Method and treatment system for reducing and recycling biological sludge based on catalytic cracking reaction

Abstract

The invention discloses a method and treatment system for reducing and recycling biological sludge based on catalytic cracking reaction, and the method comprises the following steps: adding a diluent and a scale inhibitor into dewatered biological sludge in a sewage treatment plant to carry out thermal refining treatment, so that the biological sludge is converted from a solid state to a quasi solid state, and the biological sludge after thermal refining treatment is obtained; the biological sludge subjected to thermal refining treatment is conveyed into a catalytic cracking reactor through fluidization, an oxidizing agent is added for a catalytic cracking reaction, capillary water contained in the sludge, water adsorbed by sludge particles and water in the sludge particles are partially released into free-state moisture through a controllable oxidation process of the biological sludge, and the free-state moisture is discharged into a sludge drying device; converting the biological sludge into a liquid state from a quasi-solid state, and decomposing organic matters in the biological sludge into carboxylic acid mainly comprising C2-C6 to obtain a carboxylic acid mixed solution; according to the method, the carboxylic acid mixed solution is subjected to heat exchange and cooling treatment and then is subjected to solid-liquid separation to obtain solid residues and filtrate, so that the biological sludge is reduced, and meanwhile, the resource utilization of carbon elements is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and more specifically, to a method and a treatment system for reducing and recycling biological sludge based on catalytic cracking reaction. Background Art

[0002] With the continuous growth of population, rapid expansion of urban scale and continuous development of industry around the world, the demand for sewage treatment has been further released, and the situation of sludge disposal has become increasingly severe. According to statistics, the total global sewage sludge production (in terms of dry weight of sludge) in 2017 was 45 million tons. The sewage sludge production in China is also increasing rapidly.

[0003] The narrow definition of biological sludge mainly refers to the by-product composed mainly of solid particles accumulated by the sedimentation and aggregation of suspended matter in water during the production process of urban water treatment facilities, and does not include sludge produced by other urban water bodies and soil deposition. Figure 1 As shown, according to the different sources of biological sludge, it can be divided into two types: water supply sludge and sewage sludge. Since sewage sludge is mainly treated by activated sludge method based on microbial degradation, the biggest difference between sewage sludge and water supply sludge is that the main component of sewage sludge is biomass, with some inorganic particles attached. The sludge mentioned in this application refers to sewage sludge.

[0004] Most of the existing sewage treatment plants adopt the form of screen-digestion and denitrification biochemical treatment-deep treatment-disinfection. The biological sludge mainly comes from biochemical treatment, and also contains a small amount of sand solids in the grit chamber and flocculation precipitation of coagulation and phosphorus removal. In the sewage treatment process, floating objects and large pieces of matter in domestic sewage are intercepted in the screen, and organic matter, nitrogen, phosphorus and suspended matter enter the biochemical system. Some organic matter, some nitrogen elements and almost all phosphorus elements are converted into microorganisms, and together with almost all suspended matter, they become residual sludge and are separated from the sewage system; the remaining organic matter and nitrogen are released into the air in the form of carbon dioxide and nitrogen, and very small amounts of organic matter and nitrogen and phosphorus are discharged into the environment with water that meets the standards.

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

[0006] Table 1 Designed mud quality index table

[0007] project Design sludge quality requirements Moisture content 80-85％ Organic matter content VS 8-12％ Residue on ignition (TS-VS) 8-12％ pH 6-9 Total Nitrogen 2000-4000mg / L Total Phosphorus 2000-3000mg / L Other indicators Meet relevant standard requirements

[0008] Biological sludge generally has the following hazards:

[0009] (1) Trace organic matter: A variety of difficult-to-biodegrade organic matter can be detected in sewage sludge, such as polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polycyclic aromatic hydrocarbons (PAHs) and other toxic and harmful substances. These organic matter 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 microorganisms such as pathogenic bacteria, viruses, and parasites. Humans, animals, and plants have direct contact with water, soil, and air contaminated by sludge and have the opportunity to be infected. Therefore, the spread of pathogens through the sewage treatment system needs to be paid special attention.

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

[0012] (4) Other hazards: During the stacking process, sludge will release unpleasant gases into the atmosphere, such as H2S, which will damage the quality of the environment around the water plant and affect the health of the workers. In addition, the high water content of sludge will result in a large amount of production wastewater during the treatment process. These production wastewaters contain nutrients such as nitrogen and phosphorus. Improper treatment can easily cause them to be lost into water bodies or soil, causing secondary pollution to the ecological environment.

[0013] In response to the above problems, many sludge treatment technologies have been developed at home and abroad. The commonly used technologies include: incineration, aerobic treatment, anaerobic treatment, landfill treatment, etc.

[0014] (1) Drying and incineration. Sludge drying and incineration is the most thorough treatment and disposal process with the highest degree of reduction and harmlessness. The residue after incineration is stable in nature, 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 incineration of sludge has high requirements for moisture content (generally less than 60%), and mechanical dewatering of sludge (80% moisture content) is difficult to directly meet the requirements. 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 requirements for equipment, and the operating cost is more than 500-600 yuan / ton, resulting in the drying and incineration process being widely used mainly in economically developed and land-scarce areas.

