Sludge treatment process for sewage treatment plant

Abstract

The invention discloses a sludge treatment process for a sewage treatment plant. The invention belongs to the technical field of civil engineering sludge treatment, and realizes double breakthrough of environmental benefits and economic benefits through multi-stage cooperation and resource closed-loop design. The organic matter decomposition efficiency is remarkably improved through the synergistic effect of the biochar-loaded nano material, electron transfer in the anaerobic digestion process is accelerated through the unique conductive network structure of the biochar-loaded nano material, the methane generation rate breaks through the bottleneck of a traditional technology, and biochar serves as a core medium to directly participate in building of a building body; the porous characteristic and the adsorption performance of the filter material are integrated into a filter interlayer and an ecological slope protection of a hydraulic structure to replace a traditional sand filter material and a concrete additive, so that the construction process is simplified, and the structural functionality is enhanced. Process equipment and a building space adopt a collaborative design principle, and a guide wall of an anaerobic reactor and a refractory lining of a pyrolyzing furnace are integrally poured in combination with the characteristics of a charcoal-based material, so that the matching precision of an equipment foundation and a main body structure is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of civil engineering sludge treatment, and specifically relates to a sludge treatment process for sewage treatment plants. Background Technique

[0002] Sludge treatment is an important link in the process of urban sewage treatment, which involves the process of reducing, stabilizing, and recycling the sludge generated after sewage treatment. It mainly includes steps such as sludge thickening, sludge dewatering, sludge digestion, sludge drying, and sludge incineration. Sludge thickening reduces the water content of sludge through physical methods and increases the sludge concentration; dewatering further removes the water in the sludge, significantly reducing its volume; digestion uses microorganisms to decompose the organic matter in the sludge to achieve stabilization; drying and incineration reduce the sludge volume and eliminate pathogens through reducing moisture and high-temperature combustion respectively, achieving resource utilization and harmlessness. Sludge treatment not only helps to improve environmental quality but also can recycle resources and achieve sustainable development.

[0003] However, in traditional sludge treatment processes, the electron transfer rate is limited, and there is a lack of efficient conductive media, resulting in low methane production rate, long digestion period, and easy generation of by-products such as hydrogen sulfide, which requires additional desulfurization treatment. At the same time, existing conductive materials are costly and difficult to recycle, and are prone to causing environmental burdens after being discarded; excessive addition of chemical agents leads to the accumulation of sludge salts, affecting subsequent resource utilization. Summary of the Invention

[0004] The purpose of the present invention is to provide a sludge treatment process for sewage treatment plants in order to solve the above-mentioned problems.

[0005] The technical solution adopted by the present invention is as follows: A sludge treatment process for sewage treatment plants, the treatment process includes the following steps:

[0006] S1: A civil engineering reinforced concrete ultrasonic pool body, pre-embed galvanized steel pipe threading pipes, install a 316L stainless steel vibration plate base, and integrate a CPVC calcium peroxide dosing pipeline system on the pool top;

[0007] S2: Construct a two-phase anaerobic reactor civil engineering structure, and internally install a biochar conductive medium layer;

[0008] S3: Build a microwave hydrolysis reaction pool, and pre-embed a volatile fatty acid recovery pipeline;

[0009] S4: A civil engineering solar greenhouse drying workshop, with an MOFs material adsorption layer embedded in the wall;

[0010] S5: Pour an anoxic pyrolysis kiln body structure, and support a pyrolysis gas catalytic reforming reuse pipe network;

[0011] S6: Build an acid leaching reaction pool and a crystallization device, and adopt a biochar magnesium source carrier structure;

[0012] S7: Civil engineering biological filter tower base, install activated carbon adsorption unit and CO capture pipeline;

[0013] S8: Embedded process parameter monitoring sensor network, deploy digital twin control system;

[0014] S9: Implement full-chain civil engineering transformation: embed a biological carbon filtration interlayer in the secondary sedimentation tank: anchor the stainless steel grille with concrete; backfill the rain garden with biological carbon planting soil in layers; lay geotextiles at the bottom of the municipal pipe trench to wrap the biological carbon adsorption layer, and set a detachable inspection well structure.

[0015] In a preferred embodiment, in step S1, take the concentrated sludge from the sewage treatment plant, control the initial moisture content at 95% - 97%, first treat it with a high-frequency ultrasonic reactor with a frequency of 20 kHz to 40 kHz, set the ultrasonic power density to 0.5 watts per milliliter, and keep the action time for 30 minutes. Maintain the sludge temperature below 35 °C to prevent pyrolysis of organic matter. After the treatment, add 5 grams of calcium peroxide powder per liter of sludge, stir and mix at a speed of 200 revolutions per minute for 20 minutes to evenly disperse the calcium peroxide and release active oxygen, and simultaneously complete cell wall breaking, heavy metal passivation, and inactivation of pathogenic microorganisms.

[0016] In a preferred embodiment, in step S2, the biochar-supported nanomaterials include: 60 - 70 parts by weight of sludge-based biochar, 10 - 15 parts by weight of polydopamine-coated nano-zero-valent iron, 8 - 10 parts by weight of conductive polyaniline, 5 - 8 parts by weight of superparamagnetic Fe3O4, 3 - 5 parts by weight of diammonium hydrogen phosphate, 2 - 3 parts by weight of calcium carbonate, and 1 - 2 parts by weight of KOH activator;

