Device and method for realizing quick start and stable operation of shortcut nitrification by accurately controlling sludge retention time

Abstract

The invention discloses a device and a method for realizing quick start and stable operation of shortcut nitrification by accurately controlling sludge retention time, and belongs to the field of urban sewage biological treatment. The method comprises the following specific steps: (1) by taking secondary precipitation return sludge of an urban sewage treatment plant as seed sludge and taking inlet water as simulated urban sewage, elutriating nitrite oxidizing bacteria by controlling extremely low sludge retention time in an oxygen-limited operation mode; (2) keeping the oxygen-limited operation mode and prolonging the sludge retention time to quickly enrich ammonia oxidizing bacteria, thereby realizing the quick start of the short-cut nitrification system; and (3) controlling the dissolved oxygen to be 0.1-0.5 mg / L in combination with a dissolved oxygen concentration on-line monitoring device, so that the long-term stable maintenance of the short-cut nitrification process can be realized. The method has the advantages that the control operation in the starting process is simple, and the long-term stable operation method is convenient. And long-term stable maintenance of the short-cut nitrification system can be realized under the condition of regulating and controlling fewer operating parameters.

Description

Technical Field

[0001] This invention relates to an apparatus and method for achieving rapid start-up and stable operation of short-range nitrification by precisely controlling sludge retention time, belonging to the field of wastewater treatment. Background Technology

[0002] Novel biological wastewater treatment processes such as anammox or short-cut denitrification offer advantages such as low aeration energy consumption and low organic carbon source requirements. Their application helps alleviate the problem of excessive energy consumption in wastewater treatment plants, promoting a shift from high-energy-consumption to energy self-sufficiency or even energy-producing models, aligning with my country's carbon neutrality and peak carbon goals. However, the application of these novel biological nitrogen removal processes still faces the challenge of unstable nitrite supply. In anammox or short-cut denitrification systems, nitrite is typically supplied through short-cut nitrification, short-cut denitrification, or dissimilatory reduction of nitrate to ammonium. Among these, short-cut nitrification further reduces aeration energy consumption and requires no additional organic carbon source, making it a promising nitrite supply pathway.

[0003] Selective flushing of nitrite-oxidizing bacteria is crucial for the rapid start-up and long-term stable operation of short-cut nitrification processes in treating mainstream low-ammonia-nitrogen wastewater. In short-cut nitrification, ammonia nitrogen is oxidized to nitrite by ammonia-oxidizing bacteria, but not further oxidized to nitrate by nitrite-oxidizing bacteria. The accumulation of nitrite-oxidizing bacteria competitively inhibits anaerobic ammonia-oxidizing bacteria or denitrifying bacteria, leading to a deterioration in nitrogen removal performance. Therefore, developing highly stable and easy-to-operate short-cut nitrification strategies for low-ammonia-nitrogen wastewater is a current focus in the field of biological wastewater nitrogen removal.

[0004] Large-scale wastewater treatment plants typically employ continuous flow reactors (CFBRs) as their biological treatment units. Compared to sequencing batch reactors (SBRs), CFBRs are characterized by the coupling of sludge retention time and hydraulic retention time, making it more difficult to control dissolved oxygen and substrate concentration gradients and exerting less selective pressure on the microbial community. Therefore, achieving cut-cut nitrification in CFBRs is more challenging. Currently, strategies such as online aeration control, the addition of selective inhibitors, and bioaugmentation are commonly used to selectively eliminate nitrite-oxidizing bacteria while maximizing the retention of ammonia-oxidizing bacteria to maintain stable cut-cut nitrification in the CFBR. However, these strategies often increase operating costs and complexity or require longer start-up times for cut-cut nitrification.

[0005] Selectively eluting nitrite-oxidizing bacteria by controlling the sludge retention time in the reactor is a convenient way to construct short-cut nitrification systems. Rapid elution of nitrite-oxidizing bacteria can be achieved when the sludge retention time is less than the doubling time of nitrite-oxidizing bacteria in the environment. Existing research indicates that maintaining a sludge retention time of 2-5 days can effectively achieve stable short-cut nitrification. However, currently, systems that have successfully achieved rapid start-up and long-term stable operation of short-cut nitrification systems are mainly constructed in side-flow high-ammonia nitrogen wastewater treatment systems. In contrast, establishing short-cut nitrification systems for urban wastewater is more difficult, and effective methods for constructing mainstream urban wastewater short-cut nitrification systems are still lacking. Summary of the Invention

[0006] To address the problems mentioned above in the background technology, the main objective of this invention is to develop a simple strategy to achieve simple and rapid start-up and long-term stable operation of a short-cut nitrification system in a continuous flow reactor with low influent ammonia nitrogen concentration, thereby solving the problems of long start-up time and high difficulty in controlling the long-term stable operation process that exist in traditional strategies.

