A method for deep denitrification and phosphorus removal based on polylactic acid and magnetite

Abstract

The application discloses a method for deep denitrification and phosphorus removal based on polylactic acid and pyrrhotite cooperation, which comprises the following steps: S1, activated sludge preparation; S2, activated sludge inoculation; S3, reaction component activation; S4, wastewater subsection treatment. In the method, polylactic acid is used as a heterotrophic denitrification solid carbon source, and pyrrhotite is used as an autotrophic denitrification electron donor for denitrification and phosphorus removal, a reaction component is built, and the activation method of the reaction component and the step parameters are defined in detail, so that the best treatment condition is obtained, and the polylactic acid-pyrrhotite composite filler is used for cooperation and denitrification, thereby realizing efficient wastewater denitrification and phosphorus removal.

Description

Technical Field

[0001] This invention relates to the field of water environment management technology, specifically to a method for deep denitrification and phosphorus removal based on polylactic acid synergistic with pyrrhotite denitrification. Background Technology

[0002] With the acceleration of national industrialization and urbanization, and the continuous development of the social economy, population density is constantly increasing, and urban domestic water consumption is growing rapidly. This generates a large amount of urban wastewater, mainly effluent from urban sewage treatment plants, which is gradually aggravating water pollution. The main pollutants in water bodies are nitrogen and phosphorus. Excessive nitrogen and phosphorus in the aquatic environment will cause eutrophication.

[0003] Simultaneous nitrogen and phosphorus removal is a technology developed for the purpose of high-efficiency simultaneous nitrogen and phosphorus removal. This process exhibits good nitrogen and phosphorus removal effects. However, with increasingly stringent requirements for water quality treatment and numerous problems encountered during application, the application of simple nitrogen or phosphorus removal technologies has become somewhat limited. Therefore, it is necessary to find new process solutions and improve process technologies to remove nitrogen and phosphorus simultaneously in a single treatment system, leading to the development of a series of simultaneous nitrogen and phosphorus removal technologies. Currently, the main nitrogen and phosphorus removal processes in the field of water environment treatment technology include: anaerobic-anoxic-aerobic (A2O) processes; the Bardenpho process; the UCT process; the Phoredox process; and the SBR process, etc.

[0004] Denitrification, with its low cost and high efficiency, has become the mainstream nitrogen removal method in water treatment. Based on the type of electron donor, denitrification can be divided into heterotrophic denitrification, which uses organic matter as an electron donor, and autotrophic denitrification, which does not require an organic carbon source. However, low-pollution water has a low content of electron donors such as organic matter, which affects the denitrification rate, increases the difficulty of nitrogen removal, and weakens the phosphorus removal capacity of denitrification. Therefore, it is essential to combine autotrophic and heterotrophic denitrification for synergistic nitrogen removal and to improve phosphorus removal efficiency.

[0005] Currently, research on polylactic acid (PLA) as a solid carbon source for denitrification mainly focuses on engineering applications. Fan et al. studied the sludge cultivation time (35 days) and suitable temperature (30–40℃) for PLA denitrification; Peng Shulin et al. optimized the suitable influent pH range for PLA denitrification systems to 7.8–10.1; Takahashi et al. assessed the denitrification effect of PLA with different molecular weights from the perspective of PLA hydrolysis products, indicating that lower molecular weight PLA has a better denitrification effect. However, the denitrification pathways and corresponding mechanisms of PLA with different molecular weights are still unclear. This is the theoretical basis for the efficient regulation of heterotrophic microbial denitrification processes, and no in-depth research has been conducted on this topic yet. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for deep denitrification and phosphorus removal based on polylactic acid synergistic with pyrrhotite denitrification.

[0007] The technical solution of this invention is:

[0008] A method for deep nitrogen and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite includes the following steps:

[0009] S1. Preparation of activated sludge: By weight, take 20-30 parts of heterotrophic denitrifying granular sludge and place it in a reaction vessel. Add 80-120 parts of enrichment culture medium. The mass concentration of Na2S2O3·5H2O in the enrichment culture medium is 3-6 g / L, the mass concentration of KH2PO4 is 1-3 g / L, the mass concentration of NaNO3 is 1-2 g / L, and the mass concentration of the remaining components does not exceed 3 g / L. Purge nitrogen into the reaction vessel for 3-5 minutes to purge the air. Seal and place it at room temperature for static culture for 3-4 days. After that, remove the enrichment culture medium to complete one enrichment. Repeat the enrichment process 4-5 times to obtain enriched sludge. Mix the enriched sludge with 90-100 parts of anaerobic granular sludge and stir evenly to obtain activated sludge.

[0010] S2. Activated sludge inoculation: By weight, take 20-25 parts of polylactic acid powder and 10-15 parts of pyrrhotite powder and place them in the activated sludge obtained in step S1, and stir evenly to complete the activated sludge inoculation.

[0011] S3. Activation of the reaction component: Place the inoculated activated sludge obtained in step S2 into the reaction device to form a reaction component. Take the nitrogen- and phosphorus-containing wastewater to be treated and prepare it into a NO-containing solution. 3- -N mass concentration 15-20 mg / L, PO4 3- Activated wastewater with a P concentration of 3–6 mg / L is treated by adding Na₂S₂O₃ to achieve a Na₂S₂O₃ concentration of 1500–2000 mg / L, and then adding NaHCO₃ to achieve a NaHCO₃ concentration of 40–60 mg / L. Subsequently, 50–60 parts by weight of the activated wastewater are added to the reaction apparatus to contact the activated sludge and react for 24 hours. The activated wastewater is then discharged, completing one activation cycle. This process is repeated 6–8 times. After each cycle, the NO₂ concentration in the discharged activated wastewater is measured. 3- -N and PO4 3- -P removal rate, if NO 3- -N and PO4 3- If the removal rate of -P is >95%, the reaction component is activated and proceeds to step S4. If NO 3- -N and PO4 3- If any of the removal rates of -P is less than 95%, reactivation will be performed until NO. 3--N and PO4 3- -P removal rates were all >95%;

[0012] S4. Wastewater treatment in stages: The nitrogen and phosphorus-containing wastewater to be treated is introduced into the reaction unit for continuous wastewater treatment in stages, with each stage of wastewater treatment lasting 12 hours.

