Process for preparing garden fertilizer from leather factory sludge

Abstract

The invention relates to the technical field of sludge treatment, and discloses a process for preparing garden fertilizer by using leather factory sludge, which comprises the following steps: S1, pretreatment: mechanically dehydrating the leather factory sludge; s2, acid pickling: adding the sludge treated in the step S1 into an acid solution for soaking and stirring to reduce the content of heavy metals; s3, drying: carrying out drying treatment on the sludge subjected to acid pickling in the step S2; s4, crushing and sieving: crushing and sieving the sludge dried in the step S3; s5, mixing and modifying: mixing the sludge crushed in the step S4 with humic acid substances to improve the soil structure; and S6, curing and stabilizing: adding a microbial preparation into the sludge modified in the step S5, and carrying out fermentation treatment to further degrade harmful substances and stabilize heavy metals so as to prepare the garden fertilizer. Through a treatment mode of combining acid pickling and microbial solidification, the resource utilization rate of the sludge is remarkably improved while the risk of heavy metal pollution is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and specifically to a process for preparing garden fertilizer using leather factory sludge. Background Art

[0002] A large amount of sludge is generated during the production process of the leather industry. It is rich in organic matter and trace elements and has certain potential for resource utilization. For the treatment of leather factory sludge, the existing technologies mainly include methods such as landfill, incineration, chemical extraction, and bioremediation. Landfill realizes the reduction and disposal by directly burying the sludge in a designated site; incineration uses high-temperature combustion to reduce the sludge volume and partially remove harmful substances; chemical extraction dissolves heavy metals with acid-base solutions to reduce pollution; bioremediation relies on microorganisms to degrade organic pollutants and stabilize some heavy metals. These methods are widely used in sludge treatment, alleviating the environmental pressure of the leather industry to a certain extent and providing a technical basis for the resource utilization of sludge.

[0003] However, there are significant deficiencies in the existing technologies in terms of the synergistic optimization of heavy metal removal and resource utilization. Taking landfill as an example, it does not pre-treat the sludge, resulting in ineffective removal of heavy metals (such as the Cr content can reach 500 mg / kg), easy leakage and pollution of groundwater, and at the same time, the organic matter is not utilized, causing resource waste. Although incineration can reduce the sludge volume, the high-temperature process reduces the organic matter content to about 5%, and heavy metals (such as the Cr content still reaches 300 mg / kg) partially remain in the ash residue, making it difficult to meet the safety requirements of garden fertilizer. Chemical extraction can reduce the heavy metal content to about 150 mg / kg, but the treatment efficiency is low, and a large amount of organic matter is lost in the acid-base reaction, and the resource recovery rate is less than 30%. Bioremediation can reduce the heavy metal content to 200 mg / kg through the action of microorganisms, but the retention and improvement of organic matter are limited, and the conversion of sludge into high-value-added products has not been achieved. Therefore, it is difficult for the existing technologies to fully utilize resources while efficiently removing heavy metals, restricting the application of leather factory sludge in the preparation of garden fertilizer. Summary of the Invention

[0004] In view of the deficiencies of the existing technologies, the present invention provides a process for preparing garden fertilizer using leather factory sludge, which solves the problem that it is difficult for the existing technologies to fully utilize resources while efficiently removing heavy metals.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A process for preparing garden fertilizer using leather factory sludge, including the following steps: S1. Pretreatment: Mechanically dehydrate the leather factory sludge to reduce the moisture content to less than 60%. S2. Acid pickling: Immerse and stir the sludge treated in step S1 in an acidic solution to reduce the heavy metal content. S3. Drying: The sludge after pickling in step S2 is dried to reduce the water content to below 15%. S4. Crushing and sieving: The dried sludge in step S3 is crushed and sieved to obtain particles with a particle size of 0.5 - 2 mm. S5. Mixing and modification: The crushed sludge in step S4 is mixed with humic acid substances to improve the soil structure. S6. Solidification and stabilization: A microbial agent is added to the modified sludge in step S5 for fermentation treatment to further degrade harmful substances and stabilize heavy metals, and a fertilizer for gardening is prepared.

[0006] Preferably, in step S1, a centrifuge is used for mechanical dehydration, with a rotation speed of 3000 - 5000 rpm, a treatment time of 20 - 30 minutes, and the solid content of the dehydrated sludge is 40% - 50%.

[0007] Preferably, in step S2, the acidic solution is a sulfuric acid solution with a concentration of 0.5 - 1.5 mol / L or a citric acid solution with a concentration of 0.8 - 2.0 mol / L. The mass ratio of the sludge to the acidic solution is 1:3 to 1:5, the soaking time is 2 - 4 hours, and the temperature is 25 - 40°C.

[0008] Preferably, in step S3, hot air drying oven is used for drying, with a temperature of 80 - 100°C, a drying time of 4 - 6 hours, and the water content of the dried sludge is 10% - 12%.

[0009] Preferably, in step S4, a hammer mill is used for crushing, and a 10 - 20 mesh sieve is used for sieving, and the obtained particle size is 0.5 - 2 mm.

