A modified nano-silver sulfide-assisted black soldier fly sludge treatment method and application

Abstract

The application discloses a modified nano-silver sulfide auxiliary black soldier fly sludge treatment method and application, and relates to the technical field of environmental protection.The application realizes sludge dry base reduction in a short time, shortens a treatment period, and the pile volume is also compressed due to accelerated decomposition of organic matter and formation of worm sand, thereby reducing site occupation and turning pile energy consumption, meeting efficient disposal of municipal sludge, significant reduction and volume compression; through the modified nano-silver sulfide, silver ions (Ag + ) are continuously released by means of a chitosan negative charge shell, common pathogenic bacteria in sludge are rapidly inactivated in the early stage of composting, and heavy metal elements such as cadmium, lead, arsenic and mercury in the worm sand after treatment are all lower than national standards, so that secondary disinfection or chemical stabilization treatment is not needed, direct agricultural safety application is met, a "sludge-worm sand-farmland" closed loop is realized, and good social, environmental and economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically a method and application of modified nano-silver sulfide-assisted black soldier fly larvae for sludge treatment. Background Technology

[0002] With the acceleration of urbanization, the amount of urban sewage sludge has increased significantly. This sludge contains large amounts of organic pollutants, pathogens, and heavy metals, and direct landfilling or incineration poses secondary pollution and resource waste problems. Black soldier fly larvae feed on organic waste, efficiently decomposing organic matter in sludge, shortening the treatment cycle and obtaining nutrient-rich insect sand. Current research has confirmed that black soldier fly composting can reduce some greenhouse gas emissions; however, in sludge with high moisture and high organic matter content, there are still problems with high CH4 and N2O emissions and incomplete suppression of pathogens. Utilizing the broad-spectrum antibacterial properties of nano-silver holds promise for inhibiting harmful bacteria in the early stages of composting, while simultaneously influencing microbial community metabolism, further reducing greenhouse gas emissions.

[0003] In existing black soldier fly sludge composting processes for urban sludge, pathogens are difficult to completely suppress, and the compost microenvironment is prone to anaerobic zones, leading to high emissions of methane (CH4) and nitrous oxide (N2O) and the safety risks associated with the production of insect-derived sand. Therefore, additional treatment is required before it can be used in agriculture. Thus, this invention provides a modified nano-silver sulfide-assisted black soldier fly sludge treatment method and application to solve the aforementioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method and application for sludge treatment using modified nano-silver sulfide-assisted black soldier fly larvae, in order to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for treating sludge using modified silver sulfide nanoparticles assisted by black soldier fly larvae includes the following steps:

[0007] S1: Add chitosan to anhydrous isopropanol and NaOH solution, stir, then add chloroacetic acid, heat to react, centrifuge, wash, and vacuum dry to obtain carboxymethyl chitosan (CMC).

[0008] S2: CMC was dissolved in deionized water to obtain an aqueous solution of CMC. Then, silver nitrate (AgNO3) solution was added, followed by the addition of sodium sulfide solution. The reaction was allowed to stand, centrifuged, washed, and vacuum dried to obtain core-shell silver sulfide nanoparticles (CMC@Ag2S-NPs).

[0009] S3: Mix dewatered sludge, straw powder, pig manure and wheat bran, and adjust the carbon-nitrogen ratio and moisture content to obtain a premixed matrix;

[0010] S4: Add CMC@Ag2S-NPs to the premixed substrate, inoculate with black soldier fly larvae, assemble in flower pots, and compost until the black soldier fly larvae enter the early swelling stage to obtain the antibacterial substrate;

[0011] S5: The treated antibacterial matrix is ​​then separated by a combination of sieve and airflow to recover black soldier fly larvae and insect sand. The insect sand is then air-dried to complete the sludge treatment.

[0012] Furthermore, the NaOH solution is an aqueous solution with a concentration of 25~35wt%.

[0013] Furthermore, the degree of deacetylation of the chitosan is ≥85%.

[0014] Furthermore, the mass ratio of chitosan, anhydrous isopropanol, NaOH solution, and chloroacetic acid is 1:(5~10):(4.5~4.8):(4~6).

[0015] Furthermore, in step S1, the stirring process conditions are: stirring at a speed of 200~300 rpm for 20~30 minutes.

[0016] Furthermore, in step S1, the process conditions for the heating reaction are: reacting at a temperature of 60~70℃ for 3~4 hours.

[0017] Furthermore, the mass ratio of CMC, deionized water, silver nitrate solution, and sodium sulfide solution is 0.5:(62~100):0.2:0.3.

