An aerobic granular sludge cultivation method for treating wastewater with a low carbon-to-nitrogen ratio

Abstract

This invention discloses a method for cultivating aerobic granular sludge for treating wastewater with a low C / N ratio. The method includes washing the sludge with tap water before inoculation, adding tap water as the influent source to the reactor after inoculation and aerating, and then effluent exiting from the middle of the reactor. The required wastewater is then fed into the reactor, and the settling time is adjusted. The reactor operates in a cycle of influent-anoxic-aeration-sedimentation-discharge. Based on the selective pressure principle of aerobic granular sludge, this invention optimizes the process. The cultivation of aerobic granular sludge using this method involves three stages: inoculation, emergence, and maturation. Under selective pressure, the flocculent sludge gradually aggregates, its structure becomes denser, and its color changes from dark brown to yellowish brown. This invention can obtain mature aerobic granular sludge with the ability to remove organic matter and simultaneously denitrify after an average cultivation period of 55 days. Compared with other cultivation methods, this method saves a significant amount of time and greatly shortens the granulation time.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio. Background Technology

[0002] Low COD / N ratio wastewater is one of the challenges in treating nitrogen-containing wastewater. Wastewater with a COD / N ratio below 5 is generally defined as low COD / N ratio wastewater. On the other hand, with the increasing treatment capacity of wastewater treatment plants and the strict national control over effluent quality, there is a need for effective denitrification of wastewater with low organic carbon requirements or requiring the addition of external carbon sources. Therefore, in recent decades, numerous emerging technologies such as partial nitrification, denitrification, and anaerobic ammonium oxidation have emerged.

[0003] Aerobic granular sludge is a promising wastewater treatment technology due to its rich microbial characteristics, excellent settling ability, compact structure, and tolerance to fluctuating flow loads. However, the instability of aerobic granular sludge and its long particle formation time are problems that need to be addressed. Sufficient organic matter concentration is required for the formation of aerobic granular sludge; lower organic loading rates prolong particle formation time. Furthermore, insufficient influent carbon sources inhibit the ability of denitrifying bacteria (an anaerobic heterotrophic bacterium) to convert nitrate and nitrite nitrogen into nitrogen gas, affecting total nitrogen (TN) removal efficiency. Additionally, low influent COD concentrations lead to competition between filamentous bacteria and denitrifying bacteria for limited nutrients, ultimately resulting in the proliferation of filamentous bacteria, which have a stronger ability to absorb and decompose organic matter, dominating the entire reactor and causing system collapse. Recently, researchers have attempted to overcome this challenge by utilizing mature aerobic sludge systems (AGS) for bioenhancement, adding external carbon sources, or mixing low-intensity domestic wastewater with industrial wastewater to increase the organic loading rate (OLR). However, these methods are costly and not conducive to practical application. In stable biological wastewater treatment systems, ammonia nitrogen removal efficiency and rate increase with decreasing carbon-to-nitrogen ratio. However, excessive free ammonia can limit the aggregation of functional microorganisms in wastewater treatment systems and may worsen denitrification performance.

[0004] Scholars have found that aerobic granular sludge processes generally have long start-up times, requiring at least 2 to 4 months, and sometimes even longer. This slow start-up speed has become a bottleneck restricting the large-scale application of aerobic granular sludge technology. Conversely, some scholars, in an effort to shorten the formation time of aerobic granular sludge, have cultivated sludge structures that are relatively fragile, easily breaking down during subsequent operation and affecting the system's decontamination performance. Furthermore, these methods are difficult to operate and manage in practice. Therefore, for the further development of aerobic granular sludge technology, it is urgent to explore a practical and feasible method for rapidly cultivating aerobic granular sludge with good stability. Summary of the Invention

[0005] This invention addresses the technical problems of long particle formation time and poor denitrification effect under low carbon-nitrogen ratio conditions by providing an aerobic granular sludge cultivation method for treating wastewater with low carbon-nitrogen ratio. This method can rapidly cultivate aerobic granular sludge, which has strong growth and reproduction capabilities, can efficiently carry out simultaneous nitrification and denitrification reactions, and can remain stable for a long time.

[0006] The objective of this invention is achieved by including the following steps:

[0007] S1. Before adding flocculent activated sludge as inoculum to the sequencing batch reactor (SBR), wash the sludge with tap water at least three times to minimize impurities in the suspension and prevent subsequent clogging of the reactor pipes. After sludge inoculation, add tap water to the reactor as the influent source and aerate for one day, during which the settling time is 30 minutes. Then adjust the settling time to 25 minutes and effluent from the middle of the reactor. This operation can effectively remove activated sludge with poor settling performance from the original activated sludge or effectively convert black anaerobic sludge into gray-brown activated sludge, increasing the proportion of the initial inoculum activated sludge.

[0008] S2. Low C / N ratio wastewater is fed into the reactor, which has a height-to-diameter ratio of 20-25. The reactor operates in the mode of influent-anoxic-aeration-sedimentation-discharge. The influent pH is controlled between 7 and 8, and the reactor operating temperature is controlled between 24-26℃ throughout the process. Specifically, the influent time is 5 minutes, anoxic time is 55 minutes, aeration time is 145-170 minutes, sedimentation time is 5-30 minutes, and effluent time is 5 minutes. The cycle time is 4 hours, and 6 cycles are run per day. The reactor volume exchange rate is maintained at 10-50%, the hydraulic retention time is 8 hours, and the aeration flow rate is 1.2-2.0 L / min.

