Sludge treatment method based on sludge reduction and ammonia nitrogen recovery

Abstract

The invention relates to the technical field of sludge treatment, and discloses a sludge treatment method based on sludge reduction and ammonia nitrogen recovery, which comprises the following steps: 1) alkali thermal hydrolysis: adding alkali into sludge to adjust the pH value to 9-11, and carrying out thermal hydrolysis reaction; (2) wet oxidation: heating after reaction and discharging, and carrying out wet oxidation reaction; (3) flash evaporation: carrying out heat recovery after reaction discharging, and carrying out flash evaporation to obtain a sludge mixed solution and flash evaporation steam; (4) dewatering: performing heat recovery on the sludge mixed solution, and then dewatering to obtain a sludge cake and filtrate; and (5) ammonia nitrogen air stripping: carrying out ammonia nitrogen air stripping on the filtrate by adopting steam, wherein the filtrate after air stripping can be reused as a carbon source for sewage treatment. According to the method, the oxidative degradation efficiency of the sludge is improved through coupling of alkali thermal hydrolysis and wet oxidation treatment, ammonia nitrogen recovery and sludge reduction are facilitated, and the filtrate has the characteristics of high COD and low total nitrogen and is more suitable for being used as a carbon source.

Description

Technical Field

[0001] The invention relates to the technical field of sludge treatment, and in particular to a sludge treatment method based on sludge reduction and ammonia nitrogen recovery. Background Art

[0002] With the development of industry and urbanization, my country's sewage treatment volume and sludge production have increased year by year. As a product of sewage treatment, sludge is enriched with 30-50% of organic matter and other pollutants in sewage. It has the dual attributes of "pollution" and "resource". If the sludge is not effectively treated, it will cause serious environmental pollution and waste of resources. According to the data analysis of the China Environmental Statistical Yearbook, the sludge production in 2022 has exceeded 70 million tons.

[0003] At present, high-temperature thermal hydrolysis and alkaline thermal hydrolysis processes have been widely used to treat sludge, but the COD of the sludge cracking liquid obtained by treatment can reach more than 20,000 ppm, and the concentration of Kjeldahl nitrogen (ammonia nitrogen and organic nitrogen) can usually reach thousands of ppm. Sludge can be reduced only by alkaline thermal hydrolysis, but the treatment process requires a high temperature, resulting in relatively high overall energy consumption, and the organic matter and Kjeldahl nitrogen concentrations of the sludge cracking liquid are too high, making it difficult to recycle the complex mixed system.

[0004] The sludge thermal hydrolysis coupled wet oxidation process is to first destroy the sludge floc structure and the cell wall in the sludge under certain temperature and pressure conditions through a thermal hydrolysis process, so that the intracellular substances in the sludge are dissolved, and then use air, pure oxygen or hydrogen peroxide as an oxidant for wet oxidation. A large amount of organic matter is oxidized and degraded, which can achieve better sludge reduction, but the Kjeldahl nitrogen concentration will also be high. For example, the invention patent with publication number CN104355514A discloses a sludge treatment method based on wet oxidation. During the pretreatment process, the sludge material and the hot liquid are fully mixed in the physicochemical pretreatment device. After the preparation of the sludge material is completed, the sludge material is transported into the oxidation reaction process. During the oxidation reaction process, the sludge material and the oxygen at a temperature of 60 to 80°C undergo a wet oxidation reaction in the oxidation reactor, and gas and high-temperature material are formed after the wet oxidation reaction; the high-temperature material enters the flash dehydration process, first enters the flash tank for flash evaporation to generate gas and material, and the generated material is separated into solid and liquid after passing through the heat exchanger, and the separated liquid and solid can be reused for a second time. This invention can achieve a sludge reduction of 70-75% through the process of hot water hydrolysis coupled with wet oxidation, but the wet oxidation process will also promote the conversion of organic nitrogen into ammonia nitrogen, so the Kjeldahl nitrogen concentration of the sludge cracking liquid is too high, which increases the denitrification load of the sewage treatment system and makes it difficult to make good resource utilization. Summary of the invention

[0005] In order to solve the above-mentioned technical problems, the present invention provides a sludge treatment method based on sludge reduction and ammonia nitrogen recovery. By coupling alkaline-thermal hydrolysis with wet oxidation treatment, the oxidative degradation efficiency of the sludge can be improved, and the ammonia resources are recovered only by steam stripping, which improves the stripping efficiency and obtains a high ammonia nitrogen recovery amount and ammonia nitrogen recovery rate. The water content of the sludge cake after the reaction is low, the reduction effect is significant, and the filtrate has the characteristics of higher COD and lower total nitrogen, and is more suitable for use as a carbon source.

