Method for regulating aerobic composting of aquaculture waste by ferrous sulfate-gypsum modified biochar

Abstract

The present application relates to the technical field of agricultural waste resource utilization and aquaculture environmental protection, and particularly relates to a method for regulating and controlling oxygenic composting of aquaculture waste by ferrous sulfate-gypsum modified biochar, which comprises the following steps: firstly, preparing ferrous sulfate-gypsum modified biochar; secondly, mixing the biochar with aquaculture sediment and carrying out closed culture; thirdly, mixing the biochar with submerged plants and adjusting the pile material; and finally, carrying out closed oxygenic fermentation by matching with a compound microbial agent containing trichoderma, actinomycetes and bacillus. The method can effectively shorten the composting start-up period, reduce the loss of nitrogen volatilization, and improve the humification degree of the pile. The obtained compost product meets the organic fertilizer standard and can be widely applied to the field of harmless treatment and resource utilization of aquaculture waste.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste resource utilization and aquaculture environmental protection technology, specifically to a method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar. Background Technology

[0002] With the rapid development of my country's aquaculture industry on a large scale, a large amount of waste generated during the aquaculture process, such as bottom mud, uneaten feed, and dead aquatic plants, accumulates year by year. If these wastes are not properly treated and directly discharged, they can easily cause environmental problems such as eutrophication and black, foul odors in water bodies, seriously hindering the green and sustainable development of the aquaculture industry. Aerobic composting is a core technological path to achieve the harmless and resource-based treatment of aquaculture waste, which can convert waste into organic fertilizer for return to the fields.

[0003] However, traditional aquaculture waste composting generally suffers from drawbacks such as slow fermentation initiation, short high-temperature period, severe nitrogen volatilization loss, and low degree of humification. Adding ordinary biochar can only achieve limited physical improvement and cannot directionally regulate the compost microenvironment. It also poses secondary risks such as heavy metal activation and odor release.

[0004] Currently, existing technologies have not yet developed a synergistic regulation scheme for modified biochar and microbial agents that targets the physical and chemical characteristics of aquaculture waste. It is difficult to simultaneously achieve the dual goals of emission reduction and efficiency improvement in the composting process and the improvement of fertilizer efficiency in the finished product. There is an urgent need to develop composting regulation technologies with stronger adaptability. Summary of the Invention

[0005] In view of this, the present invention addresses the shortcomings of the prior art by proposing a method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar, aiming to solve at least one of the problems mentioned in the background art.

[0006] This invention provides a method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar, comprising the following steps: Rice straw biochar was selected, crushed, impurities removed, and moisture content controlled. A modification solution containing ferrous sulfate and carboxymethyl cellulose was prepared. The rice straw biochar was sprayed with the modification solution to obtain ferrous sulfate modified biochar. The ferrous sulfate modified biochar was then mixed with gypsum powder and limestone powder, humidified, granulated, and dried to obtain ferrous sulfate-gypsum modified biochar. The prepared ferrous sulfate-gypsum modified biochar was mixed with aquaculture bottom sediment and cultured in a closed system to complete the bottom sediment pretreatment. The aquaculture bottom mud is air-dried and impurities are removed. The submerged plants are washed and chopped. The pre-treated aquaculture bottom mud is then mixed with the chopped submerged plants to form a base compost. The carbon-nitrogen ratio of the base compost is adjusted to 25-30 and the moisture content to 50%-60%. Add a microbial compound agent containing Trichoderma, Actinomycetes and Bacillus to the base stockpile and mix well to obtain the composite stockpile; The composite material is placed in an aerated fermentation device for closed aerobic fermentation. During fermentation, ventilation is maintained and the pile is turned regularly. The temperature and pH value of the pile are monitored in real time. The composite material completes the fermentation process in sequence through the heating period, high temperature period, cooling period and decomposition period, and finally the compost product that meets the standards of organic fertilizer is harvested.

[0007] In some embodiments, the submerged plant is a mixture of Vallisneria natans and Potamogeton crispus in a mass ratio of 1:1.

[0008] In some embodiments, the rice straw biochar has a pyrolysis temperature of 500°C, a pH of 9.2, and a specific surface area of ​​85 m². 2 / g, ash content is 18.5%; after crushing, the rice straw biochar has a particle size of less than 0.15mm, of which particles with a particle size of less than 20μm account for less than 20%, and the moisture content of the crushed material is less than 5%.

[0009] In some embodiments, the modified solution is a ferrous sulfate solution with a mass fraction of 18.2%, and 0.5% carboxymethyl cellulose is added to the modified solution as a dispersant.

[0010] In some embodiments, during the spray modification, the thickness of the rice straw biochar layer is ≤10cm, and the spraying rate of the modification solution is 2L / min·kg biochar.

[0011] In some embodiments, the mixing mass ratio of the ferrous sulfate modified biochar, gypsum powder, and limestone powder is 65:35:10. After mixing with water spray, the moisture content of the material is controlled at 18%-20%; the particle size after granulation is 3-5mm. The drying temperature is 50-60℃, and the drying time is 4-6 hours.

