Aquatic plant-based biochar and its preparation method and recyclable carbon-fixing ecological ditches

Abstract

This invention relates to the field of agricultural water management, particularly to the management of agricultural non-point source water bodies, and more specifically to aquatic plant-based biochar and its application in recyclable ecological ditches. The aquatic plant-based biochar has an ash content of 15±3%, a dissolution stability of 0.1±0.02 DOC / C, SUVA254 of 0.3±0.06, SUVA280 of 0.2±0.04, a pH of 7-8, a FI of 5±1, and a HIX of 8±1.6. Compared to existing technologies, this aquatic plant-based biochar exhibits superior performance. Furthermore, this invention discloses a recyclable ecological ditch obtained by mixing this biochar with Fe. Experiments show that the nitrogen removal rate, carbon sequestration intensity, and carbon storage capacity of this recyclable ecological ditch are significantly improved, making it a three-in-one management system with carbon sequestration, carbon sink enhancement, and pollution reduction functions.

Description

Technical Field

[0001] This invention relates to the field of agricultural management, particularly to the management of agricultural non-point source water bodies, and more specifically to aquatic plant-based biochar and its participation in recyclable ecological ditches. Background Technology

[0002] Ecological ditches are an ecological restoration measure that aims to improve water quality by reducing the content of nutrients such as nitrogen and phosphorus in farmland drainage through natural purification processes in the ditches.

[0003] Ecological ditches consist of an engineering component and a plant component. The ecological ditch system removes pollutants such as nitrogen and phosphorus from farmland runoff through the interception, absorption, adsorption by the substrate, and biodegradation of the plants within it, thereby achieving the purpose of water body treatment.

[0004] In recent years, the major strategic goal of "carbon peaking and carbon neutrality" has put forward new requirements and heights for the green development of agriculture. Developing "carbon sequestration and carbon sink enhancement" agricultural technologies has become an objective requirement for high-quality development in all aspects of agricultural production.

[0005] CN113336217A discloses a method for the resource recovery and utilization of wetland aquatic plants. Addressing the potential pollution risks posed by the low-temperature treatment method disclosed in the prior art CN110813238A, this method involves vacuum pyrolysis and carbonization of harvested wetland aquatic plants to prepare biochar powder. This powder is then further mixed with urea, superphosphate, potassium chloride, and a regulator, and granulated to obtain wetland plant-based biochar particles, serving as a supplementary carbon source. This method achieves the resource utilization of aquatic plants through a carbonization temperature of 550–600℃ and the addition and mixing of urea, superphosphate, potassium chloride, and a regulator.

[0006] However, this treatment method requires high temperatures and the addition of various chemical components, making it unsuitable for the requirements of modern agriculture's green, energy-saving, low-carbon, and sustainable development. Furthermore, it only considers the resource utilization of aquatic plants to prevent decay, but does not consider efficient utilization methods to simultaneously meet the needs of carbon sequestration, carbon sink enhancement, and pollution reduction during resource utilization. Summary of the Invention

[0007] This invention addresses the problems of high energy consumption and the need for additional modifiers in the current utilization of aquatic plant resources, which leads to high utilization costs and does not meet the requirements of modern green agriculture. It provides an ecological ditch recyclable resource purification system, which aims to solve the above problems and further achieve high efficiency in carbon sequestration, carbon sink enhancement, and pollution reduction in ecological ditches.

[0008] To achieve the above-mentioned objectives, this invention discloses aquatic plant-based biochar, wherein the aquatic plant-based biochar has an ash content of 15±3%, a solubility stability of 0.1±0.02 DOC / C, an absorbance of SUVA254 (at 254 nm wavelength ultraviolet light) of 0.3±0.06, an absorbance of SUVA280 (at 280 nm wavelength ultraviolet light) of 0.2±0.04, a pH of 7-8, a fluorescence intensity (FI) of 5±1, and a humification index (HIX) of 8±1.6.

[0009] Furthermore, the method for preparing the aquatic plant-based biochar includes the following steps:

[0010] S1: Dehydrate the aquatic plants and then air-dry them naturally or bake them at a temperature of 105±5℃ until dry;

[0011] S2: Grind the dried aquatic plants;

[0012] S3: Pyrolyze the ground aquatic plants at 300-400℃ for 2-4 hours;

[0013] S4: Allow the temperature to cool naturally to 200-300℃, then open the muffle furnace door to allow air to enter naturally;

[0014] S5: Continue cooling to room temperature to obtain biochar.

[0015] More preferably, the pyrolysis temperature in step S3 is 400°C.

[0016] Temperature and the presence of oxygen are crucial process parameters determining the physicochemical properties and application performance of biochar during its preparation. In this field, the pyrolysis temperature of biochar is classified as low-temperature, medium-temperature, and high-temperature. Low-temperature generally refers to temperatures below 450℃, medium-temperature to around 550℃, and high-temperature to above 650℃. It is generally considered that medium- or high-temperature preparation should be chosen because at higher temperatures, biochar exhibits higher aromaticity, better electrochemical performance, higher ash content, and lower unstable carbon content, which positively impacts biochar quality and its ability to adsorb pollutants.

