Method for rapid cultivation and stable operation of low-concentration municipal sewage aerobic granular sludge

Abstract

This application relates to the field of wastewater treatment technology, specifically disclosing a method for rapid cultivation and stable operation of aerobic granular sludge in low-concentration municipal wastewater. The method includes adding sodium acetate, potassium dihydrogen phosphate, and allyl thiourea to low-concentration municipal wastewater with COD ≤ 200 mg / L. After addition, the COD concentration of the influent increases by 100–200 mg / L, and the PO4 concentration decreases by [missing value]. 3‑ The concentration of -P is increased by 2.5–5.0 mg / L, and the concentration of ATU is increased by 5–10 mg / L. Then, activated sludge from a conventional municipal wastewater treatment plant is inoculated into the reactor at a concentration of 3000–6000 mg MLSS / L. The aerobic granular sludge is cultivated in cycles of 3–4 hours, following the sequence of influent, stirring, aeration, sedimentation, and effluent discharge. The volume exchange ratio per cycle is 33%–50%. When granulation reaches over 80%, the system enters a stable operation period. At this time, only low-concentration municipal wastewater is used as influent, with each cycle lasting 4–6 hours, and the volume exchange ratio per cycle increasing to 50%–75%. The purpose of this patent is to solve the problem of the long start-up period and difficulty in maintaining stable operation when cultivating aerobic granular sludge using low-concentration municipal wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for rapid cultivation and stable operation of aerobic granular sludge in low-concentration municipal wastewater. Background Technology

[0002] Aerobic granular sludge is a microbial aggregate formed using the principle of microbial self-flocculation. Compared with the traditional activated sludge process, the aerobic granular sludge process has many advantages, such as better sludge-water separation performance, high volumetric loading, simultaneous nitrogen and phosphorus removal, and resistance to shock loads and toxic substances. It can save about 75% of the land area and about 50% of the operating energy consumption. High-value-added products such as alginate polymers can also be extracted from aerobic granular sludge, and it is recognized as a new generation of biological wastewater treatment technology.

[0003] Practice has shown that cultivating aerobic granular sludge using low-concentration municipal wastewater often requires more than six months to achieve complete granulation. There are three main reasons for this: ① Low-concentration wastewater makes it difficult to create an ideal "feast-hunger" alternating environment, which is one of the necessary conditions for the formation of aerobic granular sludge (except for special cases such as nitrified granular sludge); ② Actual low-concentration municipal wastewater has a complex composition, with a large proportion of particulate COD and very limited high-quality carbon sources, making it difficult for microorganisms to store it as an internal carbon source, thus affecting the granulation process; ③ Current cases of aerobic granular sludge treatment of actual municipal wastewater use employ operating methods that are basically the same as those used in small-scale experiments based on artificial water distribution, without targeted improvements or optimizations. Although aerobic granular sludge can eventually be formed, the start-up period is long and difficult to maintain stably. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical problem solved by this invention is to provide a method for the rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal wastewater, thereby solving the problem that the start-up period for cultivating aerobic granular sludge from low-concentration municipal wastewater is long and it is difficult to maintain stability in existing technologies.

[0005] To solve the above problems, the technical solution adopted in this invention is: a method for rapid cultivation and stable operation of aerobic granular sludge in low-concentration municipal wastewater, comprising the following steps:

[0006] S100 influent: Sodium acetate, potassium dihydrogen phosphate, and propylene thiourea are added to low-concentration municipal wastewater with COD ≤ 200 mg / L; after addition, the COD concentration of the influent increases by 100-200 mg / L, and the PO4 concentration increases by 100-200 mg / L. 3- -P concentration increased by 2.5–5.0 mg / L, and ATU concentration increased by 5–10 mg / L;

[0007] S200 sludge inoculation: Inoculate the reactor with activated sludge from a conventional municipal wastewater treatment plant at a concentration of 3000–6000 mg MLSS / L;

[0008] Cultivation of S300 aerobic granular sludge: The reactor cycle length during the cultivation period is 3-4 hours, and the reactor is operated in the following order: slow upflow influent, stirring, aeration, sedimentation, and drainage. The influent time is 60 minutes, stirring time is 0-60 minutes, sedimentation time is 3-50 minutes, and drainage time is 3-10 minutes. The aeration time is determined by subtracting the influent, stirring, sedimentation, and drainage time from the cycle length. The volume exchange ratio of each cycle is 33%-50%.