[0010] Preferably, in step S5, a mixer is used to mix the crushed sludge with humic acid substances. The humic acid substances are sodium humate or ammonium humate, and the addition amount is 10% - 20% of the dry weight of the sludge. The pH value of the mixed soil is 6.0 - 7.5.

[0011] Preferably, in step S6, the microbial agent is a mixed bacterium agent of Bacillus subtilis and Trichoderma viride, and the addition amount is 0.5% - 1% of the dry weight of the sludge. The fermentation temperature is 30 - 35°C, the humidity is 50% - 60%, and the fermentation time is 7 - 14 days.

[0012] Preferably, the acidic solution in step S2 can be replaced with an acetic acid solution with a concentration of 0.5 - 1 mol / L.

[0013] Preferably, the humic acid substances in step S5 can be replaced with lignin or straw powder, and the addition amount is 15% - 25% of the dry weight of the sludge; The curing and stabilization in step S6 can be replaced by lime curing. The lime addition amount is 5%-10% of the dry weight of the sludge, and the curing time is 2-3 days.

[0014] Preferably, the mixer includes a housing. A motor is fixedly connected to the upper surface of the left side of the housing. The output end of the motor is connected to a stirring rod. Both ends of the stirring rod are rotatably connected inside the housing. A plurality of stirring blades are fixedly connected to the outer wall of the stirring rod. An electric push rod I is rotatably connected to the outer wall of the housing. The output end of the electric push rod I is connected to a lid. The outer wall of the lid is rotatably connected to the outer wall of the housing. Support legs are fixedly connected to the outer wall of the housing. A support plate is fixedly connected to the outer wall of the support legs. An electric push rod II is fixedly connected to the upper surface of the support plate. A bottom shell is fixedly connected to the lower surface of the housing. An opening and closing plate is arranged at the output end of the electric push rod II. The outer wall of the opening and closing plate is slidably connected inside the bottom shell. A feeding plate is fixedly connected to the inside of the housing. A plurality of feeding ports are evenly opened at the bottom of the feeding plate.

[0015] The present invention provides a process for preparing garden fertilizer using leather factory sludge. It has the following beneficial effects: 1. Through the treatment method combining pickling and microbial curing, the content of heavy metals (such as Cr) in the leather factory sludge is reduced from the initial 200-1000 mg / kg to 40-80 mg / kg, which is better than the effects of existing chemical extraction (150 mg / kg) or bioremediation (200 mg / kg). At the same time, the organic matter is retained (increased to 18%-28%) and converted into garden fertilizer. This synergistic mechanism reduces the risk of heavy metal pollution while significantly improving the resource utilization rate of the sludge.

[0016] 2. By adding humic acid substances in the mixing and modification step, the water retention rate of the prepared garden fertilizer reaches 30%-45%, and the organic matter content is increased to 18%-28%, which is much higher than the results of incineration (water retention rate 8%, organic matter 5%) or landfill (water retention rate 10%, organic matter 15%). The improvement of performance enhances the fertilizer and water retention ability of the product.

[0017] 3. The present invention controls the curing and stabilization time within 7-14 days (microbial fermentation) or 2-3 days (replaced by lime curing), which is significantly shorter than the 30-60-day cycle of bioremediation. At the same time, by optimizing parameters (such as acid concentration 0.5-1.5 mol / L, fermentation temperature 30-35 °C) to adapt to different sludge characteristics (such as Cr content 200-1000 mg / kg), the applicability of the process to various leather factory sludges is improved.

[0018] 4. The present invention reduces energy consumption by about 60%-70% through mechanical dehydration and hot air drying. At the same time, alternative solutions (such as acetic acid and lime) further reduce the input costs of chemical reagents and equipment.

[0019] 5. The present invention first stirs the sludge to make its particles loose and expose more contact surfaces, and then slowly sprinkles humic acid substances (such as sodium humate or ammonium humate) by vibration, which can ensure that the humic acid substances are evenly distributed in the sludge, avoid local accumulation or caking, and improve the uniformity by about 20%-30% compared with direct dumping and mixing, thereby improving the quality stability of the garden fertilizer prepared.

[0020] 6. The present invention slowly adds humic acid substances during the sludge stirring process, and with the aid of the vibration effect, makes them gradually adhere to the surface of the sludge in the form of fine particles or powders, which helps the humic acid substances to penetrate into the interior of the sludge particles and undergo physical and chemical combination with their organic components, increasing the effective utilization rate of humic acid from 70%-80% of direct mixing to 85%-95%, and further enhancing the aggregate structure. The water retention rate can be increased from 35% of direct mixing to 40%-45%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of a process for preparing garden fertilizer using leather factory sludge according to the present invention; Figure 2 is a front perspective structural schematic diagram of a mixer according to the present invention; Figure 3 is a rear perspective structural schematic diagram of a mixer according to the present invention; Figure 4 is a top perspective structural schematic diagram of a mixer according to the present invention; Figure 5 is a partial structural schematic diagram of the bottom shell according to the present invention; Figure 6 is a partial structural schematic diagram of the opening and closing plate according to the present invention; Figure 7 is a partial structural schematic diagram of the second electric push rod according to the present invention; Figure 8 is a partial structural schematic diagram of the stirring rod according to the present invention; Figure 9 is a partial structural schematic diagram of the blanking plate according to the present invention.

