Method for nitrogen removal, quality improvement and resource utilization of excess sludge pyrolysis liquid and application

Abstract

The invention discloses a method for nitrogen removal, quality improvement and resource utilization of excess sludge pyrolysis liquid and application, and belongs to the technical field of excess sludge treatment and disposal. The method comprises four aspects of residual sludge pyrolysis, anaerobic ammonia conversion, membrane deamination and resource utilization, the pyrolysis liquid is subjected to high-value conversion through directional organic matter conversion and efficient ammonia nitrogen removal, the pyrolysis liquid can be completely utilized as a high-quality denitrification carbon source, and the utilization rate of the residual sludge pyrolysis liquid is increased. Compared with the existing sludge pyrolysis liquid recycling technology, the method has the advantages of no residual pollutant treatment problem, thorough resource conversion, low application threshold and greater practical application and popularization potential.

Description

Technical Field

[0001] This invention relates to a method and application for denitrification, quality improvement, and resource utilization of waste sludge pyrolysis liquid, belonging to the field of waste sludge treatment and disposal technology. Background Technology

[0002] Thermal hydrolysis of waste sludge is currently the most promising method for sludge treatment. It uses high temperature and pressure to rupture the cell walls of microorganisms, releasing a large amount of organic matter, thereby reducing sludge viscosity, enhancing dewatering properties, and lowering the organic matter content, laying a good foundation for sludge resource utilization. However, the treatment and disposal of the large amount of complex, highly concentrated pyrolysis liquid remaining is a significant challenge in the application of this technology. While the pyrolysis liquid contains a large amount of organic matter with good biodegradability, making it a potential high-quality organic carbon source, its complex composition and high nitrogen content are key factors affecting its quality as an organic carbon source.

[0003] Nitrogen in sludge pyrolysis liquid exists in the form of organic nitrogen and ammonia nitrogen, with organic nitrogen mainly found in substances such as proteins and nucleic acids. Microbial metabolic transformation pathways are a feasible way to achieve nitrogen removal and quality improvement in sludge pyrolysis liquid. On one hand, microbial ammoniation is a feasible pathway for the decomposition and transformation of organic nitrogen. Microbial extracellular hydrolases break down macromolecular organic nitrogen into simple nitrogen-containing compounds such as polypeptides, amino acids, purines, and pyrimidine bases. After entering the cells, these simple nitrogen-containing compounds are converted into inorganic ammonia nitrogen (facilitating removal and recovery) through hydrolysis, reductive deammoniation, and oxidative deammoniation under the action of microbial functional enzymes. Simultaneously, under anaerobic conditions, microorganisms can convert macromolecular organic matter into organic acids (improving carbon source quality) or produce methanogens through digestion. Both of these stages can be regulated by conditions such as pH and temperature. Therefore, by regulating microbial metabolic processes, converting organic nitrogen in the pyrolysis liquid into more easily removed and recovered ammonia nitrogen, and simultaneously converting macromolecular organic matter into organic acids, thereby improving the carbon source effectiveness of the pyrolysis liquid, is a feasible approach. However, there are still two challenges in realizing this technical approach. On the one hand, the high concentration of ammonia nitrogen produced by the degradation of organic nitrogen usually inhibits the anaerobic digestion process and has a toxic effect on microorganisms, which is not conducive to efficient resource conversion. On the other hand, the production of methane during anaerobic digestion leads to the loss of organic matter, thereby limiting the potential of the pyrolysis liquid as a carbon source.

[0004] In summary, the targeted development of denitrification and quality improvement technologies for converting pyrolysis liquids into high-quality organic carbon sources, and the breaking through of key technological bottlenecks in the resource-based treatment of sludge pyrolysis, is of great significance for realizing the resource-based treatment and disposal of excess sludge, and is expected to generate enormous social, environmental and economic benefits. Summary of the Invention

[0005] Technical issues The high levels of organic nitrogen and ammonia nitrogen in waste sludge pyrolysis liquor are key factors limiting its potential as a high-quality carbon source. Currently, existing sludge pyrolysis liquor resource utilization technologies have failed to specifically achieve efficient nitrogen removal and conversion into high-quality carbon sources, severely restricting the treatment, disposal, and resource utilization of sludge pyrolysis liquor, and consequently hindering the achievement of waste sludge reduction and safe treatment and disposal goals.