[0013] Further, in step S1, the moisture content of the heterotrophic denitrifying granular sludge is 85-90%, and the composition and mass concentration of the remaining components in the enrichment medium are as follows: the mass concentration of NaHCO3 does not exceed 1 g / L, the mass concentration of NH4Cl does not exceed 0.6 g / L, the mass concentration of MgSO4·7H2O does not exceed 0.8 g / L, and the mass concentration of FeSO4·7H2O does not exceed 0.02 g / L, and the moisture content of the anaerobic granular sludge is 85-90%.

[0014] Note: Since both the autotrophic denitrification process using sodium thiosulfate and pyrrhotite as sulfur sources require the consumption of inorganic carbon, NaHCO3 was added as an inorganic carbon source during the experiment.

[0015] Further, in step S1, after nitrogen gas is introduced into the reaction vessel, the pressure in the reaction vessel is 0.005-0.2 bar, the ambient temperature is 22-26°C, and the stirring speed is 30-50 rpm.

[0016] Note: By optimizing and adjusting the parameters of nitrogen injection, the air can be completely purged during the experiment.

[0017] Further, in step S2, the polylactic acid powder has a molecular weight of 5000-10000 g / mol, a particle size of 2-3 mm, and the pyrrhotite powder has a particle size of 3-5 mm. The stirring speed is 20-30 rpm.

[0018] Note: By selecting raw materials with suitable particle size, it is easier to inoculate them onto activated sludge.

[0019] Further, in step S3, the reaction device includes a reaction cylinder. A filter plate assembly is provided in the middle of the reaction cylinder and is slidably connected to the inner wall of the reaction cylinder. The filter plate assembly includes an upper perforated plate and a lower perforated plate. Lightweight filter material is filled between the upper and lower perforated plates. A drive motor assembly is provided at the center of the top of the reaction cylinder. The drive motor assembly includes a push rod motor and a stirring motor. A telescopic stirring rod provided at the output end of the push rod motor passes through the top of the reaction cylinder and extends into the interior of the reaction cylinder. The stirring motor drives the push rod motor and the telescopic stirring rod to rotate synchronously. The telescopic stirring rod is composed of several sleeved support rods, and the extension and retraction of each support rod is driven by the push rod motor. Several stirring plates are provided on the upper outer side of each support rod. The center of the top of the upper perforated plate is rotatably connected to the bottom of the telescopic stirring rod.

[0020] The reaction cylinder has a water inlet on one side of its bottom and a water outlet on the side wall above the water inlet. A water pump is provided on the other side of the reaction cylinder corresponding to the water inlet and the water outlet. The lower end of the water pump is connected to the lower side wall of the reaction cylinder through a lower guide pipe, and the upper end of the water pump is connected to the upper side wall of the reaction cylinder through an upper guide pipe.

[0021] The inoculated activated sludge obtained in step S2 is placed inside the reaction cylinder below the filter plate assembly. During the continuous segmented wastewater treatment in step S4, the nitrogen and phosphorus-containing wastewater to be treated enters through the inlet and is discharged through the outlet. During treatment, the drive motor is turned on to drive the telescopic stirring rod for stirring, and the drainage ratio is 70-75% each time.

[0022] Furthermore, the lightweight filter material is polystyrene foam particles or ceramsite. The upper and lower perforated plates are fixedly connected by several connecting rods. The diameter of the lower perforated plate is 0.05-0.2 mm, and the diameter of the upper perforated plate is 0.5-1 mm. Each support rod is provided with 2-4 stirring plates at equal intervals in the circumferential direction, and the number of support rods is 3-5. The side walls of both the upper and lower perforated plates are provided with grooves, and the grooves are slidably connected to the limiting strips provided on both sides of the inner wall of the reaction cylinder.

[0023] Note: Lightweight filter media can further filter and adsorb other particulate pollutants in wastewater.

[0024] Furthermore, in step S4, when the sewage treatment time for each segment reaches 3, 6, and 9 hours, the water pump is turned on to pump the sewage from the upper part of the reaction cylinder through the upper guide pipe to the lower guide pipe and then back into the reaction cylinder. Filter screens are provided on the inner walls of the reaction cylinder corresponding to the upper and lower guide pipes. 15 minutes before the end of each sewage treatment segment, the drive motor is turned on to extend and retract the telescopic stirring rod so that the filter plate assembly is located at a height of 20% from the bottom of the reaction cylinder. At this time, the outlet is located above the filter plate assembly.

[0025] Note: By setting specific steps for segmented wastewater treatment, wastewater treatment can be made more thorough, and nitrogen and phosphorus removal rates can be higher.

[0026] Furthermore, in step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction assembly, it is necessary to remove NO from the nitrogen- and phosphorus-containing wastewater to be treated. 3- The concentration of NO in nitrogen- and phosphorus-containing wastewater to be treated was detected. 3- When the NO concentration is <20 mg / L, the stirring speed of the telescopic stirring rod is 80-100 rpm. 3-When the NO concentration is 20–100 mg / L, the stirring speed of the telescopic stirring rod is 120–160 rpm. When the NO concentration in the nitrogen- and phosphorus-containing wastewater to be treated is... 3- When the N mass concentration is >100 mg / L, the stirring speed of the telescopic stirring rod is 200-300 rpm.