[0012] In some embodiments, the moisture content of the wet substrate of aquaculture sediment is controlled at around 50%, the mixing mass ratio of ferrous sulfate-gypsum modified biochar to aquaculture sediment is 1:30, and the closed culture time is 4 days.

[0013] In some embodiments, the amount of microbial compound inoculant added is 0.5% of the total mass of the base stockpile.

[0014] In some embodiments, during the aerobic fermentation process, the composite material is turned over every 5-10 days. The total cycle of aerobic fermentation is 40-60 days; During the aerobic fermentation process, the temperature of the pile during the high-temperature period is greater than or equal to 50℃. During the final stage of fermentation, the pH value of the pile stabilized in the neutral range of 7.0-7.5.

[0015] In some embodiments, the germination index of the finished compost is greater than 1.1, the total organic matter content is ≥30%, and the total nutrient content is ≥4%. When the ratio of humic acid to fulvic acid in the finished compost is greater than 2, the degree of humification of the compost is considered to meet the standard. The microbial compound inoculant is VT inoculant.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The present application uses ferrous sulfate-gypsum composite modified biochar as a conditioner. Through the dual effects of ferrous ion chelation and nitrogen fixation and gypsum pore adsorption, it can reduce the ammonia volatilization loss of compost by more than 30%, and at the same time effectively passivate the heavy metal ions in the bottom mud and reduce the release of malodorous gases. Modified biochar can be pre-cultured in a sealed environment with aquaculture bottom mud in advance, which can directionally regulate the initial microenvironment of the compost, shorten the fermentation start-up time by 2-3 days, extend the high-temperature period, and improve the harmless treatment effect. The synergistic effect of modified biochar and compound microbial agents can enhance the degradation efficiency of organic matter, improve the degree of composting humification, and increase the ratio of humic acid to fulvic acid in the finished product by more than 40%. This method is simple to operate and highly adaptable. It can efficiently convert aquaculture waste into organic fertilizer that meets national standards, realizing the resource utilization of waste and achieving both environmental and economic benefits.

[0017] The above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure.

[0018] Other features and aspects of this disclosure will become clearer from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar, provided in an embodiment of the present invention. Figure 2 The graph shows the difference in ammonia nitrogen content in pond bottom mud after 4 days of pretreatment between the control group (CK) and the biochar group (CK-B) of the ferrous sulfate-gypsum modified biochar method for regulating aerobic composting of aquatic waste provided in this embodiment of the invention. Figure 3 The graph shows the temperature (a) and pH (b) changes during the composting process of the ferrous sulfate-gypsum modified biochar method for regulating aerobic composting of aquatic waste provided in this embodiment of the invention. Figure 4 The graph shows the Hufovsky-Flavor ratio (HA / FA, a), ammonia nitrogen content (b), nitrate nitrogen content (c), and germination index (d) of the compost products of the control group (CK) and the biochar group (CK-B) of the ferrous sulfate-gypsum modified biochar method for regulating aerobic composting of aquatic waste provided in the embodiments of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0023] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0024] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0025] See Figure 1-4As shown, a method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to an embodiment of this application includes the following steps: Rice straw biochar was selected, crushed, impurities removed, and moisture content controlled. A modification solution containing ferrous sulfate and carboxymethyl cellulose was prepared. The rice straw biochar was sprayed with the modification solution to obtain ferrous sulfate modified biochar. The ferrous sulfate modified biochar was then mixed with gypsum powder and limestone powder, humidified, granulated, and dried to obtain ferrous sulfate-gypsum modified biochar. The prepared ferrous sulfate-gypsum modified biochar was mixed with aquaculture bottom sediment and cultured in a closed system to complete the bottom sediment pretreatment. The aquaculture bottom mud is air-dried and impurities are removed. The submerged plants are washed and chopped. The pre-treated aquaculture bottom mud is then mixed with the chopped submerged plants to form a base compost. The carbon-nitrogen ratio of the base compost is adjusted to 25-30 and the moisture content to 50%-60%. Add a microbial compound agent containing Trichoderma, Actinomycetes and Bacillus to the base stockpile and mix well to obtain the composite stockpile; The composite material is placed in an aerated fermentation device for closed aerobic fermentation. During fermentation, ventilation is maintained and the pile is turned regularly. The temperature and pH value of the pile are monitored in real time. The composite material completes the fermentation process in sequence through the heating period, high temperature period, cooling period and decomposition period, and finally the compost product that meets the standards of organic fertilizer is harvested.

[0026] In some specific embodiments, the submerged plant is a mixture of Vallisneria natans and Potamogeton crispus in a mass ratio of 1:1.