[0017] The preparation method of the biochar-supported nanomaterials includes: First, take the dewatered sludge from the sewage treatment plant, perform stepwise pyrolysis treatment, carry out pre-carbonization at 300 °C for 30 minutes and activation treatment at 600 °C in sequence. The activation stage uses KOH impregnation with a mass ratio of 1:2, and is kept warm for 1 hour under nitrogen protection. Subsequently, wash with 0.1M HCl to remove ash, wash with deionized water, dry in vacuum, and grind to 200 meshes to obtain sludge-based biochar; then soak the biochar in a 0.5M FeSO4 solution with a solid-liquid ratio of 1:10, ultrasonically disperse for 30 minutes, and then dropwise add a 0.5M NaBH4 solution, controlling the molar ratio of Fe2+ to BH4- to be 1:2, react for 2 hours under nitrogen protection to generate nano-zero-valent iron, and then add aniline monomer with a mass ratio of 1:5 to the biochar, and carry out in-situ polymerization with ammonium persulfate as the initiator to form a polyaniline conductive coating layer; finally, dissolve FeCl2·4H2O and FeCl3·6H2O in a molar ratio of 1:2 by the co-precipitation method, dropwise add ammonia water to adjust the pH to 10, stir at 60 °C for 1 hour to prepare Fe3O4 magnetic particles, load them onto the surface of the biochar by magnetic field separation, and then ball-mill and mix with diammonium hydrogen phosphate and calcium carbonate at a rotation speed of 300 rpm for 2 hours, and finally press and granulate to obtain the finished biochar-supported nanomaterials with a particle size of 2-3 mm.

[0018] In a preferred embodiment, in the step S3, the residue after anaerobic digestion is dehydrated by a plate and frame filter press to a moisture content of 80%, and then enters a microwave-assisted hydrothermal reaction kettle. The reaction conditions are set as a microwave power of 800 watts, a heating rate of 10 degrees Celsius per minute, a target temperature of 160 degrees Celsius and maintained for 30 minutes, and the reaction pressure is stabilized at 6 bar through an automatic pressure relief valve. The material after hydrothermal hydrolysis is exported by a screw conveyor, polyaluminum chloride is added as a conditioner with a dosage of 5% of the dry sludge mass, and the moisture content is reduced to less than 60% after secondary dehydration by a belt filter press, and the sludge specific resistance is reduced to 1.0×10^12 m / kg.

[0019] In a preferred embodiment, in the step S4, the dewatered sludge is transported to a solar greenhouse with a double-layer light transmittance of 92%. The top of the greenhouse is covered with a phase change heat storage material, and a breathable and anti-seepage membrane is laid at the bottom. During the day, it is heated to 50-60 degrees Celsius by solar radiation, and at night, a heat pump is started to assist in maintaining 40 degrees Celsius, and continuous drying for 72 hours reduces the moisture content of the sludge to 65%. Subsequently, a hydrophobic metal-organic framework material adsorption bed is used for deep dehydration.

[0020] In a preferred embodiment, in step S5, the dewatered sludge enters a rotary pyrolysis furnace and is heated in three stages under a nitrogen atmosphere: in the first stage, it is heated at a rate of 15 degrees Celsius per minute to 300 degrees Celsius, and the residence time is 30 minutes to achieve preliminary cracking of organic matter; in the second stage, it is heated to 500 degrees Celsius and stays for 45 minutes to complete secondary cracking of tar; in the third stage, it is heated to 700 degrees Celsius and kept at a constant temperature for 60 minutes, and the specific surface area of the produced biochar is greater than 500 square meters per gram. The pyrolysis gas enters the catalytic reforming tower after dust removal by a cyclone separator and is reformed into syngas with a nickel-based catalyst at 850 degrees Celsius.

[0021] In a preferred embodiment, in step S6, the pyrolysis ash is ground to 100 mesh by a ball mill, and a sulfuric acid solution with a concentration of 1 mole per liter is added according to a solid-liquid ratio of 1:10, and it is stirred and leached at 80 degrees Celsius for 2 hours, and the phosphorus leaching rate exceeds 90%. After adjusting the pH of the leachate to 9.0, magnesium chloride supported by biochar is added, and struvite crystals are formed by reaction. After centrifugal separation and washing with pure water, magnesium ammonium phosphate with a purity > 95% is obtained. Further, it is calcined at 450 degrees Celsius for 2 hours.

[0022] In a preferred embodiment, in step S7, the pyrolysis tail gas enters a two-stage biological filter tower after bag dust removal: the first stage is filled with a biological filler of sulfur-oxidizing bacteria, and the residence time in the empty tower is 40 seconds, and the efficiency of removing hydrogen sulfide is > 98%; the second stage is filled with a biological film of nitrifying bacteria, and the pH of the spraying liquid is controlled at 7.5 - 8.0, and the ammonia nitrogen removal rate is > 90%. The purified tail gas is introduced into an amino-functionalized silica gel adsorption tower, the bulk density of the adsorbent is 600 kilograms per cubic meter, carbon dioxide is selectively captured at 50 degrees Celsius, and after adsorption saturation, it is desorbed by 120 degrees Celsius steam, and the purity of carbon dioxide is > 99%. After being pressurized to 30 bar, it is liquefied and stored.

[0023] In a preferred embodiment, in step S8, a digital twin system is deployed to collect 12 types of sensor data of sludge flow rate, temperature, pH, ORP, and volatile fatty acids in real time, and the database is updated every 5 seconds. A multi-variable prediction model is established using a long short-term memory neural network. The input layer contains 32 neurons, the hidden layer is set with 64 nodes, and the output layer dynamically optimizes 18 process parameters such as ultrasonic power, pyrolysis temperature, and MOF adsorption cycle.

[0024] In a preferred embodiment, in step S9, the prepared biochar is used in the advanced treatment unit after the secondary sedimentation tank at a dosage of 20 grams per ton of sewage. The total phosphorus adsorption capacity reaches 35 milligrams per gram, replacing 80% of the usage amount of traditional polyferric sulfate. The hydroxyapatite slow-release fertilizer is evenly spread by a municipal greening fertilization vehicle, with an annual application amount of 5 kilograms per mu of land, and the available phosphorus content in the soil is increased by 2.3 times. The final effluent quality of the system meets the requirements of chemical oxygen demand ≤ 30 milligrams per liter and total phosphorus ≤ 0.3 milligrams per liter. The carbon footprint of the entire sludge treatment process is reduced by 1.5 kilograms of carbon dioxide equivalent per ton of dry sludge.

