A method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions

Abstract

The present invention discloses a method for cultivating and stabilizing short-cut denitrification granular sludge in low-concentration wastewater conditions, including processes such as enhancing the aggregation capacity of flocculent sludge, increasing the content of the sludge calcium salt core, and controlling the particle size within an optimal range. The present invention can rapidly cultivate short-cut denitrification granular sludge with high granulation, stable morphology, and high nitrate removal efficiency from short-cut denitrification flocculent sludge in wastewater containing 20 to 70 mgN / L of nitrate. This method offers strong operational flexibility, significantly reduces reactor floor space, and reduces the capital construction costs of short-cut denitrification facilities.

Description

Technical Field

[0001] The invention relates to the technical field of short-cut denitrification granular sludge cultivation, and in particular to a cultivation and stabilization method of short-cut denitrification granular sludge under low-concentration wastewater conditions. Background Art

[0002] The treatment of nitrogen pollution in low-concentration wastewater has become a research focus in the water treatment field. Traditional activated sludge processes face challenges in removing nitrogen from low-concentration wastewater, such as low efficiency and high energy consumption. Therefore, short-cut denitrification technology, as a highly efficient and energy-saving denitrification method, has gradually become an ideal choice for treating low-concentration nitrogen-contaminated wastewater.

[0003] Short-cut denitrification, by partially reducing nitrate to nitrite, can achieve efficient nitrogen removal in a relatively short period of time, while reducing carbon source consumption and possessing good environmental adaptability. In this process, granular sludge, with its excellent settling properties and stability, is key to improving the efficiency of short-cut denitrification.

[0004] Compared to traditional suspended sludge, granular sludge has a stronger ability to withstand shock loads and can maintain efficient reaction performance under widely varying water quality conditions. Particularly in low-concentration wastewater, granular sludge can provide a larger specific surface area and higher microbial density, significantly improving denitrification rates and nitrogen removal efficiency.

[0005] Currently, several existing technologies have reported on technical solutions for cultivating and enriching short-range denitrification granular sludge. For example, patent specification CN118164613A discloses a dual-carbon source-driven apparatus and method for rapid enrichment of short-range denitrification granular sludge. Using glucose and sodium acetate as carbon sources, the granulation of the short-range denitrification sludge is achieved. The final short-range denitrification granular sludge contains granules with a particle size greater than 200 μm, accounting for more than 50% of the mixed sludge. Another example is patent specification CN113683192A, which discloses an apparatus and method for cultivating and enriching short-range denitrification granular sludge to provide electron acceptor nitrite nitrogen for anaerobic ammonium oxidation. The apparatus is started in sequencing batch mode and operated in continuous mode, shortening startup time, improving operational stability, and enhancing the formation of short-range denitrification granular sludge. Upon successful acclimation, the dry weight of granules with an average particle size greater than 1.0 mm accounts for more than 50% of the total sludge dry weight.

[0006] In fact, granular sludge particle size is a key factor influencing its reaction performance. Research has shown that the ideal particle size range for short-range denitrification granular sludge is 0.5 to 2 mm. Granular sludge within this range not only exhibits good settling properties and solid-liquid separation, but also provides ample attachment space for denitrifying bacteria, optimizing reaction kinetics and promoting nitrate reduction. Too small a particle size can lead to poor sludge settling performance and affect effluent quality, while too large a particle size can limit mass transfer and affect reaction efficiency.

[0007] Therefore, keeping the granular sludge within the particle size range of 0.5 to 2 mm is the key to achieving efficient short-range denitrification. Summary of the Invention

[0008] Based on this background, the present invention proposes a method for cultivating and stabilizing short-range denitrification granular sludge in low-concentration wastewater. By controlling the particle size and settleability of the granular sludge, the denitrification process is optimized, achieving efficient and stable nitrogen removal. This method, based on short-range denitrification flocculent sludge, is suitable for treating nitrogen pollution in low-concentration wastewater, offering high operational flexibility and stable treatment results.