[0018] Furthermore, in step S1, the centrifugation process conditions are: centrifugation at a speed of 2400~3000 rpm for 10~20 min.

[0019] Furthermore, in step S1, the washing process conditions are as follows: wash with 70-75% ethanol and rinse 2-3 times.

[0020] Furthermore, in step S1, the vacuum drying process conditions are as follows: vacuum drying at a temperature of 60~70°C for 1~2 hours, with a vacuum degree of 0.05~10kPa.

[0021] Furthermore, in step S2, the concentration of the CMC aqueous solution is 0.5~0.8wt%, and the pH is 8.0~9.0.

[0022] Furthermore, in step S2, the rate of adding sodium sulfide solution is 0.5~1 mL / min.

[0023] Furthermore, the concentration of the silver nitrate solution is 0.01~0.05 mol / L.

[0024] Furthermore, the concentration of the sodium sulfide solution is 0.01~0.05 mol / L.

[0025] Furthermore, in step S2, the reaction is allowed to stand for 2-3 hours under the protection of a nitrogen flow rate of 200-300 sccm, and then left to stand overnight at room temperature.

[0026] In the above technical solution, during the preparation of nano-silver sulfide (Ag2S) encapsulated in carboxymethyl chitosan (CMC), the nucleation and lattice growth of Ag2S require time. In the initial reaction stage, silver ions (Ag... + ) and sulfide ions (S 2- Ag₂S crystal nuclei are formed through coordination reactions, but they may not yet have fully developed into uniform nanoparticles. Allowing the system to stand overnight provides a longer reaction time, allowing the nuclei to grow further and refine the crystal structure, resulting in a core-shell structure with controllable size and uniform shell thickness. Prolonged standing also reduces residual Ag in the system. + The concentration of [uncoordinated Ag] inhibits uncoordinated Ag. + With S 2- Heterogeneous precipitation occurs, thereby increasing the purity of the product.

[0027] Furthermore, in step S2, the centrifugation process conditions are: centrifugation at a speed of 10000~12000 rpm for 10~20 min.

[0028] Furthermore, in step 2, the washing process is as follows: rinse 2-3 times with deionized water, then rinse 2-3 times with 70-75% ethanol, alternating between the two or three rinses.

[0029] Furthermore, in step S2, the vacuum drying process conditions are: vacuum drying at a temperature of 60~70℃ for 1~2 hours, with a vacuum degree of 0.05~10kPa.

[0030] Furthermore, in step S2, the core-shell silver sulfide nanoparticles have a particle size of 20~80nm, a shell thickness of 5~10nm, and a potential of -30~-25mVζ.

[0031] Furthermore, the mass ratio of dewatered sludge, straw powder, pig manure and wheat bran is (4~5):1:2:1.

[0032] Furthermore, in step S3, the carbon-nitrogen ratio is 20-30 and the water content is 40-50%.

[0033] Furthermore, in step S4, the amount of CMC@Ag2S-NPs added is 5~200mg / kg.

[0034] Furthermore, in step S4, the black soldier fly larvae are 7-10 days old, and the addition amount is 5-10g / 200g.

[0035] Furthermore, in step S4, the dimensions of the flowerpot are: an average diameter of 20-25cm and an average height of 15-20cm.

[0036] Furthermore, the composting process is as follows: under conditions of temperature 25~30°C and relative humidity 60~70%, the compost is turned over every 3~5 days for 10~15 consecutive days until the black soldier fly larvae enter the pre-expansion stage.

[0037] Furthermore, in step S5, the moisture content of the dried insect sand is ≤20%.

[0038] In the above technical solution, the chlorine atom (Cl) of chloroacetic acid - The amino group (-NH2) or hydroxyl group (-OH) of chitosan activates the hydroxyl group (-OH) under alkaline conditions, forming an oxonium intermediate. The amino group (-NH2) or hydroxyl group (-OH) of chitosan acts as a nucleophile, attacking the α-carbon atom of chloroacetic acid to form an amide bond (-CO-NH-) or an ester bond (-CO-O-). The resulting carboxymethyl group (-CH2COOH) undergoes deprotonation in solution, forming a negatively charged carboxylate group (-COO-). - This process imparts a negative charge to chitosan, and the negatively charged carboxymethyl chitosan adsorbs positively charged pollutants through electrostatic interactions, thereby improving removal efficiency.