[0025] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0026] 1. In the present invention, biochar, as the core medium, directly participates in the construction of the structure body. Its porous characteristics and adsorption performance are integrated into the filter interlayer and ecological slope protection of the hydraulic structure, replacing traditional sand filter materials and concrete additives, which not only simplifies the construction process but also enhances the structural functionality. The process equipment and building space adopt the principle of collaborative design. The diversion wall of the anaerobic reactor and the refractory lining of the pyrolysis furnace are integrally cast in combination with the characteristics of biochar-based materials, greatly improving the matching accuracy of the equipment foundation and the main structure. The intelligent embedded system implanted during the construction process enables the precise positioning of the sensor network and process pipelines during the concrete pouring stage, effectively avoiding structural damage caused by later grooving and demolition.

[0027] 2. In the present invention, the biochar advanced phosphorus removal unit replaces traditional chemical agents, reducing the risk of secondary pollution; the recovered phosphorus resources are modified and converted into slow-release soil conditioners, synchronously solving the dual problems of the phosphorus removal cost in the sewage treatment plant and the lack of phosphorus in urban greening. The solar-coupled adsorption dehydration technology breaks through the high energy consumption limit of traditional thermal drying, and combined with the intelligent control system, realizes the refined management of the dehydration link. The final product chain covers various high-value products such as energy gas, carbon-based materials, and slow-release fertilizers, forming a "treatment - reuse - feedback" closed-loop mode, which not only reduces the comprehensive cost of sludge disposal but also extends derivative values such as ecological restoration and carbon sink enhancement, endowing the sewage treatment plant with sustainable operation capabilities. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the process principle of the present invention. Detailed Embodiments

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Example 1:

[0031] Reference Figure 1 ,

[0032] A sludge treatment process for a sewage treatment plant, the treatment process comprising the following steps:

[0033] S1: When physically crushing concentrated sludge by high-frequency ultrasonic waves, relying on the special ultrasonic cell structure design: a 316L stainless steel vibration plate base is arranged in a reinforced concrete cell body, and stable transmission of high-frequency power is realized through embedded galvanized steel pipe threading pipes. The vibration plate amplitude is controlled within 50 - 70μm to optimize the cell wall crushing efficiency; simultaneously, a calcium peroxide dosing system is integrated on the cell top, connected to an explosion-proof metering pump using corrosion-resistant CPVC pipes, and 360° mixing of the reagent and sludge is achieved through an annular dosing device;

[0034] S2: Mix the sludge after ultrasonic treatment with food waste, add biochar-supported nanomaterials as a conductive medium, and construct a direct interspecies electron transfer (DIET) system. Using a two-phase anaerobic reactor (acidogenesis phase → methanogenesis phase), the methane production rate is increased by 30%, and the digestion cycle is shortened to 12 days;

[0035] S3: Perform microwave-assisted hydrothermal hydrolysis on the residue after anaerobic digestion (temperature 160°C, pressure 6 bar, microwave power 800 W) to decompose refractory organic substances such as lignin, improving the dewatering performance by 40%. Simultaneously, recover volatile fatty acids (VFAs) for carbon source supplementation in the sewage treatment plant;

[0036] S4: Use a solar greenhouse drying system (integrated with phase change heat storage materials) for preliminary dehydration, combined with a new hydrophobic MOFs material to adsorb moisture, reducing the sludge moisture content from 80% to 55%, and reducing energy consumption by 70% compared to traditional thermal drying;

[0037] S5: Perform stepwise pyrolysis (300°C → 500°C → 700°C) on the dehydrated sludge under anoxic conditions to generate biochar with a high specific surface area (>500 m 2 / g). The pyrolysis gas is used as a system heat source after catalytic reforming, realizing energy self-circulation;

[0038] S6: Recover phosphorus from the pyrolysis ash by acid leaching (H2SO4)-struvite crystallization method, using biochar as a magnesium source carrier, with a phosphorus recovery rate >85%. Modify the recovered phosphorus product with hydroxyapatite to prepare a slow-release soil conditioner;

[0039] S7: Integrate a biological filter tower (sulfur-oxidizing / nitrifying bacteria) and an activated carbon adsorption device to treat the pyrolysis tail gas, use amino-functionalized silica gel to capture CO and convert it into bicarbonate, achieving carbon sequestration and an odor removal rate of >95%;

[0040] S8: Deploy a digital twin system to monitor data in real time through online sensors, combine LSTM neural network to predict the optimal process parameters (such as ultrasonic intensity and pyrolysis temperature), and dynamically adjust the equipment operation status;

[0041] S9: Incorporate high specific surface area biochar produced by pyrolysis as a functional material into the civil engineering renovation of the sewage treatment plant. Embed a biochar filter interlayer on the side wall of the outlet channel of the secondary sedimentation tank, fix the carbon-based filler with a stainless steel grid frame, and reliably connect it to the concrete structure through bolt anchoring. Simultaneously, add 30% biochar to improve the planting soil during the construction of the rainwater garden in the factory area, and lay a permeable concrete surface layer after backfilling and compaction in layers to form an ecological filter bed with both nitrogen removal and phosphorus removal functions. When pre-buried slow-release phosphate fertilizer delivery pipelines in the municipal green belt, lay a biochar adsorption layer at the bottom of the trench to intercept runoff pollutants, use geotextiles to wrap carbon particles to prevent loss, and set removable inspection wells at the pipe joints to facilitate replacement and maintenance of the carbon layer, thus realizing the full chain cycle of carbon-based materials from sewage treatment to municipal engineering.