[0009] The specific technical solutions are as follows:

[0010] A method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions, comprising the steps of:

[0011] (1) Strengthening the aggregation capacity of flocculent sludge: The short-cut denitrification flocculent sludge is inoculated into a sequencing batch reactor, and the nitrate concentration in the influent of the sequencing batch reactor is 20 mgN / L to 70 mgN / L (e.g., 55-65 mgN / L, etc.). The sequencing batch reactor is operated in a typical cycle of anoxic stirring-anoxic standing, with water added before anoxic stirring and water discharged before anoxic standing. By extending the sludge age, the hydrophobicity of the extracellular polymers of the flocculent sludge is increased, so that the SVI5 is reduced to below 300 mL / g, and can be further reduced to below 200 mL / g;

[0012] (2) Increasing the content of calcium salt core in sludge: by increasing the proportion of anoxic standing time in a typical cycle, the calcium ion content of sludge reaches more than 1% of the sludge dry weight (unit can be gSS), thereby increasing the sedimentation and stability of granular sludge;

[0013] (3) Control the particle size within the optimal range: According to the nitrate concentration of the influent, the typical number of cycles of the sequencing batch reactor per day is adjusted by changing the operating time of a single typical cycle (for example, 8 times, etc.), so that the volumetric denitrification load of the sequencing batch reactor is in the range of 0.20 to 0.35 gN / L / d (for example, 0.24 to 0.26 gN / L / d, etc.) to maintain the stable form of the granular sludge.

[0014] The present invention adopts an operation mode of alternating anoxic stirring and anoxic standing in a sequencing batch reactor, improves the hydrophobicity of sludge extracellular polymers by controlling the sludge age, increases the content of sludge calcium salt core by adjusting the standing time of a typical cycle, optimizes the volumetric denitrification load rate by controlling the number of cycles, and stabilizes the sludge particle size in an ideal range of 0.5 to 2 mm.

[0015] The present invention can be used for nitrate wastewater containing 20 to 70 mgN / L. Starting from short-term denitrification flocculent sludge, it can quickly cultivate short-term denitrification granular sludge with a high degree of granulation, stable morphology and high nitrate removal efficiency. It has strong operational flexibility, can greatly save the reactor floor space, and reduce the capital construction cost of short-term denitrification facilities.

[0016] In the present invention, SVI5 refers to the volume (in milliliters) occupied by 1 gram of dry sludge in the wet state after the mud-water mixture has been settled for 5 minutes.

[0017] In some embodiments, in the method for cultivating and stabilizing the short-cut denitrification granular sludge under low-concentration wastewater conditions, in step (1), the inoculation amount of the short-cut denitrification flocculent sludge in the sequencing batch reactor can be 2.0-4.0 gSS / L.

[0018] In some embodiments, in the method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions, in step (1), the sludge age is extended when the sludge concentration in the sequencing batch reactor is lower than 2.0 gSS / L.

[0019] In some embodiments, in the method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions, in step (1), the sludge age can be extended to 20 to 60 days, for example, 40 days.

[0020] In some embodiments, the cultivation and stabilization method of the short-cut denitrification granular sludge under low-concentration wastewater conditions, the COD and NO3 in the influent of the sequencing batch reactor - The mass concentration ratio of -N can be 2.5 to 3.0:1 to ensure that the nitrate removal rate and nitrite accumulation rate are both stable at more than 80%.

[0021] In some embodiments, in the method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions, the COD concentration in the influent of the sequencing batch reactor can be 150-180 mgCOD / L.

[0022] In some embodiments, in the method for cultivating and stabilizing short-range denitrifying granular sludge under low-concentration wastewater conditions, anoxic conditions refer to maintaining a dissolved oxygen concentration within the sequencing batch reactor at a stable level below 0.5 mg / L. During the anoxic stirring process, the dissolved oxygen concentration can be controlled by controlling the stirring speed of the sequencing batch reactor to maintain anoxic conditions.

[0023] In some embodiments, in the method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions, in any typical cycle, the total volume of the sludge water during anoxic standing can be 25% to 75% of the total volume of the sludge water during anoxic stirring, for example 50%.

[0024] In some embodiments, in the method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions, for any two adjacent typical cycles, water can be added before anoxic stirring in the latter typical cycle to a total volume consistent with the total volume of mud and water during anoxic stirring in the previous typical cycle.