[0039] Sodium sulfide and AgNO3 undergo a thiolation reaction under CMC coating to generate nano-silver sulfide (Ag2S) core-shell structures. The Ag2S core-shell structure physically delays the degradation of Ag2S. + Diffusion, to avoid high concentrations of Ag + Toxicity to black soldier fly larvae; Ag2S can excite electron-hole pairs under visible light, producing reactive oxygen species (ROS)·OH and O2. 2- It degrades pollutants and organic matter, effectively inhibits the proliferation of pathogenic microorganisms, and through the interaction between Ag⁺ and the microbial cell membrane and enzyme system, it efficiently inhibits pathogenic bacteria and anaerobic methanogens and denitrifying bacteria.

[0040] A premixed substrate consisting of straw powder (cellulose), pig manure (nitrogen source), and wheat bran (carbon source) provides a carbon-nitrogen balanced nutrient substrate for the gut microbiota (Pseudomonas and Bacillus) of black soldier fly larvae. The microbiota decomposes recalcitrant organic matter in the sludge by secreting cellulase and protease, and at the same time, improves degradation efficiency by regulating metabolic pathways through quorum sensing.

[0041] In CMC@Ag2S-NPs, Ag2S reacts with heavy metal ions (Cd) via sulfur atoms. 2+ Zn 2+ This forms stable sulfide precipitates (CdS, ZnS), fixing them in the insect sand. Simultaneously, Ag₂S releases a low concentration of Ag.+ In synergy with ROS, it disrupts the cell membranes and DNA of pathogens, achieving dual inactivation of pathogens; nitrifying bacteria dominate the decomposition of organic matter, converting ammonia nitrogen in sludge into nitrates, reducing the release of odor-causing substances (NH3, H2S). CMC@Ag2S-NPs adsorb NH3... 4+ And slow release Ag + The feeding behavior of black soldier fly larvae disrupts the sludge aggregate structure, increases porosity, and promotes oxygen permeation and aerobic microbial metabolism. The excreted sediment from the black soldier fly larvae further serves as a carbon source, supporting denitrification during the post-ripening stage.

[0042] An application of a modified nano-silver sulfide-assisted black soldier fly sludge treatment method was developed, which was then applied to urban sludge treatment.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1. The sludge treatment method of the present invention, by adding modified nano-silver sulfide to the premixed matrix and inoculating it with black soldier fly larvae, can achieve a sludge dry basis reduction rate of >65% in only 10-15 days. Compared with the traditional aerobic composting method that requires 30-60 days, not only is the treatment cycle shortened by nearly 50%, but the volume of the compost pile is also compressed due to the accelerated decomposition of organic matter and the generation of insect sand, reducing site occupation and energy consumption for turning the pile, thus meeting the requirements of efficient disposal of urban sludge, significant reduction and volume compression.

[0045] 2. The sludge treatment method of the present invention utilizes modified nano-silver sulfide to continuously release Ag through the negatively charged shell of chitosan. + It can rapidly inactivate common pathogens (Escherichia coli, Salmonella, Shigella) in sludge in the early stage of composting. Moreover, the treated insect sand has been tested and found to have heavy metal elements such as Cd (cadmium), Pb (lead), As (arsenic), and Hg (mercury) below the national standard level 1 limit. It does not require secondary disinfection or chemical stabilization treatment and directly meets the requirements for safe agricultural application. It has the characteristics of broad-spectrum and high-efficiency pathogen inhibition and safety compliance.

[0046] 3. The sludge treatment method of the present invention reduces cumulative N2O emissions by 50-90% and CH4 emissions by 45-95% through the use of nano-silver sulfide additives, while CO2 emissions show no significant fluctuations. This emission reduction effect mainly stems from the selective inhibition of methanogenic bacteria (mcrA gene) and denitrifying bacteria (hao, norB genes) by nano-silver sulfide, as well as the enhancement of the activity of N2O-reducing bacteria (nosZ gene) and methanogenic bacteria (pmoA gene), effectively achieving a significant reduction in greenhouse gas emissions.

[0047] 4. The sludge treatment method of the present invention, after treatment, uses a screen and airflow separation to recover the insect sand, which is then air-dried to a moisture content of ≤20%. The insect sand has an organic matter content of >50%, total nitrogen of >3.0%, available phosphorus of >1.5%, available potassium of >2.0%, pH of 6.5~7.5, and is rich in elements such as Ca, Mg, trace Cu, Zn and beneficial bacteria communities. This significantly improves the physical and chemical properties of the soil and the quality of crops, generates nutrient-rich insect sand, and promotes plant growth.

