biochar with a large specific surface area;
FIG. 3 is an infrared spectrum of hydrothermal charcoal.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention and not to limit its scope.
The invention provides a method for restoring impoverished soil, which comprises the following steps:
step 1, crushing agricultural waste biomass;
step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water in proportion, performing solid-liquid separation on a product of the hydrothermal carbonization to obtain solid hydrothermal carbon and hydrothermal carbon liquid, and recycling the hydrothermal carbon liquid;
step 3, preparing part of the solid hydrothermal carbon in the step 2 into nutrient-rich hydrothermal carbon;
step 4, dissolving part of the solid hydrothermal carbon and the activating agent in the step 2 in water, stirring and heating until the water is completely volatilized, then carbonizing by using microwave, wherein the microwave power is 500-800W, the microwave carbonization time is 4-10min, the microwave carbonization atmosphere is air (sealed), nitrogen and argon isolated, and washing and drying the obtained charcoal after microwave carbonization to obtain porous charcoal;
and 5, uniformly mixing the hydrothermal carbon prepared in the step 2, the nutrient-rich hydrothermal carbon prepared in the step 3 and the porous biochar prepared in the step 4 according to a certain proportion to obtain a impoverished soil conditioner, and then adding the impoverished soil conditioner into impoverished soil for soil remediation.
Compared with the prior art, the restoration method for the impoverished soil in the greenhouse provided by the invention utilizes the renewable agricultural waste biomass with rich resources, low cost as the raw material, the hydrothermal carbonization has low requirement on the humidity of the waste biomass raw material, the drying process of the waste biomass is reduced, and the solid hydrothermal carbon obtained by the hydrothermal carbonization has small ash content and rich surface functional groups; the nutrient-rich hydrothermal carbon prepared from the solid hydrothermal carbon has good fertilizer efficiency and slow release effect; the porous biochar prepared from the solid hydrothermal carbon has the characteristics of porosity and large specific surface area (as shown in figure 2), and the soil conditioner prepared from the solid hydrothermal carbon, the nutrient-rich hydrothermal carbon and the porous biochar in proportion can obviously improve the characteristics of salt alkalinity, easy hardening, less nutrients and the like of depleted soil.
In the step 1, the agricultural waste biomass comprises straw, wood chips, fallen leaves, crop wastes and livestock manure, and the particle size of the crushed agricultural waste biomass is less than 0.18 mm.
In the step 2, the mass ratio of the waste biomass to water in the hydrothermal carbonization process is 1:1-1:4, the hydrothermal carbonization temperature is 180-; the yield of the hydrothermal carbon is 30-75%, and the carbon content in the hydrothermal carbon is 10-50% (the yield of the hydrothermal carbon is calculated by dividing the mass of the obtained hydrothermal carbon by the mass of the waste biomass before hydrothermal carbonization and multiplying the mass by 100%, and the carbon content is determined by an element analyzer).
In the step 2, the hydrothermal carbonization condition is controlled within the above range to ensure that the hydrothermal carbon beneficial to the subsequent use effect is obtained, and the infrared spectrogram of the hydrothermal carbon is shown in fig. 3.
When the hydrothermal carbonization liquid is recycled, the water contained therein can be subjected to hydrothermal carbonization together with the waste biomass.
In the step 4, the hydrothermal carbon is dried at the temperature of 60-100 ℃, and then hydrothermal treatment is carried out after dryingThe water content of the carbon is less than 5 percent. The activating agent is one of sodium hydroxide, potassium hydroxide and phosphoric acid, and the mass ratio of the hydrothermal carbon to the activating agent is 1: 0.5-2; the temperature was heated to less than 100 c while stirring in the activator solution. The mass ratio of the hydrothermal carbon to the activating agent is 1:0.5-2, and the activating agent and the hydrothermal carbon react mainly in the carbonization process to obtain porous biochar with a porous structure and a large specific surface area (the specific surface area is 500-2G) as shown in FIG. 2.
