Vegetable hydroponic nutrient solution based on fish manure compost product

Abstract

The invention discloses a vegetable hydroponic nutrient solution based on a fish manure compost product, which is prepared by the following steps: putting the fish manure compost product and water into a container with a cover, sealing the container, reacting in a dark place at room temperature for 3-4 days, and filtering to obtain an anaerobic vegetable hydroponic nutrient solution; a nutrient solution based on a fish manure compost product generates different responses to photosynthetic characteristics of hydroponic growth. Compared with a CK group, the nutrient solution provided by the invention has no significant difference (P is greater than 0.05) in influence on the photosynthetic characteristics of lettuce growth. The accumulated contents of chlorophyll and carotenoid in the nutrient solution provided by the invention respectively reach 0.34 mg / g.FW and 0.12 mg / g.FW. The higher chlorophyll concentration improves the photosynthetic ability of the lettuce, and the lower carotenoid concentration indicates that the lettuce is suffered from lower external stress during growth. The nutrient solution provided by the invention can increase the content of CAT, SOD, POD and flavonoid, which indicates that the addition of the nutrient solution provided by the invention can induce the generation of an antioxidant so as to reduce the influence of nutrient solution stress on the growth of lettuce. The nutrient solution is prepared from waste, the cost is low, the growth condition of lettuce is close to that of an existing nutrient solution, and the effect of recycling industrial planting and breeding waste is truly achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydroponic nutrient solutions for vegetables, and particularly relates to a hydroponic nutrient solution for vegetables based on fish manure compost products. Background Art

[0002] With the continuous increase in the cost of chemical fertilizers and people's concerns about the environmental pollution caused by chemical fertilizers, compost products have gradually received attention. Numerous studies have shown that solid compost used as organic fertilizer helps to increase and maintain the soil organic carbon level, improve the soil structure and water holding capacity, and reduce the number of pathogenic microorganisms and the occurrence of soil-borne viruses.

[0003] Compared with solid compost, the nutrient elements, humus and other nutrients in the compost extract exist in a water-soluble state, are more easily absorbed by crops and are more flexible in application (such as spray pipes, drip irrigation, foliar fertilizers, etc.). It is more suitable for the actual needs of current industrialized system aquaculture, such as the liquid nutrition requirements of the RAS hydroponic system.

[0004] The Recirculating Aquaculture System (RAS) can comprehensively apply technologies such as physics, biology, and chemistry in an industrial 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 conservation, pond conservation, high aquaculture density, and less influence from the external environment, and is the main development direction of aquaculture.

[0005] 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 NH 3 and NH 4 + -N will remain in the water body.

[0006] Fish manure has the characteristics of being easily dispersed, floating, and having a small particle size when soaked, making it difficult to separate from the aquaculture water body, resulting in relatively few studies on the resource utilization technology of RAS fish manure. 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 of 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, which is currently mainly treated by anaerobic fermentation. However, the low C / N characteristics of FS lead to limited 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, NH 4 + -N and NO 2 - -N in the aquaculture water body into less toxic NO 3 - -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 the cumulative concentration of NO 3 - -N can reach more than 100 - 1000 mg / L. High concentrations of NO 3 - -N (> 100 mg / L) can cause hypoxia in fish, affect the osmotic regulation mechanism, cause endocrine disorders, and damage the peripheral blood, gills and liver. Therefore, it is urgent to explore new technologies suitable for the resource utilization of FS in RAS. Summary of the Invention

[0007] The present invention aims to solve the technical problems existing in the prior art, and particularly innovatively proposes a hydroponic nutrient solution for vegetables based on fish manure compost products, which improves the photosynthetic ability of lettuce and the external stress on lettuce growth is relatively low.

[0008] To achieve the above object, the present invention provides a hydroponic nutrient solution for vegetables based on fish manure compost products. The fish manure compost products and water are placed in a container with a lid, the container is sealed, and the reaction is carried out in the dark at room temperature. After reacting for 3 - 4 days, the anaerobic hydroponic nutrient solution for vegetables is obtained by filtration;

[0009] The fish manure compost products are prepared according to the following method:

[0010] (1) Add fish manure and wheat straw to the fish manure rotary composting fermentation device described in any one of claims 1 - 3, adjust the carbon-nitrogen ratio, and add fish manure hydrothermal carbon;

[0011] (2) Before composting, while the fermentation box body is rotating, uniformly spray the compost leachate into the fermentation box body through the spray pipe to ensure that the moisture content of the compost pile is 55 ± 0.5%;

[0012] (3) The fermentation box body rotates once every 45 minutes, rotates for 5 minutes each time, and when rotating each time, open the ventilation holes to supplement oxygen;

[0013] (4) After the compost fermentation temperature is lower than 30 °C, use the compost leachate to adjust the moisture to 55 ± 0.5% again, put earthworms in for ripening. During the ripening process, rotate the fermentation box body once every 50 minutes, rotate for 5 minutes each time. During the rotation, open the cover plate to supplement oxygen from the ventilation holes.

[0014] The fish manure compost product of the present invention is a solid product after collecting the compost leachate.

[0015] In the above solution: the ratio of the fish manure compost product to water is 1:5 w / v.

[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, cool it to room temperature, centrifuge for solid-liquid separation, the liquid is the hydrothermal solution, and the solid is washed with water and alcohol and then dried to obtain the hydrochar.

[0018] In the above solution: the addition amount of the hydrochar is 5% of the total mass of the compost.

[0019] In the above solution: the carbon-nitrogen ratio is 25:1.

[0020] In the above solution: the vegetable is lettuce.

[0021] The fish manure rotary compost fermentation device includes a fermentation box body, and is 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 along the length direction of the rotating shaft, spray heads are evenly distributed on the spray pipe, 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. A syringe is arranged on the three-way valve for sampling gas, the feed inlet can be sealed, a valve is connected to the gas sampling port, and the valve is opened when sampling gas.

[0022] Both the end cover and the box wall of the fermentation box body have a sandwich structure, and a pearl cotton heat preservation 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. A handle is arranged on the fermentation box body.

[0023] All the air-permeable small holes are closely arranged in the middle of the end cover. A pin shaft is arranged above all the air-permeable small holes, and a cover plate is rotatably connected to the pin shaft. When the fermentation box body is rotated, 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, following the movement of the fermentation box body, the cover plate can be opened 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.

[0024] Through research, it is found that rotating the composting box for 5 minutes and then standing still for 45 minutes is the best air supplement method suitable for FS composting. By controlling the rotation frequency of the composting box, under this condition, the oxygen content in the compost pile shows an alternating change of "aerobic - anaerobic - aerobic", the relative abundances of microorganisms capable of decomposing lignin and fat are significantly increased, the formation of HS precursors is accelerated, the organic matter mineralization rate is reduced, the duration of maintaining a high temperature (≥50 °C) of the compost pile is extended, the compost seed germination rate is increased, and the energy consumption of rotating the composting box is reduced. 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 supplementation, the cumulative emissions of CO 2 equivalent greenhouse gases are reduced from 712.53 mg / kg·DM CO 2 e to 397.46 mg / kg·DM CO 2 e, and the emission reduction amount is 44.22%. By adjusting the moisture content with compost leachate and adding fish manure hydrochar as a water retention agent at the same time, the hydrochar reduces the water loss rate by improving the capillary water retention capacity of the compost pile, and only reduces by 4.81% within 16 days. It still remains above 50%, and the compost leachate does not need to be supplemented. At the same time, the degree of compost maturity and the seed germination rate are improved. The results of the cumulative emissions of greenhouse gases show that the addition of hydrochar reduces the cumulative emissions of greenhouse gases during the composting process, and is reduced by 47.29%, 65.75% and 73.29% respectively compared with the group without adding hydrochar and not replenishing water, the group only replenishing tap water and the group T3 only replenishing compost leachate. After fermentation, some limits of the compost product cannot meet the compost maturity regulations. Earthworms promote the conversion of proteins into fulvic acid and humic acid, improve the aromatization and humification degree of the compost product, and the seed germination rate of the compost reaches 98.4%, which is 13.1% higher than that of the group without earthworm composting treatment. Under the condition of coupling earthworm ripening, the complete ripening of FS can be achieved within 42 days, N 2 O, NH 3 、CO 2 and CH 4The emissions were reduced by 19.51%, 22.34%, 8.43% and 13.61% respectively compared with the group without earthworm addition. By means of burrowing, shredding food, and passing through the abdomen for transformation, earthworms increased the activities of key enzymes such as cellulase and urease in the compost heap, and increased the relative abundances of Chloroflexi, Bacteroidetes, and Patescibacteria in the compost. The results of KEEG analysis showed that the expression levels of amoA and hao were significantly increased under the optimal combination conditions, and the nitrogen metabolism levels related to NO 3 - -N reduction and NO 2 - -N oxidation and denitrification were significantly increased, and the nitrogen mineralization level was significantly reduced.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The nutrient solutions based on the fish manure compost products showed different responses to the photosynthetic characteristics of hydroponic growth. Compared with the CK group, there was no significant difference in the effect of the nutrient solution of the present invention on the photosynthetic characteristics of lettuce growth (P > 0.05). The cumulative contents of chlorophyll and carotenoid in the nutrient solution of the present invention reached 0.34 mg / g·FW and 0.12 mg / g·FW respectively. The higher chlorophyll concentration improved the photosynthetic ability of lettuce, and the lower carotenoid concentration indicated that the external stress on lettuce growth was lower.

