Modified biochar for adsorbing trace elements in urine as well as preparation method and application of modified biochar

Abstract

The invention belongs to the technical field of environmental water treatment, and particularly relates to modified charcoal for adsorbing trace elements in urine as well as a preparation method and application of the modified charcoal. The modified biochar is obtained by taking waste biomass as a raw material, carrying out high-temperature carbonization and pyrolysis and modifying by adopting levodopa, and the particle size of the modified biochar is 0.15 mm or less. The modified biochar provided by the invention has the advantages of large specific surface area, developed pores and more oxygen-containing functional groups on the surface; after the modified biochar is applied to adsorption of trace elements in urine, compared with biochar before modification, the adsorption rate of the modified biochar to boron, iron, manganese, molybdenum and zinc is remarkably increased, meanwhile, the adsorption rate of new pollutants such as sulfamethoxazole is effectively reduced, the stability is good, and the modified biochar can be desorbed, regenerated and reused after adsorption.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental water treatment, and specifically relates to a modified biochar for absorbing trace elements in urine, and a preparation method and application thereof. Background Art

[0002] As a soilless cultivation method, hydroponics supplies nutrients required by plants through nutrient solution. It is widely used in vegetable production due to its water-saving and high-efficiency characteristics. However, the main challenges facing hydroponic systems are the cost and sustainability of nutrient solutions. Traditional nutrient solutions are costly and unsustainable. To solve this problem, urine has attracted attention as a viable alternative. Urine is rich in macroelements such as nitrogen, phosphorus, and potassium required for plant growth, as well as trace elements such as iron, copper, and zinc. By recycling the nutrients in urine as part of the hydroponic nutrient solution, it can not only reduce costs, but also promote resource recycling and improve the sustainability of agriculture. At present, a large number of studies have focused on the recovery of nitrogen, phosphorus, and potassium from urine, while there are relatively few studies on the recovery of trace elements in urine. Therefore, the development of a technology that can efficiently recover trace elements from urine has become an urgent problem to be solved.

[0003] Biochar has been widely used in water treatment and soil improvement due to its good adsorption properties and environmental friendliness. The porous structure and large specific surface area of ​​biochar give it significant advantages in adsorbing heavy metals and trace elements in water bodies. However, the adsorption effect of unmodified biochar is often limited when treating complex wastewater, especially trace metal ions in urine containing organic matter and inorganic salts. In order to improve the adsorption capacity of biochar for trace elements, researchers have used various modification methods, such as chemical modification, surfactant modification and high-temperature heat treatment, to enhance its adsorption performance and selectivity.

[0004] Therefore, developing a biochar-modified material to recover trace elements in urine and use it in hydroponic nutrient solution has important practical application value and broad market prospects. Summary of the invention

[0005] The purpose of the present invention is to provide a biochar modified material in view of the shortcomings of the prior art, in order to solve the problems of low adsorption efficiency and poor selectivity of biochar in the prior art, thereby realizing the efficient recovery of trace elements in urine and their reuse in hydroponics.

[0006] The present invention provides a modified biochar for absorbing trace elements in urine. The modified biochar is obtained by using waste biomass as raw material, undergoing high-temperature carbonization and pyrolysis, and being modified by using levodopa. The particle size of the modified biochar is below 0.15 mm.

[0007] The present invention also provides a method for preparing the modified biochar described in the above technical solution, comprising the following steps: Step 1: pretreating the biomass to obtain pretreated biomass; Step 2: subjecting the pretreated biomass to high-temperature carbonization pyrolysis to obtain pyrolysis products; Step 3: Add the pyrolysis product to the L-DOPA solution and react for 24 h. After filtering, the obtained solid is acid-washed, washed with water, dried and ground to obtain modified biochar.

[0008] Preferably, the pretreatment method includes: crushing the biomass, cleaning to remove surface impurities, and drying in an oven at 50°C-100°C.

[0009] Preferably, the particle size of the pretreated biomass is less than 0.425 mm.