[0048] 5. The sludge treatment method of this invention does not require modification of existing BSF (semi-wet material crusher) composting equipment. Nano-silver sulfide is added only once during the conventional process feeding stage. The turning frequency (3-5 days / time), temperature and humidity (25-30°C, 60-70%RH) remain consistent with existing production lines, facilitating rapid deployment in community wastewater treatment plants, food processing plants, and organic waste comprehensive utilization centers. This achieves a closed loop of "sludge-insect sand-farmland," balancing environmental emission reduction and resource utilization, and yielding significant social, environmental, and economic benefits. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0050] In the following specific implementation,

[0051] Chitosan, model CS-85H, viscosity 300cps;

[0052] The NaOH solution is a 25wt% aqueous solution;

[0053] The rate of adding sodium sulfide solution was 1 mL / min;

[0054] The concentration of the silver nitrate solution is 0.01 mol / L;

[0055] The concentration of the sodium sulfide solution is 0.01 mol / L;

[0056] Flower pots, average diameter 23cm, average height 15cm;

[0057] Plastic basins, average diameter 25cm, average height 20cm;

[0058] Example 1: A method for treating sludge using modified nano-silver sulfide-assisted black soldier fly larvae, comprising the following steps:

[0059] S1: Chitosan was added to anhydrous isopropanol and NaOH solution, stirred at 200 rpm for 20 min, then chloroacetic acid was added, and the mixture was reacted at 60°C for 3 h. After centrifugation at 2400 rpm for 10 min, the mixture was washed twice with 70 v% ethanol, and then vacuum dried at 60°C for 1 h at a vacuum degree of 0.05 kPa to obtain carboxymethyl chitosan (CMC). The mass ratio of chitosan, anhydrous isopropanol, NaOH solution, and chloroacetic acid was 1:5:4.5:4.

[0060] S2: CMC was dissolved in deionized water to obtain a 0.5wt% CMC aqueous solution with pH 8.0. Silver nitrate solution was added, followed by dropwise addition of sodium sulfide solution. The reaction was carried out for 2 hours under a nitrogen flow rate of 200 sccm, and then allowed to stand overnight at room temperature. After centrifugation at 10,000 rpm for 10 minutes, the nanoparticles were washed twice with deionized water and then twice with 70 v% ethanol, alternating between the two washes. The nanoparticles were then vacuum dried at 60℃ for 1 hour at a vacuum degree of 0.05 kPa to obtain core-shell silver sulfide nanoparticles (CMC@Ag2S-NPs). The mass ratio of CMC, deionized water, silver nitrate solution, and sodium sulfide solution was 0.5:100:0.2:0.3. The particle size of CMC@Ag2S-NPs was 50 nm, the shell thickness was 5 nm, and the potential was -25 mVζ.

[0061] S3: Mix dewatered sludge, straw powder, pig manure and wheat bran, adjust the carbon-to-nitrogen ratio to 25 and the moisture content to 45% to obtain a premixed matrix; the mass ratio of dewatered sludge, straw powder, pig manure and wheat bran is 4:1:2:1;

[0062] S4: Add CMC@Ag2S-NPs to the premixed substrate at a dosage of 50 mg / kg, and inoculate 7-day-old black soldier fly larvae at a dosage of 7 g / 200 g. Assemble the substrate in flower pots and keep it at 25°C and 60% relative humidity for 15 consecutive days, turning it over every 3 days to obtain the antibacterial substrate.

[0063] S5: The treated antibacterial matrix is ​​then processed by a combination of sieve and airflow separation to recover black soldier fly larvae and insect sand. The insect sand is then air-dried to complete the sludge treatment. The moisture content of the dried insect sand is ≤20%.

[0064] Example 2: A method for treating sludge using modified nano-silver sulfide-assisted black soldier fly larvae, comprising the following steps:

[0065] S1: Chitosan was added to anhydrous isopropanol and NaOH solution, stirred at 250 rpm for 25 min, then chloroacetic acid was added, and the mixture was reacted at 65°C for 3.5 h. After centrifugation at 2600 rpm for 15 min, the mixture was washed twice with 70 v% ethanol, and then vacuum dried at 65°C for 1 h at a vacuum degree of 0.05 kPa to obtain CMC. The mass ratio of chitosan, anhydrous isopropanol, NaOH solution, and chloroacetic acid was 1:8:4.6:5.

[0066] S2: CMC was dissolved in deionized water to obtain a 0.5wt% CMC aqueous solution with pH 8.0. Silver nitrate solution was added, followed by dropwise addition of sodium sulfide solution. The reaction was carried out for 2 hours under a nitrogen flow rate of 250 sccm, and then allowed to stand overnight at room temperature. After centrifugation at 11000 rpm for 15 minutes, the mixture was washed twice with deionized water and then twice with 70 v% ethanol, alternating between the two washes. The mixture was then vacuum dried at 65℃ for 1.5 hours at a vacuum degree of 0.05 kPa to obtain CMC@Ag2S-NPs. The mass ratio of CMC, deionized water, silver nitrate solution, and sodium sulfide solution was 0.5:100:0.2:0.3. The particle size of CMC@Ag2S-NPs was 60 nm, the shell thickness was 6 nm, and the potential was -27 mVζ.

