A method for efficiently recycling excess sludge

Abstract

The present invention provides a method for efficiently recycling excess sludge, specifically comprising the following steps: S01, sludge conditioning; S02, sludge dehydration and drying; S03, sludge pyrolysis; S04, separation of sludge pyrolysis gas; and S05, preparation of modified sludge biochar. This method recycles the biochar and pyrolysis gas after sludge treatment, while simultaneously improving sludge dehydration performance and effectively avoiding the risk of heavy metal release from the biochar surface. This method maximizes and fully utilizes sludge resources, effectively reducing costs and improving sludge treatment efficiency and effectiveness.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and in particular to a method for efficiently cyclically treating excess sludge. Background Art

[0002] With the rapid development of urbanization and industrialization in my country, the discharge volume of sludge treatment is increasing. Sludge is a stable colloid with the characteristics of high microbial content, high water content, high organic matter, poor stability, porous fractal and gel-like network structure. Sludge also contains toxic and harmful substances such as heavy metal elements, carcinogenic organic matter, pathogenic microorganisms, etc. If not handled properly, it is very easy to cause secondary pollution, seriously damage the ecological environment and endanger human health.

[0003] Currently, my country's sludge treatment methods include sanitary landfill, incineration, composting, and sludge pyrolysis. Sanitary landfill cannot eliminate pollutants in sludge, and with the development of urbanization, land resources for sanitary landfill are gradually becoming saturated, and available sites are becoming increasingly scarce. Incineration can generate heat and significantly reduce sludge volume, but it also produces many toxic and harmful byproducts, such as fly ash and dioxins, which cause environmental pollution. Composting is a low-cost process that can recycle nutrients in sludge, but pollutants such as heavy metals in sludge can easily disrupt soil balance, causing changes in soil quality and thus affecting ecological balance. Sludge pyrolysis technology can achieve the conversion and utilization of biomass energy in sludge. The pyrolysis gas and bio-oil produced by its cracking can be directly used as energy. It can also produce sludge-based biochar with a large specific surface area, strong ion exchange properties, high porosity, and rich surface functional groups. It has been one of the technologies for treating excess sludge that has attracted widespread attention both domestically and internationally in recent years.

[0004] However, the dehydration and drying process before sludge pyrolysis consumes high energy and has low dehydration efficiency. The solid products of pyrolysis are difficult to utilize, and the prepared sludge biochar has the risk of releasing heavy metals on the surface. In addition, the treatment and utilization process of the synthesis gas produced by pyrolysis is complicated, which seriously restricts the development of sludge pyrolysis treatment technology. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for efficiently recycling the residual sludge, which can recycle the biochar and pyrolysis gas after sludge treatment, while improving the sludge dewatering performance and effectively avoiding the risk of heavy metal release on the surface of biochar, thereby achieving the maximum and most effective utilization of sludge resources, effectively reducing costs, and improving the efficiency and effect of sludge treatment.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for efficiently recycling excess sludge, characterized in that it specifically comprises the following steps:

[0008] S01. Sludge conditioning: persulfate, cationic polyacrylamide and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly;

[0009] S02, sludge dehydration and drying: dehydrating the remaining sludge after being fully mixed in step S01, and drying it at low temperature after dehydration to obtain dry sludge;

[0010] S03, sludge pyrolysis: placing the dried sludge in step S02 in a tubular furnace and performing a pyrolysis process to obtain sludge pyrolysis gas and sludge biochar;

[0011] S04. Separation of sludge pyrolysis gas: The sludge pyrolysis gas in step S03 is separated using an oil-gas separation device to separate oil and gas (such as heavy tar) and mixed gas (such as H2S, SO2, NH3, CO, CO2, H2, hydrocarbons and gases containing oxygen functional groups, etc.); the separated oil and gas are used for energy utilization, and the separated mixed gas is subjected to secondary separation using a gas separation device, and the modified gas is collected for standby use and the non-modified gas is removed;

[0012] S05. Preparation of modified sludge biochar: The sludge biochar prepared in step S03 is continued to be placed in the tubular furnace, and the modified gas separated in step S04 is introduced into the tubular furnace to heat the tubular furnace, thereby performing a chemical vapor deposition reaction under high temperature conditions to obtain modified sludge biochar. The modified sludge biochar serves as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

[0013] For further optimization, the mass ratio of the persulfate, cationic polyacrylamide and modified sludge biochar is: 11.5-12.5:0.8-1.2:45-55; and the dosage of the conditioning agent composed of persulfate, cationic polyacrylamide and modified sludge biochar does not exceed 50% of the dry sludge.