[0025] In some embodiments, in the method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions, in step (2), the proportion of anoxic standing time in a typical cycle can be increased to 1 / 3 to 5 / 6, and further, the proportion of anoxic standing time in a typical cycle can be increased to 1 / 2 to 5 / 6.

[0026] The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions, wherein the mode particle size, median particle size and average particle size of the short-cut denitrification granular sludge obtained in step (3) are all greater than 0.5 mm, and the number of particles in the short-cut denitrification granular sludge with a particle size range of 0.5 to 2 mm accounts for greater than 60%, and further greater than 65%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions of the present invention can be used for wastewater containing nitrate of 20 to 70 mgN / L, starting from short-cut denitrification flocculent sludge, to quickly cultivate short-cut denitrification granular sludge with a high degree of granulation, stable morphology and high nitrate removal efficiency.

[0029] The method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions of the present invention has strong operational flexibility, can greatly save the floor space of the reactor, and reduce the capital construction cost of the short-range denitrification facility. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the particle size distribution diagram of the short-range denitrification granular sludge obtained in Example 1.

[0031] Figure 2 This is the particle size distribution diagram of the short-range denitrification granular sludge obtained in Example 2. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0033] In the following examples, the operating methods without specifying specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer.

[0034] Example 1:

[0035] In this embodiment, a method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions is used. A sequencing batch reactor with an effective volume of 5.3 L is used to simulate low-concentration wastewater conditions (the influent COD concentration is controlled at 150-180 mgCOD / L, the nitrate nitrogen concentration is controlled at 55-65 mgN / L, and the COD and NO3 in the influent are controlled at 150-180 mgCOD / L and 55-65 mgN / L, respectively). - The ratio of sludge to nitrogen (N) was adjusted to 2.5-3.0:1. Short-cut denitrification flocculent sludge was inoculated into a sequencing batch reactor (SBR) with an initial inoculum concentration of 2.0 g SS / L. A strategy of alternating anoxic stirring and anoxic settling was employed. During the anoxic stirring phase, the stirring speed was adjusted to maintain a stable dissolved oxygen concentration below 0.5 mg / L. A typical cycle of anoxic stirring and anoxic settling was used. The sludge volume was filled to capacity before each anoxic stirring phase and drained to half its volume before each anoxic settling phase. By extending the sludge age to 40 days, the sludge suspension index (SVI5) was reduced to 99.4 mL / g. The settling time in the typical cycle was then increased to 5 / 6 of the total cycle, resulting in a calcium ion content of 6% of the sludge dry weight, thereby enhancing the formation of calcium salt cores. Furthermore, with eight cycles per day, the SBR volumetric denitrification load was stably controlled within the range of 0.24-0.26 g N / L / d.

[0036] After a period of continuous operation, the cultivation method of this embodiment successfully prepared short-range denitrification granular sludge with a high degree of granulation, stable morphology, and a nitrate removal efficiency continuously maintained at more than 80%, fully meeting the requirements of low-concentration wastewater treatment.

[0037] like Figure 1 As shown, the peak value of the particle size distribution of the final granular sludge was determined to be about 756 μm, the median particle size (DV50) was about 769 μm, and the number of particles with a diameter ranging from 0.5 to 2 mm accounted for more than 76%.

[0038] Example 2:

[0039] In this embodiment, a method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions is provided. A sequencing batch reactor with an effective volume of 5.3L is used to simulate a low-concentration wastewater environment. Granular sludge is cultivated by alternating anoxic stirring and anoxic standing. The dissolved oxygen concentration is stabilized below 0.5mg / L by regulating the stirring speed during the anoxic stirring stage. In addition, anoxic stirring-anoxic standing is used as a typical cycle. The water is filled to the capacity before each anoxic stirring, and the water is drained to the remaining half volume before each anoxic standing. In specific operations, the influent COD concentration is controlled within the range of 150-180mgCOD / L, the nitrate nitrogen concentration is maintained at 55-65mgN / L, and at the same time, the COD and NO3 in the influent are ensured to be equal. - -N ratio is controlled at 2.5 to 3.0:1. Short-range denitrification flocculent sludge is used as the inoculum sludge, and the concentration of the addition is 2.0gSS / L. During the operation, the sludge age is first extended to 40 days to reduce the sludge suspension index SVI5 to 176.2mL / g; then, in a typical cycle, the standing time is extended to 1 / 2 of the entire cycle, so that the calcium ion content in the sludge dry weight reaches 1.1%, effectively enhancing the sedimentation and stability of the granular sludge; during the experimental period, the reactor maintains 8 cycles per day, so that the volumetric denitrification load is controlled in the range of 0.24 to 0.26gN / L / d.