[0022] Among them, 1. housing; 2. motor; 3. stirring rod; 4. stirring blade; 5. first electric push rod; 6. lid; 7. support leg; 8. support plate; 9. second electric push rod; 10. bottom shell; 11. opening and closing plate; 12. blanking plate; 13. blanking port. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Next, in combination with the accompanying drawings of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0024] Please refer to the attached Figure 1 , an embodiment of the present invention provides a process for preparing garden fertilizer using leather factory sludge, including the following steps: S1. Pretreatment: Mechanically dehydrate the leather factory sludge to reduce the moisture content to less than 60%. S2. Acid washing: Immerse and stir the sludge treated in step S1 in an acidic solution to reduce the heavy metal content. S3. Drying: Dry the sludge after acid washing in step S2 to reduce the water content to less than 15%. S4. Crushing and sieving: Crush and sieve the dried sludge in step S3 to obtain particles with a particle size of 0.5 - 2 mm. S5. Mixing and modification: Mix the crushed sludge in step S4 with humic acid substances to improve the soil structure. S6. Solidification and stabilization: Add a microbial preparation to the modified sludge in step S5 and carry out fermentation treatment to further degrade harmful substances and stabilize heavy metals to produce garden fertilizer.

[0025] Specifically, through six-step collaborative treatment, the leather factory sludge is transformed into safe and fertile garden fertilizer. In S1 pretreatment, mechanical dehydration reduces the sludge moisture, facilitating subsequent chemical reactions; in S2 acid washing, the acidic solution is used to dissolve heavy metal ions for preliminary purification; in S3 drying, water is further removed to optimize physical properties; in S4 crushing and sieving, the particle size is adjusted to meet the air permeability requirements of garden fertilizer; in S5 mixing and modification, humic acid substances are introduced to improve fertility and structure; in S6 solidification and stabilization, microbial fermentation is used to degrade residual pollutants and fix heavy metals to ensure product safety. This process is applicable to scenarios where the moisture content of leather factory sludge is 70% - 90% and the heavy metal content (such as Cr, Pb) is 200 - 1000 mg / kg. Taking the sludge of a certain leather factory as an example, with an initial moisture content of 85% and a Cr content of 600 mg / kg, after treatment by this process, the moisture content is reduced to 12%, the Cr content is reduced to 45 mg / kg, and the organic matter is increased to 28%, meeting the standard of "Sludge Disposal for Landscaping in Municipal Wastewater Treatment Plants" (CJ / T 362 - 2011).

[0026] In step S1, a centrifugal dehydrator is used for mechanical dehydration, with a rotation speed of 3000 - 5000 rpm, a treatment time of 20 - 30 minutes, and the solid content of the dehydrated sludge is 40% - 50%.

[0027] Specifically, in the S1 pretreatment, a centrifugal dehydrator (such as model LX-500 with a power of 15 kW) is selected. The rotation speed range is 3000 - 5000 rpm, which can be adjusted according to the sludge viscosity. For example, for viscous sludge with high water content, 4500 rpm is selected. If the rotation speed is too low (such as <2000 rpm), the dehydration efficiency is insufficient; if it is too high (such as >6000 rpm), the energy consumption increases without obvious benefits. The treatment time is 20 - 30 minutes based on the matching of the sludge volume and the equipment capacity. For example, when treating 5 tons of sludge, 25 minutes are required. The solid content after dehydration of 40% - 50% is a key prerequisite for subsequent pickling. If it is lower than 40%, the acid permeability decreases; if it is higher than 50%, the uniformity may be affected due to excessive dryness.

[0028] In step S2, the acidic solution is a sulfuric acid solution with a concentration of 0.5 - 1.5 mol / L or a citric acid solution with a concentration of 0.8 - 2.0 mol / L. The mass ratio of the sludge to the acidic solution is 1:3 to 1:5, the soaking time is 2 - 4 hours, and the temperature is 25 - 40°C.

[0029] Specifically, in the S2 pickling, the sulfuric acid solution (0.5 - 1.5 mol / L) is often used for the removal of heavy metals such as Cr due to its low cost and strong reactivity. For example, 1.0 mol / L sulfuric acid can reduce the Cr content from 500 mg / kg to 80 mg / kg; the citric acid solution (0.8 - 2.0 mol / L) is environmentally friendly and suitable for scenarios sensitive to secondary pollution. For example, the Pb removal efficiency of 1.5 mol / L citric acid reaches 85%. The mass ratio of the sludge to the acid solution of 1:3 to 1:5 is based on the dissolution equilibrium, and the heavy metal removal rate and cost are optimal at 1:4. The soaking time of 2 - 4 hours is adjusted according to the type of heavy metal. For example, Cr requires 3 hours and Cd requires 2.5 hours; the temperature of 25 - 40°C avoids acid volatilization or too slow reaction. For example, the Cr removal rate increases by 10% at 30°C.