[0027] Note: By analyzing the NO content in the nitrogen- and phosphorus-containing wastewater to be treated... 3- The stirring speed during treatment is optimized by adjusting the N mass concentration, thereby improving the contact between polylactic acid, which plays a leading role in denitrification, and the wastewater, increasing the reaction rate and achieving a good removal rate.

[0028] Furthermore, in step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction assembly, it is necessary to remove the PO4 from the nitrogen- and phosphorus-containing wastewater to be treated. 3- -P mass concentration was detected when the PO4 content in the nitrogen-phosphorus wastewater to be treated was... 3- When the PO4 concentration is <8 mg / L, the drive motor is activated to extend and retract the telescopic stirring rod, positioning the filter plate assembly at a height of 40% from the bottom of the reaction cylinder. This allows the nitrogen- and phosphorus-containing wastewater to be treated to contain PO4. 3- When the PO4 concentration is 8–30 mg / L, the drive motor is activated to extend and retract the telescopic stirring rod, positioning the filter plate assembly at a height of 55% from the bottom of the reaction cylinder. This allows the nitrogen- and phosphorus-containing wastewater to contain PO4 to be treated. 3- When the mass concentration of -P is >30mg / L, the filter plate assembly is positioned at 70% of the height from the bottom of the reaction cylinder by turning on the drive motor to extend and retract the telescopic stirring rod.

[0029] Note: Based on the PO4 content in the nitrogen and phosphorus wastewater to be treated 3- -Optimizing the height of the filter plate assembly during P mass concentration treatment enhances the contact between pyrrhotite, which plays a leading role in phosphorus removal, and pollutants. This is achieved by adjusting the height of the filter plate assembly during P mass concentration optimization. 3- When the P mass concentration is low, it compresses the space of the activated sludge, reducing the damage to the polylactic acid surface that can be utilized by microorganisms.

[0030] The beneficial effects of this invention are:

[0031] (1) The present invention provides a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification with pyrrhotite. Polylactic acid is used as a heterotrophic denitrification solid carbon source and pyrrhotite is used as an autotrophic denitrification electron donor for denitrification. A reaction assembly was constructed, and the activation method and step parameters of the reaction assembly were defined in detail to obtain the optimal treatment conditions. The polylactic acid-pyrrhotite composite packing was used for synergistic denitrification to achieve efficient wastewater denitrification and phosphorus removal.

[0032] (2) The present invention provides a method for deep nitrogen and phosphorus removal based on polylactic acid and pyrrhotite denitrification. Starting from the mechanism of action, the polylactic acid surface is easily utilized by microorganisms and becomes damaged; the pyrrhotite surface is loose and porous, easily adsorbing biofilms and adsorbing pollutants such as phosphates. Therefore, a series of supporting device components and related operating methods have been developed. This method is based on the NO content in the nitrogen and phosphorus-containing wastewater to be treated. 3- The stirring speed during treatment was optimized by adjusting the -N mass concentration to improve the contact between polylactic acid (PLA), which plays a leading role in denitrification, and the wastewater, thereby increasing the reaction rate and achieving a good removal rate. This was achieved by adjusting the stirring speed based on the PO4 concentration in the nitrogen- and phosphorus-containing wastewater to be treated. 3- -Optimizing the height of the filter plate assembly during P mass concentration treatment enhances the contact between pyrrhotite, which plays a leading role in phosphorus removal, and pollutants. This is achieved by adjusting the height of the filter plate assembly during P mass concentration optimization. 3- When the P mass concentration is low, the space of the activated sludge is compressed, reducing the damage to the polylactic acid surface that can be utilized by microorganisms, thereby extending the service life of the entire reaction unit.

[0033] (3) The method of deep denitrification and phosphorus removal based on polylactic acid and pyrrhotite denitrification of the present invention can ultimately stabilize the nitrogen and phosphorus removal rate in nitrogen and phosphorus-containing wastewater at more than 98%, the COD concentration of the effluent is relatively stable and the acid and alkali in the reaction component are kept in balance, which is conducive to its promotion and use. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the reaction device structure in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention;

[0035] Figure 2 This is a schematic diagram of the internal structure of the filter plate assembly of the reaction device located at the 40% position in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention.

[0036] Figure 3 This is a schematic diagram of the internal structure of the filter plate assembly of the reaction device located at the 55% position in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention.

[0037] Figure 4 This is a schematic diagram of the internal structure of the filter plate assembly of the reaction device at the 70% position in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention.

[0038] Figure 5 This is a schematic diagram of the internal structure of the filter plate assembly of the reaction device located at the 20% position in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention.

[0039] Figure 6This is a schematic diagram of the internal structure of the drive motor unit of the reaction device in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention.

[0040] Figure 7 This is a schematic diagram of the internal structure of the connection between the bottom of the support rod and the upper orifice plate of the reaction device in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention.

[0041] Figure 8 This is a schematic diagram of the connection structure between the upper orifice plate and the limiting strip in the reaction device of a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention;

[0042] Figure 9 This is a schematic diagram of the upper orifice plate and connecting rod structure of the reaction device in a method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to the present invention;

[0043] Figure 10 This is a scanning electron microscope image of polylactic acid particles after the experiment in Example 3 of Experiment 2 of this invention.

