Sludge treatment method using modified nano silver sulfide to assist hermetia illucens and application of sludge treatment method

Abstract

The invention discloses a modified nano silver sulfide assisted hermetia illucens sludge treatment method and application, and relates to the technical field of environmental protection. According to the sludge treatment method of adding the modified nano silver sulfide into the premixed matrix and inoculating the hermetia illucens larvae, sludge dry basis reduction is realized in a short time, the treatment period is shortened, the volume of a pile is compressed due to accelerated decomposition of organic matters and generation of insect sand, the occupied field and the pile turning energy consumption are reduced, and the cost is reduced. Efficient treatment of municipal sludge, remarkable reduction and volume compression are met; silver ions (Ag < + >) are continuously released through modified nano silver sulfide by means of a chitosan negative charge shell layer, common pathogenic bacteria in sludge are rapidly inactivated in the early stage of composting, heavy metal elements such as cadmium, lead, arsenic and mercury in treated insect sand are all lower than the national standard, secondary disinfection or chemical stabilization treatment is not needed, agricultural safety application is directly met, and the method is suitable for industrial production. The closed loop of'sludge-insect sand-farmland 'is realized, and good social, environmental and economic benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, in particular to a sludge treatment method and application of modified nano silver sulfide assisted black soldier flies. Background Art

[0002] With the acceleration of urbanization, the amount of urban sludge produced has increased significantly. This sludge contains large amounts of organic pollutants, pathogens, and heavy metals. Direct landfill or incineration poses secondary pollution and waste of resources. Black soldier fly larvae feed on organic waste and can efficiently decompose organic matter in sludge, shortening the processing cycle and producing nutrient-rich insect litter. Current research has confirmed that black soldier fly composting can reduce some greenhouse gas emissions, but high CH4 and N2O emissions and incomplete suppression of pathogens remain in high-humidity, high-organic-matter sludge. Leveraging the broad-spectrum antimicrobial properties of nanosilver is expected to inhibit harmful bacteria in the early stages of composting, while also impacting microbial metabolism and further reducing greenhouse gas emissions.

[0003] Existing black soldier fly composting processes for treating municipal sludge are difficult to completely suppress pathogens, and the composting microenvironment is prone to anaerobic zones, resulting in high methane (CH4) and nitrous oxide (N2O) emissions and the production of insect sand, which poses safety risks and requires additional treatment before agricultural use. Therefore, the present invention provides a sludge treatment method and application using modified nano-silver sulfide to assist black soldier flies in their treatment, addressing these technical issues. Summary of the Invention

[0004] The purpose of the present invention is to provide a sludge treatment method and application of modified nano silver sulfide assisted black soldier flies to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions: A sludge treatment method using modified nano-silver sulfide to assist black soldier flies comprises the following steps: S1: chitosan was added to anhydrous isopropanol and NaOH solution, stirred, then chloroacetic acid was added, heated for reaction, centrifuged, washed, and vacuum dried to obtain carboxymethylated chitosan (CMC); S2: CMC was dissolved in deionized water to obtain a CMC aqueous solution, and then silver nitrate (AgNO3) solution was added, and sodium sulfide solution was added dropwise. The reaction was allowed to stand, centrifuged, washed, and vacuum dried to obtain core-shell silver sulfide nanoparticles (CMC@Ag2S-NPs). S3: mixing dehydrated sludge, straw powder, pig manure and wheat bran, adjusting the carbon-nitrogen ratio and moisture content to obtain a premixed matrix; S4: Add CMC@Ag2S-NPs to the premixed matrix, inoculate black soldier fly larvae, assemble in a flower pot, and compost until the black soldier fly larvae enter the early stage of swelling to obtain an antibacterial matrix; S5: After the treatment, the antibacterial matrix is ​​separated by a combination of a screen and air flow to recover the black soldier fly larvae and insect sand, and then the insect sand is air-dried to complete the sludge treatment.

[0006] Furthermore, the NaOH solution is an aqueous solution with a concentration of 25-35 wt%.

[0007] Furthermore, the deacetylation degree of the chitosan is ≥85%.

[0008] Furthermore, the mass ratio of chitosan, anhydrous isopropyl alcohol, NaOH solution, and chloroacetic acid is 1:(5~10):(4.5~4.8):(4~6).

