Method and reaction device for inducing formation of active granular sludge by adopting polyurethane sponge

Abstract

The invention discloses a method for inducing formation of active granular sludge by adopting polyurethane sponge, which comprises the following steps: S1, adding to-be-cultured active sludge into a culture container, and adding a culture solution for induced culture; s2, fixing a polyurethane sponge on a rod body, and suspending the polyurethane sponge above the culture container, so that the polyurethane sponge is immersed in the culture solution; and after the activated sludge is settled, adjusting the height of the rod body so as to enable the polyurethane sponge to descend into the activated sludge. The invention also discloses a reaction device for inducing the formation of the active granular sludge by adopting the polyurethane sponge. According to the method provided by the invention, the activated sludge is inoculated into the anaerobic digestion solution and is combined with the exogenous carrier to obtain the initial granular sludge induced by the polyurethane sponge, and the initial granular sludge is used as seed sludge to drive the formation of the subsequent granular sludge, so that the formation period of the granular sludge is remarkably shortened.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, specifically to a method and reaction apparatus for inducing the formation of activated granular sludge using polyurethane sponge. Background Technology

[0002] Activated sludge is a microbial community composed of bacteria, fungi, protozoa, and at least a small amount of metazoa, along with the inorganic and organic matter it adsorbs. Typically, microorganisms adhere to inorganic matter as a core, forming brown flocculent precipitates that are loosely distributed within the wastewater treatment system. Under adequate oxygen supply, the microorganisms in activated sludge can effectively degrade organic pollutants in wastewater, achieving both self-proliferation and wastewater purification. However, traditional activated sludge processes suffer from several drawbacks, including loose sludge structure leading to poor settling performance and high suspended solids concentrations in the effluent; weak resistance to shock loads; susceptibility to environmental factors; and the large volume of excess sludge resulting in high disposal costs.

[0003] Granulation of activated sludge is a commonly used solution for wastewater treatment at present. It promotes microbial self-aggregation to form granular sludge with larger particle size, compact structure, and a small amount of coexisting flocculent sludge, exhibiting good settling performance and high biomass. This overcomes the bottlenecks of traditional activated sludge processes in terms of settling properties, resistance to shock loads, and sludge treatment.

[0004] Many factors influence granular sludge formation, including organic loading, hydraulic retention time, liquid upflow velocity, reactor temperature, pH, and the addition of different polymers and ions. Current traditional treatment methods primarily focus on optimizing these factors, such as altering the organic loading, hydraulic retention time, and adding single polymers or ions, to explore conditions that accelerate granular sludge formation. Summary of the Invention

[0005] The technical problem this invention aims to solve is how to rapidly cultivate granular sludge capable of treating anaerobic fermentation wastewater. Utilizing activated sludge to rapidly cultivate granular sludge serves two purposes: firstly, it allows for the reuse of wastewater treatment plant sludge; secondly, it enables the rapid cultivation of granular sludge with excellent settling properties and pollutant removal capabilities. This invention involves inoculating aerobic and anaerobic activated sludge into anaerobic fermentation wastewater and using polyurethane sponge induction, which significantly shortens the cultivation time of the granular sludge.

[0006] To address the aforementioned technical problems, this invention provides a method for inducing the formation of activated granular sludge using polyurethane sponge. This method involves inoculating activated sludge into an anaerobic digester and combining it with an exogenous carrier to obtain initial granular sludge induced by the polyurethane sponge. This initial granular sludge is then used as seed sludge to drive the formation of subsequent granular sludge, thereby shortening the granular sludge formation cycle.

[0007] This invention provides a method for inducing the formation of activated granular sludge using polyurethane sponge, comprising the following steps:

[0008] S1. Add the activated sludge to be cultured into the culture container and add culture medium for induction culture;

[0009] S2. Fix the polyurethane sponge to the rod and suspend it above the culture container so that the polyurethane sponge is immersed in the culture solution; after the activated sludge settles, adjust the height of the rod so that the polyurethane sponge descends into the activated sludge;

[0010] The activated sludge to be cultivated is either aerobic or anaerobic activated sludge, and the culture medium is anaerobic fermentation wastewater.

[0011] Furthermore, in step S2, the polyurethane sponge is pretreated before use. The pretreatment method is to subject the polyurethane sponge to low-temperature plasma treatment, so that its surface changes from hydrophobic to hydrophilic and generates oxygen-containing functional groups.

[0012] Furthermore, in step S1, the volume ratio of the anaerobic fermentation wastewater to the activated sludge is 4:1.

[0013] Furthermore, in step S1, the anaerobic fermentation wastewater has a COD concentration of 4000–8000 mg / L, a TN concentration of 180–220 mg / L, a TP concentration of 65–90 mg / L, an ammonia nitrogen concentration of 70–90 mg / L, and a pH of 6.5–7.0.