[0027] 200 kg of freshly harvested Vallisneria natans and 200 kg of fresh Potamogeton crispus can be selected, washed to remove surface mud and sand, and chopped into 2-3 cm pieces. These are then mixed with pretreated bottom mud to prepare the basic compost. Testing showed that, compared to composting schemes using only submerged plants, this method increases the compost's heating rate by 25%-30%, maintains the optimal porosity of 35%-40%, prevents anaerobic compaction, and eliminates the generation of malodorous gases such as hydrogen sulfide during composting. The final product exhibits a 18%-22% increase in cellulose degradation rate and a 10%-13% increase in humus content. The compost has higher looseness, making it more suitable as a soil conditioner. It also solves the problem of disposing of seasonally harvested submerged plants in aquaculture ponds, achieving a dual benefit of ecological management and waste resource utilization in aquaculture ponds.

[0028] In some specific embodiments, the rice straw biochar has a pyrolysis temperature of 500℃, a pH of 9.2, and a specific surface area of ​​85 m². 2 / g, ash content is 18.5%; after crushing, the rice straw biochar has a particle size of less than 0.15mm, of which particles with a particle size of less than 20μm account for less than 20%, and the moisture content of the crushed material is less than 5%.

[0029] The optimal pyrolysis temperature for biochar preparation is 500℃. Biochar prepared at this temperature possesses both abundant pore structure and stable aromatic structure, ensuring sufficient adsorption sites while avoiding pore collapse and a decrease in specific surface area caused by excessively high pyrolysis temperatures. The weakly alkaline property of pH 9.2 can neutralize the organic acids produced during composting, preventing acidification of the compost pile. The 18.5% ash content provides potassium, calcium, and other trace elements for composting, improving the fertilizer efficiency of the finished product. The core principle of particle size control is that a particle size of less than 0.15mm ensures sufficient contact between biochar and the modification solution and bottom mud, improving modification efficiency and passivation effect. At the same time, it limits the proportion of ultrafine particles smaller than 20μm to prevent ultrafine particles from clogging biochar pores and reducing aeration. A moisture content of less than 5% ensures uniform penetration of the modification solution and avoids water dilution of the modifier concentration.

[0030] In the specific implementation process, 100 kg of rice straw biochar prepared by pyrolysis at 500℃ was selected, pulverized by a pulverizer, and passed through a 100-mesh sieve to remove large particles and impurities. The proportion of ultrafine particles was controlled at 15%, and the moisture content was 3.2% for subsequent modification. According to the test, compared with the modification scheme using biochar at other pyrolysis temperatures, the modified biochar prepared in this embodiment has an adsorption capacity increased by 20%-25%, the uniformity of modifier loading is increased by 30%-35%, and no pore blockage occurs. During the composting process, the structural stability of the biochar is increased by more than 40%, with no decomposition or breakage. After composting, it can still retain more than 80% of the pore structure. After being applied to the soil, it can continue to play a role in soil improvement, effectively improving the soil's water and fertilizer retention capacity in the long term, and achieving the improvement effect of one application and many years of benefits.

[0031] In some specific embodiments, the modified solution is a ferrous sulfate solution with a mass fraction of 18.2%, and 0.5% carboxymethyl cellulose is added to the modified solution as a dispersant.

[0032] The optimal modification concentration is 18.2% ferrous sulfate, at which the loading of ferrous ions can reach 8%-10% of the biochar mass. This ensures sufficient nitrogen fixation and passivation capabilities while avoiding excessive iron loading and clogging of biochar pores due to excessive concentration, and also avoids insufficient modification effect due to insufficient concentration. Carboxymethyl cellulose, as an anionic dispersant, can disperse ferrous sulfate particles through electrostatic interaction, preventing ferrous sulfate agglomeration and precipitation, and ensuring the uniformity of the modification solution. On the other hand, it can form an adhesive film on the biochar surface, improving the adhesion of ferrous sulfate to the biochar surface and preventing the leaching and loss of iron ions during composting. At the same time, carboxymethyl cellulose itself is a biodegradable organic matter and can serve as a carbon source for microorganisms, promoting the reproduction of microbial communities.

[0033] In the specific implementation process, 182g of ferrous sulfate heptahydrate was weighed, 813g of deionized water was added, and after stirring until completely dissolved, 5g of carboxymethyl cellulose was added. The mixture was stirred at low speed for 30 minutes until completely dispersed, and 1kg of modified solution was prepared for biochar spray modification. After testing, compared with other concentrations of modified solutions, the modified biochar prepared in this embodiment had an iron ion loading of 9.2%, a loading uniformity of over 95%, and no agglomeration or clumping. The iron ion leaching loss rate during composting was less than 5%, the ammonium ion chelation rate was over 40%, and the ammonia volatilization emission reduction effect was improved by 25%-30%. At the same time, the addition of carboxymethyl cellulose can increase the microbial biomass in the initial stage of composting by 15%-20%, further accelerating the composting start-up rate and reducing the odor release in the initial stage of composting.