[0009] Furthermore, in step S1, the stirring process conditions are: stirring at a rotation speed of 200-300 rpm for 20-30 minutes.

[0010] Furthermore, in step S1, the process conditions of the heating reaction are: at a temperature of 60-70° C. and for 3-4 hours.

[0011] Furthermore, the mass ratio of CMC, deionized water, silver nitrate solution, and sodium sulfide solution is 0.5:(62~100):0.2:0.3.

[0012] Furthermore, in step S1, the centrifugal process conditions are: centrifugation at a speed of 2400-3000 rpm for 10-20 min.

[0013] Furthermore, in step S1, the washing process conditions are: washing with 70-75v% ethanol, and rinsing 2-3 times.

[0014] Furthermore, in step S1, the process conditions for vacuum drying are: vacuum drying at a temperature of 60-70°C for 1-2 hours, and a vacuum degree of 0.05-10 kPa.

[0015] Furthermore, in step S2, the concentration of the CMC aqueous solution is 0.5-0.8 wt%, and the pH is 8.0-9.0.

[0016] Furthermore, in step S2, the rate of adding the sodium sulfide solution is 0.5-1 mL / min.

[0017] Furthermore, the concentration of the silver nitrate solution is 0.01-0.05 mol / L.

[0018] Furthermore, the concentration of the sodium sulfide solution is 0.01-0.05 mol / L.

[0019] Furthermore, in step S2, the process conditions for the reaction to stand are to react for 2 to 3 hours under the protection of a nitrogen flow rate of 200 to 300 sccm and then stand at room temperature overnight.

[0020] In the above technical solution, during the preparation process of carboxymethylated chitosan (CMC) encapsulating nano silver sulfide (Ag2S), the nucleation and lattice growth of Ag2S require time. In the initial reaction stage, silver ions (Ag + ) and sulfide ions (S 2- ) forms Ag2S nuclei through coordination reaction, but may not have fully developed into uniform nanoparticles. Leaving it to stand overnight provides a longer reaction time, allowing the nuclei to grow further and improve the crystal structure, thus forming a core-shell structure with controllable size and uniform shell thickness. Long-term standing can reduce the residual Ag in the system. + concentration, inhibiting the unliganded Ag + With S 2- Heterogeneous precipitation occurs, thereby improving product purity.

[0021] Furthermore, in step S2, the centrifugal process conditions are: centrifugation at a speed of 10,000-12,000 rpm for 10-20 min.

[0022] Furthermore, in step 2, the washing process is: rinse with deionized water 2 to 3 times, then rinse with 70 to 75 v% ethanol 2 to 3 times, alternating 2 to 3 times.

[0023] Furthermore, in step S2, the process conditions for vacuum drying are: vacuum drying at a temperature of 60-70°C for 1-2 hours, and a vacuum degree of 0.05-10 kPa.

[0024] Furthermore, 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 potential is -30--25 mVζ.

[0025] Furthermore, the mass ratio of dehydrated sludge, straw powder, pig manure and wheat bran is (4~5):1:2:1.

[0026] Furthermore, in step S3, the carbon-nitrogen ratio is 20-30, and the moisture content is 40-50%.

[0027] Furthermore, in step S4, the addition amount of CMC@Ag2S-NPs is 5~200 mg / kg.

[0028] Furthermore, in step S4, the black soldier fly larvae are 7 to 10 days old, and the added amount is 5 to 10 g / 200 g.

[0029] Furthermore, in step S4, the dimensions of the flower pots are: an average diameter of 20-25 cm, and an average height of 15-20 cm.

[0030] Furthermore, the composting process is as follows: at a temperature of 25-30°C and a relative humidity of 60-70%, the compost is turned over every 3-5 days for 10-15 consecutive days until the black soldier fly larvae enter the early stage of expansion.

[0031] Furthermore, in step S5, the moisture content of the insect sand after air-drying is ≤20%.

[0032] In the above technical solution, the chlorine atom (Cl - ) as a leaving group, activates the hydroxyl group (-OH) of chitosan under alkaline conditions to form an oxygen anion intermediate, and the amino group (-NH2) or hydroxyl group (-OH) of chitosan acts as a nucleophile to attack the α-carbon atom of chloroacetic acid to form an amide bond (-CO-NH-) or an ester bond (-CO-O-), and the generated carboxymethyl group (-CH2COOH) is deprotonated in the solution to form a negatively charged carboxylate (-COO - ), giving chitosan negative charge, the negatively charged carboxymethyl chitosan adsorbs positively charged pollutants through electrostatic action, thereby improving the removal efficiency.

