A method and a treatment system for reducing and recycling biological sludge based on catalytic cracking reaction

Abstract

The application discloses a method and a treatment system for reducing and recycling biological sludge based on catalytic cracking reaction, and comprises the following steps: adding diluent and scale inhibitor into the dewatered biological sludge of a sewage treatment plant for conditioning treatment, so that the form of the biological sludge is changed from solid state into quasi-solid state, and the conditioned biological sludge is obtained; the conditioned biological sludge is transferred into a catalytic cracking reactor through fluidization, and an oxidizing agent is added for catalytic cracking reaction; the biological sludge is partially released into free water through a controllable oxidation process, so that the form of the biological sludge is changed from quasi-solid state into liquid state, and the organic matter in the biological sludge is decomposed into C2-C6-based carboxylic acid, and a carboxylic acid mixture is obtained; the carboxylic acid mixture is treated through heat exchange and cooling, and then is subjected to solid-liquid separation, so that solid residues and filtrate are obtained, and the biological sludge is reduced and recycled at the same time.

Description

A method and treatment system for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis reaction. Technical Field

[0001] This invention relates to the field of sludge treatment technology, and more specifically, to a method and treatment system for reducing the volume and recycling biological sludge based on catalytic pyrolysis reaction. Background Technology

[0002] With the continuous growth of the global population, the rapid expansion of cities, and the sustained development of industry, the demand for wastewater treatment has been further released, and the situation regarding sludge disposal is becoming increasingly severe. According to statistics, the global total production of wastewater sludge (by dry weight) in 2017 was 45 million tons. China's wastewater sludge production is also increasing rapidly.

[0003] In a narrow sense, biological sludge refers to a byproduct mainly composed of solid particles, accumulated during the sedimentation and aggregation of suspended solids in urban water treatment facilities, excluding silt and other sediments from urban water bodies and soil. The sources of biological sludge are shown in Figure 1. Based on their origin, biological sludge can be divided into two types: water supply sludge and sewage sludge. Sewage sludge, due to its pretreatment primarily employing the activated sludge process based on microbial degradation, differs significantly from water supply sludge in that its main component is biomass, with some inorganic particles adhering to it. All sludge mentioned in this application refers to sewage sludge.

[0004] Most existing wastewater treatment plants employ a process of screen-digestion-denitrification biological treatment-advanced treatment-disinfection. The biological sludge primarily originates from the biological treatment process, with a small amount of grit from the grit chamber and flocculated sediment from coagulation and phosphorus removal. During wastewater treatment, floating debris and large particles in domestic sewage are intercepted in the screen, while organic matter, nitrogen, phosphorus, and suspended solids enter the biological system. Some organic matter, some nitrogen, and almost all phosphorus are converted into microbial matter, which, along with almost all suspended solids, becomes excess sludge and separates from the wastewater system. The remaining organic matter and nitrogen are released into the air as carbon dioxide and nitrogen gas, with very small amounts of organic matter and nitrogen / phosphorus discharged into the environment after meeting emission standards.

[0005] Therefore, biological sludge is a byproduct of urban wastewater treatment systems and an inevitable result of the transformation of pollutants from wastewater to sludge. The properties of biological sludge are mainly determined by the pollution level of the wastewater at the wastewater treatment plant. Under normal circumstances, biological sludge, after being concentrated at the wastewater treatment plant, can reach a water content of 80-85% (i.e., a solid content of 15-20%). It contains a large amount of organic matter, suspended solids intercepted from the wastewater, nutrients such as total nitrogen and total phosphorus, as well as some trace components such as calcium and magnesium ions and trace heavy metal ions. Therefore, the typical biological sludge quality indicators are as follows:

[0006] Table 1. Design Slurry Quality Indicators

[0007] The project design requires the following sludge composition: moisture content 80-85%, organic matter content (VS) 8-12%, slag residue on ignition (TS-VS) 8-12%, pH 6-9, total nitrogen 2000-4000 mg / L, total phosphorus 2000-3000 mg / L, and other indicators meeting relevant standards. surface

[0008] Biological sludge generally poses the following hazards:

[0009] (1) Trace organic matter: Various recalcitrant organic compounds can be detected in sludge, such as polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs), and polycyclic aromatic hydrocarbons (PAHs), which are toxic and harmful substances. These organic compounds take a long time to degrade naturally in the environment, and long-term exposure will cause serious harm to human health.

[0010] (2) Pathogenic microorganisms: Sludge contains a large number of pathogenic bacteria, viruses, parasites and other pathogenic microorganisms. Humans, animals and plants may be infected by direct contact with water, soil and air contaminated by sludge. Therefore, the spread of pathogens through sewage treatment systems needs to be taken seriously.

[0011] (3) Wastewater treatment plants receive some wastewater from industrial production processes, which inevitably leads to the accumulation of heavy metals in sludge. In sludge, heavy metals mostly exist in unstable forms, and changes in the acid-base environment and rainwater runoff can easily cause them to leak out, thus entering water bodies and soil, and then endangering public health through the food chain and infiltration into groundwater.

[0012] (4) Other hazards: During the sludge storage process, unpleasant gases such as H2S are released into the atmosphere, damaging the environmental quality around the water plant and affecting the health of workers. In addition, the high water content of sludge leads to the generation of a large amount of industrial wastewater during the treatment process. This industrial wastewater contains nutrients such as nitrogen and phosphorus, and improper treatment can easily cause it to be lost into water bodies or soil, causing secondary pollution to the ecological environment.

[0013] To address the above issues, numerous sludge treatment technologies and methods have been developed both domestically and internationally. Commonly used technologies include incineration, aerobic treatment, anaerobic treatment, and landfill treatment.

[0014] (1) Drying and Incineration. Sludge drying and incineration is the most thorough treatment process in terms of volume reduction and harmlessness. The residue after incineration is stable, the amount generated is small and easy to handle, and the heat generated can be used for power generation or heating. However, sludge drying and incineration mainly faces two problems: First, the sludge to be incinerated requires a high moisture content (generally below 60%), and mechanically dewatered sludge (80% moisture content) is difficult to meet the requirements directly. The sludge needs to be dried before it can be mixed with other solid pollutants to generate heat; Second, sludge drying and incineration has high equipment requirements, and the operating cost is more than 500-600 yuan / ton, which leads to the widespread adoption of the drying and incineration process mainly in economically developed areas and areas with scarce land resources.