[0067] S3: Mix dewatered sludge, straw powder, pig manure and wheat bran, adjust the carbon-to-nitrogen ratio to 28 and the moisture content to 42% to obtain a premixed matrix; the mass ratio of dewatered sludge, straw powder, pig manure and wheat bran is 4.5:1:2:1;

[0068] S4: Add CMC@Ag2S-NPs to the premixed substrate at a dosage of 100 mg / kg, and inoculate 7-day-old black soldier fly larvae at a dosage of 6 g / 200 g. Assemble the substrate in flower pots and keep it at 25°C and 60% relative humidity for 15 consecutive days, turning it over every 3 days to obtain the antibacterial substrate.

[0069] S5: The treated antibacterial matrix is ​​then processed by a combination of sieve and airflow separation to recover black soldier fly larvae and insect sand. The insect sand is then air-dried to complete the sludge treatment. The moisture content of the dried insect sand is ≤20%.

[0070] Example 3: A method for treating sludge using modified nano-silver sulfide-assisted black soldier fly larvae, comprising the following steps:

[0071] S1: Chitosan was added to anhydrous isopropanol and NaOH solution, stirred at 300 rpm for 30 min, then chloroacetic acid was added, and the mixture was reacted at 70℃ for 4 h. After centrifugation at 3000 rpm for 20 min, the mixture was washed with 70 v% ethanol three times, and then vacuum dried at 70℃ for 2 h at a vacuum degree of 10 kPa to obtain CMC. The mass ratio of chitosan, anhydrous isopropanol, NaOH solution, and chloroacetic acid was 1:10:4.8:6.

[0072] S2: CMC was dissolved in deionized water to obtain a 0.5 wt% CMC aqueous solution with pH 8.0. Silver nitrate solution was added, followed by dropwise addition of sodium sulfide solution. The reaction was carried out for 3 hours under a nitrogen flow rate of 300 sccm, and allowed to stand overnight at room temperature. The solution was then centrifuged at 12000 rpm for 20 minutes. After rinsing three times with deionized water, the solution was rinsed three times with 70 v% ethanol, alternating between the two rinses. The solution was then vacuum dried at 70°C for 2 hours at a vacuum degree of 0.05 kPa to obtain CMC@Ag2S-NPs. The mass ratio of CMC, deionized water, silver nitrate solution, and sodium sulfide solution was 0.5:100:0.2:0.3. The particle size of CMC@Ag2S-NPs was 80 nm, the shell thickness was 10 nm, and the potential was -30 mVζ.

[0073] S3: Mix dewatered sludge, straw powder, pig manure and wheat bran, adjust the carbon-nitrogen ratio to 30 and the moisture content to 50% to obtain a premixed matrix; the mass ratio of dewatered sludge, straw powder, pig manure and wheat bran is 5:1:2:1;

[0074] S4: Add CMC@Ag2S-NPs to the premixed matrix at a dosage of 200 mg / kg, and inoculate 7-day-old black soldier fly larvae at a dosage of 10 g / 200 g. Under the conditions of 25℃ and 60% relative humidity, the mixture is continuously incubated for 15 days, with the pile turned over every 3 days to obtain the antibacterial matrix.

[0075] S5: The treated antibacterial matrix is ​​then processed by a combination of sieve and airflow separation to recover black soldier fly larvae and insect sand. The insect sand is then air-dried to complete the sludge treatment. The moisture content of the dried insect sand is ≤20%.

[0076] Example 4: Application of a modified nano-silver sulfide-assisted black soldier fly sludge treatment method: including the following steps:

[0077] Step 1: Mix the dried insect sand obtained in Example 1 with the cultivation soil, take 5 kg and put it into a plastic pot to obtain a cultivation pot; the mass ratio of dried insect sand to cultivation soil is 0.03:1.

[0078] Step 2: Disinfect the spinach seeds with 70% ethanol, then rinse them with clean water to obtain the spawn;

[0079] Step 3: Under greenhouse conditions of 12 hours of light per day, 25°C, and 60% relative humidity, transplant the cultivars into cultivation pots and raise them for 7 days. Then, plant 10 seedlings in each pot and continue to cultivate them, with a plant spacing of 10cm × 10cm.