[0006] Technical content To address the aforementioned issues, this invention proposes a process for denitrification and quality improvement of waste sludge pyrolysis liquid that simultaneously enhances anaerobic ammonia conversion to acid production and membrane deammoniation. By domesticating specific microorganisms and controlling conditions such as pH, temperature, and ammonia nitrogen content, the anaerobic ammoniation / acid production process of the sludge pyrolysis liquid is strengthened. This allows for the conversion of organic nitrogen to ammonia nitrogen while simultaneously converting organic matter into small-molecule acids. Ammonia nitrogen is then removed via a deammoniation membrane, and the free ammonia level within the system is controlled to selectively inhibit methanogenesis, preventing organic matter loss. This achieves highly efficient denitrification and quality improvement of the sludge pyrolysis liquid, which can then be used as a supplementary carbon source in wastewater treatment denitrification processes, saving operating costs.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution: A method for denitrification, upgrading, and resource utilization of waste sludge pyrolysis liquid, the method comprising the following steps: S1. The remaining activated sludge is hydrothermally decomposed at high temperature to obtain sludge pyrolysis liquid; S2. Take anaerobic sludge and screen and acclimatize it to obtain anaerobic ammonia conversion microbial strains; S3. Immobilize and culture anaerobic ammonia-converting microorganisms on a biological carrier to form an anaerobic ammonia-converting biofilm system; S4. The sludge pyrolysis liquid is introduced into the anaerobic ammonia conversion biofilm system for quality improvement treatment, which converts organic nitrogen into ammonia nitrogen and organic matter into small molecule organic acids, while controlling the production of methane, thus obtaining the sludge pyrolysis liquid after quality improvement treatment.

[0008] Furthermore, the remaining sludge in step S1 is taken from the secondary sedimentation tank of the wastewater treatment plant.

[0009] Furthermore, the conditions for hydrothermal decomposition in step S1 are: temperature 120-180℃, time 0.5-3 h, and mud-water ratio 1:0.5~2.

[0010] Furthermore, in step S1, the ammonia nitrogen concentration of the sludge pyrolysis liquid is 1000~2000 mg / L, the COD is 35000~45000 mg / L, the total nitrogen concentration is 4000~5000 mg / L, and the pH is 5~6.

[0011] Furthermore, in step S2, the anaerobic sludge is taken from the anaerobic digestion section of the wastewater treatment plant.

[0012] Furthermore, the screening and domestication process in step S2 is as follows: The anaerobic fermenters were acclimatized by introducing culture medium and controlling the fermenter temperature at 30-35℃, pH at 7-8, and dissolved oxygen at <0.2 mg / L. The sludge age was maintained at 30-50 days by periodic sludge removal. After 120-150 days of screening and acclimatization, anaerobic ammonia conversion microorganisms were obtained.

[0013] Furthermore, the culture medium composition during the screening and domestication process is as follows: organic nitrogen is plant or animal protein with a concentration of 100-5000 mg / L, ammonia nitrogen is ammonium chloride, ammonium sulfate, or ammonium nitrate with a concentration of 500-1000 mg / L, sodium hydrogen phosphate with a concentration of 50-500 mg / L, and sodium bicarbonate with a concentration of 100-1000 mg / L.

[0014] Furthermore, in step S3, the biological carrier is a polyurethane sponge.

[0015] Furthermore, the immobilization process in step S3 is as follows: In a fluidized bed biofilm reactor, the domesticated anaerobic ammonia conversion microorganisms are mixed with a biological carrier for inoculation, with the biological carrier filling rate being 50-80%. One day after inoculation, culture medium is continuously introduced and cultured for 7-9 days to form an anaerobic ammonia conversion biofilm system.

[0016] Furthermore, the composition of the culture medium in the fixed culture is as follows: organic nitrogen is plant or animal protein with a concentration of 100-5000 mg / L, ammonia nitrogen is ammonium chloride, ammonium sulfate, or ammonium nitrate with a concentration of 500-1000 mg / L, sodium hydrogen phosphate with a concentration of 50-500 mg / L, and sodium bicarbonate with a concentration of 100-1000 mg / L.