[0015] (2) Anaerobic digestion. This technology is one of the most popular development directions for the resource utilization of sludge. During the anaerobic digestion process, anaerobic microorganisms in sludge hydrolyze organic matter through alienation to obtain electron donors for growth and reproduction, and then acidogenic methanogens convert the intermediate fragments into renewable biogas. Since the biogas produced by anaerobic digestion can be directly used for power generation and heat production, supplementing the energy consumption needs of urban sewage treatment plants, this technology has been widely popularized in Europe, the United States and Japan. In China, because the organic matter content in sludge is only 30%-60%, which is far lower than that in developed countries, it ultimately leads to low biogas output and high operating costs, making it difficult to promote and apply. About 60 of the urban sewage treatment plants built in the country use anaerobic digestion technology, but only more than 20 are operating normally.

[0016] (3) Aerobic composting. Dewatered sludge contains organic carbon sources and aerobic microorganisms. By adding wood chips, straw, etc. as bulking agents to the sludge to increase the porosity and air contact area of ​​the sludge, aerobic microorganisms can use organic matter as a substrate, multiply and develop in large quantities, and ferment into stable humus-like substances, which is aerobic composting. Aerobic composting products are good plant growth regulators and can be reused on land. At the same time, composting can effectively save treatment costs, and the subsequent sludge reuse has limited harm to the environment. It is particularly suitable for sewage treatment units with simple sewage sources, no industrial pollution, and small sludge production.

[0017] (4) Sanitary landfill. The dewatered sludge from the sewage treatment plant is stabilized by adding lime and other substances and then landfilled in a selected special site. Sanitary landfill has low economic cost and simple process, and has been widely used all over the world. However, it still takes 2-7 years to stabilize the landfill sludge. It not only occupies land resources, but the leachate it produces may also affect the safety of local groundwater. It has been abandoned by more and more countries and regions. After 2000, European and American countries have begun to ban the sanitary landfill of sludge, and the total amount of landfilled sludge has decreased year by year. As a backward technology, sanitary landfill of sludge is bound to be replaced by other advanced processes in the future. It is currently only allowed to be used under emergency conditions.

[0018] The organic components in biological sludge are complex and mainly composed of two substances: cell phase and extracellular polymers. Various hydrophilic organic compounds are intertwined and concentrated together to form a compact polymer structure. This structure makes it difficult to effectively remove the capillary water in the sludge, the water adsorbed by the sludge particles, and the water inside the sludge particles under the action of mechanical force. At the same time, the diversity of sewage sources determines that the sludge contains toxic and harmful pollutants, most of which are difficult to biodegrade organic matter. This makes it difficult to achieve the goal of harmlessness using traditional treatment technologies. How to find a technically feasible and economically acceptable process has always been the focus of research and development in this field. Summary of the invention

[0019] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a method and a treatment system for reducing and recycling biological sludge based on catalytic cracking reaction. Through this method, the structural characteristics of biological sludge can be changed, and the capillary water, sludge particle adsorbed water, and sludge particle internal water contained in the biological sludge can be at least partially released into free water, so that the biological sludge form is changed 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 biological sludge can be reduced while realizing the resource utilization of carbon elements in the sludge.

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

[0021] A method for reducing and recycling biological sludge based on catalytic cracking reaction, comprising the following steps:

[0022] (1) adding a diluent and a scale inhibitor to the biological sludge after dehydration in a sewage treatment plant for conditioning treatment, so that the biological sludge is transformed from a solid state to a quasi-solid state, and a conditioned biological sludge having a moisture content of 85% to 95% is obtained;

[0023] (2) The conditioned biological sludge is transferred to a catalytic cracking reactor through fluidization, and an oxidant is added to perform a catalytic cracking reaction. The conditioned biological sludge releases capillary water, sludge particle adsorbed water, and water inside sludge particles contained in the sludge into free water through a controllable oxidation process, so that the biological sludge is transformed 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) subjecting the carboxylic acid mixture to heat exchange and cooling treatment until the temperature of the carboxylic acid mixture is between room temperature and 100° C., raising the temperature of water to 120° C. to 320° C., and then subjecting the mixture to solid-liquid separation to obtain solid residue and filtrate, thereby achieving resource utilization of carbon elements while reducing the amount of biological sludge.

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

[0026] The treatment system comprises 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 dehydrated biological sludge, diluent and scale inhibitor of the sewage treatment plant to obtain the conditioned biological sludge with a water content of 80% to 99%;

[0028] The catalytic cracking unit is connected to the outlet of the conditioning unit, and the conditioned biological sludge is fluidized and transferred to the catalytic cracking unit through a power device. The catalytic cracking unit is also provided with an oxidant inlet, which is used for releasing the capillary water, sludge particle adsorbed water, and water inside the sludge particles contained in the conditioned biological sludge into free water through a controllable oxidation process under the action of the oxidant, and 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 ~ 100°C by heat exchange, and to raise the temperature of water to 120°C ~ 320°C, and then transmit it to the solid-liquid separation unit to obtain solid residue and filtrate after solid-liquid separation, so that the biological sludge can be reduced while realizing the resource utilization of carbon elements.