[0044] Among them, 1-reaction cylinder, 11-water inlet, 12-water outlet, 13-limiting strip, 14-filter screen, 2-filter plate assembly, 21-upper plate, 22-lower plate, 23-connecting rod, 24-groove, 3-drive motor assembly, 31-push rod motor, 32-stirring motor, 4-telescopic stirring rod, 41-support rod, 42-stirring plate, 5-water pump, 51-lower guide pipe, 52-upper guide pipe. Detailed Implementation

[0045] Example 1

[0046] A method for deep nitrogen and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite includes the following steps:

[0047] S1. Preparation of activated sludge: By weight, 25 parts of heterotrophic denitrifying granular sludge were placed in a reaction vessel, and 100 parts of enrichment medium were added. The mass concentration of Na2S2O3·5H2O in the enrichment medium was 4 g / L, the mass concentration of KH2PO4 was 2 g / L, the mass concentration of NaNO3 was 1.5 g / L, and the mass concentration of the remaining components did not exceed 3 g / L. Nitrogen gas was introduced into the reaction vessel for 4 minutes to purge the air. The vessel was then sealed and placed at room temperature for 3 days of static culture. The enrichment medium was then removed to complete one enrichment. This process was repeated 4 times to obtain enriched sludge. The enriched sludge was then mixed with 95 parts of anaerobic granular sludge and stirred evenly to obtain activated sludge. After introducing nitrogen gas into the reaction vessel, the pressure in the reaction vessel was 0.1 bar, the room temperature was 25℃, and the stirring speed was 40 rpm.

[0048] The moisture content of the heterotrophic denitrifying granular sludge was 87%. The composition and mass concentration of the remaining components in the enrichment medium were as follows: NaHCO3 mass concentration was 0.7 g / L, NH4Cl mass concentration was 0.4 g / L, MgSO4·7H2O mass concentration was 0.6 g / L, FeSO4·7H2O mass concentration was 0.015 g / L, and the moisture content of the anaerobic granular sludge was 88%.

[0049] S2. Activated sludge inoculation: By weight, take 22 parts of polylactic acid powder and 12 parts of pyrrhotite powder and place them in the activated sludge obtained in step S1. Stir evenly to complete the activated sludge inoculation. The molecular weight of polylactic acid powder is 8000 g / mol, the particle size of polylactic acid powder is 2.5 mm, the particle size of pyrrhotite powder is 4 mm, and the stirring speed is 25 rpm.

[0050] S3. Activation of the reaction component: Place the inoculated activated sludge obtained in step S2 into the reaction device to form a reaction component. Take the nitrogen- and phosphorus-containing wastewater to be treated and prepare it into a NO-containing solution. 3- -N mass concentration 16mg / L, PO4 3- -Activation wastewater with a P mass concentration of 4 mg / L was treated by adding Na2S2O3 to achieve a Na2S2O3 mass concentration of 1800 mg / L, and then adding NaHCO3 to achieve a NaHCO3 mass concentration of 50 mg / L. 55 parts by weight of the activated wastewater were then added to the reaction apparatus to contact the activated sludge and react for 24 hours. The activated wastewater was then discharged, completing one activation cycle. This process was repeated seven times. The NO content in the discharged activated wastewater was then measured. 3- -N and PO4 3- -P removal rate, if NO 3- -N and PO4 3- If the removal rate of -P is >95%, the reaction component is activated and proceeds to step S4. If NO 3- -N and PO4 3- If any of the removal rates of -P is less than 95%, reactivation will be performed until NO. 3- -N and PO4 3- -P removal rates were all >95%;

[0051] S4. Wastewater treatment in stages: The nitrogen and phosphorus-containing wastewater to be treated is introduced into the reaction unit for continuous wastewater treatment in stages, with each stage of wastewater treatment lasting 12 hours.

[0052] Example 2

[0053] The difference between this embodiment and Embodiment 1 is that the specific parameters are selected differently.

[0054] S1. Preparation of activated sludge: By weight, 20 parts of heterotrophic denitrifying granular sludge were placed in a reaction vessel, and 80 parts of enrichment medium were added. The mass concentration of Na2S2O3·5H2O in the enrichment medium was 3 g / L, the mass concentration of KH2PO4 was 1 g / L, the mass concentration of NaNO3 was 1 g / L, and the mass concentration of the remaining components did not exceed 3 g / L. Nitrogen gas was introduced into the reaction vessel for 3 minutes to purge the air. The vessel was then sealed and placed at room temperature for 3 days of static culture. The enrichment medium was then removed to complete one enrichment. This process was repeated 4 times to obtain enriched sludge. The enriched sludge was then mixed with 90 parts of anaerobic granular sludge and stirred evenly to obtain activated sludge. After introducing nitrogen gas into the reaction vessel, the pressure in the reaction vessel was 0.005 bar, the room temperature was 22℃, and the stirring speed was 30 rpm.

[0055] The moisture content of the heterotrophic denitrifying granular sludge was 85%. The composition and mass concentration of the remaining components in the enrichment medium were as follows: NaHCO3 mass concentration was 0.5 g / L, NH4Cl mass concentration was 0.3 g / L, MgSO4·7H2O mass concentration was 0.4 g / L, FeSO4·7H2O mass concentration was 0.01 g / L, and the moisture content of the anaerobic granular sludge was 85%.

[0056] S2. Activated sludge inoculation: By weight, take 20 parts of polylactic acid powder and 10 parts of pyrrhotite powder and place them in the activated sludge obtained in step S1. Stir evenly to complete the activated sludge inoculation. The molecular weight of polylactic acid powder is 5000 g / mol, the particle size of polylactic acid powder is 2 mm, the particle size of pyrrhotite powder is 3 mm, and the stirring speed is 20 rpm.

