A method for reducing and recycling municipal sludge

Abstract

The present invention discloses a method for reducing and recycling municipal sludge. The sludge is pumped into a reactor via a screw pump, sodium hydroxide and a catalytic oxidant are added, gas is injected to increase pressure, and heat is applied using thermal oil. The sludge is heated, pressurized, and stirred until the set temperature and pressure are maintained. During the catalytic oxidation process, nitrogen-containing organic matter produces ammonia, which then forms small molecular compound gases and is discharged. The sludge transforms from a solid phase into a liquid phase and is pumped into a plate-and-frame filter press via a screw pump to produce a filtrate and filter cake. After dewatering in the plate-and-frame filter press, the filtrate has a COD exceeding 50,000 mg / L and a total nitrogen content of approximately 1,000 mg / L, making it suitable for use as a low-quality carbon source. Due to its low organic content, the dewatered sludge can be used in brickmaking plants to produce ceramic pellets. This invention provides a method for reducing and recycling sludge. The entire process is rational and effective, with low system energy consumption, shortened reaction time, and reduced operating costs.

Description

Technical Field

[0001] The present 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] Currently, domestic sludge disposal primarily relies on landfilling and incineration. Landfilling not only occupies significant land resources and farmland, but also damages the environment, polluting groundwater and surface water, and directly endangering human health. Nitrogen and phosphorus in sludge are washed into rivers by rainwater, contributing to eutrophication. Sludge incineration is the most expensive of all sludge disposal methods, both in terms of investment and operating costs. Due to the low calorific value of sludge, power plants require the addition of natural gas for complete combustion, and sludge incineration also creates flue gas treatment issues.

[0003] Making bricks from sewage sludge is a technology that utilizes the inorganic components of sewage sludge, turning waste into treasure. This technology aligns with the strategic principle of sustainable development and contributes to the establishment of a circular economy. It eliminates potential environmental hazards from sewage sludge, reduces operating costs of sewage treatment plants, and reduces clay mining, alleviating the conflict between the brick and tile industry and agriculture over land. However, the high organic matter and moisture content in sewage sludge has hindered the development of the sewage sludge brick industry.

[0004] Due to the low C / N ratio in my country's sewage treatment plants, large amounts of carbon sources are often consumed to improve treatment efficiency. Thermal hydrolysis of sludge produces a high C / N ratio in the hydrolyzate, with a COD equivalent of 50,000 to 120,000. Furthermore, the organic matter in the hydrolyzate is primarily present as organic acids, which have good biodegradability and are easily utilized by microorganisms in the 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 response to 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: providing a sludge reduction and resource utilization treatment method based on multiple reaction equipment, including: a sludge silo, a screw pump, a reactor, a gas heating furnace, a thermal oil, a pressure relief tank, a reaction liquid storage tank, a plate and frame filter press and a desulfurization and denitrification device, comprising the following steps:

[0007] Step 1: The municipal sludge stored in the sludge silo is pumped into the reactor through a screw pump. The initial sludge injection volume is 80% of the reactor volume. Gas is then 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, catalytic oxidant and sludge.

[0008] Step 2: The heat transfer oil in the reactor jacket is heated by a gas-fired heating furnace. The heat transfer oil transfers the high temperature to the sludge in the reactor, maintaining the sludge temperature in the reactor within 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.

[0009] 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, maintaining the pressure in the reactor above 3.0 MPa. The discharged gas passes through the desulfurization and denitrification device to remove sulfur and nitrogen oxides;

[0010] 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.

[0011] 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.

[0012] In the above-mentioned treatment method based on sludge reduction and resource utilization, the amount of the catalytic oxidant added to the reactor in step 1 is 1-2‰ of the weight of the solid sludge.

[0013] In the above-mentioned treatment method based on sludge reduction and resource utilization, the catalytic oxidant is a 2-pyridone active molecule. The specific synthesis method of the 2-pyridone active molecule is as follows: take 10 mmolN-substituted 3-hydroxy-2-pyridone and 20 mmolMBH carbonate and dissolve them in 200 ml of dichloromethane, add 340 mg of triethylenediamine, let it react 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.

[0014] In the above-mentioned treatment method based on sludge reduction and resource utilization, the catalytic oxidant reacts with the sludge during the heating process to continuously generate gas, so that the pressure in the reactor reaches and is maintained at 3.0 MPa.

[0015] In the above-mentioned treatment method based on sludge reduction and resource utilization, when the pressure in the reactor exceeds 3.0 MPa, the pressure is automatically discharged to the pressure relief tank. When the pressure is lower than 3.0 MPa, the exhaust is stopped to ensure the high pressure in the reactor.

[0016] 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.

[0017] 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 of the liquid outlet is reduced by the pressure reducing valve and discharged into the reaction liquid storage tank.

[0018] In the above-mentioned treatment method based on sludge reduction and resource utilization, the moisture content of the filter cake after dehydration of the sludge in the reactor is 25-30%.