[0015] (2) Anaerobic digestion. This technology is one of the most promising development directions for sludge resource utilization. During anaerobic digestion, anaerobic microorganisms in the sludge hydrolyze organic matter through dissimilar reactions to obtain electron donors for growth and reproduction. Then, acid-producing and methanogenic bacteria convert intermediate fragments into renewable biogas. Because the biogas produced by anaerobic digestion can be directly used for power generation and heat production, supplementing the energy needs of urban wastewater treatment plants, this technology has been widely adopted in Europe, America, and Japan. However, in China, because the organic matter content in sludge is only 30%–60%, far lower than in developed countries, the biogas output is low and operating costs are high, making it difficult to promote and apply. Of the urban wastewater treatment plants built nationwide, approximately 60 have adopted anaerobic digestion technology, but only about 20 are operating normally.

[0016] (3) Aerobic composting. Dewatered sludge naturally contains organic carbon sources and aerobic microorganisms. Adding materials such as sawdust and straw as bulking agents to the sludge increases its porosity and air contact area, allowing aerobic microorganisms to multiply and develop rapidly using organic matter as a substrate, fermenting it into stable humus-like substances, which is aerobic composting. Aerobic compost products are excellent plant growth regulators and can be reused on land. At the same time, composting effectively saves treatment costs, and the subsequent reuse of sludge has limited environmental impact, making it particularly suitable for wastewater treatment units with simple wastewater sources, no industrial pollution, and small sludge production.

[0017] (4) Sanitary landfill. Sanitary landfill refers to the process of stabilizing dewatered sludge from wastewater treatment plants with lime and other substances, and then landfilling it at a selected specialized site. Sanitary landfill is economically cost-effective and simple, and was once widely used worldwide. However, the stabilization of landfilled sludge still requires 2–7 years, not only consuming land resources but also potentially affecting local groundwater safety due to leachate. Therefore, it has been increasingly abandoned by many countries and regions. Since 2000, European and American countries have banned sanitary landfill of sludge, and the proportion of landfilled sludge has been decreasing year by year. As an outdated technology, sanitary landfill of sludge will inevitably be replaced by other advanced processes in the future, and is currently only permitted for use under emergency conditions.

[0018] Biological sludge has a complex organic composition, mainly consisting of cellular phases and extracellular polymers. Various hydrophilic organic compounds are intertwined and concentrated, forming a tight polymeric structure. This structure makes it difficult to effectively remove capillary water, adsorbed water, and internal water from the sludge particles under mechanical force. Furthermore, the diversity of wastewater sources means that the sludge contains toxic and harmful pollutants, mostly recalcitrant organic matter. This makes it difficult to achieve harmlessness using traditional treatment technologies. Finding a technically feasible and economically acceptable process has always been a key research focus in this field. Summary of the Invention

[0019] The purpose of this invention is to overcome the above-mentioned defects in the existing technology and provide a method and treatment system for reducing the volume and recycling resources of biological sludge based on catalytic cracking reaction. This method can change the structural characteristics of biological sludge, releasing at least part of the capillary water, adsorbed water of sludge particles, and water inside sludge particles into free water, so that the biological sludge changes from solid to quasi-solid and then to liquid. At the same time, the organic matter in the biological sludge is at least partially decomposed into carboxylic acids mainly composed of C2-C6, so that the carbon element in the sludge can be recycled while reducing the volume of biological sludge.

[0020] To achieve the above objectives, the technical solution of the present invention is as follows:

[0021] A method for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis includes the following steps:

[0022] (1) Add diluent and scale inhibitor to the dewatered biological sludge from the sewage treatment plant for conditioning treatment, so that the biological sludge changes from solid to quasi-solid state, and obtains conditioning biological sludge with a water content of 85% to 95%.

[0023] (2) The conditioned biological sludge is transferred to the catalytic cracking reactor through fluidization, and an oxidant is added to carry out the catalytic cracking reaction. The conditioned biological sludge releases capillary water, water adsorbed by sludge particles, and water inside sludge particles into free water through a controlled oxidation process, so that the biological sludge changes from a quasi-solid state to a liquid state. At the same time, the organic matter in the biological sludge is decomposed into carboxylic acids mainly composed of C2-C6 to obtain a carboxylic acid mixture.

[0024] (3) The carboxylic acid mixture is subjected to heat exchange and cooling treatment until the temperature of the carboxylic acid mixture is between room temperature and 100°C, and the temperature of the water is raised to 120°C to 320°C. Then, solid-liquid separation is performed to obtain solid residue and filtrate, so that the biological sludge can realize the resource utilization of carbon elements while reducing the volume.

[0025] The present invention also discloses a treatment system for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis reaction, wherein the treatment system implements the method described above;

[0026] The processing system includes a conditioning unit, a catalytic cracking unit, a heat exchange unit, and a separation unit connected in sequence;

[0027] The conditioning unit is used to fully mix the dewatered biological sludge, diluent, and scale inhibitor from the wastewater treatment plant to obtain conditioned biological sludge with a moisture content of 80% to 99%.

[0028] The catalytic pyrolysis unit is connected to the outlet of the conditioning unit. The conditioned biological sludge is fluidized and transported to the catalytic pyrolysis unit by a power device. The catalytic pyrolysis unit is also equipped with an oxidant inlet, which is used to release the capillary water, sludge particle adsorbed water, and sludge particle internal water into free water through a controlled oxidation process under the action of the oxidant. At the same time, the organic matter in the biological sludge is decomposed into carboxylic acids mainly composed of C2-C6 to obtain a carboxylic acid mixture.