[0042] In step S1, concentrated sludge from a sewage treatment plant is taken, and the initial moisture content is controlled at 95% to 97%. It is first treated by a high-frequency ultrasonic reactor with a frequency of 20 kHz to 40 kHz, and the ultrasonic power density is set to 0.5 watts per milliliter. The continuous action time is 30 minutes, and the sludge temperature is maintained below 35 degrees Celsius to prevent organic matter from being pyrolyzed. After the treatment is completed, 5 grams of calcium peroxide powder is added per liter of sludge, and the mixture is stirred and mixed at a speed of 200 revolutions per minute for 20 minutes to uniformly disperse the calcium peroxide and release active oxygen, and simultaneously complete cell wall breaking, heavy metal passivation and pathogenic microorganism inactivation. The soluble chemical oxygen demand (SCOD) of the pretreated sludge is increased to more than 2.3 times that of the original mud, and the volatile solid (VS) degradation rate is less than 8%.

[0043] In step S2, the biochar-loaded nanomaterials include: 60 parts by weight of sludge-based biochar, 10 parts by weight of polydopamine-coated nano zero-valent iron, 8 parts by weight of conductive polyaniline, 5 parts by weight of superparamagnetic Fe3O4, 3 parts by weight of diammonium hydrogen phosphate, 2 parts by weight of calcium carbonate, and 1 part by weight of KOH activator;

[0044] The preparation method of biochar-supported nanomaterials includes: First, take the dewatered sludge from the sewage treatment plant, and perform cascade pyrolysis treatment. First, carry out pre-carbonization at 300 °C for 30 minutes and activation treatment at 600 °C. In the activation stage, KOH impregnation is used with a mass ratio of 1:2, and it is kept warm for 1 hour under nitrogen protection. Then, it is pickled with 0.1M HCl to remove ash, washed with deionized water, vacuum dried, and ground to 200 meshes to obtain sludge-based biochar. Then, the biochar is soaked in a 0.5M FeSO4 solution with a solid-liquid ratio of 1:10. After ultrasonic dispersion for 30 minutes, a 0.5M NaBH4 solution is added dropwise, controlling the molar ratio of Fe2+ to BH4- to be 1:2. It reacts for 2 hours under nitrogen protection to generate nano-zero-valent iron. Then, an aniline monomer with a mass ratio of 1:5 to the biochar is added, and in-situ polymerization is carried out using ammonium persulfate as an initiator to form a polyaniline conductive coating layer. Finally, FeCl2·4H2O and FeCl3·6H2O are dissolved in a molar ratio of 1:2 by the co-precipitation method, ammonia water is added dropwise to adjust the pH to 10, and it is stirred at 60 °C for 1 hour to prepare Fe3O4 magnetic particles. They are loaded onto the biochar surface by magnetic field separation, and then ball-milled and mixed with diammonium hydrogen phosphate and calcium carbonate at a rotation speed of 300 rpm for 2 hours. Finally, it is tableted and granulated to obtain a finished biochar-supported nanomaterial with a particle size of 2-3 mm.

[0045] In step S3, the residue after anaerobic digestion is dehydrated by a plate and frame filter press to a moisture content of 80%, and then enters a microwave-assisted hydrothermal reaction kettle. The reaction conditions are set as a microwave power of 800 watts, a heating rate of 10 degrees Celsius per minute, a target temperature of 160 degrees Celsius and maintained for 30 minutes, and the reaction pressure is stabilized at 6 bar through an automatic pressure relief valve. The material after hydrothermal hydrolysis is exported by a screw conveyor, and polyaluminum chloride (PAC) is added as a conditioner with a dosage of 5% of the dry sludge mass. After secondary dehydration by a belt filter press, the moisture content is reduced to less than 60%, and the sludge specific resistance is reduced to 1.0×10^12 m / kg. The simultaneously recovered volatile fatty acids are collected by a condenser with a concentration of 12000 mg / L and directly reused as a denitrification carbon source in the sewage treatment plant.

[0046] In step S4, the dewatered sludge is transported to a solar greenhouse with a double-layer light transmittance of 92%. The top of the greenhouse is covered with a phase change heat storage material (paraffin-expanded graphite composite material, phase change temperature 45 degrees Celsius), and a breathable and anti-seepage membrane is laid at the bottom. During the day, it is heated to 50-60 degrees Celsius using solar radiation, and at night, a heat pump is started to assist in maintaining 40 degrees Celsius. After continuous drying for 72 hours, the moisture content of the sludge is reduced to 65%. Then, a hydrophobic metal-organic framework material (MOF-303) adsorption bed is used for deep dehydration. The filling density of the MOF material is 200 kg per cubic meter, and the adsorption cycle is 6 hours. Finally, the moisture content of the sludge is reduced to 55%, and the unit energy consumption is 0.6 kWh per ton of water evaporation.

[0047] In step S5, the dewatered sludge enters a rotary pyrolysis furnace and is heated in three stages under a nitrogen atmosphere: in the first stage, it is heated at a rate of 15 degrees Celsius per minute to 300 degrees Celsius, and the residence time is 30 minutes to achieve the preliminary cracking of organic matter; in the second stage, it is heated to 500 degrees Celsius and stays for 45 minutes to complete the secondary cracking of tar; in the third stage, it is heated to 700 degrees Celsius and kept at a constant temperature for 60 minutes to produce biochar with a specific surface area greater than 500 square meters per gram. The pyrolysis gas enters the catalytic reforming tower after dust removal by a cyclone separator and is reformed into syngas (H+CO content > 70%) at 850 degrees Celsius with a nickel-based catalyst, and is recycled for combustion heating of the pyrolysis furnace, with an energy self-sufficiency rate of 85%.

[0048] In step S6, the pyrolysis ash is ground to 100 mesh by a ball mill, and a sulfuric acid solution with a concentration of 1 mole per liter is added at a solid-liquid ratio of 1:10, and it is stirred and leached at 80 degrees Celsius for 2 hours, and the phosphorus leaching rate exceeds 90%. After adjusting the pH of the leachate to 9.0, magnesium chloride supported on biochar (mass ratio of MgCl·6H₂O to biochar is 1:5) is added, and struvite crystals are formed by reaction. After centrifugal separation and washing with pure water, magnesium ammonium phosphate with a purity > 95% is obtained. Further, it is calcined at 450 degrees Celsius for 2 hours to be converted into hydroxyapatite slow-release fertilizer, and the phosphorus dissolution rate within 24 hours is controlled within 5%.

