Method for preparing biochar from cynoglossus semilaevis recirculating aquaculture solid waste and enteromorpha and application

Abstract

The invention belongs to the field of biochar technology and water environment restoration, and particularly relates to a method for preparing biochar from cynoglossus semilaevis recirculating aquaculture solid waste and enteromorpha and application. The method specifically comprises the following steps: mixing the cynoglossus semilaevis recirculating aquaculture solid waste and enteromorpha according to a mass ratio of 1: (1-5), and carrying out lower-limit oxygen pyrolysis at 300-800 DEG C to obtain a substance, namely biochar (BC); or mixing the pyrolyzed products to obtain the biochar. The biochar obtained by the invention has a relatively excellent specific surface area and more pollutant adsorption sites, shows relatively high adsorption performance on nitrogen and phosphorus nutritive salts in a water body, realizes resource utilization of mariculture solid wastes which are difficult to treat and enteromorpha prolifera which is ecologically harmful, and promotes sustainable development of the aquaculture industry.

Description

Technical Field

[0001] The present invention belongs to the fields of biochar technology and water environment restoration, and particularly relates to a method for preparing biochar from the solid waste of Cynoglossus semilaevis recirculating aquaculture and Enteromorpha prolifera and its application. Background Art

[0002] From a global perspective, in the past two decades, the contribution of the aquaculture industry to the total fishery output has been steadily increasing, reaching 51% in 2022, exceeding the capture output for the first time. From the perspective of developing countries, the aquaculture industry accounts for more than half of the total fishery output and supplies half of the world's population, continuously providing high-quality protein for humanity. Currently, the aquaculture industry is in a booming development period with increasing output value, but it is also accompanied by a series of environmental problems. According to the latest national pollution source census, the total pollution emissions from aquaculture only account for 6.35% of the total agricultural non-point source pollution emissions, among which the chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus are 6.66 million tons, 2.23 million tons, 9.91 million tons, and 1.61 million tons respectively. And excessive phosphate emissions into water bodies may lead to eutrophication, resulting in algal blooms, water quality deterioration, and ultimately the collapse of the aquatic ecosystem, which has become a global concern.

[0003] In the seawater aquaculture system, seawater aquaculture tailwater carries a large amount of particulate matter, nitrogen and phosphorus nutrients, etc., which are the main indicators of national and local aquaculture tailwater discharge standards and environmental protection inspections. There are limited options for treating the waste of salt-containing bait residues in the seawater aquaculture system, resulting in low reuse rates of these solid wastes. At the same time, Enteromorpha prolifera is a common seaweed, and its large-scale outbreaks every year will damage the marine ecosystem and seriously threaten the economic development of coastal areas. Therefore, to solve the above problems, it is necessary to find green, environmentally friendly, and economical treatment methods to manage and use the residual baits and feces generated in seawater aquaculture and the Enteromorpha prolifera obtained by salvage, realize the resource utilization of residual baits and feces and Enteromorpha prolifera, and promote the green and sustainable development of seawater aquaculture. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing biochar from the solid waste of Cynoglossus semilaevis recirculating aquaculture and Enteromorpha prolifera and its application.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing biochar from the solid waste of Cynoglossus semilaevis recirculating aquaculture and Enteromorpha prolifera, in which the solid waste of Cynoglossus semilaevis recirculating aquaculture and Enteromorpha prolifera are mixed and pyrolyzed under oxygen-limited conditions to prepare biochar (BC).

[0007] The mass ratio of the solid waste of Cynoglossus semilaevis recirculating aquaculture to Enteromorpha prolifera is 1:1 - 1:5. Preferably, the mass ratio of the solid waste of Cynoglossus semilaevis recirculating aquaculture to Enteromorpha prolifera is 1:5.

[0008] The oxygen-limited pyrolysis temperature is 300°C - 800°C.

[0009] During oxygen-limited pyrolysis, N2 is introduced at a rate of 50 - 60 ml / min to provide an oxygen-limited environment. At the same time, the temperature is raised at a rate of 15°C / min to 300°C - 800°C for pyrolytic carbonization for 110 - 130 min. After cooling to room temperature, the biochar is obtained. Preferably, the oxygen-limited pyrolysis temperature is 700°C.

[0010] The waste from the recirculating aquaculture of Cynoglossus semilaevis is the residual bait and / or the feces of Cynoglossus semilaevis during the aquaculture process, which are air-dried or dried in an oven and then crushed after removing impurities.

[0011] The Enteromorpha prolifera is obtained by salvaging from the coastal sea, air-dried or dried in an oven, and then crushed after removing impurities.

[0012] Furthermore, the waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera are naturally air-dried or dried in an electric oven at 70°C for 48 hours until there is no obvious water loss; then impurities are removed, and they are crushed by a ball mill or a crusher and then sieved through a 2-mm sieve. The sieved Cynoglossus semilaevis feces powder and Enteromorpha prolifera powder after crushing are stored for later use.

