Municipal sludge reduction and recycling treatment method

Abstract

The invention discloses a municipal sludge reduction and recycling treatment method, which comprises the following steps: pumping sludge into a reaction kettle through a screw pump, adding sodium hydroxide and a catalytic oxidant, injecting gas for pressurization, heating by using heat-conducting oil, heating, pressurizing, stirring, and keeping the temperature and pressure when a set value is reached. In the catalytic oxidation process, the nitrogen-containing organic matter generates ammonia, and the ammonia forms small-molecule compound gas and then is discharged. Sludge is changed into a liquid phase from a solid phase state and is pumped into a plate-and-frame filter press through a screw pump, filtrate and a filter cake are obtained, COD in the filtrate after dehydration of the plate-and-frame filter press reaches 50000 mg / L or above, the total nitrogen content is about 1000 mg / L, and the filtrate can be used as a low-quality carbon source. The dehydrated sludge is low in organic matter content, so that the sludge can be used for preparing ceramic particles through a brickmaking factory. The invention provides the method for reducing and recycling the sludge, the whole process is reasonable and takes effect quickly, the system operation energy consumption is low, the reaction time is shortened, and the operation cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge treatment, and in particular relates to a method for reducing and recycling municipal sludge. Background Art

[0002] At present, domestic sludge disposal is basically landfill and incineration. The landfill of sludge not only occupies a large amount of land resources and farmland, but also damages the environment, pollutes groundwater and surface water, and directly endangers human health; nitrogen and phosphorus in sludge are washed into rivers by rainwater, causing eutrophication of rivers. The investment and operating costs of sludge incineration are the most expensive among the sludge disposal methods. Due to the low calorific value of sludge, power plants need to add natural gas at the same time to completely burn it, and the incineration of sludge will also cause problems with flue gas treatment.

[0003] Making bricks from sewage sludge is a technology in the resource utilization of sewage sludge. It makes full use of the inorganic components in the sewage sludge to turn waste into treasure, conforms to the strategic policy of sustainable development, and is conducive to the establishment of a circular economy to eliminate the potential harm of sewage sludge to the environment, reduce the operating costs of sewage treatment plants, reduce clay mining, and ease the contradiction between the brick and tile industry and agriculture for land. However, the high organic matter and water content in the sewage sludge hinder the development of the sewage sludge brick industry.

[0004] Since the C / N ratio of my country's sewage treatment plants is relatively low, it is usually necessary to consume a large amount of carbon sources and other means to improve the treatment effect. The C / N ratio of the hydrolyzate after thermal hydrolysis of sludge is relatively high, and the COD equivalent can reach 50,000-120,000. After hydrolysis, the organic matter in the hydrolyzate mainly exists in the form of organic acids and other components, which has good biodegradability and is easy to be used by microorganisms in activated sludge. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a sludge reduction and resource utilization method with low energy consumption, high treatment efficiency and resource utilization of filtrate and dewatered water cake, in view of the defects of existing sludge treatment methods such as occupying land resources, polluting groundwater and surface water, high treatment cost and low disposal efficiency.

[0006] The technical problem to be solved by the present invention is achieved by the following technical solution: a method for reducing and recycling sludge is provided, which is based on multiple reaction equipment, including: a sludge silo, a screw pump, a reactor, a gas heating furnace, a heat transfer oil, a pressure relief tank, a reaction liquid storage tank, a plate and frame filter press, and a desulfurization and denitrification device, and includes the following steps: Step 1: The municipal sludge stored in the sludge silo is pumped into the reactor through a screw pump. The initial sludge injection amount is 80% of the reactor volume. Then, gas is injected into the reactor. When the pressure in the reactor reaches 1.0 MPa, the gas injection is stopped. Sodium hydroxide and a catalytic oxidant are added to the reactor. A stirrer is provided in the reactor to stir and mix the sodium hydroxide, the catalytic oxidant and the sludge. Step 2: The heat transfer oil in the reactor jacket is heated by a gas heating furnace. The heat transfer oil transfers the high temperature to the sludge in the reactor, so that the temperature of the sludge in the reactor is maintained in the range of 180-250°C. The sludge changes from a solid phase to a liquid phase after being heated and pressurized in the reactor; Step 3: When the temperature and pressure in the reactor reach the set value, the pressure relief valve of the pressure relief tank automatically opens to discharge the gas, keeping the pressure in the reactor above 3.0MPa. The discharged gas passes through the desulfurization and denitrification device to remove sulfur and nitrogen oxides; Step 4: After 4 hours of reaction, the liquid sludge is discharged into the reaction liquid storage tank, and the liquid sludge is pumped into the plate and frame filter press by a screw pump for dehydration to obtain filtrate and mud cake.