[0033] Sodium sulfide and AgNO3 react with each other under CMC coating to form a core-shell structure of nano silver sulfide (Ag2S). The core-shell structure of Ag2S delays the degradation of Ag by physical coating. + Diffusion, avoid high concentration of Ag + Toxicity to black soldier fly larvae; Ag2S can excite electron-hole pairs under visible light to produce reactive oxygen species (ROS) ·OH, O 2- , degrade pollutants and organic matter, effectively inhibit the proliferation of pathogenic microorganisms, and efficiently inhibit pathogens and anaerobic methanogens and denitrifying bacteria through the interaction between Ag⁺ and microbial cell membranes and enzyme systems.

[0034] The premixed matrix of straw powder (cellulose), pig manure (nitrogen source) and wheat bran (carbon source) provides a carbon-nitrogen balanced nutrient substrate for the intestinal flora (Pseudomonas and Bacillus) of black soldier fly larvae. The flora decomposes the difficult-to-degrade organic matter in the sludge by secreting cellulase and protease. At the same time, it regulates the metabolic pathway through quorum sensing to improve the degradation efficiency.

[0035] Ag2S in CMC@Ag2S-NPs binds to heavy metal ions (Cd 2+ 、Zn 2+ ) forms stable sulfide precipitation (CdS, ZnS) and fixes it in the insect sand. At the same time, the low concentration of Ag released by Ag2S +It works with ROS to destroy the cell membrane and DNA of pathogens, achieving dual inactivation of pathogens; nitrifying bacteria lead the decomposition of organic matter, converting ammonia nitrogen in sludge into nitrate, reducing the release of odorous substances (NH3, H2S). 4+ and slow release of Ag + , inhibiting the overactivity of nitrifying bacteria, preventing nitrogen loss, and improving the fertilizer efficiency of the compost product. The feeding behavior of black soldier fly larvae disrupts the sludge aggregate structure, increasing porosity, promoting oxygen permeation and aerobic microbial metabolism. The insect sand excreted by the black soldier fly larvae further serves as a carbon source, supporting denitrification during the post-ripening stage.

[0036] The invention discloses an application of a sludge treatment method using modified nano silver sulfide to assist black soldier flies, and the method is applied to municipal sludge treatment.

[0037] Compared with the prior art, the present invention has the following beneficial effects: 1. The present sludge treatment method, which adds modified nano-silver sulfide to a premixed substrate and inoculates it with black soldier fly larvae, achieves a dry-weight sludge reduction rate exceeding 65% in just 10-15 days. Compared to traditional aerobic composting, which requires 30-60 days, this method not only shortens the treatment cycle by nearly 50%, but also reduces the compost volume due to the accelerated decomposition of organic matter and the production of insect sand. This reduces site usage and compost turning energy consumption, achieving efficient municipal sludge treatment and significant sludge reduction and volume reduction.

[0038] 2. The sludge treatment method of the present invention continuously releases Ag by modifying nano silver sulfide with the help of the negatively charged shell of chitosan. + In the early stage of composting, common pathogens (Escherichia coli, Salmonella, Shigella) in sludge can be quickly inactivated, and the heavy metal elements such as Cd (cadmium), Pb (lead), As (arsenic), and Hg (mercury) in the treated insect sand have been determined to be lower than the first-level limit of the national standard. No secondary disinfection or chemical stabilization treatment is required, which directly meets the safety requirements of agricultural applications. It has the characteristics of broad-spectrum and high-efficiency pathogen inhibition and safety compliance.

[0039] 3. The sludge treatment method of the present invention, using nano-silver sulfide as an additive, reduces cumulative N2O emissions by 50-90% and CH4 emissions by 45-95%, with minimal fluctuations in CO2 emissions. This reduction is primarily due to the nano-silver sulfide's selective inhibition of methanogens (mcrA gene) and denitrifying bacteria (hao and norB genes), while enhancing the activity of N2O-reducing bacteria (nosZ gene) and methane-oxidizing bacteria (pmoA gene), effectively achieving a significant reduction in greenhouse gas emissions and addressing the "dual carbon" goals.