[0017] Furthermore, in step S4, the total biomass concentration in the anaerobic ammonia conversion biofilm system for quality improvement is 8-30 g / L, the hydraulic retention time of the sludge pyrolysis liquid is 1-3 days, the temperature is 30-35℃, the pH is 7-8, and the dissolved oxygen is <0.2 mg / L.

[0018] Preferably, before step S4, the deammoniation membrane system can be coupled in situ with the anaerobic ammonia conversion biofilm system to control the ammonia nitrogen level of the system at 1000-2000 mg / L.

[0019] Preferably, after the ammonia removal membrane system and the anaerobic ammonia conversion biofilm system are coupled in situ, the mixed liquor of the anaerobic ammonia conversion biofilm system enters the ammonia removal membrane system through an intermediate tank; the system is equipped with an ammonia nitrogen monitoring and control system, which starts the ammonia removal internal circulation when the ammonia nitrogen content exceeds 2000 mg / L, and stops the ammonia removal internal circulation when it is below 1000 mg / L.

[0020] Preferably, the deammoniation membrane used in the deammoniation membrane system is a hollow fiber membrane made of PTFE or PVDF.

[0021] Preferably, the operation process of the ammonia removal membrane system is as follows: The absorbent flows through the tube side, and the feed liquid flows through the shell side. The flow ratio of the feed liquid to the absorbent is 1:2~5. The feed flow rate is controlled at 20~70 ml / min. The residence time of the feed liquid is 10-120 min. The absorbent is an aqueous solution of sulfuric acid (concentration > 0.2 M).

[0022] The present invention provides sludge pyrolysis liquid after quality improvement treatment obtained according to the above method.

[0023] The present invention relates to the application of upgraded sludge pyrolysis liquid in wastewater treatment.

[0024] Furthermore, the wastewater treatment is denitrification.

[0025] Beneficial effects 1. Compared with existing waste sludge pyrolysis liquid resource utilization technologies, the present invention targets the characteristics of the material composition of waste sludge pyrolysis liquid, and through targeted organic matter conversion and efficient ammonia nitrogen removal, enables the pyrolysis liquid to achieve high-value conversion. It can be fully utilized as a high-quality denitrification carbon source. Compared with existing waste sludge pyrolysis liquid resource utilization technologies, there is no problem of residual pollutant treatment (traditional anaerobic fermentation to produce methane still requires further treatment of biogas slurry). The resource conversion is thorough, the application threshold is low, and it has greater potential for practical application and promotion.

[0026] 2. The anaerobic ammonia conversion technology employed in this invention aims to enhance the conversion of organic nitrogen in sludge pyrolysis liquid into ammonia nitrogen, and to convert macromolecular organic matter into small molecule acids, thereby optimizing the carbon source composition, improving its biodegradability and carbon source effectiveness, while controlling and reducing the loss of soluble COD, and maximizing the preservation of resource potential. Compared with existing technologies, this invention achieves higher-quality organic carbon source conversion through precise control of free ammonia via membrane deammoniation, and more targeted regulation of the three conversion pathways of ammonia conversion, organic acid production, and methanogenesis. This opens up a more efficient, lower-carbon, and more economical resource utilization pathway for sludge pyrolysis liquid, and is expected to provide technical support for simultaneously solving the pain points of high costs in sludge disposal and carbon source consumption in wastewater treatment plants.

[0027] 3. The membrane deammoniation coupled anaerobic ammonia conversion biofilm system adopted in this invention dynamically, in real time, and precisely controls ammonia nitrogen within the anaerobic ammonia conversion biofilm system through membrane deammoniation coupling and an automatic ammonia nitrogen monitoring and control system. This ensures that the system is stably maintained along specific ammonia conversion and organic matter conversion pathways, achieving more efficient resource conversion and recovery. Compared with existing ammonia nitrogen removal technologies, it has advantages such as high deammoniation efficiency, low organic acid volatilization loss, no secondary pollution, and the ability to recover ammonia nitrogen resources. It is a very suitable regulation method for anaerobic ammonia conversion systems.