[0014] Sludge biochar (i.e., sludge biochar obtained by direct pyrolysis) is directly used as a catalyst to activate the oxidation of persulfate to crack sludge. First, the ability of sludge biochar to catalyze persulfate is not high and the catalytic efficiency is low. It needs to be modified or loaded with functional nanoparticles to improve its catalytic efficiency. Whether it is chemical activation, physical activation, or nanomaterial modification, it increases the manufacturing cost of modified biochar, increases the use of materials, and the operation is cumbersome, which increases the cost and treatment steps of sludge treatment.

[0015] The present application directly separates the gas after the pyrolysis of excess sludge and directly performs chemical vapor deposition on the biochar produced after the pyrolysis of excess sludge to achieve the modification of sludge biochar, thereby forming a film composed of rich oxygen-containing functional groups and graphite carbon lattice on the surface of the sludge biochar. Among them, the oxygen-containing functional groups (such as -C=O, -OH, -COOH, etc.) as electron shuttles can effectively regulate the electron transfer reaction and redox properties of biochar, thereby causing persulfate to crack and release sulfate radicals, and sulfate radicals have higher redox sites, more effective mineralization rates and better stability, which can oxidize and crack sludge, thereby causing the sludge to release more water; the graphite carbon lattice can promote the electron transfer between pollutants and persulfate in a non-radical pathway, thereby transferring electrons from the sludge adsorbed on the biochar to the activated persulfate, thereby promoting the electron shuttle between the sludge and the persulfate, further promoting the cracking of the sludge by the persulfate and increasing the sludge dewatering capacity. In addition, the thin film composed of oxygen-containing functional groups and graphite carbon lattice can wrap the surface of biochar, thereby avoiding the problem of heavy metals on the surface of biochar being released into the residual sludge during sludge conditioning and increasing the heavy metal content in the residual sludge.

[0016] In addition, the modified sludge biochar has more active sites, a larger specific surface area, rich oxygen-containing functional groups and graphite carbon lattices, which serve as a skeleton building role in the residual sludge conditioning process, further improving the sludge permeability and making the free water released in the sludge easier to be separated by filtration, thereby reducing the sludge moisture content; finally, the sludge is flocculated by cationic polyacrylamide to prevent the sludge from dispersing and clogging the filter screen and pipeline of the dehydration device (specifically, the belt dehydration filter press).

[0017] For further optimization, the persulfate is either sodium persulfate or potassium persulfate.

[0018] For further optimization, in step S02, a belt dewatering filter press is used to dewater the excess sludge.

[0019] For further optimization, the temperature of the low-temperature drying in step S02 is 65-90°C.

[0020] For further optimization, the pyrolysis process in step S03 is specifically as follows: first, low-temperature preheating at 100-200°C and holding time is 3-5 minutes, and then high-temperature cracking at 650-850°C and holding time is 20-35 minutes; the pressure of the tubular furnace during the pyrolysis process is 3.5-6.5 MPa.

[0021] In the initial stage of pyrolysis, low-temperature preheating is used to quickly convert the residual moisture in the sludge into water vapor, which not only achieves further drying of the sludge, but also provides a certain amount of water vapor for subsequent high-temperature cracking. During the high-temperature cracking process, water vapor reacts with biochar to generate hydrogen, thereby increasing the hydrogen concentration in the entire system and increasing the raw gas for subsequent chemical vapor deposition modified biochar, thereby further improving the functional groups on the biochar surface during the chemical vapor deposition process.

[0022] For further optimization, the modified gas in step S04 includes H2, small molecule hydrocarbons C x H y Gases with oxygen-containing functional groups (such as alcohols, aldehydes, carboxylic acids, esters, etc.); non-modified gases are all gases after pyrolysis of residual sludge except modified gases, such as H2S, SO2, NH3, CO, CO2, etc.

[0023] For further optimization, the chemical vapor deposition temperature in step S05 is 600-800° C. and the deposition time is 30-60 min.