[0007] To address the aforementioned problems, this invention proposes a device and method for achieving rapid start-up and stable operation of short-range nitrification through precise control of sludge retention time. The device is designed as a continuous flow membrane bioreactor. The reactor is equipped with an inlet tank, an automatic temperature-controlled heater, two sets of peristaltic pumps, a continuous flow reactor, an aeration pump, an aeration disc, a dissolved oxygen monitor, an outlet tank, a hollow fiber membrane module, a fluid pressure gauge, and three sets of infrared level gauges. The inlet tank (1) is connected to the first peristaltic pump (2) via a rubber tube and is ultimately connected to the inlet of the continuous flow reactor (3). The first level gauge (4) is connected to the first peristaltic pump and is affixed to the operating liquid level height on the outer wall of the continuous flow reactor (3). The hollow fiber membrane module (5) is made of organic materials such as polyvinylidene fluoride, which are not easily involved in biochemical reactions, and has a pore size of microfiltration level (pore size less than 2 micrometers) to avoid biomass loss. The device is submerged in the continuous flow reactor and connected to the fluid pressure gauge (6) and the second peristaltic pump (7) through a rubber tube via a three-way fitting. The rubber tube extends from the second peristaltic pump (7) to the outlet tank (8). The second level gauge (9) is connected to the second peristaltic pump (7) and is attached to the outer wall of the continuous flow reactor (3) at a height 0.5 cm above the operating liquid level. The aeration pump (10) is connected to the rotor flow meter (11) through a plastic tube and is finally connected to the aeration disc (12) located at the bottom of the continuous flow reactor (3). The third level gauge (13) is connected to the aeration pump (10) and is attached to the outer wall of the continuous flow reactor (3) at a height 0.5 cm below the operating liquid level. The automatic temperature control heater (14) and the dissolved oxygen monitor (15) are placed and fixed below the operating liquid level through the reserved holes above the continuous flow reactor (3). The stirring device (16) is connected to the reactor from above.

[0008] The operation method of this continuous flow membrane bioreactor includes the following steps: Calculate the daily influent flow rate and the rotation speed of the first peristaltic pump based on the set hydraulic retention time and effective reactor volume, and specify the water distribution cycle; a water distribution interval exceeding 48 hours may lead to degradation of the influent substrate; influent enters the reactor through the first peristaltic pump to participate in the biochemical reaction; the membrane module is completely immersed in the mixed liquor, and water is drawn from the reactor to the effluent tank at a flux consistent with the influent flow rate through a negative pressure created by the second peristaltic pump; the negative pressure in the effluent unit pipeline is monitored by a fluid pressure gauge, and the pressure gauge reading reflects the degree of biomass fouling and blockage of the hollow fiber membrane module; when the fluid pressure gauge reading exceeds 0... When the pressure reaches 0.1 MPa, the membrane module should be cleaned or replaced to prevent it from being damaged by excessive negative pressure, which could lead to biomass loss. Dissolved oxygen is supplied to the biochemical reaction through an aeration pump and an aeration disc located at the bottom of the reactor. The aeration intensity is adjusted by a rotor flow meter to maintain the dissolved oxygen concentration in the reactor. The automatic temperature-controlled heater is completely immersed in the mixed liquor, enabling real-time control of the reaction temperature. The dissolved oxygen monitor can monitor the dissolved oxygen concentration in the reactor in real time. The agitator speed should ensure that the mixed liquor inside the reactor is fully mixed. Since the stirring intensity can significantly affect the dissolved oxygen concentration by influencing gas-liquid mass transfer, the agitator speed should be constant during reactor operation.