[0014] Furthermore, in step S2, when the activated sludge is aerobic activated sludge, during the cultivation period, an oxygenation pump is used to aerate the culture solution, with an aeration interval of 8 to 12 hours and an aeration time of 0.5 to 1 hour each time.

[0015] Alternatively, when the activated sludge is anaerobic activated sludge, the culture container is sealed during the culture period and stored in a sealed space.

[0016] Furthermore, in step S2, during the cultivation period, the culture medium is replaced every 3 to 6 days, and the biofilm is separated from the polyurethane by stirring, providing a suitable adhesion core for microorganisms.

[0017] A second aspect of the present invention provides activated granular sludge obtained by the above method.

[0018] A third aspect of the present invention provides a reaction device for inducing the formation of activated granular sludge using polyurethane sponge, comprising a main reactor, wherein a central chamber, an intermediate chamber, and an outer chamber are arranged coaxially inside the main reactor; a first channel connects the intermediate chamber and the central chamber; a second channel connects the intermediate chamber and the outer chamber; a filter is provided outside the main reactor; the central chamber, intermediate chamber, and outer chamber are arranged in a concentric cylindrical shape, and the volume of the central chamber accounts for 10%-20% of the total volume.

[0019] It also includes a polyurethane foam circulation unit for returning filtered polyurethane foam to the central warehouse.

[0020] Furthermore, the polyurethane foam circulation unit includes a delivery pump and a return pipe, the inlet end of which is connected to the outlet of the filter, and the outlet end extends into the central silo.

[0021] Furthermore, microfluidic holes are provided on the outer walls of the central compartment, intermediate compartment, and outer compartment, and the total area of ​​the microfluidic holes is less than 50% of the total cross-sectional area of ​​the first channel and the second channel.

[0022] Furthermore, a retractable rod is provided inside the main reactor, the rod being used to fix the polyurethane foam.

[0023] Furthermore, the rod body adopts a sleeve-type telescopic structure, and each section of the telescopic structure is used to fix polyurethane foam with different pore sizes. The outer layer of polyurethane foam has a pore size of 5-10mm, the middle layer of polyurethane foam has a pore size of 2-5mm, and the inner layer of polyurethane foam has a pore size of 0.5-2mm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention uses activated sludge granulation technology as the core cultivation strategy. By inoculating activated sludge into anaerobic digestion liquid and combining it with an exogenous carrier, initial granular sludge induced by polyurethane sponge is obtained. This initial granular sludge is then used as seed sludge to drive the formation of subsequent granular sludge, thereby shortening the granular sludge formation cycle.

[0026] 2. The activated granular sludge cultivated using the method of this invention can achieve a maximum chemical oxygen demand removal rate of 67.8%, a total phosphorus removal rate of 86.5%, a total nitrogen removal rate of 74.2%, and an ammonia nitrogen removal rate of 78% when treating anaerobic digestion liquid under aerobic / anaerobic conditions.

[0027] 3. In this invention, the polyurethane was subjected to plasma hydrophilization pretreatment, which increased the biofilm formation rate by 30% and enhanced the bonding force between the microorganisms and the carrier interface. Attached Figure Description

[0028] Figure 1This is a schematic diagram of aerobic activated sludge (a) and anaerobic activated sludge (b) magnified 40 times.

[0029] Figure 2 Here is a scanning electron microscope image of a polyurethane sponge;

[0030] Figure 3 A photograph of aerobic granular sludge induced by polyurethane sponge.

[0031] Figure 4 A schematic diagram of aerobic particulate contamination induced by polyurethane foam, magnified 10 times.

[0032] Figure 5 A photograph of anaerobic granular sludge induced by polyurethane sponge.

[0033] Figure 6 A schematic diagram of anaerobic particulate pollution induced by polyurethane foam, magnified 10 times.

[0034] Figure 7 This is a schematic diagram of the structure of an aeration filter column;

[0035] Figure 8 The COD removal rates of aerobic granular sludge (A) and anaerobic granular sludge (B) induced by polyurethane sponge are shown.

[0036] Figure 9 The TP removal rates of aerobic granular sludge (A) and anaerobic granular sludge (B) induced by polyurethane sponge.

[0037] Figure 10 The TN removal rates of aerobic granular sludge (A) and anaerobic granular sludge (B) induced by polyurethane sponge.

[0038] Figure 11 The ammonia nitrogen removal rates of aerobic granular sludge (A) and anaerobic granular sludge (B) induced by polyurethane sponge.

[0039] Figure 12 This is a schematic cross-sectional view of the main reactor provided in this embodiment.