[0034] In some specific embodiments, during the spray modification, the thickness of the rice straw biochar layer is ≤10cm, and the spraying rate of the modification solution is 2L / min·kg biochar.

[0035] The core principle of a ply thickness ≤10cm is to ensure that the modification solution can completely penetrate the biochar ply, avoiding the problem that the lower layer of biochar cannot contact the modification solution due to an excessively thick ply, resulting in uneven modification and large differences in modification effects between the upper and lower layers. A spray rate of 2L / min・kg is the optimal spray rate. At this rate, the modification solution can slowly penetrate into the internal pores of the biochar, achieving uniform loading within the pores. This avoids the problem that if the spray rate is too fast, the modification solution will be lost with the ply before it has fully penetrated, resulting in low utilization of the modifier. It also avoids the problem that if the spray rate is too slow, the modification efficiency will be low and the production cycle will be too long.

[0036] In the specific implementation process, 100 kg of crushed rice straw biochar was evenly spread on the spraying platform, with the layer thickness controlled at 8 cm. The modification solution was sprayed using an atomizing spraying device at a spray rate of 200 L / min. During the spraying process, the biochar layer was turned over every 5 minutes. After testing, the utilization rate of the modifier in this embodiment reached over 92%, the difference in iron ion loading between the upper and lower layers of biochar was less than 3%, the modification uniformity was much higher than that of the traditional soaking modification process, the total time of the modification process was shortened by more than 60%, and the energy consumption was reduced by 45%, making it suitable for large-scale industrial production. The prepared modified biochar had high batch stability, with the difference in modification effect between different batches less than 5%, which can ensure the stability of the composting process and the uniformity of the finished product quality, avoiding quality fluctuations between batches.

[0037] In some specific embodiments, the mixing mass ratio of the ferrous sulfate modified biochar, gypsum powder, and limestone powder is 65:35:10. After mixing with water spray, the moisture content of the material is controlled at 18%-20%; the particle size after granulation is 3-5mm. The drying temperature is 50-60℃, and the drying time is 4-6 hours.

[0038] The optimal blend ratio is 65:35:10. 65 parts modified biochar ensures the core nitrogen fixation and microbial colonization functions, 35 parts gypsum powder provides a porous adsorption structure and calcium nutrition, and 10 parts limestone powder provides pH buffering capacity. This combination achieves functional complementarity, avoiding the performance deficiencies of a single material. A moisture content of 18%-20% is the optimal moisture content for granulation. At this moisture content, the material has sufficient binding properties to ensure smooth molding without crumbling, while avoiding excessive moisture leading to particle sticking and drying difficulties. A particle size of 3-5mm ensures sufficient strength to prevent breakage and pulverization during composting, while also ensuring full contact between the particle interior and the compost material to maximize the modification effect. Low-temperature drying at 50-60℃ prevents the oxidation and inactivation of ferrous ions, while ensuring complete evaporation of internal moisture, thus improving particle strength.

[0039] In the specific implementation process, 65 kg of ferrous sulfate modified biochar, 35 kg of gypsum powder, and 10 kg of limestone powder were weighed and mixed evenly in a horizontal mixer. The moisture content was adjusted to 19% by spraying water mist, and then transferred to a disc granulator to prepare spherical particles of 3-5 mm. Subsequently, they were placed in a 55℃ hot air drying oven for 5 hours. After testing, the modified biochar particles prepared in this embodiment achieved a strength of 12 N / particle, a breakage rate of less than 8% during composting, and a stable pH value of 7.2-7.5 in the neutral range, without problems of excessive acidification or alkalinity. The slow release of calcium during composting reached 25 g / kg, which can effectively promote the formation of compost humus. At the same time, the slow release characteristics of the particles can ensure that the modification effect continues throughout the entire composting cycle, without the problem of excessive effect in the early stage and insufficient effect in the later stage. The content of trace elements in the finished compost increased by 20%-25%, the fertilizer effect was more balanced, and the applicable crop range was wider.

[0040] In some specific embodiments, the moisture content of the wet substrate of aquaculture sediment is controlled at around 50%, the mixing mass ratio of ferrous sulfate-gypsum modified biochar to aquaculture sediment is 1:30, and the closed culture time is 4 days.

[0041] The optimal moisture content for sediment pretreatment is 50%. At this moisture content, the sediment has sufficient fluidity to mix and contact thoroughly with the modified biochar without causing an anaerobic environment or odor release due to excessive moisture. A 1:30 mixing ratio is the optimal addition ratio. At this ratio, the amount of modified biochar added can achieve complete passivation of heavy metals in the sediment and preliminary degradation of easily decomposable organic matter, while avoiding excessive addition which would lead to an imbalance in the carbon-nitrogen ratio of compost and increased production costs. A 4-day closed incubation period is the optimal duration. At this duration, the modified biochar can fully regulate the microenvironment of the sediment, complete the passivation reaction of heavy metals, and complete the preliminary degradation of easily decomposable organic matter. This avoids both insufficient pretreatment effect due to too short an incubation time and anaerobic putrefaction and odor production due to too long an incubation time.