[0030] In step S3, hot air drying oven is used for drying, the temperature is 80 - 100°C, the drying time is 4 - 6 hours, and the water content of the dried sludge is 10% - 12%.

[0031] Specifically, in the S3 drying, a hot air drying oven (such as model HG-200 with a power of 10 kW) is used. The temperature of 80 - 100°C is based on the balance of water evaporation and energy consumption. When the temperature is 90°C, the power consumption per ton of sludge is about 150 kWh, which is lower than 500 kWh of incineration. The drying time of 4 - 6 hours is adjusted according to the initial water content of the sludge. For example, when the water content is 50%, 5 hours are required. The water content of 10% - 12% ensures smooth subsequent crushing. If it is higher than 15%, the particles are prone to adhesion; if it is lower than 8%, the energy consumption increases without additional benefits. The hot air speed of 2 - 3 m / s ensures uniform heating and avoids surface caking.

[0032] In step S4, a hammer mill is used for crushing, and a 10-20 mesh sieve is used for sieving. The resulting particle size is 0.5-2 mm.

[0033] Specifically, for S4 crushing, a hammer mill (such as model PC-400, power 7.5 kW) is selected, with a rotation speed of 800-1200 rpm, a processing capacity of 2 tons per hour, and the crushed particles are fine and uniform. A 10-20 mesh sieve (aperture 0.85-2 mm) is used for sieving. 15 mesh (1 mm) is suitable for most garden needs to ensure a balance between air permeability and water retention. The particle size of 0.5-2 mm is based on the growth characteristics of plant roots. Particles smaller than 0.5 mm are prone to caking, and those larger than 2 mm have poor water retention.

[0034] In step S5, a mixer is used to mix the crushed sludge with humic acid substances. The humic acid substances are sodium humate or ammonium humate, and the addition amount is 10%-20% of the dry weight of the sludge. After mixing, the soil pH value is 6.0-7.5.

[0035] Specifically, in S5 mixing and modification, sodium humate (humic acid content ≥ 60%) is often used for acidic sludge due to its good solubility, while ammonium humate is suitable for neutral to slightly alkaline sludge. The addition amount of 10%-20% is based on the need to increase organic matter. For example, when it is 15%, the organic matter increases from 15% to 25%. A horizontal mixer (rotation speed 50 rpm) is used for mixing, and stirring for 20 minutes ensures uniformity. The pH of 6.0-7.5 is fine-tuned by adding a small amount of lime or acid solution. For example, 0.5% lime is added to sludge with an initial pH of 5.0 to reach 6.8.

[0036] In step S6, the microbial agent is a mixed bacterium agent of Bacillus subtilis and Trichoderma viride, with an addition amount of 0.5%-1% of the dry weight of the sludge, a fermentation temperature of 30-35 °C, a humidity of 50%-60%, and a fermentation time of 7-14 days.

[0037] Specifically, in S6 solidification and stabilization, Bacillus subtilis (viable count ≥ 10 9 CFU / g) degrades organic pollutants, and Trichoderma viride (viable count ≥ 10 8 CFU / g) solidifies heavy metals. The two are mixed in a ratio of 1:1, and the addition amount of 0.5%-1% is based on the fermentation efficiency. For example, when it is 0.8%, the phenol degradation rate reaches 90%. Fermentation is carried out in a closed fermentation tank (volume 10 m 3 ), and the temperature of 30-35 °C is to avoid inactivation of the strains. The humidity of 50%-60% is regulated by spraying. The fermentation time of 7-14 days is adjusted according to the pollutant concentration. For example, when the Cr is 100 mg / kg, it takes 10 days.

[0038] The acidic solution in step S2 can be replaced with an acetic acid solution with a concentration of 0.5-1 mol / L.

[0039] Specifically, in S2, acetic acid solution (0.5 - 1 mol / L) is used as a substitute for sulfuric acid or citric acid. Due to its low cost (about 200 yuan per ton) and weak volatility, it is suitable for small-scale treatment. For example, the Cr removal efficiency of 0.8 mol / L acetic acid is 75%, slightly lower than 90% of sulfuric acid. The operation is the same as the sulfuric acid process, and the soaking time can be extended to 4.5 hours to make up for the efficiency difference. The pH of the waste liquid is relatively low (about 3.5), and alkali needs to be added to neutralize it to 6 - 7 before discharging.

[0040] The humic acid substances in step S5 can be replaced by lignin or straw powder, and the addition amount is 15% - 25% of the dry weight of the sludge; The solidification and stabilization in step S6 can be replaced by lime solidification. The addition amount of lime is 5% - 10% of the dry weight of the sludge, and the solidification time is 2 - 3 days.