[0040] 4. The sludge treatment method of the present invention is to recover the insect sand by screen and air flow separation after the treatment, and air-dry it to a moisture content of ≤20%, with an organic matter content of >50%, total nitrogen >3.0%, available phosphorus >1.5%, available potassium >2.0%, pH 6.5-7.5, and rich in elements such as Ca, Mg, trace Cu, Zn and probiotic communities, which significantly improves the physical and chemical properties of the soil and the quality of crops, generates nutrient-rich insect sand, and promotes plant growth.

[0041] 5. The sludge treatment method of this invention eliminates the need to modify existing BSF (semi-wet material pulverizer) composting equipment. Nano-silver sulfide is added only once during the conventional feeding phase. The compost turning frequency (3-5 days / time) and temperature and humidity (25-30°C, 60-70% RH) are consistent with existing production lines, making it easy to quickly deploy in community sewage treatment plants, food processing plants, and organic waste comprehensive utilization centers. This achieves a closed "sludge-worm sand-farmland" cycle, balancing environmental emission reduction and resource utilization, and delivering significant social, environmental, and economic benefits. DETAILED DESCRIPTION

[0042] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] In the following specific embodiments, Chitosan, model CS-85H, viscosity 300 cps; NaOH solution with a concentration of 25 wt% in water; The rate of adding sodium sulfide solution was 1 mL / min; The concentration of silver nitrate solution is 0.01 mol / L; The concentration of sodium sulfide solution is 0.01 mol / L; Flower pots, average diameter 23cm, average height 15cm; Plastic basins, average diameter 25 cm, average height 20 cm; Example 1: A sludge treatment method using modified nano-silver sulfide to assist black soldier flies, comprising the following steps: S1: Chitosan was added to anhydrous isopropanol and NaOH solution, stirred at 200 rpm for 20 min, then chloroacetic acid was added, reacted at 60°C for 3 h, centrifuged at 2400 rpm for 10 min, washed with 70% ethanol, rinsed twice, and vacuum dried at 60°C for 1 h at a vacuum degree of 0.05 kPa to obtain carboxymethylated chitosan (CMC); the mass ratio of chitosan, anhydrous isopropanol, NaOH solution, and chloroacetic acid was 1:5:4.5:4; S2: CMC was dissolved in deionized water to obtain a CMC aqueous solution with a concentration of 0.5wt% and a pH of 8.0, and silver nitrate solution was added, followed by dropwise addition of sodium sulfide solution. The mixture was reacted for 2 h under a nitrogen flow of 200 sccm, allowed to stand overnight at room temperature, and centrifuged at 10,000 rpm for 10 min. The mixture was rinsed twice with deionized water and then with 70v% ethanol, alternating for 2 times. The mixture was vacuum dried at 60°C for 1 h with 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. S3: Dehydrated sludge, straw powder, pig manure and wheat bran were mixed and the carbon-nitrogen ratio was adjusted to 25 and the moisture content was 45% to obtain a premixed matrix; the mass ratio of dehydrated sludge, straw powder, pig manure and wheat bran was 4:1:2:1; S4: CMC@Ag2S-NPs were added to the premixed matrix at a dosage of 50 mg / kg, inoculated with 7-day-old black soldier fly larvae at a dosage of 7 g / 200 g, assembled in a flower pot, and incubated at a temperature of 25 ° C and a relative humidity of 60% for 15 consecutive days, turning the pile every 3 days to obtain an antibacterial matrix; S5: The antibacterial matrix after treatment is separated by a combination of sieve and air flow to recover black soldier fly larvae and insect sand, and then the insect sand is air-dried to complete the sludge treatment; the moisture content of the insect sand after air-drying is ≤20%.