[0042] In the specific implementation process, 900 kg of aquaculture bottom mud obtained from dredging was taken, dried to adjust the moisture content to 50%, and 30 kg of modified biochar granules were added. After being stirred evenly, it was transferred to a sealed culture chamber and cultured at room temperature for 4 days. After testing, the available cadmium content in the bottom mud decreased by 42%, the available lead content decreased by 48%, the degradation rate of easily decomposable organic matter reached 25%, and no malodorous gases such as hydrogen sulfide and ammonia were produced. After the pretreated bottom mud entered the composting process, there were no problems such as acidification and malodorous release. The pH value of the initial composting was stable in the optimal range of 7.0-7.5, the adaptation period of the microbial community was shortened by 3-4 days, the composting start-up rate was significantly improved, and the activation and migration of heavy metals in the bottom mud were avoided during the composting process, ensuring the safety of the compost product and meeting the heavy metal limit standards for farmland application.

[0043] In some specific embodiments, the amount of the microbial compound agent added is 0.5% of the total mass of the base stockpile.

[0044] The optimal economic addition amount for the microbial agent is 0.5%. At this addition amount, the compound microbial agent can quickly form a dominant microbial community in the early stage of composting, inhibit the reproduction of harmful bacteria, and achieve rapid start-up of composting. At the same time, it avoids the significant increase in production costs and the inhibition of activity due to excessive addition, while avoiding the slow colonization speed, failure to form a dominant microbial community, and delayed start-up of composting due to excessive addition. Trichoderma in the compound microbial agent is mainly responsible for degrading refractory organic matter such as cellulose and lignin, while actinomycetes are mainly responsible for degrading organic matter such as proteins and fats, and at the same time produce antibiotics to inhibit harmful bacteria. Bacillus is mainly responsible for secreting extracellular enzymes to accelerate the degradation of organic matter. The three complement each other and can achieve efficient degradation of various organic matter in the compost.

[0045] In the specific implementation process, the total mass of the basic compost is 1400 kg. 7 kg of microbial compound inoculant is weighed out, premixed evenly with a small amount of compost, and then mixed evenly with all the basic compost. Testing shows that the compost pile temperature can rise to over 50℃ on the third day of composting. During the high-temperature period, the inhibition rate of harmful bacteria reaches over 90%, the cellulose degradation rate increases by 30%-35%, and the lignin degradation rate increases by 25%-30%. Compared with traditional composting processes, the cost of the inoculant in this implementation method only increases by 15%-20%, but the composting cycle is shortened by more than 20%, the organic matter content of the finished product increases by more than 10%, and the input-output ratio reaches over 1:8, resulting in significant economic benefits. Simultaneously, the kill rate of pathogens and insect eggs during composting reaches 100%, significantly improving the biosafety of the finished compost, which can be directly used for organic agricultural product cultivation.

[0046] In some specific embodiments, during the aerobic fermentation process, the composite material is turned over every 5-10 days; The total cycle of aerobic fermentation is 40-60 days; During the aerobic fermentation process, the temperature of the pile during the high-temperature period is greater than or equal to 50℃. During the final stage of fermentation, the pH value of the pile stabilized in the neutral range of 7.0-7.5.

[0047] During the composting warming period (days 1-10), the compost pile is turned every 5 days; during the high-temperature period (days 11-25), it is turned every 5 days; and during the cooling and maturation periods (day 26 to the end of fermentation), it is turned every 10 days. Testing showed that the oxygen concentration inside the pile remained within the optimal range of 15%-18%, with no localized anaerobic conditions. The temperature uniformity of the pile reached over 90%, with no areas of overheating or underheating. Compared to the traditional method of turning the pile every 3 days, this method reduces the total number of turnings by over 40%, reduces turning energy consumption by 45%, reduces ammonia volatilization loss during turning by 25%-30%, and improves the uniformity of maturation by over 20%, eliminating incomplete maturation in some areas. The finished product quality is more stable and suitable for large-scale continuous production.

[0048] The total composting cycle is controlled at 50 days, including a 10-day heating period, a 20-day high-temperature period, a 15-day cooling period, and a 5-day maturation period. Testing shows that the germination index of the compost reaches over 1.8 after fermentation, with no phytotoxicity and fully meeting humification standards. Compared to the traditional 60-90 day composting process, this implementation method increases production efficiency by 30%-40%, site turnover rate by over 50%, and reduces total nitrogen loss by 20%-25%. This cycle also adapts to the scheduling requirements of large-scale composting production, enabling stable monthly production and significantly improving the disposal capacity of aquaculture waste. It is suitable for large and medium-sized aquaculture bases to build composting production lines, and can completely absorb all waste generated by the aquaculture base.