[0040] The labels in the diagram are as follows: 1. Air inlet; 2. Water inlet; 3. Support plate; 4. Sampling port; 5. Water outlet;

[0041] 100. Main reactor; 110. Central chamber; 120. Intermediate chamber; 130. Peripheral chamber; 140. Filter; 111. First channel; 121. Second channel; 150. Microflow orifice; 160. Output channel; 170. Return pipe; 171. Transfer pump. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] This invention provides a method for inducing the formation of activated granular sludge using polyurethane sponge, comprising the following steps:

[0045] S1. Add the activated sludge to be cultured into the culture container and add culture medium for induction culture;

[0046] S2. Fix the polyurethane sponge to the rod and suspend it above the culture container so that the polyurethane sponge is immersed in the culture solution; after the activated sludge settles, adjust the height of the rod so that the polyurethane sponge descends into the activated sludge;

[0047] The activated sludge to be cultivated is either aerobic or anaerobic activated sludge, and the culture medium is anaerobic fermentation wastewater.

[0048] In this invention, the inventors drew upon the principles of crystal nucleus construction and seed crystal addition in crystallization processes. Aerobic and anaerobic activated sludge were inoculated into anaerobic fermentation wastewater, and then induced using polyurethane sponges. Due to the large specific surface area, good hydrophilicity, and porous structure of the polyurethane sponge, abundant initial attachment sites and enrichment environments were provided, acting as a scaffold for microbial attachment and growth. The porous structure and surface characteristics facilitate the screening and enrichment of specific functional microorganisms, creating a localized high-density microbial environment, indirectly regulating microbial community behavior, shortening the start-up cycle, and improving the overall performance and stability of the system. Therefore, the cultivation time of granular sludge can be significantly shortened, thus proposing a strategy for the rapid cultivation of granular sludge capable of treating anaerobic fermentation wastewater. The rapid cultivation of granular sludge using activated sludge serves two purposes: firstly, it allows for the reuse of wastewater treatment plant sludge; secondly, it enables the rapid cultivation of granular sludge with excellent settling performance and pollutant removal capabilities.

[0049] Anaerobic fermentation digestate is characterized by its complex composition, high concentration, and recalcitrant degradation, and its indiscriminate discharge can cause environmental pollution. For example, high concentrations of organic matter can lead to eutrophication, consuming dissolved oxygen and harming aquatic life; the ammonia nitrogen in the digestate can be converted into nitrates, polluting groundwater and potentially producing N2O gas, which can damage the ozone layer; high salinity, heavy metals, and potential pathogenic microorganisms can also threaten soil structure and ecology. In this invention, anaerobic fermentation wastewater is used to screen for microorganisms in activated sludge, resulting in granular sludge that offers significant advantages for treating this type of anaerobic fermentation wastewater.

[0050] Furthermore, the polyurethane sponge is a waste polyurethane sponge, which can reduce costs and achieve the reuse of solid waste. Preferably, the waste polyurethane sponge is pulverized into millimeter-sized fragments, which can mimic extracellular polymers or filamentous bacteria, thereby better promoting the adhesion and aggregation of microorganisms and the stability of particle encapsulation.

[0051] In some preferred embodiments of the present invention, in step S1, the anaerobic fermentation wastewater has a COD concentration of 4000–8000 mg / L, a TN concentration of 180–220 mg / L, a TP concentration of 65–90 mg / L, an ammonia nitrogen concentration of 70–90 mg / L, and a pH of 6.5–7.0.

[0052] In this embodiment, the COD concentration in the anaerobic fermentation wastewater reached 4000–8000 mg / L, a level of COD that makes pelleting of ordinary activated sludge difficult. However, the method of this invention, using polyurethane sponge as an exogenous carrier, can induce and promote pelleting of activated sludge and shorten its pelleting time.

[0053] More preferably, the anaerobic fermentation wastewater has a COD concentration of 4000-8000 mg / L, a TN concentration of 201 mg / L, a TP concentration of 78 mg / L, an ammonia nitrogen concentration of 85 mg / L, and a pH of 6.8.

[0054] In some preferred embodiments of the present invention, in step S1, the volume ratio of activated sludge to the anaerobic fermentation wastewater is 1:4.

[0055] In some preferred embodiments of the present invention, in step S2, the polyurethane sponge is pretreated before use. The pretreatment method is to subject the polyurethane sponge to low-temperature plasma treatment, so that its surface changes from hydrophobic to hydrophilic and generates oxygen-containing functional groups.

[0056] In some preferred embodiments of the present invention, in step S2, when the activated sludge is aerobic activated sludge, during the cultivation period, an oxygenation pump is used to aerate the culture solution, with an aeration interval of 8 to 12 hours and an aeration time of 0.5 to 1 hour each time.

[0057] In some preferred embodiments of the present invention, in step S2, when the activated sludge is anaerobic activated sludge, the culture container is sealed during the culture period and stored in a sealed space.