[0029] The heat exchange unit is connected to the outlet of the catalytic cracking unit and is used to cool the carboxylic acid mixture to room temperature to 100°C and raise the temperature of the water to 120°C to 320°C. The mixture is then transferred to the solid-liquid separation unit, where solid residue and filtrate are obtained after solid-liquid separation. This allows the biological sludge to be reduced in volume while simultaneously utilizing carbon resources.

[0030] Implementing the embodiments of the present invention will have the following beneficial effects:

[0031] This invention provides a method for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis. This method can change the structural characteristics of biological sludge, releasing at least a portion of the capillary water, adsorbed water in the sludge particles, and internal water in the sludge particles into free water, thus changing the sludge's morphology from quasi-solid to liquid. At the same time, the organic matter in the biological sludge is at least partially decomposed into carboxylic acids, mainly C2-C6. The solution and suspended solids are then separated by a solid-liquid separation system. The carboxylic acid products, mainly C2-C6, are sold as a carbon source, and the remaining solid residue can be used for landscaping, forestry fertilizer, and land improvement. This allows for the resource utilization of carbon elements in the biological sludge while reducing its volume.

[0032] This invention solves the problem of sludge harmlessness while significantly reducing the volume of biological sludge to 20%–40% of its original volume, and even reducing the volume of single biological sludge to less than 10% of its original volume. The most significant feature of this invention is that it achieves biological sludge reduction through a "chemical process." Compared to anaerobic digestion and aerobic composting, it requires only 10-20% of the land area of ​​these two methods, and the main process retention time is less than 1% of theirs. The operating cost and investment of this method are lower than anaerobic digestion and similar to aerobic composting. Furthermore, the solid residue after anaerobic digestion and aerobic composting can only be reduced to 50-60% of its original volume (based on 80% biological sludge moisture content), while this invention can reduce the moisture content to as low as below 10%, overcoming the bottlenecks of the aforementioned two processes. Moreover, the carboxylic acid byproduct can be separated and sold as a carbon source or miscellaneous acid (deleted), further reducing the operating cost of this process. Considering both investment and the entire operating process, this invention has strong application value. Attached Figure Description

[0033] Figure 1 is a schematic diagram of the sources of biological sludge.

[0034] Figure 2 is a flowchart of the method for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis reaction of the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0036] This invention discloses a method for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis, as shown in Figure 2, comprising the following steps:

[0037] (1) Add diluent and scale inhibitor to the dewatered biological sludge of the sewage treatment plant for conditioning treatment, so that the biological sludge changes from solid to quasi-solid state, and obtains the conditioned biological sludge with a water content of 85% to 95%.

[0038] In one specific embodiment, according to local requirements, the moisture content of the treated wastewater treatment plant's residual sludge is generally 80%–85%, although some processes treat the residual sludge to below 60% moisture content (by adding large amounts of inorganic reagents). In either case, the biological sludge at this point is in a near-solid state with a certain shape, making fluidized transport impossible. Therefore, conditioning treatment is necessary to increase the moisture content of the biological sludge from 80%–85% to 85%–95%, preferably 88%–93%, thus achieving a transformation from solid to near-solid state. Too low a moisture content makes fluidized transport difficult, while too high a moisture content will increase the COD in the mixed liquor. Cr If the concentration is too low, the entire reaction will be unable to achieve self-heating equilibrium.

[0039] In one specific embodiment, the reaction temperature of the conditioning treatment is 20℃~100℃ and the pressure is 0.1MPa~0.5MPa; preferably, the reaction temperature of the conditioning treatment is 50℃~90℃ and the pressure is 0.1MPa~0.2MPa.

[0040] Specifically, iron-based, aluminum-based, and calcium-magnesium-based metal salt coagulants, along with polyacrylamide-based coagulant aids, are added during the wastewater treatment plant's thickening process to ensure the moisture content of the biological sludge meets the requirements of local environmental protection departments. However, these agents, after entering the biological sludge during thickening, can affect the normal operation of equipment during sludge treatment, posing the following problems:

[0041] The first common problem is calcium and magnesium scaling. Scale inhibitors need to be added during conditioning to control the degree of scaling. Scale inhibitors include at least one of organophosphates, polyacrylamide, polycarboxylic acids, acrylic acid, and alkyl acrylic acids. These can reduce the risk and harm of scaling in equipment and ensure stable operation of the entire process.

[0042] In one specific embodiment, the scale inhibitor includes at least one of aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, polyacrylic acid, and hydroxyphosphonate.

[0043] In one specific embodiment, the mass ratio of the scale inhibitor to the dewatered biological sludge from the wastewater treatment plant is 0.001% to 10%.

[0044] The second common issue is the selection of sludge diluents. Adding diluents during conditioning can increase the water content of the sludge. These diluents include at least one of water, sodium hydroxide solution, aqueous solutions containing organic matter, and aqueous solutions containing oxidants. Preferably, water is the diluent. Depending on the sludge conditioning and reaction effects, alkaline substances (such as sodium hydroxide) and oxides may also be added, primarily to improve the selectivity and removal rate of the reaction.

[0045] In one specific embodiment, the oxidant in the aqueous solution containing the oxidant includes at least one of hydrogen peroxide, chlorate, hypochlorite, and persulfate.

[0046] In one specific embodiment, the mass ratio of the diluent to the dewatered biological sludge from the wastewater treatment plant is 0.001% to 10%.

[0047] The third issue is the uniformity of sludge dilution. 80% of the biological sludge is nearly solid, requiring a moisture content of 85-95%, with an optimal range of 88-93%. This process demands highly uniform sludge dilution, necessitating the use of steam for mixing or agitators. Alternatively, in practical applications, hot water with heat exchange is also used for dilution. Combining this with steam mixing and agitator mixing raises the temperature of the diluted biological sludge, objectively further reducing its viscosity and thus resolving the issue of uniform sludge dilution.

[0048] (2) The conditioned biological sludge is fluidized and transferred to a catalytic cracking reactor, where an oxidant is added for catalytic cracking. Through a controlled oxidation process, the capillary water, adsorbed water from the sludge particles, and some of the water inside the sludge particles are released as free water, transforming the sludge from a quasi-solid state to a liquid state. Simultaneously, the organic matter in the biological sludge decomposes into carboxylic acids, primarily C2-C6, increasing the added value of the entire process and yielding a carboxylic acid mixture. This process does not prioritize oxidation efficiency; the primary objective is to reduce the moisture content of the solid residue from the solid-liquid separation process.