[0027] (2) The nutrient solution of the present invention can increase the contents of CAT, SOD, POD and flavonoids, which indicates that the addition of the nutrient solution of the present invention can induce the production of antioxidants to reduce the impact of nutrient solution stress on lettuce growth. This nutrient solution is prepared from waste, with low cost, and its growth effect on lettuce is close to that of the existing nutrient solution, truly achieving the effect of recycling waste in industrialized planting and breeding. Description of the Drawings

[0028] Figure 1 is a schematic structural diagram of the fish manure rotary composting and fermenting device of the present invention.

[0029] Figure 2 is a physical diagram of the fish manure rotary composting and fermenting device of the present invention.

[0030] Figure 3 are the SEM (left) and FTIR (right) of hydrothermal carbon.

[0031] Figure 4 The corresponding relationship between the oxygen content of the compost and the rotation time.

[0032] Figure 5 is the display of the sampling points of the compost box.

[0033] Figure 6Oxygen content changes in different parts (A - E) of compost at different air - supplement frequencies and within one rotation period (F).

[0034] Figure 7 It is the temperature change of the compost pile during the composting fermentation process.

[0035] Figure 8 It is the pH change of the compost pile during the composting process.

[0036] Figure 9 It is the process of compost maturity change.

[0037] Figure 10 It is the seed germination rate of the compost product under different air - supplement methods.

[0038] Figure 11 It is N 2 O (A), NH 3 (B), CH 4 (C) and CO 2 emission rates and cumulative emissions during composting under different air - supplement conditions.

[0039] Figure 12 The influence of moisture regulation on the compost temperature.

[0040] Figure 13 The influence of different moisture regulations on pH.

[0041] Figure 14 The influence of hydrothermal carbon on the moisture state of compost.

[0042] Figure 15 It is the influence of moisture regulation on the compost seed germination index.

[0043] Figure 16 The influence of moisture regulation methods on the compost maturity.

[0044] Figure 17 It is N 2 O (A), CH 4 (B) and NH 3 emissions during composting under different moisture regulation methods.

[0045] Figure 18 Microbial community structure at the phylum (A) and genus (B) levels.

[0046] Figure 19 It is the influence of earthworms on the composting temperature.

[0047] Figure 20 It is the influence of earthworms on the pH during the compost ripening process.

[0048] Figure 21Changes 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.

[0049] Figure 22 Effect of earthworms on the seed germination rate of compost products.

[0050] Figure 23 Effect of earthworms on the maturity of compost products.

[0051] Figure 24 Changes in TN (A), NH 4 + -N and NO 3 --N (B), NH 4 + -N / NO 3 --N (C), NO 2 and NH 3

[0052] (D) during the compost ripening process.

[0053] Figure 25 Changes in CO 2 (A), CH4 (B), TOC concentration (C), DOC concentration (D), DOC proportion (E, F) during the compost ripening process.

[0054] Figure 26 Changes in the relative abundances of amoA (A) and hao (B) during the compost ripening process.

[0055] Figure 27 Schematic diagram and physical diagram of the hydroponic experiment device for the nutrient solution of the present invention.

[0056] Figure 28 Analysis of the photosynthetic characteristics of lettuce.

[0057] Figure 29 Are CAT activity (A), SOD activity (B), POD activity (C) and flavonoid content (D). Detailed implementation manners

[0058] The present invention will be further described below through examples in combination with the accompanying drawings:

[0059] The fish manure in the present invention is taken from the Factory Agriculture R & D Center of Chongqing Academy of Agricultural Sciences. The fish for breeding 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 filtration, the moisture content of the fish manure is about 65%, the COD is 17.32 ± 0.32 g / kg, the TN is 2.57 ± 0.13 g / kg, the NH 4 + -N is 0.34 ± 0.17 g / kg, and C / N = 8 - 10:1.

[0060] The compost leachate is taken from the liquid discharged from the drainage outlet of the compost bin during the composting process. Physicochemical index analysis

[0061] The results show that the concentrations of NH 4 + -N, NO 2 - -N and NO 3 - -N in the compost leachate are 176.43 ± 4.43

[0062] 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 NH 4 + -N and NO 2 - -N. Adding the compost leachate as a water replenisher back to the composting system 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.

[0063] Earthworms can use their rich enzyme systems (protease, lipase, cellulase, amylase, etc.) to quickly and thoroughly decompose organic waste into easily utilizable nutrients, thereby accelerating the compost ripening process. The earthworms used in the present invention are Eisenia fetida, which is an oligochaete of the Lumbricidae family in the order Opisthopora, also known as red earthworms. Because it has good adaptability to changes in environmental pH, temperature, and humidity, 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 environment for 24 h.

[0064] Example 1

[0065] 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, an octagon in the figure. The fermentation box body 1 is rotationally connected to a frame 3 through a rotating shaft 2. Specifically, the rotating shaft 2 is rotationally connected to the frame 3 through bearings. End covers 4 are arranged at both ends of the fermentation box body 1. Both the end covers 4 and the box wall of the fermentation box body 1 have sandwich structures, and EPE thermal insulation layers 5 are arranged in the sandwich structures. A three-way valve 6, a feed inlet 7, and a gas extraction 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 by a 100-mesh nylon net to prevent the excessive accumulation of leachate in the box body and the escape of earthworms during the earthworm ripening process. A syringe is connected to the three-way valve 6.

[0066] A residual liquid tray 10 for receiving the leachate discharged from the drain port is arranged on the frame below the fermentation box body. The residual liquid tray 10 is used for recovering the compost leachate. A spray pipe is arranged along the length direction of the rotating shaft, and nozzles (the spray pipe and nozzles are not specifically shown in the figure) are evenly distributed on the spray pipe. The compost leachate is pumped to the spray pipe by a pump and evenly sprayed through the nozzles. Vent holes 11 are distributed in the middle of the end cover. The vent holes 11 can be opened or covered by a rotatable cover plate 12. Specifically, the vent holes are closely arranged in the middle of the end cover. All the vent holes 11 enclose a circular ventilation area. A pin shaft is arranged above all the vent holes, and a cover plate is rotationally 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 vent holes.

[0067] Example 2

[0068] The fish manure rotary composting and fermenting method:

[0069] In this method, the composting and fermenting 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 with double-sided baking paint. 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, thus realizing 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.

[0070] (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 wheat straw is about 60:1, and adjust the carbon-nitrogen ratio 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.