[0044] Example 2: A sludge treatment method using modified nano-silver sulfide to assist black soldier flies, comprising the following steps: S1: chitosan was added to anhydrous isopropanol and NaOH solution, stirred at 250 rpm for 25 min, then chloroacetic acid was added, reacted at 65°C for 3.5 h, centrifuged at 2600 rpm for 15 min, washed with 70% ethanol, rinsed twice, and vacuum dried at 65°C for 1 h with 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; S2: CMC was dissolved in deionized water to obtain a CMC aqueous solution with a concentration of 0.5wt% and pH 8.0, silver nitrate solution was added, sodium sulfide solution was added dropwise, and the mixture was reacted for 2h under the protection of a nitrogen flow rate of 250sccm. The mixture was allowed to stand overnight at room temperature and centrifuged at 11000rpm for 15min. The mixture was rinsed twice with deionized water and then rinsed twice with 70v% ethanol, alternating twice. The mixture was vacuum dried at 65℃ for 1.5h with a vacuum degree of 0.05kPa 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 60nm, the shell thickness was 6nm, and the potential was -27mVζ. S3: Dehydrated sludge, straw powder, pig manure and wheat bran were mixed and the carbon-nitrogen ratio was adjusted to 28 and the moisture content was 42% to obtain a premixed matrix; the mass ratio of dehydrated sludge, straw powder, pig manure and wheat bran was 4.5:1:2:1; S4: CMC@Ag2S-NPs were added to the premixed matrix at a dosage of 100 mg / kg, and 7-day-old black soldier fly larvae were inoculated at a dosage of 6 g / 200 g. The mixture was assembled in a flower pot and incubated at a temperature of 25°C and a relative humidity of 60% for 15 consecutive days, with the pile turned every 3 days to obtain an antibacterial matrix. S5: The antibacterial matrix after treatment is separated by a combination of sieve and air flow to recover black soldier fly larvae and insect sand, and then the insect sand is air-dried to complete the sludge treatment; the moisture content of the insect sand after air-drying is ≤20%.

[0045] Example 3: A sludge treatment method using modified nano-silver sulfide to assist black soldier flies, comprising the following steps: S1: chitosan was added to anhydrous isopropanol and NaOH solution, stirred at 300 rpm for 30 min, then chloroacetic acid was added, reacted at 70°C for 4 h, centrifuged at 3000 rpm for 20 min, washed with 70% ethanol, rinsed three times, and vacuum dried at 70°C 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; S2: CMC was dissolved in deionized water to obtain a CMC aqueous solution with a concentration of 0.5wt% and pH 8.0, silver nitrate solution was added, sodium sulfide solution was added dropwise, and the mixture was reacted for 3 hours under the protection of a nitrogen flow rate of 300sccm, and allowed to stand overnight at room temperature. The mixture was centrifuged at a speed of 12000rpm for 20 minutes, and rinsed with deionized water three times, and then rinsed with 70v% ethanol three times, alternating three times, and vacuum dried at 70℃ for 2 hours with a vacuum degree of 0.05kPa 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 80nm, the shell thickness was 10nm, and the potential was -30mVζ; S3: Dehydrated sludge, straw powder, pig manure and wheat bran were mixed, and the carbon-nitrogen ratio and moisture content were adjusted to 30 and 50% to obtain a premixed matrix; the mass ratio of dehydrated sludge, straw powder, pig manure and wheat bran was 5:1:2:1; S4: CMC@Ag2S-NPs was added to the premixed matrix at a dosage of 200 mg / kg, and the premixed matrix was inoculated with 7-day-old black soldier fly larvae at a dosage of 10 g / 200 g. The matrix was kept at a temperature of 25°C and a relative humidity of 60% for 15 consecutive days, with the compost turned every 3 days to obtain an antibacterial matrix. S5: The antibacterial matrix after treatment is separated by a combination of sieve and air flow to recover black soldier fly larvae and insect sand, and then the insect sand is air-dried to complete the sludge treatment; the moisture content of the insect sand after air-drying is ≤20%.

[0046] Example 4: Application of a modified nano-silver sulfide-assisted sludge treatment method for black soldier flies: comprising the following steps: Step 1: Mix the air-dried insect sand obtained in Example 1 with cultivation soil, take 5 kg and put it into a plastic basin to obtain a cultivation basin; the mass ratio of the air-dried insect sand to the cultivation soil is 0.03:1; Step 2: Disinfect the spinach seeds with 70% ethanol and then rinse with clean water to obtain cultivated seeds; Step 3: Under greenhouse conditions of 12h / day light intensity, 25℃, and 60% relative humidity, transplant the cultivated seeds into cultivation pots and raise them for 7 days. Then, plant 10 plants in each pot and continue to cultivate them with a plant spacing of 10cm×10cm.