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

[0031] The present invention provides a method for reducing and recycling biological sludge based on catalytic cracking reaction. The method can change the structural characteristics of biological sludge, release at least part of the capillary water, sludge particle adsorbed water and sludge particle internal water contained in the biological sludge into free water, and change the biological sludge form from quasi-solid to liquid. Meanwhile, organic matter in the biological sludge is at least partly decomposed into carboxylic acids mainly composed of C2-C6. The solution and suspended matter are separated through a solid-liquid separation system. The carboxylic acid products mainly composed of C2-C6 are sold as carbon sources, and the remaining solid residues can be used as fertilizers for landscaping, forestry and land improvement, so that the biological sludge can be reduced and the carbon element in the sludge can be recycled.

[0032] The present invention can significantly reduce the amount of biological sludge to 20% to 40% of the original amount while solving the problem of sludge harmlessness, and the amount of single biological sludge can even be reduced to less than 10% of the original amount. The greatest feature of the present invention is that the reduction of biological sludge is achieved through a "chemical process". Compared with anaerobic digestion and aerobic composting, the land occupation is only 10-20% of the above two methods, and the main process residence time is only less than 1% of the above two methods. The operating cost and investment of this method are lower than anaerobic digestion, and are similar to aerobic composting; and the solid residue after anaerobic digestion and aerobic composting can only be reduced to 50-60% of the original amount (based on 80% biological sludge moisture content), while the present invention can reduce the moisture content to less than 10% at the lowest, solving the bottleneck of the above two processes, and the carboxylic acid byproduct can also be separated and sold as a carbon source or miscellaneous acid (deleted), further reducing the operating cost of this process, and has a strong application value from the perspective of investment and the entire operation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the source of biological sludge.

[0034] Figure 2 The present invention is a flowchart of a method for reducing and recycling biological sludge based on catalytic cracking reaction. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0036] The present invention discloses a method for reducing and recycling biological sludge based on catalytic cracking reaction, such as Figure 2 As shown, the following steps are included:

[0037] (1) Adding a diluent and a scale inhibitor to the biological sludge after dehydration in a sewage treatment plant for conditioning treatment, so that the biological sludge is transformed from a solid state to a quasi-solid state, and the conditioned biological sludge having a moisture content of 85% to 95% is obtained.

[0038] In a specific embodiment, according to local requirements, the residual sludge in the treated sewage treatment plant generally has a moisture content of 80% to 85% in the biological sludge, and the residual sludge is also treated to a moisture content of less than 60% (adding a large amount of inorganic agents). In either case, the biological sludge at this time is close to the solid state and has a certain shape, which makes it impossible to fluidize and transport it. Therefore, it is necessary to subject it to tempering treatment to increase the moisture content of the biological sludge from 80% to 85% to 85% to 95%, preferably 88% to 93%, to achieve the transformation of the biological sludge from solid to quasi-solid. If the moisture content is too low, fluidization transportation is difficult, and if the moisture content is too high, it will cause COD in the mixed liquid Cr The concentration is too low, making it difficult for the entire reaction to achieve self-thermal equilibrium.

[0039] In a specific embodiment, the reaction temperature of the tempering treatment is 20°C to 100°C, and the pressure is 0.1MPa to 0.5MPa; preferably, the reaction temperature of the tempering treatment is 50°C to 90°C, and the pressure is 0.1MPa to 0.2MPa.

[0040] Specifically, during the concentration process of the residual sludge in the sewage plant, iron-based, aluminum-based, calcium-magnesium-based metal salt coagulants are added, and polyacrylamide-based coagulants are also added to ensure that the moisture content of the biological sludge can meet the requirements of local environmental protection departments. However, after these agents enter the biological sludge as the sludge is concentrated, they will affect the normal use of the equipment during the sludge treatment process, and there are the following problems:

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

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

[0043] In a specific embodiment, the mass ratio of the scale inhibitor to the biological sludge after dehydration in the sewage treatment plant is 0.001% to 10%.

[0044] The second common problem is the selection of sludge diluent. The addition of diluents during conditioning can increase the water content of the sludge, including at least one of water, sodium hydroxide solution, aqueous solution containing organic matter, and aqueous solution containing oxidant. Preferably, the diluent is water, and alkaline substances (such as sodium hydroxide) and oxides are added according to the sludge conditioning and reaction effect. The main purpose is to improve the selectivity and removal rate of the reaction.

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

[0046] In a specific embodiment, the mass ratio of the diluent to the biological sludge after dehydration in the sewage treatment plant is 0.001% to 10%.

[0047] The third problem is the uniformity of sludge dilution. 80% of biological sludge is similar to solid state. The water content is increased to 85-95%, and the more suitable water content is 88-93%. This process requires the sludge to be diluted very evenly, so steam is needed for mixing and agitator mixing is also required. In addition, in the actual application process, hot water after heat exchange is also used for dilution. After combining steam mixing and agitator mixing, the temperature of the diluted biological sludge rises, which objectively further reduces the viscosity of the sludge, thereby solving the problem of uniformity of sludge dilution.