[0071] Hydrochar has a large specific surface area and surface functional groups, and is also a potential water retainer. A large amount of Ca remaining in fish manure 2+ and citric acid can further improve the water retention capacity of hydrochar. Therefore, in this invention, hydrochar was prepared from FS, the solid hydrochar was used as a water retainer and added to the composting system, and the hydrothermal liquid obtained from the hydrothermal reaction was used as a supplementary water liquid for compost moisture regulation research.

[0072] Preparation of fish manure hydrochar:

[0073] Use a high-pressure reactor with a stirring device to prepare fish manure hydrochar. Weigh about 600 g of well-stirred FS into a high-pressure reactor with a total volume of 1.5 L, seal it, heat it up to 200 °C, set the stirring speed to 100 rpm / min, take it out after 2 h, and cool it to room temperature. Obtain the solid and liquid parts by centrifugation respectively. The liquid part is stored in a 4 °C refrigerator for later use, and the solid part is dried at 60 °C for 12 h after being washed with water and ethanol several times, and stored in a dry place for later use. Analysis of physical and chemical indicators shows that the concentration of NO 3 - -N in the hydrothermal liquid is 604.3±23.11 mg / L, NO 2 - -N is 12.8±1.32 mg / L, NH 4 + -N is 46.2±2.63 mg / L, pH = 6.13±0.32, C / N = 13.52:1. The SEM of the hydrochar is as Figure 3 shown on the left, presenting irregular fragmentary shapes, with a rough surface and a large number of convex and concave structures; the specific surface area of the hydrochar is 10.32 m 2 / g, the carbon content is 34.24%, the pore volume is 0.18 cm 3 / g, and it is rich in C-O and C=O functional groups (as Figure 3 shown on the right). Toxicity analysis experiments of the hydrochar extract and the hydrothermal liquid show that the germination rates of lettuce seeds are 86.3% and 91.6% respectively, which are greater than 70%, indicating that the hydrochar and the hydrothermal liquid are non-toxic and will not be harmful to the growth of microorganisms in the composting system.

[0074] (2) Before composting, with the fermentation box body in a rotating state, uniformly spray the compost leachate into the fermentation box body through the spray pipe (during the first composting, make up with water, then collect the compost leachate after the composting is completed and use it for the next batch of composting. After each batch of composting is completed, collect the compost leachate for subsequent composting, and so on), so as to ensure that the moisture content of the compost pile is 55 ± 0.5%;

[0075] (3) The fermentation box body rotates once every 45 minutes for 5 minutes each time. When rotating each time, open the ventilation holes to supplement oxygen. After the rotation is over, close the cover plate to cover the ventilation holes, and the rotation speed is 30 - 40 rpm. In the present invention, due to the addition of fish manure hydrochar, during the fermentation process, the moisture content can be maintained above 50%, so no water needs to be supplemented during the fermentation period.

[0076] (4) When the composting fermentation temperature is lower than 30 °C, use the compost leachate to adjust the moisture to 55 ± 0.5% again, and put 150 earthworms for maturation. 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 hours. During the maturation 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 ventilation holes. When the rotation stops, close the cover plate to cover the ventilation holes, and the rotation speed is 30 - 40 rpm.

[0077] I. The present invention designs 5 groups of control experiments, namely the fermentation box body does not rotate (A), rotates for 5 minutes and stands still for 25 minutes (B), rotates for 5 minutes and stands still for 35 minutes (C), rotates for 5 minutes, stands still for 45 minutes (D), and continuous mechanical air supplementation (E). After the compost pile is evenly dispersed, the total thickness is about 21 cm, and it is evenly divided into 3 parts: upper, middle, and lower parts. Supplement a certain amount of tap water through the spraying device to control the moisture content of the compost pile at 55 ± 0.5%. During the composting process, intermittent rotation and air supplementation of the compost box are realized by adjusting the start and stop times, and the rotation speed is controlled at 30 rpm. It is found in the preliminary experiment that after rotating for 5 minutes, the O 2 content in the compost pile gradually increases to a stable state (as Figure 4 shown). When the interval time exceeds 45 minutes, the compost pile is tightly compacted and it is impossible to mix the materials 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 pile, 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 3 times, and take the average value to represent the oxygen content of the compost pile; every 2 days, at a fixed time (10:00 am), draw 25 mL of gas through a syringe with a three-way valve for testing N 2 O, CH 4 , NH3 and CO 2 Production; After taking 50 g of compost samples from the upper, middle, and lower parts of the compost and mixing them evenly, part of the compost was dried at 60 °C for the determination of the contents of pH, EC, TN, FA, etc. Part of the fresh samples was sealed and stored in a 4 °C refrigerator for the determination of seed germination rate, and part was stored in an -80 °C refrigerator for the analysis of microbial community structure.

[0078] By controlling the rotation and air supply frequency of the composting box, the effects of the rotation of the composting box body on the oxygen content in the upper, middle, and lower parts of the compost pile were studied. 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 6 C) first decreases and then increases. At the 5th day, the oxygen content in the middle part of the compost is higher than the oxygen limit of aerobic composting by 10% (11.4%), but the oxygen contents in the lower and upper parts are 8.1% and 9.8% respectively. At the end of composting, the oxygen contents in all parts of the compost pile are greater than 14%; the oxygen contents in the upper, middle, and lower parts of the compost in the D treatment group ( Figure 6 D) at the 5th day and 10th day are 4.3%, 7.4%, 5.5% and 2.3%, 3.8%, 3.4% respectively, all lower than 10%; the E treatment group ( Figure 6 E) continuously supplies air, and the oxygen content in the compost pile is 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 the B and E treatment groups are always greater than 10%, which is related to the high air supply frequency in the B treatment group and timely oxygen supplementation, as well as continuous air supply in the E treatment group. At the same time, the oxygen content in the middle part of the compost pile is always higher than that in the lower and upper parts during the composting process because the air inlet of the rotating composting box is mainly set in the middle of the side of the box body. When the box body rotates, oxygen mainly enters the box through the middle air inlet, resulting in a higher oxygen content in the middle part of the box body than in the lower and upper parts.

[0079] At the end of composting, the oxygen contents in the B, C, and D treatment groups are all greater than 10%. This may be related to the fact that at the end of composting, the microbial activity decreases and the moisture in the compost pile is lost, resulting in the compost pile becoming fluffy, improving the oxygen transfer efficiency in the compost pile, and reducing the oxygen consumption rate.

[0080] The oxygen content in 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 supply cycle (calculated as 50 min) 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 the oxygen content 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 transmission 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 static 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, static for 25 minutes, and continuous mechanical air supplementation are always in the aerobic composting process.

[0081] As Figure 7 shown. The composting 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. 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.

[0082] 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 static for 25 minutes, the temperature during the high-temperature period of the compost 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.

[0083] Under the conditions of rotating for 5 min and standing for 45 min, although the highest temperature of the compost heap 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 d. This may be related to the extended rotation interval, which led to the compaction of the compost heap 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 heap. As the composting process progressed, the temperature in the E treatment group fluctuated greatly. This was related to the fact that the continuous air supplementation treatment group mainly achieved uniform mixing of materials through manual turning, resulting in compaction of the compost heap 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 composting fermentation could be met. The temperature was the highest under the conditions of rotating for 5 min and standing for 25 min, but a shorter rotation 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 box was avoided, and the duration of high temperature during composting was extended, and compost sterilization could also be achieved.

[0084] As Figure 8 shown, during the high-temperature period of composting, at different air supplementation frequencies, the increase in pH may be caused by the mineralization and ammonification reactions of organic acids in the compost heap. The pH of the E treatment group decreased on the 10th day of composting, which was related to the fact that sufficient oxygen promoted the volatilization of NH 3 . From the 10th day, the pH of the B, C, D, and E treatment groups was stably maintained between 7.54 - 8.13. This may be because the humic acid produced in the later stage of composting played a certain buffering role. At the end of composting fermentation, the pH of the compost heap 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 NH 4 + -N to NH 3 and the conversion of NH 3 to the atmospheric environment.