[0007] In the above-mentioned treatment method based on sludge reduction and resource utilization, the gas injected into the reactor in step 1 is air or oxygen. When the pressure in the reactor reaches 1.0 MPa, the gas injection is stopped and the gas injection valve is closed.

[0008] In the above-mentioned treatment method based on sludge reduction and resource utilization, the amount of catalytic oxidant added to the reactor in step 1 is 1-2‰ of the weight of the solid sludge.

[0009] In the above-mentioned treatment method based on sludge reduction and resource utilization, the catalytic oxidant is a 2-pyridone active molecule, and the specific synthesis method of the 2-pyridone active molecule is: take 10 mmolN-substituted 3-hydroxy-2-pyridone, 20 mmolMBH carbonate is dissolved in 200 ml of dichloromethane, add 340 mg of triethylenediamine, let it stand for reaction at room temperature for 24 hours, purify it with a cation exchange resin, and elute it with an eluent, the eluent is a mixed solution of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is 10:1.

[0010] In the above-mentioned treatment method based on sludge reduction and resource utilization, the catalytic oxidant reacts with the sludge to continuously generate gas during the heating process, so that the pressure in the reactor reaches and remains at 3.0 MPa.

[0011] In the above-mentioned treatment method based on sludge reduction and resource utilization, when the pressure in the reactor exceeds 3.0MPa, the pressure is automatically discharged to the pressure relief tank, and when the pressure is lower than 3.0MPa, the exhaust is stopped to ensure the high pressure in the reactor.

[0012] In the above-mentioned treatment method based on sludge reduction and resource utilization, after the first injected sludge reacts for 4 hours, the pressure in the reactor reaches 3.0 MPa and the temperature reaches above 180°C. The reactor can continuously inject sludge, and the reacted sludge is discharged through the liquid outlet.

[0013] In the above-mentioned treatment method based on sludge reduction and resource utilization, the sludge in the reactor is continuously injected, and the sludge in the reactor becomes a liquid phase after high temperature and high pressure reaction. When the liquid level reaches the height of the liquid outlet, the pressure at the liquid outlet is reduced by a pressure reducing valve and discharged into the reaction liquid storage tank.

[0014] In the above-mentioned treatment method based on sludge reduction and resource utilization, the moisture content of the filter cake after the sludge in the reactor is dehydrated is 25-30%.

[0015] The following beneficial effects can be obtained by implementing the present invention: (1) The technology of the present invention is applicable to the dehydration of sludge with various moisture contents, and no pretreatment is required before the reaction, so the operation is simple; (2) After the addition of a catalytic oxidant, the reaction is more complete, and the condensed water in the reaction process and the filtrate after the sludge dehydration can be used as carbon sources; (3) The sludge after the reaction and dehydration is reduced by more than 85% compared with the feed sludge, and the organic matter content is greatly reduced. It can be used as a raw material for making ceramsite and bricks, which not only effectively reduces the land resources occupied by sludge during landfill treatment and reduces the occupation and consumption of natural resources, but also enables the recycling of precious resources, which is beneficial to the sustainable development of the country. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a flowchart of a sludge reduction and resource processing method. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] like Figure 1 As shown, the present invention discloses a method for reducing and recycling municipal sludge, which is based on multiple reaction equipment, including: a sludge silo, a screw pump, a reactor, a gas heating furnace, a heat transfer oil, a pressure relief tank, a reaction liquid storage tank, a plate and frame filter press, and a desulfurization and denitrification device, and specifically includes the following steps: Step 1: Pump the municipal sludge with a moisture content of ≤85% stored in the sludge silo into the reactor through a screw pump, and the first sludge injection volume is 80% of the reactor volume. Then inject gas into the reactor, the injected gas can be air or oxygen, and when the pressure in the reactor reaches 1.0MPa, stop injecting gas and close the gas injection valve. Sodium hydroxide and catalytic oxidant are added to the reactor, and the catalytic oxidant is a 2-pyridone active molecule. The specific synthesis method of 2-pyridone active molecule is: take 10mmolN-substituted 3-hydroxy-2-pyridone, 20mmolMBH carbonate is dissolved in 200ml dichloromethane, add 340mg triethylenediamine, and stand at room temperature for 24h, purify with cation exchange resin, and elute with eluent, the eluent is a mixed solution of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is 10:1. The dosage of catalytic oxidant is about 1-2‰ of the solid sludge, and the dosage of sodium hydroxide is 5% of the solid sludge injection amount. A stirrer is installed in the reactor to mix sodium hydroxide, catalytic oxidant and sludge. The purpose of adding sodium hydroxide is to destroy the bacterial flocs and organic particles in the sludge through its strong alkaline environment, while inactivating the cells, hydrolyzing and breaking the cell wall (membrane), so as to release proteins and intracellular substances. This treatment method helps the protein in the sludge to further degrade into low molecular weight substances in the liquid phase, thereby achieving the wall breaking and cell lysis of the sludge. By adding the active molecules of the co-oxidation catalyst 2-pyridone, the thermal hydrolysis of the sludge is catalyzed, the separation of organic and inorganic matter in the sludge and the reduction of sludge are promoted, providing a carbon source for sewage treatment and raw materials for sludge brick making, which promotes the replacement of sludge thermal hydrolysis process.