[0009] S400 Stable Operation Period: When the mass fraction of granular sludge in the reactor reaches 80% or more of the total sludge, the reactor enters the stable operation period. The granular sludge particle size is greater than 0.2 mm. At this time, only low-concentration municipal sewage with COD ≤ 200 mg / L is used as influent. Each cycle of the stable operation period lasts 4-6 hours, and the reactor operates in the following sequence: upflow slow influent, stirring, aeration, sedimentation, and drainage. Influent time is 60-90 minutes, stirring time is 0-90 minutes, sedimentation time is 3-25 minutes, and drainage time is 3-10 minutes. The aeration time is determined by subtracting the influent, stirring, sedimentation, and drainage time from the cycle duration. The volume exchange ratio of each cycle increases to 50%-75%.

[0010] The technical principles and beneficial effects of this solution are as follows:

[0011] 1) During the granular sludge cultivation period, a composite agent consisting of sodium acetate, phosphate, and allyl thiourea is added. Sodium acetate is a common carbon source, easily converted into an internal carbon source by microorganisms in the activated sludge, such as polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria. Potassium dihydrogen phosphate is added to maintain a suitable C / P ratio, allowing the formed granular sludge to accumulate more polyphosphate-accumulating bacteria, thus improving phosphorus removal. Allyl thiourea inhibits nitrification, preventing the rbCOD of the influent from being consumed by denitrifying bacteria, thereby affecting the proliferation of polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria. In summary, this composite agent promotes the proliferation of polyphosphate-accumulating bacteria through the above multiple effects. Polyphosphate-accumulating bacteria are typical slow-growing microorganisms, which are conducive to the formation of compact granular sludge and can rapidly cultivate aerobic granular sludge. At the same time, the enrichment of polyphosphate-accumulating bacteria also ensures efficient phosphorus removal.

[0012] 2) During the granular sludge cultivation and stable operation periods, by controlling the stirring time of each cycle, the external carbon source is converted into the internal carbon source of the microorganisms to the maximum extent, avoiding various negative impacts caused by the aerobic degradation of rbCOD, such as the rapid growth of common heterotrophic bacteria (OHOs), sludge finger growth, or even sludge filamentous bacteria expansion, which leads to slow and / or unstable formation of granular sludge.

[0013] 3) During the stable operation period, the nitrate nitrogen and nitrite nitrogen (NO) produced in the previous nitration reaction are diluted by increasing the volume exchange ratio. x - To reduce its impact on polyphosphate-accumulating bacteria; by controlling dissolved oxygen and relying on the characteristics of aerobic granular sludge, simultaneous nitrification and denitrification phosphorus removal are achieved, ensuring effluent quality while reducing NO in the reactor. x - And its adverse effects on the anaerobic phosphorus release process of polyphosphate-accumulating bacteria.

[0014] 4) Experimental testing showed that after 20 days of operation according to the set cycle and cultivation parameters during the aerobic granular sludge cultivation period, visible aerobic granular sludge (i.e., sludge particle size greater than 0.2 mm) appeared in the reactor. Continuing operation for another 15-30 days, the granular sludge accounted for over 80% of the total sludge mass, achieving SVI. 30 The concentration of sludge in the reactor is less than 50 mL / g, and the MLSS concentration can reach over 6000 mg / L. The entire aerobic granular sludge cultivation process takes 35–50 days, far less than the more than 6 months required for granulation under current low-concentration municipal wastewater conditions.

[0015] After 130 days of stable operation according to the set cycle and cultivation parameters, the granular sludge in the system remained stable, with the average particle size increasing to 0.64 mm. The system's average removal rates for COD, ammonia nitrogen, total nitrogen, and total phosphorus were 88%, 94%, 76%, and 99%, respectively.

[0016] Furthermore, in steps S300 and S400, the stirring time is controlled so that at the end of stirring, the bCOD content in the mixture is less than 20% of the total bCOD. The control of the stirring time is mainly to ensure that the bCOD removal rate in the anaerobic stage is not less than 80%. If the condition that the bCOD content in the mixture is less than 20% of the total bCOD is already met, stirring is not required.

