Method for inhibiting sludge bulking through hypoxia-anoxic intermittent aeration

Abstract

The invention provides a method for inhibiting sludge bulking through hypoxia-anoxic intermittent aeration. The method comprises the following steps: inoculating activated sludge into a sequencing batch reactor, introducing sewage to be treated, mixing, and carrying out intermittent aeration treatment; wherein the intermittent aeration treatment comprises at least one cycle formed by alternation of a low-oxygen treatment time period and an anoxic treatment time period; and in the low-oxygen treatment period, the dissolved oxygen concentration in the reactor is controlled to be higher than that in the anoxic treatment period through aeration. According to the method, through low-oxygen-oxygen-deficiency alternate environment regulation and control, efficient nitrification and denitrification are achieved, meanwhile, filamentous bacterium growth is selectively inhibited, flora structure optimization is promoted, the sludge settling performance is rapidly recovered, the system denitrification efficiency is improved, and the method has the advantages of being simple in process, environmentally friendly and low in operation cost.

Description

Technical Field

[0001] This invention belongs to the field of biological treatment of domestic sewage and activated sludge technology, and relates to a method for inhibiting sludge bulking through intermittent aeration with low oxygen and anoxic conditions. Background Technology

[0002] Sludge bulking caused by the proliferation of filamentous bacteria is a typical problem in the operation of urban wastewater treatment systems. Traditional wastewater treatment processes often control the dissolved oxygen concentration above 2 mgO2 / L during the aerobic stage to ensure stable nitrification. Wastewater treatment processes are transitioning towards energy-saving and consumption-reducing low-oxygen nitrification. However, a long-term low-dissolved-oxygen operating environment limits the aerobic respiration of flocculent heterotrophic bacteria and their degradation efficiency of organic substrates, thus enhancing the competitive advantage of filamentous bacteria under low-oxygen conditions (reference 1). The proliferation of filamentous bacteria easily leads to the dispersion of activated sludge floc structure, deterioration of settling performance, and a sharp increase in the sludge volume index (SVI), which in turn causes sludge-water separation obstacles and increased sludge loss in the secondary settling tank. Furthermore, this phenomenon weakens the oxygen mass transfer efficiency of the biological treatment tank, interferes with the nitrification process, affects effluent quality, and seriously restricts the stable operation and further application of low-oxygen processes (reference 2).

[0003] Currently, commonly used methods for controlling sludge bulking mostly rely on the addition of chemical agents or biological inhibitors to specifically inhibit the growth of filamentous bacteria, thereby improving sludge settling performance. For example:

[0004] Reference 3 discloses a filamentous sludge bulking inhibitor and its application method. Although this technology uses conventional sludge as a low-cost raw material, the preparation process involves multiple complex steps such as ultrasonication, centrifugation, extraction, rotary evaporation, extraction, and dissolution.

[0005] Reference 4 discloses a method for simultaneously inhibiting filamentous bulking and viscous bulking in activated sludge. It proposes to operate a sequencing batch reactor in an alternating aeration mode to achieve simultaneous control of filamentous bulking and viscous bulking. However, vanillin still needs to be added as a filamentous bacteria inhibitor during the process.

[0006] Reference 5 discloses a biological phosphorus removal method for wastewater using anoxic starvation treatment. This method involves soaking mixed sludge and wastewater in a solution containing nitrite nitrogen to promote the proliferation of fermentative polyphosphate-accumulating bacteria and inhibit filamentous bacteria. However, prolonged exposure to a nitrite nitrogen environment may inhibit the metabolic activity of ammonia-oxidizing bacteria, thereby affecting the overall nitrification capacity of the system.

[0007] It should be noted that the above methods are all preventative measures for sludge bulking. However, research on how to effectively optimize and maintain the settling performance of bulked sludge that has already experienced a large proliferation of filamentous bacteria remains insufficient. Therefore, without the addition of additional chemical agents, rapidly inhibiting the excessive growth of filamentous bacteria and restoring sludge settling performance through reasonable control of process operating parameters has become crucial for solving the sludge bulking problem and promoting the stable operation and high-quality development of low-oxygen nitrification processes.

[0008] References:

[0009] Reference 1: Liu Hui, Li Xueqiang, Wang Xiaodong. Production test study on operation control of filamentous bacterial bulking of activated sludge [J]. China Water & Wastewater, 2013, 29 (3): 83-86.

