Culture and stability maintaining method for short-cut denitrification granular sludge under low-concentration wastewater condition

Abstract

The invention discloses a method for culturing and maintaining stability of short-cut denitrification granular sludge under a low-concentration wastewater condition. The method comprises the processes of enhancing the flocculent sludge aggregation capability, increasing the content of sludge calcium salt cores, controlling the particle size of particles to be in an optimal range and the like. The short-cut denitrification granular sludge which is high in granulation degree, stable in form and high in nitrate removal efficiency can be rapidly cultured from short-cut denitrification flocculent sludge by aiming at the nitrate wastewater containing 20-70mgN / L, the operation flexibility is relatively high, the occupied area of a reactor can be greatly saved, and the capital construction cost of short-cut denitrification facilities is reduced.

Description

Technical Field

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

[0002] As water pollution becomes increasingly serious, the treatment of nitrogen pollution in low-concentration wastewater has become a research focus in the field of water treatment. The traditional activated sludge method faces problems such as low efficiency and high energy consumption in the denitrification process of low-concentration wastewater. Therefore, short-range denitrification technology, as an efficient and energy-saving denitrification method, has gradually become an ideal choice for treating low-concentration nitrogen-polluted wastewater.

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

[0004] Compared with traditional suspended sludge, granular sludge has stronger resistance to shock loads and can maintain efficient reaction performance under highly variable water quality conditions. Especially in low-concentration wastewater, granular sludge can provide a larger specific surface area and higher microbial density, thereby significantly improving the denitrification rate and nitrogen removal efficiency.

[0005] At present, some prior art reports have reported technical solutions for cultivating and enriching short-range denitrification granular sludge. For example, the patent specification with publication number CN118164613A discloses a device and method for rapid enrichment of short-range denitrification granular sludge driven by dual carbon sources, and uses glucose and sodium acetate as carbon sources to achieve granulation of short-range denitrification sludge. In the final short-range denitrification granular sludge, the proportion of granular sludge with a particle size greater than 200 μm in the mixed sludge is greater than 50%. For another example, the patent specification with publication number CN113683192A discloses a device and method for cultivating and enriching short-range denitrification granular sludge that provides electron acceptor nitrite nitrogen for anaerobic ammonia oxidation. It is started in a batch water inlet mode and operated in a continuous water inlet mode, which shortens the startup time, improves the operation stability, and strengthens the formation of short-range denitrification granular sludge. When the granular sludge is successfully domesticated, the dry weight of granular sludge with an average particle size greater than 1.0 mm accounts for more than 50% of the dry weight of the sludge.

[0006] In fact, the particle size of granular sludge is a key factor affecting its reaction performance. Studies have shown that the ideal particle size range of short-range denitrification granular sludge is 0.5-2 mm. Granular sludge within this range not only has good sedimentation and solid-liquid separation performance, but also can provide sufficient attachment space for denitrifying bacteria, optimize reaction kinetics, and promote nitrate reduction reactions. Too small a particle size may lead to poor sludge sedimentation performance and affect effluent water quality; while too large a particle size may lead to limited 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 the above background, the present invention proposes a short-range denitrification granular sludge cultivation and stabilization method under low-concentration wastewater conditions, which optimizes the denitrification process by controlling the particle size and sedimentation of the granular sludge, thereby achieving efficient and stable nitrogen removal. Starting from short-range denitrification flocculent sludge, this method is suitable for the treatment of nitrogen pollution in low-concentration wastewater, and has high operational flexibility and stable treatment effect.

[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-range denitrification flocculent sludge is inoculated into a sequencing batch reactor. 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). The sequencing batch reactor is operated in a typical cycle of anoxic stirring-anoxic standing. The water is introduced before anoxic stirring and the water is discharged before anoxic standing. By extending the sludge age, the hydrophobicity of the extracellular polymers of the flocculent sludge is increased, so that the SVI 5 Reduced to below 300 mL / g, and 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), so as to increase the sedimentation and stability of granular sludge;

[0013] (3) Controlling the particle size within the optimal range: According to the influent nitrate concentration, the typical number of cycles per day of the sequencing batch reactor is adjusted by changing the operating time of a single typical cycle (e.g., 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 (e.g., 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 inner 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, short-term denitrification granular sludge with high granulation degree, stable morphology and high nitrate removal efficiency can be quickly cultivated. It has strong operational flexibility, can greatly save the floor space of the reactor, and reduce the capital construction cost of the short-term denitrification facility.

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

[0017] In some embodiments, in the method for culturing and stabilizing 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 culturing and stabilizing short-range 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 culturing 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, such as 40 days.

[0020] In some embodiments, the method for cultivating and stabilizing the short-range denitrification granular sludge under low-concentration wastewater conditions, the COD and NO in the influent of the sequencing batch reactor 3 - 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-range 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 denitrification granular sludge under low-concentration wastewater conditions, anoxic means that the dissolved oxygen concentration in the sequencing batch reactor is stabilized below 0.5 mg / L. During the anoxic stirring process, the dissolved oxygen concentration can be controlled to be in anoxic conditions by controlling the stirring speed of the sequencing batch reactor.