[0028] 4. The denitrification and quality improvement technology for residual sludge pyrolysis liquid proposed in this invention can effectively solve the problem of residual by-products from sludge pyrolysis reduction, open up key technical links in the resource-based treatment of sludge pyrolysis, and form a feasible and effective new approach for the treatment and disposal of residual sludge. Compared with existing residual sludge treatment methods, such as landfill, incineration, and anaerobic fermentation, it will be a lower-carbon, cleaner, and more economical approach for the full resource-based treatment of sludge, with expected significant social, environmental, and economic benefits. Attached Figure Description

[0029] Figure 1 The graph shows the changes in ammonia nitrogen in the pyrolysis liquid entering and leaving the anaerobic ammonia conversion system (top graph) and the changes in total nitrogen (bottom graph).

[0030] Figure 2 The graph shows the changes in ammonia nitrogen / total nitrogen ratio in the pyrolysis solution entering and leaving the anaerobic ammonia conversion system (top figure), the changes in content, and the organic nitrogen conversion rate (bottom figure).

[0031] Figure 3 The graph shows the changes in ammonia nitrogen and COD in the pyrolysis liquid entering and leaving the anaerobic ammonia conversion system (top figure) and the changes in COD removal rate (bottom figure).

[0032] Figure 4 The figure shows the changes in VFAs in the pyrolysis liquid entering and leaving the anaerobic ammonia conversion system (top figure), and the changes in the proportion of VFAs in the effluent (bottom figure).

[0033] Figure 5 The diagram illustrates the enhancement of anaerobic ammonia conversion to acid production efficiency through deammoniation membrane coupling. 5A represents the organic acid production of the anaerobic ammonia conversion reactor, while 5B represents the organic acid production after coupling the deammoniation membrane with the anaerobic digestion reactor. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments. Obviously, the described embodiments are only a part of the implementation of the present invention, and not all of the embodiments. The embodiments of the present invention are all optimal conditions for verifying the feasibility of the present invention, but do not limit the scope of protection of the present invention.

[0035] Detection steps In the examples, ammonia nitrogen, total nitrogen, and COD were all determined using national standard methods; volatile fatty acids were determined using gas chromatography; and the sample was prepared by mixing water and phosphoric acid at a 1:1 ratio.

[0036] Example 1 I. Preparation of raw sludge pyrolysis liquid 1. Raw material selection: The excess sludge is taken from the filter cake (moisture content ~80%) after sludge pressing in the secondary sedimentation tank of the sewage treatment plant.

[0037] 2. Pyrolysis process: The remaining sludge and clean water are mixed at a mass ratio of 1:1 and placed in a high-pressure reactor. The mixture is then pyrolyzed at 150°C for 150 minutes. After pyrolysis, the mixture is filtered to obtain the original sludge pyrolysis liquid.

[0038] 3. Characteristics of raw sludge pyrolysis liquid: initial ammonia nitrogen concentration is approximately 1500 mg / L, COD is approximately 40000 mg / L, total nitrogen concentration is approximately 4500 mg / L, and initial pH is approximately 5.5.

[0039] II. Domestication and Screening of Anaerobic Ammonia Transforming Microorganisms 1. Inoculation sludge: Taken from the anaerobic digestion section of a wastewater treatment plant.

[0040] 2. Acclimation process: Acclimation was carried out in an anaerobic fermenter. The culture medium composition was: protein 5000 mg / L, ammonia nitrogen 500 mg / L, sodium hydrogen phosphate 100 mg / L, and sodium bicarbonate 1000 mg / L. The fermenter temperature was controlled at 35℃ and pH=7.5. The sludge age was maintained at 50 days by regular sludge removal. After 120 days of gradual screening and acclimation, stable anaerobic ammonia conversion microorganisms were obtained.

[0041] III. Construction of Anaerobic Ammonia Conversion Biofilm System 1. Carrier selection: Polyurethane sponge was used as the biofilm carrier, with a size of 2cm*2cm*2cm.

[0042] 2. Biofilm culture: The domesticated anaerobic ammonia conversion microorganisms were mixed and inoculated with polyurethane sponge carrier in a fluidized bed biofilm reactor (effective volume 3L). The filling rate of the polyurethane sponge carrier was 60%. One day after inoculation, the above culture medium was continuously introduced. After 7 days of continuous culture, the biofilm matured (the system stably produced ammonia conversion effect as the judgment standard), and an anaerobic ammonia conversion biofilm system was formed (the total biomass was measured to be 10 g / L).