[0017] Furthermore, in step S300, the sedimentation time is shortened by 0.5 to 1.5 minutes every 6 to 8 cycles after the initial time is determined, until sludge with a sedimentation rate greater than 6 m / h is screened out. By gradually reducing the sedimentation time, hydraulic selective pressure can be formed to wash sludge with poor settling properties, and sludge with good settling properties can be screened out; thereby shortening the aerobic granular sludge cultivation time.

[0018] Furthermore, in step S300, the dissolved oxygen concentration in the mixed liquor is controlled at 1.5–2.5 mg / L during the aeration stage. When the dissolved oxygen concentration is maintained at 2.0 ± 0.5 mg / L, sufficient oxygen can be provided for polyphosphate-accumulating bacteria, promoting their growth and reproduction, thereby enhancing the phosphorus removal effect of the system.

[0019] Furthermore, in step S400, the initial dissolved oxygen concentration for each aeration cycle is controlled at 1.5–2.5 mg / L. When the ammonia nitrogen concentration drops to 3 mg / L, the dissolved oxygen concentration drops to 0.2–0.8 mg / L. This promotes simultaneous nitrification, denitrification, and phosphorus removal, obtaining high-quality effluent while also reducing NO remaining in the reactor. x - The content should be kept as low as possible to reduce its consumption of external carbon sources in the influent, allowing polyphosphate-accumulating bacteria to release phosphorus more fully. Attached Figure Description

[0020] Figure 1 This is a graph showing the SVI variation according to an embodiment of the present invention.

[0021] Figure 2 This is a morphological diagram of the granular sludge cultivated according to an embodiment of the present invention.

[0022] Figure 3 This is a diagram illustrating the COD removal effect of an embodiment of the present invention. an : Anaerobic end COD, COD eff : Effluent COD,).

[0023] Figure 4 The nitrogen and phosphorus in the effluent of this invention are as follows: Detailed Implementation

[0024] The following detailed description illustrates the specific implementation method:

[0025] This embodiment is a pilot-scale experiment demonstrating the application of this invention to treat low-concentration municipal wastewater. The SBR reactor used in the experiment has a total height of 3 meters and an inner diameter of 43 centimeters. The composition of the low-concentration municipal wastewater treated is as follows (unit: mg / L): COD Cr 51–178; BOD5 32.1–76.4; NH3-N 10.2–29.1; TN 11.7–36.4; TP 0.72–2.81; SS 45–143. The activated sludge used for inoculation was taken from a full-scale wastewater treatment plant that treated this wastewater. The sludge concentration was MLSS = 4300 mg / L, and the sludge volume index (SVI) was 45–143 mg / L. 30 =147 mg / L. The water temperature was 19–30℃ and the pH was 7.2–7.6 throughout the experiment.

[0026] S100 influent: Sodium acetate (NaAc), potassium dihydrogen phosphate (KH2PO4), and allyl thiourea (ATU) were added to the above-mentioned low-concentration municipal wastewater. The concentrations after addition were 200 mg / L COD and 5.0 mg / L PO4, respectively. 3- -P and 10 mg / L ATU.

[0027] Sodium acetate is a common carbon source and is easily converted into an internal carbon source by microorganisms in activated sludge (such as polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria). Potassium dihydrogen phosphate is used to maintain a suitable C / P ratio, allowing the formed granular sludge to accumulate more polyphosphate-accumulating bacteria, thus improving phosphorus removal. Allyl thiourea can inhibit nitrification, preventing the rbCOD of the influent from being consumed by denitrifying bacteria, thereby affecting the proliferation of polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria. All of these effects are beneficial to the formation of granular sludge.