[0080] Comparative Example 1:

[0081] This comparative example provides a method for treating sludge using modified nano-silver sulfide-assisted black soldier fly larvae. CMC@Ag2S-NPs are not added to the premixed matrix, and the rest of the method is the same as in Example 1.

[0082] Comparative Example 2:

[0083] This comparative example provides a method for treating sludge using modified nano-silver sulfide-assisted black soldier fly larvae. No black soldier fly larvae are added to the premixed substrate, and the rest of the method is the same as in Example 1.

[0084] Comparative Example 3:

[0085] This comparative example provides a method for treating sludge using modified nano-silver sulfide-assisted black soldier fly larvae. The premixed matrix does not contain CMC@Ag2S-NPs or black soldier fly larvae, and the rest of the method is the same as in Example 1.

[0086] Comparative Example 4:

[0087] This comparative example provides an application of a modified nano-silver sulfide-assisted method for treating sludge from black soldier flies. Compared with Example 4, only 5 kg of cultivation soil was added to the cultivation pot, while the rest of the methods remained the same.

[0088] Comparative Example 5:

[0089] This comparative example provides an application of a modified nano-silver sulfide-assisted method for treating sludge from black soldier flies. Compared with Example 4, 5 kg of uncomposted sludge and cultivation soil are added to the cultivation pot, with a mass ratio of uncomposted sludge to cultivation soil of 0.03:1. The rest of the methods are the same.

[0090] Comparative Example 6:

[0091] This comparative example provides an application of a modified nano-silver sulfide-assisted method for treating sludge from black soldier flies. Compared with Example 4, 5 kg of compost sludge without silver worm sand is added to the cultivation pot, and the mass ratio of the compost sludge without silver worm sand to the cultivation soil is 0.03:1. The rest of the methods are the same.

[0092] experiment:

[0093] During the composting process of Examples 1-3 and Comparative Examples 1-3, the degradation effect of the mixed substrate was measured and the results were recorded.

[0094] Sludge dry basis weight reduction test: Using GB4284-2018 as the reference standard, the initial sludge weight was weighed, mechanically dewatered, and then dried at 105℃ until constant weight was achieved. The dry basis mass was then weighed, and the weight reduction rate was calculated.

[0095] Cumulative CH4, N2O, and CO2 emission tests: Using GB4284-2018 as the reference standard, a closed-chamber sampling method was adopted to periodically collect the gas in the matrix head space and measure the concentrations of CH4, N2O, and CO2 respectively.

[0096] Pathogen detection rate test: Using GB4284-2018 as the reference standard, take 10g of sludge sample, add 100mL of sterile physiological saline, shake for 30min to prepare a 1:10 dilution, take 1mL of the dilution and inoculate it into the culture medium, incubate at 37℃ for 2 days, and count the number of colonies.

[0097] Heavy metal content test: Using GB4284-2018 as the reference standard, take 2g of sludge sample, add 5mL of nitric acid, 2mL of hydrofluoric acid and 1mL of perchloric acid, heat to digest until white fumes are emitted, cool and make up to 50mL, and use atomic absorption spectrometry to determine the content of Cd (cadmium), Pb (lead), As (arsenic) and Hg (mercury).

[0098] In the heavy metal content test, the concentration of nitric acid was 65v, the concentration of hydrofluoric acid was 40v, and the concentration of perchloric acid was 70v.

[0099] Organic matter content test: Using GB4284-2018 as the reference standard, the potassium dichromate titration method was adopted. Take 0.5g of sludge sample, add 5mL of 0.8mol / L potassium dichromate solution and 5mL of concentrated sulfuric acid (70v%), heat in a boiling water bath for 5min, cool and dilute with distilled water, titrate with 0.2mol / L ferric sulfate solution until green, record the volume consumed, and calculate the organic matter content.

[0100] Total nitrogen test: Using GB4284-2018 as the reference standard, the Kjeldahl method was adopted. 0.5g of sludge sample was taken, 5mL of concentrated sulfuric acid and 0.37g of catalyst were added, and the sample was digested until clear. The digestion solution was transferred to a distillation apparatus, NaOH solution was added for distillation, and NH3 was collected into the boric acid absorption solution. The boric acid absorption solution was titrated with 0.01mol / L sulfuric acid solution, and the nitrogen content was calculated.

[0101] In the total nitrogen test, the catalyst was a mixture of copper sulfate and potassium sulfate in a mass ratio of 1:10.