[0010] Preferably, the heating rate of the high-temperature carbonization pyrolysis in step 2 is 8-12°C / min, the carbonization temperature is 300°C-700°C, and the carbonization time is 2-4 h.

[0011] Preferably, the amount of the pyrolysis product added to the levodopa solution in step 3 is 0.01-10 g / L.

[0012] Preferably, the concentration of levodopa in the levodopa solution is 0.01-0.5 g / L; the solvent of the levodopa solution is 0.01-0.5 M Tris-HCl solution with a pH of 8-9.

[0013] Preferably, in step 3, the steps of solid acid washing, water washing, drying and grinding include: washing with 0.01M hydrochloric acid for more than 3 times, washing with ultrapure water until the pH does not change, then drying in a 50°C-100°C forced air drying oven to constant weight, grinding and sieving to obtain modified biochar.

[0014] The present invention also provides the use of the modified biochar described in the above technical solution or the modified biochar prepared by the preparation method described in the above technical solution in adsorbing trace elements in urine. Preferably, the application is specifically: adding the modified biochar in an amount of 0.01-10 g / L to artificially synthesized fresh urine, placing it on a magnetic stirrer, and completing the adsorption under stirring.

[0015] Preferably, the artificial fresh urine is composed of the following substances: sodium chloride 2.571 g / L, sodium sulfate 2.131 g / L, potassium chloride 2.982 g / L, magnesium chloride 0.813 g / L, sodium dihydrogen phosphate 2.400 g / L, calcium chloride 0.588 g / L, urea 15.015 g / L, sodium citrate 0.794 g / L, creatinine 0.882 g / L, copper 0.100 µg / mL, iron 0.500 µg / mL, manganese 0.050 µg / mL, boron 0.800 µg / mL, zinc 0.100 µg / mL and molybdenum 0.050 µg / mL.

[0016] Beneficial effects of the present invention: 1. The modified biochar provided by the present invention is modified by a chemical modification method, has considerable stability, can be desorbed, regenerated and reused after adsorption, has the advantages of large specific surface area, developed pores, and many surface oxygen-containing functional groups, can effectively adsorb trace elements in urine, and hardly adsorbs sulfonamide drugs. The solution after desorption can be directly used as a nutrient solution for hydroponic plant growth.

[0017] 2. The preparation method provided by the present invention adopts the principle of self-polymerization of levodopa at a specific pH, so that poly-levodopa molecules can adhere to the surface of biochar. After the biochar is modified, the number of functional groups such as hydroxyl, amino and carboxyl groups on the surface increases, which can increase the active sites for adsorbing trace element ions, and the adsorption performance of heavy metals is greatly improved; the hydrophilicity is improved, so the adsorption performance of hydrophobic drugs such as sulfonamides is greatly reduced.

[0018] 3. The preparation method provided by the present invention is simple and easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0020] Figure 1 are scanning electron microscope photos of modified biochar and original biochar; a is a scanning electron microscope photo of modified biochar, and b is a scanning electron microscope photo of original biochar; Figure 2 are Fourier transform infrared spectra of modified biochar and original biochar; a is the Fourier transform infrared spectrum of modified biochar, and b is the Fourier transform infrared spectrum of original biochar; Figure 3This is a comparison chart of the adsorption rates of trace elements and calcium and magnesium in urine by modified biochar and original biochar; Figure 4 This is a comparison of the adsorption kinetics of SMX in urine by modified biochar and original biochar; Figure 5 This is the relationship diagram between the pH change of modified biochar and original biochar and the initial pH. DETAILED DESCRIPTION

[0021] The present invention provides a modified biochar for absorbing trace elements in urine, wherein the modified biochar is obtained by using waste biomass as raw material, undergoing high-temperature carbonization and pyrolysis, and being modified by using levodopa; the particle size of the modified biochar is less than 0.15 mm. The modified biochar provided by the present invention is obtained by chemical modification, has the advantages of large specific surface area, developed pores, and many oxygen-containing functional groups on the surface, can effectively absorb trace elements in urine, and hardly absorbs sulfonamide drugs.

