Fish manure rotary composting fermentation device and fermentation method

Abstract

The invention discloses a fish manure rotary composting fermentation device and fermentation method.The fish manure rotary composting fermentation device comprises a fermentation box body, the fermentation box body is rotationally connected to a rack through a rotating shaft, end covers are arranged at the two ends of the fermentation box body, the upper side of the fermentation box body is provided with a three-way valve, a feeding port and a gas collecting port, and the lower side of the fermentation box body is provided with a liquid discharging port; a spraying pipe is arranged on the rotating shaft in the length direction of the rotating shaft, spraying heads are evenly distributed on the spraying pipe, small ventilation holes are distributed in the middle of the end cover, and the small ventilation holes can be opened or covered through the rotatable cover plate. The method has the advantages that accumulated emission of greenhouse gases in the composting process is reduced, 'aerobic-anoxic-aerobic 'alternate change is shown, relative abundance of microorganisms with lignin and fat decomposition is increased remarkably, formation of HS precursors is accelerated, mineralization rate of organic matters is reduced, maintenance time of high temperature (higher than or equal to 50 DEG C) of compost is prolonged, and germination rate of compost seeds is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of fish manure, and particularly relates to a fish manure rotary composting and fermenting device and a fermenting method. Background Art

[0002] A Recirculating Aquaculture System (RAS) can comprehensively apply technologies such as physics, biology, and chemistry in a factory workshop to adjust and control the living environment of aquaculture aquatic animals and plants, and realize the recycling of treated aquaculture tail water. Compared with traditional pond aquaculture technology, RAS has the advantages of water saving, pond saving, high aquaculture density, and little influence from the external environment, and is the main development direction of aquaculture.

[0003] The baits used in aquaculture mainly use soybeans, corn, wheat bran, etc. as the main raw materials, and the crude protein content is mostly greater than 50%. The RAS bait coefficient is generally 1.0 - 1.3, resulting in a large amount of unabsorbed nutrients being released into the aquaculture pond. As a highly intensive aquaculture mode, the high-density and high feeding amount in RAS lead to more obvious fecal pollution with high nitrogen content in the water body compared with traditional pond aquaculture. Some studies have shown that for every 1.0 kg of feed fed, 0.25 - 0.50 kg of fish manure (including uneaten bait, etc.) and 0.02 - 0.04 kg of NH3 and NH4 + -N will remain in the water body.

[0004] Fish manure has the characteristics of being easily dispersed when soaked, floating easily, and having a small particle size, making it difficult to separate from the aquaculture water body, resulting in relatively few studies on RAS fish manure resource utilization technology. The applicant previously developed a combined process of "vertical flow sedimentation tank + high-pressure air flushing and quantitative spraying concentrator" to achieve the efficient concentration of low-concentration fish manure, obtaining fish manure concentrated sediment (FS, TN > 2.57 ± 0.13 g / kg, C / N = 8 - 10:1, water content is 65 ± 2.3%) and fish manure concentrated supernatant (FW, TN > 350 mg / L, C / N = 5 - 7:1), providing the possibility for studying fish manure resource utilization technology. FS is a typical nitrogen-rich and low-carbon manure, and currently, it is mainly treated by anaerobic fermentation. However, the low C / N characteristic of FS limits the growth of microorganisms during the fermentation process, and additional carbon sources need to be supplemented to maintain the normal growth and metabolism of microorganisms. At the same time, anaerobic fermentation has a long fermentation cycle, a large amount of greenhouse gas emissions, complex operation and control processes, and a large floor area. FW mainly converts organic nitrogen, NH4 + -N and NO2 - -N in the aquaculture water body into less toxic NO3 - -N. However, the high dissolved oxygen concentration and low C / N in the aquaculture water body limit the denitrification process in the biological filter, and NO3 --N cumulative concentration can reach above 100 - 1000 mg / L. High concentration of NO3 - -N (>100 mg / L) can cause hypoxia in fish, affect the osmotic regulation mechanism, cause endocrine disorders, and cause damage to peripheral blood, gills and liver. Therefore, there is an urgent need to explore new technologies suitable for FS resource utilization in RAS.

[0005] Aerobic composting has a short reaction cycle, high product safety, less generation of malodorous gases, and strong nitrogen fixation ability. It is one of the main resource utilization technologies for organic solid waste. Oxygen content and moisture content are the key indicators affecting aerobic composting. Continuous air supply can provide sufficient oxygen for the compost pile, but it may cause the compost raw materials to be too dry, affect the microbial activity, and increase energy consumption and operating costs. Compared with continuous air supply, intermittent air supply helps to control the internal temperature of the compost, avoid overheating, save energy consumption, and has gradually attracted attention in recent years.

[0006] At present, intermittent air supply is mainly achieved through mechanical air supply and manual turning of the pile. The ideal moisture content during the composting process is usually 50% - 60%. Excessive moisture content (such as exceeding 65%) will fill the pores of the composting materials with water, hinder air circulation, and lead to the formation of anaerobic conditions; too low moisture content (such as below 40%) will cause microorganisms to lose water and dehydration, affecting their metabolic activities and reproduction. Adding a water replenishing solution is a common way to maintain the stable moisture content of the compost pile. Tap water is the most commonly used liquid for moisture adjustment, but tap water cannot provide additional nutrients. Summary of the Invention

[0007] The present invention aims to solve the technical problems existing in the prior art, and particularly innovatively proposes a fish manure rotary composting fermentation device and a fermentation method, which reduce the cumulative emissions of greenhouse gases during the composting process, show an alternating change of "aerobic - anaerobic - aerobic", have a significantly increased relative abundance of microorganisms capable of decomposing lignin and fat, accelerate the formation of HS precursors, reduce the organic matter mineralization rate, extend the duration of the compost pile at high temperature (≥50 °C), and improve the compost seed germination rate.

[0008] To achieve the above first object, the present invention provides a fish manure rotary composting fermentation device, including a fermentation box body, characterized in that: the fermentation box body is rotationally connected to the frame through a rotating shaft, both ends of the fermentation box body are provided with end covers, a three-way valve, a feed inlet, and a gas sampling port are arranged on the upper side of the fermentation box body, a liquid discharge port is arranged on the lower side of the fermentation box body, a spray pipe is arranged on the rotating shaft along its length direction, spray heads are evenly distributed on the spray pipe, and air permeable small holes are distributed in the middle of the end cover, and the air permeable small holes can be opened or covered by a rotatable cover plate. A syringe is arranged on the three-way valve for sampling gas, the feed inlet can be sealed, and a valve is connected to the gas sampling port, and the valve is opened during gas sampling.

[0009] In the above solution: both the end cap and the wall of the fermentation box body have a sandwich structure, and an EPE thermal insulation layer is provided in the sandwich structure. A residual liquid tray for receiving the leaching liquid discharged from the drain port is provided on the frame below the fermentation box body. A handle is provided on the fermentation box body.

[0010] In the above solution: all the air-permeable small holes are closely arranged in the middle of the end cap. A pin shaft is provided above all the air-permeable small holes, and a cover plate is rotatably connected to the pin shaft. When the fermentation box body rotates, the cover plate opens, and when the rotation stops, the cover plate covers the air-permeable small holes. The cover plate is rotatably connected to the pin shaft, so that when rotating, it can follow the movement of the fermentation box body to open the cover plate for ventilation. Of course, the cover plate can also be manually opened during rotation, such as uncovering the cover plate and placing it beside to keep the air-permeable small holes ventilated.

[0011] The second object of the present invention is achieved as follows: A method for rotating compost fermentation of fish manure, characterized in that the fermentation is carried out according to the following method:

[0012] (1) Add fish manure and wheat straw to the fish manure rotating compost fermentation device described in any one of claims 1-3, adjust the carbon-nitrogen ratio, and add fish manure hydrochar.

[0013] (2) Before composting, when the fermentation box body is rotating, evenly spray the compost leaching liquid into the fermentation box body through the spray pipe to ensure that the moisture content of the compost pile is 55±0.5%.

[0014] (3) The fermentation box body rotates once every 45 minutes for 5 minutes each time. When rotating each time, open the air-permeable small holes to supplement oxygen.

[0015] In the above solution: when the compost fermentation temperature is lower than 30°C, use the compost leaching liquid to re-adjust the moisture to 55±0.5%, put in earthworms for decomposition. During the decomposition process, rotate the fermentation box body once every 50 minutes for 5 minutes each time. During the rotation process, open the cover plate to supplement oxygen from the air-permeable small holes. Accelerate the decomposition of the compost pile through earthworms.

[0016] In the above solution: The rotation speed is 30-40 rpm.

[0017] In the above solution: The preparation of fish manure hydrochar is as follows: Stir the fish manure evenly, add it to an autoclave, seal it and heat it to 200°C, stir, take it out after the reaction is completed, cool it to room temperature, and centrifuge for solid-liquid separation. The liquid is the hydrothermal liquid, and the solid is washed with water, washed with alcohol and then dried to obtain hydrochar.

[0018] In the above solution: The addition amount of the hydrochar is 5% of the total mass of the compost. The carbon-nitrogen ratio is 25:1.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) It is found through research that rotating the compost bin for 5 minutes and then standing still for 45 minutes is the best way to supply air for FS composting. By controlling the rotation frequency of the compost bin, the oxygen content in the compost pile shows an alternating change of "aerobic - anaerobic - aerobic" under this condition. The relative abundances of microorganisms capable of decomposing lignin and fat are significantly increased, accelerating the formation of HS precursors, reducing the organic matter mineralization rate, prolonging the duration of the high-temperature stage (≥50 °C) of the compost pile, increasing the compost seed germination rate, and reducing the energy consumption of rotating the compost bin. At the same time, under the condition of rotating for 5 minutes and standing still for 45 minutes, the cumulative emissions of greenhouse gases are reduced. Compared with continuous air supply, the cumulative emissions of CO2-equivalent greenhouse gases are reduced from 712.53 mg / kg·DM CO2e to 397.46 mg / kg·DM CO2e, and the emission reduction rate is 44.22%.