In the step 4, the microwave power is 500-800W, the microwave carbonization time is 4-10min, and the microwave carbonization atmosphere is air-isolated (sealed), nitrogen and argon. Compared with the existing carbonization mode, the carbonization time of microwave carbonization adopted by the invention is obviously reduced (from 4-7h to 5-10min), the microwave carbonization is different from the carbonization heating mode of the tubular furnace, and the microwave generated by the microwave carbonization can achieve uniform temperature rise inside and outside the solid material, thereby being beneficial to quickly preparing the porous biochar material.
The microwave carbonization atmosphere is controlled to be isolated air (sealed), nitrogen or argon atmosphere, so that the carbonization process can be better controlled, the biochar with relatively uniform pore diameter structure is obtained, if the atmosphere is not controlled, the carbonization process is introduced with air or oxidized, the carbon combustion in the carbonization process is easily caused, the yield of the porous biochar is reduced, and the porous biochar is not uniform.
In the step 4, the biochar washing medium is water, the pH value of the washed biochar is 6.5-7.5, the drying temperature is 80-120 ℃, and the drying time is 300-. Because the biochar is prepared by acid or alkali activation, the carbonized biochar has strong acidity or basicity and needs to be washed to be neutral by water.
In the step 5, the mass ratio of the hydrothermal carbon, the nutrient-rich hydrothermal carbon and the porous biochar is 1:0.5-1:0.4-0.8, and the addition amount of the nutrient-rich hydrothermal carbon to the impoverished soil is 3% -10%.
In step 3, the preparation method of the nutrient-rich hydrothermal carbon comprises the following steps:
step i, adding the solid hydrothermal carbon into the nutrient solution, fully stirring, separating out the solid hydrothermal carbon, and drying to obtain dry hydrothermal carbon; the solid hydrothermal carbon is added into the nutrient solution, and the hydrothermal carbon can adsorb substances in the solution, so that nutrients such as phosphorus, potassium, nitrogen, magnesium and the like are attached to the surface of the hydrothermal carbon, and the fertilizer efficiency of the hydrothermal carbon is improved.
In the step i, the nutrient solution is one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, magnesium phosphate and calcium superphosphate, the concentration of the nutrient solution is 500-1500mg/L, and the drying temperature of the hydrothermal carbon is lower than 70 ℃;
step ii, adding urea into a granulator, spraying a certain amount of binder, and then adding a certain amount of dry hydrothermal carbon for granulation and molding;
in the step ii, the particle size of the urea is 0.074-0.1mm, and the binder is polyvinyl alcohol aqueous solution with the mass concentration of 3.0-10.0%; the mass ratio of the hydrothermal carbon to the urea is 1:4-10, and the diameter of the formed particles is 0.2-0.4 mm.
And iii, continuously spraying a certain amount of binder to the granulator, then adding a certain amount of dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size of the nutrient-rich hydrothermal carbon to obtain multilayer and granular nutrient-rich hydrothermal carbon.
In step iii, the particle diameter of the formed nutrient-rich hydrothermal carbon is 0.5-1.0 mm. The particle size of the nutrient-rich hydrothermal carbon is controlled within the range, so that the slow release effect of the fertilizer efficiency of the nutrient-rich hydrothermal carbon can be ensured.
The total nutrient of the nutrient-rich hydrothermal carbon prepared by the invention is 20-50%, the cumulative release rate of nutrients in 30 days is less than 60%, and the slow release effect of the slow release fertilizer is good.
Example 1
The embodiment provides a method for restoring impoverished soil, which comprises the following steps:
step 1, crushing agricultural waste biomass including straws, sawdust, fallen leaves, crop wastes and livestock manure; the particle size of the crushed agricultural waste biomass is 0.17 mm.