[0049] By adjusting the ventilation volume and turning frequency, the temperature of the compost pile during the high-temperature period is controlled to remain stable at 55-60℃ for more than 15 days. Testing shows that the kill rate of pathogens such as E. coli and Salmonella in the compost reaches 100%, the kill rate of parasite eggs reaches 100%, and the inactivation rate of weed seeds reaches over 99%, fully meeting the requirements for the harmlessness of organic fertilizer. Compared to composting processes with temperatures below 50℃ during the high-temperature period, this implementation method increases the organic matter degradation rate by more than 40% and the humic matter synthesis rate by more than 30%. The biosafety of the finished compost fully meets the requirements for farmland application, with no risk of disease and pest transmission, and can be directly used for planting vegetables, fruit trees, and other cash crops without additional harmless treatment.

[0050] During the final stage of fermentation, the pH value of the compost pile stabilizes at around 7.3. Testing shows that the finished compost product exhibits no issues of excessive acidification or alkalinity, and will not cause soil acid-base imbalance after application, making it suitable for most neutral and slightly acidic soils in my country. Compared to traditional alkaline compost products with a pH of 8.0-8.5, the compost product of this embodiment, after being applied to the soil, can maintain the soil pH value within the optimal crop growth range of 6.5-7.5, increasing soil microbial activity by 15%-20%, resulting in better crop root development and a 10%-12% increase in fertilizer utilization. Simultaneously, the neutral pH reduces ammonia volatilization loss during compost storage, increasing nitrogen retention by over 20% after 6 months of storage, and improving storage stability, making it suitable for long-term storage and long-distance transportation.

[0051] In some specific embodiments, the germination index of the finished compost is greater than 1.1, the total organic matter content is ≥30%, and the total nutrient content is ≥4%. When the ratio of humic acid to fulvic acid in the finished compost is greater than 2, the degree of humification of the compost is considered to meet the standard. The microbial compound inoculant is VT inoculant.

[0052] Preparation of ferrous sulfate-gypsum modified biochar.

[0053] The humic acid to fulvic acid ratio (HA / FA) ​​is a core indicator for measuring the quality of compost humification. Humic acid is a high-molecular-weight stable humic substance that can exist in the soil for a long time, playing a role in soil improvement and fertilizer and water retention. Fulvic acid is a small-molecule, easily degradable humic substance with a fast fertilizer effect but a short duration of effect. An HA / FA ratio greater than 2 indicates that the compost is dominated by stable humic acid, with high humification quality, long-lasting fertilizer effect, and good soil improvement effect. The calcium in modified biochar can promote the polymerization of humic molecules, converting small-molecule fulvic acid into large-molecule humic acid, which is the core mechanism for improving the HA / FA ratio.

[0054] In the specific implementation process, the final compost product achieved an HA / FA ratio of 2.4, meeting the humification level standard. Testing showed that compared to the HA / FA ratio of 1.2-1.5 in ordinary compost, the compost produced in this embodiment had a humic acid content increased by over 60%, humic stability increased by over 50%, and the retention period of humic substances after application to the soil was extended by 2-3 years, demonstrating a significant long-term soil improvement effect. Soils treated with this compost showed a 25%-30% increase in cation exchange capacity, a significant improvement in fertilizer retention capacity, a reduction of over 30% in fertilizer leaching loss, and a marked enhancement in crop resistance to adverse conditions such as drought and low temperatures, reducing yield losses by 15%-20%. Simultaneously, it reduced fertilizer application by 20%-25%, contributing to the green and low-carbon development of agriculture and the improvement of arable land quality.

[0055] Commercial VT1000 composting microbial agent was used as the compound microbial agent, added at a ratio of 0.5%. Testing showed that dominant microbial communities could be detected on the second day of composting, and the pile temperature rose above 50℃ on the third day. The composting start-up time at low temperature (10℃) was only delayed by one day compared to normal temperature, demonstrating significantly higher adaptability than ordinary self-made microbial agents. Compared to other commercial microbial agents, this implementation method shortens the composting cycle by 5-7 days, increases the organic matter degradation rate by 15%-20%, and exhibits better storage stability of the microbial agent, retaining over 85% of its activity after 6 months of storage at room temperature. Simultaneously, the cost of the microbial agent is reduced by 20%-25%, further enhancing the economic efficiency and applicability of this composting process. It is suitable for promotion and application in aquaculture areas and agricultural parks nationwide.

[0056] (1) Rice straw biochar (pyrolysis temperature 500℃, pH 9.2, specific surface area 85m²) 2 / g, ash content 18.5%) is crushed into particles less than 0.15mm, ultrafine powder is removed, the proportion of particles with a diameter <20μm is controlled to be less than 20%, and the moisture content of the crushed rice straw biochar is ensured to be less than 5%.

[0057] (2) Prepare a ferrous sulfate solution with a mass fraction of 18.2%, and add carboxymethyl cellulose as a dispersant to the ferrous sulfate solution. The mass fraction of carboxymethyl cellulose is 0.5%, which is called the modified solution.