[0021] (2) By adjusting the moisture content with compost leachate and adding fish manure hydrochar as a water retainer at the same time, the hydrochar reduces the water loss rate by improving the water retention capacity of capillary water in the compost pile. It only decreases by 4.81% within 16 days and still remains above 50%, so it is not necessary to supplement the compost leachate. At the same time, the degree of compost maturity and the seed germination rate are increased. The results of cumulative greenhouse gas emissions show that the addition of hydrochar reduces the cumulative greenhouse gas emissions during composting, and is reduced by 47.29%, 65.75% and 73.29% respectively compared with the group without adding hydrochar and without watering, the group only supplemented with tap water, and the group T3 only supplemented with compost leachate.

[0022] (3) After fermentation, some limits of the compost product do not meet the requirements of compost maturity. Earthworms promote the conversion of protein into fulvic acid and humic acid, increasing the degree of aromatization and humification of the compost product. The seed germination rate of the compost reaches 98.4%, which is 13.1% higher than that of the composting treatment group without earthworms. Under the condition of coupling with earthworm maturation, complete maturity of FS can be achieved within 42 days. The emissions of N2O, NH3, CO2 and CH4 are reduced by 19.51%, 22.34%, 8.43% and 13.61% respectively compared with the group without adding earthworms. Through means such as burrowing, crushing food, and abdominal transformation, earthworms increase the activities of key enzymes such as cellulase and urease in the compost pile, and increase the relative abundances of Chloroflexi, Bacteroidetes, and Patescibacteria in the compost. The results of KEEG analysis show that the expression levels of amoA and hao are significantly increased under the optimal combination conditions, and the nitrogen metabolism levels related to NO3 - -N reduction and NO2 - -N oxidation and denitrification are significantly increased, and the nitrogen mineralization level is significantly reduced. Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of the device of the present invention.

[0024] Figure 2 This is a physical diagram of the device of the present invention.

[0025] Figure 3 SEM (left) and FTIR (right) of hydrothermal carbon.

[0026] Figure 4 Corresponding relationship between oxygen content of compost and rotation time.

[0027] Figure 5 Sampling point display of compost bin.

[0028] Figure 6 Oxygen content changes in different parts (A - E) of compost and within one rotation period (F) under different air - supplement frequencies.

[0029] Figure 7 Temperature change of compost heap during composting fermentation process.

[0030] Figure 8 pH change of compost heap during composting process.

[0031] Figure 9 Change process of compost maturity.

[0032] Figure 10 Seed germination rate of compost products under different air - supplement methods.

[0033] Figure 11 Emission rates and cumulative emissions of N2O (A), NH3 (B), CH4 (C) and CO2 (D) under different air - supplement conditions.

[0034] Figure 12 Effect of moisture regulation on compost temperature.

[0035] Figure 13 Effect of different moisture regulations on pH.

[0036] Figure 14 Effect of hydrothermal carbon on moisture state of compost.

[0037] Figure 15 Effect of moisture regulation on compost seed germination index.

[0038] Figure 16 Effect of moisture regulation method on compost maturity.

[0039] Figure 17 Emissions of N2O (A), CH4 (B) and NH3 (C) during composting process under different moisture regulation methods.

[0040] Figure 18 Microbial community structure at phylum (A) and genus (B) levels.

[0041] Figure 19 Effect of earthworms on the decomposition temperature

[0042] Figure 20 Effect of earthworms on the pH during the composting maturation process

[0043] Figure 21 Changes in the activities of cellulase (A), β-glucosidase (B), laccase (C), lignin peroxidase (D), manganese peroxidase (E), xylanase (F), acetyl esterase (G), urease (H) and protease (I) during the composting process

[0044] Figure 22 Effect of earthworms on the seed germination rate of compost products

[0045] Figure 23 Effect of earthworms on the maturity of compost products

[0046] Figure 24 Changes in TN (A), NH4 + -N and NO3--N (B), NH4 + -N / NO3--N (C), NO2 and NH3

[0047] (D) during the composting maturation process

[0048] Figure 25 Changes in CO2 (A), CH4 (B), TOC concentration (C), DOC concentration (D), and DOC proportion

[0049] (E, F) during the composting maturation process

[0050] Figure 26 Changes in the relative abundances of amoA (A) and hao (B) during the composting maturation process Specific implementation manners

[0051] The present invention will be further described below through examples in combination with the accompanying drawings:

[0052] The fish manure of the present invention is taken from the Factory Agriculture R & D Center of the Chongqing Academy of Agricultural Sciences. The fish being cultured is perch, and the feed is sourced from Chongqing Haida Feed Co., Ltd. (particle size: 2.0 mm, crude protein ≥ 49%, crude fiber ≤ 3.5%, crude ash ≤ 18.0%, calcium: 0.8 - 4.0%, total phosphorus ≥ 1.2%, crude fat ≥ 5.0%, lysine ≥ 3.0%, moisture ≤ 10.0%), which is a typical nitrogen-rich bait. After filtering the fish manure, the moisture content is approximately 65%, the COD is 17.32 ± 0.32 g / kg, the TN is 2.57 ± 0.13 g / kg, and the NH4 + -N is 0.34 ± 0.17 g / kg, and C / N = 8 - 10:1

[0053] The compost leachate is taken from the liquid discharged from the drainage outlet of the compost bin during the composting process. The results of physical and chemical index analysis show that the concentrations of NH4 + -N, NO2 - -N and NO3 - -N in the compost leachate are 176.43±4.43 mg / L, 381.61±7.71 mg / L and 88.19±3.38 mg / L respectively, and the pH is 7.6±0.2, which is a typical nutrient solution rich in NH4 + -N and NO2 - -N. Adding the compost leachate back to the composting system as a water supplement can not only reduce the loss of nutrients during the composting process, save water resources, avoid environmental pollution caused by the discharge of leachate, but also re-inoculate the beneficial microorganisms in the leachate into the composting system.

[0054] Earthworms can use their rich enzyme systems (protease, lipase, cellulase, amylase, etc.) to quickly and thoroughly decompose organic waste and convert it into easily utilizable nutrients, thus accelerating the compost ripening process. The earthworms used in this invention are Eisenia fetida, which is an annelid of the family Lumbricidae in the order Opisthopora, also known as red earthworms. Because it has good adaptability to changes in environmental pH, temperature, humidity, etc., the earthworms are taken from cow dung and crop straw as the food source for earthworms. The selected earthworms are all earthworms with strong vitality and no reproductive rings, and the average weight is 152.43±5.43 mg / earthworm. The earthworms are added after the compost fermentation is completed and the temperature of the compost pile drops to 30°C. Before adding, the surface of the earthworms is washed with sterile water and then placed in a clean petri dish with a moist filter paper, and kept in the dark for 24 hours.

[0055] Example 1

[0056] The fish manure rotary composting and fermenting device includes a fermentation box body 1. The fermentation box body 1 is designed in a polygon shape, which is an octagon in the figure. The fermentation box body 1 is rotationally connected to the frame 3 through a rotating shaft 2. Specifically, the rotating shaft 2 is rotationally connected to the frame 3 through a bearing. End caps 4 are arranged at both ends of the fermentation box body 1. The end caps 4 and the box wall of the fermentation box body 1 both have sandwich structures, and pearl cotton insulation layers 5 are arranged in the sandwich structures. A three-way valve 6, a feed inlet 7, and a gas sampling port 8 are arranged on the upper side of the fermentation box body 1. A drain port 9 is arranged on the fermentation box body 1 for discharging the compost leachate, and a valve is arranged on the drain port. The drain port 9 is blocked with a 100-mesh nylon net to prevent the over-accumulation of leachate in the box body and the escape of earthworms during the ripening process. A syringe is connected to the three-way valve 6.

[0057] A residue pan 10 for receiving the leaching solution discharged from the drain outlet is provided on the frame below the fermentation box body. The residue pan 10 is used to recover the compost leachate. A spray pipe is arranged along the length direction of the rotating shaft, and spray nozzles are evenly distributed on the spray pipe (the spray pipe and the spray nozzles are not specifically shown in the figure). The compost leachate is pumped to the spray pipe by a pump and evenly sprayed through the spray nozzles. Ventilation holes 11 are distributed in the middle of the end cover. The ventilation holes 11 can be opened or covered by a rotatable cover plate 12. Specifically, the ventilation holes are closely arranged in the middle of the end cover. All the ventilation holes 11 enclose a circular ventilation area. A pin shaft is arranged above all the ventilation holes, and a cover plate is rotatably connected to the pin shaft. When the fermentation box body rotates, the cover plate can be opened along with it. When the rotation stops, the cover plate covers the ventilation holes.

[0058] Example 2

[0059] Fish manure rotary composting fermentation method:

[0060] In this method, the compost fermentation device of Example 1 is used. The total volume of the fermentation box body 1 is 30L, and it is made of 304 stainless steel double-sided baked paint material. During the rotation of the fermentation box body, the organic waste in the inner cylinder is cut and stirred with each other under the action of 8 stainless steel thin steel sheets. The large mixture is cut and impacted, and finally chopped and cut off, so as to realize the mixing and aeration of the biomass materials. The rotation of the box body (0 - 50 rpm) and the control of the air supplement frequency are realized through the PLC system. The syringe on the three-way valve 6 is used for gas collection. When the fermentation temperature of the compost pile drops below 30°C, earthworms are added to the compost box to carry out the earthworm ripening experiment.

[0061] (1) Add fish manure and wheat straw to the fish manure rotary composting fermentation device, and adjust the carbon-nitrogen ratio. Specifically, the initial C / N ratio of the wheat straw is about 60:1, and the carbon-nitrogen ratio is adjusted to 25:1 according to m(FS):m(wheat straw)=2.3, ensuring that the total mass of the compost pile is 10 kg. Add fish manure hydrochar according to 5% of the total mass of the compost pile.

[0062] Hydrochar has a large specific surface area and surface functional groups, and is also a potential water retention agent. A large amount of Ca remaining in the fish manure 2+ and citric acid can further improve the water retention capacity of hydrochar. Therefore, in the present invention, hydrochar is prepared from FS as the raw material, the solid hydrochar is used as a water retention agent and added to the composting system, and the hydrothermal solution obtained from the hydrothermal reaction is used as a supplementary water solution for compost water regulation research.