[0041] Specifically, in S5, lignin (cellulose content ≥ 70%) or straw powder (particle size 0.5 - 1 mm) is used to replace humic acid. The addition amount of 15% - 25% is due to its low cost (about 150 yuan per ton) and wide source. For example, 20% lignin can increase the organic matter content to 22%. The stirring time is extended to 25 minutes to ensure uniformity. The water retention capacity is slightly lower than that of humic acid (about 35%), but the air permeability is increased by 10%; In S6, lime solidification replaces microbial fermentation. The addition amount of lime (CaO content ≥ 85%) is 5% - 10% based on the heavy metal stabilization requirement. For example, when the addition amount is 7%, the Cr migration rate drops to 30 mg / kg. The solidification is carried out in an open stirring tank, completed in 2 - 3 days, the stirring speed is 30 rpm, and it is turned over once a day. The cost is low (about 50 yuan per ton of sludge), but the organic matter retention rate is only 70%.

[0042] Please refer to the attached Figure 2 - attached Figure 9 , the mixer includes a housing 1. The left upper surface of the housing 1 is fixedly connected with a motor 2. The output end of the motor 2 is connected with a stirring rod 3. Both ends of the stirring rod 3 are rotatably connected inside the housing 1. The outer wall of the stirring rod 3 is fixedly connected with a plurality of stirring blades 4. The outer wall of the housing 1 is rotatably connected with an electric push rod 5. The output end of the electric push rod 5 is connected with a lid 6. The outer wall of the lid 6 is rotatably connected to the outer wall of the housing 1. The outer wall of the housing 1 is fixedly connected with support legs 7. The outer wall of the support legs 7 is fixedly connected with a support plate 8. The upper surface of the support plate 8 is fixedly connected with an electric push rod 9. The lower surface of the housing 1 is fixedly connected with a bottom shell 10. The output end of the electric push rod 9 is provided with a switch plate 11. The outer wall of the switch plate 11 is slidably connected inside the bottom shell 10. The inside of the housing 1 is fixedly connected with a blanking plate 12. A plurality of blanking openings 13 are evenly arranged at the bottom of the blanking plate 12.

[0043] Specifically, a discharge port is provided at the bottom of the housing 1, and the size of the discharge port can just be blocked by the opening and closing plate 11. When hybrid modification is required, first, the electric push rod 1 is activated to drive the lid 6 to rotate and open. Then, the sludge crushed in step S4 is placed inside the housing 1, and the humic acid substances are placed inside the feeding plate 12. Next, the motor 2 is activated to drive the stirring rod 3 and the stirring blades 4 to stir the sludge. First, the sludge is stirred and dispersed. During the process of the motor 2 driving the stirring rod 3 and the stirring blades 4 to stir, the housing 1 will vibrate. During the vibration of the housing 1, the feeding plate 12 will be driven to vibrate. At the same time, the humic acid substances inside the feeding plate 12 will be evenly scattered inside the housing 1 through the feeding port 13 and slowly and evenly mixed with the sludge. After the sludge and the humic acid substances inside the housing 1 are mixed, the electric push rod 2 9 is activated. The electric push rod 2 9 will drive the outer wall of the opening and closing plate 11 to slide inside the bottom shell 10. After the opening and closing plate 11 slides, the discharge port at the bottom of the housing 1 is opened for discharging.

[0044] The following is an introduction in combination with specific embodiments: Example 1: The lowest data process flow Background: Treating the sludge of a certain leather factory, with an initial water content of 70%, a Cr content of 200 mg / kg, applicable to small-scale and low-pollution scenarios.

[0045] S1 Pretreatment: Using a small centrifugal dehydrator (power 10 kW), rotation speed 3000 rpm, treatment time 20 minutes, sludge volume 1 ton, water content after dehydration 60%, solid content 40%.

[0046] S2 Acid washing: Using a 0.5 mol / L sulfuric acid solution, the mass ratio of sludge to acid solution is 1:3, soaking for 2 hours, temperature 25 °C, Cr content reduced to 60 mg / kg, removal rate 70%.

[0047] S3 Drying: Using a hot air drying oven (power 5 kW), temperature 80 °C, wind speed 2 m / s, drying for 4 hours, water content reduced to 15%.

[0048] S4 Crushing and sieving: Using a hammer mill (rotation speed 800 rpm), passing through a 10-mesh sieve (aperture 2 mm), particle size 0.5 - 2 mm, average 1.5 mm.

[0049] S5 Hybrid modification: Adding sodium humate (content 50%), addition amount 10% of the dry weight of the sludge (0.04 ton), stirring for 20 minutes, pH 6.0, organic matter increased to 18%.

[0050] S6 Solidification and stabilization: Adding a mixed bacterium agent of Bacillus subtilis and Trichoderma viride (viable bacteria count 10 8CFU / g), addition amount 0.5% (2 kg), fermentation temperature 30 °C, humidity 50%, fermentation for 7 days, Cr bioavailability decreased to 20 mg / kg.

[0051] Result: 0.5 tons of garden fertilizer was prepared, with a water content of 12%, a Cr content of 40 mg / kg, and a water retention rate of 30%, meeting the basic greening requirements.

[0052] Example 2: Background of the highest data process flow: Treating highly polluted sludge from a leather factory, with an initial water content of 90% and a Cr content of 1000 mg / kg, suitable for large-scale and efficient treatment scenarios.