[0017] However, in this invention, we unexpectedly discovered a new biochar preparation process. This process involves pyrolysis at low temperatures and the introduction of air within a temperature range of 200–300°C during natural cooling to obtain biochar with excellent physicochemical and biological properties. When this biochar is mixed with Fe, it can simultaneously achieve carbon sequestration, carbon sequestration enhancement, and pollution reduction in ecological ditches. The introduction of air here only requires opening the muffle furnace door, making it an air oxidation treatment that does not require specific limits or emphasis on the amount of air introduced. This process offers advantages in terms of being green, economical, and environmentally friendly, and all aspects can achieve good and consistent modification effects during the modification process.

[0018] More preferably, the pyrolysis temperature in step S3 is obtained by gradually increasing the temperature from room temperature at a rate of 7–10 °C / min.

[0019] As a preferred technical solution, the heating rate is 10℃ / min.

[0020] Furthermore, the present invention also discloses an Fe-biochar pack obtained by mixing the above-mentioned biochar with Fe, wherein the Fe is sponge iron.

[0021] More preferably, the volume ratio of Fe to biochar is 1:3.

[0022] Meanwhile, the present invention also discloses a recyclable carbon-fixing ecological ditch involving the above-obtained biochar, including aquatic plants, substrate soil, and Fe-biochar bags placed in the substrate soil. The Fe-biochar bags are formed by encapsulating sponge iron and biochar prepared by the above method in a porous filter bag.

[0023] Preferably, the perforated filter bag is a 100-200 mesh perforated filter bag, including but not limited to 100 mesh, 150 mesh, and 200 mesh, with 100 mesh being the most preferred.

[0024] More preferably, the particle size of the sponge iron is 1-5 mm, and in a preferred embodiment, the particle size of the sponge iron is 1-3 mm.

[0025] This invention discloses an aquatic plant-based biochar and its preparation method. Compared with the prior art, the aquatic plant-based biochar has superior performance. Furthermore, this invention also discloses a recyclable ecological ditch obtained by mixing the biochar with Fe. Experiments show that the nitrogen removal rate, carbon sequestration intensity, and carbon storage capacity of the recyclable ecological ditch are significantly improved. It is a three-in-one treatment system with carbon sequestration, carbon sink enhancement, and pollution reduction functions. Attached Figure Description

[0026] Figure 1 This is a graph showing data on nitrogen removal rate, carbon sequestration intensity, and carbon storage capacity. Detailed Implementation

[0027] To better understand the present invention, we will further elaborate on the present invention below with reference to specific embodiments.

[0028] Example 1

[0029] Emergent, floating, and submerged aquatic plants planted in the ecological ditches were harvested. The harvested aquatic plants were placed in an oven and dried at 105°C. The dried aquatic plants were then ground into powder less than 2mm in size and placed in a covered iron crucible. The crucible was then placed in a muffle furnace for pyrolysis, with the furnace temperature gradually increased at a rate of 10°C / min until it reached 400°C. Pyrolysis was carried out at this temperature for 4 hours. After pyrolysis, the furnace was allowed to cool naturally while continuously monitoring the temperature. When the temperature reached 200–300°C, the furnace door was opened, and the furnace was allowed to continue cooling to room temperature with air circulated, yielding biochar.

[0030] The physicochemical properties of the biochar were determined as follows: the ash content of the aquatic plant-based biochar was 15±3%, the solubility stability was 0.1±0.02DOC / C, SUVA254 was 0.3±0.06, SUVA280 was 0.2±0.04, the pH was 7~8, the FI was 5±1, and the HIX was 8±1.6.

[0031] As can be seen, the aquatic plant-based biochar obtained by this invention has low dissolution stability, is relatively stable in water, and is not prone to dissolution and secondary pollution. At the same time, it has excellent aromatic structure and a large number of oxygen-containing functional groups, and is expected to have high carbon sequestration intensity and high carbon sequestration capacity.

[0032] Example 2

[0033] The biochar obtained in Example 1 was mixed with sponge iron (particle size 1-5 mm) at a volume ratio of 1:3 and then packed into a 100-mesh nylon filter bag to obtain Fe-biochar packs.

[0034] An equal amount of biochar (also from Example 1) as described above was placed into a 100-mesh nylon filter bag to obtain a biochar bag.

[0035] The same plant configuration and planting density were used, along with an equal amount of 10cm thick substrate soil (the substrate soil required for the experiment was obtained from paddy field soil, which was air-dried, ground, and sieved through a 10-mesh sieve before use). Three groups of ecological ditches were set up, defined as Fe-biochar-based ecological ditches (Fe-H group), biochar-based ecological ditches (H group), and pure plant ecological ditches (Plant group), with three replicates in each group.

[0036] In the Fe-H group, Fe-biochar bags were added to the substrate soil, and in the H group, biochar bags were added to the substrate soil. The Plant group contained only substrate soil and plants. This allowed us to examine the water purification and carbon sequestration effects of Fe-biochar-based ecological ditches, biochar-based ecological ditches, and purely plant-based ecological ditches.