[0049] In step S7, the pyrolysis tail gas enters a two-stage biological filter tower after bag dust removal: the first stage is filled with a biological filler of sulfur-oxidizing bacteria, and the residence time in the empty tower is 40 seconds, and the removal efficiency of hydrogen sulfide > 98%; the second stage is filled with a biological film of nitrifying bacteria, and the pH of the spraying liquid is controlled at 7.5 - 8.0, and the ammonia nitrogen removal rate > 90%. The purified tail gas is introduced into an amino-functionalized silica gel adsorption tower, the bulk density of the adsorbent is 600 kg / m³, carbon dioxide is selectively captured at 50 degrees Celsius, and after adsorption saturation, it is desorbed by steam at 120 degrees Celsius, and the purity of carbon dioxide > 99%, and it is liquefied and stored after being pressurized to 30 bar.

[0050] In step S8, a digital twin system is deployed to collect 12 types of sensor data such as sludge flow rate, temperature, pH, ORP, volatile fatty acids in real time, and update the database every 5 seconds. A multi-variable prediction model is established using a long short-term memory neural network (LSTM). The input layer contains 32 neurons, the hidden layer is set with 64 nodes, and the output layer dynamically optimizes 18 process parameters such as ultrasonic power, pyrolysis temperature, and MOF adsorption cycle. The system generates a global optimization plan every 24 hours through a reinforcement learning algorithm, the equipment control response time is less than 1 second, and the comprehensive energy consumption is reduced by 12%.

[0051] In step S9, the prepared biochar is used in the post-secondary treatment unit after the secondary sedimentation tank at a dosage of 20 grams per ton of sewage. Its total phosphorus adsorption capacity reaches 35 milligrams per gram, replacing 80% of the usage of traditional polyferric sulfate agents. The hydroxyapatite slow-release fertilizer is evenly spread by a municipal greening fertilization vehicle, with an annual application rate of 5 kilograms per mu of land, and the available phosphorus content in the soil is increased by 2.3 times. The final effluent quality of the system meets the requirements of chemical oxygen demand (COD) ≤ 30 milligrams per liter and total phosphorus ≤ 0.3 milligrams per liter. The carbon footprint of the entire sludge treatment process is reduced by 1.5 kilograms of carbon dioxide equivalent per ton of dry sludge.

[0052] It can be seen from the above that:

[0053] In the present invention, the biochar, as the core medium, directly participates in the construction of the structure body. Its porous characteristics and adsorption performance are integrated into the filter interlayer and ecological slope protection of the hydraulic structure, replacing traditional sand filter materials and concrete additives, which not only simplifies the construction process but also enhances the structural functionality. The process equipment and building space adopt the principle of collaborative design. The diversion wall of the anaerobic reactor and the refractory lining of the pyrolysis furnace are integrally cast in combination with the characteristics of the biochar-based material, greatly improving the matching accuracy of the equipment foundation and the main structure. The intelligent embedded system implanted during the construction process enables the precise positioning of the sensor network and process pipelines during the concrete pouring stage, effectively avoiding the structural damage caused by later grooving and demolition.

[0054] In the present invention, through multi-stage collaboration and resource closed-loop design, double breakthroughs in environmental benefits and economic benefits have been achieved. The synergistic effect of the biochar loaded with nanomaterials significantly improves the efficiency of organic matter decomposition. Its unique conductive network structure accelerates the electron transfer during anaerobic digestion, enabling the methane production rate to break through the bottleneck of traditional processes, while effectively inhibiting the generation of malodorous by-products such as hydrogen sulfide. The superparamagnetic component endows the material with efficient recovery characteristics. Combined with the slow-release nutrition system, while reducing the dependence on chemical agents, it greatly enhances the microbial metabolic activity, ensuring the stabilization of heavy metals and the inactivation of pathogens. The energy and material cycle design of each link of the process converts the sludge pyrolysis gas into the self-used heat source of the system, forming an internal energy cycle link, significantly reducing the demand for external energy input.

[0055] In the present invention, the biochar deep phosphorus removal unit replaces traditional chemical agents, reducing the risk of secondary pollution. The recovered phosphorus resources are modified and converted into slow-release soil conditioners, simultaneously solving the dual problems of the phosphorus removal cost of the sewage treatment plant and the lack of phosphorus in urban greening. The solar energy-coupled adsorption dehydration technology breaks through the high energy consumption limit of traditional thermal drying. Combined with the intelligent control system, it realizes the refined management of the dehydration link. The final product chain covers various high-value products such as energy gas, carbon-based materials, and slow-release fertilizers, forming a "treatment - reuse - feedback" closed-loop mode, which not only reduces the comprehensive cost of sludge disposal but also extends derivative values such as ecological restoration and carbon sink enhancement, endowing the sewage treatment plant with sustainable operation capabilities.