[0009] The sequencing batch reactor (SBR) system used in this invention is a well-known SBR reactor to those skilled in the art. It consists of a main reactor, an influent system, a drainage system, an aeration system, and a corresponding automatic control system. The reactor operates sequentially through influent, anoxic, aerobic aeration, sedimentation, and drainage processes to achieve simultaneous removal of COD and inorganic nitrogen from wastewater.

[0010] Preferably, during the early stage of aerobic granular sludge formation, the physical properties of the sludge are tested periodically: MLSS, MLVSS, and SVI. 30 SVI 30 / SVI5, F / M, effluent SS and particle size, influent and effluent concentration changes: COD, ammonia nitrogen, NO x - -N and observation of sludge morphology using electron microscopy; under normal culture conditions: SVI5 and SVI 30The concentration will gradually decrease from an initial 100-150 mL / g to below 60 mL / g; under a microscope, it can be observed that the flocculent matter in the system gradually decreases, and is replaced by small, oval-shaped particles; SVI 30 The SVI / SVI ratio will gradually approach 1; by monitoring the above indicators and after the activated sludge is successfully added to the reactor and aerated for one day, the settling time is directly adjusted from 30 min to 25 min, after which the SVI / SVI ratio will decrease. 30 For every 10-15 mL / g decrease, shorten the settling time by 5 min and correspondingly increase the aeration time by 5 min. By adjusting the system's settling time, flocculent sludge with poor settling performance cannot settle to the bottom within the specified settling time and can only remain suspended inside the system, while sludge with good settling performance settles at the bottom of the reactor. Therefore, using a peristaltic pump to drain water from the middle of the reactor can effectively remove flocculents with poor settling performance from the system with the water flow, while the sludge remaining inside the reactor is preserved.

[0011] Preferably, when the sludge concentration MLSS of the system continuously decreases to below 1 g / L or the effluent SS concentration is as high as 250 mg / L, it indicates that the sludge loss inside the system is serious, and the settling time is adjusted to 8-15 min. If the sludge concentration MLSS is between 0.8-1 g / L, the settling time is adjusted back to 8 min. If the MLSS is below 0.8 g / L, the settling time can be adjusted back to 15 min. When it is found that the sludge concentration begins to rise to greater than or equal to 1 g / L and remains there for at least 7 days, the settling time is restored to 5 min. When the sludge volume in the system continuously decreases, indicating a decline, it signifies that aerobic granulation has entered its most critical sludge selection phase. During this period, the system will discharge a large amount of flocculent sludge with poor settling performance, causing fluctuations in the overall pollutant removal capacity. As this is a crucial period for particle formation, the reduction in sludge volume is normal. At this time, referring to the sludge concentration MLSS variation pattern mentioned earlier in this manual, the settling time can be adjusted to 8-15 minutes to maintain the sludge volume within a stable range. Based on the sludge elimination mechanism, the unique operation of the SBR reactor allows for the induction of aggregate phenotypes and the retention of rapidly settling microbial aggregates within the system. Ultimately, under the action of hydraulic shear force and EPS, dense aerobic granular sludge is formed. When the sludge concentration begins to increase, the system settling time should be further shortened, eventually reducing it to 5 minutes. Once the system's pollutant removal performance stabilizes, the SVI (Sludge Volume Index) should be adjusted accordingly. 30 When the SVI5 value stabilizes at around 1, and particles with a diameter greater than 200 μm are clearly visible inside the system and this state is maintained for at least 10 days, it indicates that aerobic granular sludge has formed in the system, and the cultivation is successful.

[0012] Preferably, during system operation, when the F / M (food-to-microbe ratio, defined as the organic load borne by a unit mass of activated sludge per unit time) value is higher than 0.5 g / gVss d or lower than 0.3 g / gVss d, the influent COD load of the system is adjusted: when the F / M value is higher than 0.5, it indicates that filamentous bacteria are prone to multiplying in large quantities and affecting the stability of the system. At this time, the influent organic load is reduced to restore the F / M value to normal; when the F / M value is lower than 0.3 g / gVss d, the presence of protozoa will destroy the particle physical structure and cause the system to collapse. At this time, the influent organic load is increased or sludge is discharged from the bottom of the reactor to adjust the F / M to 0.3-0.5 g / gVss d (normal range).

[0013] By analyzing the changes in the above indicators, the system settling time can be adjusted in a timely manner to remove flocculent sludge with poor settling performance from the system; this helps the sludge retained in the system to further accelerate the formation of aerobic granular sludge.

[0014] Most of the COD is effectively utilized by denitrifying bacteria as electron donors in the pre-anoxic zone, with only a small amount entering the subsequent aerobic zone. After aeration begins in the system cycle, the small amount of COD is quickly adsorbed and degraded. At this point, there is sufficient time in a single cycle to degrade NH4+-N, so a large number of nitrifying bacteria (slow-growing bacteria) can remain in the system. At the same time, there is also a sufficient starvation period for heterotrophic microorganisms to reach a stable state, thus maintaining the stability of the entire system.