[0043] IV. Anaerobic ammonia conversion, denitrification, and quality improvement treatment of sludge pyrolysis liquid 1. Feed preparation: Take the original sludge pyrolysis liquid, adjust its pH to 8, take samples to test and record the concentrations of ammonia nitrogen, total nitrogen, COD and VFAs in the influent.

[0044] 2. Reaction Operation: The original sludge pyrolysis liquid after pH adjustment is introduced into the above-mentioned anaerobic ammonia conversion biofilm system (effective volume 3L), and the hydraulic retention time is controlled at 3 days. The material is homogenized by mechanical stirring in the reactor, and a baffle is installed between the inlet and outlet to keep the internal temperature stable at 35℃.

[0045] 3. pH control: Add NaOH to the reactor daily to maintain the pH of the reaction system within the range of 7.0~7.8.

[0046] 4. Product acquisition: After the reactor has been running for 3 days, samples are taken from the outlet to test the concentrations of ammonia nitrogen, total nitrogen, COD and VFAs in the effluent, and the upgraded sludge pyrolysis liquid is obtained.

[0047] 5. System stability verification: The above anaerobic ammonia conversion process was continuously run for multiple cycles under the same conditions, with each cycle running stably for about 3 days.

[0048] V. Evaluation of the Resource Utilization of Upgraded Pyrolysis Liquid and the Effectiveness of Carbon Sources 1. Resource utilization: Mix the upgraded sludge pyrolysis liquid with the influent to be treated (total nitrogen content 50mg / L) and add it directly to the denitrification filter; control the COD concentration in the filter to be 250~350mg / L, pH to be 7.8~8.5, and hydraulic retention time to be 6h to carry out the denitrification reaction.

[0049] 2. Control Experiment: Using untreated sludge pyrolysis liquid and sodium acetate as control carbon sources, denitrification experiments were conducted under the same denitrification filter operating conditions to compare and evaluate the carbon source effectiveness of the three sources. Relevant results are shown in Table 1 below. Figures 1-4 .

[0050] Depend on Figures 1-4 As can be seen, the anaerobic ammonia conversion treatment method for waste sludge pyrolysis liquid proposed in this invention still exhibits good ammonia conversion efficiency under high concentrations of ammonia nitrogen and COD. Under neutral pH conditions, the ammonia nitrogen growth rate exceeds 80%, the total nitrogen concentration remains basically unchanged, and the ammonia nitrogen / total nitrogen ratio can stably increase to 0.65 or higher, with an organic nitrogen conversion rate exceeding 40%. Simultaneously, COD in the pyrolysis liquid is also well retained, with the COD removal rate generally maintained below 10%, without significant loss. Analysis of effluent VFAs shows that macromolecular organic matter in the pyrolysis liquid is converted into VFAs, with the effluent VFA concentration increasing 6-9 times compared to the influent, and the composition becoming more diverse, containing six types of VFAs, primarily acetic acid and propionic acid. Therefore, the anaerobic ammonia conversion method for waste sludge pyrolysis liquid proposed in this invention can ensure efficient conversion of organic nitrogen to ammonia nitrogen while inhibiting the activity of methanogenic bacteria and promoting the conversion of organic matter into VFAs. This lays a solid foundation for subsequent use as an organic carbon source for denitrification or for further resource utilization of the pyrolysis liquid.

[0051] Table 1 Evaluation of the effectiveness of carbon source in sludge pyrolysis liquid after anaerobic ammonia conversion treatment

[0052] As shown in Table 1, when the original sludge pyrolysis liquid is used as a denitrification carbon source, its denitrification efficiency is 60-70%, indicating that a considerable portion of the organic matter in the pyrolysis liquid cannot be effectively utilized. However, after the pyrolysis liquid is treated with anaerobic ammonia conversion, its denitrification efficiency as a denitrification carbon source increases to over 80%, indicating that anaerobic ammonia conversion treatment can significantly improve the carbon source availability of the pyrolysis liquid and greatly increase its resource utilization potential. This is because anaerobic ammonia conversion microorganisms convert organic nitrogen and macromolecular organic matter into small molecule organic acids that are more easily utilized by denitrifying microorganisms through metabolic transformation, optimizing the organic matter composition and quality of the pyrolysis liquid, and significantly improving the carbon source availability of the pyrolysis liquid. This lays the foundation for realizing the resource utilization pathway of using sludge pyrolysis liquid in situ as a denitrification carbon source.

