Microorganism rapid biofilm formation method based on dissolved oxygen stress

Abstract

The application discloses a kind of microbial quick biofilm formation methods based on dissolved oxygen stress, belong to sewage treatment technical field.The core of the method is that through high dissolved oxygen aerobic activation and the alternative cycle of critical low dissolved oxygen anoxic stress, active physiological acclimation and screening are carried out to microbial community, and after each stress cycle, microaerophilic gas supply and low C / N ratio environment are used for directional enrichment, so that in a short time, the biological membrane rich in high-activity nitrifying bacteria and dense structure is quickly constructed on the surface of MABR membrane.The application breaks through the technical bottleneck of long biofilm formation period, intense competition of flora and easy shedding of biological membrane in traditional method, realizes efficient, rapid and stable start of MABR system, and is especially suitable for treatment of high ammonia nitrogen and low carbon nitrogen ratio sewage.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a rapid microbial biofilm formation method based on dissolved oxygen stress, and more particularly to a biofilm formation method based on dissolved oxygen stress and niche regulation to achieve rapid and directional enrichment of nitrifying bacteria on the surface of a MABR membrane. Background Technology

[0002] Currently, the activated sludge process is widely used in ammonia nitrogen wastewater treatment due to its advantages of large treatment capacity, high efficiency, and good effluent quality. Various modified versions of the activated sludge process exhibit good nitrogen and phosphorus removal performance and are widely used in urban wastewater treatment. However, its disadvantages include difficulty in achieving high aerobic microbial biomass in the activated sludge system, low nitrification efficiency leading to weak shock resistance of the nitrification system, incomplete nitrification, and the need for large aeration volumes and retention times. Furthermore, its operation, maintenance, and management are relatively difficult. In recent years, with the continuous improvement of biological wastewater treatment technologies, biofilm processes have gradually been applied in biological nitrogen removal technologies. Due to their advantages such as stable operation, low sludge residue, simple management, strong removal capacity for ammonia nitrogen and recalcitrant pollutants, and adaptability to a wide range of water quality variations, they are increasingly being used in the treatment of domestic sewage and industrial wastewater.

[0003] The biofilm method refers to the introduction of microorganisms (nitrifying bacteria and denitrifying bacteria) into wastewater treatment, allowing them to attach to or become fixed on the surface of biological packing materials, forming a biofilm. Through contact between the wastewater and the biofilm, mass transfer occurs between the solid and liquid phases, achieving the biodegradation of pollutants such as ammonia nitrogen in the wastewater. Depending on the operating method, it can be divided into biological filters, biological rotating discs, biological contact oxidation, etc. Although their structures differ greatly, their basic principles are the same.

[0004] Membrane biofilm reactors (MABRs) are an emerging wastewater treatment technology that utilizes hollow fiber membranes for bubble-free oxygen supply. Oxygen diffuses directly to the biofilm attached to the membrane surface, enabling simultaneous nitrification and denitrification processes. This results in significant advantages such as high oxygen mass transfer efficiency, low energy consumption, and excellent nitrogen removal. However, the widespread application of MABR technology is severely limited by its slow start-up phase (i.e., the "microbial biofilm formation" phase). Existing biofilm formation methods typically employ direct submersion natural biofilm formation or low-load continuous operation, which suffer from the following drawbacks:

[0005] 1. Long biofilm formation period: Due to the slow growth rate of nitrifying bacteria (including ammonia oxidizing bacteria AOB and nitrite oxidizing bacteria NOB), natural biofilm formation usually takes 20-40 days or even longer, which seriously affects the commissioning progress and economic benefits of the project.

[0006] 2. Disadvantage in microbial competition: In the early stage of biofilm formation, fast-growing heterotrophic bacteria will preferentially occupy the ecological niche on the biofilm surface, compete for oxygen and space, and inhibit the attachment and growth of nitrifying bacteria, resulting in a low proportion and poor activity of nitrifying bacteria in the final biofilm, and limited denitrification capacity.

[0007] 3. Unstable biofilm structure: Biofilms formed by traditional methods have a loose structure and weak adhesion to the membrane surface. They are prone to large-scale detachment under hydraulic scouring and load impact, resulting in unstable system treatment efficiency.

[0008] 4. Inefficient process control: There is a lack of precise and dynamic control over key parameters such as dissolved oxygen (DO) and carbon-nitrogen ratio (C / N). The success rate and efficiency of biofilm formation depend on experience and have poor repeatability.