[0013] The biochar prepared by the method has the characteristics of a large specific surface area and a rich pore structure.

[0014] An application of the biochar, the biochar is used as an adsorbent for nutrients in water.

[0015] The nutrients in water are PO4

[0016] , + ,

[0019] ,

[0018] ,

[0017] , , , 3 , , -P or NH4 + -N.

[0016] The advantages of the present invention:

[0017] The present invention uses the waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera as raw materials for biochar. The crude protein content of the waste is 22.51 ± 1.22%, and the crude protein content of Enteromorpha prolifera is 18.40 ± 0.05%. Compared with the crude protein content of crop straws (corn straw 9.3%, rice straw 3.2%, wheat straw 2.6%), it has significant advantages. The higher the crude protein content in the biochar raw materials, the greater the aromaticity of the prepared biochar and the more types of aromatic functional groups it has, which can improve the chemical adsorption effect of biochar on pollutants.

[0018] The co-pyrolysis technology adopted by the present invention can increase the specific surface area of biochar, improve the pore structure, and increase the abundance of surface functional groups, which will further improve the adsorption performance of biochar.

[0019] The biochar obtained by the present invention has a relatively excellent specific surface area, more pollutant adsorption sites, shows a high adsorption performance for nitrogen and phosphorus nutrients in water bodies, realizes the resource utilization of difficult-to-treat seawater aquaculture solid waste and the ecologically harmful Enteromorpha prolifera, and promotes the sustainable development of the aquaculture industry.

[0020] The biochar prepared by the present invention contains rich organic substances, which is conducive to the retention of oxygen-rich functional groups on the surface of the biochar prepared from the solid waste of Cynoglossus semilaevis circulating water and Enteromorpha prolifera, making the obtained biochar have a large specific surface area, providing more pollutant adsorption sites, and greatly improving the adsorption performance. At 25 °C, BC700-5 has the most stable adsorption effect on PO4 3 -P (63.23%), and at the same time has a relatively high removal rate of NH4 + -N (94.57%). It provides an effective way for the resource utilization of the solid waste of Cynoglossus semilaevis circulating water and Enteromorpha prolifera. Description of the Drawings

[0021] Figure 1 It is the electron microscope image of obtaining different biochars provided by the embodiments of the present invention. Among them, A is BC300-1, B is BC300-3, C is BC300-5, D is BC500-1, E is BC500-3, F is BC500-5, G is BC700-1, H is BC700-3, I is BC700-5, J is BC800-1, K is BC800-3, and L is BC800-5.

[0022] Figure 2 It is the functional group distribution diagram obtained by the embodiments of the present invention. Detailed Embodiments

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be noted here that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. The experimental methods in the following embodiments are all conventional methods unless otherwise specified.

[0024] The biochar obtained by the present invention has a relatively excellent specific surface area, pore volume, and more pollutant adsorption sites, and shows a high adsorption performance for ammonia nitrogen and phosphate in water bodies.

[0025] The aquaculture solid waste used in the following embodiments was collected from a Cynoglossus semilaevis circulating water aquaculture farm in Tianjin, China. The main aquaculture species in this farm is Cynoglossus semilaevis. The Enteromorpha prolifera was obtained from the offshore area of Qingdao.

[0026] Example 1

[0027] Collection and drying: The aquaculture solid waste and Enteromorpha prolifera were dried at 70 °C for 48 hours until there was no obvious moisture.

[0028] Crushing: Pick out the stone chips and sundries, and then crush them with a ball mill or a high-speed crusher, and pass through a 2 mm standard sieve.

[0029] Mixing: Mix the above powders according to aquaculture solid waste: Enteromorpha prolifera (mass ratio) = 1:1 (1), 1:3 (3) or 1:5 (5).

[0030] Pyrolysis: Put the above-mentioned uniformly mixed different samples into a quartz boat and place it in a tube furnace, and pass N2 at a rate of 50 ml / min. The initial temperature is 25 °C, the heating rate is 15 °C / min, and it is heated to 300, 500, 7,00 °C or 800 °C, and pyrolyzed for 120 min for carbonization. Cool the obtained biochar to room temperature, take it out to obtain biochar samples prepared under different conditions (BC300, BC500, BC700, BC800), and store them in a sealed desiccator for later use.

[0031] The above different samples are marked as BC300-1, BC300-3, BC300-5, BC500-1, BC500-3, BC500-5, BC700-1, BC700-3, BC700-5, BC800-1, BC800-3, BC800-5.