[0102] Available phosphorus test: Using GB4284-2018 as the reference standard, take 2.5g of sludge sample, add 50mL of 0.5mol / L sodium bicarbonate solution, shake for 30min, centrifuge at 2400rpm for 10min, take the supernatant, add 5mL of molybdenum antimony reagent, make up to 50mL, develop color at room temperature for 30min, measure the absorbance at 880nm wavelength, plot the standard curve and calculate the available phosphorus content.

[0103] Available potassium test: Using GB4284-2018 as the reference standard, take 2.5g of sludge sample, add 50mL of 1mol / L ammonium acetate solution, shake for 30min, filter, and directly determine K in the filtrate using a flame photometer. + Concentration, effective potassium content is calculated based on the standard curve.

[0104] pH test: Using GB4284-2018 as the reference standard, take sludge samples and deionized water at a ratio of 1:2.5, mix for 30 minutes, let stand for 30 minutes, and measure with a calibrated pH meter.

[0105] The properties of sludge mixed with nano-silver sulfide after being composted by black soldier flies

[0106]

[0107] Spinach obtained in Example 4 and Comparative Examples 4-6 was cultivated for 30 days. The water level in the tray was maintained at 1 cm, and water was replenished as needed. Integrated fertigation was implemented without additional fertilization. After treatment, the fresh weight and biomass of the aboveground parts of the spinach were counted, and leaves and stems of the plants were collected. The contents of trace elements such as Fe, Zn, Mn, and Cu were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) to evaluate the effects of insect-sand fertilizer on the growth and nutritional quality of spinach.

[0108] Total dry weight biomass test: Using GB / T 45724-2025 as the reference standard, spinach leaves were cut off, the fresh weight of the sample was weighed immediately, the ambient temperature and humidity were recorded, the sample was placed in an oven, blanched at 105℃ for 30 minutes, then adjusted to 65℃ for constant drying until constant weight, cooled to room temperature, and the dry weight was weighed.

[0109] Average plant height test: Using GB / T 45724-2025 as the reference standard, the average plant height of spinach was measured and calculated.

[0110] Leaf chlorophyll content test: Using GB / T 45724-2025 as the reference standard, cut leaves, chop them, weigh them, add 5 mL of ethanol and calcium carbonate, grind into a homogenate, centrifuge at 2400 rpm for 30 min, extract the supernatant, and determine the chlorophyll content by spectrophotometry.

[0111] In the leaf chlorophyll content test, the ethanol concentration was 80 v.

[0112] Spinach yield, plant height, and leaf chlorophyll content under different treatments

[0113]

[0114] Note: The numbers in the table are the averages of four repeated trials. The same letter after the number indicates that there is no significant difference in the same column by the LSD (Least Significant Difference) test (P=0.05).

[0115] Content of cadmium, copper, zinc, calcium, nitrogen, phosphorus, and potassium in the aboveground parts of crops under each treatment (dry weight)

[0116]

[0117] Note: The numbers in the table are the averages of four replicates. The same letter after the number indicates that there is no significant difference in the same column by the LSD test (P=0.05).

[0118] Based on the data in the table above, the following conclusions can be clearly drawn:

[0119] Compared with Comparative Examples 1-3, Examples 1-3 showed lower CH4, N2O and CO2 emissions, lower pathogen content, heavy metal content meeting national standards, increased organic matter content, increased total nitrogen content, decreased available phosphorus, increased available potassium, and a slightly acidic pH value.

[0120] Compared with Comparative Examples 4-6, the spinach and soil total dry weight biomass obtained in Example 4 were higher, the average plant height was higher, and the chlorophyll content of the leaves was higher.

[0121] Comparing Example 4 with Comparative Examples 4-6, it can be seen that the concentrations of cadmium, copper, and zinc in the plants of the sludge treatment group without composting were significantly increased (Cd reached 5.9 mg / kg, and Zn reached 264.2 mg / kg), indicating that the sludge without stabilization treatment has a greater risk of heavy metal migration.

[0122] Comparing Example 4 with Comparative Examples 5-6, it can be seen that the Cd content of spinach in Example 4 is only 1.8 mg / kg, which is significantly lower than that in Comparative Examples 5-6. This indicates that silver worm sand has a good heavy metal passivation ability and can effectively reduce the accumulation of pollutants in plants.

[0123] In Example 4, the levels of calcium (32.0 g / kg), nitrogen (54.0 g / kg), phosphorus (6.2 g / kg), and potassium (96.0 g / kg) in spinach were significantly higher than in other treatments, indicating that this treatment not only effectively avoided heavy metal stress but also improved the absorption efficiency of major nutrients by spinach. The calcium content was significantly higher than in other comparative examples (P<0.05), which may be related to the synergistic effect of the calcium carbonate and silica-alumina framework structure contained in the silver worm sand on soil pH buffering and calcium release.