[0010] Cited literature 2: António MP Martins, Krishna Pagilla, Joseph J Heijnen, Mark CM van Loosdrecht. Filamentous bulking sludge-a critical review[J]. Water Research, 2004, 38 (4): 793-817.

[0011] Reference 3: CN110117078A

[0012] Reference 4: CN119038737A

[0013] Reference 5: CN120004421A Summary of the Invention

[0014] The problem the invention aims to solve

[0015] As mentioned above, existing methods for inhibiting sludge bulking have the following limitations:

[0016] 1) Reliance on chemical additives, which can easily lead to secondary pollution and increased costs: Current mainstream methods generally require the addition of special chemical or biological inhibitors (such as vanillin). Such additives not only increase operating costs, but their residues may also cause potential secondary pollution to subsequent sludge disposal or the aquatic environment, and long-term use may lead to a decline in the adaptability of the microbial community.

[0017] 2) Complex process and difficult operation: Some methods (such as reference 3) involve multiple extraction and preparation processes, which are complicated and require high operation and management. They are not easy to be directly promoted and applied in existing sewage treatment systems, and are especially unsuitable for small and medium-sized sewage treatment facilities.

[0018] 3) Most of the measures are preventative and lack the ability to correct already bulked sludge: Existing technologies are mostly focused on preventing the excessive proliferation of filamentous bacteria. However, for sludge systems that have already experienced severe filamentous bulking (such as SVI > 250 mL / g and filamentous bacteria abundance > 40%), there is a lack of rapid, effective and stable recovery methods, resulting in long system recovery cycles and high operational risks.

[0019] 4) May affect the overall denitrification efficiency of the system: Some methods (such as reference 5) may inhibit the activity of ammonia-oxidizing bacteria and interfere with the nitrification process by introducing conditions such as nitrite nitrogen while inhibiting filamentous bacteria, resulting in a decrease in denitrification efficiency. It is difficult to balance sludge settling performance and denitrification effect in low-oxygen nitrification process.

[0020] 5) High energy consumption, which is inconsistent with the trend of low-carbon operation: Some methods require maintaining a high dissolved oxygen level, which leads to increased energy consumption and does not meet the current needs of energy conservation, consumption reduction and process transformation in the wastewater treatment industry.

[0021] Based on this, the present invention provides a sludge bulking inhibition method that requires no chemical additives, is simple to operate, has low energy consumption, is applicable to already bulked sludge systems, and can simultaneously improve denitrification efficiency. Specifically, the present invention provides a method for inhibiting sludge bulking through low-oxygen-anoxic intermittent aeration. Its core lies in creating a periodically changing dissolved oxygen environment by adjusting the aeration-to-stop time ratio and the dissolved oxygen level in the reactor. This promotes the growth of flocculent nitrifying bacteria and facultative heterotrophic bacteria (including denitrifying bacteria) while inhibiting the proliferation of filamentous bacteria, thereby optimizing sludge settling performance and improving denitrification efficiency.

[0022] Furthermore, the method of this invention introduces a periodic anoxic phase into a low-oxygen nitrification system containing organic matter. It utilizes the differences in adaptability of filamentous bacteria (mostly obligate aerobic bacteria) and flocculent heterotrophic bacteria (mostly facultative bacteria) to different oxygen environments to achieve selective inhibition of filamentous bacteria. In addition, this operating mode also creates favorable conditions for simultaneous nitrification and denitrification, improving sludge settling performance while enhancing the system's nitrogen removal capacity, and simultaneously achieving energy conservation, consumption reduction, and operational stability.

[0023] Solution for solving the problem

[0024] It has been found that the above-mentioned technical problems can be solved by implementing the following technical solutions:

[0025] [1]. A method for inhibiting sludge bulking by low-oxygen-anoxic intermittent aeration, comprising the following steps: inoculating activated sludge into a sequencing batch reactor and mixing it with wastewater to be treated before intermittent aeration treatment;

[0026] The intermittent aeration treatment includes at least one cycle consisting of alternating periods of low oxygen treatment and anoxic treatment; and during the low oxygen treatment period, the dissolved oxygen concentration in the reactor is controlled to be higher than that during the anoxic treatment period by aeration, and the duration ratio of the low oxygen treatment period to the anoxic treatment period is 1:(0.3~1.2).

[0027] During the low-oxygen treatment period, the dissolved oxygen concentration in the reactor is controlled to be below 1.0 mg O2 / L by aeration.

[0028] Furthermore, before the intermittent aeration treatment, the sludge volume index of the activated sludge is not less than 250 mL / g.

