A method for passivating copper and zinc in pig manure using black soldier flies and minerals.

Abstract

This invention provides a method for passivating copper and zinc in pig manure using black soldier flies and minerals. Pig manure is spread evenly on the ground, and 5-day-old black soldier flies and minerals are sprinkled onto its surface for passivation treatment for 9-12 days, resulting in passivated pig manure. The minerals are hydroxyapatite or calcium carbonate. This invention involves adding hydroxyapatite or calcium carbonate to pig manure and then raising black soldier flies, using biochemical coupling technology to improve the stability of copper and zinc passivation. The feeding and crawling activities of the black soldier flies promote the full binding of hydroxyapatite or calcium carbonate with copper and zinc. The hydroxyapatite or calcium carbonate provides phosphate or carbonate ions, effectively causing free copper and zinc to chemically precipitate, reducing the risk of secondary release.

Description

Technical Field

[0001] This invention relates to the field of heavy metal pollution technology in pig manure, specifically to a method for passivating copper and zinc in pig manure using black soldier flies and minerals. Background Technology

[0002] my country has the world's largest pig farming industry. To promote piglet growth and prevent diarrhea, high concentrations of copper and zinc are allowed in feed, with Cu up to 125 mg / kg and Zn up to 1600 mg / kg (《Feed Additive Safety Use Standard》). Approximately 60% of Cu and Zn are not utilized and are excreted through manure. The annual amount of pig manure is about 2 billion tons, of which 70% is used as fertilizer for the soil, leading to the accumulation of Cu and Zn in the soil year by year, causing potential agricultural and environmental risks. The concentration of Cu and Zn in agricultural soils that have been fertilized with pig manure for a long time has reached the warning line, posing an ecological and environmental risk [He Tengbing, Huang Huiqian, et al. 2018. Heavy metal distribution and risk assessment in yellow soil profiles after 10 years of application of pig manure fertilizer [J]. Journal of Safety and Environment, 8(2):789-794].

[0003] Currently, the main methods for treating pig manure are composting and anaerobic fermentation. However, these methods have drawbacks such as long processing cycles and a high risk of secondary release of Cu and Zn. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to passivate the free copper and zinc in pig manure and reduce the risk of secondary release.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] This invention provides a method for passivating copper and zinc in pig manure using black soldier flies and minerals. The pig manure is spread flat on the ground, and 5-day-old black soldier flies and minerals are sprinkled on its surface for passivation treatment for 9-12 days to obtain passivated pig manure. The minerals are hydroxyapatite or calcium carbonate.

[0007] Beneficial Effects: This invention involves feeding black soldier flies with hydroxyapatite or calcium carbonate added to pig manure. Through biochemical coupling technology, the stability of copper and zinc passivation is improved. The feeding and crawling activities of the black soldier flies promote the full binding of hydroxyapatite or calcium carbonate with copper and zinc. The hydroxyapatite or calcium carbonate provides phosphate or carbonate ions, effectively causing the free copper and zinc to chemically precipitate, reducing the risk of secondary release.

[0008] Preferably, 5-day-old black soldier flies are obtained by the following method: black soldier fly eggs are hatched at 30°C and 70% relative humidity, and the hatched larvae are fed with wheat bran with a moisture content of 70% for 5 days to obtain 5-day-old black soldier flies.

[0009] Preferably, the pig manure is spread evenly on the ground with a waterproof cloth, and the moisture content of the pig manure is adjusted to 60-80%.

[0010] Preferably, the pig manure is spread evenly on the ground covered with a waterproof cloth, and the thickness of the pig manure is 5-10 cm.

[0011] Preferably, the particle size of the mineral is 325-400 mesh.

[0012] Preferably, the mass of 5-day-old black soldier flies applied per kilogram of pig manure is 1.5 to 3.0 g.

[0013] Preferably, the amount of minerals applied per kilogram of pig manure is 12-25 g.

[0014] Preferably, during passivation treatment, the pig manure is turned over every 2 to 4 days.

[0015] Preferably, the passivation treatment temperature is 25~30℃.

[0016] Preferably, the relative humidity for passivation treatment is 55-75%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes the biochemical function of black soldier flies to passivate Cu and Zn heavy metals in pig manure, and adds hydroxyapatite or calcium carbonate minerals to make the passivation of pig manure more stable and reduce the risk of secondary release of Cu and Zn heavy metals.