[0085] 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 was 1.5 - 1.9, it indicated that the compost was mature. Compared with continuous air supplementation, intermittent air supplementation was more conducive to the composting fermentation process. Among them, under the air supplementation frequency of rotating for 5 min and standing for 45 min, the degree of maturity of the composting fermentation product was higher. This may be related to the fact that the duration of high temperature during composting was the longest under this condition, which promoted the degradation of dissolved organic matter by microorganisms, but still could not meet the quality requirements of the compost product and needed further ripening.

[0086] As Figure 10As shown, the seed germination indices of the compost products at 5 rotational air-supplement frequencies were 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 was greater than 70%. When rotating for 5 minutes and standing for 45 minutes for air supplementation, the molecular weight of humic acid was smaller, which was easier to penetrate the cell wall of plant roots and was transported and exchanged on the cell membrane of root cells, so as to be absorbed and utilized by plant roots.

[0087] As Figure 11 shown in Table 1

[0088] Table 1 Changes in carbon dioxide equivalent under different air-supplement conditions

[0089]

[0090] The CO 2 equivalent emissions (CO 2 equivalent emissions, CO 2 e) of each treatment group were 151.81 g / kg·DM CO 2 e, 573.53 g / kg·DM CO 2 e, 461.44 g / kg·DM CO 2 e, 397.46 g / kg·DM CO 2 e and 712.53 g / kg·DM CO 2 e respectively. Except for treatment group A in the "dead bed" state, the greenhouse gas CO 2 e was the smallest under the air-supplement frequency of supplementing air for 5 minutes and standing for 45 minutes in treatment group D, and the impact on the atmospheric environment was relatively small.

[0091] Moreover, the abundances of biomarkers with lignin and fat decomposition such as Actinomycetes, Clostridium, Tepidimicrobium, and Atopobium in treatment group D were much higher than those in treatment groups B and C, which could accelerate the formation of HS precursors, promote the formation of HA in the compost maturity stage, and reduce the mineralization rate of organic matter and the generation of greenhouse gases (CO 2 and CH 4 ).

[0092] II. Effects of water regulation methods on the composting process and product quality

[0093] Before composting began, the moisture content of the compost pile with adjusted C / N was adjusted to 55% by spraying different water replenishing liquids while the compost bin was rotating. Four treatment groups were set up for the moisture control 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.

[0094] 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 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 re-adjusted to 55% by supplementing different water replenishing liquids. Before composting began, 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 N 2 O, CH 4 、NH 3 and CO 2 production; 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, mixed evenly, and stored in a -80 °C refrigerator for microbiomics-related analysis.

[0095] Such as Figure 12As shown in the figure, 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). The maintenance times at the temperature for inactivating pathogenic microorganisms (>55 °C) were T6 (8 d) > T3 (5 d) > T4 (3 d) = T7 (3 d) > T5 (2 d) > T2 (0 d) = T1 (0 d). 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 large amount of nutrients in T3 and T4. After reuse, they could provide more nutrients directly available for microorganisms in composting. At the same time, the rich microorganisms in T3 were re-inoculated into the composting system, which helped 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 group had the longest high-temperature maintenance time, indicating that recycling the compost leachate to the composting system helped extend the high-temperature stage of composting and the ability to inactivate pathogenic microorganisms, which was beneficial for the subsequent resource utilization of composting. 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 large specific surface area of hydrochar increasing the attachment ability of microorganisms and improving the relative abundance of microorganisms in the compost pile. Generally speaking, the hydrochar + compost leachate treatment group had significant advantages in increasing the composting temperature and maintaining the high temperature of composting.

[0096] The change in pH can reflect the process of organic matter degradation during composting. The change process of pH during composting is as Figure 13 shown. It can be seen from the figure that during the temperature-rising stage of composting under the action of T2, T3, and T4, 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 adding 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 under the action of microorganisms to produce NH 3 . The increase in pH in the later stage may be related to the production of organic acids under the action of nitrification decomposition of ammonia nitrogen and other compounds and the decomposition of organic matter. After adding hydrochar, the pH of the compost decreased because hydrochar reduced the mass transfer of water and air and inhibited the decomposition of organic acids.

[0097] The influence of water regulation methods on the moisture content and water state of compost

[0098] As shown in Table 2.

[0099] Table 2 Compost moisture change rate during the composting process

[0100]

[0101] As can be seen from the table, in the treatment groups of T1, T2, T3, and T4, the moisture content decreased to below 50% within every 2 days and re - watering was required. Meanwhile, the moisture change rate during the compost heating period and high - temperature period was significantly higher than that during the compost cooling period. Compared with the one - time watering method of the T1 treatment group, the multiple - stage segmented watering of the T2 treatment group significantly reduced the moisture change rate of the compost pile within every 2 days. Compared with the T2 treatment group, the multiple - stage segmented addition of compost leachate (T3) and hydrothermal solution (T4) further reduced the moisture change rate during the composting process. After adding hydrochar, the moisture change rate of the compost pile decreased significantly, and the moisture change rate within 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 require watering, while the other groups all required watering.

[0102] 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 compost pile temperature 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 - retaining ability 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 CO 2 and water. After adding hydrochar, the water - retaining abilities of the compost piles in the T5, T6, and T7 treatment groups were significantly higher than those of the T1, T2, T3, and T4 treatment groups, indicating that hydrochar has good application potential in maintaining the moisture of organic waste compost. The better water - retaining performance of hydrochar is also related to the large amount of calcium ions existing in the FS. Calcium ions can regulate the osmotic pressure in the cell membrane and intracellular fluid, improving the overall water - retaining ability inside and outside the cells. Generally speaking, the hydrochar + compost leachate treatment group (T5) has the best effect on maintaining the moisture stability of the compost pile.

[0103] The state of water in the mixed organic system is affected by different binding forces, which are in turn influenced by the moisture content, chemical composition, and physical structure of the environment where the water is located. Controlling the binding forces to regulate the water state and water content in the composting system is of great significance for optimizing the water replenishment strategy. To determine the effect of adding hydrochar on the state of water 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 14 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 water state during the composting process. During the entire composting process, the content of MMLW remained at a low level for a long time and was always maintained 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. The research shows that the order of the binding forces 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 the balance of water content

[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 converting 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 water fixation ability.

[0104] As Figure 15 shown, the seed germination rate of T1 at the end of composting was 59.3%, which was 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%,

[0105] 83.08%, 87.72%, and 83.37% respectively, indicating that the compost products had high safety and reliability. Compared with the air-supplementing method, changing 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.

[0106] The results are as Figure 16 and Table 3 shown.

[0107] Table 3 Comparison of compost maturity parameters

[0108]

[0109] EC can directly reflect the salt content of compost products and indicate whether the final compost products 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 16 shown. It can be seen from the figure that the EC of the compost pile shows a trend of increasing first and then decreasing. Among them, the EC of T3 and T4 increases 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 rises slowly in the first 1-2 days of composting and gradually decreases to a relatively stable state in the later stage of composting. The EC of the T3 and T4 treatment groups increases rapidly during the composting heating period and the high-temperature period, which may be related to the rapid mineralization and degradation of organic matter in the compost pile into small-molecule substances. The decrease in EC in the later stage of composting may be related to the volatilization of organic acids and NH 4 + -N, the precipitation of mineral salts, and the directional humification of small-molecule components. The EC of the T5, T6, and T7 treatment groups remains stable in the later stage of composting, which may be due to the adsorption or coprecipitation reaction between hydrothermal carbon and the water-soluble salts produced by the degradation of organic matter. At the end of composting, the EC of the compost products is 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 pile 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 decreases with the progress of composting. At the end of composting, the degradation rates of FA in each treatment group are 24.32%, 30.27%, 55.24%, 45.87%, 52.71%, 58.55%, and 56.19% respectively. Different from the change law of FA, HA continuously increases throughout the composting process. At the end of composting, the HA contents of T1, T2, T3, T4, T5, T6, and T7 are 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 accelerates the degradation of FA during the composting process. Among them, the degradation of FA in the T6 treatment group is the most obvious. A large number of microorganisms in the compost leachate are re-inoculated into the composting system, increasing the relative abundance of microorganisms conducive to the degradation of FA and the hydrothermal carbon providing a suitable growth environment for the growth of microorganisms.