Step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water, wherein the mass ratio of the biomass to the water in the hydrothermal carbonization process is 1:1, the hydrothermal carbonization temperature is 180 ℃, the hydrothermal carbonization time is 59min, performing solid-liquid separation on a product of the hydrothermal carbonization, and performing mechanical filtration or centrifugal separation to obtain solid hydrothermal carbon and hydrothermal carbon liquid; recycling the hydrothermal carbon liquid;
step 3, preparing part of the solid hydrothermal carbon into nutrient-rich hydrothermal carbon; the preparation method of the eutrophic hydrothermal carbon comprises the following steps:
step i, adding hydrothermal carbon into nutrient solution potassium dihydrogen phosphate with the concentration of 500mg/L, fully stirring, separating out hydrothermal carbon, and drying at the temperature of lower than 69 ℃ to obtain dry hydrothermal carbon;
step ii, adding urea into a granulator, spraying a polyvinyl alcohol aqueous solution with the mass concentration of 3.0%, and then adding dry hydrothermal carbon for granulation and forming; the particle size of the urea is 0.074 mm; the mass ratio of the hydrothermal carbon to the urea is 1:4, and the diameter of the formed particles is 0.2 mm.
And iii, continuously spraying the binder to a granulator, adding dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size requirement to obtain the nutrient-rich hydrothermal carbon with the particle diameter of 0.5 mm.
Step 4, dissolving part of the solid hydrothermal carbon and sodium hydroxide obtained in the step 2 in water to obtain a mixture, stirring and heating until the water in the mixture is completely volatilized, and then carbonizing by using microwaves, wherein the microwave power is 500W, the microwave carbonization time is 4min, the microwave carbonization atmosphere is air (sealed), nitrogen and argon, and the obtained charcoal is washed and dried after microwave carbonization to obtain porous charcoal; the drying temperature of the hydrothermal carbon is 59 ℃, and the water content of the hydrothermal carbon after drying is less than 4%; the heating temperature during stirring in the sodium hydroxide solution was 98 ℃. The biochar washing medium is water, the pH value of the washed biochar is 6.5, the drying temperature is 80 ℃, and the drying time is 300 min.
Step 5, mixing the hydrothermal carbon prepared in the step 2, the nutrient-rich hydrothermal carbon prepared in the step 3 and the porous biochar prepared in the step 4 according to the mass ratio of 1:0.5:0.8 to obtain a depleted soil conditioner; and adding the impoverished soil conditioner into the impoverished soil for soil remediation, wherein the addition amount of the conditioner is 4%. The soil conditioner is added into impoverished soil planted in the greenhouse, shallow cultivation is carried out on the impoverished soil on the inner surface layer of the greenhouse by adopting a turning-in machine, the soil conditioner which is spread on the ground surface is buried into the shallow soil, and the improved soil planted in the greenhouse is obtained, wherein the porosity of the improved soil is increased by 2%, the water retention is increased by 5%, and the organic carbon is increased by 3.8%.
The first set of experiments was carried out by planting ryegrass in the impoverished and improved soils respectively, and comparing the dry weight of the ryegrass after 15 days of growth, the growth rate of the ryegrass planted in the improved soil prepared by the invention is improved by 20%.
The second set of experiments was to grow vegetables (shanghai green) in the impoverished and improved soils, respectively, with a 25% increase in yield of vegetables grown in the improved soils prepared using the present invention over vegetables grown in the impoverished soils.
Example 2
The embodiment provides a method for restoring impoverished soil, which comprises the following steps:
step 1, crushing agricultural waste biomass including straws, sawdust, fallen leaves, crop wastes and livestock manure; the particle size of the crushed agricultural waste biomass is less than 0.15 mm.
Step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water, wherein the mass ratio of the biomass to the water in the hydrothermal carbonization process is 1:3, the hydrothermal carbonization temperature is 240 ℃, the hydrothermal carbonization time is 240min, and performing solid-liquid separation on a product of the hydrothermal carbonization, wherein the solid-liquid separation mode is mechanical filtration or centrifugal separation to obtain solid hydrothermal carbon and hydrothermal carbon liquid; recycling the hydrothermal carbon liquid;
step 3, preparing part of the solid hydrothermal carbon into nutrient-rich hydrothermal carbon; the preparation method of the eutrophic hydrothermal carbon comprises the following steps:
step i, adding hydrothermal carbon into a ammonium dihydrogen phosphate solution with the concentration of 1000mg/L, fully stirring, separating out hydrothermal carbon, and drying at the temperature of less than 65 ℃ to obtain dry hydrothermal carbon;
step ii, adding urea into a granulator, spraying a polyvinyl alcohol aqueous solution with the mass concentration of 8.0%, and then adding dry hydrothermal carbon for granulation and forming; the particle size of the urea is 0.09 mm; the mass ratio of the hydrothermal carbon to the urea is 1:7, and the diameter of the formed particles is 0.3 mm.