[0024] The present invention has the following technical effects:

[0025] The present application uses the gas separated from the pyrolysis of the residual sludge and modifies the biochar produced after the pyrolysis of the residual sludge, thereby realizing the maximum and most complete resource utilization of the sludge, realizing the recycling of the sludge, reducing the use of raw materials for sludge biochar modification, and saving material costs; at the same time, the present application can carry out the modification of sludge pyrolysis biochar and biochar in the same pyrolysis furnace, thereby simplifying the operating process, effectively saving equipment costs and labor costs, and reducing the cost of sludge treatment. In addition, the modified sludge biochar of the present application can effectively promote the decomposition of persulfate to release persulfate radicals, thereby increasing the catalytic effect of the sludge biochar, prompting the sludge to release more water, and then increasing the subsequent sludge dehydration effect, thereby reducing the moisture content of the sludge cake after filter press dehydration, bringing convenience to subsequent treatment.

[0026] This application process is simple, easy to operate, and has a wide range of applications. It can be used in various sludge treatment plants. The by-products and treatment gases after sludge treatment can be recycled during sludge treatment, realizing waste resource utilization, thereby effectively reducing the use of energy and materials, being green and environmentally friendly, with low treatment costs and high treatment efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a cycle flow chart of the excess sludge treatment of the present invention. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1:

[0030] A method for efficiently recycling excess sludge, characterized in that it specifically comprises the following steps:

[0031] S01. Sludge conditioning: persulfate, cationic polyacrylamide and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly;

[0032] The mass ratio of persulfate, cationic polyacrylamide and modified sludge biochar is 11.5:0.8:45; and the dosage of the conditioning agent composed of persulfate, cationic polyacrylamide and modified sludge biochar does not exceed 50% of the dry sludge; the persulfate is sodium persulfate;

[0033] S02, sludge dehydration and drying: The residual sludge after being fully mixed in step S01 is dehydrated using a belt dehydration filter press (the belt dehydration filter press can be a common structure in the art, which is well understood by those skilled in the art), and then low-temperature drying is performed after dehydration, with the low-temperature drying temperature being 65° C. to obtain dried sludge;

[0034] S03, sludge pyrolysis: The dried sludge from step S02 is placed in a tubular furnace (the tubular furnace adopts the device disclosed in Chinese patent document CN215924871U. No protective gas is required during the sludge pyrolysis process, and no subsequent separation of the protective gas and the pyrolysis gas is required). The pyrolysis process is carried out, specifically: low-temperature preheating at 100°C and holding for 3 minutes, followed by high-temperature cracking at 650°C and holding for 20 minutes. The pressure of the tubular furnace during the pyrolysis process is 3.5 MPa, thereby obtaining sludge pyrolysis gas and sludge biochar.

[0035] S04, separation of sludge pyrolysis gas: the sludge pyrolysis gas in step S03 is separated by an oil-gas separation device, thereby separating oil and gas (such as heavy tar) and mixed gas (such as H2S, SO2, NH3, CO, CO2, H2, hydrocarbons and gases containing oxygen functional groups, etc.); the separated oil and gas are used for energy utilization, and the separated mixed gas is subjected to secondary separation by a gas separation device, and the modified gas is collected for standby use and the non-modified gas is removed (Note: the removal of non-modified gas described herein does not mean directly discharging the non-modified gas into the air, but rather treating it by chemical or physical means, or collecting it, or removing it under conditions that do not pollute the air, which can be understood by those skilled in the art); the modified gas includes H2, small molecule hydrocarbons C x H y and gases containing oxygen-containing functional groups (such as alcohols, aldehydes, carboxylic acids, esters, etc.); non-modified gases are all gases after pyrolysis of excess sludge except modified gases, such as H2S, SO2, NH3, CO, CO2, etc. (the gas separation device can separate the non-modified gas step by step, or directly separate the modified gas. This application does not make specific restrictions, and those skilled in the art can understand it);

[0036] S05. Preparation of modified sludge biochar: The sludge biochar in step S03 is continued to be placed in the tubular furnace, and the modified gas separated in step S04 is introduced into the tubular furnace at the same time, and the modified gas to be separated is refluxed into the tubular furnace, and the tubular furnace is heated, thereby performing a chemical vapor deposition reaction under high temperature conditions. The chemical vapor deposition temperature is 600°C and the deposition time is 30 minutes to obtain modified sludge biochar. The modified sludge biochar is used as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