[0048] (2) The conditioned biological sludge is transferred to a catalytic cracking reactor through fluidization, and an oxidant is added for catalytic cracking reaction. The conditioned biological sludge releases the capillary water, adsorbed water of sludge particles, and water inside sludge particles contained in the sludge into free water through a controlled oxidation process, so that the biological sludge is transformed 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, thereby increasing the added value of the entire process and obtaining a carboxylic acid mixture. This process does not pursue the oxidation effect, and everything is based on reducing the moisture content of the solid residue in the solid-liquid separation process as the inspection standard.

[0049] Specifically, in addition to water, the main component of biological sludge is organic matter, and its element ratio can be expressed as (C5H7NO2) n It means that it is mainly composed of microorganisms such as algae and fungi, as well as carbon-containing compounds and nitrogen compounds obtained by decomposition. In addition to microorganisms, the remaining organic matter is not decomposed by microorganisms, and these substances are difficult to decompose organic matter, such as cell walls, lignin, and some difficult-to-degrade organic matter in sewage. Therefore, we consider using the "chemical process" to solve environmental protection problems. Through catalytic cracking technology, the capillary water in the biological sludge, the adsorbed water of the sludge particles, and the water inside the sludge particles are all released into free water, and the cell walls, lignin, difficult-to-degrade organic matter and other polymeric organic matter are opened or ring-opened to eliminate possible unsafe factors. After high-temperature catalytic oxidation, the moisture content of the remaining solid residue can be reduced to less than 30%, and the reduction of biological sludge can be reduced to the original 20-30% (based on 80% biological sludge moisture content). Single biological sludge can even be reduced to less than 10% of the original. The main advantage of the present invention is reduction, which solves the biggest pain point of other treatment technologies except incineration.

[0050] Specifically, after the conditioning treatment, the biological sludge is transformed from a solid state to a quasi-solid state, and can be fluidized and transferred to a catalytic cracking reactor for a catalytic cracking reaction. The catalytic cracking reaction is essentially an oxidation reaction. The oxidant is used as a breakthrough to achieve controllable oxidation of the biological sludge and release the water that cannot be released in the biological sludge, which is more conducive to reducing the moisture content of the solid residue in the solid-liquid separation process.

[0051] In a 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°C to 220°C, preferably 150°C to 200°C, the reaction pressure is 0.5MPa to 10MPa, preferably 0.6MPa to 1.2MPa, and the residence time is 0.1h to 10h, preferably 0.5h to 2h.

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

[0053] Specifically, in the high-temperature catalytic cracking reaction, the biological sludge releases all the capillary water, adsorbed water on the sludge particles, and water inside the sludge particles contained in the sludge into free water through a controllable 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 basically decomposed into carboxylic acids mainly composed of C2-C6.

[0054] Specifically, compared with low-temperature catalytic cracking reaction, the biggest feature of high-temperature catalytic cracking reaction is reduction. Due to the improvement of reaction conditions, the water in the biological sludge is completely released into free water, and the cell walls of biological cells, lignin, refractory organic matter and other polymeric organic substances are basically open-chain or open-ring, which greatly decomposes the polymeric organic substances into carbon dioxide and small molecular carboxylic acids. After high-temperature catalytic oxidation, the remaining solid residue is mainly inorganic, with a low organic content and a water content of less than 30%. The reduction of biological sludge can be reduced to 20-30% of the original (based on 80% biological sludge water content), and a single biological sludge can even be reduced to less than 10% of the original. Compared with low-temperature catalytic cracking reaction, high-temperature catalytic cracking aims at substantial sludge reduction, and the carbon source loss is higher than that of low-temperature reaction, but the carboxylation level is much higher than that of low-temperature reaction.

[0055] Specifically, after the oxidant is introduced into the catalytic cracking 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 degradable proteins and organic matter will also be decomposed from long chains or cyclic chains into small molecular acids. The generation of C2-C6 carboxylic acids can be controlled by the amount of oxidant added and the degree of oxidation.

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

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

[0058] In a specific embodiment, the sludge COD per unit time Cr The total amount refers to the COD measured by the sludge according to the solution chemical oxygen demand (potassium dichromate method) CrConcentration, 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 room temperature to 100°C, and the temperature of the water is raised to 120°C to 320°C, followed by solid-liquid separation to obtain solid residue and filtrate, so that the biological sludge can be reduced in volume while realizing resource utilization of carbon elements.

[0060] Specifically, since the temperature and pressure of the carboxylic acid mixed solution are relatively high, it needs to be subjected to heat exchange treatment. In addition, the carboxylic acid mixed solution contains a certain proportion of suspended matter, which comes from the suspended matter existing in the original sewage, and a part of it comes from the solid precipitation after the metal ions in the solution combine with phosphate groups. These suspended matter needs to be separated from the mixed solution by solid-liquid separation.

[0061] In a 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 a 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 increased to 220°C to 300°C.

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

[0064] In a specific embodiment, the solid residue can be recycled and used as fertilizer for landscaping, forestry and land improvement; the filtrate can be sold as a carbon source, or the carboxylic acids can be separated and sold by classification after concentration.

[0065] In a specific embodiment, for catalytic cracking reactions under relatively low temperature conditions (for example, at 120° C. to 170° C.), heat exchange and cooling can be omitted, and the solid-liquid separation process can be directly performed.