[0053] S1 Pretreatment: Using a large centrifugal dehydrator (power 20 kW), rotation speed 5000 rpm, treatment time 30 minutes, sludge volume 10 tons, water content after dehydration 55%, solid content 50%.

[0054] S2 Acid pickling: Using 1.5 mol / L sulfuric acid solution, mass ratio of sludge to acid solution 1:5, soaking for 4 hours, temperature 40 °C, Cr content decreased to 100 mg / kg, removal rate 90%.

[0055] S3 Drying: Using a hot air drying oven (power 15 kW), temperature 100 °C, wind speed 3 m / s, drying for 6 hours, water content decreased to 10%.

[0056] S4 Crushing and sieving: Using a hammer mill (rotation speed 1200 rpm), passing through a 20-mesh sieve (aperture 0.85 mm), particle size 0.5 - 1 mm, average 0.8 mm.

[0057] S5 Mixing and modification: Adding sodium humate (content 60%), addition amount 20% of the dry weight of sludge (1 ton), stirring for 25 minutes, pH 7.5, organic matter increased to 28%.

[0058] S6 Solidification and stabilization: Adding a mixed bacterium agent of Bacillus subtilis and Trichoderma viride (viable count 10 9 CFU / g), addition amount 1% (50 kg), fermentation temperature 35 °C, humidity 60%, fermentation for 14 days, Cr bioavailability decreased to 30 mg / kg.

[0059] Result: 5 tons of garden fertilizer was prepared, with a water content of 10%, a Cr content of 70 mg / kg, and a water retention rate of 45%, suitable for high-standard greening projects.

[0060] Example 3: Background of the lowest data alternative: Treating sludge with a water content of 75% and a Cr content of 300 mg / kg, using a partial alternative to reduce costs.

[0061] S1 Pretreatment: Rotation speed 3000 rpm, time 20 minutes, water content 60%, solid content 40%.

[0062] S2 Pickling: Use 0.5 mol / L acetic acid solution (instead of sulfuric acid), mass ratio 1:3, soak for 4 hours, temperature 25°C, Cr reduced to 90 mg / kg, removal rate 70%.

[0063] S3 Drying: Temperature 80°C, wind speed 2 m / s, dry for 4 hours, water content 15%.

[0064] S4 Crushing and Sieving: 10-mesh sieve, particle size 0.5 - 2 mm, average 1.8 mm.

[0065] S5 Mixing and Modifying: Add lignin (instead of humic acid), addition amount 15% (0.06 tons), pH 6.0, organic matter increased to 20%.

[0066] S6 Solidification and Stabilization: Use lime solidification (instead of microorganisms), addition amount 5% (20 kg), solidify for 2 days, Cr bioavailability reduced to 40 mg / kg.

[0067] Result: 0.6 tons of garden fertilizer is prepared, water content 13%, Cr content 60 mg / kg, water retention rate 32%, suitable for low-cost application.

[0068] Example 4: Highest Data Replacement Scheme Background: The water content of the treated sludge is 85%, the Cr content is 800 mg / kg, and an alternative scheme is used to optimize the efficiency.

[0069] S1 Pretreatment: Rotation speed 5000 rpm, time 30 minutes, water content 55%, solid content 50%.

[0070] S2 Pickling: Use 1.0 mol / L acetic acid solution, mass ratio 1:5, soak for 4.5 hours, temperature 40°C, Cr reduced to 120 mg / kg, removal rate 85%.

[0071] S3 Drying: Temperature 100°C, wind speed 3 m / s, dry for 6 hours, water content 10%.

[0072] S4 Crushing and Sieving: 20-mesh sieve, particle size 0.5 - 1 mm, average 0.7 mm.

[0073] S5 Mixing and Modifying: Add straw powder, addition amount 25% (1.25 tons), pH 7.0, organic matter increased to 25%.

[0074] S6 Solidification and Stabilization: Lime solidification, addition amount 10% (0.5 tons), solidify for 3 days, Cr bioavailability reduced to 50 mg / kg.

[0075] Results: 5.5 tons of fertilizer for gardens were produced, with a water content of 11%, a Cr content of 80 mg / kg, a water retention rate of 38%, and it is suitable for rapid large-scale treatment.

[0076] Example 5: Mixing parameter process flow Background: The sludge to be treated has a water content of 80% and a Cr content of 500 mg / kg. By combining the lowest and highest parameters, the flexibility of the process is verified.

[0077] S1 Pretreatment: Rotation speed 4000 rpm, time 25 minutes, water content 58%, solid content 45%.

[0078] S2 Pickling: Using 1.0 mol / L citric acid solution, mass ratio 1:4, soaking for 3 hours, temperature 30 °C, Cr reduced to 80 mg / kg, removal rate 84%.

[0079] S3 Drying: Temperature 90 °C, wind speed 2.5 m / s, drying for 5 hours, water content 12%.

[0080] S4 Crushing and sieving: 15-mesh sieve, particle size 0.5 - 1.5 mm, average 1 mm.

[0081] S5 Mixing and modification: Adding ammonium humate, addition amount 15% (0.75 tons), pH 6.8, organic matter increased to 24%.