[0029] [2]. According to the method described in [1], wherein,

[0030] Before the intermittent aeration treatment, the relative abundance of filamentous bacteria in the activated sludge is not less than 40%.

[0031] [3]. According to the method described in [1] or [2], wherein,

[0032] During the low-oxygen treatment period, the dissolved oxygen concentration in the reactor is controlled to be below 0.5 mg O2 / L by aeration.

[0033] [4]. According to any one of [1]-[3], wherein,

[0034] In a single cycle, the duration of the hypoxia treatment period is 0.7 to 3 hours, and the duration of the anoxic treatment period is 0.1 to 3 hours.

[0035] [5]. According to any one of [1]-[4], wherein,

[0036] The duration ratio of the hypoxia treatment period to the anoxic treatment period is 1:(0.3~1).

[0037] [6]. According to any one of [1]-[5], wherein,

[0038] The reactor operates in a cyclical manner, with each cycle consisting of: an influent stage, an intermittent aeration treatment stage, a sludge settling stage, and a drainage stage.

[0039] [7]. According to any one of [1]-[6], wherein,

[0040] After the intermittent aeration treatment is completed, the sludge volume index of the activated sludge is below 150 mL / g.

[0041] [8]. According to any one of [1]-[7], wherein,

[0042] After the intermittent aeration treatment is completed, the relative abundance of filamentous bacteria in the activated sludge is below 15%.

[0043] [9]. According to any one of [1]-[8], wherein,

[0044] The method operates without the addition of any additional chemical reagents.

[0045] The effects of the invention

[0046] By implementing the above technical solution, the present invention can achieve the following technical effects:

[0047] 1) Green economy and easy operation: Sludge bulking can be inhibited simply by adjusting the operation and aeration program, without the need to add any chemical agents, thus fundamentally avoiding secondary pollution, and has the advantages of low cost and simple operation.

[0048] 2) Significant inhibition effect and stable operation: It can quickly and effectively inhibit the growth of filamentous bacteria, significantly improve sludge settling performance, maintain stable system operation under different aeration time ratios, and has strong anti-interference ability.

[0049] 3) Improved nitrogen removal efficiency and stable water quality: While maintaining efficient nitrification, the system's simultaneous nitrification and denitrification capabilities have been enhanced, achieving a simultaneous improvement in nitrogen removal efficiency and ensuring stable compliance of effluent water quality.

[0050] 4) Significant energy saving and consumption reduction, with broad application prospects: The operation mode of low oxygen combined with intermittent aeration significantly reduces aeration energy consumption, providing reliable technical support for energy saving, consumption reduction and stable operation of sewage treatment plants, and has broad application prospects. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the reactor structure and its operating conditions.

[0052] Figure 2 The graph shows the change of dissolved oxygen concentration over time during three typical cycles.

[0053] Figure 3 The graph shows the test results of sludge settling performance in the reactor.

[0054] Figure 4 The graph shows the test results of ammonia nitrogen in the reactor influent and nitrogen concentrations in the effluent.

[0055] Figure 5 The graph shows the test results for the total nitrogen removal rate of the reactor.

[0056] Figure 6 The graph shows the test results of COD concentration and removal rate in the reactor influent and effluent;

[0057] Figure 7 This is a graph showing the relative abundance changes of the microbial community at the genus level within the reactor. Detailed Implementation

[0058] The present invention will now be described in detail. The descriptions of the technical features described below are based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0059] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0060] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0061] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0062] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0063] In this specification, "room temperature" or "room temperature" refers to an indoor ambient temperature of "23±2℃", and unless otherwise specified, the "sludge volume index" of this invention refers to the sludge volume index at this temperature.

[0064] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" indicates weight or mass percentage.

[0065] In this specification, the term "substantially" is used to indicate that the standard deviation from the theoretical model or theoretical data is within a range of 5%, preferably 3%, and more preferably 1%.

[0066] In this specification, the terms “comprising” and / or “including” are used to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0067] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0068] The present invention provides a method for inhibiting sludge bulking by low-oxygen-anoxic intermittent aeration, which includes the following steps: inoculating activated sludge into a sequencing batch reactor, and then mixing it with wastewater to be treated and performing intermittent aeration treatment.

[0069] The intermittent aeration treatment includes at least one cycle consisting of alternating low-oxygen treatment periods and anoxic treatment periods; and during the low-oxygen treatment periods, the dissolved oxygen concentration in the reactor is controlled to be higher than that during the anoxic treatment periods through aeration.