[0066] The present invention also discloses a treatment system for reducing and recycling biological sludge based on catalytic cracking reaction, and the treatment system realizes the method as in any embodiment of the present invention; the treatment system comprises a conditioning unit, a catalytic cracking unit, a heat exchange unit and a solid-liquid separation unit connected in sequence. The conditioning unit is used for fully mixing the biological sludge, diluent and scale inhibitor after dehydration in the sewage treatment plant to obtain the conditioned biological sludge with a water content of 85% to 95%. The catalytic cracking unit is connected to the outlet of the conditioning unit, and the conditioned biological sludge is fluidized and transmitted to the catalytic cracking unit through a power device. The catalytic cracking unit is also provided with an oxidant inlet, which is used for the conditioned biological sludge to release the capillary water, sludge particle adsorbed water and sludge particle internal water contained in the sludge into free water through a controllable oxidation process under the action of the oxidant, and 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. 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 ~ 100°C by heat exchange, and to raise the temperature of the water to 120°C ~ 320°C, and then transmit it to the solid-liquid separation unit to obtain solid residue and filtrate after solid-liquid separation, so that the biological sludge can be reduced in volume while realizing the resource utilization of carbon elements.

[0067] In a specific embodiment, the main function of the power equipment is to transport the quasi-solid sludge to the catalytic cracking reactor. The power equipment commonly used is a screw pump, a twin-screw pump, a plunger pump, a gear pump, a pneumatic diaphragm pump and other power equipment with a higher head. It may also be a tank that inputs through compressed air pressure regulation.

[0068] In a specific embodiment, the heat exchanger used in the heat exchange unit includes a shell and tube heat exchanger, a plate heat exchanger, a heat storage heat exchanger, a hybrid heat exchanger, etc., and the shell and tube heat exchanger and the heat storage heat exchanger are more commonly used.

[0069] In a specific embodiment, since the sludge contains a lot of suspended matter, there is no need for a pre-concentration process, and the traditional solid-liquid separation method can be directly used for separation; there are many methods for solid-liquid separation, including but not limited to centrifugal separation, high-pressure plate and frame, spiral separation, gravity sedimentation, etc., and high-pressure plate and frame and centrifugal separation are preferred.

[0070] Specifically, the moisture content of the solid residue after solid-liquid separation is 10%-40%. If there are less inorganic suspended matter in the biological sludge, the moisture content of the solid residue can even be lower than 10%. However, since most of the inorganic suspended matter in the biological sludge comes from the raw water, the moisture content of the solid residue is also determined by the content of inorganic suspended matter in the raw water. According to experimental measurements, it is generally between 10-40%. At the same time, the relevant physical and chemical properties of the solid residue meet the requirements of GBT 23485-2009 Mud for mixed landfill of sludge from urban sewage treatment plants, GBT 23486-2009 Mud for landscaping in urban sewage treatment plants, GBT 24600-2009 Mud for land improvement in urban sewage treatment plants, GBT 25031-2010 Mud for brick making in urban sewage treatment plants, and CJ / T314 Mud for cement clinker production in urban sewage treatment plants. COD of carboxylic acid solution after solid-liquid separation Cr The concentration is between 10000-50000 mg / L and can be sold directly as a carbon source or sold as a carbon source after further concentration.

[0071] The following are specific embodiments

[0072] Example 1

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

[0074] (1) Water (volume ratio 1:1) and aminotri(methylenephosphonic acid) (concentration 0.1%) were added to the biological sludge (water content 80%) after dehydration from the sewage treatment plant for conditioning treatment. The reaction temperature of the conditioning treatment was 80°C and the pressure was 0.1 MPa. The biological sludge was changed from solid to quasi-solid state, and the conditioned biological sludge with a water content of 90% was obtained. COD Cr 50,000 mg / L.

[0075] (2) The conditioned biological sludge is transferred to a low-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction is 170°C, the reaction pressure is 0.8 MPa, and the residence time is 2 h. A carboxylic acid mixed solution is obtained. The COD 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 subjected to heat exchange and cooling treatment using a tubular heat exchanger with a residence time of 0.2 h until the temperature of the carboxylic acid mixture dropped from 170°C to 80°C, and the water temperature was raised from 20°C to 150°C. Subsequently, a high-pressure plate-and-frame solid-liquid separation was used to obtain a solid residue and a filtrate. The COD of the carboxylic acid solution Cr 30,000 mg / L, solid residue 45% moisture content.

[0077] Example 1 was used as the standard reaction condition for the low-temperature catalytic cracking route, and other Examples 2-6 were compared with this standard by varying the conditions, reflecting the influence of different reaction conditions on the reaction results.

[0078] Example 2

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

[0080] (1) The treatment steps were the same as those in Example 1, and the conditioned biological sludge with a moisture content of 95% was obtained. Cr 25,000 mg / L.

[0081] (2) The treatment steps are the same as those in Example 1 to obtain a carboxylic acid mixed solution. The COD Cr 18,000 mg / L, of which the total content of carboxylic acids accounts for 18% of the total organic matter.