[0018] 2. This invention uses hydroxyapatite or calcium carbonate to chemically precipitate pig manure, converting free Cu and Zn in the pig manure into stable phosphates or carbonates, thereby improving the safety of pig manure as fertilizer.

[0019] 3. The feeding and activity of black soldier flies in pig manure promotes full contact between hydroxyapatite or calcium carbonate minerals and free Cu and Zn, further enhancing the uniformity of the passivation effect. At the same time, the hydroxyapatite or calcium carbonate minerals reduce the toxicity of Cu and Zn to the growth and development of black soldier flies and increase the production of insect protein.

[0020] 4. The phosphate groups in hydroxyapatite can increase the phosphorus content in pig manure, enhancing its quality as fertilizer. Compared to natural apatite, modified hydroxyapatite does not contain harmful fluoride ions and will not cause the release of fluoride ions during the passivation of Cu and Zn heavy metals.

[0021] 5. After passivation treatment, the pig manure was subjected to a modified BCR continuous extraction method to separate Cu and Zn in weakly acid-soluble, reducible, oxidizable, and residual states. The environmental risks of Cu and Zn, from highest to lowest, were: weakly acid-soluble > reducible > oxidizable > residual. The results showed that the passivation treatment of pig manure reduced the weakly acid-soluble Zn by 88%, significantly reducing its bioavailability, while increasing the content of the relatively stable oxidizable Zn by 4.5 times; the reducible Cu content was reduced by 98.7%, and the oxidizable Cu content increased by 1.8 times. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0024] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0025] Example 1 This embodiment provides a method for passivating copper and zinc in pig manure using black soldier flies and minerals, specifically including the following steps: S1. Hatch black soldier fly eggs at 30℃ and 70% relative humidity. The hatched larvae are fed with wheat bran with 70% moisture content for 5 days. The larvae are about 5-8 mm in length and are considered 5-day-old black soldier flies.

[0026] S2. Spread fresh pig manure evenly on a ground covered with a waterproof cloth, adjust the moisture content of the pig manure to 70%, and make the thickness of the pig manure 6cm. Then, evenly sprinkle 375 5-day-old black soldier flies on the surface of each kilogram of pig manure. The weight of 375 5-day-old black soldier flies is about 2.3g.

[0027] S3. Spread 12.5 g of hydroxyapatite evenly on the surface of each kilogram of pig manure. The particle size of the hydroxyapatite is 325 mesh. Passivate the manure for 10 days at 30℃ and 70% relative humidity. During the 10 days of passivation, turn the pig manure over every 3 days to promote full contact between the black soldier fly larvae, hydroxyapatite and the pig manure, and finally obtain the passivated pig manure.

[0028] Example 2 This embodiment provides a method for passivating copper and zinc in pig manure using black soldier fly larvae and minerals. The difference between this embodiment and Embodiment 1 is that 12.5 g of hydroxyapatite is replaced with 25 g of hydroxyapatite.

[0029] Example 3 This embodiment provides a method for passivating copper and zinc in pig manure using black soldier fly larvae and minerals. The difference between this embodiment and Embodiment 1 is that 12.5 g of hydroxyapatite is replaced with 25 g of calcium carbonate.

[0030] Comparative Example 1 This comparative example provides a method for treating pig manure using black soldier flies, specifically including the following steps: S1. Hatch black soldier fly eggs at 30℃ and 70% relative humidity. The hatched larvae are fed with wheat bran with 70% moisture content for 5 days. When the larvae reach a length of 5-8 mm, they are ready for use as 5-day-old black soldier flies.

[0031] S2. Spread fresh pig manure evenly on a waterproof cloth-covered surface, adjusting the moisture content of the manure to 70% and creating a 6 cm layer. Then, evenly sprinkle 375 five-day-old black soldier flies (approximately 2.3 g) onto the surface of each kilogram of manure. Perform passivation treatment at 30℃ and 70% relative humidity for 10 days, turning the manure over every 3 days during this period to obtain passivated manure.

[0032] Comparative Example 2 This comparative example provides a method for passivating copper and zinc in pig manure using black soldier fly larvae and minerals. The difference between this comparative example and Example 1 is that 12.5 g of hydroxyapatite is replaced with 25 g of coconut shell activated carbon.