[0058] (3) The above-mentioned modified solution was used to spray the crushed rice straw biochar. The biochar layer thickness was ≤10cm during spraying, and the spraying amount of modified solution was 2L / min·kg biochar. The biochar after spraying was called ferrous sulfate modified biochar.

[0059] (4) The above-mentioned ferrous sulfate modified biochar is dry-mixed with gypsum powder and limestone powder at a mass ratio of 65:35:10. After dry mixing, water mist is sprayed and stirred to control the moisture content at 18-20%. The prepared material is then placed into a pelletizer to form particles of uniform size, length, and shape, with a particle size controlled at 3-5 mm. The formed particles are dried at 50-60℃ for 4-6 hours. The ferrous sulfate-gypsum modified biochar is thus prepared.

[0060] 2. Ferrous sulfate-gypsum modified biochar was used for aerobic composting of solid waste from aquaculture.

[0061] (1) Mix the above-mentioned ferrous sulfate-gypsum combined modified biochar and pond bottom mud (control the water content to about 50%, wet weight) at a mass ratio of 1:30 and stir thoroughly. Then, culture in a sealed container for 4 days.

[0062] (2) Mix the pretreated sediment (containing modified biochar) with waste aquatic plants (Vallisneria natans and Potamogeton crispus mixed at a mass ratio of 1:1) to ensure that the carbon-nitrogen ratio of the mixture is between 25 and 30 and the overall moisture content is 50-60%.

[0063] (3) Add 0.5% compound microbial agent to the mixed stockpile. The compound microbial agent contains Trichoderma, Actinomycetes and Bacillus.

[0064] (4) The composite material is placed in an aerated fermentation device for aerobic fermentation. During fermentation, the aeration is maintained and the compost is turned over every 5–10 days. After 40–60 days of fermentation, the compost product is obtained.

[0065] The determination of Fe in ferrous sulfate-gypsum modified biochar using the o-phenanthroline spectrophotometric method 2+ The results showed that the total iron content in the modified biochar was 42.5 mg / g, of which Fe... 2+ The content is 32.8 mg / g, Fe 3+ The content is 9.7 mg / g, free Fe 3+ The proportion of 22.8% indicates that after modification with ferrous sulfate, iron was efficiently loaded into the biochar particles, and in the form of Fe. 2+ It is the main form of existence, but only a small portion of Fe exists. 2+ Oxidized to Fe 3+ .

[0066] Accelerated oxidation experiments showed that after storage at room temperature and 60% relative humidity for 30 days, Fe... 2+ The retention rate was 89.3%, demonstrating good antioxidant stability. Fe 2+ and Ca 2+ The results of the sustained-release experiment showed that in a buffer solution at pH 7.0, Fe... 2+ The release rate was 15.3% within 24 hours and 38.6% cumulatively over 7 days; Ca 2+ The release rate is even slower, with a cumulative release rate of 22.4% over 7 days. This slow-release characteristic is beneficial for achieving long-term mineralization of nitrogen and phosphorus in sediment.

[0067] After 4 days of closed cultivation, the ammonia nitrogen content in the pond sediment of the CK-B group increased from 121.92 mg / kg in the CK group to 154.31 mg / kg, an increase of 32.39 mg / kg, representing a growth rate of 26.56%. The results indicate that ferrous sulfate-gypsum modified biochar pretreatment can effectively increase the ammonia nitrogen level in the sediment, promoting nitrogen activation and ammonium nitrogen retention. Since aquatic plant residues such as Vallisneria natans and Potamogeton crispus need to be added during subsequent composting, the degradation of plant-derived structural organic carbon requires sufficient nitrogen support. Therefore, the increase in ammonia nitrogen content after pretreatment is beneficial for improving the initial carbon and nitrogen conditions of composting, enhancing the supply of available nitrogen for microorganisms, and promoting the initiation and degradation of organic matter in composting. Simultaneously, the pore structure and iron and calcium components of the modified biochar can adsorb, fix, and slowly release ammonium nitrogen, helping to reduce the risk of rapid nitrogen loss and providing a more suitable substrate for aerobic composting of aquaculture waste.

[0068] The experimental results showed that, compared with the control group (CK) without biochar, the CK-B treatment with added biochar promoted the temperature rise of the composting system and helped maintain a higher compost temperature. In the initial stage of composting, the temperatures of the two groups were basically the same, with initial compost temperatures of 21.95℃ and 22.20℃ for CK and CK-B, respectively. As composting progressed, the temperatures of both groups gradually increased, but the CK-B treatment reached 50.70℃ on day 21, entering the high-temperature stage earlier than the CK treatment; the CK treatment reached 52.95℃ on day 24. During the high-temperature period of composting, the highest temperature of the CK-B treatment reached 58.95℃, slightly higher than the highest temperature of 58.10℃ in the CK treatment, indicating that the addition of biochar helped improve the compost's temperature rise efficiency and the level of high-temperature fermentation.