[0063] Preparation of fish manure hydrochar:

[0064] Hydrothermal carbon was prepared from fish manure using a high-pressure reactor with a stirring device. Approximately 600 g of well-stirred FS was weighed into a high-pressure reactor with a total volume of 1.5 L. After sealing, it was heated to 200 °C, the stirring speed was set at 100 rpm / min, and it was taken out after 2 h and cooled to room temperature. The solid and liquid parts were obtained by centrifugation respectively. The liquid part was stored in a 4 °C refrigerator for later use, and the solid part was washed with water and ethanol several times and then dried at 60 °C for 12 h and stored in a dry place for later use. According to the analysis of physical and chemical indicators, the concentration of NO3 - -N in the hydrothermal solution was 604.3 ± 23.11 mg / L, and that of NO2 - -N was 12.8 ± 1.32 mg / L, and that of NH4 + -N was 46.2 ± 2.63 mg / L, pH = 6.13 ± 0.32, and C / N = 13.52:1. The SEM of the hydrothermal carbon is as shown on the Figure 3 left side, presenting an irregular fragment shape, with a rough surface and a large number of convex and concave structures; the specific surface area of the hydrothermal carbon was 10.32 m 2 / g, the carbon content was 34.24%, the pore volume was 0.18 cm 3 / g, and it was rich in C-O and C=O functional groups (as shown on the Figure 3 right side). The toxicity analysis experiments of the hydrothermal carbon extract and the hydrothermal solution showed that the germination rates of lettuce seeds were 86.3% and 91.6% respectively, which were greater than 70%, indicating that the hydrothermal carbon and the hydrothermal solution were non-toxic and would not be toxic to the growth of microorganisms in the composting system.

[0065] (2) Before composting, with the fermentation box body rotating, the compost leachate was evenly sprayed into the fermentation box body through the spray pipe (when composting for the first time, water was used to supplement, and then the compost leachate was collected after the composting ended and used for the next batch of composting. After each batch of composting ended, the compost leachate was collected and used for the next batch of composting, and so on) to ensure that the moisture content of the compost pile was 55 ± 0.5%;

[0066] (3) The fermentation box body rotated once every 45 min for 5 min each time. When rotating each time, the ventilation holes were opened to supplement oxygen. After rotation, the cover plate was closed to cover the ventilation holes, and the rotation speed was 30 - 40 rpm. In the present invention, due to the addition of fish manure hydrothermal carbon, during the fermentation process, the moisture content can be maintained above 50%, so no water needs to be supplemented during the fermentation period.

[0067] (4) After the compost fermentation temperature drops below 30 °C, use the compost leachate to adjust the moisture content to 55 ± 0.5% again, put 150 earthworms for ripening. Before adding, wash the surface of the earthworms with sterile water and place them in a clean petri dish with a moist filter paper, and keep them in the dark environment for 24 h. During the ripening process, rotate the fermentation box once every 50 min for 5 min each time. During the rotation, open the cover plate to supplement oxygen through the ventilation holes. When the rotation stops, close the cover plate to cover the ventilation holes, and the rotation speed is 30 - 40 rpm.

[0068] I. The present invention designed 5 groups of control experiments, namely, the fermentation box does not rotate (A), rotates for 5 min and stands still for 25 min (B), rotates for 5 min and stands still for 35 min (C), rotates for 5 min, stands still for 45 min (D), and continuous mechanical air supply (E). After the compost is evenly dispersed, the total thickness is about 21 cm, and it is evenly divided into three parts: upper, middle, and lower. Supplement a certain amount of tap water through the spraying device to control the moisture content of the compost at 55 ± 0.5%. During the composting process, intermittent rotation and air supply of the compost box are achieved by adjusting the start and stop times, and the rotation speed is controlled at 30 rpm. The preliminary experiment found that after rotating for 5 min, the O2 content in the compost gradually increased to a stable level (as Figure 4 shown). When the interval time exceeds 45 min, the compost is tightly compacted, and it is impossible to mix the materials evenly during the rotation of the compost box. The sampling points and key parameter monitoring points of the compost box are as Figure 5 shown. Select three different time points every day to monitor the temperature of the compost at different parts of the compost body, and take the average value to represent the compost temperature of the day; use a portable oxygen analyzer to measure the oxygen content at the end of the rotation of the compost box in 3 times, and take the average value to represent the oxygen content of the compost body; every 2 d, draw 25 mL of gas through a syringe with a three-way valve at a fixed time (10:00 am) to test the production amounts of N2O, CH4, NH3, and CO2; take 50 g of compost samples from the upper, middle, and lower parts of the compost, mix them evenly, dry a part of the compost at 60 °C for the determination of the contents of pH, EC, TN, FA, etc., seal a part of the fresh samples in a 4 °C refrigerator for the determination of the seed germination rate, and store a part in an -80 °C refrigerator for the analysis of the microbial community structure.

[0069] By controlling the rotation and air supply frequency of the compost box, the influence of the rotation of the rotating compost box on the oxygen content in the upper, middle, and lower parts of the compost body was studied, and the results are as Figure 6 shown. It can be seen from the figure that as the composting progresses, the oxygen content in the A treatment group ( Figure 6 A) continues to decrease; the oxygen content in the B treatment group ( Figure 6 B) is always higher than 10%; the oxygen content in the C treatment group ( Figure 6C) The oxygen content first decreased and then increased. At the 5th day, the oxygen content in the middle of the compost was 10% higher than the oxygen limit of aerobic composting (11.4%), but the oxygen contents in the lower and upper parts were 8.1% and 9.8% respectively. At the end of composting, the oxygen content in each part of the compost pile was greater than 14%; Treatment group D ( Figure 6 D) At the 5th and 10th days, the oxygen contents in the upper, middle, and lower parts of the compost were 4.3%, 7.4%, 5.5% and 2.3%, 3.8%, 3.4% respectively, all lower than 10%; Treatment group E ( Figure 6 E) Continuous air supplementation was carried out, and the oxygen content in the compost pile was always greater than 10%. Generally, it is considered that aerobic composting occurs when the oxygen concentration exceeds 10%. During the entire composting process, only the oxygen contents in treatment groups B and E were always greater than 10%, which is related to the high air supplementation frequency and timely oxygen supplementation in treatment group B and continuous air supplementation in treatment group E. At the same time, during the composting process, the oxygen content in the middle of the compost pile was always higher than that in the lower and upper parts. This is because the air inlet of the rotary composting box is mainly set in the middle of the side of the box. When the box rotates, oxygen mainly enters the box through the middle air inlet, resulting in a higher oxygen content in the middle of the box than in the lower and upper parts.

[0070] At the end of composting, the oxygen contents in treatment groups B, C, and D were all greater than 10%. This may be related to the decrease in microbial activity and the loss of moisture in the compost pile at the end of composting, resulting in the fluffiness of the compost pile, improving the oxygen transfer efficiency in the compost pile and reducing the oxygen consumption rate.

[0071] The oxygen content during the high-temperature stage of composting is the key to affecting the composting maturity efficiency. The change in the oxygen content in the compost pile within one air supplementation cycle (calculated as 50 minutes) during the high-temperature stage of composting is as Figure 3As shown in Figure F. When the composting bin rotates for 5 minutes, the oxygen content in the compost can be increased to more than 14 mg / L, which is basically the same as that under continuous air supplementation. During the static period of the composting bin, the oxygen content in the intermittent air supplementation treatment group decreases rapidly. The longer the air supplementation interval, the faster the oxygen consumption rate in the compost. The oxygen consumption rates of treatment groups B, C, and D are 0.02% / kg·min, 0.027% / kg·min, and 0.038% / kg·min, respectively. The oxygen consumption rate accelerates with the increase of the air supplementation interval. This may be related to the fact that the longer the rotation air supplementation interval, the higher the compactness of the compost, and there is no sufficient transfer channel for oxygen in the compost, which accelerates the oxygen spillover. Under the condition of intermittent air supplementation, only at the air supplementation frequency of rotating for 5 minutes and standing for 25 minutes, the oxygen content in the compost meets the limit value of more than 10% for oxygen content in aerobic composting. With the decrease of the air supplementation frequency of the rotating composting bin, the oxygen content in the compost during the heating period and the high-temperature period is less than 10%, which is a typical "aerobic - anaerobic - aerobic" alternating composting process. Compared with aerobic composting, the aerobic - anaerobic alternating composting process can improve the activities of phosphatase and catalase during the composting process and promote the humification process of compost. Therefore, rotating for 5 minutes, standing for 25 minutes, and continuous mechanical air supplementation are all in the aerobic composting process all the time.

[0072] As Figure 7 shown. The compost temperatures of each treatment group all showed the changing rule of first increasing and then decreasing. With the progress of the composting fermentation process, treatment groups A, B, C, D, and E reached their respective highest temperatures on the 10th day, 8th day, 9th day, 9th day, and 7th day, which were 53.52 °C, 60.37 °C, 56.75 °C, 56.34 °C, and 59.71 °C respectively, and maintained at a high temperature environment above 55 °C for 1 day, 3 days, 3 days, 4 days, and 2 days respectively. At the same time, the temperature of treatment group E increased rapidly in the initial stage of composting, and there were obvious fluctuations in the temperature during the composting process. When the composting fermentation process reached 16 days, the temperatures of all treatment groups dropped to the ambient temperature, and the composting fermentation process ended.

[0073] The inactivation of pathogenic microorganisms can be achieved when the compost temperature is maintained above 55 °C for more than 3 days. The above conditions are met under different air supplementation frequencies. Under the condition of rotating for 5 minutes and standing for 25 minutes, the temperature of the compost during the high-temperature period is the highest and the heating rate is the fastest. This is related to the timely supplementation of the oxygen content in the compost under the condition of high-frequency rotation of the composting bin, which increases the porosity and free air space of the compost and promotes the composting fermentation.

[0074] Under the conditions of rotating for 5 min and standing for 45 min, although the highest temperature of the compost pile was 4.03 °C lower than that under the conditions of rotating for 5 min and standing for 25 min, the duration of high temperature above 55 °C was extended by 1 day. This may be related to the extended rotation interval, which led to the compaction of the compost pile and the inability of heat to dissipate in time. At the initial stage of continuous air supplementation, the temperature increased rapidly, which may be related to the fact that continuous air supplementation provided sufficient oxygen for the compost pile. As the composting process progressed, the temperature of treatment group E fluctuated greatly. This is related to the fact that the continuous air supplementation treatment group mainly achieved uniform mixing of materials through manual turning, resulting in the compaction of the compost pile and uneven moisture distribution, causing phenomena such as inhibition of microbial metabolic activity and heat production. Generally speaking, under different air supplementation frequencies, the temperature conditions for killing pathogenic bacteria and eggs during compost fermentation can be met. The temperature was the highest under the conditions of rotating for 5 min and standing for 25 min, but a shorter rotation and air supplementation cycle increased the energy consumption during the composting process; under the conditions of rotating for 5 min and standing for 45 min, the energy consumption of high-frequency rotation of the compost bin was avoided, and the duration of high temperature during composting was extended, and compost sterilization could also be achieved.