[0037] Example 2:

[0038] A method for efficiently recycling excess sludge, characterized in that it specifically comprises the following steps:

[0039] S01. Sludge conditioning: persulfate, cationic polyacrylamide and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly;

[0040] The mass ratio of persulfate, cationic polyacrylamide and modified sludge biochar is 12:1:50; and the dosage of the conditioning agent composed of persulfate, cationic polyacrylamide and modified sludge biochar does not exceed 50% of the dry sludge; the persulfate is sodium persulfate;

[0041] S02, sludge dehydration and drying: The residual sludge after being fully mixed in step S01 is dehydrated using a belt dehydration filter press (the belt dehydration filter press can be a common structure in the art, which is well understood by those skilled in the art), and then low-temperature drying is performed after dehydration, with the low-temperature drying temperature being 80° C. to obtain dried sludge;

[0042] S03, sludge pyrolysis: The dried sludge from step S02 is placed in a tubular furnace (the tubular furnace adopts the device disclosed in Chinese patent document CN215924871U. No protective gas is required during the sludge pyrolysis process, and no subsequent separation of the protective gas and pyrolysis gas is required). The pyrolysis process is carried out, specifically: low-temperature preheating at 150°C and holding for 4 minutes, followed by high-temperature cracking at 750°C and holding for 28 minutes. The pressure of the tubular furnace during the pyrolysis process is 5 MPa. Sludge pyrolysis gas and sludge biochar are obtained.

[0043] S04, separation of sludge pyrolysis gas: the sludge pyrolysis gas in step S03 is separated by an oil-gas separation device, thereby separating oil and gas (such as heavy tar) and mixed gas (such as H2S, SO2, NH3, CO, CO2, H2, hydrocarbons and gases containing oxygen functional groups, etc.); the separated oil and gas are used for energy utilization, and the separated mixed gas is subjected to secondary separation by a gas separation device, and the modified gas is collected for standby use and the non-modified gas is removed (Note: the removal of non-modified gas described herein does not mean directly discharging the non-modified gas into the air, but rather treating it by chemical or physical means, or collecting it, or removing it under conditions that do not pollute the air, which can be understood by those skilled in the art); the modified gas includes H2, small molecule hydrocarbons C x H y and gases containing oxygen-containing functional groups (such as alcohols, aldehydes, carboxylic acids, esters, etc.); non-modified gases are all gases after pyrolysis of excess sludge except modified gases, such as H2S, SO2, NH3, CO, CO2, etc. (the gas separation device can separate the non-modified gas step by step, or directly separate the modified gas. This application does not make specific restrictions, and those skilled in the art can understand it);

[0044] S05. Preparation of modified sludge biochar: The sludge biochar in step S03 is continued to be placed in the tubular furnace, and the modified gas separated in step S04 is introduced into the tubular furnace at the same time, and the modified gas to be separated is refluxed into the tubular furnace, and the tubular furnace is heated, thereby performing a chemical vapor deposition reaction under high temperature conditions. The chemical vapor deposition temperature is 700°C and the deposition time is 45 minutes to obtain modified sludge biochar. The modified sludge biochar is used as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

[0045] Example 3:

[0046] A method for efficiently recycling excess sludge, characterized in that it specifically comprises the following steps:

[0047] S01. Sludge conditioning: persulfate, cationic polyacrylamide and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly;

[0048] The mass ratio of persulfate, cationic polyacrylamide and modified sludge biochar is 12.5:1.2:55; and the dosage of the conditioning agent composed of persulfate, cationic polyacrylamide and modified sludge biochar does not exceed 50% of the dry sludge; the persulfate is potassium persulfate;

[0049] S02, sludge dehydration and drying: The residual sludge after being fully mixed in step S01 is dehydrated using a belt dehydration filter press (the belt dehydration filter press can be a common structure in the art, which is well understood by those skilled in the art), and then low-temperature drying is performed after dehydration, with the low-temperature drying temperature being 90° C. to obtain dried sludge;

[0050] S03, sludge pyrolysis: The dried sludge from step S02 is placed in a tubular furnace (the tubular furnace adopts the device disclosed in Chinese patent document CN215924871U. No protective gas is required during the sludge pyrolysis process, and no subsequent separation of the protective gas and pyrolysis gas is required). The pyrolysis process is carried out, specifically: low-temperature preheating at 200°C and holding for 5 minutes, followed by high-temperature cracking at 850°C and holding for 35 minutes. The pressure of the tubular furnace during the pyrolysis process is 6.5 MPa, thereby obtaining sludge pyrolysis gas and sludge biochar.