[0037] Three sets of nine simulated experiments were run simultaneously under identical experimental conditions, using simulated wastewater (agricultural runoff or rural surface runoff). This wastewater was slightly polluted, with pollutant concentrations of TN = 8-12 mg / L, TP = 0.8-1.5 mg / L, and COD = 30-60 mg / L. A sequencing batch reactor was used, with a hydraulic retention time of 3 days. Gas samples were collected consistently between 9:00 AM and 11:30 AM. Greenhouse gases were collected using a static chamber method, with the chamber made of transparent acrylic glass to ensure normal photosynthesis by the plants. Carbon dioxide concentration was determined using a gas chromatograph equipped with an electron capture detector (ECD) and a flame ionization detector (FID). The carbon content of the plants, substrate soil, and biochar was determined using an elemental analyzer, and the total carbon concentration in the water samples was determined using a TOC analyzer.

[0038] Experimental results are as follows Figure 1 As shown, compared to ecological ditches planted solely with vegetation, the nitrogen removal rate is further improved after adding the biochar disclosed in this invention. In particular, the addition of Fe-biochar packets formed by mixing sponge iron significantly increases the carbon sequestration intensity and carbon storage capacity within the ecological ditches. However, the added biochar has an activating effect on the carbon in the underlying soil, leading to increased organic carbon mineralization and carbon loss. Ultimately, this results in a lower carbon storage capacity in the underlying soil compared to ecological ditches planted solely with vegetation. However, the coupling of Fe effectively mitigates the negative effects of biochar. By increasing the content of active iron and iron oxides, it not only enhances the protection of underlying organic carbon but also generates more iron-bound organic matter, improving rust carbon sequestration and ultimately promoting organic carbon accumulation. Fe-biochar helps ecological ditches achieve simultaneous enhancements in nitrogen removal capacity, carbon sequestration intensity, and carbon storage capacity.

[0039] The above describes specific embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. Aquatic plant-based biochar, characterized by: The aquatic plant-based biochar has an ash content of 15±3%, a solubility stability of 0.1±0.02 DOC / C (0.3±0.06 for SUVA254 and 0.2±0.04 for SUVA280), a pH of 7~8, a fluorescence intensity (FI) of 5±1, and a humification index (HIX) of 8±1.

6. The method for preparing aquatic plant-based biochar includes the following steps: S1: Dehydrate the aquatic plants and then air-dry them naturally or bake them at a temperature of 105±5℃ until dry; S2: Grind the dried aquatic plants; S3: Pyrolyze the ground aquatic plants at 300~400℃ for 2~4 hours; S4: Allow the temperature to cool naturally to 200~300℃, then open the muffle furnace door to allow air to enter naturally; S5: Continue cooling to room temperature to obtain biochar.

2. The method for preparing aquatic plant-based biochar according to claim 1, characterized in that, Includes the following steps: S1: Dehydrate the aquatic plants and then air-dry them naturally or bake them at a temperature of 105±5℃ until dry; S2: Grind the dried aquatic plants; S3: Pyrolyze the ground aquatic plants at 300~400℃ for 2~4 hours; S4: Allow the temperature to cool naturally to 200~300℃, then open the muffle furnace door to allow air to enter naturally; S5: Continue cooling to room temperature to obtain biochar.

3. The method for preparing aquatic plant-based biochar according to claim 2, characterized in that, The pyrolysis temperature in step S3 is 400℃.

4. The method for preparing aquatic plant-based biochar according to claim 2, characterized in that, In step S3, the pyrolysis temperature is obtained by gradually increasing the temperature from room temperature at a rate of 7~10℃ / min.

5. The method for preparing aquatic plant-based biochar according to claim 4, characterized in that, The heating rate is 10℃ / min.

6. The Fe-biochar pack obtained by mixing biochar and Fe according to claim 1, wherein Fe is sponge iron.

7. The Fe-biochar pack according to claim 6, characterized in that, Biochar and sponge iron were mixed at a volume ratio of 3:

1.

8. The biochar-based recyclable carbon sequestration ecological ditch according to claim 1, characterized in that, It includes aquatic plants, substrate soil, and Fe-biochar packs placed in the substrate soil. The Fe-biochar packs are formed by encapsulating sponge iron and biochar in a porous filter bag.

9. The biochar-infused recyclable carbon sequestration ecological ditch according to claim 8, characterized in that, The perforated filter bag is a 100-200 mesh perforated filter bag.

10. The biochar-infused recyclable carbon sequestration ecological ditch according to claim 8, characterized in that, The perforated filter bag is a 100-mesh, 150-mesh, or 200-mesh perforated filter bag.

11. The biochar-infused recyclable carbon sequestration ecological ditch according to claim 8, characterized in that, The perforated filter bag is a 100-mesh perforated filter bag.

12. The biochar-infused recyclable carbon sequestration ecological ditch according to claim 8, characterized in that, The particle size of the sponge iron is 1~5mm.

13. The biochar-infused recyclable carbon sequestration ecological ditch according to claim 8, characterized in that, The particle size of the sponge iron is 1~3mm.

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