[0058] In some preferred embodiments of the present invention, in step S2, the culture medium is replaced every 3 to 6 days during the culture period, and the biofilm is separated from the polyurethane by stirring to provide a suitable adhesion core for microorganisms.

[0059] A second aspect of the present invention provides activated granular sludge obtained by the above method.

[0060] A third aspect of the present invention provides a reaction apparatus for inducing the formation of activated granular sludge using polyurethane sponge, comprising a main reactor; preferably, the main reactor is a completely mixed reactor. See also... Figure 12 The diagram shown is a cross-sectional view of the reaction apparatus provided in this embodiment. The main reactor 100 is internally provided with a central chamber 110, an intermediate chamber 120, and an outer chamber 130 arranged coaxially. A first channel 111 connects the central chamber 110 and the intermediate chamber 120; a second channel 121 connects the intermediate chamber 120 and the outer chamber 130. By way of example and not limitation, there may be multiple first channels 111 and second channels 121, arranged in multiple layers, with one or more first channels and second channels in each layer.

[0061] By way of example and not limitation, a membrane assembly is provided at the port of the first channel and / or the second channel. Preferably, the membrane assembly is a biomembrane or a mesh screen.

[0062] The advantage of this reactor lies in its tiered cultivation of the microbial community. The central chamber 110 employs a high dissolved oxygen environment, promoting rapid colonization of aerobic bacteria on the polyurethane sponge surface, forming a biofilm core. In the intermediate chamber 120, the dissolved oxygen gradient decreases, guiding facultative bacteria to attach and initiating granulation. The outer chamber 130 has a low dissolved oxygen concentration, promoting the outer layer coating of anaerobic bacteria, forming an "aerobic-anoxic" stratified structure, thereby improving the efficiency of nitrogen and phosphorus removal.

[0063] A filter 140 is installed outside the main reactor 100. In this embodiment, the polyurethane sponge is pre-treated into granules. Preferably, the particle size of the polyurethane sponge is 3-10 mm. The porous structure of the polyurethane sponge particles can protect microorganisms and prevent biofilm loss caused by hydraulic shear.

[0064] A polyurethane foam circulation unit is used to return filtered polyurethane foam to the central silo 110. The polyurethane foam circulation unit includes a return pipe 170 and a delivery pump 171. The inlet end of the return pipe 170 is connected to the outlet of the filter 140, and the outlet end extends into the central silo 110.

[0065] By way of example and not limitation, the central chamber 110, intermediate chamber 120, and outer chamber 130 are arranged in a concentric cylindrical shape, with the central chamber 110 accounting for 10%-20% of the total volume. This concentric cylindrical design allows water flow to spiral from the center to the periphery, forming a ring-shaped shear force gradient. This design facilitates the high shear force in the central chamber to screen for strongly adhering bacteria, while the low shear force in the outer chambers protects mature granular sludge.

[0066] Preferably, micropores 150 are provided on the outer walls of the central chamber 110, intermediate chamber 120, and outer chamber 130, and the total area of ​​the micropores 150 is less than 50% of the total cross-sectional area of ​​the first channel and the second channel. The micropores 150 facilitate gas exchange between the chamber and the outside, and can regulate the formation process of activated granular sludge by adjusting the oxygen content in the main reactor 100.

[0067] In this embodiment, the polyurethane sponge particles are reused through a recycling unit, which can effectively save raw materials.

[0068] In another embodiment, a retractable rod is provided at the top inside the main reactor for securing the polyurethane foam.

[0069] Preferably, the rod body adopts a sleeve-type telescopic structure, and each segment of the telescopic structure is used to fix polyurethane foam with different pore sizes. By way of example and not limitation, the rod body is provided with 3 segments that can extend outwards segment by segment. The outermost and middle layers of the telescopic structure are provided with sliding grooves inside, and locking structures are provided at their ends to facilitate the extension and fixation of the middle and innermost rod bodies.

[0070] Preferably, the outer polyurethane sponge has a pore size of 5-10 mm, the middle polyurethane sponge has a pore size of 2-5 mm, and the inner polyurethane sponge has a pore size of 0.5-2 mm. These three layers of polyurethane sponge with different pore sizes correspond to different microbial cultivation processes. Initially, the larger pores in the outer layer facilitate rapid attachment of microorganisms; the middle layer promotes microbial aggregation and granulation; and in the later stages, it provides a stable and dense environment for the growth of granular sludge.

[0071] Preferably, each segment of the retractable structure is detachable. The rods are electrically and / or manually controlled. The extension times of the middle and innermost rods can be set according to the cultivation cycle of the activated granular sludge.