[0110] 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 greater the HA / FA, the better the safety of the compost products. During the composting process, the change process of HA / FA in each treatment group is as shown in Figure 16 Figure D. As can be seen from the figure, with the progress of composting, 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 hydrochar addition, the HA / FA of the T6 compost heap is the highest, which indicates that the addition of 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 the addition of hydrochar helps to maintain the moisture of the compost heap, improve the degree of polymerization of compost products, and accelerate the maturity of compost. In order to further evaluate the maturity of compost products, the C / N and E4 / E6 of compost products 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 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 further maturity. The results of seed germination rate, HA / FA, etc. show that the T6 treatment group has a more obvious promotion effect on compost maturity.

[0111] The emissions of N 2 O under different moisture regulation methods were monitored, and the results are as shown in Figure 17 Figure. In the early stage of compost fermentation, the N 2 O emissions remained at a low level. When the compost entered the high-temperature period and the cooling period, the N 2 O 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 N 2 O was relatively low, which may be related to the inhibition of the growth of nitrifying bacteria and denitrifying bacteria during the heating period and high-temperature period of composting.

[0112] In the later stage of composting, the production of N 2 O increased rapidly, which may be related to the decrease in the temperature and pH of the compost heap in the later stage of composting, the dominance of nitrifying bacteria, and NH 4 +-N gradually turns into NO 3 - -N transformation. Compared with the T1 and T2 treatment groups, the cumulative emissions of N 2 O in the T3 treatment group increased significantly during the later stage of composting because the main components in the compost leachate were NO 2 - -N and NH 4 + -N and other nitrogen-rich substances. As a by-product of nitrification or an intermediate substance in denitrification, NO 2 - -N greatly increased the content of available nitrogen during the reaction process, thus promoting the production of N 2 O. At the same time, the alternation of relatively dry and re-wetting of the compost pile would also cause an increase in the availability of carbon and O 2 consumption in the compost pile, and then cause an increase in N 2 O emissions. The main nitrogen-rich substance in the T4 treatment group was NO 3 - -N. During the denitrification process, NO 3 - -N and N 2 O would compete with each other as terminal electron acceptors, inhibiting the activity of N 2 O reductase, and then causing a decrease in the content of N 2 O. No large emissions of N 2 O were detected in the T5, T6, and T7 treatment groups during the composting stage, which was related to the good adsorption and fixation ability of hydrothermal carbon for gases. CH 4 is also an important greenhouse gas and one of the main by-products generated during the anaerobic process of organic waste, with a GWP 25 times that of CO 2 . The variation law of CH 4 during composting is as shown in Figure 17 B. CH 4 was mainly produced during the high-temperature stage of composting. The production time of CH4 in the T5, T6, and T7 treatment groups was earlier than that in the T1, T2, T3, and T4 groups. During the entire composting stage, the cumulative emissions of CH 4 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. CH 4It is produced in large quantities during the high-temperature stage of composting. This is because as the temperature and pH of the compost pile increase, the activity of thermophilic microorganisms enhances, 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 forms in some areas. In the later stage of composting, the CH 4 emission decreases, 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 CH4 yield of 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, which makes it easier for the compost pile to form an anaerobic environment, resulting in CH 4 caused by low oxidation. With the continuous addition of nitrogen-rich substances, the cumulative yield of CH 4 within 2 days gradually decreases, which is related to the inhibition of the activity of methanogens with the increase of ammonia volatilization and NH 4 + -N concentration. The generation time of CH 4 in the T5, T6, and T7 treatment groups is earlier than that in the T1, T2, T3, and T4 treatment groups. This is related to the rich specific surface area of hydrothermal carbon providing a good living environment for thermophilic microorganisms, resulting in enhanced activity of thermophilic microorganisms, increased oxygen consumption, and the formation of an anaerobic environment in advance. Combining the N 2 O and CH 4 emissions of each treatment group, the cumulative greenhouse gas emissions of each treatment group are 22.61 g / kg·DM CO 2 e, 34.83 g / kg·DM CO 2 e, 44.66 g / kg·DM CO 2 e, 27.01 g / kg·DM CO 2 e, 16.26 g / kg·DM CO 2 e, 11.93 g / kg·DM CO 2 e, 14.08 g / kg·DM CO 2 e.

[0113] During aerobic composting, due to the decomposition of organic matter, nitrogen is inevitably lost in the form of NH 3 , which will not only reduce the agricultural value of the compost but also have an adverse impact on the surrounding environmental sanitation due to the odor generated. The emission pattern of NH 3 during composting is as shown in Figure 17 C. The emission of NH 3 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 cumulative NH 3 emission of the T3 treatment group is the highest. At the end of composting, the NH 3The cumulative emissions were 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. In the T1 treatment group, NH 3 The lowest cumulative emissions may be related to the rapid drying of the compost pile during the composting process in T1. In T3, NH 3 The highest cumulative emissions are related to the high moisture content of the compost pile, which causes NH3 to dissolve in water in the form of NH 4 + -N, and the continuous reuse of the leachate leads to the accumulation of NH 4 + -N and the gradual increase in pH in the compost pile. In T4, the lower NH 3 emissions are related to the decrease in the pH of the compost pile due to the access of hydrothermal liquid. In the T5, T6, and T7 treatment groups, the NH 3 cumulative emissions are lower than those in the T2, T3, and T4 treatment groups. Hydrothermal carbon can absorb part of the NH 4 + -N, reduce the physiological toxicity of NH 4 + -N to nitrifying bacteria, and improve the nitrogen fixation ability of the compost pile.

[0114] As shown in Table 4, during the composting process, the microbial abundance and temperature showed an opposite trend of change. During the composting heating stage, 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 thermophilic bacteria became the dominant bacteria, resulting in a decrease in the richness and diversity of bacteria in the compost pile. During the composting cooling period, 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 is helpful to improve the abundance and diversity of bacteria in the compost. Compared with the multiple water replenishment methods, the water-retaining method of hydrothermal carbon is more conducive to maintaining the abundance and diversity of bacteria in the compost pile.

[0115] Table 4 OTU values at different composting stages

[0116]

[0118] Figure 18A shows the changes in the microbial community structure at the phylum level during the composting process under different moisture regulations. The results show that Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes are the main bacterial phyla. Among them, Actinobacteria can promote microorganisms to produce more lignocellulose-degrading enzymes, especially cellulase, to promote the degradation of organic matter. At the same time, Actinobacteria can also secrete antibiotics to inhibit the growth of pathogenic bacteria. During the high-temperature period of composting, the relative abundance of Actinobacteria in each experimental group is relatively low, and the abundances are in the order of T5 (42.4%) > T7 (41.1%)

[0119] > T4 (37.6%) > T6 (35.4%) > T2 (34.1%) > T3 (32.1%) > T1 (24.5%). Comparing the temperature change trend 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 is always greater than 30%, indicating that Actinobacteria play an important role in the composting process. The relative abundance of Firmicutes is relatively high in 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. The relative abundance of Firmicutes decreased to 13.5%, 22.3%, 24.1%, 18.4%, 21.3%, 23.4%, and 15.5% respectively during the cooling stage of composting, 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. During the entire 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 multiple water replenishment method, the "hydrothermal carbon + one-time water replenishment" combination method can better increase the relative abundances of Actinobacteria and Firmicutes in the compost. On the one hand, the rich porosity of hydrothermal carbon provides a "shelter" for Actinobacteria to protect it from the adverse effects of high temperatures. At the same time, it is also related to the higher porosity of hydrothermal carbon increasing the ventilation and water retention capacity of the compost pile and 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 Figure 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 the phylum 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 content, 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 in the compost liquor into the composting system to form a cyclic inoculation system, improving the ability of the compost pile to resist the external environment.

[0120] III. In order to achieve the complete maturity of the compost product, further research on earthworm maturation of the compost fermentation product was carried out.