[0047] Comparative Example 1: This comparative example provides a sludge treatment method for black soldier flies assisted by modified nano-silver sulfide. No CMC@Ag2S-NPs is added to the premixed matrix, and the rest of the method is the same as in Example 1.

[0048] Comparative Example 2: This comparative example provides a sludge treatment method using modified nano-silver sulfide to assist black soldier flies. Black soldier fly larvae are not added to the premixed matrix, and the remaining methods are the same as those in Example 1.

[0049] Comparative Example 3: This comparative example provides a sludge treatment method using modified nano-silver sulfide to assist black soldier fly larvae. No CMC@Ag2S-NPs or black soldier fly larvae are added to the premixed matrix, and the remaining methods are the same as those in Example 1.

[0050] Comparative Example 4: This comparative example provides an application of a modified nano-silver sulfide-assisted sludge treatment method for black soldier flies. Compared with Example 4, only 5 kg of cultivation soil was added to the cultivation pot, and the rest of the method was the same.

[0051] Comparative Example 5: This comparative example provides an application of a modified nano-silver sulfide-assisted sludge treatment method for black soldier flies. Compared with Example 4, 5 kg of uncomposted sludge and cultivation soil were added to the cultivation pot, and the mass ratio of uncomposted sludge to cultivation soil was 0.03:1. The rest of the method was the same.

[0052] Comparative Example 6: This comparative example provides an application of a modified nano-silver sulfide-assisted sludge treatment method for black soldier flies. Compared with Example 4, 5 kg of compost sludge without silver worm sand was added to the cultivation pot. The mass ratio of compost sludge without silver worm sand to cultivation soil was 0.03:1, and the rest of the method was the same.

[0053] experiment: During the composting process of Examples 1-3 and Comparative Examples 1-3, the degradation effect of the mixed matrix was tested and the test results were recorded: Sludge dry basis reduction rate test: Using GB4284-2018 as the reference standard, weigh the initial sludge, mechanically dehydrate it, and dry it at 105°C to a constant weight. Weigh the dry basis mass and calculate the reduction rate.

[0054] Cumulative CH4, N2O, and CO2 emission test: Using GB4284-2018 as the reference standard and the closed-chamber sampling method, the matrix headspace gas was collected regularly to measure the concentrations of CH4, N2O, and CO2 respectively.

[0055] Pathogen detection rate test: Using GB4284-2018 as the reference standard, take 10 g of sludge sample, add 100 mL of sterile saline, shake for 30 minutes, make a 1:10 dilution, take 1 mL of the dilution and inoculate it into the culture medium, culture at 37°C for 2 days, and count the number of colonies.

[0056] Heavy metal content test: Using GB4284-2018 as the reference standard, take 2 g of sludge sample, add 5 mL of nitric acid, 2 mL of hydrofluoric acid, and 1 mL of perchloric acid, heat and digest until white smoke appears, cool and adjust the volume to 50 mL, and use atomic absorption spectrometry to determine the contents of Cd (cadmium), Pb (lead), As (arsenic), and Hg (mercury).

[0057] In the heavy metal content test, the nitric acid concentration was 65v%, the hydrofluoric acid concentration was 40v%, and the perchloric acid concentration was 70v%.

[0058] Organic matter content test: Using GB4284-2018 as the reference standard and the potassium dichromate volumetric method, take 0.5 g of sludge sample, add 5 mL of 0.8 mol / L potassium dichromate solution and 5 mL of concentrated sulfuric acid (70v%), heat in a boiling water bath for 5 minutes, cool and dilute with distilled water, titrate with 0.2 mol / L ferric sulfate solution until green, record the consumed volume, and calculate the organic matter content.

[0059] Total nitrogen test: Using GB4284-2018 as the reference standard and the Kjeldahl method, take 0.5 g of sludge sample, add 5 mL of concentrated sulfuric acid and 0.37 g of catalyst, digest until clear, transfer the digestate to a distillation apparatus, add NaOH solution for distillation, collect NH3 into boric acid absorption liquid, titrate the boric acid absorption liquid with 0.01 mol / L sulfuric acid solution, and calculate the nitrogen content.

[0060] In the total nitrogen test, the catalyst was a mixture of copper sulfate and potassium sulfate with a mass ratio of 1:10.