[0009] The reactor's automatic operation is controlled by a set of level gauges and corresponding operating logic. Specifically: the third level gauge controls the start and stop of the aeration pump and also serves as the first safety measure; when the reactor level is higher than the height of the third level gauge, the aeration pump stops operating to prevent excessively high dissolved oxygen concentrations from disrupting the short-cut nitrification process. The first level gauge controls the start and stop of the first aeration pump and also serves as the second safety measure; when the reactor level is higher than the first level gauge, the first peristaltic pump stops operating to maintain the liquid level at the operating level. The second level gauge controls the start and stop of the second peristaltic pump and also serves as the third safety measure; when the reactor level is lower than the second level gauge, the second peristaltic pump stops operating to prevent continuous water output from causing the liquid level to fall below the operating level. The control logic is set up based on the following principles: First, excessively high dissolved oxygen concentration caused by over-aeration will disrupt the short-cut nitrification process, so the start and stop of the aeration pump should be controlled first. Second, the temporary accumulation of ammonia nitrogen does not affect the short-cut nitrification process, so the start and stop of the influent pump is placed after the aeration pump by adjusting the level gauge height. Finally, the effluent pump should be kept running continuously to maintain a constant hydraulic residence time in the reactor, so the start and stop of the effluent pump is placed after the influent pump by adjusting the level gauge height. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the overall structure of the present invention. Detailed Implementation

[0011] The technical steps for rapidly starting up a short-cut nitrification system and maintaining its long-term stable operation using this continuous flow membrane bioreactor are as follows:

[0012] During the nitrification recovery stage, the recycled sludge from the secondary sedimentation tank is inoculated into the continuous flow reactor. The initial sludge concentration is maintained at 3000–4000 mg / L. The substrate enters the continuous flow reactor with the influent and reacts. No active pH control is required during this process. The hydraulic retention time of the continuous flow reactor is set to 12 hours. No mixed liquor is actively discharged during this stage. The operating water temperature of the continuous flow reactor is controlled at 33–35℃, and the dissolved oxygen concentration is controlled at 0.5–1.0 mg / L. At reactor startup, the simulated urban wastewater influent contains 40 mg / L ammonia nitrogen and 100 mg / L COD. The concentrations of ammonia nitrogen, nitrite, nitrate, and COD in the reactor influent and effluent are periodically monitored. During this stage, the ammonia nitrogen concentration in the influent and the reactor aeration intensity are increased. Ammonia nitrogen and nitrite nitrogen concentrations in the continuous flow reactor are sampled and measured periodically. When the residual ammonia nitrogen concentration in the reactor is below 5 mg / L, the ammonia nitrogen concentration in the influent is increased. When the dissolved oxygen is below 0.5 mg / L, the aeration intensity is increased until the influent substrate reaches 90% concentration. 110 mg / L ammonia nitrogen and 180-220 mg / L; when the ammonia nitrogen removal rate is higher than 90% and the nitrate accumulation rate reaches more than 80%, it indicates that the nitrification activity of the seed mud has been restored.

[0013] After the nitrification activity of the seed sludge is restored, the short-cut nitrification system is rapidly started up. During this stage, there is no need to actively control the pH in the reactor. The hydraulic retention time of the continuous flow reactor is set to 12 hours, the operating water temperature is controlled at 33–35℃, and the feed water maintains 90–110 mg / L ammonia nitrogen and 180–220 mg / L organic matter matrix. By actively discharging 10% of the reactor's effective operating volume of mixed liquor daily, the average sludge retention time is controlled to 10 days, and the sludge concentration is maintained at 3000–4000 mg / L. Simultaneously, the dissolved oxygen concentration is lowered and controlled to 0.05–0.2 mg / L to achieve selective washing of nitrite-oxidizing bacteria. In the reactor performance enhancement stage, when the ammonia nitrogen concentration in the continuous flow reactor exceeds 20 mg / L, the ammonia nitrogen concentration in the short-cut nitrification system is increased by increasing the aeration intensity. When the ammonia nitrogen concentration in the continuous flow reactor falls below 10 mg / L and the nitrite accumulation rate reaches more than 50%, the short-cut nitrification system is considered successfully started up.

[0014] After successfully constructing the short-cut nitrification system, maintain its long-term stable operation. During this stage, there is no need to actively control the pH in the reactor. The hydraulic retention time of the continuous flow reactor is set to 12 hours, the operating water temperature is controlled at 33–35℃, and the feed water maintains 90–110 mg / L ammonia nitrogen and 180–220 mg / L organic matrix. 5% of the reactor's effective operating volume of mixed liquor is actively discharged daily, maintaining an average sludge retention time of 20 days, a sludge concentration of 3000–4000 mg / L, and a dissolved oxygen concentration of 0.2–0.5 mg / L to achieve long-term inhibition of nitrite-oxidizing bacteria. Other reactor operating conditions remain consistent with the previous step. During this stage, when the ammonia nitrogen concentration in the reactor is below 5 mg / L, the ammonia nitrogen concentration in the short-cut nitrification system is adjusted by reducing the aeration intensity; when the ammonia nitrogen concentration in the reactor is above 20 mg / L, the ammonia nitrogen concentration in the short-cut nitrification system is adjusted by increasing the aeration intensity; when the ammonia nitrogen concentration in the continuous flow reactor is below 10 mg / L and the nitrite accumulation rate is maintained above 70%, it indicates that the long-term stable operation of short-cut nitrification has been successfully achieved.