[0051] S04, separation of sludge pyrolysis gas: the sludge pyrolysis gas in step S03 is separated by an oil-gas separation device, thereby separating oil and gas (such as heavy tar) and mixed gas (such as H2S, SO2, NH3, CO, CO2, H2, hydrocarbons and gases containing oxygen functional groups, etc.); the separated oil and gas are used for energy utilization, and the separated mixed gas is subjected to secondary separation by a gas separation device, and the modified gas is collected for standby use and the non-modified gas is removed (Note: the removal of non-modified gas described herein does not mean directly discharging the non-modified gas into the air, but rather treating it by chemical or physical means, or collecting it, or removing it under conditions that do not pollute the air, which can be understood by those skilled in the art); the modified gas includes H2, small molecule hydrocarbons C x H yand gases containing oxygen-containing functional groups (such as alcohols, aldehydes, carboxylic acids, esters, etc.); non-modified gases are all gases after pyrolysis of excess sludge except modified gases, such as H2S, SO2, NH3, CO, CO2, etc. (the gas separation device can separate the non-modified gas step by step, or directly separate the modified gas. This application does not make specific restrictions, and those skilled in the art can understand it);

[0052] S05. Preparation of modified sludge biochar: The sludge biochar in step S03 is continued to be placed in the tubular furnace, and the modified gas separated in step S04 is introduced into the tubular furnace at the same time, and the modified gas to be separated is refluxed into the tubular furnace, and the tubular furnace is heated, thereby performing a chemical vapor deposition reaction under high temperature conditions. The chemical vapor deposition temperature is 800°C and the deposition time is 60 minutes to obtain modified sludge biochar. The modified sludge biochar is used as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

[0053] Comparative Example 1:

[0054] A method for recycling excess sludge, characterized by comprising the following steps:

[0055] S01. Sludge conditioning: persulfate, cationic polyacrylamide and sludge biochar are added to the residual sludge and stirred to mix thoroughly;

[0056] The mass ratio of persulfate, cationic polyacrylamide and sludge biochar is 12:1:50; and the dosage of the conditioning agent composed of persulfate, cationic polyacrylamide and sludge biochar does not exceed 50% of the dry sludge; the persulfate is sodium persulfate;

[0057] S02, sludge dehydration and drying: the residual sludge after being fully mixed in step S01 is dehydrated using a belt dehydration filter press, and then dried at low temperature at a temperature of 80° C. to obtain dried sludge;

[0058] S03, sludge pyrolysis: The dried sludge in step S02 is placed in a tubular furnace (the tubular furnace adopts the device disclosed in Chinese patent document CN215924871U. No protective gas is required during the sludge pyrolysis process, and there is no need to separate the protective gas and the pyrolysis gas subsequently) for pyrolysis. The specific process is: low-temperature preheating at 150°C and a holding time of 4 minutes, followed by high-temperature cracking at 750°C and a holding time of 28 minutes; the pressure of the tubular furnace during the pyrolysis process is 5 MPa; thereby, sludge pyrolysis gas and sludge biochar are obtained; the sludge biochar serves as a component of the conditioning agent in step S01 to realize the circulation of the sludge biochar, and the pyrolysis gas is used to generate heat and convert it into thermal energy or electrical energy (using common methods in this field).

[0059] Comparative Example 2:

[0060] A method for efficiently recycling excess sludge, characterized in that it specifically comprises the following steps:

[0061] S01. Sludge conditioning: persulfate, cationic polyacrylamide, and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly. The mass ratio of persulfate, cationic polyacrylamide, and modified sludge biochar is 12:1:50. The dosage of the conditioning agent composed of persulfate, cationic polyacrylamide, and modified sludge biochar does not exceed 50% of the dry sludge. Sodium persulfate is used as the persulfate.