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

[0083] Compared with Example 1, the moisture content of the biological sludge after conditioning treatment in this example is changed to 95%, the organic matter concentration of the sludge is equivalent to 50% of that in Example 1, and the heat exchange treatment is omitted. Other conditions remain unchanged. It is found that the COD Cr 18,000 mg / L, the moisture content of the solid residue is 45%. It can be seen 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 of reducing and recycling biological sludge based on low-temperature catalytic cracking reaction in this embodiment includes the following steps:

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

[0087] (2) The conditioned biological sludge is transferred to a low-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction is 120°C, the reaction pressure is 0.6 MPa, and the residence time is 2 h. A carboxylic acid mixed solution is obtained. The COD 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 is separated into solid and liquid by high pressure plate and frame to obtain solid residue and filtrate, and the COD of the carboxylic acid solution is Cr 42,000 mg / L, solid residue 55% moisture content.

[0089] Compared with Example 1, this example changes the water content of the quenched and tempered mixed liquid to 90%, the reaction temperature of the low-temperature catalytic cracking to 120°C, the reaction pressure to 0.6MPa, and omits the heat exchange treatment, while other conditions remain unchanged. It is found that the CODCr of the low-temperature catalytic cracking reaction is 42,000 mg / L, and the water content of the solid residue is 55%. It can be seen that lowering the reaction temperature and reaction pressure of the low-temperature catalytic cracking has a great influence on the water content of the solid residue after the final solid-liquid separation. The lower the reaction temperature and reaction pressure, the higher the water content of the solid residue.

[0090] Example 4

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

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

[0093] (2) The conditioned biological sludge is transferred to a low-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction is 170°C, the reaction pressure is 0.8 MPa, and the residence time is 2 h. A carboxylic acid mixed solution is obtained. The COD Cr 28,000 mg / L, of which the total content of carboxylic acids accounts for 16% of the total organic matter.

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

[0095] Compared with Example 1, this example changes the water content of the first conditioning mixed liquid to 90%, adjusts the total chemical oxygen demand and the effective equivalent ratio of the oxidant for low-temperature catalytic cracking to 1:2, and omits the heat exchange treatment, while other conditions remain unchanged. It is found that the CODCr of the low-temperature catalytic cracking reaction is 28,000 mg / L, and the water content of the solid residue is 42%. It can be seen that the water content of the solid residue is slightly reduced by increasing the total chemical oxygen demand and the effective equivalent ratio of the oxidant.

[0096] Example 5

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

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

[0099] (2) The conditioned biological sludge is transferred to a low-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction is 200°C, the reaction pressure is 1.2 MPa, and the residence time is 2 h. A carboxylic acid mixed solution is obtained. The COD Cr 28,000 mg / L, of which the total content of carboxylic acids accounts for 24% of the total organic matter.

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

[0101] Compared with Example 1, the water content of the first tempering mixed liquid is changed to 90%, the reaction temperature of the low-temperature catalytic cracking is 200°C, the reaction pressure is 1.2MPa, and other conditions remain unchanged. Cr 28,000 mg / L, the moisture content of the solid residue is 42%. It can be seen that increasing the reaction temperature and reaction pressure of warm catalytic cracking has a great influence on the moisture content of the solid residue after the final solid-liquid separation. The higher the reaction temperature and reaction pressure, the lower the moisture content of the solid residue.

[0102] Example 6

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

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

[0105] (2) The conditioned biological sludge is transferred to a low-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for low-temperature catalytic cracking reaction. The reaction temperature of the low-temperature catalytic cracking reaction is 170°C, the reaction pressure is 1.2 MPa, and the residence time is 2 h. A carboxylic acid mixed solution is obtained. The COD 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 subjected to heat exchange and cooling treatment using a tubular heat exchanger for a residence time of 0.2 h until the temperature of the carboxylic acid mixture dropped from 170°C to 80°C, and the water temperature was raised from 20°C to 190°C, followed by centrifugation to obtain solid residue and filtrate, and the COD of the carboxylic acid solution was Cr 28,000 mg / L, solid residue 65% moisture content.

[0107] Compared with Example 1, this example adopts centrifugal separation, and other conditions remain unchanged. It is found that the CODCr of the low-temperature catalytic cracking reaction is 28,000 mg / L, and the moisture content of the solid residue is 65%. The centrifugal separation effect is not as good as the high-pressure plate frame.

[0108] Example 7

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

[0110] (1) Water (volume ratio 1:1) and aminotri(methylenephosphonic acid) (concentration 0.1%) were added to the biological sludge (water content 80%) after dehydration from the sewage treatment plant for conditioning treatment. The reaction temperature of the conditioning treatment was 80°C and the pressure was 0.1 MPa. The biological sludge was changed from solid to quasi-solid state, and the conditioned biological sludge with a water content of 90% was obtained. COD Cr 50,000 mg / L.

[0111] (2) The conditioned biological sludge is transferred to a high-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for high-temperature catalytic cracking reaction. The reaction temperature of the high-temperature catalytic cracking reaction is 270°C, the reaction pressure is 10 MPa, and the residence time is 2 h to obtain a carboxylic acid mixed solution. The COD Cr 18,000 mg / L, of which the total content of carboxylic acids accounts for 65% of the total organic matter.