And iii, continuously spraying the binder to a granulator, adding dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size requirement to obtain the nutrient-rich hydrothermal carbon with the particle diameter of 0.8 mm.
Step 4, dissolving part of the solid hydrothermal carbon and potassium hydroxide obtained in the step 2 in water to obtain a mixture, stirring and heating until the water in the mixture is completely volatilized, and then carbonizing by using microwaves, wherein the microwave power is 700W, the microwave carbonization time is 7min, the microwave carbonization atmosphere is air (sealed), nitrogen and argon, and the obtained charcoal is washed and dried after microwave carbonization to obtain porous charcoal; the drying temperature of the hydrothermal carbon is 85 ℃, and the water content of the hydrothermal carbon after drying is 4%. The heating temperature during stirring in the potassium hydroxide solution was 90 ℃. The biochar washing medium is water, the pH value of the washed biochar is 6.9, the drying temperature is 100 ℃, and the drying time is 450 min.
Step 5, mixing the hydrothermal carbon prepared in the step 2, the nutrient-rich hydrothermal carbon prepared in the step 3 and the porous biochar prepared in the step 4 according to the mass ratio of 1:0.7:0.6 to obtain a depleted soil conditioner;
in the embodiment, the soil conditioner is added into the impoverished soil planted in the greenhouse in a mass ratio of 8%, the impoverished soil on the inner surface layer of the greenhouse is subjected to shallow tillage by using a turning-in machine, so that the soil conditioner spread on the ground surface is buried into the shallow soil, and the improved soil planted in the greenhouse is obtained, wherein the porosity of the improved soil is increased by 10%, the water retention is increased by 10%, and the organic carbon is increased by 5.8%.
The first set of experiments was carried out by planting ryegrass in barren soil and improved soil respectively, and comparing the dry weight of the ryegrass after the ryegrass grows for 15 days, the growth rate of the ryegrass planted in the improved soil prepared by the invention is improved by 25%.
The second set of experiments was conducted in which vegetables (shanghai green) were grown in depleted soil and in improved soil, respectively, and the yield of vegetables grown in improved soil prepared using the present invention was increased by 30% relative to vegetables grown in depleted soil.
Example 3
The embodiment provides a method for restoring impoverished soil, which comprises the following steps:
step 1, crushing agricultural waste biomass including straws, sawdust, fallen leaves, crop wastes and livestock manure; the particle size of the crushed agricultural waste biomass is less than 0.12 mm.
Step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water, wherein the mass ratio of the biomass to the water in the hydrothermal carbonization process is 1:4, the hydrothermal carbonization temperature is 290 ℃, the hydrothermal carbonization time is 350min, performing solid-liquid separation on a product of the hydrothermal carbonization, and performing mechanical filtration or centrifugal separation to obtain solid hydrothermal carbon and hydrothermal carbon liquid; recycling the hydrothermal carbon liquid;
step 3, preparing part of the solid hydrothermal carbon into nutrient-rich hydrothermal carbon; the preparation method of the eutrophic hydrothermal carbon comprises the following steps:
step i, adding the hydrothermal carbon into a calcium superphosphate solution with the concentration of 1480mg/L, fully stirring, separating out the hydrothermal carbon, and drying at the temperature of 45 ℃ to obtain the dry hydrothermal carbon.