[0049] Specifically, besides water, the main component of biological sludge is organic matter, and its elemental composition can be represented by (C5H7NO2). n The wastewater mainly consists of algae, fungi, and other microorganisms, as well as carbon-containing compounds and nitrogen oxides obtained from their decomposition. Besides the microorganisms, the remaining organic matter is not decomposed by them and is difficult to decompose, such as cell walls, lignin, and some recalcitrant organic matter in wastewater. Therefore, we consider using a "chemical process" to solve the environmental problem. Through catalytic pyrolysis technology, capillary water, adsorbed water in sludge particles, and internal water in sludge particles are released into free water. This process breaks down the polymeric structures of cell walls, lignin, and recalcitrant organic matter, eliminating potential safety hazards. After high-temperature catalytic oxidation, the moisture content of the remaining solid residue can be reduced to below 30%, and the volume reduction of biological sludge can be reduced to 20-30% of the original (based on an 80% biological sludge moisture content). For single-sludge systems, the volume reduction can even be reduced to below 10%. The main advantage of this invention is volume reduction, solving the biggest pain point of other treatment technologies besides incineration.

[0050] Specifically, after conditioning, the biological sludge changes from a solid to a quasi-solid state and can be fluidized and transported to a catalytic cracking reactor for catalytic cracking reaction. Catalytic cracking reaction is essentially an oxidation reaction. By using an oxidant as a breakthrough, the biological sludge can be controlled to be oxidized, and the water that cannot be released from the biological sludge can be released, which is more conducive to reducing the water content of the solid residue in the solid-liquid separation process.

[0051] In one specific embodiment, the catalytic cracking reaction is a low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction is 100℃~220℃, preferably 150℃~200℃, the reaction pressure is 0.5MPa~10MPa, preferably 0.6MPa~1.2MPa, and the residence time is 0.1h~10h, preferably 0.5h~2h.

[0052] In one specific embodiment, the catalytic cracking reaction is a high-temperature catalytic cracking reaction, wherein the reaction temperature is 220℃~350℃, preferably 250℃~300℃, the reaction pressure is 5MPa~20MPa, preferably 8MPa~15MPa, and the residence time is 0.1h~10h, preferably 0.5h~2h.

[0053] Specifically, in the high-temperature catalytic pyrolysis reaction, the biological sludge releases all the capillary water, adsorbed water in the sludge particles, and internal water in the sludge particles into free water through a controlled oxidation process. The biological sludge changes from a quasi-solid state to a liquid state. At the same time, the organic matter in the biological sludge is also basically decomposed into carboxylic acids, mainly C2-C6.

[0054] Specifically, compared to low-temperature catalytic pyrolysis, the most significant characteristic of high-temperature catalytic pyrolysis lies in volume reduction. Due to the enhanced reaction conditions, the water in the biological sludge is completely released as free water, and the cell walls, lignin, and other polymeric organic compounds in the biological cells undergo significant chain or ring opening, maximizing the decomposition of these polymeric organic compounds into carbon dioxide and small-molecule carboxylic acids. The remaining solid residue after high-temperature catalytic oxidation is primarily composed of inorganic matter, with a low organic content and a water content that can be reduced to below 30%. The volume reduction of biological sludge can be reduced to 20-30% of its original volume (based on an 80% biological sludge water content), and for single-sludge organisms, it can even be reduced to below 10%. Compared to low-temperature catalytic pyrolysis, high-temperature catalytic pyrolysis aims for substantial sludge volume reduction, resulting in higher carbon source loss but a much higher level of carboxylation.

[0055] Specifically, after the oxidant is introduced into the catalytic pyrolysis reaction, the cell walls of the cells in the biological sludge will rupture, and the water and tissue fluid inside the cells will flow out. At the same time, some easily decomposed proteins and organic matter will also decompose from long chains or cyclic chains into small molecule acids. The generation of C2-C6 carboxylic acids can be controlled by the amount of oxidant added and the degree of oxidation.

[0056] In one specific embodiment, the oxidant includes at least one selected from air, oxygen, hydrogen peroxide, chlorate, hypochlorite, and persulfate.

[0057] In one specific embodiment, since the main function of this process is to change the state of the biological sludge from a quasi-solid to a liquid mixture, excessive use of oxidants is not recommended. The amount of oxidant used per unit time is related to the sludge COD. Cr The ratio of the total amount is 0.1 to 5, preferably 0.8 to 2.0.

[0058] In one specific embodiment, the sludge COD per unit time Cr Total amount refers to the COD measured by the chemical oxygen demand (potassium dichromate method) of sludge. Cr Concentration, then converted into sludge COD per unit time. Cr The total amount is then converted into the total amount of oxidant per unit time based on the redox relationship.

[0059] (3) The carboxylic acid mixture is subjected to heat exchange and cooling treatment until the temperature of the carboxylic acid mixture is between room temperature and 100°C. The temperature of the water is raised to 120°C to 320°C. Then, solid-liquid separation is performed to obtain solid residue and filtrate, so that the biological sludge can realize the resource utilization of carbon elements while reducing the volume.

[0060] Specifically, due to the high temperature and pressure of the carboxylic acid mixture, heat exchange treatment is required. In addition, the carboxylic acid mixture contains a certain proportion of suspended solids, which come from the suspended solids present in the original wastewater, and some of them come from the solid precipitate formed after metal ions in the solution combine with phosphate ions. These suspended solids need to be separated from the mixture through solid-liquid separation.

[0061] In one specific embodiment, when the catalytic cracking reaction in step (2) is a low-temperature catalytic cracking reaction, the temperature of the carboxylic acid mixture is reduced to 40°C to 80°C; and the temperature of the water is raised to 160°C to 180°C.