[0056] Example Two:

[0057] Refer to Figure 1 ,

[0058] A sludge treatment process for sewage treatment plants, the treatment process includes the following steps:

[0059] S1: Physically crush the thickened sludge by high-frequency ultrasonic waves to break the microbial cell wall and release intracellular organic matter, improving the subsequent treatment efficiency. Add calcium peroxide for chemical oxidation pretreatment to simultaneously achieve heavy metal passivation and pathogen inactivation;

[0060] S2: Mix the sludge after ultrasonic treatment with food waste, add biochar-supported nanomaterials as conductive media to construct a direct interspecies electron transfer (DIET) system. Use a two-phase anaerobic reactor (acidogenesis phase → methanogenesis phase), with the methane production rate increased by 30% and the digestion period shortened to 12 days;

[0061] S3: Conduct microwave-assisted hydrothermal hydrolysis on the residue after anaerobic digestion (temperature 160 °C, pressure 6 bar, microwave power 800 W) to decompose refractory organic matters such as lignin, improving the dewatering performance by 40%. Simultaneously recover volatile fatty acids (VFAs) for carbon source supplementation in sewage treatment plants;

[0062] S4: Use a solar greenhouse drying system (integrated with phase change heat storage materials) for preliminary dehydration, and cooperate with a new type of hydrophobic MOFs material to adsorb moisture, reducing the sludge moisture content from 80% to 55%, and the energy consumption is reduced by 70% compared with traditional thermal drying;

[0063] S5: Carry out stepwise pyrolysis (300 °C → 500 °C → 700 °C) on the dehydrated sludge under anoxic conditions to generate biochar with a high specific surface area (>500 m 2 / g). The pyrolysis gas is catalytically reformed and reused as the system heat source to achieve energy self-circulation;

[0064] S6: Recover phosphorus from the pyrolysis ash by acid leaching (H2SO4)-struvite crystallization method, use biochar as a magnesium source carrier, and the phosphorus recovery rate > 85%. Modify the recovered phosphorus product with hydroxyapatite to prepare a slow-release soil conditioner;

[0065] S7: Integrate a biological filter tower (sulfur-oxidizing / nitrifying bacteria groups) and an activated carbon adsorption device to treat the pyrolysis tail gas, use amino-functionalized silica gel to capture CO and convert it into bicarbonate to achieve carbon sequestration and the removal rate of odor substances > 95%;

[0066] S8: Deploy the digital twin system, monitor data in real time through online sensors, combine with the LSTM neural network to predict the optimal process parameters (such as ultrasonic intensity, pyrolysis temperature), and dynamically adjust the operating state of the equipment;

[0067] S9: The biochar is used for deep phosphorus removal in sewage treatment plants, and the slow-release phosphate fertilizer feeds back to municipal greening. The effluent of the system meets the first-class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002), and the carbon emission reduction amount of the whole process is > 1.2 kg CO equivalent / ton of sludge.

[0068] In step S1, take the concentrated sludge from the sewage treatment plant, control the initial moisture content at 95% - 97%. First, treat it with a high-frequency ultrasonic reactor with a frequency of 20 kHz to 40 kHz, set the ultrasonic power density at 0.5 watts per milliliter, and keep the action time for 30 minutes. Maintain the sludge temperature below 35 °C to prevent the pyrolysis of organic matter. After the treatment, add 5 grams of calcium peroxide powder per liter of sludge, stir and mix at a speed of 200 revolutions per minute for 20 minutes to evenly disperse the calcium peroxide and release active oxygen, and simultaneously complete cell wall breaking, heavy metal passivation and inactivation of pathogenic microorganisms. The soluble chemical oxygen demand (SCOD) of the pretreated sludge is increased to more than 2.3 times that of the original sludge, and the degradation rate of volatile solids (VS) is less than 8%.

[0069] In step S2, the biochar-supported nanomaterials include: 70 parts by weight of sludge-based biochar, 15 parts by weight of polydopamine-coated nano-zero-valent iron, 10 parts by weight of conductive polyaniline, 8 parts by weight of superparamagnetic Fe3O4, 5 parts by weight of diammonium hydrogen phosphate, 3 parts by weight of calcium carbonate, and 2 parts by weight of KOH activator;

[0070] The preparation method of the biochar-supported nanomaterials includes: First, take the dewatered sludge from the sewage treatment plant, perform stepwise pyrolysis treatment, carry out pre-carbonization at 300 °C for 30 minutes and activation treatment at 600 °C in sequence. The activation stage uses KOH impregnation with a mass ratio of 1:2, and is kept warm for 1 hour under nitrogen protection. Then, it is pickled with 0.1M HCl to remove ash, washed with deionized water, vacuum dried, and ground to 200 meshes to obtain sludge-based biochar; Next, the biochar is soaked in a 0.5M FeSO4 solution with a solid-liquid ratio of 1:10. After ultrasonic dispersion for 30 minutes, a 0.5M NaBH4 solution is added dropwise, controlling the molar ratio of Fe2+ to BH4- to be 1:2. It reacts for 2 hours under nitrogen protection to generate nano-zero valent iron. Then, aniline monomer with a mass ratio of 1:5 to the biochar is added, and in-situ polymerization is carried out using ammonium persulfate as an initiator to form a polyaniline conductive coating layer; Finally, FeCl2·4H2O and FeCl3·6H2O are dissolved in a molar ratio of 1:2 by the co-precipitation method, ammonia water is added dropwise to adjust the pH to 10, and it is stirred at 60 °C for 1 hour to prepare Fe3O4 magnetic particles. They are loaded onto the biochar surface through magnetic separation, and then ball-milled and mixed with diammonium hydrogen phosphate and calcium carbonate at a rotation speed of 300 rpm for 2 hours. Finally, it is tableted and granulated to obtain the finished biochar-supported nanomaterials with a particle size of 2 - 3 mm.

[0071] In step S3, the residue after anaerobic digestion is dehydrated by a plate and frame filter press to a moisture content of 80%, and then enters a microwave-assisted hydrothermal reaction kettle. The reaction conditions are set as a microwave power of 800 watts, a heating rate of 10 degrees Celsius per minute, a target temperature of 160 degrees Celsius and maintained for 30 minutes, and the reaction pressure is stabilized at 6 bar through an automatic pressure relief valve. The material after hydrothermal hydrolysis is exported by a screw conveyor, polyaluminum chloride (PAC) is added as a conditioner with a dosage of 5% of the dry sludge mass, and the moisture content is reduced to less than 60% after secondary dehydration by a belt filter press, and the sludge specific resistance is reduced to 1.0×10^12 m / kg. The simultaneously recovered volatile fatty acids are collected by a condenser with a concentration reaching 12000 mg / L and directly reused as the denitrification carbon source in the sewage treatment plant.