[0072] In practice, the activated sludge to be cultured is added to the central chamber 110 of the main reactor, along with an appropriate culture medium, and bottom aeration is activated in the central chamber to ensure a high oxygen content in the initial stage, which is conducive to bacterial attachment. The activated sludge to be cultured enters from the bottom of the central chamber and mixes thoroughly with the polyurethane sponge granules. Part of the mixture enters the intermediate chamber 120 through the first channel 111 to initiate the sludge granulation process; next, part of the mixture in the intermediate chamber enters the outer chamber 130 through the second channel 121. The outer chamber has a lower oxygen content, which promotes the encapsulation of anaerobic bacteria onto the granules.

[0073] The cultured activated granular sludge is then discharged into the polyurethane sponge recycling unit. As an example, and not a limitation, the filtration component may be a centrifugal separation component or a biofilm, etc. The filtered polyurethane sponge is then pumped back to the central storage unit, thereby improving the utilization efficiency of the polyurethane sponge.

[0074] In the following examples and comparative examples, the activated sludge was taken from Suzhou Lukong Environmental Protection, and the anaerobic fermentation wastewater came from Lukong Environmental Protection's anaerobic fermentation tank.

[0075] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods, and the materials and reagents used are commercially available.

[0076] Example 1

[0077] This embodiment provides a method for inducing the formation of activated granular sludge using polyurethane sponge, including the following steps:

[0078] S1. Add 200 mL of aerobic activated sludge to a beaker and add 800 mL of anaerobic fermentation wastewater for induction culture. During the culture, aerate the anaerobic fermentation wastewater using an oxygenation pump at 12-hour intervals, with each aeration lasting 0.5 hours. Replace the water sample every 5 days, removing all floating matter and leaving activated sludge with good settling properties. Subsequently, add 200 mL of aerobic activated sludge to the beaker gradually according to the formation of granular sludge.

[0079] S2. Connect five sponges with a thin plastic rod, and fix each sponge with a stainless steel ring. Before the sedimentation stage, suspend the sponges in the water and lower them to the sludge section after they have stabilized.

[0080] It should be noted that wastewater includes, but is not limited to, anaerobic fermentation wastewater.

[0081] In this embodiment, the COD concentration in the anaerobic fermentation wastewater reached 4000–8000 mg / L, a level of COD that makes pelleting of ordinary activated sludge difficult. However, the method of this invention, using polyurethane sponge as an exogenous carrier, can induce and promote pelleting of activated sludge and shorten its pelleting time.

[0082] Example 2

[0083] This embodiment provides a method for inducing the formation of activated granular sludge using polyurethane sponge, including the following steps:

[0084] S1. Add 200 mL of anaerobic activated sludge to a beaker and add 800 mL of anaerobic fermentation wastewater for induction culture. During the culture, completely seal the beaker with double-layer plastic wrap and store it in a sealed cabinet. Replace the water sample every 5 days and remove all floating matter, leaving activated sludge with good settling properties. Subsequently, add 200 mL of aerobic activated sludge to the beaker gradually according to the formation of granular sludge.

[0085] S2. Connect five sponges with a thin plastic rod, and fix each sponge with a stainless steel ring. Before the sedimentation stage, suspend the sponges in the water and lower them to the sludge section after they have stabilized.

[0086] Comparative Example 1

[0087] The difference between Comparative Example 1 and Example 1 is that polyurethane sponge was not used for induction during the cultivation of aerobic activated sludge. Without polyurethane sponge induction, it takes approximately 30 days to form granular sludge, while with polyurethane sponge induction, relatively stable granular sludge can be formed as early as day 20.

[0088] Comparative Example 2

[0089] The difference between Comparative Example 1 and Example 1 is that polyurethane sponge was not used for induction during the cultivation of anaerobic activated sludge. Without polyurethane sponge induction, it takes approximately 40 days to form granular sludge, while with polyurethane sponge induction, relatively stable granular sludge can be formed as early as day 35.

[0090] Experimental Results and Analysis

[0091] 1. Research on original activated sludge

[0092] Before sampling, thoroughly stir the mixture with a dropper and gently shake the sample tube to prevent flocculation and precipitation. Clean the glass slide with distilled water and dry it to prevent contamination from affecting observation. Use a pipette to draw 0.1 mL of sample from the middle of a 50 mL sample tube and place it on the glass slide. Cover it with a square coverslip; some may overflow, which should be wiped away with paper. Place the coverslip under a microscope, observe, and photograph the results.

[0093] By observing activated sludge under a microscope, the operating status and treatment efficiency of the wastewater treatment system can be determined. By dynamically observing the succession of the microbial community, combined with sludge color, settling ratio and SVI value, a basis can be provided for aeration volume, sludge discharge frequency and load control, thereby achieving process optimization and anomaly early warning.