[0062] In one specific embodiment, when the catalytic cracking reaction in step (2) is a high-temperature catalytic cracking reaction, the temperature of the carboxylic acid mixture is reduced to 40°C to 80°C; and the temperature of the water is raised to 220°C to 300°C.

[0063] In one specific embodiment, solid-liquid separation includes, but is not limited to, centrifugal separation, high-pressure plate and frame separation, screw press separation, gravity sedimentation, etc., with high-pressure plate and frame separation and centrifugal separation being preferred.

[0064] In one specific embodiment, the solid residue can be recycled for use as landscaping, forestry fertilizer, and land improvement; the filtrate can be sold as a carbon source, or it can be concentrated to separate the carboxylic acid and then sold separately.

[0065] In one specific embodiment, for catalytic cracking reactions at lower temperature conditions (e.g., 120°C to 170°C), heat exchange and cooling can be omitted, and the reaction can proceed directly to the solid-liquid separation process.

[0066] This invention also discloses a treatment system for reducing and recycling biological sludge based on catalytic pyrolysis. The treatment system implements the method described in any embodiment of this invention. The treatment system includes a conditioning unit, a catalytic pyrolysis unit, a heat exchange unit, and a solid-liquid separation unit connected in sequence. The conditioning unit is used to thoroughly mix the dewatered biological sludge from the wastewater treatment plant, diluent, and scale inhibitor to obtain conditioned biological sludge with a water content of 85%–95%. The catalytic pyrolysis unit is connected to the outlet of the conditioning unit. The conditioned biological sludge is fluidized and transported to the catalytic pyrolysis unit via a power device. The catalytic pyrolysis unit is also equipped with an oxidant inlet, which, under the action of the oxidant, releases capillary water, adsorbed water from sludge particles, and internal water from sludge particles into free water through a controlled oxidation process. Simultaneously, the organic matter in the biological sludge decomposes into carboxylic acids, mainly C2-C6, to obtain a carboxylic acid mixture. The heat exchange unit is connected to the outlet of the catalytic cracking unit, which is used to cool the carboxylic acid mixture to room temperature to 100°C and raise the temperature of the water to 120°C to 320°C. The mixture is then transferred to the solid-liquid separation unit, where solid residue and filtrate are obtained after solid-liquid separation, enabling the biological sludge to achieve carbon resource utilization while reducing its volume.

[0067] In one specific embodiment, the main function of the power equipment is to transport the quasi-solid sludge to the catalytic cracking reactor. Commonly used power equipment includes high-head power equipment such as screw pumps, twin screw pumps, plunger pumps, gear pumps, and pneumatic diaphragm pumps. It may also be a tank that receives the sludge by adjusting the pressure of compressed air.

[0068] In one specific embodiment, the heat exchanger used in the heat exchange unit includes shell-and-tube heat exchangers, plate heat exchangers, regenerative heat exchangers, and mixing heat exchangers, with shell-and-tube heat exchangers and regenerative heat exchangers being the most commonly used.

[0069] In one specific embodiment, since the sludge contains a lot of suspended solids, there is no need for a pre-concentration process, and it can be directly separated by traditional solid-liquid separation methods. There are many solid-liquid separation methods, including but not limited to centrifugal separation, high-pressure plate and frame separation, screw press separation, gravity sedimentation, etc., with high-pressure plate and frame separation and centrifugal separation being preferred.

[0070] Specifically, the moisture content of the solid residue after solid-liquid separation is between 10% and 40%. If the inorganic suspended solids in the biological sludge are low, the moisture content of the solid residue can even be lower than 10%. However, since most of the inorganic suspended solids in biological sludge come from the raw water, the final moisture content of the solid residue also depends on the content of inorganic suspended solids in the raw water, which is generally between 10% and 40% according to experimental measurements. Meanwhile, the relevant physicochemical properties of the solid residue meet the requirements of standards such as GB / T 23485-2009 Sludge for Mixed Landfill Disposal of Sludge from Urban Wastewater Treatment Plants, GB / T 23486-2009 Sludge for Landscaping Disposal of Sludge from Urban Wastewater Treatment Plants, GB / T 24600-2009 Sludge for Land Improvement Disposal of Sludge from Urban Wastewater Treatment Plants, GB / T 25031-2010 Sludge for Brick Making Disposal of Sludge from Urban Wastewater Treatment Plants, and CJ / T314 Sludge for Cement Clinker Production Disposal of Sludge from Urban Wastewater Treatment Plants. COD of carboxylic acid solution after solid-liquid separation Cr With a concentration between 10,000 and 50,000 mg / L, it can be sold directly as a carbon source or after further concentration.

[0071] The following are specific embodiments.

[0072] Example 1

[0073] The method for reducing the volume and recycling resources of biological sludge based on low-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0074] (1) Water (volume ratio 1:1) and aminotrimethylphosphonic acid (concentration 0.1%) were added to the dewatered biological sludge (moisture content 80%) from the wastewater treatment plant for conditioning treatment. The conditioning treatment reaction temperature was 80℃ and the pressure was 0.1MPa, which changed the sludge morphology from solid to quasi-solid, resulting in conditioned biological sludge with a moisture content of 90% and COD. Cr 50,000 mg / L.

[0075] (2) The conditioned biological sludge was fluidized and transferred to a low-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction was 170℃, the reaction pressure was 0.8MPa, and the residence time was 2h, to obtain a carboxylic acid mixture. The COD in the mixture was... Cr 30,000 mg / L, of which the total content of carboxylic acids accounts for 20% of the total organic matter.

[0076] (3) The carboxylic acid mixture was cooled using a tubular heat exchanger for 0.2 hours until the temperature of the carboxylic acid mixture dropped from 170°C to 80°C. The water temperature was raised from 20°C to 150°C. Subsequently, a high-pressure plate and frame solid-liquid separation was performed to obtain solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 30,000 mg / L, solid residue with 45% moisture content.

[0077] Example 1 was used as the standard reaction condition for the low-temperature catalytic cracking route. Other Examples 2-6 were compared by changing the conditions to show the effect of different reaction conditions on the reaction results.