[0061] Available phosphorus test: Using GB4284-2018 as the reference standard, take 2.5 g of sludge sample, add 50 mL of 0.5 mol / L sodium bicarbonate solution, shake for 30 minutes, centrifuge at 2400 rpm for 10 minutes, take the supernatant, add 5 mL of molybdenum antimony reagent, dilute to 50 mL, develop color at room temperature for 30 minutes, measure the absorbance at a wavelength of 880 nm, and draw a standard curve to calculate the available phosphorus content.

[0062] Effective potassium test: Using GB4284-2018 as the reference standard, take 2.5 g of sludge sample, add 50 mL of 1 mol / L ammonium acetate solution, shake for 30 min, filter, and directly measure K in the filtrate using a flame photometer + The concentration was calculated based on the standard curve.

[0063] pH test: Using GB4284-2018 as the reference standard, take a sludge sample and mix it with deionized water in a ratio of 1:2.5, stir for 30 minutes, let it stand for 30 minutes, and measure it with a calibrated pH meter.

[0064] Properties of worm sand after black soldier fly composting of sludge mixed with nano-silver sulfide The spinach obtained in Example 4 and Comparative Examples 4-6 was cultivated for 30 days. The water level of the pad was controlled to maintain 1 cm, water was replenished in time, and integrated fertilizer and water management was implemented without additional fertilization. After the treatment, the fresh weight and biomass of the aboveground part of the spinach were counted, and the 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 effect of the insect sand fertilizer on the growth and nutritional quality of spinach.

[0065] Total dry weight biomass test: Using GB / T 45724-2025 as the reference standard, cut the spinach leaf part and immediately weigh the fresh weight of the sample. Record the ambient temperature and humidity. Place the sample in an oven at 105°C for 30 min, then adjust the temperature to 65°C and dry it to constant weight. Cool it to room temperature and weigh the dry weight.

[0066] Average plant height test: Using GB / T 45724-2025 as the reference standard, the spinach plant height was measured and the average value was calculated.

[0067] Leaf chlorophyll content test: Using GB / T 45724-2025 as the reference standard, cut the leaves, weigh them, add 5 mL of ethanol and calcium carbonate, grind them into a homogenous slurry, centrifuge at 2400 rpm for 30 minutes, extract the supernatant, and determine the chlorophyll content by spectrophotometry.

[0068] In the leaf chlorophyll content test, the ethanol concentration was 80v%.

[0069] Spinach yield, plant height and leaf chlorophyll content under each treatment Note: The numbers in the table are the mean of 4 repeated experiments. The same letters after the numbers mean that there is no significant difference in the same column by LSD (least significant difference) test (P=0.05).

[0070] Contents of cadmium, copper, zinc, calcium, nitrogen, phosphorus and potassium in the aboveground parts of crops under each treatment (dry weight) Note: The numbers in the table are the mean of 4 repeated experiments. The same letters after the numbers mean that there is no significant difference in the same column by LSD test (P=0.05).

[0071] According to the data in the above table, we can clearly draw the following conclusions: Compared with Comparative Examples 1-3, the CH4, N2O and CO2 emissions in the matrix of Examples 1-3 are less, the pathogen content is reduced, the heavy metal content meets the national standards, the organic matter content is increased, the total nitrogen content is increased, the available phosphorus is reduced, the available potassium is increased, and the pH value is acidic.

[0072] Compared with comparative examples 4-6, the spinach and soil obtained in Example 4 had a high total dry weight biomass, a high average plant height, and a high chlorophyll content in the leaves.

[0073] 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 increased significantly (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.

[0074] By comparing Example 4 with Comparative Examples 5-6, it can be seen that in Example 4, the Cd content of spinach is only 1.8 mg / kg, which is significantly lower than that of Comparative Examples 5-6, indicating that silver worm sand has good heavy metal passivation ability and can effectively reduce the accumulation of pollutants in plants.

[0075] In Example 4, spinach showed significantly higher levels of calcium (32.0 g / kg), nitrogen (54.0 g / kg), phosphorus (6.2 g / kg), and potassium (96.0 g / kg) than in other treatments, demonstrating that this treatment not only effectively prevented heavy metal stress but also improved spinach's absorption efficiency of key nutrients. Calcium content was significantly higher than in other control groups (P < 0.05), likely due to the synergistic effects of the calcium carbonate and silica-alumina skeleton in silverworm sand on soil pH buffering and calcium release.