[0033] Comparative Example 3 This comparative example provides a method for passivating copper and zinc in pig manure using black soldier fly larvae and minerals. The difference between this comparative example and Example 1 is that 12.5 g of hydroxyapatite is replaced with 25 g of montmorillonite.

[0034] Comparative Example 4 This comparative example provides a method for passivating copper and zinc in pig manure using black soldier fly larvae and minerals. The difference between this comparative example and Example 1 is that 12.5 g of hydroxyapatite is replaced with 25 g of palygorskite.

[0035] Performance testing The passivated pig manure obtained from Examples 1-3 and Comparative Examples 1-4 was separated from black soldier fly larvae by passing it through a sieve with a pore size of 3 mm. The pig manure was then dried and ground. Subsequently, a modified BCR continuous extraction method was used to extract Cu and Zn in weakly acid-soluble, reducible, oxidizable, and residual forms. Three replicates were set for each treatment group. The content of each Cu and Zn form was determined by ICP-MS. The modified BCR continuous extraction method is referenced in [Zhang Chaoyang, Peng Pingan, et al. 2012. Improved BCR method for analyzing chemical speciation of heavy metals in national soil standard materials [J]. Journal of Ecology and Environment, 21(11): 1881-1884]. The test results are shown in Tables 1 and 2.

[0036] Table 1. Passivation effect of Zn in pig manure (unit: mg / kg)

[0037] As shown in Table 1, the addition of different masses of hydroxyapatite or calcium carbonate in Examples 1-3 significantly reduced the bioavailability of Zn in pig manure. The concentration of weakly acid-soluble Zn decreased from a maximum of 346.4±135.0 mg / kg to 42.5±0.8 mg / kg, a reduction of 88%. Simultaneously, the concentration of more stable oxidizable Zn increased from 126.5±60.4 mg / kg to 582.9±27.4 mg / kg, an increase of 4.5 times, indicating that Examples 1-3 had a good passivation effect on zinc.

[0038] Table 2. Passivation effect of Cu on pig manure (unit: mg / kg)

[0039] As shown in Table 2, the addition of different masses of hydroxyapatite or calcium carbonate in Examples 1-3 significantly reduced the bioavailability of Cu in pig manure. The concentration of reducible Cu decreased from a maximum of 199.3±72.6 mg / kg to 2.6±0.2 mg / kg, a reduction of 98.7%. The concentration of relatively stable oxidizable Cu increased from 179.1±29.0 mg / kg to 313.5±38.6 mg / kg, an increase of 1.8 times.

[0040] In summary, this invention utilizes black soldier fly larvae and minerals to chemically passivate zinc and copper in pig manure, altering the forms of these heavy metals. This transforms the high-risk, weakly acid-soluble zinc and copper into relatively safer, reducible and oxidizable forms, i.e., reducing the content of the weakly acid-soluble form and increasing the content of the oxidizable and reducible forms. This invention demonstrates excellent passivation effects on zinc and copper in pig manure, effectively improving the stability of Zn and Cu in pig manure as fertilizer and reducing its exposure risk to soil and crops.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for passivating copper and zinc in pig manure using black soldier fly larvae and minerals, characterized in that, Pig manure is spread flat on the ground, and 5-day-old black soldier flies and minerals are sprinkled on its surface for passivation treatment for 9-12 days to obtain passivated pig manure; the minerals are hydroxyapatite or calcium carbonate.

2. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, Five-day-old black soldier flies were obtained by hatching black soldier fly eggs at 30°C and 70% relative humidity. The hatched larvae were then fed wheat bran with 70% moisture content for 5 days to obtain five-day-old black soldier flies.

3. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, Spread the pig manure evenly on the ground covered with a waterproof cloth, and adjust the moisture content of the pig manure to 60-80%.

4. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, The pig manure is spread evenly on the ground covered with a waterproof cloth, with a thickness of 5-10 cm.

5. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, The mineral has a particle size of 325-400 mesh.

6. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, The mass of 5-day-old black soldier flies spread per kilogram of pig manure is 1.5~3.0 g.

7. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, The amount of minerals spread per kilogram of pig manure is 12-25 g.

8. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, During passivation treatment, the pig manure should be turned over every 2 to 4 days.

9. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, The passivation treatment temperature is 25~30℃.

10. The method for passivating copper and zinc in pig manure using black soldier flies and minerals according to claim 1, characterized in that, The relative humidity for passivation treatment is 55-75%.

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