[0078] Example 2

[0079] The method for reducing the volume and recycling resources of biological sludge based on low-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0080] (1) The treatment steps are the same as in Example 1, resulting in conditioned biological sludge with a moisture content of 95% and a COD of [missing information]. Cr 25,000 mg / L.

[0081] (2) The processing steps are the same as in Example 1, resulting in a carboxylic acid mixture. The COD in the mixture is... Cr 18,000 mg / L, of which carboxylic acids account for 18% of the total organic matter.

[0082] (3) The carboxylic acid mixture was subjected to high-pressure plate and frame solid-liquid separation to obtain solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 18,000 mg / L, solid residue with 45% moisture content.

[0083] Compared to Example 1, this example changed the moisture content of the conditioned biological sludge to 95%, the organic matter concentration of the sludge to 50% of that in Example 1, and omitted the heat exchange treatment. Other conditions remained unchanged, and it was found that the COD of the low-temperature catalytic cracking reaction was significantly reduced. Cr The concentration was 18,000 mg / L, and the moisture content of the solid residue was 45%. This shows that lowering the temperature of the catalytic cracking reaction has little effect on the moisture content of the solid residue after the final solid-liquid separation.

[0084] Example 3

[0085] The method for reducing the volume and recycling resources of biological sludge based on low-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0086] (1) The treatment steps are the same as in Example 1, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0087] (2) The conditioned biological sludge was fluidized and transferred to a low-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction was 120℃, the reaction pressure was 0.6MPa, and the residence time was 2h, to obtain a carboxylic acid mixture. The COD in the mixture was... Cr 42,000 mg / L, of which the total content of carboxylic acids accounts for 5% of the total organic matter.

[0088] (3) The carboxylic acid mixture was subjected to high-pressure plate and frame solid-liquid separation to obtain solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 42,000 mg / L, solid residue with 55% moisture content.

[0089] Compared to Example 1, this example changed the water content of the conditioning mixture to 90%, the reaction temperature of the low-temperature catalytic cracking to 120°C and the reaction pressure to 0.6 MPa, and omitted the heat exchange treatment, while keeping other conditions unchanged. It was found that the CODcr of the low-temperature catalytic cracking reaction was 42,000 mg / L, and the water content of the solid residue was 55%. This shows that lowering the reaction temperature and pressure of the low-temperature catalytic cracking has a significant impact on the water content of the solid residue after solid-liquid separation; the lower the reaction temperature and pressure, the higher the water content of the solid residue.

[0090] Example 4

[0091] The method for reducing the volume and recycling resources of biological sludge based on low-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0092] (1) The treatment steps are the same as in Example 1, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0093] (2) The conditioned biological sludge was fluidized and transferred to a low-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction was 170℃, the reaction pressure was 0.8MPa, and the residence time was 2h, to obtain a carboxylic acid mixture. The COD in the mixture was... Cr 28,000 mg / L, of which carboxylic acids account for 16% of the total organic matter.

[0094] (3) The carboxylic acid mixture was subjected to high-pressure plate and frame solid-liquid separation to obtain solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 28,000 mg / L, solid residue with 42% moisture content.

[0095] Compared to Example 1, this example changed the water content of the primary conditioning mixture to 90%, adjusted the ratio of total chemical oxygen demand (COD) to effective oxidant equivalent in low-temperature catalytic cracking to 1:2, and omitted the heat exchange treatment, while keeping other conditions unchanged. It was found that the CODCr of the low-temperature catalytic cracking reaction was 28,000 mg / L, and the water content of the solid residue was 42%. This shows that increasing the total COD and the effective oxidant equivalent ratio slightly reduced the water content of the solid residue.

[0096] Example 5

[0097] The method for reducing the volume and recycling resources of biological sludge based on low-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0098] (1) The treatment steps are the same as in Example 1, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0099] (2) The conditioned biological sludge was fluidized and transferred to a low-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction was 200℃, the reaction pressure was 1.2MPa, and the residence time was 2h, resulting in a carboxylic acid mixture. The COD in the mixture was... Cr 28,000 mg / L, of which carboxylic acids account for 24% of the total organic matter.

[0100] (3) The carboxylic acid mixture was cooled using a tubular heat exchanger for 0.2 hours until the temperature of the carboxylic acid mixture dropped from 200°C to 80°C. The water temperature was raised from 20°C to 170°C. Subsequently, a high-pressure plate and frame solid-liquid separation was performed to obtain solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 28,000 mg / L, solid residue with 42% moisture content.

[0101] Compared to Example 1, this example changed the water content of the primary conditioning solution to 90%, the reaction temperature of the low-temperature catalytic cracking to 200°C, and the reaction pressure to 1.2 MPa, while keeping other conditions unchanged. It was found that the COD of the low-temperature catalytic cracking reaction... Cr The concentration was 28,000 mg / L, and the water content of the solid residue was 42%. It can be seen that increasing the reaction temperature and reaction pressure of the catalytic cracking has a great influence on the water content of the solid residue after the final solid-liquid separation. The higher the reaction temperature and reaction pressure, the lower the water content of the solid residue.

[0102] Example 6

[0103] The method for reducing the volume and recycling resources of biological sludge based on low-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0104] (1) The treatment steps are the same as in Example 1, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0105] (2) The conditioned biological sludge was fluidized and transferred to a low-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction was 170℃, the reaction pressure was 1.2MPa, and the residence time was 2h, to obtain a carboxylic acid mixture. The COD in the mixture was... Cr 30,000 mg / L, of which the total content of carboxylic acids accounts for 20% of the total organic matter.

[0106] (3) The carboxylic acid mixture was cooled using a tubular heat exchanger for 0.2 hours until the temperature of the carboxylic acid mixture dropped from 170°C to 80°C. The water temperature was raised from 20°C to 190°C. Subsequently, centrifugation was used to separate the solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 28,000 mg / L, solid residue with 65% moisture content.

[0107] Compared with Example 1, this example uses centrifugal separation while keeping other conditions unchanged. It was found that the CODcr of the low-temperature catalytic cracking reaction was 28,000 mg / L and the water content of the solid residue was 65%. The centrifugal separation effect was not as good as that of high-pressure plate and frame separator.