[0015] Preferably, when the system consistently achieves a COD removal rate of 85% and an ammonia nitrogen removal rate of 90% for at least one week, and small aerobic granular sludge particles with a particle size >200um begin to appear inside the system, the settling time is directly adjusted to 5 minutes.

[0016] Preferably, a microporous aeration head is installed at the bottom of the reactor, and an air compressor or constant pressure aeration pump is used in conjunction with the aeration head to supply air. The aeration volume is adjusted by a rotor flow meter, and the pH value of the system is controlled at 7-8.

[0017] Preferably, after the aerobic particles are successfully cultured, the sludge is used for the treatment of high-load wastewater with a low carbon-to-nitrogen ratio.

[0018] Preferably, the influent COD load of the high-load wastewater is 1000 mg / L and the ammonia nitrogen load is 250 mg / L. The aeration is adjusted to 290 min, and the reactor operation cycle is 6 hours. At this time, the removal rates of COD and ammonia nitrogen can both reach more than 95%.

[0019] Preferably, during the S2 step of cultivation, the influent COD load is 200-500 mg / L, and the ammonia nitrogen load is 20-125 mg / L.

[0020] Preferably, during the S2 step of cultivation, when the effluent nitrate nitrogen concentration is higher than 30 mg / L, an external circulation operation is added. Specifically, an external circulation operation is added to the anoxic section to divert the sewage 5-10 cm below the water level in the reactor to the sludge at the bottom of the reactor. The speed of the peristaltic pump is set to 30-40 r / min.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] 1. The aerobic granular sludge cultivation method of this invention involves three stages: inoculation, emergence, and maturation. Under selective pressure, the flocculent sludge gradually aggregates, its structure becomes denser, and its color changes from dark brown to yellowish brown. During granulation, the granular sludge undergoes slight disintegration, then reforms into granules through self-regulation. This indicates that the formation of aerobic granular sludge is a fluctuating process, and the granules are not stable in the short term. Aerobic granular sludge needs continuous self-regulation to eventually reach a stable equilibrium. This invention can obtain mature aerobic granular sludge with organic matter removal and simultaneous denitrification capabilities in an average of 55 days of cultivation, saving significant time compared to other cultivation methods and greatly shortening the granulation time. After the granules form and mature, the system officially enters the operational phase, capable of treating low C / N ratio wastewater for extended periods. It can also be used to conduct research on wastewater treatment performance and the long-term stability of the granules.

[0023] 2. The aerobic granular sludge cultivated by this invention can also be used for the treatment of wastewater with a low carbon-nitrogen ratio and a high load. That is, if the influent COD value is kept constant under the conditions of a high carbon-nitrogen load and a low carbon-nitrogen ratio, the ammonia nitrogen load can be further increased. At the same time, the aeration time needs to be further increased to allow for full ammoniation, which can also achieve effective denitrification. As the carbon-nitrogen load increases, the COD utilization rate in the anoxic section also increases accordingly, and the pre-anoxic denitrification performance is improved, which can further prepare for the increase of ammonia nitrogen load and increase the adaptability of aerobic granular sludge to different carbon-nitrogen loads.

[0024] 3. Based on the selective pressure principle of aerobic granular sludge, this invention proposes a method for rapidly cultivating aerobic granular sludge with outstanding organic matter removal capabilities and long-term stable operation. Compared with previous SBR methods for cultivating aerobic granular sludge, this invention optimizes the process: a pre-anoxic stage is added before the aerobic aeration stage to enhance TN removal and improve COD utilization in the anoxic stage. Multiple testing indicators are used to guide the adjustment of the granulation process and maintain particle stability during subsequent operation. Results show that the cultivation method of this invention can cultivate dense and smooth aerobic granular sludge in a short time, with an average particle size of 300-600 mm. Furthermore, all equipment used are standard laboratory wastewater consumables, and the method is effective and easy to implement. Attached Figure Description

[0025] Figure 1 This is a conventional electron microscope image of the mature aerobic granular sludge obtained by culturing for 52 days in Example 1 of this invention;

[0026] Figure 2 This is a scanning electron microscope image of the mature aerobic granular sludge obtained through Example 2 of the present invention;

[0027] Figure 3 This is a conventional electron microscope image of the aerobic granular sludge obtained after 24 days of cultivation according to Example 1 of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0029] Example 1

[0030] This embodiment uses a cylindrical sequencing batch reactor (SBR) made of plexiglass to treat wastewater with a low C / N ratio. The reactor has an inner diameter of 5 cm, an effective working volume of 2 L, an effective height of 115 cm, and a height-to-diameter ratio (H / D) of 23. The reactor has bottom inlet and middle outlet outlet, with a volume exchange rate (VER) of 50%. Both inlet and outlet water are transported by peristaltic pumps. During the aerobic aeration stage, an air pump provides sufficient airflow to ensure thorough mixing of the sludge and water in the reactor and to provide the oxygen required for microbial growth. The aeration rate is controlled by an electromagnetic flow meter, with the airflow rate controlled at 2 L / min. The entire experiment is conducted at 25°C, and all electrical components are controlled by time relays.