[0057] S3. Activation of the reaction component: Place the inoculated activated sludge obtained in step S2 into the reaction device to form a reaction component. Take the nitrogen- and phosphorus-containing wastewater to be treated and prepare it into a NO-containing solution. 3- -N mass concentration 15mg / L, PO4 3- -Activation wastewater with a P concentration of 3 mg / L was treated by adding Na₂S₂O₃ to achieve a Na₂S₂O₃ concentration of 1500 mg / L, and then adding NaHCO₃ to achieve a NaHCO₃ concentration of 40 mg / L. Subsequently, 50 parts by weight of the activation wastewater were added to the reaction apparatus to contact the activated sludge and react for 24 hours. The activation wastewater was then discharged, completing one activation cycle. This process was repeated six times. The NO₂ concentration in the discharged activation wastewater was then measured. 3- -N and PO4 3- -P removal rate.

[0058] Example 3

[0059] The difference between this embodiment and Embodiment 1 is that the specific parameters are selected differently.

[0060] S1. Preparation of activated sludge: By weight, 30 parts of heterotrophic denitrifying granular sludge were placed in a reaction vessel, and 120 parts of enrichment medium were added. The mass concentration of Na2S2O3·5H2O in the enrichment medium was 6 g / L, the mass concentration of KH2PO4 was 3 g / L, the mass concentration of NaNO3 was 2 g / L, and the mass concentration of the remaining components did not exceed 3 g / L. Nitrogen gas was introduced into the reaction vessel for 5 minutes to purge the air. The vessel was then sealed and placed at room temperature for 4 days of static culture. The enrichment medium was then removed to complete one enrichment cycle. This process was repeated 5 times to obtain enriched sludge. The enriched sludge was then mixed with 100 parts of anaerobic granular sludge and stirred evenly to obtain activated sludge. After introducing nitrogen gas into the reaction vessel, the pressure in the reaction vessel was 0.2 bar, the room temperature was 26℃, and the stirring speed was 50 rpm.

[0061] The moisture content of the heterotrophic denitrifying granular sludge was 90%. The composition and mass concentration of the remaining components in the enrichment medium were as follows: NaHCO3 mass concentration was 1 g / L, NH4Cl mass concentration was 0.6 g / L, MgSO4·7H2O mass concentration was 0.8 g / L, FeSO4·7H2O mass concentration was 0.02 g / L, and the moisture content of the anaerobic granular sludge was 90%.

[0062] S2. Activated sludge inoculation: By weight, take 25 parts of polylactic acid powder and 15 parts of pyrrhotite powder and place them in the activated sludge obtained in step S1. Stir evenly to complete the activated sludge inoculation. The molecular weight of polylactic acid powder is 10000 g / mol, the particle size of polylactic acid powder is 3 mm, the particle size of pyrrhotite powder is 5 mm, and the stirring speed is 30 rpm.

[0063] S3. Activation of the reaction component: Place the inoculated activated sludge obtained in step S2 into the reaction device to form a reaction component. Take the nitrogen- and phosphorus-containing wastewater to be treated and prepare it into a NO-containing solution. 3- -N mass concentration 20mg / L, PO4 3- -Activation wastewater with a P concentration of 6 mg / L was treated by adding Na₂S₂O₃ to achieve a Na₂S₂O₃ concentration of 2000 mg / L, and then adding NaHCO₃ to achieve a NaHCO₃ concentration of 60 mg / L. Subsequently, 60 parts by weight of the activated wastewater were added to the reaction apparatus to contact the activated sludge and react for 24 hours. The activated wastewater was then discharged, completing one activation cycle. This process was repeated eight times. The NO₂ concentration in the discharged activated wastewater was then measured. 3- -N and PO4 3- -P removal rate.

[0064] Example 4

[0065] like Figure 1 , Figure 2 , Figure 6 , Figure 7 As shown, this embodiment is a further limitation of embodiment 1. In step S3, the reaction device includes a reaction cylinder 1. A filter plate assembly 2 is provided in the middle of the reaction cylinder 1 and is slidably connected to the inner wall of the reaction cylinder 1. The filter plate assembly 2 includes an upper perforated plate 21 and a lower perforated plate 22. Lightweight filter material is filled between the upper perforated plate 21 and the lower perforated plate 22. A drive motor assembly 3 is provided at the top center of the reaction cylinder 1. The drive motor assembly 3 includes a push rod motor 31 and a stirring motor 32. A telescopic stirring rod 4 is provided at the output end of the push rod motor 31, which passes through the top of the reaction cylinder 1 and extends into the interior of the reaction cylinder 1. The stirring motor 32 drives the push rod motor 31 and the telescopic stirring rod 4 to rotate synchronously. The telescopic stirring rod 4 is composed of four sleeved support rods 41, and the push rod motor 31 drives the extension and retraction of each support rod 41. Several stirring plates 42 are provided on the upper outer side of each support rod 41. The top center of the upper perforated plate 21 is rotatably connected to the bottom of the telescopic stirring rod 4.

[0066] like Figures 7-9 As shown, the lightweight filter material is polystyrene foam particles or ceramsite. The upper perforated plate 21 and the lower perforated plate 22 are fixedly connected by 6 connecting rods 23. The diameter of the lower perforated plate 22 is 0.1 mm, and the diameter of the upper perforated plate 21 is 0.7 mm. Each support rod 41 is provided with 3 stirring plates 42 at equal intervals in the circumferential direction. The two side walls of the upper perforated plate 21 and the lower perforated plate 22 are provided with grooves 24. The grooves 24 are slidably connected to the limiting strips 13 provided on both sides of the inner wall of the reaction cylinder 1.

[0067] like Figure 1 As shown, a water inlet 11 is provided on one side of the bottom of the reaction cylinder 1, and a water outlet 12 is provided on the side wall of the reaction cylinder 1 above the water inlet 11. A water pump 5 is provided on the other side of the reaction cylinder 1 corresponding to the water inlet 11 and the water outlet 12. The lower end of the water pump 5 is connected to the lower side wall of the reaction cylinder 1 through the lower guide pipe 51, and the upper end of the water pump 5 is connected to the upper side wall of the reaction cylinder 1 through the upper guide pipe 52.