[0075] As Figure 8 shown, during the high-temperature period of composting, under different air supplementation frequencies, the increase in pH may be caused by the mineralization of organic acids and the occurrence of ammonification reactions in the compost pile. The pH of treatment group E decreased on the 10th day of composting, which was related to the fact that sufficient oxygen promoted the volatilization of NH3. From the 10th day, the pH of treatment groups B, C, D, and E was stably maintained between 7.54 - 8.13, which may be due to the buffering effect of humic acid produced in the later stage of composting. At the end of compost fermentation, the pH of the compost pile was the lowest under the air supplementation frequency of rotating for 5 min and an interval of 25 min, and the highest under the air supplementation frequency of rotating for 5 min and standing for 45 min. The high air supplementation frequency promoted the conversion of NH4 + -N to NH3 and the conversion of NH3 to the atmospheric environment.

[0076] As Figure 9 shown, at the end of composting, the E4 / E6 values of each treatment were 2.43, 2.13, 2.04, 1.96, and 2.17 respectively. When the E4 / E6 ratio is 1.5 - 1.9, it indicates that the compost is mature. Compared with continuous air supplementation, intermittent air supplementation is more conducive to the compost fermentation process. Among them, under the air supplementation frequency of rotating for 5 min and standing for 45 min, the maturity of the compost fermentation product is higher. This may be related to the fact that the duration of high temperature during composting is the longest under this condition, which promotes the degradation of dissolved organic matter by microorganisms, but still cannot meet the quality requirements of the compost product and needs further ripening.

[0077] As Figure 10As shown, the seed germination indices of the compost products at 5 rotational air-supplement frequencies are 47.42%, 56.44%, 66.89%, 72.76% and 54.32% respectively. Only when rotating for 5 minutes and standing for 45 minutes for air supplementation, the seed germination index of the compost is greater than 70%. When rotating for 5 minutes and standing for 45 minutes for air supplementation, the molecular weight of humic acid is smaller, which is easy to penetrate the cell wall of plant roots and is transported and exchanged on the cell membrane of root cells, so as to be absorbed and utilized by plant roots.

[0078] As Figure 11 shown in Table 1

[0079] Table 1 Changes in carbon dioxide equivalent under different air-supplement conditions

[0080]

[0081] The CO2 equivalent emissions of each treatment group (CO2 equivalent emissions, CO2e) are shown in Table 1, which are 151.81 g / kg·DM CO2e, 573.53 g / kg·DM CO2e, 461.44 g / kg·DM CO2e, 397.46 g / kg·DM CO2e and 712.53 g / kg·DM CO2e respectively. Except for treatment group A in the "dead bed" state, treatment group D has the lowest greenhouse gas CO2e at the air-supplement frequency of rotating for 5 minutes and standing for 45 minutes, and has less impact on the atmospheric environment.

[0082] And the abundances of biomarkers with lignin and fat decomposition such as Actinomycetes, Clostridium, Tepidimicrobium, and Atopobium in treatment group D are much higher than those in treatment groups B and C, which can accelerate the formation of HS precursors, promote the formation of HA in the mature stage of composting, and reduce the mineralization rate of organic matter and the generation of greenhouse gases (CO2 and CH4).

[0083] II. Effects of moisture regulation methods on the composting process and product quality

[0084] Before the start of composting, the moisture content of the compost pile with adjusted C / N was adjusted to 55% by spraying different water replenishing liquids under the rotating state of the compost bin. Four treatment groups were set up for the moisture regulation experiment, namely no water replenishment (T1), tap water replenishment (T2), compost leachate replenishment (T3), hydrothermal liquid replenishment (T4), tap water + fish manure hydrochar combined replenishment (T5), compost leachate + fish manure hydrochar combined replenishment (T6), and hydrothermal liquid + fish manure hydrochar combined replenishment (T7). Fish manure hydrochar was added in advance.

[0085] The experiment was carried out in a rotating compost bin. The compost bin was intermittently aerated at a frequency of rotating for 5 minutes and standing still for 45 minutes, and the rotation speed was 30 rpm. When the moisture content of the compost pile was lower than 50%, the moisture content of the compost pile was readjusted to 55% by supplementing different water replenishing solutions. Before the start of composting, hydrochar was evenly added to the compost pile at 5% of the total compost mass (the total compost mass was 10 kg as before). The temperature of different parts of the compost pile was monitored at 9:00, 15:00 and 21:00 every day, and the average value was taken to represent the compost temperature of the day. The moisture content of different parts of the compost pile was monitored every 2 days, and the average value was taken as the moisture content of the compost pile to determine whether to replenish water; the maturity of the compost was evaluated by testing the compost seed germination rate, EC, FA, HA and HA / FA; every 2 days, at a fixed time (10:00 am), 25 mL of gas was extracted through a syringe with a three-phase valve for testing the production amounts of N2O, CH4, NH3 and CO2; at the compost heating stage (the 2nd day), high temperature stage (the 7th day) and cooling stage (the 12th day), 50 g of compost fermentation products from the upper, middle and lower parts of the compost pile were taken respectively, mixed evenly and stored in a -80 °C refrigerator for microbiomics-related analysis.

[0086] As Figure 12 shown, during the entire composting process, the temperatures of the compost piles in all treatment groups first increased and then decreased. Each treatment group entered the high-temperature stage of composting (>50 °C) on the 5th day of composting. The high-temperature maintenance times were T6 (12 d) > T3 (10 d) > T4 (9 d) > T7 (8 d) > T2 (5 d) > T5 (4 d) > T1 (3 d) respectively. The maintenance times at the pathogenic microorganism inactivation temperature (>55 °C) were T6 (8 d) > T3 (5 d) > T4 (3 d) = T7 (3 d) > T5 (2 d) > T2 (0 d) = T1 (0 d) respectively. Compared with the T2 treatment group, the T3 and T4 treatment groups significantly extended the high-temperature stage of composting, which was related to the fact that T3 and T4 contained a large amount of nutrients, and after reuse, they could provide more nutrients directly available for microorganisms in the compost. At the same time, the rich microorganisms in T3 were re-inoculated into the composting system, which helped to improve the composting efficiency and further extended the duration of the high-temperature stage of composting. The compost leachate and the compost leachate + hydrochar treatment groups had the longest high-temperature maintenance time, indicating that reusing the compost leachate into the composting system helped to extend the high-temperature stage of composting and the pathogenic microorganism inactivation ability, which was beneficial to the subsequent resource utilization of the compost. After adding hydrochar, the optimal temperature of the compost treatment group was significantly higher than that of the corresponding treatment group without adding hydrochar, which was related to the fact that the rich specific surface area of hydrochar increased the attachment ability of microorganisms and improved the relative abundance of microorganisms in the compost pile. Generally speaking, the hydrochar + compost leachate treatment group had significant advantages in increasing the compost temperature and maintaining the high temperature of the compost.

[0087] The change of pH can reflect the organic matter degradation process during composting. The change process of pH during composting is as Figure 13As shown. It can be seen from the figure that under the action of T2, T3, and T4 during the compost temperature-rising stage, the pH of the compost pile showed a trend of first increasing and then decreasing. The pH values of the T1, T2, T3, and T4 treatment groups reached their peaks on the 15th day, 12th day, 8th day, and 10th day, respectively, which were 7.62, 8.03, 8.31, and 8.24. After the addition of hydrochar, the pH of the compost showed a 1-2-day decline period at the initial stage of composting, and then gradually increased. On the 8th day, 10th day, and 10th day, the pH values of the T5, T6, and T7 treatment groups reached their peaks, which were 7.73, 7.82, and 7.68, respectively. The decline in the pH of the T2, T3, and T4 treatment groups in the early stage of composting may be related to the decomposition of organic matter by microorganisms to produce NH3. The increase in pH in the later stage may be related to the production of organic acids by the nitrification decomposition of ammonia nitrogen and other compounds and the decomposition of organic matter. After the addition of hydrochar, the pH of the compost decreased because hydrochar reduced the mass transfer of moisture and air and inhibited the decomposition of organic acids.

[0088] Influence of Moisture Regulation Methods on Compost Moisture Content and Moisture State

[0089] As shown in Table 2.

[0090] Table 2 Compost Moisture Change Rate during Composting

[0091]

[0092] It can be seen from the table that in the T1, T2, T3, and T4 treatment groups, the moisture content dropped below 50% every 2 days and needed to be re-supplemented with water. At the same time, the moisture content change rate during the compost temperature-rising period and high-temperature period was significantly higher than that during the compost cooling period. Compared with the one-time water supplementation method of the T1 treatment group, the multiple-stage water supplementation of the T2 treatment group significantly reduced the moisture content change rate of the compost pile every 2 days. Compared with the T2 treatment group, the multiple-stage supplementation of compost leachate (T3) and hydrothermal solution (T4) further reduced the moisture change rate during composting. After the addition of hydrochar, the moisture change rate of the compost pile decreased significantly, and the moisture content change rate every 2 days was significantly lower than that of the T2, T3, and T4 treatment groups. At the end of composting, the moisture contents of the T5, T6, and T7 compost piles were 46.4%, 50.19%, and 48.86%, respectively. The T6 group did not need to be supplemented with water, and the rest of the groups needed to be supplemented with water.