[0070] Wastewater to be treated

[0071] The wastewater to be treated in this invention is primarily an aqueous system containing inorganic nitrogen and a certain amount of organic matter. In some specific embodiments of this invention, the amount of inorganic nitrogen present in the wastewater to be treated is expressed as ammonia nitrogen (NH4). + The concentration of N (calculated as -N) is below 60 mgN / L, preferably 10~60 mgN / L.

[0072] Furthermore, there are no particular requirements in principle for the chemical oxygen demand (COD) value of the wastewater to be treated in this invention, as it is related to its source. In some specific embodiments of this invention, the organic matter content in the wastewater to be treated is such that the COD value is not greater than 500 mg / L, preferably 200~300 mg / L.

[0073] Furthermore, the wastewater to be treated in this invention includes simulated domestic sewage or actual domestic sewage, such as urban domestic sewage or rural domestic sewage.

[0074] Activated sludge

[0075] The activated sludge used in this invention comes from an activated sludge nitrification system that has been operating under low-oxygen conditions for a long time and has experienced severe filamentous bulking.

[0076] In some specific implementation schemes, before the intermittent aeration treatment, the sludge volume index (SVI) of the activated sludge is not less than 250 mL / g, preferably above 300 mL / g, more preferably above 350 mL / g, and even more preferably above 400 mL / g. The SVI of activated sludge is a key indicator reflecting its degree of bulking. A higher SVI indicates that the sludge settling performance has significantly deteriorated, making it suitable for rapid recovery using this method.

[0077] In some specific implementations, prior to the intermittent aeration treatment, the relative abundance of filamentous bacteria in the activated sludge is not less than 40%, preferably more than 45%, and more preferably more than 50%. This condition helps to confirm that sludge bulking is mainly caused by filamentous bacteria, thereby allowing the inhibitory effect of this method to be more targeted.

[0078] In some specific implementations, the sequencing batch reactor employs a treatment mode that alternates between low-oxygen and anoxic treatment periods. The low-oxygen treatment period is primarily used to acclimate and enrich nitrifying bacteria (including full-process nitrifying bacteria, traditional ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria) to enable them to efficiently complete biological nitrification (including ammonia oxidation and nitrite oxidation). The anoxic treatment period focuses on acclimatizing and enriching denitrifying bacteria to achieve deep nitrogen removal.

[0079] In some specific embodiments, during the low-oxygen treatment period, the dissolved oxygen concentration in the reactor is controlled to be below 1.0 mg O2 / L, preferably below 0.5 mg O2 / L, and more preferably 0.1~0.5 mg O2 / L, for example, 0.1 mg O2 / L, 0.2 mg O2 / L, 0.3 mg O2 / L, 0.4 mg O2 / L, 0.5 mg O2 / L, etc. By controlling the dissolved oxygen concentration to below 1.0 mg O2 / L during the low-oxygen treatment period, this invention helps reduce aeration energy consumption while avoiding excessive impact on the nitrifying bacteria community of the low-oxygen nitrification system. There are no particular limitations on the aeration operation method of this invention. In some specific embodiments, for example, aeration heads can be installed in the reactor, and aeration can be carried out under the action of an air pump.

[0080] In some specific embodiments, the dissolved oxygen concentration during the anoxic treatment period is below 0.1 mg O2 / L, preferably below 0.03 mg O2 / L, and more preferably below 0.01 mg O2 / L. For example, it can be 0 mg O2 / L, 0.005 mg O2 / L, 0.01 mg O2 / L, 0.02 mg O2 / L, 0.03 mg O2 / L, 0.05 mg O2 / L, 0.08 mg O2 / L, etc. By controlling the dissolved oxygen concentration during the anoxic treatment period to below 0.1 mg O2 / L, this invention effectively avoids inhibiting the activity of denitrifying bacteria, allowing anaerobic or facultative anaerobic bacteria to utilize the organic matter in the influent as a carbon source and convert the NO generated during the low-oxygen treatment period... X - -N is reduced to N2, achieving the effect of denitrification.

[0081] In some specific implementations, the duration of the hypoxia treatment period in a single cycle is 0.7 to 3 hours, for example, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, etc.; the duration of the anoxic treatment period is 0.1 to 3 hours, for example, 0.1 hours, 0.2 hours, 0.3 hours, 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, etc.