[0072] In step S4, the dewatered sludge is transported to a solar greenhouse with a double-layer light transmittance of 92%. The top of the greenhouse is covered with a phase change heat storage material (paraffin-expanded graphite composite material, phase change temperature 45 degrees Celsius), and a breathable and anti-seepage membrane is laid at the bottom. During the day, it is heated by solar radiation to 50 - 60 degrees Celsius, and at night, a heat pump is started to assist in maintaining 40 degrees Celsius. It is continuously dried for 72 hours to reduce the sludge moisture content to 65%. Then, a hydrophobic metal-organic framework material (MOF-303) adsorption bed is used for deep dehydration. The filling density of the MOF material is 200 kg per cubic meter, and the adsorption cycle is 6 hours. Finally, the sludge moisture content is reduced to 55%, and the unit energy consumption is 0.6 kWh per ton of water evaporation.

[0073] In step S5, the dewatered sludge enters a rotary pyrolysis furnace and is heated in three stages under a nitrogen atmosphere: in the first stage, it is heated at a rate of 15 degrees Celsius per minute to 300 degrees Celsius, and stays for 30 minutes to achieve preliminary cracking of organic matter; in the second stage, it is heated to 500 degrees Celsius and stays for 45 minutes to complete secondary cracking of tar; in the third stage, it is heated to 700 degrees Celsius and kept at a constant temperature for 60 minutes, generating biochar with a specific surface area greater than 500 square meters per gram. The pyrolysis gas enters the catalytic reforming tower after dust removal by a cyclone separator, and is reformed into syngas (H+CO content > 70%) at 850 degrees Celsius with a nickel-based catalyst, and is recycled for combustion heating of the pyrolysis furnace, with an energy self-sufficiency rate of 85%.

[0074] In step S6, the pyrolysis ash is ground to 100 mesh by a ball mill, and a sulfuric acid solution with a concentration of 1 mole per liter is added according to a solid-liquid ratio of 1:10, and stirred and leached at 80 degrees Celsius for 2 hours, with a phosphorus leaching rate exceeding 90%. After adjusting the pH of the leachate to 9.0, magnesium chloride loaded on biochar (mass ratio of MgCl·6H₂O to biochar is 1:5) is added, and struvite crystals are formed by reaction. After centrifugal separation and washing with pure water, magnesium ammonium phosphate with a purity > 95% is obtained. Further calcined at 450 degrees Celsius for 2 hours, it is converted into hydroxyapatite slow-release fertilizer, and the phosphorus dissolution rate within 24 hours is controlled within 5%.

[0075] In step S7, the pyrolysis tail gas enters a two-stage biological filter tower after bag dust removal: the first stage is filled with a biological filler of sulfur-oxidizing bacteria, and the empty tower residence time is 40 seconds, with a hydrogen sulfide removal efficiency > 98%; the second stage is filled with a nitrifying bacteria biofilm, and the pH of the spraying liquid is controlled at 7.5 - 8.0, with an ammonia nitrogen removal rate > 90%. The purified tail gas is introduced into an amino-functionalized silica gel adsorption tower, the bulk density of the adsorbent is 600 kg / m³, carbon dioxide is selectively captured at 50 degrees Celsius, and after adsorption saturation, it is desorbed by 120 degrees Celsius steam, with a carbon dioxide purity > 99%, and liquefied and stored after being pressurized to 30 bar.

[0076] In step S8, a digital twin system is deployed to collect 12 types of sensor data such as sludge flow rate, temperature, pH, ORP, volatile fatty acids in real time, and update the database every 5 seconds. A multivariate prediction model is established using a long short-term memory neural network (LSTM). The input layer contains 32 neurons, the hidden layer is set with 64 nodes, and the output layer dynamically optimizes 18 process parameters such as ultrasonic power, pyrolysis temperature, MOF adsorption cycle, etc. The system generates a global optimization plan every 24 hours through a reinforcement learning algorithm, the equipment control response time is less than 1 second, and the comprehensive energy consumption is reduced by 12%.

[0077] In step S9, the prepared biochar is used in the post-secondary sedimentation deep treatment unit at a ratio of 20 grams per ton of sewage, with a total phosphorus adsorption capacity of 35 milligrams per gram, replacing 80% of the usage of traditional polyferric sulfate agents. The hydroxyapatite slow-release fertilizer is evenly spread by a municipal greening fertilization vehicle, with an annual application rate of 5 kilograms per mu of land, and the available phosphorus content in the soil is increased by 2.3 times. The final effluent quality of the system meets the requirements of chemical oxygen demand (COD) ≤ 30 milligrams per liter and total phosphorus ≤ 0.3 milligrams per liter, and the carbon footprint of the entire sludge treatment process is reduced by 1.5 kilograms of carbon dioxide equivalent per ton of dry sludge.

[0078] It can be seen from the above that:

[0079] In the present invention, through multi-stage coordination and resource closed-loop design, double breakthroughs in environmental benefits and economic benefits are achieved. The synergistic effect of biochar-supported nanomaterials significantly improves the efficiency of organic matter decomposition. Its unique conductive network structure accelerates the electron transfer in the anaerobic digestion process, enabling the methane production rate to break through the bottleneck of traditional processes, while effectively inhibiting the generation of malodorous by-products such as hydrogen sulfide. The superparamagnetic component endows the material with efficient recovery characteristics. Combined with the slow-release nutrient system, while reducing the dependence on chemical agents, it greatly enhances the microbial metabolic activity, ensuring the stabilization of heavy metals and the inactivation effect of pathogenic bacteria. The energy and material cycle design of each link of the process converts the sludge pyrolysis gas into a self-used heat source for the system, forming an internal energy cycle link, significantly reducing the demand for external energy input.