[0031] The reactor culture method is operated according to the following procedure:

[0032] The inoculated sludge was taken from the Jingyuan Wastewater Treatment Plant of Kunming University of Science and Technology. The influent wastewater was artificially simulated domestic wastewater with a COD concentration of 500 mg / L, an ammonia nitrogen concentration of 25 mg / L, an initial C / N ratio of 20, and an influent pH controlled between 7.5 and 8. The culture temperature was maintained at 25 degrees Celsius. The inoculated sludge was cleaned according to the instructions and continuously aerated for one day. The settling time was then adjusted to 25 min. The reactor was operated in a cycle of influent-anoxic-aeration-sedimentation-discharge, with the influent pH controlled between 7 and 8 and the reactor operating temperature maintained at 25 degrees Celsius throughout. Specifically, the cycle consisted of 5 min of influent, 55 min of anoxic, 145-170 min of aeration, 5-30 min of settling, and 5 min of effluent discharge, with a cycle time of 4 hours. Six cycles were run per day, maintaining a reactor volume exchange rate of 10-50%, a hydraulic retention time of 8 hours, an aeration flow rate of 2.0 L / min, and the external circulation system was kept open throughout the process. The experiment monitored SVI5 or SVI... 30 The descent was relatively stable and met the above conditions. The settling time was reduced by 5 minutes every 10 days. During the cultivation period, the MLSS sludge concentration in the system was observed to remain above 1 g / L; therefore, there was no need to extend the settling time during cultivation. The system's F / M value remained between 0.3 and 0.5 g / gVss d. At day 24 of cultivation, small particles were observed under a microscope, such as... Figure 3 As shown: sludge flocs did not appear in the system; instead, dark brown particles were present. After 30-40 days of cultivation, the system's pollutant removal performance remained stable at over 90% for ten days, and on day 40, the settling time was directly shortened from the normal 10 minutes to 5 minutes.

[0033] After 52 days of cultivation, mature aerobic granular sludge was formed. The sludge morphology is shown in the image below. Figure 1 As shown: Compared to the small particles formed at 24 days, the average particle size at this point is 1.5 mm. After particle formation, the influent COD load was kept constant, while the influent ammonia nitrogen load was gradually increased from 50 mg / L to 125 mg / L, thereby gradually reducing the carbon-to-nitrogen ratio to 4. At 290 days of system cultivation, the F / M value was found to be 0.28 g / gVssd, lower than the normal range. To prevent protozoa from damaging the particle structure, 500 mg / L of sludge was discharged from the bottom of the reactor every 3-4 days during this period. Sludge discharge continued until day 310, when the F / M value returned to normal (0.3-0.5 g / gVssd), and sludge discharge was stopped. The system then operated stably for 370 days, during which time the system operated stably without any adjustments to the relevant operating parameters. During the subsequent treatment of low carbon-to-nitrogen ratio wastewater, the COD removal rate reached over 95%. The ammonia nitrogen removal performance fluctuated during the initial particle formation period, but the removal rate stabilized at over 85% after the particles occupied the reactor. The pollutant removal performance of both was not affected by changes in the carbon-to-nitrogen ratio.

[0034] During the subsequent granular culture period, the aerobic granular sludge exhibits a smooth and intact morphology, with particle sizes fluctuating between 400-600 μm. When filamentous bacteria are found inside the system, they temporarily increase the particle size and reduce the particle settling ability. However, the proliferation of filamentous bacteria can be effectively inhibited by hydraulic shear force and adjustments to the influent organic matter load, thus restoring the settling performance of the aerobic granular sludge.

[0035] Example 2

[0036] This embodiment uses a cylindrical sequencing batch reactor (SBR) made of plexiglass to treat wastewater with a low C / N ratio. The effective height is 115 cm, and the height-to-diameter ratio (H / D) is 23. The aeration flow rate is controlled at 1.2 L / min; other operating parameters are set the same as in Embodiment 1.

[0037] The inoculated sludge was taken from the Jingyuan Wastewater Treatment Plant of Kunming University of Science and Technology. The influent wastewater was artificially simulated domestic wastewater with a COD concentration of 200 mg / L, an ammonia nitrogen concentration of 40 mg / L, and an initial carbon-to-nitrogen ratio of 5. The reactor was operated using the cultivation method described in this invention.

[0038] The inoculated sludge was cleaned and continuously aerated for one day as described in the instructions. The settling time was then adjusted to 25 minutes. The reactor was operated in a cycle of influent-anoxic-aeration-sedimentation-discharge, with the influent pH controlled between 7 and 8, and the ambient temperature maintained at 25℃ throughout the operation. The cycle consisted of: 5 minutes of influent, 55 minutes of anoxic treatment, 145-170 minutes of aeration, 5-30 minutes of settling, and 5 minutes of effluent discharge, with a cycle time of 4 hours. Four cycles were performed daily, maintaining a reactor volume exchange rate of 10-50%, a hydraulic retention time of 8 hours, and an aeration flow rate of 1.2 L / min. SVI5 or SVI was monitored experimentally. 30 The nitrate concentration decreased relatively steadily, and the settling time was reduced by 5 minutes every 10 days. On day 43, the nitrate nitrogen concentration was found to be 40 mg / L, higher than the required 30 mg / L, indicating poor denitrification. At this point, external circulation was added, and the peristaltic pump speed was adjusted to 33 r / min and kept running thereafter. After 23 days of system cultivation, filamentous bacteria appeared inside the system, indicating a lack of sufficient nutrients. Therefore, the COD concentration was adjusted to 400 mg / L, the ammonia nitrogen concentration to 50 mg / L, and the carbon-to-nitrogen ratio to 8 until smooth and dense aerobic granular sludge was successfully cultivated.