[0082] In some specific implementations, the duration ratio of the hypoxic treatment period (aeration stage) to the anoxic treatment period (non-aeration or aeration-stopped stage) is 1:(0.3~1.2), preferably 1:(0.3~1), for example, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.3:1, etc. By controlling the duration ratio of the hypoxic treatment period to the anoxic treatment period within the above range, sufficient nitrification and organic matter degradation in the hypoxic stage can be ensured, while providing sufficient time for denitrification in the anoxic stage. This effectively inhibits the excessive growth of filamentous bacteria while achieving efficient nitrogen removal and maintaining stable system operation.

[0083] In some specific implementations, the reactor is equipped with a mechanical stirring device. This mechanical stirring device is either a plug-flow agitator or a paddle agitator, and its motor is either a variable frequency motor or a fixed frequency motor. This stirring device has a dual function: firstly, by forcing fluid movement, it prevents the deposition of activated sludge flocs or inorganic particles, maintaining a homogeneous sludge-wastewater system and ensuring sufficient contact between microorganisms and wastewater; secondly, it promotes the uniform distribution of dissolved oxygen during low-oxygen treatment periods, avoiding excessively high local oxygen concentrations that inhibit denitrification, while simultaneously accelerating the transfer of nitrates to the surface of microorganisms during anoxic treatment periods.

[0084] In some specific implementations, the reactor operates in a cyclical manner, with each cycle sequentially comprising: an influent stage, an intermittent aeration stage, a sludge settling stage, and a effluent stage. A complete operating cycle is preferably controlled within 2–12 hours, ideally 4–8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours. This cycle range balances the efficiency of organic matter degradation, nitrification, and denitrification processes, and is beneficial for maintaining the metabolic activity of the sludge microbial community and the long-term stability of the system.

[0085] In some specific implementations, after the intermittent aeration treatment, the sludge volume index of the activated sludge is below 150 mL / g, preferably below 120 mL / g, and more preferably below 100 mL / g. This index is significantly lower than the high level before treatment (typically >250 mL / g), indicating a fundamental improvement in sludge settling performance and effective control of filamentous bulking problems.

[0086] In some specific implementations, after the intermittent aeration treatment, the relative abundance of filamentous bacteria in the activated sludge is less than 15%, preferably less than 10%, and more preferably less than 5%. This indicator is significantly lower than before treatment (typically ≥40%), indicating that the overgrowth of filamentous bacteria has been effectively suppressed and the sludge microbial community structure has been optimized. This is also direct microbiological evidence for the significant improvement in sludge settling performance (SVI).

[0087] In some specific implementations, the method operates without the addition of additional chemical agents. This method relies entirely on process control to adjust sludge structure and improve denitrification performance, thus combining environmental friendliness and economic efficiency.

[0088] By implementing the above method, the present invention can achieve a COD removal rate of over 95% and an ammonia nitrogen removal rate of nearly 100%.

[0089] This invention achieves efficient nitrification and denitrification through alternating low-oxygen and anoxic environmental regulation, while selectively inhibiting the growth of filamentous bacteria and promoting the optimization of the microbial community structure. This rapidly restores sludge settling performance and improves the system's nitrogen removal efficiency. It has the advantages of simple process, environmental friendliness, and low operating cost.

[0090] Example

[0091] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0092] In this embodiment of the invention, the sludge volume index (SVI) is calculated as follows:

[0093]

[0094] SVI represents the sludge volume index (mL / g), and the SVI range for normal activated sludge is 50~120 mL / g; SV 30 MLSS represents the sludge settling volume (mL / L), which is the ratio of the volume of sludge settled after 30 minutes of settling to the volume of the mixed liquor taken; MLSS represents the suspended solids concentration of the mixed liquor (g / L).

[0095] The testing methods for each water quality indicator are as follows: ammonia nitrogen (NH4) + -N), Nessler's reagent spectrophotometry; nitrite nitrogen (NO2) - -N), N-(1-naphthyl)-ethylenediamine spectrophotometric method; nitrate nitrogen (NO3) --N), ultraviolet spectrophotometry; total nitrogen (TN) is represented by the sum of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen; chemical oxygen demand (COD) is determined by the potassium dichromate method.