[0121] After the temperature of the compost fermentation product in the rotary composting bin drops to 30 °C, the moisture content of the compost pile is readjusted to 55 ± 0.5% using compost leachate. The experiment was respectively set up with an earthworm ripening treatment group (T1) and a natural ripening treatment group (CK). 150 earthworms without reproductive rings that had adapted to the dark environment for 24 h were introduced into the earthworm ripening treatment group. During the earthworm compost ripening process, the air supply frequency of the composting bin was to rotate for 5 min every 50 min, and the rotation speed of the composting bin was 30 rpm.

[0122] 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 for 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 under the optimal air supply frequency, the evaporation of moisture in the compost pile was accelerated, and local or temporary water shortage inhibited the microbial activity, resulting in a decrease in the heat production rate of the compost pile; while under the optimal water supply conditions, although the nutrient concentration in the compost pile and the relative abundance of compost microorganisms increased, continuous air supply led to an increase in the heat dissipation rate of 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 difficult-to-degrade 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.

[0123] 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 composting on the 42nd day. After adding earthworms, the compost pH could reach 8.79 and dropped to 8.04 at the end of composting 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 NH 4 + -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 NH 4 +-N is released through nitrification, resulting in 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 fact that earthworms can increase the growth rate and activity of microorganisms in the compost, 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. In the later stage of vermicomposting, physiological processes such as earthworm feeding and burrowing increase the porosity of the composting system, promote gas exchange between the compost and the outside world, and to a certain extent inhibit the occurrence of denitrification, resulting in a decrease in the pH of the compost.

[0124] 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 after earthworm digestion and excretion. The addition of earthworms increases the activity of enzymes related to compost maturity, promotes the further maturity of the compost, and improves the safety of the compost product.

[0125] As Figure 22 , during the composting process, microorganisms will decompose to 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 the compost product and its potential threat to the environment, and is an important indicator for evaluating the safety of the compost product. 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 with the single methods of aeration and water adjustment, and the seed germination rate increases 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 needed 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 that of the vermicomposting treatment group is 98.4%. This indicates that the addition of earthworms further improves the transformation of toxic and harmful substances during the composting process, and improves the safety and reliability of the compost product. EC is often used as an index for the content of soluble salts (such as Na + , K + , Cl - , SO 4 2- , NO 3 - etc.) in the reactor compost, which is closely related to the degradation of organic matter during the composting process and is a parameter for evaluating the maturity of the compost and the potential toxicity to 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 process, 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 the vermicomposting stage, the 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 the vermicomposting process 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 degree of condensation and aromatization of humic acid

[250] . This value decreases with the increase in the degree of condensation 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, the E4 / E6 of the non-vermicomposting treatment group 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. For the vermicomposting treatment group, the E4 / E6 of the compost pile continuously decreased. The continuous increase in E4 / E6 during the composting process was related to the continuous decrease in the degree of humification and aromatization of organic matter under the action of mineralization in the early stage of composting fermentation. During the vermicomposting stage, the E4 / E6 of the vermicomposting treatment group continuously decreased, which 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 the composting process. The change processes of HA, FA, and HA / FA during the compost maturity process are respectively as follows Figure 23As shown in C of [ID] and D of [ID]. During the composting and maturation 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 - treated compost 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 - matured treatment group increased by 17.24% compared to 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 - humus parts in fish manure, which transformed into HA. The HA in the earthworm - matured 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. Throughout the composting and maturation process, the HA / FA showed an increasing trend. During the composting stage, HA / FA increased from 0.79 to 1.5. During the earthworm - matured stage, HA / FA in the earthworm - treated compost group increased to 2.78, much higher than 1.94 in the non - earthworm - added treatment group. The above experiments showed that the addition of earthworms during composting could significantly increase the degradation of FA or non - humus substances, promote the formation of stable HA during composting, and improve the maturity of compost products.

[0126] As shown in Table 5.

[0127] Table 5 Pathogen content in each experimental group at the end of composting

[0128]

[0129] Note: The number of fecal coliforms and the mortality rate of Ascaris eggs were determined according to the provisions of GB / T19524.1 and GB / T19524.2 respectively. NA indicates not detected.

[0130] 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 at the end of composting and maturation. This indicated that the addition of earthworms was of great significance in pathogen removal, ensuring 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 their body surfaces, thus improving the harmlessness level of compost. At the same time, the hydrothermal carbon added in the earthworm - treated 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 vital activities 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.

[0131] During the FS composting and maturation process, the change rule of TN was as Figure 24As shown in Figure A. It can be seen from the figure that during the composting fermentation stage, the TN continued to increase, while during the vermicomposting maturation stage, the TN in the treatment group with added earthworms decreased rapidly. The continuous increase of TN during the composting fermentation process 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 continuous decomposition of a large amount of soluble organic matter in fish manure. At the same time, the nitrogen produced by earthworm excrement is lost in the form of NH 3 、N 2 O, etc. or retained in the earthworms, which will also cause nitrogen loss in the compost. When the fish manure composting ended, 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.

[0132] The change process of NH 4 + -N during the composting process is as shown in Figure B. Different from the TN change rule, NH Figure 24 -N in the composting fermentation process first increased and then decreased, and NH 4 + -N continued to decline to the lowest point and then slowly rebounded during the vermicomposting maturation stage. The increase of NH 4 + -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 NH 4 + -N collected by the gas collection bag during the composting process gradually increased, indicating that NH 3 in the compost pile was gradually converted into NH 4 + 3 . When the composting ended, the content of NH 4 + 3 -N was 356 mg / kg, less than 400 mg / kg, indicating that the compost product had been matured.

[0133] During the composting fermentation stage, the concentration of NO 3 - -N first decreased and then increased rapidly. During the vermicomposting maturation stage, NO3--N showed a continuous increase to stability. The decrease in the concentration of NO 3 - -N may be related to the inhibition of nitrifying bacteria by high-concentration NH 4 + -N at the initial stage of composting, resulting in the hindrance of the conversion of NO 2 - -N to v. During the vermicomposting maturation stage, the concentration of NO 3 - -N gradually increased, which was related to the improved tolerance and abundance of nitrifying bacteria in the compost pile, increasing the NH 4+ -N is assimilated into NO 3 - -N. At the end of the reaction, the v concentration in the earthworm composting treatment group was 1159.42 mg / kg, which was 23.92% higher than that in the treatment group without earthworms.

[0134] During composting, N 2 The emission of O not only causes nitrogen loss during composting, but also leads to serious air pollution. During composting, N 2 The change of O is as Figure 24 shown in C. The content of N2O was low in the initial stage of compost fermentation. With the increase of compost temperature, the emission of N 2 O increased rapidly. When the compost entered the high-temperature stage, high temperature, high NH 4 + -N and high pH inhibited the normal progress of nitrification reaction, and the cumulative concentration of NO 3 - -N was low and not enough to form N 2 O emission. In the cooling stage of compost fermentation, the inhibition of nitrification reaction was released, and the emission rate of N 2 O increased significantly. Compared with the treatment without earthworms, the addition of earthworms reduced the emission of N 2 O 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 progress of denitrification reaction. The high adsorption capacity of mature compost can also reduce the emission of N 2 O to a certain extent. At the end of composting, the cumulative emission of N 2 O in the experimental group was 143.35 mg / kg·DM, which was 19.51% lower than the cumulative emission of 171.30 mg / kg·DM in the blank group. The emission of NH 3 is mainly caused by the strong mineralization of organic nitrogen to NH 4 + -N, and it will be further promoted under high temperature and alkaline environment for the conversion of NH 4 + -N to NH 3 of. As shown by Figure 24 D, the emission of NH 3 has a certain lag compared with N 2 O emission. Generally, it begins to increase on the 5-6th day of the compost fermentation stage and reaches the maximum value when the compost pile reaches the high-temperature stage (9-10d). With the decrease of the temperature of the compost pile, NH 3The emission rate also showed a downward trend. Different from the continuous decrease in NH3 emissions in the control group, the NH3 emissions in the earthworm maturation stage first increased rapidly and then decreased, which may be related to the increase in the pile pH after the addition of earthworms. In the later stage of compost maturity, with the improvement of the pile porosity under the action of earthworms and the high adsorption performance of mature compost, the NH 3 emissions gradually decreased. In addition, the addition of earthworms promoted the increase in the abundance of nitrogen-fixing related functional microorganisms. At the end of the reaction, the cumulative NH 3 emissions in the experimental group were 4.93 g / kg·DM, which was 22.34% lower than the cumulative emissions of 6.03 g / kg·DM in the blank group.