[0039] During the cultivation period, the MLSS sludge concentration in the system did not fall below 1 g / L, therefore, there was no need to extend the settling time. Aerobic granular sludge appeared in the system on day 19, and by day 60, large particles were observed to occupy the entire reactor, indicating that the aerobic granular sludge had matured. On day 63, the microscopic morphology of the particles was observed as follows... Figure 2As shown, the mature aerobic granular sludge was observed to be ellipsoidal with a clear outline under a scanning electron microscope. Subsequently, the ammonia nitrogen load was increased to 80 mg / L, while the COD load remained unchanged, and the carbon-to-nitrogen ratio was reduced to 5, operating as low-carbon-to-nitrogen wastewater for 93 days. On day 94, the ammonia nitrogen concentration was increased to 100 mg / L, at which point the carbon-to-nitrogen ratio was 4. During subsequent operation, the carbon-to-nitrogen ratio was kept constant, and the system effectively removed high concentrations of COD and ammonia nitrogen even as the influent carbon-to-nitrogen load was gradually increased. At day 130, the MLSS sludge concentration was monitored to have dropped to 980 mg / L, below 1 g / L. At this point, the settling time was adjusted to 8 minutes and maintained for 5 days. Afterward, the MLSS recovered to above 1.6 g / L, and the settling time was adjusted back to 5 minutes. When the carbon and nitrogen load is 1000 / 250, the system circulation time is extended to 6 hours (compared to 4 hours for the previous gradient of 600 / 150). The extra 2 hours are used to extend the aeration time, which is now 290 minutes. The time for each of the other stages remains unchanged. The system has now been running stably for 240 days without any abnormalities. The COD and ammonia nitrogen removal efficiencies of the reactor remain excellent, reaching 96.9% and 99.8% respectively, unaffected by the increase in carbon and nitrogen load. The aerobic granular sludge obtained through this cultivation method shows that a low COD / N ratio (4-5) promotes the accumulation of slow-growing bacteria such as AOB and NOB, resulting in smaller, denser, and more stable granules, thus improving the system's nitrogen removal efficiency. Simultaneously, the system exhibits good stability and can continue to operate.

[0040] The above embodiments demonstrate that the cultivation method of the present invention can effectively prevent the proliferation of filamentous bacteria, improve system stability, and the cultivated aerobic particles have a short formation time, strong resistance to hydraulic shock loads, good stability, and the ability to efficiently remove wastewater with a low carbon-to-nitrogen ratio.

[0041] Example 3

[0042] A method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio includes the following steps:

[0043] S1. Before adding flocculent activated sludge as inoculum sludge to the sequencing batch reactor (SBR), wash the sludge with tap water. After the sludge is inoculated, add tap water to the reactor as the influent source, aerate for 1 day, then adjust the settling time to 30 minutes, and then discharge the water from the middle of the reactor.

[0044] S2. Low C / N ratio wastewater is fed into the reactor, which has a height-to-diameter ratio of 20. The reactor operates in the mode of influent-anoxic-aeration-sedimentation-discharge. The influent pH is controlled between 7 and 7, and the reactor operating environment temperature is controlled at 24℃ throughout the process. Specifically, the influent time is 5 min, anoxic time is 55 min, aeration time is 145-170 min, sedimentation time is 5-30 min, and effluent time is 5 min. The cycle time is 4 hours, and 6 cycles are run per day. The reactor volume exchange rate is maintained at 10%, the hydraulic retention time is 8 hours, and the aeration flow rate is 1.2 L / min.

[0045] During the initial aerobic granular sludge formation period, the sludge physical properties were tested regularly: MLSS, MLVSS, and SVI. 30 SVI 30 / SVI5, F / M, effluent SS and particle size, influent and effluent concentration changes: COD, ammonia nitrogen, NO x - -N and observation of sludge morphology using electron microscopy; under normal culture conditions: SVI5 and SVI 30 The concentration will gradually decrease from an initial 100-150 mL / g to below 60 mL / g; under a microscope, it can be observed that the flocculent matter in the system gradually decreases, and is replaced by small, oval-shaped particles; SVI 30 The SVI / SVI ratio will gradually approach 1; by monitoring the above indicators and after the activated sludge is successfully added to the reactor and aerated for one day, the settling time is directly adjusted from 30 min to 25 min, after which the SVI / SVI ratio will decrease. 30 For every 10 mL / g decrease, shorten the settling time by 5 min and correspondingly increase the aeration time by 5 min;

[0046] When the system consistently achieves a COD removal rate of 85% and an ammonia nitrogen removal rate of 90% for at least one week, and small aerobic granular sludge particles with a particle size >200um begin to appear inside the system, the settling time is directly adjusted to 5 minutes.