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

[0113] Example 7 was used as the standard reaction condition for the high temperature catalytic cracking route, and other Examples 8-13 were compared with this standard by varying the conditions, reflecting the influence of different reaction conditions on the reaction results.

[0114] Example 8

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

[0116] (1) The treatment steps were the same as those in Example 7, and the conditioned biological sludge with a moisture content of 95% was obtained. Cr 25,000 mg / L.

[0117] (2) The treatment steps are the same as those in Example 7 to obtain a carboxylic acid mixed solution. The COD Cr 12,000 mg / L, of which the total content of carboxylic acids accounts for 67% of the total organic matter.

[0118] (3) The treatment steps are the same as those in Example 7 to obtain a solid residue and a filtrate, and the COD of the carboxylic acid solution Cr 12,000 mg / L, solid residue 20% moisture content.

[0119] Compared with Example 7, the moisture content of the biological sludge after conditioning treatment in this example is changed to 95%, and the organic matter concentration of the sludge is equivalent to 50% of that in Example 1. Other conditions remain unchanged. It is found that the COD Cr 12,000 mg / L, the moisture content of the solid residue is 20%, which can reduce the COD of the reaction Cr The 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 of reducing and recycling biological sludge based on high temperature catalytic cracking reaction in this embodiment includes the following steps:

[0122] (1) The treatment steps were the same as those in Example 7, and the conditioned biological sludge with a moisture content of 90% was obtained. Cr 50,000 mg / L.

[0123] (2) The conditioned biological sludge is transferred to a high-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for high-temperature catalytic cracking reaction. The reaction temperature of the high-temperature catalytic cracking reaction is 220°C, the reaction pressure is 5 MPa, and the residence time is 2 h to obtain a carboxylic acid mixed solution. The COD Cr 27,000 mg / L, of which the total content of carboxylic acids accounts for 43% of the total organic matter.

[0124] (3) The treatment steps are the same as those in Example 7 to obtain a solid residue and a filtrate, and the COD of the carboxylic acid solution Cr 27,000 mg / L, solid residue 40% moisture content.

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

[0126] Example 10

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

[0128] (1) The treatment steps were the same as those in Example 7, and the conditioned biological sludge with a moisture content of 90% was obtained. Cr 50,000 mg / L.

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

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

[0131] Compared with Example 7, this example changes the total chemical oxygen demand and the effective equivalent ratio of the oxidant in the high temperature catalytic cracking to 1:2, and other conditions remain unchanged. Cr 13,000 mg / L, the solid residue was reduced to 18%. It can be seen that the increase of total chemical oxygen demand and effective equivalent ratio of oxidant leads to better effect of solid residue reduction.

[0132] Embodiment 11

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

[0134] (1) The treatment steps were the same as those in Example 7, and the conditioned biological sludge with a moisture content of 90% was obtained. Cr 50,000 mg / L.

[0135] (2) The conditioned biological sludge is transferred to a high-temperature catalytic cracking reactor through fluidization, and air is added as an oxidant (the total chemical oxygen demand and the effective equivalent ratio of the oxidant are 1:1) for high-temperature catalytic cracking reaction. The reaction temperature of the high-temperature catalytic cracking reaction is 300°C, the reaction pressure is 15 MPa, and the residence time is 2 h to obtain a carboxylic acid mixed solution. The COD Cr 12,000 mg / L, of which the total content of carboxylic acids accounts for 82% of the total organic matter.

[0136] (3) The treatment steps are the same as those in Example 7 to obtain a solid residue and a filtrate, and the COD of the carboxylic acid solution Cr 12,000 mg / L, solid residue 15% moisture content.

[0137] Compared with Example 7, this example changes the reaction temperature of high temperature catalytic cracking to 300°C and the reaction pressure to 15 MPa, while other conditions remain unchanged. Cr 12,000 mg / L, the solid residue was reduced to 15%. It can be seen that increasing the reaction temperature and reaction pressure of warm catalytic cracking has a great influence on the reduction of solid residue after the final solid-liquid separation. The higher the reaction temperature and reaction pressure, the better the solid residue reduction.

[0138] Example 12

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

[0140] (1) The treatment steps were the same as those in Example 7, and the conditioned biological sludge with a moisture content of 90% was obtained. Cr 50,000 mg / L.

[0141] (2) The treatment steps are the same as those in Example 7 to obtain a carboxylic acid mixed solution. The COD Cr 18,000 mg / L, of which the total content of carboxylic acids accounts for 65% of the total organic matter.

[0142] (3) The carboxylic acid mixture was subjected to heat exchange and cooling treatment using a tubular heat exchanger for a residence time of 0.2 h until the temperature of the carboxylic acid mixture dropped from 270°C to 80°C, and the water temperature was raised from 20°C to 250°C, followed by centrifugation to obtain solid residue and filtrate, and the COD of the carboxylic acid solution. Cr 18,000 mg / L, solid residue 58% moisture content.

[0143] Compared with Example 7, this example adopts centrifugal separation, and other conditions remain unchanged. It is found that the COD Cr 18,000 mg / L, the solid residue is reduced to 58%, and the centrifugal separation effect is not as good as the high-pressure plate and frame.