[0068] like Figure 5 As shown, the inoculated activated sludge obtained in step S2 is placed inside the reaction cylinder 1 below the filter plate assembly 2. When the nitrogen and phosphorus-containing wastewater to be treated is continuously treated in step S4, it enters through the inlet 11 and is discharged through the outlet 12. During treatment, the drive motor 3 is turned on to drive the telescopic stirring rod 4 for stirring. The drainage ratio is 72% each time.

[0069] like Figure 5As shown, in step S4, when the sewage treatment time for each segment reaches 3, 6, and 9 hours, the water pump 5 is turned on to pump the sewage in the upper part of the reaction cylinder 1 through the upper guide pipe 52 to the lower guide pipe 51 and then back into the reaction cylinder 1. Filter screens 14 are provided on the inner walls of the reaction cylinder 1 at the corresponding upper guide pipe 52 and lower guide pipe 51. 15 minutes before the end of each segment of sewage treatment, the drive motor 3 is turned on to drive the telescopic stirring rod 4 to extend and retract so that the filter plate assembly 2 is located at a height of 20% from the bottom of the reaction cylinder 1. At this time, the outlet 12 is located above the filter plate assembly.

[0070] like Figures 2-4 As shown, in step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction unit, it is necessary to remove NO from the wastewater. 3- The concentration of NO in nitrogen- and phosphorus-containing wastewater to be treated was detected. 3- When the NO concentration is <20 mg / L, the stirring speed of the telescopic stirring rod 4 is 90 rpm. 3- When the NO concentration is 20–100 mg / L, the stirring speed of the telescopic stirring rod 4 is 140 rpm. When the NO concentration in the nitrogen- and phosphorus-containing wastewater to be treated is... 3- When the mass concentration of -N is >100mg / L, the stirring speed of the telescopic stirring rod 4 is 250rpm;

[0071] like Figures 2-4 As shown, in step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction unit, the PO4 in the wastewater needs to be reduced. 3- -P mass concentration was detected when the PO4 content in the nitrogen-phosphorus wastewater to be treated was... 3- When the PO4 concentration is <8 mg / L, the drive motor 3 is activated to extend and retract the telescopic stirring rod 4, causing the filter plate assembly 2 to be positioned at a height of 40% from the bottom of the reaction cylinder 1. When the PO4 concentration in the nitrogen- and phosphorus-containing wastewater to be treated is <8 mg / L, the PO4 concentration is increased. 3- When the PO4 mass concentration is 8-30 mg / L, the drive motor 3 is activated to extend and retract the telescopic stirring rod 4, causing the filter plate assembly 2 to be positioned at 55% of the height from the bottom of the reaction cylinder 1. When the PO4 content in the nitrogen- and phosphorus-containing wastewater to be treated is... 3- When the mass concentration of -P is greater than 30 mg / L, the drive motor unit 3 is turned on to drive the telescopic stirring rod 4 to extend and retract, so that the filter plate assembly 2 is located at a height of 70% from the bottom of the reaction cylinder 1.

[0072] Example 5

[0073] The difference between this embodiment and embodiment 4 is that the specific parameters are selected differently.

[0074] The lower orifice plate 22 has an orifice diameter of 0.05 mm, the upper orifice plate 21 has an orifice diameter of 0.5 mm, and each support rod 41 is provided with two stirring plates 42 at equal intervals in the circumferential direction. There are three support rods 41, and the drainage ratio is 70% each time.

[0075] In step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction unit, the NO in the wastewater needs to be removed. 3- The concentration of NO in nitrogen- and phosphorus-containing wastewater to be treated was detected. 3- When the NO concentration is <20 mg / L, the stirring speed of the telescopic stirring rod 4 is 80 rpm. 3- When the NO concentration is 20–100 mg / L, the stirring speed of the telescopic stirring rod 4 is 120 rpm. When the NO concentration in the nitrogen- and phosphorus-containing wastewater to be treated is... 3- When the mass concentration of -N is >100mg / L, the stirring speed of the telescopic stirring rod 4 is 200rpm.

[0076] Example 6

[0077] The difference between this embodiment and embodiment 4 is that the specific parameters are selected differently.

[0078] The lower orifice plate 22 has an orifice diameter of 0.2 mm, the upper orifice plate 21 has an orifice diameter of 1 mm, and each support rod 41 is provided with 4 stirring plates 42 at equal intervals in the circumferential direction. There are 5 support rods 41, and the drainage ratio is 75% each time.

[0079] In step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction unit, the NO in the wastewater needs to be removed. 3- The concentration of NO in nitrogen- and phosphorus-containing wastewater to be treated was detected. 3- When the NO concentration is <20 mg / L, the stirring speed of the telescopic stirring rod 4 is 100 rpm. 3- When the NO concentration is 20–100 mg / L, the stirring speed of the telescopic stirring rod 4 is 160 rpm. When the NO concentration in the nitrogen- and phosphorus-containing wastewater to be treated is... 3- When the mass concentration of -N is >100mg / L, the stirring speed of the telescopic stirring rod 4 is 300rpm.