[0082] S6 Solidification and stabilization: Adding 0.8% (40 kg) of microbial inoculant, fermenting at 32 °C, humidity 55%, for 10 days, Cr bioavailability reduced to 25 mg / kg.

[0083] Results: 5.2 tons of fertilizer for gardens were produced, with a water content of 11%, a Cr content of 55 mg / kg, a water retention rate of 40%, taking into account both efficiency and quality.

[0084] Table 1: Comparison of different examples with the prior art Explanation of table characters: 1. Treatment method: Meaning: Represents different sludge treatment processes, including five examples of the present invention (Examples 1 - 5) and four prior arts (landfill, incineration, chemical extraction, bioremediation).

[0085] Specific explanation: Example 1 (lowest data): Adopting the process with the lowest parameters (such as the lowest rotation speed, the lowest acid concentration), suitable for low-pollution, small-scale sludge.

[0086] Example 2 (highest data): Adopting the process with the highest parameters (such as the highest rotation speed, the highest acid concentration), suitable for high-pollution, large-scale sludge.

[0087] Example 3 (Lowest Substitution): Based on the lowest parameters, use substitution options (such as acetic acid, lignin, lime) to reduce costs.

[0088] Example 4 (Highest Substitution): Based on the highest parameters, use substitution options to optimize efficiency.

[0089] Example 5 (Mixed Parameters): Combine intermediate parameters to verify process flexibility.

[0090] Prior Art - Landfill: Directly bury sludge without resource treatment.

[0091] Prior Art - Incineration: High-temperature combustion of sludge to reduce volume but lose resources.

[0092] Prior Art - Chemical Extraction: Use chemical reagents to remove heavy metals, but with limited efficiency.

[0093] Prior Art - Bioremediation: Use microorganisms to degrade pollutants, with a relatively long cycle.

[0094] 2. Water Content (%): Meaning: The percentage of water content in the treated sludge or garden fertilizer, reflecting the dryness of the product and the convenience of use.

[0095] Unit: Percentage (%). Significance: The lower the water content, the easier the product is to store and transport, but too low may increase energy consumption. The ideal water content for garden fertilizer is usually 10% - 20%.

[0096] Data Interpretation: The Invention: 10% - 13%, moderate and convenient for application.

[0097] Landfill: 80%, untreated, high wet weight, not suitable for direct use.

[0098] Incineration: 5%, too dry, losing soil characteristics.

[0099] Chemical Extraction: 20%, on the high side, affecting subsequent utilization.

[0100] Bioremediation: 25%, relatively high humidity, requiring additional drying.

[0101] 3. Cr Content (mg / kg): Meaning: The content of chromium (Cr) in the treated sludge or garden fertilizer, representing the degree of heavy metal pollution.

[0102] Unit: Milligrams per kilogram (mg / kg).

[0103] Data Interpretation: The Invention: 40 - 80 mg / kg, far lower than the standard, with high safety.

[0104] Landfill: 500 mg / kg, untreated, seriously exceeding the standard.

[0105] Incineration: 300 mg / kg, still on the verge of compliance, with high pollution risk.

[0106] Chemical extraction: 150 mg / kg, partially removed but not optimal.

[0107] Bioremediation: 200 mg / kg, limited removal, need for improvement.

[0108] 4. Organic matter content (%): Meaning: The percentage of organic matter in the garden fertilizer after treatment, reflecting soil fertility and plant growth support ability.

[0109] Unit: Percentage (%). Significance: The higher the organic matter content, the more fertile the soil. The ideal value is 15%-30%. Existing technologies often result in loss of organic matter, while the present invention focuses on retention and enhancement.

[0110] Data interpretation: The present invention: 18%-28%, significantly improved, approaching the ideal upper limit.

[0111] Landfill: 15%, untreated, only maintaining the original level.

[0112] Incineration: 5%, high temperature destroys organic matter, extremely low fertility.

[0113] Chemical extraction: 12%, serious loss during the chemical process.

[0114] Bioremediation: 18%, retained well but no obvious improvement.

[0115] 5. Water retention rate (%): Meaning: The percentage of water retention capacity of the garden fertilizer after treatment, indicating the ability of the soil to retain water, which affects plant growth.

[0116] Unit: Percentage (%). Significance: The higher the water retention rate, the more suitable the soil is for arid environments. The ideal value is 30%-50%. The present invention improves water retention through modification.

[0117] Data interpretation: The present invention: 30%-45%, reaching an excellent level for greening fertilizers.

[0118] Landfill: 10%, unmodified, poor water retention.

[0119] Incineration: 8%, particles are loose, extremely low water retention capacity.

[0120] Chemical extraction: 15%, structure not optimized, insufficient water retention.

[0121] Bioremediation: 20%, slightly improved but still relatively low.

[0122] 1. Amount of fertilizer for garden use (tons): Meaning: The weight of the fertilizer for garden use finally obtained from the initial sludge, reflecting the resource utilization efficiency.

[0123] Unit: ton (t). Significance: The higher the output, the higher the resource recovery rate. The present invention aims to maximize the amount of sludge converted into usable fertilizer.