[0062] S02, sludge dehydration and drying: The residual sludge after being fully mixed in step S01 is dehydrated using a belt dehydration filter press (the belt dehydration filter press can be a common structure in the art, which is well understood by those skilled in the art), and then low-temperature drying is performed after dehydration, with the low-temperature drying temperature being 80° C. to obtain dried sludge;

[0063] S03, sludge pyrolysis: The dried sludge in step S02 is placed in a tubular furnace (the tubular furnace adopts the device disclosed in Chinese patent document CN215924871U. No protective gas is required during the sludge pyrolysis process, and no subsequent separation of the protective gas and the pyrolysis gas is required). The pyrolysis process is carried out. The specific process is: low-temperature preheating at 150°C and holding time for 4 minutes, followed by high-temperature cracking at 750°C and holding time for 28 minutes. The pressure of the tubular furnace during the pyrolysis process is 5 MPa. Sludge pyrolysis gas and sludge biochar are obtained. The pyrolysis gas is used to generate heat and converted into heat energy or electricity (using common methods in the art), and the sludge biochar is used for subsequent modification.

[0064] S04. Preparation of modified sludge biochar: The sludge biochar obtained in step S03 is soaked in a 4 mol / L to 5 mol / L (preferably 4.5 mol / L) NaOH solution for 12 to 24 h (preferably 18 h), thereby alkali-modifying the sludge biochar in step S03 to obtain modified sludge biochar. After washing and drying, the modified sludge biochar is used as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

[0065] Comparative Example 3:

[0066] A method for efficiently recycling excess sludge, characterized in that it specifically comprises the following steps:

[0067] S01. Sludge conditioning: persulfate, cationic polyacrylamide, and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly. The mass ratio of persulfate, cationic polyacrylamide, and modified sludge biochar is 12:1:50. The dosage of the conditioning agent composed of persulfate, cationic polyacrylamide, and modified sludge biochar does not exceed 50% of the dry sludge. Sodium persulfate is used as the persulfate.

[0068] S02, sludge dehydration and drying: The residual sludge after being fully mixed in step S01 is dehydrated using a belt dehydration filter press (the belt dehydration filter press can be a common structure in the art, which is well understood by those skilled in the art), and then low-temperature drying is performed after dehydration, with the low-temperature drying temperature being 80° C. to obtain dried sludge;

[0069] S03, sludge pyrolysis: The dried sludge in step S02 is placed in a tubular furnace (the tubular furnace adopts the device disclosed in Chinese patent document CN215924871U. No protective gas is required during the sludge pyrolysis process, and no subsequent separation of the protective gas and the pyrolysis gas is required). The pyrolysis process is carried out. The specific process is: low-temperature preheating at 150°C and holding time for 4 minutes, followed by high-temperature cracking at 750°C and holding time for 28 minutes. The pressure of the tubular furnace during the pyrolysis process is 5 MPa. Sludge pyrolysis gas and sludge biochar are obtained. The pyrolysis gas is used to generate heat and converted into heat energy or electricity (using common methods in the art), and the sludge biochar is used for subsequent modification.

[0070] S04. Preparation of modified sludge biochar: Under argon atmosphere, the sludge biochar obtained in step S03 is placed in a 0.05 mol / L FeSO4·7H2O solution, the pH value is adjusted to 5, and then a 0.1 mol / L NaBH4 solution is added dropwise while stirring to modify the sludge biochar in step S03 into a magnetic material to obtain modified sludge biochar. After washing and drying, the modified sludge biochar is used as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

[0071] Example 2 and Comparative Examples 1-3 were used to treat the same amount of excess sludge, and the sludge decomposition rates of the modified sludge biochars obtained in Example 2 and Comparative Examples 1-3 (wherein Comparative Example 1 was sludge biochar) were tested respectively. At the same time, the moisture content and heavy metal inlet and outlet toxicity of the sludge cakes after the sludge was treated with the modified sludge biochars obtained in Example 2 and Comparative Examples 1-3 (wherein Comparative Example 1 was sludge biochar) were tested. The test results are shown in Table 1 below:

[0072] Among them, the sludge breakdown rate, that is, the sludge breakdown degree (DD COD ) is specifically as follows:

[0073] Sludge cracking degree is a parameter that characterizes the sludge cracking effect. It refers to the ratio of the change in SCOD after sludge cracking to the COD in the solid phase before sludge cracking. The calculation formula for sludge cracking degree is:

[0074]