[0080] Experimental Example 1

[0081] The following experiment demonstrates the effectiveness of the method and related reaction components of this invention in wastewater treatment. Following the method described in Example 4, a total of 12 wastewater samples were treated. The stirring speed or the height of the filter plate assembly 2 was adjusted according to the mass concentration of pollutants in each wastewater sample. The NO content in the first wastewater sample was... 3- The -N concentration is 45 mg / L, and the NO at the outlet is... 3-The NO concentration was 0.62 mg / L, with a removal rate of 98.63%. The final stage of wastewater treatment... 3- The -N concentration is 125 mg / L, and the NO at the outlet is... 3- -N concentration was 0.88 mg / L, removal rate was 99.3%; PO4 in the first stage of wastewater 3- -P concentration is 6 mg / L, PO4 at the outlet 3- -P concentration was 0.08 mg / L, removal rate was 98.7%, and PO4 in the last stage of wastewater... 3- -P concentration is 23 mg / L, PO4 at the outlet 3- -P concentration was 0.13 mg / L, removal rate was 99.4%, indicating that the method and related reaction components of this invention can achieve a nitrogen and phosphorus removal rate of over 98% in wastewater;

[0082] Experimental Example 2

[0083] The optimal polylactic acid (PLA) molecular weight in the method of this invention was tested below. Taking the parameters in Example 1 as an example, several comparative examples were also set up. In Comparative Example 1, the molecular weight of the PLA powder was 2000 g / mol, and in Comparative Example 2, the molecular weight of the PLA powder was 12000 g / mol. The results showed that the denitrification effect in Example 4 was better than that in Comparative Examples 1 and 2. In the denitrification experiment, the electron donors for denitrification were small molecule carbon sources produced by microbial decomposition of PLA and easily degradable organic matter such as soluble microbial metabolites. In contrast, the selected PLA molecular weights in Examples 1 to 3 all resulted in relatively stable carbon release. Figure 10 The image shows a scanning electron microscope (SEM) image of polylactic acid (PLA) particles after the experiment in Example 3. The PLA particles have pores that extend into the crystal, indicating that microorganisms achieved deep hydrolysis of PLA to release carbon sources during the experiment.

[0084] Experimental Example 3

[0085] The method of the present invention will be compared with conventional methods and with comparative examples below. Comparative Example 3 is basically the same as Example 1, but the reaction device of Example 4 is not used; instead, a conventional reaction device is used. Furthermore, the reaction space of the activated sludge is not adjusted according to the concentration of pollutants in step S4. After being put into use, when treating 32 stages of wastewater, the PO4 at the effluent... 3- -P removal rate began to decrease, and in the subsequent 20 stages of wastewater treatment, PO4 levels were found to be low in 3 stages. 3- -P removal rate is less than 98%, and NO in one section of wastewater... 3- -N removal rate was less than 98%; in contrast, after the method and related reaction equipment in Example 4 were put into use, the PO4 at the effluent outlet was significantly reduced after treating 55 sections of wastewater. 3--P removal rate only started to decrease after that, and in the subsequent 20 stages of wastewater treatment, only one stage of wastewater had PO4 removal. 3- -P removal rate is less than 98%.

Claims

1. A method for deep nitrogen and phosphorus removal based on polylactic acid synergistic with pyrrhotite denitrification, characterized in that, Includes the following steps: S1. Preparation of activated sludge: By weight, take 20-30 parts of heterotrophic denitrifying granular sludge and place it in a reaction vessel. Add 80-120 parts of enrichment culture medium. The mass concentration of Na2S2O3·5H2O in the enrichment culture medium is 3-6 g / L, the mass concentration of KH2PO4 is 1-3 g / L, the mass concentration of NaNO3 is 1-2 g / L, and the mass concentration of the remaining components does not exceed 3 g / L. Purge nitrogen into the reaction vessel for 3-5 minutes to purge the air. Seal and place it at room temperature for static culture for 3-4 days. After that, remove the enrichment culture medium to complete one enrichment. Repeat the enrichment process 4-5 times to obtain enriched sludge. Mix the enriched sludge with 90-100 parts of anaerobic granular sludge and stir evenly to obtain activated sludge. S2. Activated sludge inoculation: By weight, take 20-25 parts of polylactic acid powder and 10-15 parts of pyrrhotite powder and place them in the activated sludge obtained in step S1, and stir evenly to complete the activated sludge inoculation. S3. Activation of the reaction component: Place the inoculated activated sludge obtained in step S2 into the reaction device to form a reaction component. Take the nitrogen- and phosphorus-containing wastewater to be treated and prepare it into a NO-containing solution. 3- -N mass concentration 15~20mg / L, PO4 3- -Activation wastewater with a P concentration of 3-6 mg / L is treated by adding Na2S2O3 to achieve a Na2S2O3 concentration of 1500-2000 mg / L, and then adding NaHCO3 to achieve a NaHCO3 concentration of 40-60 mg / L. Subsequently, 50-60 parts by weight of the activation wastewater are added to the reaction apparatus to contact the activated sludge and react for 24 hours. The activation wastewater is then discharged, completing one activation cycle. This process is repeated 6-8 times. After each cycle, the NO content in the discharged activation wastewater is measured. 3- -N and PO4 3- -P removal rate, if NO 3- -N and PO4 3- If the removal rate of -P is >95%, the reaction component is activated and proceeds to step S4. If NO 3- -N and PO4 3- If any of the removal rates of -P is less than 95%, reactivation will be performed until NO. 3- -N and PO4 3- -P removal rates were all >95%; S4. Wastewater treatment in stages: The nitrogen and phosphorus-containing wastewater to be treated is fed into the reaction unit for continuous wastewater treatment in stages, with each stage of wastewater treatment lasting 12 hours. In step S3, the reaction apparatus includes a reaction cylinder (1). A filter plate assembly (2) is slidably connected to the inner wall of the reaction cylinder (1) in its middle section. The filter plate assembly (2) includes an upper perforated plate (21) and a lower perforated plate (22). Lightweight filter material is filled between the upper perforated plate (21) and the lower perforated plate (22). A drive motor assembly (3) is located at the center of the top of the reaction cylinder (1). The drive motor assembly (3) includes a push rod motor (31) and a stirring motor (32). The push rod motor (31)... The telescopic stirring rod (4) provided at the output end passes through the top of the reaction cylinder (1) and extends into the interior of the reaction cylinder (1). The stirring motor (32) drives the push rod motor (31) and the telescopic stirring rod (4) to rotate synchronously. The telescopic stirring rod (4) is composed of several sleeved support rods (41), and the push rod motor (31) drives the extension and retraction of each support rod (41). Several stirring plates (42) are provided on the upper outer side of each support rod (41). The top center of the upper hole plate (21) is rotatably connected to the bottom of the telescopic stirring rod (4). The reaction cylinder (1) has an inlet (11) on one side of its bottom and an outlet (12) on the side wall of the reaction cylinder (1) above the inlet (11). A water pump (5) is provided on the other side of the reaction cylinder (1) corresponding to the inlet (11) and the outlet (12). The lower end of the water pump (5) is connected to the lower side wall of the reaction cylinder (1) through a lower guide pipe (51), and the upper end of the water pump (5) is connected to the upper side wall of the reaction cylinder (1) through an upper guide pipe (52). The inoculated activated sludge obtained in step S2 is placed inside the reaction cylinder (1) below the filter plate assembly (2). During the continuous segmented wastewater treatment in step S4, the nitrogen and phosphorus wastewater to be treated enters through the inlet (11) and is discharged through the outlet (12). During treatment, the drive motor (3) is turned on to drive the telescopic stirring rod (4) for stirring. The drainage ratio is 70~75% each time.