[0053] Example 2 I. Preparation of raw sludge pyrolysis liquid 1. Preparation method: The original sludge pyrolysis liquid was obtained using the same preparation process as in Example 1.

[0054] 2. Characteristics of raw sludge pyrolysis liquid: initial ammonia nitrogen concentration is approximately 1500 mg / L, COD is approximately 40000 mg / L, total nitrogen concentration is approximately 4500 mg / L, and initial pH is approximately 5.5.

[0055] II. Construction of Anaerobic Ammonia Conversion Biofilm System 1. Domestication and screening of microorganisms: The same domestication and screening method as in Example 1 was used.

[0056] 2. Construction of anaerobic ammonia conversion biofilm system: The same biofilm culture method as in Example 1 was used.

[0057] III. Enhanced Anaerobic Ammonium Conversion via Membrane Deamination 1. Feed preparation: Take the original sludge pyrolysis liquid, adjust its pH to 8, take samples to test and record the original ammonia nitrogen, total nitrogen and COD concentrations of the influent.

[0058] 2. Start-up of the anaerobic ammonia conversion reactor: The adjusted raw sludge pyrolysis liquid is introduced into the anaerobic ammonia conversion biofilm system (effective volume 3L), and the hydraulic retention time is controlled at 3 days; the material is homogenized by mechanical stirring inside the reactor, and a baffle is installed between the inlet and outlet to keep the internal temperature stable at 35℃.

[0059] 3. pH control: Add NaOH to the anaerobic ammonia conversion biofilm reactor daily to maintain the pH of the reaction system within the range of 7.0~7.8.

[0060] 4. Interconnected operation of the membrane ammonia removal system: The anaerobic ammonia conversion biofilm system is connected to the membrane ammonia removal unit via an intermediate water tank (effective volume 1L) through a flow measurement method. The specific operation is as follows: (1) The mixed liquor in the anaerobic ammonia conversion biofilm system first enters the intermediate water tank, and after adjusting the pH to 9, it is introduced into the membrane deammoniation device for deammoniation treatment; (2) An ammonia nitrogen monitoring and control system is installed in the reactor. When the ammonia nitrogen content in the system exceeds 2000 mg / L, the internal circulation for ammonia removal is started; when the ammonia nitrogen content is below 1000 mg / L, the internal circulation is stopped. (3) The feed mixture flows through the shell side, and 0.2M sulfuric acid is used as the absorbent in the tube side; the flow ratio of the feed liquid to the absorbent is set to 1:4, and the feed flow rate is controlled at 50ml / min.

[0061] 5. Continuously monitor the organic acid content in the anaerobic ammonia conversion biofilm system and track changes in acid production efficiency.

[0062] IV. Control Group Setup 1. Set up a control group, which only performs the operations in steps 1 to 3 above, i.e. the operations in Example 1, without simultaneous membrane deammoniation treatment; at the same time, the organic acid production in the anaerobic ammonia conversion biofilm system of the control group is measured daily, and the acid production efficiency is compared with that of the experimental group (including membrane deammoniation).

[0063] 2. A control group was set up, and the ammonia nitrogen level in the system was adjusted to <500 mg / L and 2000-3000 mg / L respectively through membrane deammoniation. At the same time, the organic acid production in the anaerobic ammonia conversion biofilm system of the control group was measured daily, and the acid production efficiency was compared with that of the experimental group (including membrane deammoniation).

[0064] V. Resource Utilization and Effect Evaluation The upgraded pyrolysis solutions from the experimental group (treated with enhanced anaerobic ammonia conversion via membrane deamination) and the control group (treated without membrane deamination) were used in denitrification filters. The carbon source availability of the two pyrolysis solutions was evaluated by comparing their denitrification efficiency. The results are shown in Table 2 and [Table data missing]. Figure 5 .