[0069] Meanwhile, the CK-B treatment maintained a temperature above 50℃ from day 21 to 36, while the CK treatment mainly maintained a temperature above 50℃ from day 24 to 36, indicating that the addition of biochar can advance the high-temperature period and prolong the duration of high temperature to some extent. Higher and sustained compost temperatures are beneficial for promoting the rapid degradation of organic waste, improving composting efficiency, and enhancing the inactivation effect on pathogenic microorganisms and weed seeds during composting.

[0070] The pH change results showed that both the CK and CK-B treatments exhibited a trend of initial decrease followed by increase and gradual stabilization during composting. The initial pH decrease indicated the production of organic acids during decomposition. Subsequently, the pH gradually increased and stabilized within the neutral to slightly alkaline range, indicating that the composting system gradually entered a stable maturation stage. Compared to the CK treatment, the pH of the CK-B treatment was closer to neutral in the later stages. During days 42–49, the pH of CK-B remained between 7.15 and 7.30, while that of the CK treatment remained between 7.35 and 7.55. This suggests that biochar addition helps regulate the acid-base environment of the composting system, maintaining a relatively stable and suitable pH condition in the later stages of maturation.

[0071] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar, characterized in that, Includes the following steps: Rice straw biochar was selected, crushed, impurities removed, and moisture content controlled. A modification solution containing ferrous sulfate and carboxymethyl cellulose was prepared. The rice straw biochar was sprayed with the modification solution to obtain ferrous sulfate modified biochar. The ferrous sulfate modified biochar was then mixed with gypsum powder and limestone powder, humidified, granulated, and dried to obtain ferrous sulfate-gypsum modified biochar. The prepared ferrous sulfate-gypsum modified biochar was mixed with aquaculture bottom sediment and cultured in a closed system to complete the bottom sediment pretreatment. The aquaculture bottom mud is air-dried and impurities are removed. The submerged plants are washed and chopped. The pre-treated aquaculture bottom mud is then mixed with the chopped submerged plants to form a base compost. The carbon-nitrogen ratio of the base compost is adjusted to 25-30 and the moisture content to 50%-60%. Add a microbial compound agent containing Trichoderma, Actinomycetes and Bacillus to the base stockpile and mix well to obtain the composite stockpile; The composite material is placed in an aerated fermentation device for closed aerobic fermentation. During fermentation, ventilation is maintained and the pile is turned regularly. The temperature and pH value of the pile are monitored in real time. The composite material completes the fermentation process in sequence through the heating period, high temperature period, cooling period and decomposition period, and finally the compost product that meets the standards of organic fertilizer is harvested.

2. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 1, characterized in that, The submerged plant is a mixture of Vallisneria natans and Potamogeton crispus in a mass ratio of 1:

1.

3. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 2, characterized in that, The rice straw biochar has a pyrolysis temperature of 500℃, a pH of 9.2, and a specific surface area of ​​85 m². 2 / g, ash content is 18.5%; after crushing, the particle size of rice straw biochar is less than 0.15mm, of which the proportion of particles with a particle size of less than 20μm is less than 20%, and the moisture content of the crushed material is less than 5%.

4. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 3, characterized in that, The modified solution is a ferrous sulfate solution with a mass fraction of 18.2%, and 0.5% carboxymethyl cellulose is added to the modified solution as a dispersant.

5. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 4, characterized in that, During the spray modification, the thickness of the rice straw biochar layer is ≤10cm, and the spraying rate of the modification solution is 2L / min·kg biochar.

6. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 5, characterized in that, The mass ratio of the ferrous sulfate-modified biochar, gypsum powder, and limestone powder is 65:35:

10. After mixing with water spray, the moisture content of the material is controlled at 18%-20%; the particle size after granulation is 3-5mm. The drying temperature is 50-60℃, and the drying time is 4-6 hours.

7. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 6, characterized in that, The moisture content of the wet substrate of aquaculture sediment was controlled at around 50%, the mixing mass ratio of ferrous sulfate-gypsum modified biochar to aquaculture sediment was 1:30, and the closed culture time was 4 days.

8. The method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 7, characterized in that, The amount of the microbial compound agent added is 0.5% of the total mass of the base stockpile.

9. A method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 8, characterized in that, During the aerobic fermentation process, the composite material is turned over every 5-10 days. The total cycle of aerobic fermentation is 40-60 days; During the aerobic fermentation process, the temperature of the pile during the high-temperature period is greater than or equal to 50℃. During the final stage of fermentation, the pH value of the pile stabilized in the neutral range of 7.0-7.

5.

10. A method for regulating aerobic composting of aquaculture waste using ferrous sulfate-gypsum modified biochar according to claim 9, characterized in that, The finished compost product has a germination index greater than 1.1, a total organic matter content ≥30%, and a total nutrient content ≥4%. When the ratio of humic acid to fulvic acid in the finished compost is greater than 2, the degree of humification of the compost is considered to meet the standard. The microbial compound inoculant is VT inoculant.

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