[0006] The purpose of the present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a sludge treatment method based on sludge reduction and ammonia nitrogen recovery, comprising the following steps: (1) Alkali thermal hydrolysis: add alkali to the sludge to adjust the pH to 9-11, the alkali is one or more of NaOH, Ca(OH)2 and CaO, and perform thermal hydrolysis reaction; (2) Wet oxidation: After the reaction is completed, the temperature is raised to carry out a wet oxidation reaction; (3) Flash evaporation: After the reaction material is discharged, heat is recovered and then flash evaporation is performed to obtain a sludge mixture and flash steam; (4) Dehydration: The sludge mixed liquid is heat recovered and then dehydrated to obtain sludge cake and filtrate; (5) Ammonia nitrogen stripping: The filtrate is stripped of ammonia nitrogen with steam. The filtrate after stripping can be reused as a carbon source for wastewater treatment.

[0007] The present invention improves the efficiency of thermal hydrolysis and reduces the reaction time by adding alkali during the thermal hydrolysis process, and then performs wet oxidation to oxidatively degrade the organic matter in the sludge, including converting the organic nitrogen in the sludge cracking liquid into ammonia nitrogen and oxidatively degrading the macromolecular organic matter into small-molecule organic acid. The oxidation process also releases a large amount of heat to maintain the temperature of the reactor. The alkali added during the thermal hydrolysis process can maintain the material in an alkaline environment during the wet oxidation process, which is conducive to promoting the conversion of organic nitrogen into ammonia nitrogen. Therefore, the sludge cracking liquid after the alkaline thermal hydrolysis coupled with wet oxidation treatment contains a high concentration of ammonia nitrogen and is still alkaline. The high concentration of ammonia nitrogen and the alkaline environment are conducive to more efficient ammonia nitrogen recovery, and improve the ammonia nitrogen recovery amount and ammonia nitrogen recovery rate.

[0008] Then, the high-temperature steam formed after flash evaporation can be used for ammonia nitrogen stripping to achieve heat recovery. High-temperature steam strips ammonia nitrogen from the sludge mixture after the reaction. The high-temperature reaction conditions can increase the stripping rate and efficiency. No additional reagents are required for pH adjustment, and a large amount of ammonia nitrogen in the sludge filtrate can be recovered. The treated sludge can be dehydrated mechanically to obtain a low-water content sludge cake and a filtrate that can be reused as a carbon source for sewage treatment. The overall process operation energy consumption is low, realizing the resource recovery of sludge ammonia and the reduction and resource utilization of sludge.

[0009] Preferably, in step (1), the moisture content of the sludge is 92-98 wt%.

[0010] Preferably, in step (1), after adjusting the pH to 9 to 11, stirring is performed for 10 to 30 minutes.

[0011] Preferably, in step (1), alkali is added to the sludge to adjust the pH to 10-11.

[0012] Preferably, in step (1), the thermal hydrolysis reaction is carried out under the conditions of 100-170° C. and 4-6 MPa with stirring for 30-60 min, more preferably, under the conditions of 150-170° C. and 4-6 MPa with stirring for 30-60 min.

[0013] Preferably, in step (2), the wet oxidation reaction is carried out at 240-260° C. and 4-6 MPa, with a residence time of 20-40 min.

[0014] Preferably, in step (2), in the wet oxidation reaction, the amount of oxygen introduced is 0.5 to 1.1 times the TCOD of the feed sludge.

[0015] Preferably, in step (3), the material is cooled to 180-210° C. by heat recovery; and the flash evaporation pressure is 0.1-0.5 MPa.

[0016] Preferably, in step (4), the material is cooled to 20-60° C. by heat recovery.

[0017] Preferably, in step (4), the moisture content of the sludge cake is not more than 45wt%.

[0018] Preferably, in step (5), during the ammonia nitrogen stripping process, the gas-liquid ratio G / L of steam to material is 500 to 3000:1.