[0080] In the present invention, the biochar deep phosphorus removal unit replaces traditional chemical agents, reducing the risk of secondary pollution; the recovered phosphorus resources are modified and converted into slow-release soil conditioners, simultaneously solving the dual problems of the phosphorus removal cost in wastewater treatment plants and the lack of phosphorus in urban greening. The solar-coupled adsorption dehydration technology breaks through the high energy consumption limit of traditional thermal drying. Combined with an intelligent control system, it realizes the refined management of the dehydration link. The final product chain covers various high-value products such as energy gases, carbon-based materials, and slow-release fertilizers, forming a closed-loop mode of "treatment - reuse - feedback". This not only reduces the comprehensive cost of sludge disposal, but also extends derivative values such as ecological restoration and carbon sink enhancement, endowing the wastewater treatment plant with sustainable operation capabilities.

[0081] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sludge treatment process for a sewage treatment plant, characterized in that: The treatment process comprises the following steps: S1: Civil construction of reinforced concrete ultrasonic pool body, pre-buried galvanized steel pipe threading pipe, installation of 316L stainless steel vibration plate base, and integrated CPVC calcium peroxide dosing pipeline system on the top of the pool; S2: Construction of the civil structure of the two-phase anaerobic reactor with a built-in biochar conductive medium layer; S3: Build a microwave hydrolysis reaction pool and pre-bury the supporting volatile fatty acid recovery pipeline; S4: Civil construction solar greenhouse drying workshop, with MOFs material adsorption layer embedded in the wall; S5: Casting of the anoxic pyrolysis kiln structure and supporting the pyrolysis gas catalytic reforming and recycling pipeline network; S6: construct an acid leaching reaction tank and a crystallization device, using a biochar magnesium source carrier structure; S7: Civil construction of biofilter tower base, installation of activated carbon adsorption unit and CO capture pipeline; S8: Pre-embed the process parameter monitoring sensor network and deploy the digital twin control system; S9: Implement full-chain civil engineering renovation: embed biochar filtration interlayer in the secondary sedimentation tank: anchor concrete with stainless steel grids; backfill biochar planting soil in layers in the rain garden; lay geotextile wrapped biochar adsorption layer at the bottom of the municipal trench, and set up a detachable inspection well structure.

2. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In the step S1, concentrated sludge from a sewage treatment plant is taken, and the initial moisture content is controlled at 95% to 97%. It is first treated by a high-frequency ultrasonic reactor with a frequency of 20 kHz to 40 kHz, and the ultrasonic power density is set to 0.5 watts per milliliter. The continuous action time is 30 minutes, and the sludge temperature is maintained below 35 degrees Celsius to prevent thermal decomposition of organic matter.

3. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In step S2, the biochar-loaded nanomaterials include: 60-70 parts by weight of sludge-based biochar, 10-15 parts by weight of polydopamine-coated nano zero-valent iron, 8-10 parts by weight of conductive polyaniline, 5-8 parts by weight of superparamagnetic Fe3O4, 3-5 parts by weight of diammonium hydrogen phosphate, 2-3 parts by weight of calcium carbonate, and 1-2 parts by weight of KOH activator.

4. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In step S3, the residue after anaerobic digestion is dehydrated to a moisture content of 80% by a plate and frame filter press, and then enters a microwave-assisted thermal hydrolysis reactor; the reaction conditions are set to a microwave power of 800 watts, a heating rate of 10 degrees Celsius per minute, a target temperature of 160 degrees Celsius and maintained for 30 minutes, and the reaction pressure is stabilized at 6 bar through an automatic pressure relief valve.

5. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In the step S4, the dehydrated sludge is transported to a double-layer solar greenhouse with a light transmittance of 92%, the top of the greenhouse is covered with a phase change heat storage material, and the bottom is paved with a breathable and impermeable membrane; During the day, solar radiation is used to raise the temperature to 50-60 degrees Celsius.

6. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In step S5, the dehydrated sludge enters a rotary pyrolysis furnace and is heated in three stages under a nitrogen atmosphere: in the first stage, the temperature is increased to 300 degrees Celsius at 15 degrees Celsius per minute and the residence time is 30 minutes to achieve initial cracking of organic matter; in the second stage, the temperature is increased to 500 degrees Celsius and the residence time is 45 minutes to complete secondary cracking of tar; in the third stage, the temperature is increased to 700 degrees Celsius and kept constant for 60 minutes.

7. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In the step S6, the pyrolysis ash is crushed to 100 mesh by a ball mill, and a sulfuric acid solution with a concentration of 1 mol / L is added at a solid-liquid ratio of 1:10, and leaching is carried out under stirring at 80 degrees Celsius for 2 hours, and the phosphorus leaching rate exceeds 90%; after the pH of the leachate is adjusted to 9.0, magnesium chloride loaded with biochar is added to react to generate struvite crystals, and after centrifugal separation and pure water washing, magnesium ammonium phosphate with a purity of >95% is obtained; and further calcined at 450 degrees Celsius for 2 hours.

8. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In step S7, the pyrolysis tail gas enters a two-stage biological filter tower after bag dust removal: the first stage is filled with sulfur oxidizing bacteria biological filler, the empty tower residence time is 40 seconds, and the hydrogen sulfide removal efficiency is greater than 98%; the second stage is filled with nitrifying bacteria biofilm, the spray liquid pH is controlled at 7.5-8.0, and the ammonia nitrogen removal rate is greater than 90%.

9. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In step S8, a digital twin system is deployed to collect 12 types of sensor data including sludge flow, temperature, pH, ORP, and volatile fatty acids in real time, and the database data is updated every 5 seconds.

10. A sludge treatment process for a sewage treatment plant as claimed in claim 1, characterized in that: In step S9, the prepared biochar is added at a ratio of 20 grams per ton of sewage and used in the deep treatment unit after the secondary sedimentation tank, with a total phosphorus adsorption capacity of 35 mg per gram, replacing 80% of the traditional polyferric sulfate agent.

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