[0135] As Figure 25 shown, by comparing the DOC ratio in the pile at the end of composting, the protein content in the earthworm compost group was 7.26% lower than that in the group without earthworms, and the contents of fulvic acid and humic acid increased by 3.18%. The above results indicate 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.

[0136] Table 6 Relative abundances of dominant bacterial phyla (>1%) during composting

[0137]

[0138] 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 98% of the total ASV abundance during the vermicomposting stage. 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 anaerobic, 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. 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 were increased.

[0139] As Figure 26 shown, the relative abundances of amoA and hao first increased and then decreased with the progress of 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 was stronger under the optimal composting conditions.

[0140] Example 4

[0141] Compared with solid compost, nutrients such as nutrient elements and humus in compost extract exist in a water-soluble state, are more easily absorbed by crops, and are more flexible to apply (such as sprinkler irrigation, drip irrigation, foliar fertilizer, hydroponics, etc.). It can quickly and intuitively reflect the performance of compost products and is the main way to evaluate the performance of compost products. Since the extraction method of compost extract will significantly affect the performance of compost extract products, therefore, according to whether O is introduced during the extraction process of compost extract, the present invention 2 studied the effects of aerated compost tea (ACT), non-aerated compost tea (NCT), and direct compost tea (DCT) as nutrient solutions on the growth performance of lettuce. The extracts were all used within 24 hours after preparation or stored in a 4°C refrigerator for later use. The extraction methods are as follows:

[0142] (1) Preparation of anaerobic extract (NCT): The compost product (the solid product obtained after fermenting and decomposing fish manure compost and extracting the leachate) and water were put into a plastic bucket with a lid at a ratio of 1:5 (w / v). The bucket mouth was sealed and placed in the dark at 25°C for 3 days of dark reaction (light avoidance reaction). After filtering through double-layer gauze, the filtrate was collected to obtain the non-aerated extract as the nutrient solution..

[0143] (2) Preparation of aerated extract (ACT): The compost product (the solid product obtained after fermenting and decomposing fish manure compost and extracting the leachate) and water were added to a plastic bucket at a ratio of 1:5 (w / v). An air pump was used to aerate the bucket evenly to maintain the dissolved oxygen content in the bucket higher than 6.0 mg / L. After dark cultivation (light avoidance cultivation) at 25°C for 3 days, the filtrate was collected by filtering through double-layer gauze.

[0144] (3) Preparation of direct extract (DCT): The compost product (the solid product obtained after fermenting and decomposing fish manure compost and extracting the leachate) and water were fully mixed at a ratio of 1:5 (w / v), continuously stirred for 20 minutes, and after standing for 10 minutes, the filtrate was collected by filtering through double-layer gauze.

[0145] The physical and chemical properties of the extracts obtained by different extraction methods and the existing Yamazaki nutrient solution (CK) are shown in Table 7:

[0146] Table 7 Physical and chemical parameters of different compost extracts and Yamazaki nutrient solution

[0147]

[0148] The pH values of ACT and DCT are close, and the pH of NCT is the highest, but the pH values of all compost extracts are between 7.34 and 7.89. The EC of the NCT treatment group is 5.73 ms / cm, which is 20.59% and 11.69% higher than that of DCT and ACT respectively, indicating that the anaerobic extract contains more electrolytes or ions. Total water-soluble organic carbon (TWSOC) is the organic carbon that can be directly utilized by soil microorganisms and has an important impact on the transformation, migration, and degradation of organic and inorganic substances in the soil. The content of TWSOC in NCT is significantly higher than that in DCT and ACT, increasing by 26.96% and 9.85% compared to DCT and ACT respectively. Nitrogen is an important component of chlorophyll and the main component of proteins and enzymes in crops. There are significant differences in the TN content between NCT and DCT and ACT (P < 0.05), which are 337.32 mg / L, 306.76 mg / L, and 275.13 mg / L respectively. Phosphorus is an essential element for forming nuclear protein and lecithin, which can accelerate cell division and promote the accelerated growth of roots and above-ground parts. The TP content in NCT has increased significantly, being 1.74 times that of DCT and 1.51 times that of ACT respectively. Potassium can increase the intensity of photosynthesis, promote the formation of starch and sugar in plants, enhance the stress resistance and disease resistance of crops, and improve the nitrogen utilization efficiency of crops. There is no significant difference in the TK content in the extracts under different conditions (P > 0.05).

[0149] Before use, KH 2 PO 4 was added to the extract and CK group to adjust the EC to 1.6 - 2.5 ms / cm, and KNO 3 and NaHCO 3 were used to adjust the pH of the nutrient solution to 5.5 - 6.5, and the temperature of the extract was maintained at 18 - 25 °C by an air-source heat pump. The cultivation of the seedlings was carried out in a rectangular pipe hydroponic tank as shown in Figure 27 . The pipes were laid above the ground, and the slope angle was set at 1.0% to facilitate the flow of the liquid in the pipes. Lettuce was fixed on the planting cups with planting cotton, and the planting cups were placed on the foam floating boards. Various nutrient solutions were stored in 50 L nutrient tanks respectively, and the circulation of the nutrient solution in the pipes and reoxygenation were achieved by water pumps. After the lettuce was fixed on the 25×25 cm planting cups, it was placed in the cultivation holes.

[0150] The seedlings were treated with a 1 / 2 concentration of nutrient solution, and a standard concentration of nutrient solution was used during the growth period. Lettuce seedlings with consistent growth vigor were selected and planted in 25×25 cm cultivation pipes, with 200 plants planted in each treatment group, and the circulation of the extract was achieved by a water pump. The culture solution was replaced on the 14th day, 20th day, and 25th day respectively. The light intensity in the factory was controlled at 75 - 80 μmol / m 2·s, and the day-night temperature is 18 - 30 °C. By comparing the net photosynthetic efficiency, stomatal conductance, intercellular CO 2 concentration, and transpiration rate of lettuce growth, combined with photosynthetic pigment content (chlorophyll a and carotenoids), Fv / Fm, Fv / F0 and other parameters, the photosynthetic performance of lettuce was evaluated; the growth status of lettuce was reflected by measuring the activities of CAT, SOD, and POD and the flavonoid content in lettuce; by testing the main growth indexes of lettuce such as plant height, stem diameter, total leaf area, and fresh weight, the effects of different extracts on growth yield were compared.

[0151] 1. The light saturation point of lettuce leaves is 400 - 600 μmol / m 2 ·s. Therefore, the present invention selects a light quantum intensity of 500 μmol / m 2 ·s to measure the net photosynthetic efficiency, stomatal conductance, intercellular carbon dioxide, and transpiration rate of each sample. The results are shown in Table 7. The net photosynthetic efficiency of lettuce leaves in CK is 18.32%, 14.86%, and 4.47% higher than those in the DCT, ACT, and NCT treatment groups, respectively. There is no significant difference in the net photosynthetic efficiency between CK and the NCT treatment group (P > 0.05). There is no obvious difference in the stomatal conductance among CK, DCT, ACT, and NCT, but compared with CK and NCT, the intercellular CO 2 concentration in the DCT and ACT leaves increases significantly. The intercellular CO 2 concentrations in the CK, DCT, ACT, and NCT treatment groups are 226.71 μmol / L, 284.86 μmol / L, 265.83 μmol / L, and 237.47 μmol / L, respectively. In addition, the compost extract reduces the transpiration rate of lettuce leaves. Compared with CK, the transpiration rates of DCT, ACT, and NCT are reduced by 21.36%, 16.62%, and 5.61%, respectively.