Claims

1. A device for achieving rapid start-up and stable operation of short-cut nitrification by precisely controlling sludge retention time, characterized in that: The apparatus includes: an inlet tank, an automatic temperature-controlled heater, a peristaltic pump, a continuous flow reactor, an aeration pump, an aeration disc, a dissolved oxygen monitor, an outlet tank, a central control fiber membrane module, a fluid pressure gauge, and an infrared level gauge. The inlet tank is connected to the first peristaltic pump via a rubber hose and ultimately to the continuous flow reactor. The first level gauge is connected to the first peristaltic pump and is affixed to the operating liquid level on the outer wall of the continuous flow reactor. The membrane module is immersed in the continuous flow reactor and connected to both the fluid pressure gauge and the second peristaltic pump via a rubber hose and a T-joint fitting. The rubber hose extends from the second peristaltic pump to the outlet tank. The second level gauge is connected to the second peristaltic pump and is affixed to the outer wall of the continuous flow reactor at a height 0.5 cm above the operating liquid level. The aeration pump is connected to a rotor flow meter via a plastic tube and ultimately to the aeration disc located at the bottom of the continuous flow reactor. The third level gauge is connected to the aeration pump and is affixed to the outer wall of the continuous flow reactor at a height 0.5 cm below the operating liquid level. A stirring device is connected to the reactor from above.

2. A method for rapid start-up and stable operation of short-range nitration using the apparatus as described in claim 1, characterized in that, Includes the following steps: The sludge returned from the secondary sedimentation tank was inoculated into the continuous flow reactor, with the initial sludge concentration maintained at 3000–4000 mg / L. The operating water temperature of the continuous flow reactor was controlled at 33–35℃, and the dissolved oxygen concentration was controlled at 0.5–1.0 mg / L. The reactor influent contains ammonia nitrogen and organic matrix. The matrix reacts in the continuous flow reactor along with the influent. No active pH control is required during this process. The hydraulic retention time of the continuous flow reactor is set to 12 hours. The hollow fiber membrane module is pumped out at a constant flux via a second peristaltic pump. The pump's start and stop are controlled by a level gauge to ensure consistent influent and effluent flow rates. When the pressure gauge reading exceeds 0.1 MPa, the hollow fiber membrane is backwashed with tap water or the membrane module is replaced. Reactor influent and effluent samples are collected daily, and ammonia nitrogen and nitrite nitrogen concentrations are measured. The ammonia nitrogen removal rate and nitrite nitrogen accumulation rate are calculated based on the ammonia nitrogen and nitrite nitrogen concentrations in the influent and effluent. To improve pollutant removal efficiency, 10% of the reactor's effective operating volume of mixed liquor is actively discharged daily, controlling the average sludge retention time to 10 days to achieve selective washing of nitrite-oxidizing bacteria. When the ammonia nitrogen concentration in the continuous flow reactor is below 5 mg / L... When the ammonia nitrogen concentration in the influent is 20 mg / L, the ammonia nitrogen removal rate of the reactor is improved by simultaneously increasing the influent ammonia nitrogen concentration and the aeration intensity. When the ammonia nitrogen concentration in the continuous flow reactor is higher than 20 mg / L, the ammonia nitrogen removal rate of the reactor is adjusted by increasing the aeration intensity. When the ammonia nitrogen concentration in the reactor is lower than 10 mg / L and the nitrite accumulation rate reaches more than 50%, it indicates that the short-cut nitrification system has been successfully started. During operation, 5% of the effective volume of the reactor's mixed liquor is actively discharged daily to control the average sludge retention time at 20 days, thereby inhibiting nitrite-oxidizing bacteria. When the ammonia nitrogen concentration in the reactor is below 5 mg / L, the ammonia nitrogen concentration in the reactor is adjusted by reducing the aeration intensity. When the ammonia nitrogen concentration in the reactor is above 20 mg / L, the ammonia nitrogen removal rate of the reactor is adjusted by reducing the ammonia nitrogen concentration in the influent.

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