Step ii, adding urea into a granulator, spraying a polyvinyl alcohol aqueous solution with the mass concentration of 9.4%, and then adding dry hydrothermal carbon for granulation and forming; the particle size of the urea is 0.1 mm; the mass ratio of the hydrothermal carbon to the urea is 1:9, and the diameter of the formed particles is 0.4 mm.
And iii, continuously spraying a binder to the granulator, adding dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size requirement to obtain the nutrient-rich hydrothermal carbon with the particle diameter of 1.0 mm.
Step 4, dissolving part of the solid hydrothermal carbon and phosphoric acid obtained in the step 2 in water to obtain a mixture, stirring and heating until the water in the mixture is completely volatilized, and then carbonizing by using microwaves, wherein the microwave power is 800W, the microwave carbonization time is 10min, the microwave carbonization atmosphere is air (sealing), nitrogen and argon are isolated, and the obtained charcoal is washed and dried after microwave carbonization to obtain porous charcoal; the drying temperature of the hydrothermal carbon is 100 ℃, and the water content of the hydrothermal carbon after drying is 3%. The heating temperature during stirring in the phosphoric acid solution was 75 ℃. The biochar washing medium is water, the pH value of the washed biochar is 7.5, the drying temperature is 120 ℃, and the drying time is 590 min.
Step 5, mixing the hydrothermal carbon prepared in the step 2, the nutrient-rich hydrothermal carbon prepared in the step 3 and the porous biochar prepared in the step 4 according to the mass ratio of 1:1:0.7 to obtain a depleted soil conditioner;
in the embodiment, the soil conditioner is added into the impoverished soil planted in the greenhouse in a mass ratio of 10%, the impoverished soil on the inner surface layer of the greenhouse is subjected to shallow tillage by using a turning-in machine, so that the soil conditioner spread on the ground surface is buried into the shallow soil, and the improved soil planted in the greenhouse is obtained, wherein the porosity of the improved soil is increased by 12%, the water retention is increased by 13%, and the organic carbon is increased by 6.9%.
The first set of experiments was carried out by planting ryegrass in barren soil and improved soil respectively, and comparing the dry weight of the ryegrass after the ryegrass grows for 15 days, the growth rate of the ryegrass planted in the improved soil prepared by the invention is improved by 24%.
The second set of experiments was conducted in which vegetables (shanghai green) were grown in depleted soil and in improved soil, respectively, and the yield of vegetables grown in improved soil prepared using the present invention was increased by 31% relative to vegetables grown in depleted soil.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A method of remediating depleted soil comprising the steps of:
step 1, crushing agricultural waste biomass;
step 2, performing hydrothermal carbonization on the crushed agricultural waste biomass and water, and performing solid-liquid separation on a product of the hydrothermal carbonization to obtain solid hydrothermal carbon and hydrothermal carbon liquid; recycling the hydrothermal carbon liquid;
step 3, preparing part of the solid hydrothermal carbon into nutrient-rich hydrothermal carbon;
in the step 3, the preparation method of the nutrient-rich hydrothermal carbon comprises the following steps:
step i, adding the hydrothermal carbon into a nutrient solution with the concentration of 500-1500mg/L, fully stirring, separating out the hydrothermal carbon, and drying at the temperature lower than 70 ℃ to obtain dry hydrothermal carbon; the nutrient solution is one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, magnesium phosphate and calcium superphosphate;
step ii, adding urea into a granulator, spraying a binder, and then adding dry hydrothermal carbon for granulation and forming;
in the step ii, the particle size of the urea is 0.074-0.1mm, and the binder adopts 3.0-10.0% of polyvinyl alcohol aqueous solution by mass concentration; the mass ratio of the hydrothermal carbon to the urea is 1:4-10, and the diameter of the formed particles is 0.2-0.4 mm;
step iii, continuously spraying a binder to the granulator, then adding dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size requirement to finally obtain the nutrient-rich hydrothermal carbon with the particle diameter of 0.5-1.0 mm;