[0108] Example 7

[0109] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0110] (1) Water (volume ratio 1:1) and aminotrimethylphosphonic acid (concentration 0.1%) were added to the dewatered biological sludge (moisture content 80%) from the wastewater treatment plant for conditioning treatment. The conditioning treatment reaction temperature was 80℃ and the pressure was 0.1MPa, which changed the sludge morphology from solid to quasi-solid, resulting in conditioned biological sludge with a moisture content of 90% and COD. Cr 50,000 mg / L.

[0111] (2) The conditioned biological sludge was fluidized and transferred to a high-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the high-temperature catalytic cracking reaction. The reaction temperature of the high-temperature catalytic cracking reaction was 270℃, the reaction pressure was 10MPa, and the residence time was 2h, resulting in a carboxylic acid mixture. The COD in the mixture was... Cr 18,000 mg / L, of which carboxylic acids account for 65% of the total organic matter.

[0112] (3) The carboxylic acid mixture was cooled using a tubular heat exchanger for 0.2 hours until the temperature of the carboxylic acid mixture dropped from 270°C to 80°C. The water temperature was raised from 20°C to 250°C. Subsequently, a high-pressure plate and frame solid-liquid separation was performed to obtain solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 18,000 mg / L, solid residue with 25% moisture content.

[0113] Example 7 was used as the standard reaction condition for the high-temperature catalytic cracking route. Other examples 8-13 were compared by changing the conditions to show the effect of different reaction conditions on the reaction results.

[0114] Example 8

[0115] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0116] (1) The treatment steps are the same as in Example 7, resulting in conditioned biological sludge with a moisture content of 95% and a COD of [missing information]. Cr 25,000 mg / L.

[0117] (2) The processing steps are the same as in Example 7, resulting in a carboxylic acid mixture. The COD in the mixture is... Cr 12,000 mg / L, of which carboxylic acids account for 67% of the total organic matter.

[0118] (3) The processing steps are the same as in Example 7, resulting in solid residue and filtrate, and the carboxylic acid solution COD Cr 12,000 mg / L, solid residue with 20% moisture content.

[0119] Compared to Example 7, this example changed the moisture content of the conditioned biological sludge to 95%, and the organic matter concentration of the sludge to 50% of that in Example 1, while keeping other conditions unchanged. It was found that the COD from the high-temperature catalytic cracking reaction was significantly reduced. Cr With a concentration of 12,000 mg / L and a solid residue moisture content of 20%, the reaction COD can be reduced. Cr Concentration has little effect on the reduction of solid residue after solid-liquid separation, but the effect is slightly better.

[0120] Example 9

[0121] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0122] (1) The treatment steps are the same as in Example 7, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0123] (2) The conditioned biological sludge was fluidized and transferred to a high-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the high-temperature catalytic cracking reaction. The reaction temperature of the high-temperature catalytic cracking reaction was 220℃, the reaction pressure was 5MPa, and the residence time was 2h, resulting in a carboxylic acid mixture. The COD in the mixture was... Cr 27,000 mg / L, of which carboxylic acids account for 43% of the total organic matter.

[0124] (3) The processing steps are the same as in Example 7, resulting in solid residue and filtrate, and the carboxylic acid solution COD Cr 27,000 mg / L, solid residue with 40% moisture content.

[0125] Compared with Example 7, this example changed the reaction temperature and reaction pressure of high-temperature catalytic cracking while keeping other conditions unchanged. It was found that the CODcr of the high-temperature catalytic cracking reaction was 27,000 mg / L and the solid residue was reduced to 40%. It can be seen that reducing the reaction temperature and reaction pressure of catalytic cracking has a great impact on the water content of the solid residue after the final solid-liquid separation. The lower the reaction temperature and reaction pressure, the worse the reduction of solid residue.

[0126] Example 10

[0127] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0128] (1) The treatment steps are the same as in Example 7, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0129] (2) The processing steps are the same as in Example 7, except that air is added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:2) to carry out a high-temperature catalytic cracking reaction, resulting in a carboxylic acid mixture. The COD in the mixture is... Cr 13,000 mg / L, of which carboxylic acids account for 72% of the total organic matter.

[0130] (3) The processing steps are the same as in Example 7, resulting in solid residue and filtrate, and the carboxylic acid solution COD Cr 13,000 mg / L, with a solid residue moisture content of 18%.

[0131] Compared to Example 7, this example changed the total chemical oxygen demand (COD) and effective oxidant equivalence ratio in the high-temperature catalytic cracking to 1:2, while keeping other conditions unchanged. It was found that the COD of the high-temperature catalytic cracking reaction... Cr With a concentration of 13,000 mg / L, the solid residue was reduced to 18%, demonstrating that increasing the total chemical oxygen demand and the effective equivalent ratio of the oxidant resulted in a better reduction in solid residue.

[0132] Example 11

[0133] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0134] (1) The treatment steps are the same as in Example 7, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0135] (2) The conditioned biological sludge was fluidized and transferred to a high-temperature catalytic cracking reactor. Air was added as an oxidant (total chemical oxygen demand to effective oxidant equivalent ratio 1:1) to carry out the high-temperature catalytic cracking reaction. The reaction temperature of the high-temperature catalytic cracking reaction was 300℃, the reaction pressure was 15MPa, and the residence time was 2h, resulting in a carboxylic acid mixture. The COD in the mixture was... Cr 12,000 mg / L, of which carboxylic acids account for 82% of the total organic matter.

[0136] (3) The processing steps are the same as in Example 7, resulting in solid residue and filtrate, and the carboxylic acid solution COD Cr 12,000 mg / L, solid residue with 15% moisture content.

[0137] Compared to Example 7, this example changed the reaction temperature of the high-temperature catalytic cracking to 300°C and the reaction pressure to 15 MPa, while keeping other conditions unchanged. It was found that the COD of the high-temperature catalytic cracking reaction... Cr With a concentration of 12,000 mg / L, the solid residue was reduced to 15%. This shows that increasing the reaction temperature and pressure of the catalytic cracking has a significant impact on the reduction of solid residue after the final solid-liquid separation. The higher the reaction temperature and pressure, the better the reduction of solid residue.