[0076] By 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 enrichment of heavy metals is effectively suppressed, reflecting the multifunctionality of the present invention, that is, it has the dual effects of "fertilizer efficiency improvement + heavy metal passivation".

[0077] Comparing Example 4 with Comparative Examples 4-6, the total dry weight biomass reached the highest level, reaching 1654 g / pot, significantly higher than the other comparative examples (P < 0.05) and approximately 3.6 times higher than that of Comparative Example 4, demonstrating the excellent growth-promoting effect of Yinchongsha. This suggests that Yinchongsha, as a modifier, effectively enhances nutrient release and plant absorption efficiency in sludge fertilizer.

[0078] Comparing Example 4 with Comparative Examples 4-6, it can be seen that the plant height of spinach in Example 4 is 26 cm, which is significantly improved, but the difference is not large compared with Comparative Example 6, suggesting that the promoting effect of silver worm sand on the growth of the aboveground part is mainly reflected in the accumulation of dry matter.

[0079] The chlorophyll content of Example 4 was the highest (38 mg / kg), followed by Comparative Example 6 (22 mg / kg). Compared with Comparative Example 4 (11 mg / kg), both were significantly higher, indicating that the modified sludge can effectively improve the photosynthesis capacity of spinach and enhance its physiological activity.

[0080] Comprehensive analysis shows that modified sludge containing silverworm sand exhibits significant advantages in promoting plant dry matter accumulation and increasing chlorophyll content, demonstrating promising potential for agricultural applications. This product not only improves the utilization efficiency of sludge resources but also, through the structural stability and trace element regulation properties of silverworm sand, improves the plant rhizosphere environment and enhances the synergistic effect of fertilizer release and nutrient absorption.

[0081] 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 embodied 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 illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for treating sludge by modified nano-silver sulfide-assisted black soldier flies, characterized by: S1: chitosan was added to anhydrous isopropyl alcohol and NaOH solution, stirred, and then chloroacetic acid was added, heated for reaction, centrifuged, washed, and vacuum dried to obtain carboxymethylated chitosan; S2: adding carboxymethylated chitosan to deionized water to dissolve it to obtain a carboxymethylated chitosan aqueous solution, then adding a silver nitrate solution, and dropwise adding a sodium sulfide solution. The reaction is allowed to stand, centrifuged, washed, and vacuum dried to obtain core-shell silver sulfide nanoparticles. S3: mixing dehydrated sludge, straw powder, pig manure and wheat bran, adjusting the carbon-nitrogen ratio and moisture content to obtain a premixed matrix; S4: adding core-shell silver sulfide nanoparticles to a premixed matrix, inoculating black soldier fly larvae, assembling the matrix in a flower pot, and composting the matrix until the black soldier fly larvae enter the early stage of swelling to obtain an antibacterial matrix; S5: After the treatment, the antibacterial matrix is ​​separated by a combination of a screen and air flow to recover the black soldier fly larvae and insect sand, and then the insect sand is air-dried to complete the sludge treatment.

2. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 1, characterized in that: The mass ratio of carboxymethylated chitosan, deionized water, silver nitrate solution, and sodium sulfide solution is 0.5:(62~100):0.2:0.

3.

3. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 1, characterized in that: In step S2, the concentration of the carboxymethylated chitosan aqueous solution is 0.5-0.8 wt %, and the pH value is 8.0-9.

0.

4. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 1, characterized in that: 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 potential is -30--25 mVζ.

5. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 1, characterized in that: The mass ratio of dehydrated sludge, straw powder, pig manure and wheat bran is (4~5):1:2:

1.

6. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 1, characterized in that: In step S3, the carbon-nitrogen ratio is 20-30, and the water content is 40-50%.

7. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 1, characterized in that: In step S4, the amount of core-shell silver sulfide nanoparticles added is 5-200 mg / kg.

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

9. The method for treating sludge by modified nano-silver sulfide-assisted black soldier flies according to claim 2, characterized in that: The concentration of silver nitrate solution is 0.01~0.05mol / L; the concentration of sodium sulfide solution is 0.01~0.05mol / L.

10. Application of a modified nano-silver sulfide-assisted sludge treatment method for black soldier flies, characterized by: Used in municipal sludge treatment.

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