[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, before anoxic stirring is performed in the latter typical cycle, water can be added to be 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 culturing 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-range denitrification granular sludge under low-concentration wastewater conditions, wherein the mode particle size, median particle size and average particle size of the short-range denitrification granular sludge obtained in step (3) are all greater than 0.5 mm, and the number of particles in the short-range denitrification granular sludge with a particle size in the 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-range 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-range denitrification flocculent sludge, to quickly cultivate short-range denitrification granular sludge with high granulation degree, 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 in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0033] The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0034] Embodiment 1:

[0035] In this embodiment, a method for cultivating and stabilizing short-range 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 influent COD and NO 3 - -N ratio was adjusted to 2.5-3.0:1). The short-range denitrification flocculent sludge was inoculated into the sequencing batch reactor, with an initial inoculation sludge concentration of 2.0gSS / L, and an alternating strategy of anoxic stirring and anoxic standing was adopted. During the anoxic stirring stage, the dissolved oxygen concentration was stabilized below 0.5mg / L by adjusting the stirring speed. Anoxic stirring-anoxic standing was used as a typical cycle. Water was added to the tank before each anoxic stirring, and water was drained to half the remaining volume before each anoxic standing. The sludge age was first extended to 40 days to make the sludge suspension index SVI 5 The concentration of calcium ions in the sludge was reduced to 99.4 mL / g; the standing time in the typical cycle was extended to 5 / 6 of the entire cycle, so that the calcium ion content in the dry weight of the sludge reached 6%, thereby enhancing the formation of the calcium salt core; further, under the condition of 8 cycles per day, the volumetric denitrification load of the sequencing batch reactor was stably controlled in the range of 0.24-0.26 gN / L / d.

[0036] After a period of continuous operation, the cultivation method of this embodiment successfully prepared short-range denitrification granular sludge with high granulation degree, stable morphology and nitrate removal efficiency continuously maintained at more than 80%, which fully met 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 particle size range of 0.5 to 2 mm accounted for more than 76%.

[0038] Embodiment 2:

[0039] In this embodiment, a method for cultivating and stabilizing short-range denitrification granular sludge under low-concentration wastewater conditions is used. 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 at below 0.5mg / L by regulating the stirring speed during the anoxic stirring stage. In addition, taking anoxic stirring-anoxic standing as a typical cycle, the water is filled to full before each anoxic stirring, and the water is drained to half the remaining volume before each anoxic standing. In specific operations, the influent COD concentration is controlled within the range of 150-180mgCOD / L, and the nitrate nitrogen concentration is maintained at 55-65mgN / L, while ensuring that the COD and NO in the influent are consistent. 3 - -N ratio is controlled at 2.5-3.0:1. Short-range denitrification flocculent sludge is used as inoculated sludge, and the concentration is 2.0gSS / L. During operation, the sludge age is first extended to 40 days to make the sludge suspension index SVI 5 Then, in a typical cycle, the standing time was extended to 1 / 2 of the entire cycle, so that the calcium ion content in the dry weight of the sludge reached 1.1%, effectively enhancing the sedimentation and stability of the granular sludge; during the experimental period, the reactor maintained 8 cycles per day, so that the volumetric denitrification load was controlled in the range of 0.24-0.26gN / 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 sedimentation of granular sludge, thereby achieving efficient and stable nitrogen removal. The method of the present invention starts from short-range denitrification flocculent sludge, is suitable for the treatment of nitrogen pollution in low-concentration wastewater, and has high operational flexibility and stable treatment effect.

[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-range denitrification granular sludge under low-concentration wastewater conditions, characterized in that: Includes steps: (1) Strengthening the aggregation capacity of flocculent sludge: Inoculate the short-range denitrification flocculent sludge into a sequencing batch reactor. The nitrate concentration in the influent of the sequencing batch reactor is 20 mgN / L to 70 mgN / L. The sequencing batch reactor is operated in a typical cycle of anoxic stirring-anoxic standing. The water is added before anoxic stirring and the water is drained before anoxic standing. The hydrophobicity of the extracellular polymers of the flocculent sludge is increased by extending the sludge age, so that the SVI5 is reduced to below 300 mL / g. (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 dry weight of sludge, thereby increasing the sedimentation and stability of granular sludge; (3) Control the particle size within the optimal range: According to the influent nitrate concentration, 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 0.20-0.35 gN / L / d to maintain the stable form of the granular sludge.

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

3. The method for cultivating and stabilizing short-range 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-range 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-range 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-range 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-range 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 anaerobic static state is 25-75% of the total volume of muddy water during anaerobic stirring state.

8. The method for cultivating and stabilizing short-range 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 previous typical cycle.

9. The method for cultivating and stabilizing short-range 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-range 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-range denitrification granular sludge obtained in step (3) are all greater than 0.5 mm, and the number of particles in the short-range denitrification granular sludge with a particle size ranging from 0.5 to 2 mm accounts for more than 60%.

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