[0019] Preferably, in step (5), the steam comprises water vapor generated during flash evaporation; and the temperature of the steam is 120-180°C.

[0020] The recovery of ammonia nitrogen in wastewater requires alkaline conditions and the higher the temperature, the better the stripping effect. Using the flash steam after the reaction to strip ammonia from the alkaline high-temperature sludge filtrate can improve the recovery efficiency and save energy and reagents.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Alkaline-thermal hydrolysis coupled with wet oxidation treatment improves the oxidative degradation efficiency of sludge and increases the ammonia nitrogen concentration, which is beneficial for further ammonia nitrogen recovery and sludge reduction; (2) There is no need to add reagents for ammonia nitrogen stripping again. Ammonia resources can be recovered only through steam stripping, which improves the stripping efficiency and ammonia nitrogen recovery and saves operating energy consumption; (3) The filtrate has the characteristics of higher COD and lower total nitrogen, making it more suitable as a carbon source; (4) The moisture content of the sludge cake after the reaction is low, and the reduction effect is significant. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is described below with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0023] The sludge treatment method based on sludge reduction and ammonia nitrogen recovery in the present invention comprises the following steps: (1) Alkali-thermal hydrolysis: Concentrated sludge or dehydrated sludge is sent to a sludge conditioning tank, and water is added to adjust the sludge moisture content to 92-98 wt% to maintain its fluidity. An appropriate amount of alkali (the alkali is one or more of NaOH, Ca(OH)2 and CaO) is added to the sludge, the pH of the system is adjusted to 9-11, and the sludge is stirred for 10-30 minutes. Then, the sludge is continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30-60 minutes at 100-170°C and 4-6 MPa.

[0024] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor by the internal pressure of the reactor into the feed port at the bottom of the wet oxidation reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240-260°C and 4-6MPa. The oxygen introduction rate is 0.5-1.1 times the TCOD of the feed sludge, and the residence time is 20-40 min.

[0025] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, reducing the material temperature to 180-210°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.1-0.5 MPa.

[0026] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 40-60°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of no more than 45wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0027] (5) Ammonia nitrogen stripping: Steam (flash steam and / or external steam) at a temperature of 120-180°C is introduced into the filtrate to strip the ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 500-3000:1. The filtrate after stripping can be reused as a carbon source for sewage treatment, and the stripping gas after stripping is used to absorb ammonia nitrogen.

[0028] In the specific embodiments of the present invention, the same municipal sludge is used for sludge treatment.

[0029] In a specific embodiment of the present invention, the heat recovered in step (3) and step (4) is recycled for preheating the feed at the front end of the process.

[0030] In a specific embodiment of the present invention, sludge dewatering is performed by using a plate and frame dewatering machine, a belt dewatering machine, a centrifugal dewatering machine or other dewatering processes.

[0031] In a specific embodiment of the present invention, ammonia nitrogen absorption is any ammonia absorption process such as water absorption, acid absorption, etc.

[0032] Example 1 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 4.5 MPa.

[0033] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 260°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0034] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0035] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 28.5wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0036] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0037] Example 2 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 150°C and 4.5 MPa.

[0038] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 260°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0039] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0040] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 30.2wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0041] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0042] Example 3 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 4.5 MPa.

[0043] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0044] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0045] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 36.4wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0046] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0047] Example 4 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 230 min at 170°C and 4.5 MPa.

[0048] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 20min.

[0049] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0050] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 42.5wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0051] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0052] Example 5 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 40 min at 170°C and 4.5 MPa.

[0053] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 260°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 40min.

[0054] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0055] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 27.3wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0056] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0057] Example 6 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 6.0 MPa.

[0058] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 260°C and 6.0 MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30 min.

[0059] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0060] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 29.2wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0061] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0062] Example 7 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 9, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 4.5 MPa.

[0063] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 260°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0064] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0065] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 35.3wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0066] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0067] Example 8 (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 4.5 MPa.

[0068] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 260°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0069] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0070] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 30±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 28.5wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0071] (5) Ammonia nitrogen stripping: Steam at a temperature of 120°C (including 120°C flash steam and 120°C raw steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2500:1. The stripping gas after stripping absorbs ammonia nitrogen. The filtrate after stripping can be reused as a carbon source for sewage treatment.

[0072] Comparative Example 1 The difference from Example 3 is that no alkali is added.