[0022] The present invention also provides a method for preparing the modified biochar described in the above technical solution, comprising the following steps: Step 1: pretreating the biomass to obtain pretreated biomass; Step 2: subjecting the pretreated biomass to high-temperature carbonization pyrolysis to obtain pyrolysis products; Step 3: Add the pyrolysis product to the L-DOPA solution, react for 24 hours, filter, acid-wash, wash with water, dry, and grind the resulting solid to obtain modified biochar.

[0023] The present invention firstly pretreats the biomass to obtain the pretreated biomass.

[0024] In the present invention, the biomass is preferably corn stalks; the particle size of the pretreated biomass is preferably less than 0.425 mm; the pretreatment method preferably includes: crushing the biomass, washing to remove surface impurities, and drying in an oven at 50°C-100°C. In the present invention, before crushing the corn stalks, it is preferably washed and air-dried before crushing.

[0025] After obtaining the pretreated biomass, the present invention performs high-temperature carbonization pyrolysis on the pretreated biomass to obtain a pyrolysis product.

[0026] The present invention preferably further screens the pretreated corn stalks before subjecting them to high-temperature carbonization pyrolysis; in the present invention, the heating rate of the high-temperature carbonization pyrolysis is preferably 8-12°C / min, more preferably 10°C / min; the carbonization temperature is preferably 300°C-700°C, more preferably 700°C; the carbonization time is preferably 2-4 h, more preferably 2 h; and the high-temperature carbonization pyrolysis is preferably carried out in a muffle furnace.

[0027] The present invention further adds the pyrolysis product to the levodopa solution, reacts for 24 hours, and after filtering, the obtained solid is acid-washed, washed with water, dried, and ground to obtain the modified biochar.

[0028] The concentration of levodopa in the levodopa solution is preferably 0.1-5 g / L, more preferably 2 g / L; the solvent of the levodopa solution is preferably 0.01-0.5M Tris-HCl solution with a pH of 8-9, more preferably 0.1M Tris-HCl solution with a pH of 8.5; the preparation method of the levodopa solution is preferably: 0.01M levodopa is added to 0.1M Tris-HCl solution with a pH of 8.5 to obtain a levodopa solution. The present invention utilizes the principle of self-polymerization of levodopa at a specific pH, so that polylevodopa molecules can adhere to the surface of biochar, effectively increasing the number of functional groups such as hydroxyl, amino and carboxyl groups on the surface of the modified biochar, so that the surface of the modified biochar can be used as an active site for adsorbing trace element ions, thereby significantly enhancing its adsorption performance and hydrophilicity for heavy metals.

[0029] In the present invention, the amount of the pyrolysis product added to the levodopa solution is preferably 0.01-10 g / L, more preferably 1-2 g / L, and more preferably 1 g / L; the solid acid washing, water washing, drying, and grinding steps preferably include: washing with 0.01M hydrochloric acid for more than 3 times, washing with ultrapure water until the pH does not change, then drying in a 50°C-100°C air drying oven to constant weight, grinding and sieving, and obtaining modified biochar. The present invention is preferably dried to constant weight in a 50°C-100°C air drying oven, and more preferably dried to constant weight in an 80°C air drying oven.

[0030] The present invention also provides the use of the modified biochar described in the above technical solution or the modified biochar prepared by the preparation method described in the above technical solution in adsorbing trace elements in urine, and the application is preferably: adding the modified biochar to artificially synthesized fresh urine at an addition amount of 0.01-10 g / L, placing it on a magnetic stirrer, and completing adsorption under stirring; more preferably: adding the modified biochar to artificially synthesized fresh urine at an addition amount of 2.4 g / L, placing it on a magnetic stirrer, and completing adsorption under stirring. The time for completing adsorption under stirring is preferably 2 hours.

[0031] In the present invention, the artificial fresh urine is preferably composed of the following substances: sodium chloride 2.571 g / L, sodium sulfate 2.131 g / L, potassium chloride 2.982 g / L, magnesium chloride 0.813 g / L, sodium dihydrogen phosphate 2.400 g / L, calcium chloride 0.588 g / L, urea 15.015 g / L, sodium citrate 0.794 g / L, creatinine 0.882 g / L, copper 0.100 µg / mL, iron 0.500 µg / mL, manganese 0.050 µg / mL, boron 0.800 µg / mL, zinc 0.100 µg / mL and molybdenum 0.050 µg / mL.