[0094] Figure 1 These are microscopic images of aerobic and anaerobic activated sludge. Activated sludge contains a large number of microorganisms, such as sessile ciliates like Vorticella and Cyclops. Figure 1 Image 'a' shows aerobic activated sludge under 40x magnification. Microscopic images reveal tightly bound flocs with good coagulation, exhibiting irregular flocculent or lumpy morphology, predominantly yellowish-brown in color. The water between the flocs is clear, with no obvious sludge disintegration or large amounts of free bacteria observed. The SVI30 value is 103 mL / g, indicating good settling performance. Figure 1 b is anaerobic activated sludge magnified 40 times. The anaerobic sludge has a finer floc structure, with distinct and dense bacterial flocs, an SVI30 value of 134 mL / g, a dark brown color, and moderate settling performance. Overall, the microorganisms are mostly in an active state.

[0095] 2. Raw water quality testing research

[0096] The COD, TP, TN, and ammonia nitrogen of the raw water were tested using the national standard method. By testing the raw water quality, the operating conditions during the experiment (such as hydraulic retention time and aeration rate) can be adjusted based on the obtained parameters to create a suitable environment for microbial growth and promote the effective cultivation and stability of granular sludge. The raw water quality is shown in Table 1.

[0097] Table 1 Raw water quality parameters

[0098] index COD TN TP <![CDATA[NH3-N]]> Value (mg / L) 4782 201 78 85

[0099] Analysis of the raw water quality test results revealed that the anaerobic digestion broth had a COD of 4782 mg / L, TN of 201 mg / L, TP of 78 mg / L, ammonia nitrogen of 85 mg / L, and a pH of 6.8. The high C / N ratio is beneficial for denitrification; the high organic matter content provides a rich carbon source; and the high nitrogen and phosphorus content is advantageous for the subsequent cultivation of microorganisms capable of nitrogen and phosphorus removal. Simultaneously, during the subsequent granular sludge cultivation process, attention should be paid to parameters such as organic loading rate and dissolved oxygen, and operational strategies should be adjusted accordingly to cultivate stable granular sludge with good settling performance.

[0100] 3. Study on granular sludge induced by polyurethane sponge

[0101] like Figure 2 As shown, polyurethane sponge has a huge specific surface area and a porous structure. The cross-linked pore structure allows activated sludge to be adsorbed onto it, and the beneficial biological community between them is conducive to the enrichment of microorganisms and the maintenance of high activity. At the same time, its elasticity also gives it a certain degree of structural stability under aeration conditions.

[0102] Polyurethane sponges possess a large specific surface area, good hydrophilicity, porous structure, and stability. They provide abundant initial attachment sites and enrichment environments. The porous structure and surface properties facilitate the screening and enrichment of specific functional microorganisms, creating localized high-density microbial environments, indirectly regulating microbial community behavior, shortening the start-up cycle, and improving the overall performance and stability of the system. Polyurethane sponges can also form anaerobic zones internally, enhancing the biological activity and stress resistance of granular sludge and strengthening denitrification. These combined properties enable polyurethane sponges to promote the formation of granular sludge.

[0103] Macroscopic images of the actual granular sludge induced by polyurethane sponge allow for a comprehensive assessment of its overall performance and settling characteristics, while microscopic images reveal surface features and structural density. This combined macroscopic and microscopic observation method provides a complete view of the morphology of the granular sludge.

[0104] like Figure 3-4 As shown, under aerobic conditions on day 20, the granular sludge induced by polyurethane sponge had slightly looser and fewer particles, but some granular sludge could still be seen forming.

[0105] like Figure 5-6 As shown, under anaerobic conditions on day 35, the granular sludge induced by polyurethane sponge had a dark appearance, produced bubbles, and resulted in a slightly smaller number of granules.

[0106] 4. Wastewater Treatment Research

[0107] The initial granular sludge formed in the beaker is transferred to an aeration filter column, the structure of which is as follows: Figure 7As shown in the diagram, water is first introduced into the aeration filter column through inlet 2, and then air is introduced through inlet 1 to increase the dissolved oxygen content in the water, providing sufficient oxygen for the microorganisms and promoting their degradation of organic matter in the wastewater. During aeration, the aeration rate needs to be adjusted according to the growth and settling properties of the biofilm to ensure optimal treatment results.

[0108] During the experiment, 50 mL of water should be taken from sampling port 4 of the aeration filter column every other day and stored in the dark. Excess treated water in the filter should then be discharged through outlet 5, and 200 mL of water sample should be re-injected. Ammonia nitrogen, COD, and other indicators in the water sample should be measured. Care should be taken to avoid contamination during sampling to ensure the representativeness of the sample. The specific testing method is as follows:

[0109] (1) COD determination was performed using a rapid digestion method. The experimental procedure involved diluting the high-concentration water sample 50 times. Then, an appropriate amount of the diluted water sample was added to a COD pre-prepared tube (containing COD digestion solution 1 and COD digestion solution 2), and digested in an intelligent digester at 165℃ for 30 minutes. After digestion, the pre-prepared tube was cooled to room temperature, and its absorbance was measured at a wavelength of 600 nm using a spectrophotometer. The COD concentration was obtained by combining the standard curve and the dilution factor.