[0073] (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt% and the system pH to 7-7.5. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for reaction at 170°C and 4.5 MPa for 30 min.

[0074] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0075] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0076] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 46.1wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0077] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripped filtrate and stripping gas are obtained, and the stripping gas is used to absorb ammonia nitrogen.

[0078] Comparative Example 2 The difference from Example 3 is that a base is added in step (5) instead.

[0079] (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt% and the system pH to 7-7.5. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for reaction at 170°C and 4.5 MPa for 30 min.

[0080] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0081] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0082] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 45.3wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0083] (5) Ammonia nitrogen stripping: Add NaOH to the filtrate to adjust the system pH to 11, and stir for 15 minutes. Then introduce steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material G / L is 2000:1. The stripped filtrate and stripping gas are obtained, and the stripping gas is used to absorb ammonia nitrogen.

[0084] Comparative Example 3 The difference from Example 3 is that the initial pH is 8.

[0085] (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 8, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 4.5 MPa.

[0086] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 30min.

[0087] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0088] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 38.5wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0089] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripped filtrate and stripping gas are obtained, and the stripping gas is used to absorb ammonia nitrogen.

[0090] Comparative Example 4 The difference from Example 3 is that the residence time of the wet oxidation reaction is 120 min.

[0091] (1) Alkaline thermal hydrolysis: Municipal sludge was sent to a sludge conditioning tank, and water was added to adjust the sludge moisture content to 95 wt%. NaOH was added to the sludge to adjust the system pH to 11, and stirred for 15 min. Then, it was continuously pumped to a thermal hydrolysis reactor by a high-pressure diaphragm pump, and heated and stirred for 30 min at 170°C and 4.5 MPa.

[0092] (2) Wet oxidation: The material is discharged from the top of the thermal hydrolysis reactor into the bottom feed port of the wet oxidation reactor through the internal pressure of the reactor. In the wet oxidation reactor, the oxidation reaction is carried out under the reaction conditions of 240°C and 4.5MPa. The oxygen introduction rate is 0.8 times the TCOD of the feed sludge, and the residence time is 120min.

[0093] (3) Flash evaporation: The reaction discharge is passed through a primary heat recovery device to recover the heat therein, and the material temperature is reduced to 200±3°C, and then enters the flash tank for flash evaporation. The flash evaporation pressure is 0.2MPa.

[0094] (4) Dehydration: After the reaction, multi-stage heat recovery is carried out to reduce the material temperature to 55±3°C. The resulting sludge mixture is dehydrated to form a sludge cake with a moisture content of 26.4wt%. The filtrate enters the subsequent ammonia nitrogen stripping reactor.

[0095] (5) Ammonia nitrogen stripping: Steam at a temperature of 130°C (including 120°C flash steam and 150°C live steam) is introduced into the filtrate to strip the filtrate of ammonia nitrogen. The gas-liquid ratio of steam to material (G / L) is 2000:1. The stripped filtrate and stripping gas are obtained, and the stripping gas is used to absorb ammonia nitrogen.

[0096] Table 1 Table 2 Note: Ammonia nitrogen concentration refers to the concentration of free ammonia (NH3) and ammonium ions (NH 4+ ) in the form of nitrogen; total nitrogen concentration refers to the total amount of inorganic and organic nitrogen in various forms in water, including ammonia nitrogen concentration; ammonia nitrogen recovery amount = ammonia nitrogen concentration of the discharge after oxidation - ammonia nitrogen concentration of the discharge after stripping; ammonia nitrogen recovery rate = (ammonia nitrogen concentration of the discharge after oxidation - ammonia nitrogen concentration of the discharge after stripping) / ammonia nitrogen concentration of the discharge after oxidation * 100%.

[0097] As shown in Table 1, the relevant parameter settings of the thermal hydrolysis reaction and the wet oxidation reaction in Examples 1-8 are shown in Table 2, and the recovery rates of ammonia nitrogen stripping in Examples 1-8 and Comparative Examples 1-5, as well as the COD and total nitrogen contents in the final filtrate are shown. The data show that the present invention can improve the oxidative degradation efficiency of the sludge and increase the ammonia nitrogen concentration through alkaline thermal hydrolysis coupled with wet oxidation treatment, which is beneficial to further recovery of ammonia nitrogen and obtain a higher ammonia nitrogen recovery amount and ammonia nitrogen recovery rate. The moisture content of the sludge cake after the reaction is low, and the reduction effect is significant. The filtrate has the characteristics of higher COD and lower total nitrogen, and is more suitable for use as a carbon source.