[0075] Where: TCOD—total chemical oxygen demand (mg / L); SCOD—soluble chemical oxygen demand (mg / L); SCOD0—SCOD of unbroken sludge (mg / L);

[0076] In the above formula, the TCOD analysis method is: pretreat the sludge sample with sodium hydroxide solution (0.5mol / L) for 24 hours, filter it with qualitative filter paper after pretreatment, and the COD of the resulting filtrate is the TCOD of the sludge; the SCOD analysis method is: place the sludge sample in a refrigerated centrifuge and centrifuge it at 8000r / min for 20 minutes. After the centrifugation is completed, aspirate the filtrate with a needle and filter it with a 0.45μm filter membrane. The COD of the measured filtrate is SCOD. The above TCOD and SCOD are both determined using the potassium dichromate method.

[0077] The leaching toxicity test method refers to (Solid Waste - Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method) "HJ / T299-2007".

[0078]

[0079] It can be seen from the above table that: the separation gas after the pyrolysis of the residual sludge is used in the present application to perform chemical vapor deposition on the biochar produced after the pyrolysis of the residual sludge, thereby realizing the modification of the biochar produced by the residual sludge. Compared with the unmodified, alkali-modified, and magnetic material-modified biochar, the activated persulfate produces more free radicals and the sludge cracking degree is higher; that is, the present application modifies the biochar by pyrolysis gas, which can form a film on the surface of the sludge biochar composed of rich oxygen-containing functional groups that promote the cracking of sulfate and release sulfate radicals and graphite carbon lattices that promote electron shuttle between sludge and persulfate, thereby improving the degree of sludge cracking. At the same time, the film generated by the modification of biochar by sludge pyrolysis gas in the present application can also effectively wrap the heavy metals on the surface of the biochar, making the leaching toxicity of the biochar weak; in addition, through the modification method of the present application, the moisture content of the sludge cake can also be effectively reduced to ensure the dehydration effect.

[0080] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for efficiently recycling excess sludge, characterized by: The specific steps include: S01. Sludge conditioning: persulfate, cationic polyacrylamide and modified sludge biochar are added to the residual sludge and stirred to mix thoroughly; S02, sludge dehydration and drying: dehydrating the remaining sludge after being fully mixed in step S01, and drying it at low temperature after dehydration to obtain dry sludge; S03, sludge pyrolysis: placing the dried sludge in step S02 in a tubular furnace and performing a pyrolysis process to obtain sludge pyrolysis gas and sludge biochar; S04. Separation of sludge pyrolysis gas: The sludge pyrolysis gas in step S03 is separated using an oil-gas separation device to separate oil, gas, and mixed gas. The separated oil and gas are used for energy utilization, and the separated mixed gas is subjected to secondary separation using a gas separation device to collect modified gas for backup and remove non-modified gas. The modified gas includes H2, small molecular hydrocarbons CxHy, and gases containing oxygen functional groups. The non-modified gas is all gases remaining after sludge pyrolysis except the modified gas. S05. Preparation of modified sludge biochar: The sludge biochar prepared in step S03 is continued to be placed in the tubular furnace, and the modified gas separated in step S04 is introduced into the tubular furnace to heat the tubular furnace, thereby performing a chemical vapor deposition reaction under high temperature conditions to obtain modified sludge biochar. The chemical vapor deposition temperature is 600-800°C and the deposition time is 30-60 minutes. The modified sludge biochar serves as a component of the conditioning agent in step S01 to realize the circulation of the modified sludge biochar.

2. The method for efficiently recycling excess sludge according to claim 1, characterized in that: The mass ratio of the persulfate, cationic polyacrylamide and modified sludge biochar is: 11.5-12.5:0.8-1.2:45-55; and the addition amount of the conditioning agent composed of persulfate, cationic polyacrylamide and modified sludge biochar does not exceed 50% of the dry sludge.

3. The method for efficiently recycling excess sludge according to claim 1 or 2, characterized in that: The persulfate is either sodium persulfate or potassium persulfate.

4. The method for efficiently recycling excess sludge according to claim 3, characterized in that: In step S02, a belt dewatering filter press is used to dewater the excess sludge.

5. The method for efficiently recycling excess sludge according to claim 3, characterized in that: The temperature of the low-temperature drying in step S02 is 65-90°C.

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