[0047] When the sludge concentration MLSS continuously decreases to below 1 g / L or the effluent SS concentration reaches 250 mg / L, the settling time is adjusted to 8 min. If the sludge concentration MLSS is at 0.8 g / L, the settling time is adjusted back to 8 min. If the MLSS is below 0.8 g / L, the settling time can be adjusted back to 15 min. When the sludge concentration is found to start to rise to 1 g / L and remain there for at least 7 days, the settling time is restored to 5 min.

[0048] During system operation, when the F / M value is higher than 0.5 g / gVss d or lower than 0.3 g / gVss d, the influent COD load should be adjusted: when the F / M value is higher than 0.5, the influent organic load should be reduced to restore the F / M value to normal; when the F / M value is lower than 0.3 g / gVss d, the presence of protozoa can damage the particle physical structure and cause system collapse. In this case, the influent organic load should be increased or sludge should be discharged from the bottom of the reactor to adjust the F / M to 0.3-0.5 g / gVss d.

[0049] The bottom of the reactor is equipped with microporous aeration heads, and air is supplied by an air compressor or constant pressure aeration pump in conjunction with the aeration heads. The aeration volume is adjusted by a rotor flow meter, and the pH value of the system is controlled at 7.

[0050] Once the aerobic granules are successfully cultured, the sludge is used for the treatment of high-load wastewater with a low carbon-to-nitrogen ratio.

[0051] Once the particles are formed, they are used to treat wastewater with a high load. The influent COD load is 1000 mg / L, the ammonia nitrogen load is 250 mg / L, the aeration is adjusted to 290 min, and the reactor operation cycle is 6 hours.

[0052] During the S2 step culture period, the influent COD load was 200 mg / L and the ammonia nitrogen load was 20 mg / L.

[0053] During the S2 step of cultivation, when the effluent nitrate nitrogen concentration is higher than 30 mg / L, an external circulation operation is added. Specifically, an external circulation operation is added to the anoxic section to divert the sewage 5 cm below the water level in the reactor to the sludge at the bottom of the reactor. The speed of the peristaltic pump is set to 30 r / min.

[0054] Example 4

[0055] A method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio includes the following steps:

[0056] S1. Before adding flocculent activated sludge as inoculum sludge to the sequencing batch reactor (SBR), wash the sludge with tap water. After the sludge is inoculated, add tap water to the reactor as the influent source, aerate for 1 day, then adjust the settling time to 30 minutes, and then discharge the water from the middle of the reactor.

[0057] S2. Low C / N ratio wastewater is fed into the reactor, which has a height-to-diameter ratio of 25. The reactor operates in the mode of influent-anoxic-aeration-sedimentation-discharge. The influent pH is controlled between 8 and 8, and the reactor operating temperature is controlled at 26℃ throughout the process. The cycle is as follows: influent 5 min, anoxic 55 min, aeration 145-170 min, sedimentation 5-30 min, effluent 5 min, cycle time 4 h, 6 cycles per day, reactor volume exchange rate is maintained at 50%, hydraulic retention time is 8 h, and aeration flow rate is 2.0 L / min.

[0058] During the initial aerobic granular sludge formation period, the sludge physical properties were tested regularly: MLSS, MLVSS, and SVI. 30 SVI 30 / SVI5, F / M, effluent SS and particle size, influent and effluent concentration changes: COD, ammonia nitrogen, NO x - -N and observation of sludge morphology using electron microscopy; under normal culture conditions: SVI5 and SVI 30 The concentration will gradually decrease from an initial 100-150 mL / g to below 60 mL / g; under a microscope, it can be observed that the flocculent matter in the system gradually decreases, and is replaced by small, oval-shaped particles; SVI 30 The SVI / SVI ratio will gradually approach 1; by monitoring the above indicators and after the activated sludge is successfully added to the reactor and aerated for one day, the settling time is directly adjusted from 30 min to 25 min, after which the SVI / SVI ratio will decrease. 30 For every 15 mL / g decrease, shorten the settling time by 5 min and correspondingly increase the aeration time by 5 min;

[0059] When the system consistently achieves a COD removal rate of 85% and an ammonia nitrogen removal rate of 90% for at least one week, and small aerobic granular sludge particles with a particle size >200um begin to appear inside the system, the settling time is directly adjusted to 5 minutes.

[0060] When the sludge concentration MLSS of the system continuously decreases to below 1 g / L or the effluent SS concentration is as high as 250 mg / L, the settling time is adjusted to 15 min. If the sludge concentration MLSS is at 1 g / L, the settling time is adjusted back to 8 min. If the MLSS is below 0.8 g / L, the settling time can be adjusted back to 15 min. When the sludge concentration is found to start to rise to greater than or equal to 1 g / L and remain there for at least 7 days, the settling time is restored to 5 min.