[0019] Step 2: The heat transfer oil in the reactor jacket is heated by a gas heating furnace. The heat transfer oil transfers the high temperature to the sludge in the reactor, so that the sludge temperature in the reactor is maintained in the range of 180-250°C. After the sludge is heated and pressurized in the reactor, the organic matter in the sludge is converted into small molecular compounds, and the sludge is converted from a solid phase to a liquid phase.

[0020] Based on step 1 and step 2, the catalytic oxidant converts part of the organic nitrogen in the sludge into ammonia during the heating process. Under the action of the catalytic oxidant, the ammonia forms small molecular compounds NO and NO2 gas. The pressure in the reactor is further increased by the continuously generated gas, and finally the pressure in the reactor reaches 3.0MPa.

[0021] Step 3: When the temperature and pressure in the reactor reach the above set values, the pressure relief valve of the pressure relief tank automatically opens to discharge the gas, keeping the pressure in the reactor above 3.0MPa. The discharged gas passes through the desulfurization and denitrification device to remove sulfur and nitrogen oxides. The gas only contains CO and CH4, which can be recycled as clean energy.

[0022] Step 4: After 4 hours of high temperature and high pressure reaction, when the liquid level reaches the outlet, the pressure relief valve set at the outlet is used to reduce the outlet pressure, and the liquid sludge is discharged into the reaction liquid storage tank. The liquid sludge is pumped into the plate and frame filter press by a screw pump for dehydration to obtain filtrate and mud cake. The moisture content of the filter cake after sludge dehydration is 25%-30%. The dehydrated mud cake can be used as a raw material for making ceramsite and bricks, and the dehydrated filtrate can be returned to the front end of the sewage treatment plant as a carbon source. In this step, after the first injected sludge has reacted for 4 hours, the pressure in the reactor reaches 3.0MPa and the temperature reaches 180-250℃. The reactor can continuously inject sludge, and the reacted sludge is discharged through the outlet until the sludge treatment is completed.

[0023] The sludge reduction and resource treatment method provided by the present invention, the hydroxyl radicals generated under alkaline thermal hydrolysis destroy the macromolecular organic nitrogen, the organic nitrogen is decomposed into ammonia nitrogen and free ammonia, and the free ammonia is not easy to remain in the liquid phase under alkaline conditions, and enters the atmosphere as the pressure is released, and the ammonia nitrogen reduction effect in the filtrate is significant, the total nitrogen TN is only 1000mg / L, and the 2-pyridone active molecules produce a co-oxidation reaction with the organic matter in the sludge, and substances such as benzene rings and heterocycles achieve a good ring-opening effect during the thermal hydrolysis process, and insoluble organic matter is hydrolyzed to form soluble small molecule organic acids, and the COD after the reaction is as high as 50000mg / L, and the biodegradability is good. In summary, the preparation of carbon sources by alkaline thermal hydrolysis increases the carbon content of the product while reducing the total nitrogen content, which is an efficient and high-quality carbon source. The treated sludge has the characteristic of small specific resistance. The moisture content is 25-30% after filter pressing, which can be used as raw material for making expanded clay and bricks. The filtrate after reaction and dehydration can be returned to the front end of the sewage treatment plant as a carbon source. The condensed water in the reaction process can also be returned to the front end of the sewage treatment plant as a carbon source. The whole process realizes the recycling of sludge resources.