[0096] Example 1:

[0097] This embodiment provides a method for inhibiting sludge bulking through intermittent low-oxygen-anoxic aeration, which includes the following steps:

[0098] 1. Reactor construction and sludge inoculation

[0099] A laboratory-scale sequencing batch reactor (SBR) with an effective volume of 3.6L was used, including an agitator, aerators, and a gas flow meter. The sludge inoculated into the reactor was activated sludge taken from a traditional nitrification system that had been operating under low oxygen conditions for a long time and had undergone severe filamentous bulking, with an initial sludge volume index (SVI) higher than 400 mL / g. Therefore, in the initial stage of the reactor (Stage I), a membrane module (Biyuan RF-0.5 ultrafiltration membrane module) was added to the SBR to filter the effluent for effective sludge-water separation.

[0100] 2. Operating Method

[0101] like Figure 1 As shown, the reactor operates stably in 6-hour cycles, each cycle consisting of: influent (15 min), intermittent aeration, sludge settling, and effluent. The influent is simulated domestic sewage, with a chemical oxygen demand (COD) of 250 mg / L (using glucose as the carbon source) and ammonia nitrogen (NH4+). + The nitrogen concentration (N) was 50 mg N / L (using ammonium chloride as the nitrogen source). The hydraulic retention time was 21.6 h.

[0102] The system operates in a low-oxygen-anoxic intermittent aeration mode: In Phase I (days 0-26), the aeration time is set to 1.5 h / 0.5 h, and the aeration flow rate during aeration is controlled at 100 mL / min using a gas flow meter; after the system stabilizes, to enhance the denitrification effect, in Phase II (days 26-46), the aeration rate is reduced to 60 mL / min, and the dissolved oxygen (DO) concentration during aeration is not higher than 0.5 mg O2 / L; in Phase III (days 46-66), to further enhance the denitrification effect, the aeration / stop time is adjusted to 1 h / 1 h, and the aeration rate is 60 mL / min.

[0103] The changes in dissolved oxygen concentration over time during the typical three-stage cycle are as follows: Figure 2As shown, Stage I uses a relatively large aeration rate (100 mL / min), but the dissolved oxygen concentration during the aeration period remains basically below 1 mg O2 / L, lower than the 2 mg O2 / L control level commonly used in traditional nitrification processes. Therefore, the overall environment is low-oxygen. During the non-aeration period, the dissolved oxygen drops rapidly, and the reactor becomes anoxic. As the filamentous bacteria die off and the sludge concentration decreases during operation, the oxygen mass transfer efficiency of the mixed liquor improves significantly, and the dissolved oxygen concentration rises rapidly at the same aeration flow rate.

[0104] Therefore, in Stage II, the aeration rate was adjusted to 60 mL / min to bring the reactor to a stable operating state. During the first 240 minutes of aeration in this stage, the dissolved oxygen concentration was maintained at approximately 0.1 mg O2 / L, while it was close to zero during the non-aeration period. By the last aeration period, since ammonia nitrogen and COD had been largely degraded, continuous aeration caused the dissolved oxygen to gradually increase.

[0105] Phase III further shortened the aeration time while maintaining the same aeration flow rate. During the aeration period, when the oxygen consumption rate and the aeration rate reached equilibrium, dissolved oxygen could be stably maintained at an extremely low level (approximately 0.01 mg O2 / L), and no surge in dissolved oxygen concentration due to over-aeration occurred at the end of the cycle.

[0106] 3. Performance

[0107] After two months of continuous operation, the system performance has been significantly improved, with the specific results as follows:

[0108] 3.1 Sludge settling performance:

[0109] Test results are as follows Figure 3 As shown, on day 10, the SVI value reached an inflection point and began to decline rapidly, with the sludge concentration decreasing simultaneously. Subsequently, the SVI value continued to fall, dropping below 120 mL / g for the first time on day 30, and eventually stabilizing at around 100 mL / g, indicating a significant improvement in sludge settling performance and sustained suppression of bulking. After the sludge concentration experienced a decline, it remained stable within the range of 1.7-1.9 g / L, suggesting that the good settling performance in stages (II and III) was not due to mass microbial death, but more likely related to changes in the microbial community structure driven by intermittent aeration.

[0110] This demonstrates that the sludge settling performance has been fundamentally improved. The sludge volume index (SVI) decreased continuously from an initial high level (>400 mL / g) and eventually stabilized at a normal level of approximately 100 mL / g, indicating that sludge bulking has been successfully suppressed. After the sludge settling performance optimization (stages II and III), sludge-water separation can be effectively achieved without the need for membrane filtration during the sedimentation and effluent stages of the reactor.