[0032] In order to further illustrate the present invention, the modified biochar for adsorbing trace elements in urine and its preparation method and application provided by the present invention are described in detail below in combination with the accompanying drawings and examples, but they should not be understood as limiting the scope of protection of the present invention.

[0033] Example 1 S1. Wash the corn stalks with ultrapure water to remove surface impurities, and then dry them to obtain solid raw material powder with a particle size less than 0.425 mm. Put the raw material powder into a muffle furnace with a heating time of 10℃ / min, and carbonize it at 700℃ for 2 h to obtain the pyrolysis product biochar, as shown in the electron microscope image. Figure 1 As shown in b; S2. Prepare 1 L of 0.1M Tris-HCl buffer solution with a pH of 8.5, add 2 g of L-dopa powder to obtain a L-dopa solution; take 1 g of the biochar obtained in step S1 and add it to the L-dopa solution, stir magnetically for 24 h, filter, wash the obtained solid three times with 0.01M HCl solution, then wash with ultrapure water until the pH does not change, dry in an oven at 80°C to constant weight, grind through a 100-mesh sieve, and obtain modified biochar, the electron microscope image of which is shown in the figure. Figure 1 As shown in a.

[0034] according to Figure 1 Comparing the biochar before modification in a and b, it can be seen that there is a rough film on the surface of the modified biochar. BET tests were performed on the biochar before and after modification, and the results are shown in Table 1.

[0035] Table 1 BET test of modified biochar and original biochar It can be seen from Table 1 that the specific surface area, porosity and particle size of the modified biochar and the original biochar are basically unchanged.

[0036] Fourier transform infrared spectra of modified and original biochar are shown in Figure 2As shown, a is the Fourier transform infrared spectrum of the modified biochar, and b is the Fourier transform infrared spectrum of the original biochar. Figure 2 It can be seen that the modified biochar has increased the number of hydroxyl, amino and carboxyl functional groups compared with the original biochar.

[0037] Test Example 1 S1. Preparation of artificial synthetic fresh urine: sodium chloride (NaCl) 2.571 g / L, sodium sulfate (Na2SO4) 2.131 g / L, potassium chloride (KCl) 2.982 g / L, magnesium chloride (MgCl2·6H2O) 0.813 g / L, sodium dihydrogen phosphate (NaH2PO4) 2.4 g / L, calcium chloride (CaCl2·2H2O) 0.588 g / L, urea 15.015 g / L, sodium citrate (Na3Citrate·2H2O) 0.794 g / L, creatinine (C4H7N3O) 0.882 g / L, copper 0.100 µg / mL, iron 0.500 µg / mL, manganese 0.050 µg / mL, boron 0.800 µg / mL, zinc 0.100 µg / mL, molybdenum 0.050 µg / mL; then, 10 µM sulfamethoxazole (SMX) was added to the artificial fresh urine, and 0.12 g of modified biochar and 0.12 g of original biochar were added to 50 mL of artificial urine containing trace elements. After shaking at 180 rpm for 2 h, the insoluble matter was filtered out with a 0.45 µm needle filter membrane.

[0038] S2. After diluting the solution before and after adsorption by 2% dilute nitric acid 10 times, the concentration of each element was measured by ICP-OES, and the adsorption rate was calculated. The adsorption rate comparison chart is shown in Figure 3 shown by Figure 3 It can be seen that the modified biochar increased the adsorption rate of trace elements.

[0039] Test Example 2 0.12 g of the modified biochar prepared in Example 1 was weighed and added to 50 mL of synthetic urine containing 10 µM SMX. The sample was then placed in a shaker at 180 rpm and 25°C. Samples were taken at regular intervals and filtered through a water filter membrane. The concentration of SMX in the filtrate was then determined. The same steps were taken for the unmodified biochar as a comparison. The results are shown in FIG. Figure 4 shown.