[0138] Example 12

[0139] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0140] (1) The treatment steps are the same as in Example 7, resulting in conditioned biological sludge with a moisture content of 90% and a COD of [missing information]. Cr 50,000 mg / L.

[0141] (2) The processing steps are the same as in Example 7, resulting in a carboxylic acid mixture. The COD in the mixture is... Cr 18,000 mg / L, of which carboxylic acids account for 65% of the total organic matter.

[0142] (3) The carboxylic acid mixture was cooled using a tubular heat exchanger for 0.2 hours until the temperature of the carboxylic acid mixture dropped from 270°C to 80°C. The water temperature was raised from 20°C to 250°C. Subsequently, centrifugation was used to separate the solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 18,000 mg / L, solid residue with 58% moisture content.

[0143] Compared to Example 7, this example uses centrifugation while keeping other conditions unchanged, and it was found that the COD from the high-temperature catalytic cracking reaction... Cr The concentration was 18,000 mg / L, and the solid residue was reduced to 58%. Centrifugal separation was less effective than high-pressure plate and frame separators.

[0144] Example 13

[0145] The method for reducing the volume and recycling resources of biological sludge based on high-temperature catalytic pyrolysis reaction in this embodiment includes the following steps:

[0146] (1) Water (volume ratio 1:1) and aminotrimethylphosphonic acid (concentration 0.1%) were added to the biological sludge (moisture content 80%, influent free of inorganic suspended solids) of the chemical plant wastewater treatment plant for conditioning treatment, resulting in conditioned biological sludge with a moisture content of 90% and COD... Cr 50,000 mg / L.

[0147] (2) The processing steps are the same as in Example 7, resulting in a carboxylic acid mixture. The COD in the mixture is... Cr 15,000 mg / L, of which carboxylic acids account for 76% of the total organic matter.

[0148] (3) The carboxylic acid mixture was cooled using a tubular heat exchanger for 0.2 hours until the temperature of the carboxylic acid mixture dropped from 270°C to 80°C. The water temperature was raised from 20°C to 250°C. Subsequently, centrifugation was used to separate the solid residue and filtrate. The COD of the carboxylic acid solution was... Cr 15,000 mg / L, solid residue with 8% moisture content.

[0149] Compared to Example 1, this example uses biological sludge from a chemical plant wastewater treatment plant. This wastewater is process water and does not contain inorganic suspended solids. With other conditions unchanged, the COD from the high-temperature catalytic cracking reaction was found to be significantly reduced. Cr With a concentration of 15,000 mg / L and a solid residue reduction to 8%, it is evident that the inorganic suspended solids content in biological sludge is the main factor affecting the moisture content of solid residue.

[0150] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for reducing the volume and recycling resources of biological sludge based on catalytic pyrolysis reaction, characterized in that, Includes the following steps: (1) Add diluent and scale inhibitor to the dewatered biological sludge from the wastewater treatment plant for conditioning treatment, so that the biological sludge changes from solid to quasi-solid state, and obtains conditioned biological sludge with a water content of 85%~95%; (2) Transfer the conditioned biological sludge to the catalytic cracking reactor through fluidization, and add oxidant to carry out catalytic cracking reaction. The conditioned biological sludge releases capillary water, adsorbed water of sludge particles, and water inside sludge particles into free water through a controlled oxidation process, so that the biological sludge changes from quasi-solid state to liquid state. At the same time, the organic matter in the biological sludge decomposes into carboxylic acids mainly composed of C2-C6, and obtains carboxylic acids. Mixed liquid; (3) The carboxylic acid mixture is subjected to heat exchange and cooling treatment until the temperature of the carboxylic acid mixture is room temperature ~ 100℃, and the temperature of the water is raised to 120℃ ~ 320℃. Then, solid residue and filtrate are obtained by solid-liquid separation, so that the biological sludge can realize the resource utilization of carbon elements while reducing the volume; In step (2), the reaction temperature of the catalytic cracking reaction is 120℃ ~ 350℃, the reaction pressure is 0.5MPa ~ 20MPa, and the residence time is 0.1h ~ 10h; In step (2), the oxidant includes at least one of air, oxygen, hydrogen peroxide, chlorate, hypochlorite, and persulfate; The amount of oxidant used per unit time is related to the sludge COD Cr The ratio of the total is 0.1 to 5.

2. The method for reducing and recycling biological sludge based on catalytic pyrolysis reaction according to claim 1, characterized in that, In step (1), the moisture content of the conditioned biological sludge is 88%~93%.

3. The method for reducing and recycling biological sludge based on catalytic pyrolysis reaction according to claim 1, characterized in that, In step (1), the moisture content of the biological sludge after dewatering from the wastewater treatment plant is 80%~85%.

4. The method for reducing and recycling biological sludge based on catalytic pyrolysis reaction according to claim 1, characterized in that, In step (1), the reaction temperature of the conditioning treatment is 20℃~100℃ and the pressure is 0.1MPa~0.5MPa.

5. The method for reducing and recycling biological sludge based on catalytic pyrolysis reaction according to claim 1, characterized in that, In step (1), the diluent includes at least one of water, sodium hydroxide solution, aqueous solution containing organic matter, and aqueous solution containing oxidant; the oxidant in the aqueous solution containing oxidant includes at least one of hydrogen peroxide, chlorate, hypochlorite, and persulfate; the mass ratio of the diluent to the dewatered biological sludge from the wastewater treatment plant is 0.001% to 10%.

6. The method for reducing and recycling biological sludge based on catalytic pyrolysis reaction according to claim 1, characterized in that, In step (1), the scale inhibitor includes at least one of organophosphates, polyacrylamide, polycarboxylic acid, acrylic acid, and alkyl acrylic acid; the scale inhibitor includes at least one of aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, polyacrylic acid, and hydroxyphosphonate; the mass ratio of the scale inhibitor to the dewatered biological sludge from the wastewater treatment plant is 0.001% to 10%.

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