[0144] Example 13

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

[0146] (1) Water (volume ratio 1:1) and aminotri(methylenephosphonic acid) (concentration 0.1%) were added to the biological sludge of the chemical plant sewage treatment station (water content 80%, the incoming water did not contain inorganic suspended matter) for conditioning treatment to obtain the conditioned biological sludge with a water content of 90%. COD Cr 50,000 mg / L.

[0147] (2) The treatment steps are the same as those in Example 7 to obtain a carboxylic acid mixed solution. The COD Cr 15,000 mg / L, of which the total content of carboxylic acids accounts for 76% of the total organic matter.

[0148] (3) The carboxylic acid mixture was subjected to heat exchange and cooling treatment using a tubular heat exchanger for a residence time of 0.2 h until the temperature of the carboxylic acid mixture dropped from 270°C to 80°C, and the water temperature was raised from 20°C to 250°C, followed by centrifugation to obtain solid residue and filtrate, and the COD of the carboxylic acid solution. Cr 15,000 mg / L, 8% moisture content of solid residue.

[0149] Compared with Example 1, this example uses biological sludge from a chemical plant sewage treatment station. The sewage is process water and does not contain inorganic suspended matter. Other conditions remain unchanged. It is found that the COD Cr 15,000 mg / L, the solid residue was reduced to 8%. It can be seen that the content of inorganic suspended matter in biological sludge is the main factor affecting the moisture content of solid residue.

[0150] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for reducing and recycling biological sludge based on catalytic cracking reaction, characterized in that: The following steps are involved: (1) adding a diluent and a scale inhibitor to the biological sludge after dehydration in a sewage treatment plant for conditioning treatment, so that the biological sludge is transformed from a solid state to a quasi-solid state, and a conditioned biological sludge having a moisture content of 85% to 95% is obtained; (2) The conditioned biological sludge is transferred to a catalytic cracking reactor through fluidization, and an oxidant is added to perform a catalytic cracking reaction. The conditioned biological sludge releases capillary water, sludge particle adsorbed water, and water inside sludge particles contained in the sludge into free water through a controllable oxidation process, so that the biological sludge is transformed 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; (3) subjecting the carboxylic acid mixture to heat exchange and cooling treatment until the temperature of the carboxylic acid mixture is between room temperature and 100° C., raising the temperature of water to 120° C. to 320° C., and then subjecting the mixture to solid-liquid separation to obtain solid residue and filtrate, thereby achieving resource utilization of carbon elements while reducing the amount of biological sludge.

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

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

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

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

6. The method for reducing and recycling biological sludge based on catalytic cracking reaction according to claim 1, characterized in that: In step (1), the scale inhibitor includes at least one of organic phosphate, polyacrylamide, polycarboxylic acid, acrylic acid and alkyl acrylic acid; The scale inhibitor comprises at least one of amino trimethylene phosphonic acid, hydroxy ethylene diphosphonic acid, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, polyacrylic acid and hydroxy phosphonate; The mass ratio of the scale inhibitor to the biological sludge dehydrated from the sewage treatment plant is 0.001% to 10%.

7. The method for reducing and recycling biological sludge based on catalytic cracking reaction according to claim 1, characterized in that: In step (2), the reaction temperature of the catalytic cracking reaction is 120° C. to 350° C., the reaction pressure is 0.5 MPa to 20 MPa, and the residence time is 0.1 h to 10 h.

8. The method for reducing and recycling biological sludge based on catalytic cracking reaction according to claim 1, characterized in that: In step (2), the oxidant comprises at least one of air, oxygen, hydrogen peroxide, chlorate, hypochlorite, and persulfate; The amount of oxidant used per unit time and the sludge COD Cr The total ratio is 0.1 to 5.

9. The method for reducing and recycling biological sludge based on catalytic cracking reaction according to claim 1, characterized in that: In step (3), the solid residue can be recycled and used as fertilizer for landscaping, forestry and land improvement.

10. A treatment system for reducing and recycling biological sludge based on catalytic cracking reaction, characterized in that: The processing system implements the method according to any one of claims 1 to 9; The treatment system comprises a conditioning unit, a catalytic cracking unit, a heat exchange unit and a separation unit connected in sequence; The conditioning unit is used to fully mix the dehydrated biological sludge, diluent and scale inhibitor of the sewage treatment plant to obtain the conditioned biological sludge with a water content of 85% to 95%; The catalytic cracking unit is connected to the outlet of the conditioning unit, and the conditioned biological sludge is fluidized and transferred to the catalytic cracking unit through a power device. The catalytic cracking unit is also provided with an oxidant inlet, which is used for releasing the capillary water, sludge particle adsorbed water, and water inside the sludge particles contained in the conditioned biological sludge into free water through a controllable oxidation process under the action of the oxidant, and 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; 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 ~ 100°C by heat exchange, and to raise the temperature of water to 120°C ~ 320°C, and then transmit it to the solid-liquid separation unit to obtain solid residue and filtrate after solid-liquid separation, so that the biological sludge can be reduced while realizing the resource utilization of carbon elements.

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