[0040] Depend on Figure 4 It can be seen that the maximum adsorption capacity of modified biochar is 1 / 4 of that of unmodified biochar, and surface modified biochar can reduce the adsorption of SMX.

[0041] Test Example 3 Prepare 0.1M NaNO3 solution, adjust the pH to a continuous value between 3 and 12 by adding 0.1M HNO3 or 0.1M NaOH, take 0.2 g of modified biochar and add it to 40 mL of the above solution, measure the final pH reached after 24 h, and plot it against the initial pH, as shown in Figure 2. Figure 5 As shown, the pH of the modified biochar pzc 5.3; the same steps were taken for the original biochar as a comparison, such as Figure 5 As shown, the pH of the original biochar pzc The pH of the original biochar is 9.4. pzc is 9.4, indicating that in the urine system with pH = 6, its surface is positively charged and tends to adsorb anions. In contrast, the pH of the modified biochar is pzc It is 5.3, indicating that in the urine system, its surface is negatively charged, which is more conducive to the adsorption of cations.

[0042] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A modified biochar for adsorbing trace elements in urine, characterized in that: The modified biochar is obtained by using waste biomass as raw material, undergoing high-temperature carbonization and pyrolysis, and modifying with L-DOPA; the particle size of the modified biochar is below 0.15 mm.

2. The method for preparing modified biochar according to claim 1, characterized in that: The following steps are involved: Step 1: pretreating the biomass to obtain pretreated biomass; Step 2: subjecting the pretreated biomass to high-temperature carbonization pyrolysis to obtain pyrolysis products; Step 3: Add the pyrolysis product to the L-DOPA solution and react for 24 h. After filtering, the obtained solid is acid-washed, washed with water, dried and ground to obtain modified biochar.

3. The preparation method according to claim 2, characterized in that: The pretreatment method includes: crushing the biomass, cleaning to remove surface impurities, and drying in an oven at 50°C-100°C.

4. The preparation method according to claim 2, characterized in that: The particle size of the pretreated biomass is less than 0.425 mm.

5. The preparation method according to claim 2, characterized in that: In the step 2, the heating rate of the high-temperature carbonization pyrolysis is 8°C-12°C / min, the carbonization temperature is 300°C-700°C, and the carbonization time is 2-4 h.

6. The preparation method according to claim 2, characterized in that: In step 3, the amount of the pyrolysis product added to the levodopa solution is 0.01-10 g / L.

7. The preparation method according to claim 2, characterized in that: The concentration of levodopa in the levodopa solution is 0.1-5 g / L; the solvent of the levodopa solution is a 0.01-0.5M Tris-HCl solution with a pH of 8-9.

8. The preparation method according to claim 2, characterized in that: In step 3, the steps of solid acid washing, water washing, drying and grinding include: washing with 0.01M hydrochloric acid for more than 3 times, washing with ultrapure water until the pH value does not change, then drying in a 50°C-100°C forced air drying oven to constant weight, grinding and sieving to obtain modified biochar.

9. Use of the modified biochar according to claim 1 or the modified biochar prepared by the preparation method according to any one of claims 2 to 8 in adsorbing trace elements in urine, characterized in that: The modified biochar is added into artificial fresh urine at an amount of 0.01-10 g / L, placed on a magnetic stirrer, and adsorption is completed under stirring.

10. The use according to claim 9, characterized in that: The artificial fresh urine is composed of the following substances: sodium chloride 2.571 g / L, sodium sulfate 2.131 g / L, potassium chloride 2.982 g / L, magnesium chloride 0.813 g / L, sodium dihydrogen phosphate 2.400 g / L, calcium chloride 0.588 g / L, urea 15.015 g / L, sodium citrate 0.794 g / L, creatinine 0.882 g / L, copper 0.100 µg / mL, iron 0.500 µg / mL, manganese 0.050 µg / mL, boron 0.800 µg / mL, zinc 0.100 µg / mL and molybdenum 0.050 µg / mL.

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