[0093] In the early stage of compost fermentation, the moisture change rate of the compost pile was relatively high, which was related to the fact that there were more easily degradable organic matters in the FS, and the relatively high temperature of the compost pile accelerated the volatilization of moisture. The moisture change rates of T3 and T4 were lower than those of the T2 treatment group because there was a certain amount of citric acid residue (from feed) in T3 and T4. Citric acid is a common bait additive, which has physiological functions such as acidifying feed, protecting feed quality, improving feed palatability, feed intake, digestive enzyme activity, immune function, stress resistance, and the digestion and absorption rate of nutrients, and reducing the pH of the digestive tract of fish and shrimp. At the same time, citric acid can combine with water molecules to form compounds such as calcium citrate, thereby increasing the viscosity of water and improving the water retention capacity of water molecules. During the high-temperature period of composting, the moisture change rates of the compost piles in the T3 and T4 treatment groups were relatively high, which was related to the fact that high temperature promoted water evaporation and citric acid gradually decomposed into CO2 and water. After the addition of hydrochar, the water retention capacity of the compost piles in the T5, T6, and T7 treatment groups was significantly higher than that in the T1, T2, T3, and T4 treatment groups, indicating that hydrochar has good application potential in maintaining the moisture of organic waste compost. The good water retention performance of hydrochar was also related to the large amount of calcium ions in the FS. Calcium ions can regulate the osmotic pressure in the cell membrane and intracellular fluid, improving the overall water retention capacity inside and outside the cell. Generally speaking, the hydrochar + compost leachate treatment group (T5) had the best effect on maintaining the moisture stability of the compost pile.

[0094] The state of water existence in the mixed organic system is affected by different binding forces, and the binding forces are affected by the moisture content, chemical components, and physical structure of the environment where the water is located. It is of great significance to optimize the water replenishment strategy by controlling the binding forces to regulate the water state and water content in the composting system. To determine the effect of hydrochar addition on the state of water existence in the compost pile, the change processes of three water states, namely MMLW, EW, and CW, in the compost pile were monitored, and the results are as Figure 14As shown, at the beginning of composting, the initial contribution rate of EW in each treatment group was greater than 78%, indicating that EW was the main moisture state during the composting process. During the entire composting process, the MMLW content was maintained at a low level for a long time and always remained at 4.5 - 6.3%, indicating that the addition of hydrochar had little effect on MMLW. During the entire composting process, EW continued to increase while CW gradually decreased. Research shows that the order of the binding forces exerted on water in the mixed organic matter system is MW > MMLW > CW > EW. Since CW is more difficult to remove than EW, retaining more water as CW in the composting system is more conducive to moisture content balance

[183] . At the end of composting, the CW content was T6 > T5 > T7 > T1. The CW in T5, T6, and T7 was higher than that in T1, indicating that the addition of hydrochar increased the capillary force, slowed down the process of CW conversion to EW in the composting system, inhibited the decrease in the moisture content of the compost pile, and maintained the stability of the moisture in the compost pile. The rate of CW conversion to EW in the T7 group was significantly higher than that in the T5 and T6 groups because the hydrothermal solution in T7 had undergone a high-temperature and high-pressure digestion process and was rich in more abundant easily degradable organic matter. The degradation of organic matter during composting would cause the destruction of the closed structure and promote the conversion of CW to EW. Hydrochar inhibited the decrease in the moisture content of the compost pile by increasing the maintenance ability of capillary water in the compost pile. Among them, the T6 treatment group had the best moisture fixation ability.

[0095] As Figure 15 shown, the seed germination rate of T1 at the end of composting was 59.3%, lower than the specified value of the seed germination index ≥ 70% in "Organic Fertilizer" (NY / T525 - 2021), and there was a certain risk in using it in agricultural production. The seed germination rates of the remaining treatment groups were all higher than 70%, which were 74.54%, 76.69%, 82.43%, 83.08%, 87.72%, and 83.37% respectively, indicating that the compost products had high safety and reliability. Compared with the air-supplementing method, the change in the water-adjusting method was more conducive to improving the seed germination rate of the compost. Among them, the T6 treatment group had the highest seed germination rate of the compost product.

[0096] The results are as Figure 16 shown in

[0097] Table 3 Comparison of compost maturity parameters

[0098]

[0099] EC can directly reflect the salt content of the compost product and indicate whether the final compost product will cause phytotoxicity or inhibit plant growth, which is closely related to the degradation of organic matter during the composting process. The change process of EC is as Figure 16As shown. It can be seen from the figure that the EC of the compost heap shows a trend of first increasing and then decreasing. Among them, the EC of T3 and T4 increased rapidly in the first 8 days, reaching 2743 us / cm and 2821 us / cm respectively. The EC of the T5, T6, and T7 treatment groups increased slowly in the first 1-2 days of composting and gradually decreased to a relatively stable state in the later stage of composting. The EC of the T3 and T4 treatment groups increased rapidly during the temperature-rising period and high-temperature period of composting, which may be related to the rapid mineralization and degradation of organic matter in the compost heap into small-molecule substances. The decrease in EC in the later stage of composting may be related to the volatilization of organic acids and NH4 + -N, mineral salt precipitation, and the directional humification of small-molecule components. The EC of the T5, T6, and T7 treatment groups remained stable in the later stage of composting, which may be due to the adsorption or coprecipitation reaction between hydrothermal carbon and water-soluble salts produced by the degradation of organic matter. At the end of composting, the EC of all compost products was less than 4000 us / cm, indicating that the compost can be safely used for agricultural production. Fulvic acid (FA) and Humic acid (HA) are the products of the degradation of organic matter. Among them, FA is a water-soluble organic acid, and HA is an organic acid insoluble in water. The changes in the contents of HA and FA are also important indicators for measuring the maturity of compost. The changes in the contents of FA and HA in the compost heap during the composting process are as Figure 16 shown in Figure B of 16 and Figure C of 16. It can be seen from the figure that the FA of all treatment groups gradually decreased with the progress of composting. At the end of composting, the degradation rates of FA in each treatment group were 24.32%, 30.27%, 55.24%, 45.87%, 52.71%, 58.55%, and 56.19% respectively. Different from the change law of FA, HA continued to increase throughout the composting process. At the end of composting, the HA contents of T1, T2, T3, T4, T5, T6, and T7 were 5.34%, 7.13%, 7.43%, 7.56%, 7.67%, 7.96%, and 7.74% respectively. During the composting process, the continuous decrease of FA may be related to the fact that thermophilic microorganisms preferentially use easily degradable organic matter to provide energy for their own growth and reproduction. The addition of hydrothermal carbon accelerated the degradation of FA during the composting process. Among them, the degradation of FA in the T6 treatment group was the most obvious. A large number of microorganisms in the compost leachate were re-inoculated into the composting system, increasing the relative abundance of microorganisms conducive to the degradation of FA and providing a suitable growth environment for the growth of microorganisms by hydrothermal carbon.

[0100] HA / FA can evaluate the degree of polymerization of compost products. When HA / FA is greater than 1.6, it indicates that the compost products are mature. The larger HA / FA is, the better the safety of the compost products. During the composting process, the change process of HA / FA in each treatment group is as Figure 16As shown in Figure D. It can be seen from the figure that as the composting progresses, the HA / FA of each treatment group gradually increases. At the end of composting, the HA / FA of each treatment group is 1.23, 1.74, 2.89, 2.43, 2.83, 3.34, and 3.07 respectively. Under the condition of adding hydrochar, the HA / FA of the T6 compost pile is the highest, indicating that adding hydrochar is beneficial to improving the composting conditions (such as increasing porosity and oxygen diffusion, etc.), increasing the metabolic activity of key functional microorganisms beneficial to the degradation of organic matter, such as Bacillus, etc., promoting the decomposition of macromolecular organic matter (such as lignin, hemicellulose, cellulose) into phenolic and other humus precursor substances, and improving the humification process. The chemical oxidation of hydrochar and the adsorption of humic substances can also accelerate the formation of aromatic polymers. The above results show that adding hydrochar helps to maintain the moisture of the compost pile, improve the polymerization degree of the compost product, and accelerate the maturity of the compost. In order to further evaluate the maturity of the compost product, the C / N and E4 / E6 of the compost product at the end of composting were also monitored, and the results are shown in Table 3. When the C / N ratio is lower than 20 or the E4 / E6 is in the range of 1.5 - 1.9, it indicates that the compost is mature. At the end of composting, the C / N and E4 / E6 of each treatment group cannot meet the limit values specified for compost maturity and still need to be further matured. Results such as seed germination rate and HA / FA show that the T6 treatment group is more obvious in promoting compost maturity.

[0101] The emissions of N2O under different moisture control methods were monitored, and the results are as Figure 17 shown. In the early stage of compost fermentation, the N2O emissions remained at a low level. When the compost entered the high-temperature period and the cooling period, the N2O emissions increased rapidly. At the end of composting, the cumulative N2O emissions of T1, T2, T3, T4, T5, T6, and T7 reached 68.35 mg / kg·DM, 105.88 mg / kg·DM, 138.04 mg / kg·DM, 79.67 mg / kg·DM, 48.03 mg / kg·DM, 34.62 mg / kg·DM, and 41.14 mg / kg·DM respectively. In the initial stage of composting, the production of N2O was low, which may be related to the inhibition of the growth of nitrifying bacteria and denitrifying bacteria during the temperature-rising period and high-temperature period of composting.