[0061] During system operation, when the F / M value is higher than 0.5 g / gVss d or lower than 0.3 g / gVss d, the influent COD load is adjusted: when the F / M value is higher than 0.5, the influent organic load is reduced to restore the F / M value to normal; when the F / M value is lower than 0.3 g / gVss d, the presence of protozoa can damage the particle physical structure and cause system collapse. In this case, the influent organic load is increased or sludge is discharged from the bottom of the reactor to adjust the F / M to 0.5 g / gVss d.

[0062] The bottom of the reactor is equipped with microporous aeration heads, and air is supplied by an air compressor or constant pressure aeration pump in conjunction with the aeration heads. The aeration volume is adjusted by a rotor flow meter, and the pH value of the system is controlled at 8.

[0063] Once the aerobic granules are successfully cultured, the sludge is used for the treatment of high-load wastewater with a low carbon-to-nitrogen ratio.

[0064] Once the particles are formed, they are used to treat wastewater with a high load. The influent COD load is 1000 mg / L, the ammonia nitrogen load is 250 mg / L, the aeration is adjusted to 290 min, and the reactor operation cycle is 6 hours.

[0065] During the S2 stage of cultivation, the influent COD load was 500 mg / L, and the ammonia nitrogen load was 125 mg / L.

[0066] During the S2 step of cultivation, when the effluent nitrate nitrogen concentration is higher than 30 mg / L, an external circulation operation is added. Specifically, an external circulation operation is added to the anoxic section to divert the sewage 10 cm below the water level in the reactor to the sludge at the bottom of the reactor. The speed of the peristaltic pump is set to 40 r / min.

[0067] Example 5

[0068] A method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio includes the following steps:

[0069] S1. Before adding flocculent activated sludge as inoculum sludge to the sequencing batch reactor (SBR), wash the sludge with tap water. After the sludge is inoculated, add tap water to the reactor as the influent source, aerate for 1 day, then adjust the settling time to 30 minutes, and then discharge the water from the middle of the reactor.

[0070] S2. Low C / N ratio wastewater is fed into the reactor, which has a height-to-diameter ratio of 22.5. The reactor operates in the mode of influent-anoxic-aeration-sedimentation-discharge. The influent pH is controlled between 7.5 and 7.5. The ambient temperature of the reactor is controlled at 25℃ throughout the entire process. The cycle is as follows: influent 5 min, anoxic 55 min, aeration 145-170 min, sedimentation 5-30 min, effluent 5 min, cycle time 4 h, 6 cycles per day, reactor volume exchange rate is maintained at 30%, hydraulic retention time is 8 h, and aeration flow rate is 1.6 L / min.

[0071] During the initial aerobic granular sludge formation period, the sludge physical properties were tested regularly: MLSS, MLVSS, and SVI. 30 SVI 30 / SVI5, F / M, effluent SS and particle size, influent and effluent concentration changes: COD, ammonia nitrogen, NO x - -N and observation of sludge morphology using electron microscopy; under normal culture conditions: SVI5 and SVI 30 The concentration will gradually decrease from an initial 100-150 mL / g to below 60 mL / g; under a microscope, it can be observed that the flocculent matter in the system gradually decreases, and is replaced by small, oval-shaped particles; SVI 30 The SVI / SVI ratio will gradually approach 1; by monitoring the above indicators and after the activated sludge is successfully added to the reactor and aerated for one day, the settling time is directly adjusted from 30 min to 25 min, after which the SVI / SVI ratio will decrease. 30 For every 12.5 mL / g decrease, shorten the settling time by 5 min and correspondingly increase the aeration time by 5 min;

[0072] When the system consistently achieves a COD removal rate of 85% and an ammonia nitrogen removal rate of 90% for at least one week, and small aerobic granular sludge particles with a particle size >200um begin to appear inside the system, the settling time is directly adjusted to 5 minutes.

[0073] When the sludge concentration MLSS continuously decreases to below 1 g / L or the effluent SS concentration reaches 250 mg / L, the settling time is adjusted to 11.5 min. If the sludge concentration MLSS is 0.9 g / L, the settling time is adjusted back to 8 min. If the MLSS is below 0.8 g / L, the settling time can be adjusted back to 15 min. When the sludge concentration is found to start to rise to greater than or equal to 1 g / L and remain there for at least 7 days, the settling time is restored to 5 min.

[0074] During system operation, when the F / M value is higher than 0.5 g / gVss d or lower than 0.3 g / gVss d, the influent COD load is adjusted: when the F / M value is higher than 0.5, the influent organic load is reduced to restore the F / M value to normal; when the F / M value is lower than 0.3 g / gVss d, the presence of protozoa can damage the particle physical structure and cause system collapse. In this case, the influent organic load is increased or sludge is discharged from the bottom of the reactor to adjust the F / M to 0.4 g / gVss d.

[0075] The bottom of the reactor is equipped with microporous aeration heads, and air is supplied by an air compressor or constant pressure aeration pump in conjunction with the aeration heads. The aeration volume is adjusted by a rotor flow meter, and the pH value of the system is controlled at 7.5.

[0076] Once the aerobic granules are successfully cultured, the sludge is used for the treatment of high-load wastewater with a low carbon-to-nitrogen ratio.