[0028] S200 sludge inoculation: Inoculate the reactor with activated sludge from a conventional municipal wastewater treatment plant, with an inoculation sludge concentration of MLSS = 4300 mg / L;

[0029] Cultivation of S300 aerobic granular sludge: The reactor operates according to a cultivation cycle, with each cycle lasting 3 hours. The cycle proceeds in the following sequence: slow upflow influent, stirring, aeration, sedimentation, and drainage. Influent time is 60 minutes, stirring time is 30 minutes, and sedimentation time is gradually reduced from 25 minutes to 10 minutes, decreasing by 1 minute each day (i.e., decreasing by 1 minute every 8 cycles). Drainage time is 5 minutes. Aeration time is gradually increased from 60 minutes to 75 minutes, increasing by 1 minute each day. The volume exchange ratio per cycle is 50%, the drain outlet is 1 meter from the bottom of the reactor, and the liquid level is 2 meters high at the end of influent. Details are as follows;

[0030] S301 water intake; pumped evenly from four symmetrical inlets at the bottom of the reactor using two dual-channel industrial peristaltic pumps for a total of 60 minutes;

[0031] S302 Stirring; Stirring can be achieved by a stirring paddle or nitrogen aeration. A stirring paddle is suitable for full-scale wastewater treatment plants, while nitrogen aeration is suitable for small-scale and pilot-scale stages. This embodiment uses nitrogen aeration for stirring; the nitrogen flow rate is 5 L / min. After 30 minutes of stirring, the mixture is filtered through medium-speed qualitative filter paper to remove sludge. COD is then measured, confirming that the bCOD content of the mixture is less than 20% of the total bCOD, meaning the anaerobic stage removes at least 80% of the bCOD.

[0032] S303 aeration; aeration adopts microporous aeration method, and the aeration time is gradually increased from 60min to 75min; the main purpose of aeration in this stage is aerobic phosphorus uptake without considering nitrogen removal, and dissolved oxygen is controlled at 2.0±0.5mg / L;

[0033] S304 sedimentation: Due to the good settling properties of the inoculated sludge, the initial sedimentation time was set at 25 minutes, corresponding to a sludge flow rate of 2.4 m³ / h. This time was then gradually shortened by 1 minute each day, until the sedimentation time was reduced to 10 minutes on the 16th day. Sludge with a sedimentation rate greater than 6 m³ / h was then screened out. Continuously shortening the sedimentation time creates hydraulic selective pressure to wash away sludge with poor settling properties, allowing the sludge with good settling properties to be screened out.

[0034] S305 drainage; drainage time is 5 minutes, and water output is controlled by an electric valve.

[0035] like Figure 1-2 As shown, after running the above steps for 20 days, visible aerobic granular sludge appeared in the reactor, meaning the sludge particles had a diameter greater than 0.2 mm. After continuing operation for 21 days, the granular sludge in the reactor, with a particle size greater than 0.2 mm, accounted for 81% of the total sludge mass, achieving SVI. 30 =31mL / g, SVI5 / SVI 30 ≈1. The MLSS concentration of sludge in the reactor reaches 6500 mg / L. The entire aerobic granular sludge cultivation process takes 41 days, far less than the more than 6 months required for granulation under current low-concentration municipal wastewater conditions.

[0036] S400 Stable Operation Period: When the particle size reaches 80% or more, the reactor enters the stable operation period; in this example, it entered stable operation on day 49. Each cycle of the stable operation period lasts 4 hours, and the process follows the sequence of upflow slow water intake, stirring, aeration, sedimentation, and drainage. Specifically, the cycle consists of 90 minutes of water intake, 30 minutes of stirring, 100 minutes of aeration, 15 minutes of sedimentation, and 5 minutes of drainage. The volume exchange ratio is increased to 60% per cycle, the drain outlet is 1 meter from the bottom of the reactor, and the liquid level is 2.5 meters high at the end of the water intake. Details are as follows;

[0037] S401 influent; the influent uses low-concentration municipal wastewater, without the addition of sodium acetate, potassium dihydrogen phosphate, and propylene thiourea; allowing the inhibited nitrification reaction to gradually recover; the influent duration is 90 minutes. The increased volume exchange ratio dilutes the nitrate and nitrite nitrogen (NOx) produced in the previous nitrification cycle. x - To reduce its impact on polyphosphate-accumulating bacteria.

[0038] S402 stirring; stirring is carried out by nitrogen aeration; nitrogen flow rate is 5L / min. After stirring for 30 minutes, the COD of the mixture is measured. It is determined that the bCOD content of the mixture is less than 20% of the total bCOD, that is, the removal rate of bCOD in the anaerobic stage is not less than 80%.