[0040] After a period of continuous operation, the prepared short-range denitrification granular sludge showed a high degree of granulation and excellent structural stability, and the nitrate removal efficiency was always maintained above 80%, fully meeting the requirements of low-concentration wastewater treatment.

[0041] like Figure 2 As shown, the peak value of the particle size distribution of the final granular sludge was determined to be about 589 μm, the median particle size (DV50) was about 578 μm, and the number of particles with a particle size range of 0.5 to 2 mm accounted for more than 65%.

[0042] In summary, the present invention optimizes the denitrification process by controlling the particle size and settleability of granular sludge, thereby achieving efficient and stable nitrogen removal. The method of the present invention, which uses short-term denitrification of flocculent sludge, is suitable for treating nitrogen pollution in low-concentration wastewater, offering high operational flexibility and stable treatment results.

[0043] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions, characterized in that: Including steps: (1) Strengthening the aggregation capacity of flocculent sludge: Short-cut denitrification flocculent sludge was inoculated into a sequencing batch reactor. The nitrate concentration in the influent of the sequencing batch reactor was 20 mgN / L to 70 mgN / L. The sequencing batch reactor was operated in a typical cycle of anoxic stirring-anoxic standing. The water was added before anoxic stirring and drained before anoxic standing. By extending the sludge age, the hydrophobicity of the extracellular polymers of the flocculent sludge was increased, and the SVI5 was reduced to below 300 mL / g. (2) Increase the content of calcium salt core in sludge: by increasing the proportion of anoxic standing time in a typical cycle, the calcium ion content of sludge reaches more than 1% of the sludge dry weight, thereby increasing the sedimentation and stability of granular sludge; (3) Control the particle size within the optimal range: According to the nitrate concentration of the influent, the typical number of cycles of the sequencing batch reactor per day is adjusted by changing the operating time of a single typical cycle, so that the volumetric denitrification load of the sequencing batch reactor is in the range of 0.20 to 0.35 gN / L / d to maintain the stable form of the granular sludge.

2. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: In step (1), the inoculum amount of the short-cut denitrification flocculent sludge in the sequencing batch reactor is 2.0-4.0 gSS / L.

3. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1 or 2, characterized in that: In step (1), when the sludge concentration in the sequencing batch reactor is lower than 2.0 gSS / L, the sludge age is extended.

4. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: In step (1), the sludge age is extended to 20 to 60 days.

5. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: COD and NO3 in the influent of sequencing batch reactor - The mass concentration ratio of -N is 2.5 to 3.0:1 to ensure that the nitrate removal rate and nitrite accumulation rate are both stable at more than 80%.

6. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: Anoxic means that the dissolved oxygen concentration in the sequencing batch reactor is stable below 0.5 mg / L; During the anoxic stirring process, the dissolved oxygen concentration is controlled under anoxic conditions by controlling the stirring speed of the sequencing batch reactor.

7. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: In any typical cycle, the total volume of muddy water during anoxic standing is 25 to 75% of the total volume of muddy water during anoxic stirring.

8. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: For any two adjacent typical cycles, water is added before anoxic mixing in the latter typical cycle until the total volume of mud and water is consistent with that during anoxic mixing in the former typical cycle.

9. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: In step (2), the proportion of hypoxic rest time in a typical cycle is increased to 1 / 3 to 5 / 6.

10. The method for cultivating and stabilizing short-cut denitrification granular sludge under low-concentration wastewater conditions according to claim 1, characterized in that: The mode particle size, median particle size and average particle size of the short-cut denitrification granular sludge obtained in step (3) are all greater than 0.5 mm, and the number of particles in the short-cut denitrification granular sludge with a particle size range of 0.5 to 2 mm accounts for more than 60%.

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