[0152] Table 8 Photosynthetic characteristics of lettuce

[0153]

[0154] Photosynthetic pigments such as chlorophyll in lettuce can drive electron transport in photosystem II (PSII) by capturing light, participate in regulating crop physiological metabolism and gene expression, and play an important role in light capture, energy absorption, and conversion. The chlorophyll content of the leaves in each treatment group is as Figure 28As shown in A. Compared with the CK treatment group, the chlorophyll contents of DCT, ACT, and NCT decreased by 16.61%, 10.46%, and 5.56% respectively. There were significant differences in chlorophyll contents between CK and DCT and ACT culture conditions (P < 0.05), while there was no significant difference in content under NCT culture conditions (P > 0.05). A higher chlorophyll content can improve the photosynthesis ability of crops and provide energy for crop growth and cell division. Carotenoid is a non-enzymatic antioxidant. The conjugated double bonds in its molecular chain can absorb and consume the excitation energy of singlet oxygen, scavenge free radicals, and protect cell membranes from damage. At the end of the culture, the carotenoid content in the CK group was 0.11 mg / g·FW, and the carotenoid contents of DCT, ACT, and NCT were 0.16 mg / g·FW, 0.15 mg / g·FW, and 0.12 mg / g·FW respectively. The significant increase in carotenoid content under DCT and ACT culture conditions indicates that the growth of lettuce is inhibited, and it resists oxidative stress caused by stress through the secretion of carotenoids.

[0155] The Fv / Fm value is used to represent the maximum efficiency of chlorophyll molecules in absorbing and utilizing light energy under light-saturated conditions. Detecting Fv / Fm can quickly evaluate the adaptability of microalgae to the growth environment. The results are as Figure 28 shown in B. During the entire growth period of lettuce, the Fv / Fm ranges under CK, DCT, ACT, and NCT culture conditions were 0.681 - 0.774, 0.443 - 0.571, 0.563 - 0.655, and 0.673 - 0.737 respectively. Generally speaking, when Fv / Fm is greater than 0.6, it indicates that the crop is less affected by external stress. The minimum values of Fv / Fm in CK and NCT are both greater than 0.65, indicating that CK and NCT did not cause stress to the growth of lettuce. Fv / F0 is another important parameter for evaluating the change amplitude of chlorophyll fluorescence signal and can be used to characterize photosynthesis efficiency and plant physiological state. The results are as Figure 28 shown in C. Compared with CK, Fv / F0 of DCT, ACT, and NCT decreased by 11.23%, 10.35%, and 2.34% respectively within 30 days. The decrease in Fv / F0 indicates that the water-splitting complex on the donor side of lettuce collapses and the electron transport ability decreases.

[0156] ΦPSII can reveal the physiological state of lettuce growth and the operating state of PSII under different environmental conditions. Under CK, DCT, ACT, and NCT culture conditions, the ΦPSII values of each treatment group are as Figure 28As shown in D, at the end of the cultivation, they were 0.32, 0.13, 0.24, and 0.30 respectively. Compared with CK, the compost extracts all caused a decrease in ΦPSII. The reduced ΦPSII may change the photochemical electron transport of PSII and affect the growth rate of lettuce. Qp is often used to evaluate the carbon assimilation ability of crops. The results are as Figure 28 As shown in D, at the end of the cultivation, the Qp values decreased by 29.41%, 33.78%, and 4.46% compared with the CK group respectively, indicating that the compost extracts inhibited the photochemical conversion efficiency of lettuce growth. NPQ can quantify the dissipation process of the extra light absorbed in the form of heat and reflects the potential heat dissipation ability of PSII. Under the cultivation conditions of CK, DCT, ACT, and NCT, NPQ showed different change rules. Among them, the NPQ of CK and NCT always remained at a low level, 0.14 and 0.17 respectively, while under the cultivation conditions of DCT and ACT, NPQ increased to 0.34 and 0.32 respectively. This indicates that the relevant protection mechanisms of the PSII reaction center can be activated under the cultivation conditions of CK and NCT, and most of the light energy is dissipated in the form of heat. DCT and ACT will inhibit the light energy heat dissipation of crops.

[0157] 2. Effects of nutrient solutions on the enzyme activities of lettuce growth

[0158] There are various antioxidant defense systems in normally growing crops to scavenge toxic and harmful free radicals and protect cells from oxidative stress interference. Among them, CAT uses the protein containing tetrameric heme in itself to catalyze the disproportionation of H 2 O 2 into H 2 O and O 2 to achieve intracellular detoxification of H 2 O 2 ; SOD can directly regulate the contents of O 2 - and H 2 O 2 ; Peroxidase (POD) participates in the intracellular detoxification of H 2 O 2 through the oxidation of chemical substrates. The changes in the enzyme activities of lettuce with different compost extracts are as Figure 29As shown. Compared with the CK treatment group, the activities of CAT and SOD in the DCT, ACT, and NCT treatment groups did not change significantly during the hydroponic cultivation of lettuce. However, the POD in the DCT and ACT treatment groups increased by 16.62% and 11.93% respectively compared with the CK treatment group. This indicates that oxidative stress did occur in lettuce cultured with different compost extracts, and also shows that POD is more sensitive to different compost extracts than CAT and SOD. Compared with the CK group, the flavonoid content in the lettuce leaves of the DCT and ACT treatment groups increased by 18.84% and 12.36% respectively. This substance can directly act on ROS and can also serve as a substrate for different CATs. Compost extracts formed under different process conditions can increase the POD and flavonoid contents, indicating that the addition of compost extracts can induce the production of antioxidants to mitigate the impact of compost extract stress on lettuce growth.

[0159] 3. Effects of nutrient solution on lettuce yield

[0160] Table 9 Main growth indicators of lettuce

[0161]

[0162] As shown in Table 9: The plant height ranking of each treatment group was CK > NCT > ACT > DCT in turn. There was no significant difference between the CK and NCT treatment groups, and the plant heights of the DCT and ACT treatment groups were significantly lower than those of the CK and NCT treatment groups. The stem diameter ranking was CK > NCT > DCT > ACT, and the stem diameter of the ACT treatment group was significantly lower than that of the other treatment groups. Among each treatment group, the total leaf area of CK was the largest, followed by the NCT treatment group. In terms of fresh weight, the NCT and CK treatment groups were significantly higher than the ACT and DCT treatment groups. From the perspective of lettuce growth, the CK and NCT treatment groups were the most suitable for hydroponic cultivation of lettuce.

Claims

1. A vegetable hydroponic nutrient solution based on fish manure compost products, wherein the fish manure compost products and water are placed in a container with a lid, the container is sealed, and reacted at room temperature in the dark, and after reacting for 3-4 days, an anaerobic vegetable hydroponic nutrient solution is obtained by filtration; The fish manure compost product is prepared according to the following method: (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. (4) When the compost fermentation temperature is lower than 30°C, the water content is adjusted to 55±0.5% using compost extract, and earthworms are added for decomposition. During the decomposition process, the fermentation box is rotated once every 50 minutes, and each rotation lasts for 5 minutes. During the rotation process, the cover is opened to supplement oxygen through the ventilation holes.

2. The vegetable hydroponic nutrient solution based on fish manure compost product according to claim 1, characterized in that: The ratio of the fish manure compost product to water is 1:5 w / v.

3. The vegetable hydroponic nutrient solution based on fish manure compost product according to claim 2, characterized in that: Rotation speed 30-40rpm.

4. The vegetable hydroponic nutrient solution based on fish manure compost product according to any one of claims 1 to 3, 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.

5. The vegetable hydroponic nutrient solution based on fish manure compost product according to claim 4, characterized in that: The amount of the hydrothermal charcoal added is 5% of the total mass of the compost.

6. The vegetable hydroponic nutrient solution based on fish manure compost product according to claim 5, characterized in that: Carbon-nitrogen ratio 25:

1.

7. The vegetable hydroponic nutrient solution based on fish manure compost product according to claim 1, characterized in that: The vegetable is lettuce.

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