the eutrophic hydrothermal carbon has a multilayer structure, the eutrophic hydrothermal carbon takes urea as a nitrogen fertilizer, the urea is wrapped at the core of the granular eutrophic hydrothermal carbon, and the shell of the eutrophic hydrothermal carbon is a plurality of layers of the dry hydrothermal carbon;
the total nutrient of the nutrient-rich hydrothermal carbon is 20-50%, and the accumulative release rate of nutrients in 30 days is less than 60%;
step 4, dissolving part of the solid hydrothermal carbon and the activating agent in the step 2 in water to obtain a mixture, stirring and heating the mixture until the water in the mixture is completely volatilized, then carbonizing the mixture by using microwaves, and washing and drying the generated hydrothermal carbon after the carbonization by the microwaves to obtain porous biochar;
the microwave power during microwave carbonization is 500-800W, the microwave carbonization time is 4-10min, and the microwave carbonization atmosphere is air, nitrogen or argon isolation;
step 5, mixing the hydrothermal carbon prepared in the step 2, the rich-nutrient hydrothermal carbon prepared in the step 3 and the porous biochar prepared in the step 4 in proportion to obtain a depleted soil conditioner; adding the impoverished soil conditioner into impoverished soil for soil remediation;
in the step 5, the mass ratio of the hydrothermal carbon to the nutrient-rich hydrothermal carbon to the porous biochar is 1:0.5-1:0.4-0.8, and the addition amount of the nutrient-rich hydrothermal carbon to the impoverished soil is 3% -10%.
2. The method of remediating depleted soil of claim 1, wherein in step 1, the agricultural waste biomass comprises straw, wood chips, fallen leaves, crop waste, livestock manure, and the size of the crushed agricultural waste biomass is less than 0.18 mm.
3. The method for restoring depleted soil according to claim 1, wherein in the step 2, the mass ratio of biomass to water in the hydrothermal carbonization process is 1:1-1:4, the hydrothermal carbonization temperature is 180-.
4. The method for remediating depleted soil as defined in claim 1, wherein in step 4, the hydrothermal charcoal is dried at a temperature of 60-100 ℃ and has a water content of less than 5% after drying.
5. The method for remediating depleted soil as defined in claim 1, wherein in the step 4, the activating agent is one of sodium hydroxide, potassium hydroxide, and phosphoric acid;
the temperature was heated to less than 100 c while stirring in the activator solution.
6. The method for remediating depleted soil as defined in claim 1, wherein in the step 4, the biochar washing medium is water, the pH of the washed biochar is 6.5-7.5, the drying temperature is 80-120 ℃, and the drying time is 300-600 min.
7. The method for restoring depleted soil according to claim 1, wherein in the step 5, the mass ratio of the hydrothermal carbon, the nutrient-rich hydrothermal carbon and the porous biochar is 1:0.7-1:0.6-0.8, and the addition amount of the porous biochar to the depleted soil is 4% -10%.
8. The method for remediating depleted soil as claimed in any one of claims 1 to 7, wherein in step 3, the method for preparing nutrient-rich hydrothermal char comprises the steps of:
step i, adding the hydrothermal carbon into a nutrient solution with the concentration of 1000-1500mg/L, fully stirring, separating out the hydrothermal carbon, and drying at the temperature lower than 65 ℃ to obtain dry hydrothermal carbon;
step ii, adding urea into a granulator, spraying a binder, and then adding dry hydrothermal carbon for granulation and forming;
and iii, continuously spraying a binder to the granulator, adding dry hydrothermal carbon for granulation and molding, and repeating the steps according to the particle size requirement to obtain the nutrient-rich hydrothermal carbon with the particle diameter of 0.8-1.0 mm.
9. The method for remediating depleted soil as recited in claim 8, wherein in step ii, the urea particle size is 0.090-0.1mm, and the binder is 3.0-10.0% by mass polyvinyl alcohol aqueous solution; the mass ratio of the hydrothermal carbon to the urea is 1:7-10, and the diameter of the formed particles is 0.3-0.4 mm.
10. The method for remediating depleted soil as recited in claim 8, wherein in step i, the nutrient solution is potassium dihydrogen phosphate.
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