[0039] S403 aeration; aeration adopts microporous aeration method, with an aeration time of 100 minutes. The main purpose of aeration in this stage is to simultaneously nitrify and denitrify for phosphorus removal. The initial dissolved oxygen in each aeration cycle is controlled at 2.0±0.5 mg / L. When the ammonia nitrogen concentration drops to 3 mg / L, the dissolved oxygen drops to 0.5±0.3 mg / L to promote simultaneous nitrification and denitrification for phosphorus removal. While obtaining high-quality effluent, this also reduces NO remaining in the reactor. x -The content should be kept as low as possible to reduce its consumption of external carbon sources in the influent, allowing polyphosphate-accumulating bacteria to release phosphorus more fully.

[0040] S404 sedimentation; the sedimentation time is set to 15 minutes, slightly longer than the sedimentation time on the last day of the granular sludge cultivation period. The flocculent sludge with a settling rate of less than 6 m / h will still flow out of the reactor with the effluent.

[0041] S405 drain; draining time is 5 minutes, and the water output is controlled by an electric valve.

[0042] like Figure 3-4 As shown, following the above steps for another 91 days, the granular sludge in the system remained stable, with the average particle size increasing to 0.64 mm. The system's average removal rates for COD, ammonia nitrogen, total nitrogen, and total phosphorus were 88%, 94%, 76%, and 99%, respectively.

[0043] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal wastewater, characterized in that: Includes the following steps: S100 influent: sodium acetate, potassium dihydrogen phosphate and propylene thiourea were added to low concentration municipal wastewater with COD≤200 mg / L; after addition, the COD concentration of the influent was increased by 100-200 mg / L, PO43 3- - P concentration increased by 2.5-5.0 mg / L, ATU concentration increased by 5-10 mg / L; S200 sludge inoculation: Inoculate the reactor with activated sludge from a typical municipal wastewater treatment plant at a concentration of 3000–6000 mg MLSS / L; Cultivation of S300 aerobic granular sludge: The reactor cycle length during the cultivation period is 3-4 hours, and the operation is carried out in the following sequence: slow upflow influent, stirring, aeration, sedimentation, and drainage. The influent time is 60 minutes, stirring time is 0-60 minutes, sedimentation time is 3-50 minutes, and drainage time is 3-10 minutes. The aeration time is determined by subtracting the influent, stirring, sedimentation, and drainage time from the cycle length. The volume exchange ratio per cycle is 33%-50%. The stirring time is controlled so that at the end of stirring, the bCOD content in the mixed liquor is less than 20% of the total bCOD. S400 Stable Operation Period: When the mass fraction of granular sludge in the reactor reaches 80% or more of the total sludge, the reactor enters the stable operation period. The granular sludge particle size is greater than 0.2 mm. At this time, only low-concentration municipal sewage with COD ≤ 200 mg / L is used as the influent. The stable operation period lasts for 4-6 hours per cycle, and is carried out in the order of upflow slow influent, stirring, aeration, sedimentation, and drainage. Among them, influent time is 60-90 minutes, stirring time is 0-90 minutes, sedimentation time is 3-25 minutes, and drainage time is 3-10 minutes. The aeration time is determined by subtracting the influent, stirring, sedimentation, and drainage time periods from the cycle duration. The volume exchange ratio of each cycle increases to 50%-75%. The initial dissolved oxygen concentration of each aeration cycle is controlled at 1.5-2.5 mg / L. When the ammonia nitrogen concentration drops to 3 mg / L, the dissolved oxygen concentration drops to 0.2-0.8 mg / L.

2. The method for rapid cultivation and stable operation of aerobic granular sludge in low-concentration municipal wastewater according to claim 1, characterized in that: In step S300, the sedimentation time is shortened by 0.5 to 1.5 minutes every 6 to 8 cycles after the initial time is determined, until sludge with a sedimentation rate greater than 6 m / h is screened out.

3. The method for rapid cultivation and stable operation of aerobic granular sludge in low-concentration municipal wastewater according to claim 1, characterized in that: In step S300, the dissolved oxygen concentration in the mixed liquor is controlled at 1.5–2.5 mg / L during the aeration stage.

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