[0032] Comparative Example 1

[0033] Pyrolysis: Put the Enteromorpha prolifera powder of Example 1 into a quartz boat and place it in a tube furnace, and pass N2 at a rate of 50 ml / min. The initial temperature is 25 °C, the heating rate is 15 °C / min, and it is heated to 700 °C, and pyrolyzed for 120 min for carbonization. Cool the obtained biochar to room temperature, take it out to obtain the obtained biochar denoted as BC70-Algae

[0034] Comparative Example 2

[0035] Pyrolysis: Put the powder of the circulating water aquaculture solid waste of Cynoglossus semilaevis of Example 1 into a quartz boat and place it in a tube furnace, and pass N2 at a rate of 50 ml / min. The initial temperature is 25 °C, the heating rate is 15 °C / min, and it is heated to 700 °C, and pyrolyzed for 120 min for carbonization. Cool the obtained biochar to room temperature, take it out to obtain the obtained biochar denoted as BC700-Feces.

[0036] For the biochar obtained in the examples of the present invention, scanning electron microscopy (SEM, see Figure 1 ), functional group distribution map (see Figure 2 ), pH, specific surface area analysis (BET) (see Table 1).

[0037] As can be seen from Table 1, when the pyrolysis temperature is 700 °C, the specific surface area of biochar is the largest. When the pyrolysis temperature is less than 700 °C, the specific surface area of biochar is relatively low. However, when the pyrolysis temperature is greater than 800 °C, the specific surface area of biochar begins to decline. The reason is that the increase in pyrolysis temperature leads to the collapse of the pore structure of biochar, resulting in the reduction of the specific surface area. Therefore, the optimal pyrolysis temperature is 700 °C.

[0038] As Figure 1 can be seen, when the pyrolysis temperature is 700 °C, the pore structure of biochar is the best. When the pyrolysis temperature is 300 °C, biochar is still in the stage of water evaporation, and the surface pore structure is not obvious. When the pyrolysis temperature is 500 °C, the pore structure gradually forms on the surface of biochar, but the pore development is not complete. When the pyrolysis temperature is greater than 800 °C, the pore structure of biochar undergoes obvious collapse, resulting in problems such as a decrease in specific surface area, a reduction in pore volume, and a decrease in surface adsorption sites. Therefore, the optimal pyrolysis temperature is 700 °C.

[0039] As Figure 2 can be seen, biochar has extremely similar spectra in FTIR spectral analysis ( Figure 2 ). All biochars have an obvious absorption peak near 3400 cm -1 , representing the stretching vibration of -OH groups and / or phenols. There are two peaks near 2800 - 3000 cm -1 , both representing aliphatic methylene (-CH2-). The peak near 1600 cm -1 is related to the stretching vibration of aromatic C=O and C=C. The peak near 1436 cm -1 is related to the vibration of C-H. All biochars show C-O-C stretching vibration at 1030 - 1040 cm -1 . Therefore, biochar contains a large amount of aromatic compounds. The hydroxyl groups (-OH), aliphatic methylene (-CH2-), aromatic C=O and C=C, C-H, and C-O-C functional groups in biochar may all play a role in adsorbing nutrient salts. These functional groups promote the adsorption of nutrient salts together through hydrogen bonding, van der Waals forces, hydrophobic interactions, and interactions with the π-electron system.

[0040] Table 1 pH and specific surface area of biochar

[0041]

[0042]

[0043] Note: Different lowercase letters represent significant differences between different mixing ratio groups at the same pyrolysis temperature, and different capital letters represent significant differences between different pyrolysis temperature groups at the same mixing ratio (P < 0.05)

[0044] Application Example 1: Adsorption Effects of Different Biochars on Common Pollutants in Water

[0045] The different biochars BC300-1, BC300-3, BC300-5, BC500-1, BC500-3, BC500-5, BC700-1, BC700-3, BC700-5, BC800-1, BC800-3, BC800-5, BC700-Algae, BC700-Feces obtained above were respectively used for the adsorption of NH4 + -N and PO4 3 -P.

[0046] Specifically:

[0047] Ammonium chloride (NH4Cl) and potassium dihydrogen phosphate (KH2PO4) were used to prepare the initial concentrations of NH4 + -N and PO4 3 -P to be 30 mg / L. Each of the above biochars (0.15 g) was respectively added to 30 ml of the NH4 + , PO4 3— solution, and the mixture was shaken at 150 r / min at 25 °C for 4 h until apparent equilibrium was reached. Thereafter, the supernatant was separated by centrifugation and collected, and filtered through a 0.45-μm membrane. The contents of NH4 + -N and PO4 3 -P in the sample solution were respectively determined by the hypobromite oxidation method and the ammonium molybdate spectrophotometric method. All experiments were repeated three times, and the average values were recorded. The contents of each ion were calculated according to the corresponding standard curve.

[0048]

[0049] where C0 is the initial concentration (mg / L) and C t is the final concentration (mg / L).