[0102] In the later stage of composting, the production of N2O increased rapidly, which may be related to the decrease of the temperature and pH of the compost pile in the later stage of composting, the dominance of nitrifying bacteria, and the gradual conversion of NH4 + -N to NO3 - -N. Compared with the T1 and T2 treatment groups, the cumulative N2O emissions of the T3 treatment group increased significantly in the later stage of composting because the main components of the compost leachate are nitrogen-rich substances such as NO2 - -N and NH4 + -N, and NO2 --N, as a byproduct of nitrification or an intermediate substance in denitrification, greatly increases the content of available nitrogen in the reaction process, thus promoting the production of N2O. At the same time, the alternation of relatively dry and re-wetting of the compost pile also causes an increase in the availability of carbon and the O2 consumption in the pile, thereby leading to an increase in N2O emissions. The main nitrogen-rich substance in the T4 treatment group is NO3 - -N. During denitrification, NO3 - -N and N2O compete with each other as terminal electron acceptors, inhibiting the activity of N2O reductase, and thus causing a decrease in the content of N2O. No significant emissions of N2O were detected in the T5, T6, and T7 treatment groups during the composting stage, which is related to the good adsorption and fixation ability of hydrothermal carbon for gases. CH4 is also an important greenhouse gas and one of the main byproducts generated during the anaerobic process of organic waste, with a GWP 25 times that of CO2. The variation pattern of CH4 during composting is as Figure 17 shown in B. CH4 is mainly produced during the high-temperature stage of composting. The production time of CH4 in the T5, T6, and T7 treatment groups is earlier than that in the T1, T2, T3, and T4 groups. During the entire composting stage, the cumulative emissions of CH4 in the T1, T2, T3, T4, T5, T6, and T7 treatment groups were 89.54 mg / kg·DM, 131.11 mg / kg·DM, 140.81 mg / kg·DM, 130.78 mg / kg·DM, 77.73 mg / kg·DM, 64.47 mg / kg·DM, and 72.55 mg / kg·DM, respectively. CH4 is produced in large quantities during the high-temperature stage of composting because as the temperature and pH of the compost pile increase, the activity of thermophilic microorganisms increases, and a large amount of degradable organic matter decomposes rapidly, resulting in the oxygen supply in the compost being unable to meet the needs of microbial life activities, and an anaerobic environment is formed in some areas. In the later stage of composting, the emissions of CH4 decrease, which is related to the decrease in microbial oxygen consumption, the increase in oxygen content in the compost, and the inhibition of methanogens. Compared with the T2 treatment group, the cumulative yield of CH4 in the T3 and T4 treatment groups increased within every 2 days during the high-temperature period of composting. This may be due to the addition of nitrogen-rich substances causing the compost pile to be more likely to form an anaerobic environment, resulting in low oxidation of CH4. With the continuous addition of nitrogen-rich substances, the cumulative yield of CH4 within 2 days gradually decreases, which is related to the methanogens following ammonia volatilization and NH4 +-N concentration increases, which is related to the inhibition of activity. The production time of CH4 in the T5, T6, and T7 treatment groups was earlier than that in the T1, T2, T3, and T4 treatment groups. This is related to the fact that the rich specific surface area of hydrothermal carbon provides a good living environment for thermophilic microorganisms, resulting in enhanced activity of thermophilic microorganisms, increased oxygen consumption, and the early formation of an anaerobic environment. Combining the N2O and CH4 emissions of each treatment group, the cumulative greenhouse gas emissions of each treatment group are 22.61 g / kg·DM CO2e, 34.83 g / kg·DM CO2e, 44.66 g / kg·DM CO2e, 27.01 g / kg·DM CO2e, 16.26 g / kg·DM CO2e, 11.93 g / kg·DM CO2e, and 14.08 g / kg·DM CO2e.

[0103] During aerobic composting, due to the decomposition of organic matter, nitrogen is inevitably lost in the form of NH3, which will not only reduce the agricultural value of compost but also have an adverse impact on the surrounding environmental hygiene due to the odor generated. The emission pattern of NH3 during composting is as Figure 17 shown in C. The emission of NH3 during composting is mainly concentrated in the high-temperature period of composting. Compared with T1, the NH3 emissions of the other treatment groups have all increased. Among them, the T3 treatment group has the highest cumulative NH3 emissions. At the end of composting, the cumulative NH3 emissions of each treatment group are 1.51 g / kg·DM, 6.41 g / kg·DM, 8.55 g / kg·DM, 2.51 g / kg·DM, 2.37 g / kg·DM, 2.16 g / kg·DM, and 1.99 g / kg·DM, respectively. The lowest cumulative NH3 emissions in the T1 treatment group may be related to the rapid drying of the compost pile during composting. The highest cumulative NH3 emissions in T3 are related to the fact that the high moisture content of the compost pile causes NH3 to dissolve in water in the form of NH4 + -N, and the continuous reuse of the leachate leads to the accumulation of NH4 + -N and the gradual increase in pH in the compost pile. The lower NH3 emissions in T4 are related to the reduction of the pH of the compost pile by the access of hydrothermal liquid. The cumulative NH3 emissions of the T5, T6, and T7 treatment groups are lower than those of the T2, T3, and T4 treatment groups. Hydrothermal carbon can absorb part of the NH4 + -N, reduce the physiological toxicity of NH4 + -N to nitrifying bacteria, and improve the nitrogen fixation ability of the compost pile.

[0104] As shown in Table 4, the microbial abundance and temperature showed opposite trends during the composting process. During the heating-up stage of composting, mesophilic and thermophilic bacteria degraded and utilized easily degradable organic matter (such as crude protein, soluble monosaccharides, etc.) for their own physiological activities, thereby increasing the number and abundance of bacteria. During the high-temperature stage, with the decrease of nutrient components and the change of enzyme activity, mesophilic bacteria were in an inactivated or dormant state, and heat-resistant bacteria became the dominant bacteria, resulting in a decrease in the richness and diversity of bacteria in the compost pile. During the cooling period of composting, the composting environment was suitable for the growth of bacteria, and the activity of mesophilic bacteria increased again. During the whole composting process, the richness and diversity of bacteria were in the order of T6>T3>T5>T7>T4>T2>T1, indicating that maintaining the relative stability of the moisture content of the compost pile was helpful to improve the abundance and diversity of bacteria in the compost. Compared with the multiple water-supplying method, the water-holding method of hydrochar was more conducive to maintaining the abundance and diversity of bacteria in the compost pile.

[0105] Table 4 OTUs values at different composting stages

[0106]

[0108] Figure 18 A shows the changes in the microbial community structure at the phylum level during the composting process under different moisture regulations. The results showed that Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, etc. were the main bacterial phyla. Among them, actinomycetes could promote microorganisms to produce more lignocellulose-degrading enzymes, especially cellulase, to promote the degradation of organic matter. At the same time, actinomycetes could also secrete antibiotics to inhibit the growth of pathogenic bacteria. During the high-temperature period of composting, the relative abundance of actinomycetes in each experimental group was low, and the abundances were in the order of T5 (42.4%)>T7 (41.1%)

[0109] > T4 (37.6%) > T6 (35.4%) > T2 (34.1%) > T3 (32.1%) > T1 (24.5%). Comparing the temperature change trends during the high-temperature stage of composting, it can be seen that except for T1, the higher the temperature of the compost pile, the smaller the relative abundance of Actinobacteria, indicating that Actinobacteria are relatively sensitive to high temperatures. Throughout the high-temperature stage, the relative abundance of Actinobacteria always remains greater than 30%, indicating that Actinobacteria play an important role during the composting process. The relative abundance of Firmicutes is relatively high during both the initial and high-temperature stages of composting. The relative abundances of T1, T2, T3, T4, T5, T6, and T7 are 33.4%, 47.5%, 54.3%, 44.3%, 45.4%, 51.3%, and 43.8% respectively. During the cooling stage of composting, the relative abundances of Firmicutes decreased to 13.5%, 22.3%, 24.1%, 18.4%, 21.3%, 23.4%, and 15.5% respectively, indicating that Firmicutes are typical heat-resistant bacteria and play an important role in the degradation of organic matter during the high-temperature stage of composting. Throughout the high-temperature period of composting, the cumulative relative abundances of Actinobacteria and Firmicutes in the T1, T2, T3, T4, T5, T6, and T7 treatment groups are 57.9%, 81.6%, 86.4%, 81.9%, 86.4%, 87.6%, and 84.9% respectively, indicating that the regulation of moisture helps the accumulation of Actinobacteria and Firmicutes. At the same time, compared with the method of replenishing water multiple times, the combination method of "hydrochar + one-time water replenishment" can better increase the relative abundances of Actinobacteria and Firmicutes in the compost. On the one hand, the rich porosity of hydrochar provides a "shelter" for Actinobacteria, protecting them from the adverse effects of high temperatures. At the same time, it is also related to the fact that the relatively high porosity of hydrochar increases the ventilation and water retention capacity of the compost pile, promoting the growth and reproduction of the main microorganisms. The succession law of the bacterial community structure at the genus level is as Figure 18As shown in B. Before the start of composting, the main dominant genera in fish manure were Jeotgalicoccus, Corynebacterium, and Pseudoxanthomonas. As the composting temperature increased, the relative abundances of the above dominant genera decreased significantly. On the contrary, during the high-temperature period of composting, the abundances of Planifilum, Thermobifida, Thermobacillus, and Bacillus increased significantly. Bacillus belongs to Firmicutes and can accelerate the degradation of lignocellulose. Like Bacillus, Planifilum, Thermobifida, and Thermobacillus are also typical thermophilic bacteria that can promote the degradation of lignocellulose and the formation of humus. During the high-temperature period of composting, the relative abundances of Planifilum, Thermobifida, Thermobacillus, and Bacillus in T1, T2, T3, T4, T5, T6, and T7 were 34.73%, 46.71%, 54.51%, 47.85%, 59.32%, 57.41%, and 48.13% respectively. During the cooling period of composting, the relative abundances of Planifilum, Thermobifida, Thermobacillus, and Bacillus decreased significantly, and the cumulative relative abundances decreased to 22.37%, 32.51%, 36.34%, 30.44%, 34.95%, 32.31%, and 27.17%. Pseudoxanthomonas can secrete carboxymethyl cellulase, which promotes the degradation of polysaccharides and lignocellulose and improves the degradation efficiency of polysaccharides and cellulose. Compared with the high-temperature period of composting, the relative abundances of Pseudoxanthomonas in T1, T2, T3, T4, T5, T6, and T7 increased from 4.32%, 6.73%, 8.43%, 5.53%, 5.89%, 6.54%, and 5.29% to 9.31%, 14.12%, 19.71%, 12.08%, 13.01%, 16.71%, and 11.55% respectively. Therefore, by adjusting the moisture, the relative abundances of bacteria that are beneficial to the degradation of organic substances such as cellulose and polysaccharides can be significantly increased. The relative abundances of bacteria that are beneficial to the degradation of organic substances in the T3 treatment group and the T6 treatment group were always higher than those in other experimental groups, which is related to the re-inoculation of beneficial microorganisms that have been domesticated for a long time in the compost liquid into the composting system to form a cyclic inoculation system, improving the ability of the compost heap to resist the external environment.

[0110] III. In order to achieve the complete maturity of the compost product, further earthworm maturation research was carried out on the compost fermentation product.

[0111] After the temperature of the compost fermentation product in the rotating compost bin drops to 30 °C, the moisture content of the compost pile is readjusted to 55 ± 0.5% using compost leachate. The experiment set up an earthworm ripening treatment group (T1) and a natural ripening treatment group (CK). In the earthworm ripening treatment group, 150 earthworms without reproductive rings that had adapted to the dark environment for 24 h were introduced. During the earthworm compost ripening process, the air supply frequency of the compost bin was to rotate for 5 min every 50 min, and the rotation speed of the compost bin was 30 rpm.