[0077] Once the particles are formed, they are used to treat wastewater with a high load. The influent COD load is 1000 mg / L, the ammonia nitrogen load is 250 mg / L, the aeration is adjusted to 290 min, and the reactor operation cycle is 6 hours.

[0078] During the S2 stage of cultivation, the influent COD load was 350 mg / L, and the ammonia nitrogen load was 72.5 mg / L.

[0079] During the S2 step of cultivation, when the effluent nitrate nitrogen concentration is higher than 30 mg / L, an external circulation operation is added. Specifically, an external circulation operation is added to the anoxic section to divert the wastewater 7.5 cm below the water level in the reactor to the sludge at the bottom of the reactor. The speed of the peristaltic pump is set to 35 r / min.

Claims

1. A method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio, characterized in that... Includes the following steps: S1. Before adding flocculent activated sludge as inoculum sludge into the sequencing batch reactor (SBR), wash the sludge with tap water. After the sludge is inoculated, tap water is added to the reactor as the influent source, and aeration is carried out for 1 day. Then the settling time is adjusted to 30 minutes, and the water is discharged from the middle of the reactor. S2. Low C / N ratio wastewater is fed into the reactor, which has a height-to-diameter ratio of 20-25. The reactor operates in the following mode: influent-anoxic-aeration-sedimentation-discharge. The influent pH is controlled between 7 and 8, and the reactor operating temperature is controlled between 24-26℃ throughout the process. Specifically, the influent time is 5 minutes, anoxic time is 55 minutes, aeration time is 145-170 minutes, sedimentation time is 5-30 minutes, and effluent time is 5 minutes. The cycle time is 4 hours, and 6 cycles are run per day. The reactor volume exchange rate is maintained at 10-50%, the hydraulic retention time is 8 hours, and the aeration flow rate is 1.2-2.0 L / min. During system operation, when the F / M value is higher than 0.5 g / (gVss·d) or lower than 0.3 g / (gVss·d), the COD load of the influent should be adjusted: when the F / M value is higher than 0.5, the influent organic load should be reduced to restore the F / M value to normal; when the F / M value is lower than 0.3 g / (gVss·d), the presence of protozoa will damage the particle physical structure and cause the system to collapse. At this time, the influent organic load should be increased or sludge should be discharged from the bottom of the reactor to adjust the F / M to 0.3-0.5 g / (gVss·d).

2. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1, characterized in that... During the initial aerobic granular sludge formation period, the sludge physical properties were tested regularly: MLSS, MLVSS, and SVI. 30 SVI 30 / SVI5, F / M, effluent SS and particle size, influent and effluent concentration changes: COD, ammonia nitrogen, NO x - -N and observation of sludge morphology using electron microscopy; under normal culture conditions: SVI5 and SVI 30 The concentration will gradually decrease from an initial 100-150 mL / g to below 60 mL / g; under a microscope, it can be observed that the flocculent matter in the system gradually decreases, and is replaced by small oval particles; SVI 30 The SVI / SVI ratio will gradually approach 1; monitor the above-mentioned physical properties of the sludge and changes in influent and effluent concentrations, and after the activated sludge is successfully added to the reactor and aerated for one day, directly adjust the settling time from 30 min to 25 min, and then the SVI / SVI ratio will be adjusted accordingly. 30 For every 10-15 mL / g decrease, shorten the settling time by 5 min and correspondingly increase the aeration time by 5 min.

3. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1 or 2, characterized in that... When the system consistently achieves a COD removal rate of 85% and an ammonia nitrogen removal rate of 90% for at least one week, and small aerobic granular sludge particles with a diameter >200um begin to appear inside the system, the settling time should be adjusted to 5 minutes.

4. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1 or 2, characterized in that... When the sludge concentration MLSS of the system continuously decreases to below 1 g / L or the effluent SS concentration is as high as 250 mg / L, the settling time is adjusted to 8-15 min. If the sludge concentration MLSS is between 0.8-1 g / L, the settling time is adjusted back to 8 min. If the MLSS is below 0.8 g / L, the settling time is adjusted back to 15 min. When the sludge concentration is found to start to rise to greater than or equal to 1 g / L and remain there for at least 7 days, the settling time is restored to 5 min.

5. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1, characterized in that... The bottom of the reactor is equipped with microporous aeration heads, and air is supplied by an air compressor or constant pressure aeration pump in conjunction with the aeration heads. The aeration volume is adjusted by a rotor flow meter, and the pH value of the system is controlled at 7-8.

6. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1, characterized in that... Once the aerobic granules are successfully cultured, the sludge is used for the treatment of high-load wastewater with a low carbon-to-nitrogen ratio.

7. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1, characterized in that... During the S2 stage of cultivation, the influent COD load is 200-500 mg / L, and the ammonia nitrogen load is 20-125 mg / L.

8. The method for cultivating aerobic granular sludge for treating wastewater with a low carbon-to-nitrogen ratio according to claim 1, characterized in that... During the S2 step of cultivation, when the effluent nitrate nitrogen concentration is higher than 30 mg / L, an external circulation operation is added. Specifically, an external circulation operation is added to the anoxic section to divert the sewage 5-10 cm below the water level in the reactor to the sludge at the bottom of the reactor. The speed of the peristaltic pump is set to 30-40 r / min.

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