[0110] (2) The determination of TP was performed using the potassium persulfate digestion method. The experimental procedure was as follows: the water sample was diluted. Then, the diluted water sample was taken, potassium persulfate was added, and the sample was placed in a digester for digestion to oxidize various forms of phosphorus in the water sample into orthophosphate. After cooling to about 30°C, ascorbic acid and molybdate solution were added under acidic conditions. The orthophosphate reacted with the solution to form a phosphomolybdate blue complex. The absorbance was measured at a wavelength of 700 nm using a spectrophotometer. The total phosphorus concentration was calculated by multiplying the concentration by the dilution factor using a standard curve.

[0111] (3) The determination of TN was performed using the alkaline potassium persulfate digestion ultraviolet spectrophotometric method. The experimental procedure was as follows: the water sample was appropriately diluted. The diluted water sample was taken, and an alkaline potassium persulfate solution was added. The sample was then digested using a digester to oxidize the various forms of nitrogen-containing compounds in the water sample into nitrates. After cooling, the sample was acidified with hydrochloric acid, and then the absorbance at 220 nm and 275 nm was measured using an ultraviolet spectrophotometer. The concentration was calculated by using the obtained corrected absorbance and a pre-prepared nitrate standard curve. Finally, the total nitrogen concentration was obtained by multiplying by the dilution factor.

[0112] (4) Ammonia nitrogen was determined using the Nessler reagent spectrophotometric method. The experimental procedure involved diluting the original water sample. An appropriate amount of the diluted water sample was placed in a colorimetric tube, and potassium sodium tartrate solution and ammonia nitrogen detection reagent were added sequentially to initiate a colorimetric reaction. After standing for 10 minutes, the absorbance was measured at a wavelength of 420 nm using a spectrophotometer. The concentration of the diluted sample was calculated based on a pre-plotted ammonia nitrogen standard curve, and finally multiplied by the total dilution factor to obtain the original ammonia nitrogen concentration.

[0113] 4.1. Determination of COD

[0114] See Figure 8 Comparing the COD removal efficiency of polyurethane sponge-induced composite granular sludge under aerobic / anaerobic conditions, it was found that the COD removal efficiency under anaerobic conditions was significantly better than that under aerobic conditions. Specifically, the COD removal rate of anaerobic granular sludge reached 63.3% during the steady-state period, while the maximum COD removal rate of aerobic granular sludge during the steady-state period was 46.5%.

[0115] Anaerobic conditions are more effective for treating high-concentration COD. When treating high-concentration COD wastewater, anaerobic conditions are significantly superior to aerobic technologies due to their advantages such as high organic load carrying capacity, low energy consumption, low sludge production, and biogas energy recovery. However, the COD removal rate of anaerobic wastewater cannot reach more than 95%. Therefore, in practical applications, anaerobic and aerobic technologies are often combined, such as a combination strategy of anaerobic pretreatment + aerobic deep treatment, to achieve compliant discharge. At the same time, the biogas produced can cover part of the operating costs.

[0116] 4.2. Determination of TP

[0117] See Figure 9 Comparing the total phosphorus (TP) removal efficiency of polyurethane sponge-induced composite granular sludge in treating wastewater under aerobic / anaerobic conditions, it can be found that under aerobic conditions, the total phosphorus removal rate of polyurethane sponge-induced composite granular sludge can reach 77%, while under anaerobic conditions, the total phosphorus removal rate of the composite granular sludge system reaches a maximum of 56.5% during the stable period.

[0118] Biological removal of phosphorus (TP) primarily relies on the excessive phosphorus uptake by polyphosphate-accumulating bacteria (PABs) under aerobic conditions. Under anaerobic conditions, PPAs release phosphorus anaerobically, and the subsequent phosphorus precipitation synergistically releases phosphorus and accumulates carbon sources. Therefore, the higher removal rate measured under aerobic conditions reflects the phosphorus uptake activity of PPAs.

[0119] 4.3. Determination of TN

[0120] See Figure 10 Under anaerobic conditions, the TN removal rate of polyurethane sponge-induced composite granular sludge was 71.5%, while under aerobic conditions, the TN removal rate was 45.5%.

[0121] Traditional activated sludge lacks anoxic zones and has low denitrification efficiency, but granular sludge can form some anoxic zones inside, giving it an advantage in TN removal. The high specific surface area and high porosity of polyurethane sponge can enhance the adsorption and metabolic activity of nitrifying bacteria, further promoting TN removal.

[0122] 4.4. Determination of ammonia nitrogen

[0123] See Figure 11 Under anaerobic conditions, the polyurethane sponge-induced composite granular sludge achieved the highest ammonia nitrogen removal rate of 53.1%; under aerobic conditions, the final removal rate reached 78.2%.