[0019] The following beneficial effects can be achieved 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) The reaction is more complete after the addition of a catalytic oxidant, and both 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, which can be used as a raw material for making ceramic pellets and bricks. It 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

[0020] Figure 1 The present invention is a flowchart of a sludge reduction and resource utilization treatment method. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] 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 thermal 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:

[0023] Step 1: Municipal sludge with a moisture content of ≤85% stored in a sludge silo is pumped into the reactor via a screw pump. The initial sludge injection volume is 80% of the reactor volume. Gas, either air or oxygen, is then injected into the reactor. When the pressure in the reactor reaches 1.0 MPa, gas injection is stopped and the gas injection valve is closed. Sodium hydroxide and a catalytic oxidant, 2-pyridone, are added to the reactor. The catalytic oxidant is a 2-pyridone active molecule. The specific synthesis method for the 2-pyridone active molecule is as follows: 10 mmol of N-substituted 3-hydroxy-2-pyridone and 20 mmol of MBH carbonate are dissolved in 200 ml of dichloromethane. 340 mg of triethylenediamine is added and the mixture is allowed to react at room temperature for 24 hours. The mixture is then purified using a cation exchange resin and eluted with a mixture of petroleum ether and ethyl acetate in a volume ratio of 10:1. The catalytic oxidant dosage is approximately 1-2‰ of the solid sludge volume, and the sodium hydroxide dosage is 5% of the solid sludge volume. A stirrer is installed within the reactor to mix the sodium hydroxide, catalytic oxidant, and sludge. The addition of sodium hydroxide aims to disrupt the bacterial flocs and organic particles in the sludge through its strong alkaline environment, while simultaneously inactivating the cells and hydrolyzing and breaking the cell walls (membranes), thereby releasing proteins and intracellular substances. This treatment method further degrades proteins in the sludge into low-molecular-weight substances in the liquid phase, thereby achieving cell wall breakdown and cell lysis. The addition of the co-oxidation catalyst, 2-pyridone, catalyzes the thermal hydrolysis of the sludge, promoting the separation of organic and inorganic matter and sludge reduction. This provides a carbon source for wastewater treatment and raw materials for sludge brick making, promoting the replacement of sludge thermal hydrolysis processes.

[0024] Step 2: The heat transfer oil in the reactor jacket is heated by a gas-fired 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 changes from a solid phase to a liquid phase.

[0025] Based on steps 1 and 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, ammonia forms small molecular compounds NO and NO2 gas. The continuously generated gas further increases the pressure in the reactor, and finally the pressure in the reactor reaches 3.0 MPa.

[0026] 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, maintaining the pressure range 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.

[0027] Step 4: After 4 hours of high-temperature, high-pressure reaction, when the liquid level reaches the outlet, the outlet pressure is reduced via a pressure-reducing valve installed at the outlet, and the liquid sludge is discharged into the reaction liquid storage tank. A screw pump then pumps the liquid sludge into a plate-and-frame filter press for dehydration, producing a filtrate and a mud cake. After dehydration, the filter cake has a moisture content of 25%-30%. The dehydrated mud cake can be used as a raw material for ceramic pellets and bricks, and the dehydrated filtrate can be returned to the front end of the sewage treatment plant for use as a carbon source. In this step, after the initial injection of sludge has reacted for 4 hours, the pressure in the reactor reaches 3.0 MPa and the temperature reaches 180-250°C. Sludge can be continuously injected into the reactor, and the reacted sludge is discharged through the outlet until the sludge treatment is complete.

[0028] The sludge reduction and resource utilization treatment method provided by the present invention, the hydroxyl radicals generated under alkaline thermal hydrolysis destroy the macromolecular organic nitrogen, and the organic nitrogen is decomposed into ammonia nitrogen and free ammonia. At the same time, free ammonia is not easy to remain in the liquid phase under alkaline conditions. As the pressure is released into the atmosphere, the ammonia nitrogen reduction effect in the filtrate is significant, and the total nitrogen TN is only 1000mg / L. At the same time, 2-pyridone active molecules produce a co-oxidation reaction with organic matter in the sludge, and substances such as benzene rings and heterocycles achieve a good ring-opening effect during the thermal hydrolysis process. Soluble small molecule organic acids are formed after hydrolysis of insoluble organic matter. 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 low specific resistance. After filtration, the moisture content is 25-30%, 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.

[0029] Table 2 shows the experimental data of COD and total nitrogen TN of the filtrate.

[0030] Table 2:

[0031] COD mg / L TN mg / L 49960 2480 53870 2578 58610 2930 50380 2475 51880 2456

[0032] During the denitrification process of municipal sewage treatment plants, 1g of N-NO3 - 2.86g of carbon source is consumed. In actual operation, it is often necessary to ensure that the C / N ratio reaches 4-6. The C / N ratio of the sludge thermal hydrolysis condensate is as high as 18-20, and the C / N ratio of the pyrolysis liquid is as high as 20, both of which can provide additional carbon sources for municipal sewage treatment plants. The sludge reduction and resource utilization treatment method provided by the present invention achieves a C / N ratio of 19 or more for the sludge thermal hydrolysis condensate, and a C / N ratio of 20 or more for the filtrate. Therefore, the C / N ratios of the sludge thermal hydrolysis condensate and filtrate obtained by the sludge treatment method of the present invention meet the standards, 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 equipment, comprising: The sludge silo, screw pump, reactor, gas heating furnace, thermal oil, pressure relief tank, reaction liquid storage tank, plate and frame filter press and desulfurization and denitrification device are characterized by comprising 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. Gas is then 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. The catalytic oxidant is a 2-pyridone active molecule. The specific synthesis method of the 2-pyridone active molecule is as follows: 10 mmol N-substituted 3-hydroxy-2-pyridone and 20 mmol MBH carbonate are dissolved in 200 ml dichloromethane, 340 mg triethylenediamine is added, and the mixture is allowed to react at room temperature for 24 hours. A cation exchange resin is used for purification, and the mixture is eluted 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. Step 2: The heat transfer oil in the reactor jacket is heated by a gas-fired heating furnace. The heat transfer oil transfers the high temperature to the sludge in the reactor, maintaining the sludge temperature in the reactor within 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, maintaining the pressure in the reactor above 3.0 MPa. 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. The 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 phase sludge.

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

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

6. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: After the first injection of 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.

7. The 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 liquid after high temperature and high pressure reaction. When the liquid level reaches the height of the liquid outlet, the pressure of the liquid outlet is reduced by the pressure reducing valve and discharged into the reaction liquid storage tank.

8. The 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%.

Images