[0124] Data interpretation: For the present invention: 0.5 - 5.5 tons, with a high recovery rate according to the sludge amount and parameter changes.

[0125] Landfill: 0 tons, no resource output.

[0126] Incineration: 0.2 tons, only a small amount of ash remains, without practicality.

[0127] Chemical extraction: 0.8 tons, with limited output and low quality.

[0128] Bioremediation: 1.0 tons, with medium output but low efficiency.

[0129] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing garden fertilizer using leather factory sludge, characterized in that: The following steps are involved: S1, pretreatment, mechanical dehydration of tannery sludge to reduce the moisture content to below 60%; S2, pickling, adding the sludge treated in step S1 into an acidic solution for soaking and stirring to reduce the heavy metal content; S3, drying, drying the sludge after pickling in step S2 to reduce the water content to below 15%; S4, crushing and sieving, crushing and sieving the sludge dried in step S3 to obtain particles with a particle size of 0.5-2 mm; S5, mixing and modification, mixing the sludge crushed in step S4 with humic acid substances to improve the soil structure; S6, solidification and stabilization, adding microbial preparations to the sludge modified in step S5, and fermentation treatment to further degrade harmful substances and stabilize heavy metals to obtain garden fertilizer.

2. The process for preparing garden fertilizer using tanneries sludge according to claim 1, characterized in that: In the step S1, mechanical dehydration uses a centrifugal dehydrator with a rotation speed of 3000-5000 rpm and a processing time of 20-30 minutes. The solid content of the sludge after dehydration is 40%-50%.

3. The process for preparing garden fertilizer using tanneries sludge according to claim 1, characterized in that: In step S2, the acidic solution is a sulfuric acid solution with a concentration of 0.5-1.5 mol / L or a citric acid solution with a concentration of 0.8-2.0 mol / L, the mass ratio of sludge to the acidic solution is 1:3 to 1:5, the soaking time is 2-4 hours, and the temperature is 25-40°C.

4. The process for preparing garden fertilizer using tanneries sludge according to claim 1, characterized in that: In step S3, a hot air drying oven is used for drying at a temperature of 80-100° C. for a drying time of 4-6 hours. The moisture content of the sludge after drying is 10%-12%.

5. The process for preparing garden fertilizer using tanneries sludge according to claim 1, characterized in that: In the step S4, a hammer mill is used for pulverizing and a 10-20 mesh screen is used for sieving, and the particle size of the obtained particles is 0.5-2 mm.

6. The process for preparing garden fertilizer using leather factory sludge according to claim 1, characterized in that: In step S5, the pulverized sludge is mixed with a humic acid substance using a mixer. The humic acid substance is sodium humate or ammonium humate, and the addition amount is 10%-20% of the dry weight of the sludge. The soil pH value after mixing is 6.0-7.

5.

7. The process for preparing garden fertilizer using tanneries sludge according to claim 1, characterized in that: In step S6, the microbial preparation is a mixed agent of Bacillus subtilis and Trichoderma, the addition amount is 0.5%-1% of the dry weight of the sludge, the fermentation temperature is 30-35°C, the humidity is 50%-60%, and the fermentation time is 7-14 days.

8. The process for preparing garden fertilizer using leather factory sludge according to claim 1, characterized in that: The acidic solution in step S2 can be replaced by an acetic acid solution with a concentration of 0.5-1 mol / L.

9. The process for preparing garden fertilizer using tanneries sludge according to claim 1, characterized in that: The humic acid substances in step S5 can be replaced by lignin or straw powder, and the added amount is 15%-25% of the dry weight of the sludge; The solidification stabilization in step S6 can be replaced by lime solidification, with the amount of lime added being 5%-10% of the dry weight of the sludge and the solidification time being 2-3 days.

10. The process for preparing garden fertilizer using leather factory sludge according to claim 6, characterized in that: The mixer comprises a shell (1), a motor (2) is fixedly connected to the upper left surface of the shell (1), an output end of the motor (2) is connected to a stirring rod (3), both ends of the stirring rod (3) are rotatably connected to the inside of the shell (1), a plurality of stirring blades (4) are fixedly connected to the outer wall of the stirring rod (3), an electric push rod (5) is rotatably connected to the outer wall of the shell (1), an output end of the electric push rod (5) is connected to a cover (6), the outer wall of the cover (6) is rotatably connected to the outer wall of the shell (1), and the outer wall of the shell (1) is connected to the outer wall of the shell (1). The outer wall is fixedly connected to a support leg (7), the outer wall of the support leg (7) is fixedly connected to a support plate (8), the upper surface of the support plate (8) is fixedly connected to an electric push rod 2 (9), the lower surface of the shell (1) is fixedly connected to a bottom shell (10), an opening and closing plate (11) is provided at the output end of the electric push rod 2 (9), the outer wall of the opening and closing plate (11) is slidably connected to the inside of the bottom shell (10), and a blanking plate (12) is fixedly connected to the inside of the shell (1), and a plurality of blanking openings (13) are evenly provided at the bottom of the blanking plate (12).

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