[0065] Figure 5 The diagram illustrates the enhancement of acid production efficiency in the anaerobic ammonia conversion reactor by deammoniation membrane coupling. It is evident that after anaerobic ammonia conversion, a large amount of organic matter in the sludge pyrolysis liquid can be converted into organic acids, with acetic acid being the main product. However, after the third day of reaction, the acid production in the reactor reaches equilibrium, with a cumulative acid production of approximately 6800 mg / L. Further extending the reaction time does not significantly increase acid production. This is because, as anaerobic digestion progresses, a large amount of ammonia nitrogen accumulates in the reactor (e.g., ...). Figure 1As shown in the figure, the anaerobic ammonia conversion process was significantly inhibited, resulting in a low acid production rate. In contrast, after coupling the deammoniation membrane with the anaerobic digester, the acid production of the reactor continued to increase, reaching more than 16,300 mg / L on day 6, which was more than twice that of the control group. This is because the coupling of the deammoniation membrane can continuously and synchronously absorb and remove ammonia nitrogen in the reactor, thereby achieving dynamic and precise control of the ammonia nitrogen level in the reactor. This prevents the ammonia conversion and acid production process from being inhibited, while still maintaining the inhibition of the methanogenesis process. This achieves targeted regulation of acid production and greatly improves the system's acid production efficiency.

[0066] Table 2 Evaluation of the effectiveness of membrane deammoniation in improving the carbon source of anaerobic ammonia conversion pyrolysis liquid

[0067] As shown in Table 2, the denitrification efficiency of the original sludge pyrolysis liquor as a carbon source for denitrification was only 60.95%. However, after the pyrolysis liquor underwent anaerobic ammonia conversion treatment, its denitrification efficiency as a carbon source for denitrification increased to 84.01%, indicating that anaerobic ammonia conversion treatment significantly improved the carbon source effectiveness of the pyrolysis liquor by converting organic nitrogen into small molecule organic acids. When the pyrolysis liquor treated by membrane deammoniation coupled with anaerobic ammonia conversion process was used as a carbon source for denitrification, its denitrification efficiency reached 92.89%, which can replace more than 90% of sodium acetate with the same COD equivalent. Compared with the original sludge pyrolysis liquor, the denitrification rate increased by more than 30%, indicating that the coupling of membrane deammoniation further improved the carbon source effectiveness of the pyrolysis liquor. This is mainly related to its ability to dynamically and accurately control the ammonia nitrogen level in the reactor and reasonably alleviate the inhibitory effect of ammonia nitrogen. In summary, through the treatment of waste sludge pyrolysis liquid coupled with membrane denitrification and anaerobic ammonia conversion, significant denitrification and quality improvement were achieved. It can be effectively used as a carbon source for the denitrification process, and can even replace the supplementary carbon source for the denitrification process, which has very high practical value.

[0068] Table 3. Effects of different ammonia nitrogen levels on acid production efficiency of anammox membrane bioreactors.

[0069] Table 3 shows the effects of different ammonia nitrogen levels on the quality improvement efficiency of anammonia conversion sludge pyrolysis liquid by adjusting the ammonia nitrogen level in the anammonia conversion biofilm reactor through membrane deammoniation operation. The results showed that under high ammonia nitrogen levels (2000-3000 mg / L), both organic acid production and methanogenesis in the anammox biofilm system were low. This was due to the severe inhibition of acid-producing and methanogenic bacteria by ammonia nitrogen. However, by coupling membrane deammoniation to control the ammonia nitrogen level in the anammox biofilm system to a low level (<500 mg / L), the methanogenesis efficiency of the system was significantly improved, reaching more than 6 times that of the group without membrane deammoniation control. This was due to the contact effect of ammonia nitrogen inhibition. However, the highly efficient methanogenesis pathway resulted in a significant reduction in the cumulative organic acid content in the pyrolysis solution, reaching only 5510 mg / L. From the perspective of converting the pyrolysis solution into a high-quality carbon source, excessive methanogenesis would lead to the loss of organic acids, which is not conducive to obtaining high carbon source utilization efficiency. Under the condition of controlling the ammonia nitrogen level at 1000-2000 mg / L, the acid production of the anammox biofilm system reached its maximum value of 16300 mg / L. At this ammonia nitrogen level (mg / L), methanogenesis remains relatively low. This is because at this level, acid-producing bacteria are not significantly inhibited, while methanogenic bacteria are significantly inhibited. This results in the efficient conversion of organic matter in the sludge pyrolysis liquid into a high-quality carbon source, without excessive loss due to methanogenesis. Therefore, controlling the ammonia nitrogen level under appropriate conditions is crucial from the perspective of utilizing the pyrolysis liquid as a high-quality carbon source.