2. The method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, In step S1, the moisture content of the heterotrophic denitrifying granular sludge is 85-90%, and the composition and mass concentration of the remaining components in the enrichment medium are as follows: the mass concentration of NaHCO3 does not exceed 1 g / L, the mass concentration of NH4Cl does not exceed 0.6 g / L, the mass concentration of MgSO4·7H2O does not exceed 0.8 g / L, and the mass concentration of FeSO4·7H2O does not exceed 0.02 g / L. The moisture content of the anaerobic granular sludge is 85-90%.

3. The method for deep nitrogen and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, In step S1, after nitrogen gas is introduced into the reaction vessel, the pressure in the reaction vessel is 0.005-0.2 bar, the ambient temperature is 22-26℃, and the stirring speed is 30-50 rpm.

4. The method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, In step S2, the polylactic acid powder has a molecular weight of 5000~10000g / mol, a particle size of 2~3mm, and the pyrrhotite powder has a particle size of 3~5mm. The stirring speed is 20~30rpm.

5. The method for deep denitrification and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, The lightweight filter material is polystyrene foam particles or ceramic particles. The upper perforated plate (21) and the lower perforated plate (22) are fixedly connected by several connecting rods (23). The diameter of the lower perforated plate (22) is 0.05~0.2mm, and the diameter of the upper perforated plate (21) is 0.5~1mm. Each support rod (41) is provided with 2~4 stirring plates (42) at equal intervals in the circumferential direction. The number of support rods (41) is 3~5. The upper perforated plate (21) and the lower perforated plate (22) are provided with grooves (24) on both sides. The grooves (24) are slidably connected to the limiting strips (13) provided on both sides of the inner wall of the reaction cylinder (1).

6. The method for deep nitrogen and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, In step S4, when the sewage treatment time reaches 3, 6 and 9 hours, the water pump (5) is turned on to pump the sewage in the upper part of the reaction cylinder (1) through the upper guide pipe (52) into the lower guide pipe (51) and then back into the reaction cylinder (1). The inner wall of the reaction cylinder (1) at the corresponding upper guide pipe (52) and lower guide pipe (51) is provided with filter screens (14). 15 minutes before the end of each sewage treatment, the drive motor (3) is turned on to drive the telescopic stirring rod (4) to extend and retract so that the filter plate assembly (2) is located at a height of 20% from the bottom of the reaction cylinder (1). At this time, the outlet (12) is located above the filter plate assembly.

7. The method for deep nitrogen and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, In step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction assembly, it is necessary to remove NO from the wastewater. 3- The concentration of NO in nitrogen- and phosphorus-containing wastewater to be treated was detected. 3- When the NO concentration is <20 mg / L, the stirring speed of the telescopic stirring rod (4) is 80~100 rpm. 3- When the NO concentration of nitrogen-phosphorus wastewater is 20~100 mg / L, the stirring speed of the telescopic stirring rod (4) is 120~160 rpm. 3- When the mass concentration of -N is >100mg / L, the stirring speed of the telescopic stirring rod (4) is 200~300rpm.

8. The method for deep nitrogen and phosphorus removal based on polylactic acid synergistic denitrification of pyrrhotite according to claim 1, characterized in that, In step S4, before the nitrogen- and phosphorus-containing wastewater to be treated is introduced into the reaction unit, it is necessary to remove PO4 from the wastewater. 3- -P mass concentration was detected when the PO4 content in the nitrogen-phosphorus wastewater to be treated was... 3- When the P mass concentration is <8mg / L, the drive motor (3) is turned on to drive the telescopic stirring rod (4) to extend and retract, so that the filter plate assembly (2) is located at a height of 40% from the bottom of the reaction cylinder (1). When the PO4 in the nitrogen- and phosphorus-containing wastewater to be treated is <8mg / L, 3- When the PO4 concentration is 8~30mg / L, the drive motor (3) is turned on to drive the telescopic stirring rod (4) to extend and retract, so that the filter plate assembly (2) is located at a height of 55% from the bottom of the reaction cylinder (1). When the PO4 concentration in the nitrogen-phosphorus wastewater to be treated is 8~30mg / L, 3- When the mass concentration of -P is >30mg / L, the drive motor unit (3) is turned on to drive the telescopic stirring rod (4) to extend and retract so that the filter plate assembly (2) is located at a height of 70% from the bottom of the reaction cylinder (1).

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