[0124] Comparing Example 4 with Comparative Example 6, it can be seen that while ensuring the supply of nutrients such as nitrogen, phosphorus, and potassium, the calcium level is further improved, and the accumulation of heavy metals is effectively inhibited, demonstrating the multifunctionality of the present invention, that is, it has the dual function of "enhancing fertilizer efficiency + passivating heavy metals".

[0125] Comparing Example 4 with Comparative Examples 4-6, the total dry weight biomass was the highest, reaching 1654 g / pot, significantly higher than the other comparative examples (P<0.05), and approximately 3.6 times higher than Comparative Example 4, demonstrating the excellent growth-promoting effect of silver worm sand. This indicates that silver worm sand, as a modifier, effectively enhances the nutrient release and plant absorption efficiency of sludge fertilizer.

[0126] Comparing Example 4 with Comparative Examples 4-6, it can be seen that the plant height of spinach in Example 4 was 26cm, which is significantly improved, but the difference is not significant compared with Comparative Example 6. This suggests that the promoting effect of silver worm sand on the aboveground growth is mainly reflected in the accumulation of dry matter.

[0127] Example 4 showed the highest chlorophyll content (38 mg / kg), followed by Comparative Example 6 (22 mg / kg). Compared to Comparative Example 4 (11 mg / kg), both were significantly higher, indicating that the modified sludge can effectively enhance the photosynthetic capacity of spinach and strengthen its physiological activity.

[0128] Comprehensive analysis shows that modified sludge containing silver worm sand has significant advantages in promoting plant dry matter accumulation and increasing chlorophyll content, demonstrating good potential for agricultural applications. This product not only improves the utilization efficiency of sludge resources, but also improves the plant rhizosphere environment and enhances the synergistic effect of fertilizer release and nutrient absorption through the structural stability and micronutrient regulation characteristics of silver worm sand.

[0129] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A modified nano-silver sulfide assisted black soldier fly sludge treatment method, characterized in that: S1: chitosan is added to anhydrous isopropyl alcohol, NaOH solution, stirred, chloroacetic acid is added, heated and reacted, centrifuged, washed, and vacuum dried to obtain carboxymethyl chitosan; S2: the carboxymethyl chitosan is dissolved in deionized water to obtain a carboxymethyl chitosan aqueous solution, then silver nitrate solution is added, sodium sulfide solution is added dropwise, and the reaction is allowed to stand, centrifuged, washed, and vacuum dried to obtain core-shell silver sulfide nanoparticles; S3: dewatered sludge, straw powder, pig manure and wheat bran are mixed, and the carbon-nitrogen ratio and moisture content are adjusted to obtain a premixed substrate; S4: the core-shell silver sulfide nanoparticles are added to the premixed substrate, black soldier fly larvae are inoculated, and the composting is carried out in a flowerpot until the black soldier fly larvae enter the pre-swelling stage to obtain an antibacterial substrate; S5: the antibacterial substrate after the treatment is separated by a screen and air flow, and the black soldier fly larvae and insect sand are recovered, and the insect sand is air dried to complete the sludge treatment. The mass ratio of carboxymethyl chitosan, deionized water, silver nitrate solution and sodium sulfide solution is 0.5: (62-100): 0.2: 0.

3. In step S2, the concentration of the carboxymethyl chitosan aqueous solution is 0.5-0.8 wt%, and the pH is 8.0-9.

0. In step S2, the particle size of the core-shell silver sulfide nanoparticles is 20-80 nm, the shell thickness is 5-10 nm, and the zeta potential is -30 to -25 mV. The mass ratio of dewatered sludge, straw powder, pig manure and wheat bran is (4-5): 1: 2:

1. In step S3, the carbon-nitrogen ratio is 20-30, and the moisture content is 40-50%.

2. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: In step S4, the addition amount of core-shell silver sulfide nanoparticles is 5-200 mg / kg.

3. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: In step S4, the black soldier fly larvae are 7-10 days old, and the addition amount is 5-10 g / 200 g.

4. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: The concentration of the silver nitrate solution is 0.01-0.05 mol / L, and the concentration of the sodium sulfide solution is 0.01-0.05 mol / L.

5. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: It is applied to urban sludge treatment.

6. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: ​ 7. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: ​ 8. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 1, characterized in that: ​ 9. The modified nano-silver sulfide assisted black soldier fly sludge treatment method according to claim 2, characterized in that: ​ 10. The use of a modified nanosilver sulfide auxiliary black soldier fly for sludge treatment according to any one of claims 1 to 9, characterized in that: ​

Images