[0112] The results are as Figure 19 shown. During the compost fermentation stage, the temperature of the compost pile reached the high-temperature threshold (>50 °C) on the 5th day, and the highest temperature reached 67.5 °C. Moreover, the temperature of the compost pile remained above 55 °C for more than 3 days, meeting the inactivation conditions of pathogenic microorganisms in the compost. At the same time, both the highest temperature of the compost pile and the duration of high temperature maintenance increased compared with the individual optimal air supply frequency and the optimal moisture control method. This is because the accelerated evaporation of moisture in the compost pile under the optimal air supply frequency led to local or temporary water shortage, which inhibited the microbial activity and caused the heat production rate of the compost pile to decline; while under the optimal water supply conditions, although the nutrient concentration in the compost pile and the relative abundance of compost microorganisms increased, the continuous air supply led to an increased rate of heat loss from the compost pile. After the temperature dropped to 30 °C, earthworms were added to carry out the research on the earthworm ripening process of the compost. After adding earthworms, the temperature of the compost pile rose to 35.4 °C within 2 days and then dropped rapidly. It was basically the same as the room temperature on the 42nd day, while the temperature of the compost pile in the treatment group without adding earthworms continued to drop. During the earthworm ripening stage, the temperature of the compost pile in the earthworm addition treatment group first increased and then decreased. This may be because the addition of earthworms promoted the degradation efficiency of refractory organics such as cellulose, and the degradation of substances such as cellulose was achieved within a short period of time. On the 42nd day, the temperatures of the compost piles in both treatment groups dropped to room temperature, and the compost fermentation and ripening stages ended.

[0113] The results are as Figure 20 shown. During the compost fermentation stage and the earthworm ripening stage, the pH of the compost pile showed a trend of first rising and then falling. Compared with the treatment group without adding earthworms, the pH of the compost product after earthworm ripening was generally higher. In the treatment group without adding earthworms, the pH reached the highest value of 8.35 on the 28th day and then dropped to 8.03 at the end of the compost on the 42nd day. After adding earthworms, the compost pH could reach 8.79 and dropped to 8.04 at the end of the compost on the 42nd day. The increase in pH during the composting process may be caused by the mineralization of organic matter in the fish manure to produce NH4 + -N and its accumulation as well as the decomposition of small molecular organic acids. At the same time, the pH during the composting stage was always maintained between 6.32 and 8.79, and the suitable pH range for Eisenia fetida is 5.0 - 9.0, ensuring the survival rate of subsequent earthworms. In the later stage of composting, the decrease in pH may be related to NH4 +-N is released through nitrification, causing the accumulation of organic acids. During the vermicomposting maturation stage, the overall pH is higher than that of the treatment group without earthworms, which is related to the ability of earthworms to increase the growth rate and activity of microorganisms in the compost pile, change the microbial community structure, and improve the organic matter decomposition process. At the same time, earthworms can also promote the mineralization of organic matter through feeding and digestion processes, thereby increasing the pH of the compost pile. In the later stage of earthworm composting, physiological processes such as earthworm feeding and burrowing increase the porosity of the composting system, promote gas exchange between the compost pile and the outside world, and to a certain extent inhibit the occurrence of the denitrification process, resulting in a decrease in the pH of the compost pile.

[0114] As Figure 21 shown, the rich soluble proteins and carbohydrates in fish manure provide sufficient substrates for the conversion of earthworms through the gut, resulting in an increase in protease activity in the compost pile after earthworm digestion and excretion. The addition of earthworms increases the activity of enzymes related to compost maturity, promotes the further maturity of compost, and improves the safety of compost products.

[0115] As Figure 22 , during the composting process, microorganisms will decompose and produce toxic compounds such as organic acids, polyphenols, and alcohols, which inhibit seed germination and growth. The change in GI can reflect the toxicity of compost products and their potential threat to the environment, and is an important indicator for evaluating the safety of compost products. The results of the seed germination rate of the product leachate during the composting fermentation and vermicomposting maturation processes are as Figure 22 shown. As the composting time extends, the seed germination rate gradually increases, which is related to the degradation of toxic and harmful substances that affect seed germination during the composting process. The completion time of the composting fermentation stage is shortened by 9 days compared to the separate methods of supplementing air and adjusting water, and the seed germination rates are increased by 8.64% and 2.68% respectively. However, the C / N ratio in the compost maturity evaluation index cannot meet the conditions, and further treatment is required to improve the compost maturity. At the end of the vermicomposting maturation stage, the GI of the treatment group without earthworms is 85.3%, and the GI of the vermicomposting treatment group is 98.4%. This indicates that the addition of earthworms further improves the conversion of toxic and harmful substances during the composting process, and improves the safety and reliability of compost products. EC is often used as an index for the content of soluble salts in the reactor compost (such as Na + , K + , Cl - , SO4 2- , NO3 - , etc.), which is closely related to the degradation of organic matter during the composting process, and is a parameter for evaluating the maturity of compost and the potential toxicity of plants. During the FS composting fermentation and vermicomposting maturation processes, the change process of EC is as Figure 23As shown in A. During the entire composting fermentation and vermicomposting processes, the EC first decreased and then continuously increased. The initial decrease in EC was mainly related to the precipitation of mineral salts and the volatilization of ammonia nitrogen. In the later stage of composting fermentation and during vermicomposting, fish manure was continuously degraded by microorganisms, generating a large amount of soluble mineral elements, resulting in an increase in EC. At the same time, the continuous reduction in the weight of the compost pile during vermicomposting led to a "concentration effect" in the pile, which also caused the EC of the pile to continuously rise. At the end of the reaction, the EC of the vermicomposting treatment group reached 2846 μS / cm, while that of the non-vermicomposting treatment group was 2312 μS / cm. The EC of both treatment groups was less than 4000 μS / cm, indicating that the compost could be safely used in agricultural production. E4 / E6 is the ratio of the absorbance of the compost at 465 nm and 665 nm, and it is an important indicator for evaluating the quality or condensation degree and aromatization degree of humic acid

[250] . This value decreases with the increase in the condensation degree of humic acid and is one of the indicators for evaluating the degree of compost maturity. The change in E4 / E6 during the entire compost maturity process is as follows Figure 23 shown in B. During the composting stage (1 - 7 d), E4 / E6 showed an upward trend; during the vermicomposting stage, in the non-vermicomposting treatment group, E4 / E6 continued to increase, reaching a maximum value of 2.25 at 28 d, and then gradually decreasing to 1.96 at the end of composting. In the vermicomposting treatment group, the E4 / E6 of the compost pile continuously decreased. The continuous increase in E4 / E6 during composting was related to the continuous decrease in the degree of humification and aromatization of organic matter during the mineralization of organic matter in the early stage of composting fermentation. During the vermicomposting stage, the continuous decrease in E4 / E6 in the vermicomposting treatment group was related to the promotion of the condensation and aromatization of humus in the compost pile by the addition of earthworms. Some studies have shown that when the E4 / E6 value is 1.5 - 1.9, it indicates that the compost has been completely matured. In this study, at the end of the compost maturity process, the E4 / E6 values of the non-vermicomposting treatment group and the vermicomposting treatment group were 1.96 and 1.64 respectively, indicating that the addition of earthworms promoted the composting process of fish manure and improved the safety of FS utilization. The change in HA / FA can indirectly reflect the transformation process of organic matter during composting. The change processes of HA, FA, and HA / FA during the compost maturity process are respectively as follows Figure 23As shown in C of and D of . During the composting process, FA gradually decreased as the composting proceeded. At the end of the reaction, the degradation rates of FA in the non-earthworm group and the earthworm composting treatment group were 43.46% and 52.11% respectively, indicating that the addition of earthworms helped improve the degradation efficiency of FA. Different from FA, HA showed a pattern of increasing first and then stabilizing. At the end of the reaction, HA in the earthworm-ripened treatment group increased by 17.24% compared with the non-earthworm treatment group. The increase in HA might be related to the polymerization of intermediates generated during the degradation of FA and non-humic substances in fish manure into HA. The HA in the earthworm-ripened treatment group was higher than that in the non-earthworm treatment group, suggesting that the addition of earthworms helped convert unstable FA into stable HA. During the entire composting process, HA / FA showed an increasing trend. Among them, HA / FA increased from 0.79 to 1.5 during the composting stage, and in the earthworm-ripening stage, HA / FA in the earthworm composting treatment group increased to 2.78, much higher than 1.94 in the non-earthworm treatment group. The above experiments showed that the addition of earthworms during composting could significantly increase the degradation of FA or non-humic substances, promote the formation of stable HA during composting, and improve the maturity of compost products.

[0116] As shown in Table 5.

[0117] Table 5 Pathogen content in each experimental group at the end of composting

[0118]

[0119] Note: The number of fecal coliforms and the mortality rate of Ascaris eggs were carried out in accordance with the provisions of GB / T19524.1 and GB / T19524.2 respectively. NA indicates not detected.

[0120] Compared with the end of composting fermentation, the addition of earthworms significantly reduced the number of fecal coliforms and the content of Ascaris eggs in the compost pile at the end of composting ripening, indicating that the addition of earthworms was of great significance in pathogen removal and ensured that the FS compost products met the requirements of farmland reuse and sanitation and epidemic prevention. Earthworms could inactivate or kill pathogenic microorganisms by secreting antibacterial enzymes or mucus on the body surface, thereby improving the harmlessness level of compost. At the same time, the hydrothermal carbon added in the earthworm treatment group had a nanoscale particle size, and strong oxidizing free radicals or reactive oxygen species were easily generated on the surface, inducing pathogenic microorganisms to reduce their viability or directly die through cellular oxidative stress reactions. At the end of composting, a certain amount of Escherichia coli and Ascaris eggs still existed in the non-earthworm treatment group, restricting its resource utilization.

[0121] During the FS composting process, the change rule of TN was as Figure 24As shown in A. It can be seen from the figure that during the composting fermentation stage, TN continued to increase, while during the vermicomposting maturation stage, TN in the treatment group with added earthworms decreased rapidly. During the composting fermentation process, TN continuously increased, which may be related to the biomass loss caused by the respiration of nitrogen-fixing microorganisms and the decomposition of a large amount of soluble organic matter in fish manure. During the vermicomposting maturation stage, the rapid decline of TN was caused by the excrement, mucus and decomposed tissues of earthworms, the biomass loss caused by respiration, and the continued decomposition of a large amount of soluble organic matter in fish manure. At the same time, the nitrogen produced by earthworm excrement was lost in the form of NH3, N2O, etc. or retained in the earthworms, which also caused the loss of nitrogen in the compost. At the end of the fish manure composting, the TN content increased by 1.2% compared with the raw material, reaching 2609.6 mg / kg, which was related to the reduction of the dry matter content of the compost pile caused by vermicomposting, forming a concentration effect.