[0098] In comparative example 1, no alkali is added for thermal hydrolysis, and the oxidative degradation efficiency of the sludge is significantly reduced, and the ammonia nitrogen recovery amount and the ammonia nitrogen recovery rate are also significantly reduced. Although comparative example 2 can improve the ammonia nitrogen stripping efficiency by adding alkali before ammonia nitrogen stripping, the oxidation reaction is not complete, and the cells are not cracked to release more organic nitrogen, the total nitrogen concentration is low, and the ammonia nitrogen recovery amount is also low. The higher filtrate COD is due to the fact that there are more organic matter in the original sludge mixed liquor, and it is not oxidized and degraded into small molecules. The oxidation temperature is reduced, which also leads to a decrease in the oxidative degradation efficiency. The original organic matter is not oxidized and degraded into small molecules, resulting in a higher filtrate COD. Therefore, by controlling the conditions of thermal hydrolysis and oxidation reaction, the cells can be cracked to release more organic matter and improve the efficiency of oxidizing and degrading organic matter into small molecules, thereby improving the ammonia nitrogen recovery amount and the ammonia nitrogen recovery rate.

[0099] Although comparative example 3 carried out alkaline thermal hydrolysis, the oxidation degradation efficiency was low due to the small amount of alkali added and the low initial pH. The pH of the oxidized sludge mixed liquor was also low, which was not conducive to efficient ammonia nitrogen stripping, and the ammonia nitrogen recovery amount and ammonia nitrogen recovery rate were low.

[0100] The wet oxidation time in Comparative Example 4 is too long. Although it is conducive to a more thorough oxidation reaction, it is beneficial to breaking down cells to release more organic matter and oxidizing and degrading organic matter into small molecules, and the ammonia nitrogen concentration of the output is high, the disadvantages are high energy consumption, large volume required for the device, relatively low COD of the output, and less recovered carbon source.

[0101] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A sludge treatment method based on sludge reduction and ammonia nitrogen recovery, characterized in that: The steps include: (1) Alkali thermal hydrolysis: add alkali to the sludge to adjust the pH to 9-11, the alkali is one or more of NaOH, Ca(OH)2 and CaO, and perform thermal hydrolysis reaction; (2) Wet oxidation: After the reaction is completed, the temperature is raised to carry out wet oxidation reaction; (3) Flash evaporation: After the reaction material is discharged, heat is recovered and then flash evaporation is performed to obtain sludge mixed liquid and flash steam; (4) Dehydration: The sludge mixed liquid is heat recovered and then dehydrated to obtain sludge cake and filtrate; (5) Ammonia nitrogen stripping: The filtrate is stripped of ammonia nitrogen with steam. The filtrate after stripping can be reused as a carbon source for wastewater treatment.

2. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 is characterized in that: In step (1), the moisture content of the sludge is 92-98 wt %.

3. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 or 2, characterized in that: In step (1), after adjusting the pH to 9-11, stir for 10-30 minutes.

4. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 is characterized in that: In step (1), the thermal hydrolysis reaction is carried out by stirring at 100-170°C and 4-6MPa for 30-60 minutes.

5. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 is characterized in that: In step (2), the wet oxidation reaction is carried out at 240-260° C. and 4-6 MPa, with a residence time of 20-40 min.

6. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1, 4 or 5, characterized in that: In step (2), in the wet oxidation reaction, the amount of oxygen introduced is 0.5 to 1.1 times the TCOD of the feed sludge.

7. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 is characterized in that: In step (3), the material is cooled to 180-210° C. by heat recovery and then flash evaporated; the flash evaporated pressure is 0.1-0.5 MPa.

8. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 or 7, characterized in that: In step (4), the material is cooled to 20-60°C by heat recovery.

9. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1, characterized in that: In step (5), during the ammonia nitrogen stripping process, the gas-liquid ratio of steam to material G / L is 500~3000:

1.

10. The sludge treatment method based on sludge reduction and ammonia nitrogen recovery according to claim 1 or 9, characterized in that: In step (5), the steam includes water vapor generated during the flash evaporation process; the temperature of the steam is 120-180°C.

Images