[0024] Table 2 shows the experimental data of COD and total nitrogen TN of the filtrate.

[0025] Table 2: COD mg / L TN mg / L 49960 2480 53870 2578 58610 2930 50380 2475 51880 2456 During the denitrification process of municipal sewage treatment plants, 1g of N-NO3 - It needs to consume 2.86g of carbon source. In the actual operation process, it is often necessary to ensure that the C / N reaches 4-6. The C / N of the condensed water of sludge thermal hydrolysis is as high as 18-20, and the C / N of the pyrolysis liquid is as high as 20, which can provide additional carbon sources for municipal sewage treatment plants. The sludge reduction and resource treatment method provided by the present invention has a C / N of condensed water of sludge thermal hydrolysis as high as 19 or more, and a C / N of the filtrate as high as 20 or more. Therefore, the C / N of the condensed water of sludge thermal hydrolysis and the C / N of the filtrate obtained by the method for treating sludge of the present invention are up to standard, and can provide a carbon source for municipal sewage treatment plants.

Claims

1. A method for reducing and recycling municipal sludge, based on multiple reaction devices, comprising: The sludge silo, screw pump, reactor, gas heating furnace, heat transfer oil, pressure relief tank, reaction liquid storage tank, plate and frame filter press and desulfurization and denitrification device are characterized in that the steps are as follows: Step 1: The municipal sludge stored in the sludge silo is pumped into the reactor through a screw pump. The initial sludge injection amount is 80% of the reactor volume. Then, gas is injected into the reactor. When the pressure in the reactor reaches 1.0 MPa, the gas injection is stopped. Sodium hydroxide and a catalytic oxidant are added to the reactor. A stirrer is provided in the reactor to stir and mix the sodium hydroxide, the catalytic oxidant and the sludge. Step 2: The heat transfer oil in the reactor jacket is heated by a gas heating furnace. The heat transfer oil transfers the high temperature to the sludge in the reactor, so that the temperature of the sludge in the reactor is maintained in the range of 180-250°C. The sludge changes from a solid phase to a liquid phase after being heated and pressurized in the reactor; Step 3: When the temperature and pressure in the reactor reach the set value, the pressure relief valve of the pressure relief tank automatically opens to discharge the gas, keeping the pressure in the reactor above 3.0MPa. The discharged gas passes through the desulfurization and denitrification device to remove sulfur and nitrogen oxides; Step 4: After 4 hours of reaction, the liquid sludge is discharged into the reaction liquid storage tank, and the liquid sludge is pumped into the plate and frame filter press by a screw pump for dehydration to obtain filtrate and mud cake.

2. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: The gas injected into the reactor is air or oxygen. When the pressure in the reactor reaches 1.0 MPa, the gas injection is stopped and the gas injection valve is closed.

3. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: The dosage of the catalytic oxidant is 1-2‰ of the solid sludge.

4. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: The catalytic oxidant is a 2-pyridone active molecule, and the specific synthesis method of the 2-pyridone active molecule is as follows: 10mmol N-substituted 3-hydroxy-2-pyridone and 20mmol MBH carbonate are dissolved in 200ml dichloromethane, 340mg triethylenediamine is added, and the mixture is allowed to react at room temperature for 24 hours, purified by a cation exchange resin, and eluted by an eluent, wherein the eluent is a mixed solution of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is 10:

1.

5. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: The catalytic oxidant reacts with the sludge to continuously generate gas during the heating process, so that the pressure in the reactor reaches and remains at 3.0 MPa.

6. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: When the pressure in the reactor exceeds 3.0MPa, the pressure is automatically discharged to the pressure relief tank. When the pressure is lower than 3.0MPa, the exhaust is stopped to ensure the high pressure in the reactor.

7. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: After the first injected sludge reacts for 4 hours, the pressure in the reactor reaches 3.0 MPa and the temperature reaches above 180° C. The reactor can continue to inject sludge, and the reacted sludge is discharged through the liquid outlet.

8. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: The sludge in the reactor is continuously injected, and the sludge in the reactor becomes a liquid phase after high temperature and high pressure reaction. When the liquid level reaches the height of the liquid outlet, the pressure at the liquid outlet is reduced by a pressure reducing valve and discharged into the reaction liquid storage tank.

9. A method for reducing and recycling municipal sludge according to claim 1, characterized in that: The moisture content of the filter cake after sludge dehydration is 25%-30%.

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