[0070] Although the present invention discloses only the embodiments for verifying feasibility as described above, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for denitrification, quality improvement, and resource utilization of waste sludge pyrolysis liquid, characterized in that, The method includes the following steps: S1. The remaining activated sludge is hydrothermally decomposed at high temperature to obtain sludge pyrolysis liquid; S2. Take anaerobic sludge from the anaerobic digestion section of the wastewater treatment plant and screen and acclimate it to obtain anaerobic ammonia conversion microbial strains. The screening and acclimatization process is as follows: acclimatize in an anaerobic fermenter, introduce culture medium and control the fermenter temperature at 30-35℃, pH=7-8, and dissolved oxygen <0.2 mg / L. Maintain the sludge age at 30-50 days by periodic sludge discharge. After 120-150 days of screening and acclimatization, obtain anaerobic ammonia conversion microorganisms. S3. Immobilize and culture anaerobic ammonia-converting microorganisms on a biological carrier to form an anaerobic ammonia-converting biofilm system; The fixed-bed culture process is as follows: The domesticated anaerobic ammonia-converting microorganisms are mixed and inoculated with a biological carrier in a fluidized bed biofilm reactor, with the biological carrier filling rate being 50-80%. One day after inoculation, culture medium is continuously introduced, and culture continues for 7-9 days to form an anaerobic ammonia-converting biofilm system. S4. The sludge pyrolysis liquid is introduced into the anaerobic ammonia conversion biofilm system for upgrading treatment, thus obtaining the upgraded sludge pyrolysis liquid. During the upgrading treatment, the ammonia nitrogen level in the system is controlled by coupling the ammonia removal membrane system and maintained at 1000-2000 mg / L. The total biomass concentration in the anaerobic ammonia conversion biofilm system is 8-30 g / L. The hydraulic retention time of the sludge pyrolysis liquid is 1-3 days, the temperature is 30-35℃, the pH is 7-8, and the dissolved oxygen is <0.2 mg / L.

2. The method according to claim 1, characterized in that, The remaining sludge in step S1 is taken from the secondary sedimentation tank of the sewage treatment plant.

3. The method according to claim 1, characterized in that, In step S1, the ammonia nitrogen concentration of the sludge pyrolysis liquid is 1000~2000 mg / L, the COD is 35000~45000 mg / L, the total nitrogen concentration is 4000~5000 mg / L, and the pH is 5~6.

4. The method according to claim 1, characterized in that, The culture medium used in steps S2 and S3 consists of the following components: organic nitrogen is plant or animal protein at a concentration of 100-5000 mg / L; ammonia nitrogen is ammonium chloride, ammonium sulfate, or ammonium nitrate at a concentration of 500-1000 mg / L; sodium hydrogen phosphate at a concentration of 50-500 mg / L; and sodium bicarbonate at a concentration of 100-1000 mg / L.

5. The method according to claim 1, characterized in that, In step S3, the biological carrier is a polyurethane sponge.

6. The method according to claim 1, characterized in that, After the ammonia removal membrane system and the anaerobic ammonia conversion biofilm system are coupled in situ, the mixed liquor of the anaerobic ammonia conversion biofilm system enters the ammonia removal membrane system through the intermediate tank. The system is equipped with an ammonia nitrogen monitoring and control system. When the ammonia nitrogen content exceeds 2000 mg / L, the ammonia removal internal circulation is activated, and when it is below 1000 mg / L, the ammonia removal internal circulation is stopped.

7. The method according to claim 1, characterized in that, The deammonia removal membrane system uses a hollow fiber membrane made of PTFE or PVDF.

8. The method according to claim 1, characterized in that, The operation process of the ammonia removal membrane system is as follows: The absorbent flows through the tube side, and the feed liquid flows through the shell side. The flow ratio of the feed liquid to the absorbent is 1:2~5. The feed flow rate is controlled at 20~70 ml / min. The residence time of the feed liquid is 10-120 min. The absorbent is an aqueous solution of sulfuric acid.

9. The upgraded sludge pyrolysis liquid obtained by the method according to any one of claims 1 to 8.

10. The application of the upgraded sludge pyrolysis liquid as described in claim 9 in wastewater treatment, characterized in that, The application involves using sludge pyrolysis liquid as a carbon source for denitrification.

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