[0111] 3.2 Effluent water quality:

[0112] nitration effect :

[0113] Depend on Figure 4 It can be seen that during the reactor start-up phase, the high sludge concentration limited mass transfer, resulting in a low nitrification rate and the accumulation of small amounts of ammonia nitrogen and nitrite nitrogen in the effluent. After about two weeks of acclimatization, the system's nitrification performance stabilized, and the effluent ammonia nitrogen and nitrite nitrogen levels dropped to below the detection limit, while the nitrate nitrogen concentration increased accordingly.

[0114] After reducing the aeration rate in Stage II, the reactor was still able to completely remove ammonia nitrogen without the accumulation of nitrite. The reduction in aeration rate also enhanced denitrification, resulting in a decrease in nitrate nitrogen concentration in the effluent and a continuous decrease in total nitrogen in the effluent.

[0115] Phase III further shortens the aeration time, and under the premise of maintaining no accumulation of ammonia nitrogen and nitrite nitrogen, the denitrification effect is further enhanced, the total nitrogen concentration in the effluent is further reduced, and the overall denitrification performance of the system is optimized.

[0116] This demonstrates that the system exhibits excellent and stable nitrification performance, with the effluent ammonia nitrogen concentration consistently close to 0 (below the detection limit), a removal rate approaching 100%, and no nitrite accumulation observed.

[0117] Total nitrogen (TN) removal rate test results:

[0118] Depend on Figure 5 It can be seen that the total nitrogen removal rate of the reactor was maintained at 30%-40% during the start-up phase. In the later stage of Stage I, as the sludge concentration decreased and mass transfer performance improved, the anoxic zone within the reactor decreased, and denitrification was somewhat inhibited, resulting in a slight decrease in the total nitrogen removal rate. In Stage II, by reducing the aeration rate, denitrification conditions were improved, and the total nitrogen removal rate gradually recovered. In Stage III, after further shortening the aeration time, denitrification efficiency continued to improve, and the system's total nitrogen removal rate further increased to 50%-60%.

[0119] This shows that the total nitrogen (TN) removal rate of the system gradually increases with operating time, eventually reaching 59%.

[0120] Chemical oxygen demand (COD) test results:

[0121] Depend on Figure 6 It can be seen that the method of the present invention has a significant effect on COD degradation, and the COD removal rate is always maintained above 95% throughout the entire operation.

[0122] 3.3 Changes in the microbial community:

[0123] Tracking analysis of the microbial community showed that ( Figure 7The typical filamentous bacterium *Thiothrix* was dominant in the initial stage, but its relative abundance decreased sharply during operation, from an initial 56.8% to 7.52% on day 26, and remained below 15% even after subsequent reductions in aeration levels. Another filamentous bacterium, *Kouleothrix*, also showed a decreasing trend from day 0 to 26, but experienced a slight rebound after reducing aeration. The significant decrease in overall filamentous bacterium abundance was consistent with the trend of improved sludge settling performance.

[0124] Meanwhile, the relative abundance of *Gnaphalium noranke f. Saprospiraceae* gradually increased from 0.77% to 5-10%. *Gnaphalium noranke f. Saprospiraceae* possesses the ability to decompose complex carbon sources such as extracellular polymers and participates in interbacterial predation; previous studies have suggested that it contributes to the formation and stabilization of aerobic granular sludge. Therefore, it is speculated that *Gnaphalium noranke f. Saprospiraceae* may play a promoting role in the inhibition of filamentous bacteria and the improvement of sludge settling properties in this study. Furthermore, *Gnaphalium noranke o. Saccharimonadales*, *Gnaphalium noranke* Terrimonas, and *Gnaphalium noranke o. Chitinophagales* have also been reported to have strong hydrolytic functions and may have similar effects.

[0125] Regarding nitrifying bacteria, the inoculated sludge was a low-oxygen nitrifying sludge dominated by nitrifying bacteria (comammox Nitrospira) and nitrite-oxidizing bacteria (NOB) of the genus Nitrospira. Therefore, the dominant genus in the nitrification process was Nitrospira, which includes both nitrifying bacteria and traditional NOB (initially about 5.0%). During operation, Nitrospira remained dominant, rising to over 10% by day 26, while the relative abundance of traditional ammonia-oxidizing bacteria Nitrosomonas remained low (≤0.17%). On the other hand, the proportion of denitrifying microorganisms such as g__Terrimonas, g__Denitratisoma, g__Hyphomicrobium, and g__unclassified_f__Comamonadaceae increased significantly. This is consistent with the anoxic environment provided during the non-aeration phase of the operation cycle, and the enrichment of denitrifying bacteria corresponds to the gradual optimization of the reactor's nitrogen removal efficiency.