[0122] The change process of NH4 + -N during the composting process is as shown in Figure 24 B. Different from the change law of TN, NH4 + -N increased first and then decreased during the composting fermentation process, and NH4 + -N continued to decline to the lowest point and then slowly rebounded during the vermicomposting maturation stage. The increase of NH4 + -N was related to the large decomposition of nitrogen-containing organic matter in fish manure under the action of microorganisms. At the same time, the concentration of NH3 collected by the gas collection bag during the composting process gradually increased, indicating that NH4 + -N in the compost pile was gradually converted into NH3. At the end of the composting, the content of NH4 + -N was 356 mg / kg, less than 400 mg / kg, indicating that the compost product had been matured.

[0123] During the composting fermentation stage, the concentration of NO3 - -N decreased first and then increased rapidly. During the vermicomposting maturation stage, NO3--N showed a continuous increase to stability. The decrease in the concentration of NO3 - -N may be related to the inhibition of nitrifying bacteria by high-concentration NH4 + -N at the initial stage of composting, resulting in the hindrance of the conversion of NO2 - -N to v. During the vermicomposting maturation stage, the concentration of NO3 - -N gradually increased, which was related to the improved tolerance and abundance of nitrifying bacteria in the compost pile, increasing the ability to assimilate NH4 + -N into NO3 - -N. At the end of the reaction, the concentration of v in the vermicomposting treatment group was 1159.42 mg / kg, which was 23.92% higher than that of the treatment group without added earthworms.

[0124] The emission of N2O during the composting process not only causes the loss of nitrogen during the composting process, but also causes serious air pollution. The change of N2O during the composting process is as shown in Figure 24As shown in C of Figure, the content of N2O is low in the initial stage of compost fermentation. With the increase of compost temperature, the N2O emission rate rises rapidly. When the compost enters the high-temperature stage, high temperature, high NH4 + -N and high pH inhibit the normal progress of nitrification reaction, and the cumulative concentration of NO3 - -N is low and not enough to form N2O emission. In the cooling stage of compost fermentation, the inhibition of nitrification reaction is lifted and the N2O emission rate increases significantly. Compared with the treatment without adding earthworms, the addition of earthworms reduces the N2O emission in the cooling stage of compost, which may be because earthworms have the living habit of burrowing, increasing the porosity of the compost pile, improving the reoxygenation ability of the compost, and inhibiting the denitrification reaction. The high adsorption capacity of mature compost can also reduce the N2O emission to a certain extent. At the end of composting, the cumulative N2O emission of the experimental group is 143.35 mg / kg·DM, which is 19.51% lower than that of the blank group (171.30 mg / kg·DM). The emission of NH3 is mainly caused by the strong mineralization of organic nitrogen to NH4 + -N, and the conversion of NH4 + -N to NH3 will be further promoted in high-temperature and alkaline environments. As shown in D of Figure Figure 24 , the emission of NH3 has a certain lag compared with that of N2O. Generally, it begins to increase on the 5th - 6th day of the compost fermentation stage and reaches the maximum value when the compost pile reaches the high-temperature stage (9 - 10 days). With the decrease of the compost pile temperature, the NH3 emission rate also shows a downward trend. Different from the continuous decrease of NH3 emission in the control group, the NH3 emission in the earthworm maturation stage first increases rapidly and then decreases, which may be related to the increase of the pH of the compost pile after adding earthworms. In the later stage of compost maturity, with the improvement of the porosity of the compost pile under the action of earthworms and the high adsorption performance of mature compost, the NH3 emission gradually decreases. In addition, the addition of earthworms promotes the increase of the abundance of nitrogen-fixing related functional microorganisms. At the end of the reaction, the cumulative NH3 emission of the experimental group is 4.93 g / kg·DM, which is 22.34% lower than that of the blank group (6.03 g / kg·DM).

[0125] As Figure 25 shown, by comparing the DOC ratio in the compost pile at the end of composting, the protein content in the earthworm compost group is 7.26% lower than that in the treatment without adding earthworms, and the contents of fulvic acid and humic acid increase by 3.18%. The above results show that earthworms can promote the conversion of protein into fulvic acid and humic acid, improve the aromatization and humification degree of compost products, and facilitate the subsequent resource utilization of compost.

[0126] Table 6 Relative abundances of dominant bacterial phyla (>1%) during composting

[0127]

[0128] During the entire composting process, Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes were the dominant phyla. Among them, during the composting fermentation stage, the top 6 phyla accounted for approximately 97% of the total ASV abundance, and in the vermicomposting stage, they accounted for 98% of the total ASV abundance. Among them, the abundances of Actinobacteria and Chloroflexi increased relatively in the early and late stages of the vermicomposting stage, and the relative abundance of Bacteroidetes increased in the middle stage. During the entire composting process, Proteobacteria remained at a relatively high level. The microorganisms of this phylum are involved in various stages such as anaerobic, aerobic, and facultative aerobic, and are also the main microbial flora during the composting of waste such as vegetable tailings and cow dung. The increase in the concentration of soluble organic carbon can promote the reproduction of Actinobacteria microorganisms. During vermicomposting, organic matter is transformed through the earthworm's digestive tract, decomposing lipids, cellulose, phenolic compounds, etc., forming a large amount of soluble organic carbon, which promotes the growth of Actinobacteria. Actinobacteria can hydrolyze lignin and polysaccharides by secreting β-glucosidase and xylanase (XYL), accelerating the composting process. The relative abundance of Bacteroidetes gradually increased with the prolongation of vermicomposting time. Bacteroidetes are anaerobic bacteria that can decompose substances such as proteins, starches, and cellulose during composting, facilitating the transformation and utilization by other microorganisms. At the end of vermicomposting, the relative abundance of Chloroflexi in the compost reached 24%. Chloroflexi is a typical aerobic thermophile, which has good tolerance to high-temperature environments and can utilize oxygen to achieve its own proliferation under high-temperature conditions, and can also grow through photosynthesis under anaerobic conditions. Some studies have shown that the phylum Patescibacteria is often found in groundwater and is related to the nitrogen and sulfur cycles in water. At the beginning of composting, the relative abundance of Patescibacteria was observed to be 2%, which may be related to the fact that the recirculating aquaculture system mainly uses groundwater for water replenishment. At the end of composting, the relative abundance of the phylum Patescibacteria increased, which is related to the fact that Patescibacteria has a large specific surface area and strong nutrient adsorption ability. As can be seen from Table 6, the relative abundances of Chloroflexi, Bacteroidetes, and Patescibacteria in the compost increased.

[0129] As Figure 26 shown, the relative abundances of amoA and hao first increased and then decreased during composting, indicating that nitrifying bacteria are relatively sensitive to temperature, and an increase in temperature will accelerate the growth of nitrifying bacteria and increase the nitrification reaction rate. During the entire composting process, the expression levels of amoA and hao in the T treatment group were significantly higher than those in the CK (P < 0.05), indicating that the ammonia oxidation effect of composting under the optimal composting conditions was stronger.

Claims

1. A fish manure rotary composting fermentation device, comprising a fermentation box, characterized in that: The fermentation box body is rotatably connected to the frame through a rotating shaft, end covers are arranged at both ends of the fermentation box body, a three-way valve, a feed port, and a gas collection port are arranged on the upper side of the fermentation box body, and a liquid discharge port is arranged on the lower side of the fermentation box body. A spray pipe is arranged on the rotating shaft along its length direction, and nozzles are evenly distributed on the spray pipe. Small ventilation holes are distributed in the middle of the end cover, and the ventilation holes can be opened or covered by a rotatable cover plate.

2. The fish manure rotary composting fermentation device according to claim 1, characterized in that: The end cover and the box wall of the fermentation box body both have a sandwich structure, and a pearl cotton insulation layer is arranged in the sandwich structure. A residual liquid tray for receiving the leaching liquid discharged from the liquid discharge port is arranged on the frame below the fermentation box body.

3. The fish manure rotary composting fermentation device according to claim 2, characterized in that: All the ventilation holes are closely arranged in the middle of the end cover, and a pin is arranged above all the ventilation holes. A cover plate is rotatably connected to the pin. When the fermentation box body is rotated, the cover plate is opened, and when the rotation stops, the cover plate covers the ventilation holes.

4. A method for rotating composting and fermenting fish manure, characterized in that: Fermentation was carried out as follows: (1) adding fish manure and wheat straw to the fish manure rotary composting fermentation device according to any one of claims 1 to 3, adjusting the carbon-nitrogen ratio, and adding fish manure hydrochar; (2) Before composting, the compost extract is evenly sprayed into the fermentation box through a spray pipe while the fermentation box is rotating to ensure that the moisture content of the compost is 55±0.5%; (3) The fermentation box rotates once every 45 minutes for 5 minutes each time. During each rotation, the ventilation holes are opened to supplement oxygen.

5. The fish manure rotary composting fermentation method according to claim 4, characterized in that: When the compost fermentation temperature is lower than 30℃, use compost extract to readjust the moisture to 55±0.5%, put in earthworms for decomposition. During the decomposition process, rotate the fermentation box once every 50 minutes, and each rotation is 5 minutes. During the rotation process, open the cover to supplement oxygen from the ventilation holes.

6. The fish manure rotary composting fermentation method according to claim 5, characterized in that: Rotation speed 30-40rpm.

7. The fish manure rotary composting fermentation method according to any one of claims 4 to 6, characterized in that: The preparation of fish manure hydrothermal charcoal is as follows: stir the fish manure evenly, add it to an autoclave, seal it, heat it to 200°C, stir it, take it out after the reaction is completed, cool it to room temperature, centrifuge it to separate the solid and liquid, the liquid is the hydrothermal liquid, wash the solid with water and alcohol, and then dry it to obtain the hydrothermal charcoal.

8. The fish manure rotary composting fermentation method according to claim 7, characterized in that: The amount of the hydrothermal charcoal added is 5% of the total mass of the compost.

9. The fish manure rotary composting fermentation method according to claim 1, characterized in that: Carbon-nitrogen ratio 25:1.

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