[0050] Table 2 Removal Rates of NH4 + -N and PO4 3 -P by Different Biochars

[0051]

[0052]

[0053] As can be seen from Table 2, the biochars with a pyrolysis temperature of 700 °C have relatively better removal rates for NH4 + -N and PO4 3 -P. Among them, the biochar BC700-5 has the best removal rate for NH4 +-N, PO4 3 -The removal rate of P. Compared with the biochars pyrolyzed at 300 °C and 500 °C, the biochar pyrolyzed at 700 °C has a higher pH, making the surface of the biochar negatively charged, and enhancing the removal of NH4 + -N through charge attraction. On the other hand, the pore structure of the biochar pyrolyzed at 700 °C is well-developed, making it have a stronger removal rate of NH4 + -N, PO4 3 -P than the biochar in the group pyrolyzed at 300 °C. Compared with the biochar pyrolyzed at 800 °C, the biochar pyrolyzed at 700 °C does not have a collapse of the pore structure. The collapse of the pore structure will lead to a decrease in the removal rate of NH4 + -N, PO4 3 -P.

[0054] BC700 - Algae has a certain ability to remove NH4 + -N, but it is lower compared to the biochar in Example 1. At the same time, BC700 - Feces has no ability to remove NH4 + -N and has a low ability to remove PO4 3 -P. The reason for this phenomenon may be related to the fact that Enteromorpha, as a plant - derived biomass, has the ability to form a better pore structure, while the aquaculture solid waste is relatively more loose and difficult to form a pore structure. However, through the co - pyrolysis method in the present invention, using Enteromorpha as the main framework of the biochar and taking advantage of the high - protein content of the aquaculture solid waste to enrich the functional group structure on the biochar surface can effectively improve the various properties of the biochar.

[0055] In summary, the present invention uses the biochar prepared from Cynoglossus semilaevis circulating aquaculture solid waste and Enteromorpha to explore its feasibility in wastewater treatment. According to its physicochemical properties and adsorption test results, the co - pyrolysis of Enteromorpha and aquaculture solid waste can increase the specific surface area, total pore volume, and pore diameter of the biochar, and increase the types and abundances of oxygen - containing functional groups. When the proportion of Enteromorpha in the biomass raw material increases, on the one hand, it may lead to a decrease in the abundance of hydroxyl (-OH) functional groups in the biochar, and on the other hand, it may lead to a decrease in the specific surface area and ion - exchange ability of the biochar. This change will weaken the chemical adsorption mechanism of the biochar with NH4 + -N and PO4 3- -P, thereby reducing the adsorption ability of the biochar to these target pollutants. Therefore, BC700 - 5 has the most stable adsorption effect on PO4 3 -P (63.23%), and at the same time has a certain adsorption effect on NH4 +-The removal rate of N (94.57%) is also relatively high. This also provides an effective way for the resource utilization of the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera. Therefore, the application of the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera to produce biochar may be an effective and environmentally friendly option for wastewater treatment, providing a new way for the resource utilization of solid waste from marine aquaculture.

Claims

1. A method for preparing biochar using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera, characterized in that: The solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera are mixed and pyrolyzed under limited oxygen to prepare biochar (BC).

2. The method for preparing biochar from the solid waste of the circular water culture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 1, characterized in that: The mass ratio of the solid waste from the recirculating aquaculture of Cynoglossus semilaevis to Enteromorpha prolifera is 1:1 - 1:

5.

3. The method for preparing biochar by using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 2, characterized in that: The mass ratio of the solid waste from the recirculating aquaculture of Cynoglossus semilaevis to Enteromorpha prolifera is 1:

5.

4. The method for preparing biochar by using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 1, characterized in that: The limited oxygen pyrolysis temperature is 300°C - 800°C.

5. The method for preparing biochar by using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 4, characterized in that: During limited oxygen pyrolysis, N2 is introduced at a rate of 50 - 60 ml / min to provide a limited oxygen environment. At the same time, the temperature is raised at a heating rate of 15°C / min to 300°C - 800°C for pyrolytic carbonization for 110 - 130 min. After cooling to room temperature, the biochar is taken out.

6. The method for preparing biochar by using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 5, wherein: The limited oxygen pyrolysis temperature is 700°C.

7. The method for preparing biochar by using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 1, wherein: The solid waste from the recirculating aquaculture of Cynoglossus semilaevis is the residual bait and / or the feces of Cynoglossus semilaevis during the aquaculture process, which are air-dried or dried and then crushed after removing impurities.

8. The method for preparing biochar by using the solid waste from the recirculating aquaculture of Cynoglossus semilaevis and Enteromorpha prolifera according to claim 1, characterized in that: The Enteromorpha prolifera is obtained by salvaging from the coastal sea, air-dried or dried and then crushed after removing impurities.

9. A biochar prepared by the method according to claim 1.

10. Use of the biochar according to claim 9, characterized in that: The biochar is used as an adsorbent for nutrients in water bodies.

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