[0126] The relative abundance of the typical filamentous bacterium *Thiothrix* dropped sharply from an initial dominant 56.8% to 7.52% on day 26, and remained below 15% even after further reductions in aeration levels. Meanwhile, the relative abundance of genera with denitrification functions (such as *Terrimonas* and *Denitratisoma*) and genera that help improve sludge settling performance (such as *Saprospiraceae*) increased significantly, resulting in a more optimized microbial community structure.

[0127] Comparative Example 1:

[0128] The operation is basically the same as in Example 1, except that the aeration / stop time is adjusted to 0.67h / 1.33h in stages I to III (days 0-66), that is, the ratio of aeration time to stop time is about 1:2.

[0129] Under these operating conditions, the overall treatment efficiency of the process will face a significant risk of decline. The main problem lies in insufficient aeration time, leading to a persistently low dissolved oxygen supply in the reactor, which severely weakens the efficiency of nitrification and organic matter carbonization. Especially when the influent ammonia nitrogen load is high, the activity of nitrifying bacteria decreases significantly due to insufficient dissolved oxygen, easily leading to an increase in effluent ammonia nitrogen concentration and even causing nitrite accumulation.

[0130] Furthermore, the microbial community structure and sludge performance are also negatively affected. On the one hand, excessively short continuous aeration periods are insufficient to maintain the growth dominance of functional bacteria such as nitrifying bacteria and aerobic heterotrophic bacteria. Long-term operation may lead to a decrease in the proportion of nitrifying bacteria, a decrease in sludge activity, and a weakening of system functional stability and resistance to shock loads. On the other hand, some filamentous bacteria (such as Microthrix parvicella) have a strong ability to adapt to low-oxygen environments or exhibit a competitive advantage under anoxic conditions (NIELSEN PH, ROSLEV P, DUEHOLM TE, et al. Microthrix parvicella, aspecialized lipid consumer in anaerobic-aerobic activated sludge plants [J]. Water Science & Technology, 2002, 46(1-2): 73-80). Therefore, excessively long anoxic periods may actually weaken the inhibitory effect on filamentous bacteria, thereby leading to a deterioration in sludge settling performance.

[0131] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0132] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for inhibiting sludge bulking by low oxygen-anoxic intermittent aeration, characterized by, The method comprises the following steps: inoculating activated sludge into a sequencing batch reactor, and mixing sewage to be treated and then performing intermittent aeration treatment; The intermittent aeration treatment comprises at least one cycle formed by alternating a low-oxygen treatment period and an anoxic treatment period; the dissolved oxygen concentration in the reactor is controlled to be higher in the low-oxygen treatment period than in the anoxic treatment period, and the length ratio of the low-oxygen treatment period to the anoxic treatment period is 1:(0.3-1.2); The dissolved oxygen concentration in the reactor is controlled to be 1.0 mg O2 / L or less in the low-oxygen treatment period; Before the intermittent aeration treatment, the sludge volume index of the activated sludge is not less than 250 mL / g.

2. The method according to claim 1, wherein Before the intermittent aeration treatment, the relative abundance of filamentous bacteria in the activated sludge is not less than 40%.

3. The method according to claim 1 or 2, wherein The dissolved oxygen concentration in the reactor is controlled to be 0.5 mg O2 / L or less in the low-oxygen treatment period.

4. The method according to any one of claims 1-3, wherein In a single cycle, the length of the low-oxygen treatment period is 0.7-3 h, and the length of the anoxic treatment period is 0.1-3 h.

5. The method according to any one of claims 1-4, wherein The length ratio of the low-oxygen treatment period to the anoxic treatment period is 1:(0.3-1).

6. The method according to any one of claims 1-5, wherein The reactor is operated in a periodic mode, and each operation cycle comprises, in sequence, a water feeding stage, an intermittent aeration treatment stage, a sludge settling stage, and a water discharge stage.

7. The method according to any one of claims 1-6, wherein After the intermittent aeration treatment, the sludge volume index of the activated sludge is 150 mL / g or less.

8. The method according to any one of claims 1-7, wherein After the intermittent aeration treatment, the relative abundance of filamentous bacteria in the activated sludge is 15% or less.

9. The method according to any one of claims 1-8, wherein The method is operated without additional chemical agents.

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