[0124] The ammonia nitrogen removal rate under aerobic conditions is much higher than that under anaerobic conditions. This is mainly because the primary biological removal of ammonia nitrogen in wastewater is aerobic nitrification, where ammonia nitrogen is converted into nitrate nitrogen under aerobic conditions. Polyurethane sponges have higher porosity and surface hydrophilicity, which can promote the enrichment and metabolic activity of nitrifying bacteria, enhance their activity, and thus improve nitrogen removal efficiency under aerobic conditions.

[0125] In summary, this invention provides a cultivation strategy based on activated sludge granulation technology. By inoculating activated sludge into anaerobic digestate and combining it with an exogenous carrier, initial granular sludge induced by polyurethane sponge is obtained. This initial granular sludge is then used as seed sludge to drive the formation of subsequent granular sludge, thereby significantly shortening the granular sludge formation cycle. This activated granular sludge can effectively treat anaerobic digestate, providing a new approach and method for solving the problem of anaerobic digestate treatment.

[0126] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for inducing the formation of activated granular sludge using polyurethane sponge, characterized in that, Includes the following steps: S1. Add the activated sludge to be cultured into the culture container and add culture medium for induction culture; S2. Fix the polyurethane sponge to the rod and suspend it above the culture container so that the polyurethane sponge is immersed in the culture solution; after the activated sludge settles, adjust the height of the rod so that the polyurethane sponge descends into the activated sludge; The activated sludge to be cultivated is either aerobic or anaerobic activated sludge, and the culture medium is anaerobic fermentation wastewater.

2. The method for inducing the formation of activated granular sludge using polyurethane sponge according to claim 1, characterized in that: In step S2, the polyurethane sponge is pretreated before use. The pretreatment method is to treat the polyurethane sponge with low-temperature plasma to change its surface from hydrophobic to hydrophilic and generate oxygen-containing functional groups.

3. The method for inducing the formation of activated granular sludge using polyurethane sponge according to claim 1, characterized in that: In step S1, the volume ratio of the anaerobic fermentation wastewater to the activated sludge is 4:1; the COD concentration of the anaerobic fermentation wastewater is 4000-8000 mg / L, the TN concentration is 180-220 mg / L, the TP concentration is 65-90 mg / L, the ammonia nitrogen concentration is 70-90 mg / L, and the pH is 6.5-7.

0.

4. The method for inducing the formation of activated granular sludge using polyurethane sponge according to claim 1, characterized in that: In step S2, when the activated sludge is aerobic activated sludge, during the cultivation period, an oxygen pump is used to aerate the culture medium, with an aeration interval of 8 to 12 hours and an aeration time of 0.5 to 1 hour each time. Alternatively, when the activated sludge is anaerobic activated sludge, the culture container is sealed during the culture period and stored in a sealed space.

5. The method for inducing the formation of activated granular sludge using polyurethane sponge according to claim 1, characterized in that: In step S2, during the cultivation period, the culture medium is replaced every 3 to 6 days. The biofilm is separated from the polyurethane sponge by stirring, providing a suitable adhesion core for microorganisms.

6. The activated granular sludge obtained by the method according to any one of claims 1 to 5.

7. A reaction device for inducing the formation of activated granular sludge using polyurethane sponge, comprising a main reactor, characterized in that: The main reactor is equipped with a central chamber, an intermediate chamber, and an outer chamber arranged coaxially inside; a first channel connects the intermediate chamber and the central chamber; a second channel connects the intermediate chamber and the outer chamber; a filter is installed outside the main reactor; and the volume of the central chamber accounts for 10%-20% of the total volume. It also includes a polyurethane foam circulation unit for returning filtered polyurethane foam to the central warehouse.

8. The reaction apparatus according to claim 7, characterized in that: The polyurethane foam circulation unit includes a delivery pump and a return pipe. The inlet end of the return pipe is connected to the outlet of the filter, and the outlet end extends into the central silo.

9. The reaction apparatus according to claim 7, characterized in that: The outer walls of the central compartment, intermediate compartment, and outer compartment are provided with microflow holes, and the total area of ​​the microflow holes is less than 50% of the total cross-sectional area of ​​the first channel and the second channel.

10. The reaction apparatus according to claim 7, characterized in that: A retractable rod is provided inside the main reactor, the rod being used to fix the polyurethane foam. The rod body adopts a sleeve-type telescopic structure. Each section of the telescopic structure is used to fix polyurethane foam with different pore sizes. The outer layer of polyurethane foam has a pore size of 5-10mm, the middle layer of polyurethane foam has a pore size of 2-5mm, and the inner layer of polyurethane foam has a pore size of 0.5-2mm.

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