[0009] Therefore, there is an urgent need in this field for a biofilm attachment method that can overcome the limitations of natural microbial growth and actively, rapidly, and directionally enrich highly active nitrifying bacteria on the surface of MABR membranes. Summary of the Invention

[0010] This invention aims to overcome the shortcomings of existing technologies by proposing an alternating oscillating cycle of high-DO aerobic activation treatment and critically low-DO hypoxic stress. It utilizes the differences in the sensitivity of nitrifying bacteria to sudden hypoxia to achieve competitive screening of highly active strains, breaking through the biological selection blind spot of traditional submerged natural static biofilm formation. This provides a rapid microbial biofilm formation method with an extremely short formation cycle, uniform biofilm formation, high nitrifying bacteria enrichment efficiency, and stable system operation. To achieve the above objectives, this invention employs the following technical solution:

[0011] This invention proposes a method for rapid microbial biofilm formation based on dissolved oxygen stress, comprising:

[0012] Step 1: Prepare inoculum: Place the microbial raw material containing nitrifying bacteria into the inoculation tank;

[0013] Step 2, Dissolved Oxygen Stress Cycling and Targeted Enrichment: The inoculation tank is alternately subjected to high DO aerobic activation treatment and critical low DO hypoxia stress treatment to form a stress cycle. After each cycle, the MABR membrane module to be attached is immersed in the inoculation tank for targeted enrichment. After 4 to 6 stress cycles and targeted enrichment, the initial membrane attachment is achieved.

[0014] In the high-DO aerobic activation step, the dissolved oxygen concentration is greater than 3.0 mg / L, and the duration is 2-4 hours.

[0015] In the critical low DO hypoxia stress step, dissolved oxygen drops below 0.8 mg / L and is maintained for 30-40 minutes;

[0016] In the directional enrichment step, the gas supply to the MABR membrane module is controlled to be 0.005~0.02 Nm³. 3 / (m 2 •h) Targeted enrichment was carried out under the conditions that the ammonia nitrogen concentration in the inoculation tank was 15~30 mg / L and the carbon-nitrogen ratio was less than 3:1, with each immersion time being 2~4 hours;

[0017] Step 3: On-site acclimatization and steady-state operation: The MABR membrane module that has completed the initial membrane attachment is placed in the anoxic unit of the actual wastewater treatment system for on-site acclimatization and stable operation.

[0018] Optionally, the microbial raw material containing nitrifying bacteria in step one is selected from at least one of the following: sludge from the aerobic tank of a municipal wastewater treatment plant, mature biological packing material of a moving bed biofilm reactor, or residual sludge from a secondary sedimentation tank.

[0019] Preferably, in step one, the concentration of suspended solids in the inoculation tank is greater than 8000 mg / L, and the ratio of the concentration of volatile suspended solids to the concentration of suspended solids in the mixture is greater than 55%.

[0020] Preferably, the nitrifying bacteria include ammonia nitrogen oxidizing bacteria and nitrite oxidizing bacteria.

[0021] Optionally, in the critical low dissolved oxygen hypoxia stress treatment of step two, the inoculation tank is stirred at a speed of 20-60 rpm.

[0022] Optionally, in the steady-state operation phase of step three, an intermittent pulse scrubbing mode is used to control the biofilm thickness between 100-300 μm.

[0023] Optionally, the pulse scrubbing is initiated when the biofilm thickness is greater than 200 μm, operates for 10-20 seconds, and stops for 100-120 seconds.

[0024] Optionally, in step three, after entering the steady-state operation stage, the reflux ratio is gradually reduced or the influent flow rate is increased by 15% to 30% to improve the treatment load.

[0025] Optionally, the wastewater treated by the actual wastewater treatment system in step three is wastewater with high ammonia nitrogen or low carbon-to-nitrogen ratio; preferably, the wastewater is at least one of urban domestic sewage, rural decentralized sewage, livestock and poultry breeding wastewater, and industrial wastewater.

[0026] In step three, during the on-site acclimatization process, dissolved oxygen is controlled at 0.5~0.8 mg / L; the influent flow rate and reflux ratio are adjusted, the influent ammonia nitrogen concentration is 10~15 mg / L, the hydraulic retention time is 2~5 hours, and the MABR gas supply is maintained at 0.005~0.02 Nm³. 3 / (m 2 •h); When the oxygen volume concentration at the membrane module exhaust port drops below 17% and the ammonia nitrogen removal load reaches 0.8 gN / (m2 When ·d) or above, it enters the steady-state operation stage.

[0027] The present invention also proposes a MABR membrane module enriched with highly active nitrifying bacteria obtained by the above method.

[0028] Compared with the prior art, the present invention has the following outstanding advantages:

[0029] (1) Extremely fast biofilm formation: By using the alternating oscillation cycle strategy of "high DO aerobic activation and critical low DO hypoxia stress", the sensitivity difference of nitrifying bacteria to sudden hypoxia is used to achieve targeted screening of highly active strains. At the same time, by taking advantage of the high oxygen permeability and high oxygen concentration on the surface of the MABR membrane, highly active nitrifying bacteria are targetedly enriched on the surface of the MABR membrane, shortening the biofilm formation cycle that traditionally requires several weeks to 2-3 days, greatly improving biofilm formation efficiency.

[0030] (2) High quality biofilm: The formed biofilm has a dense and uniform structure, is firmly attached to the membrane surface, and is not easy to fall off. The enrichment density and proportion of nitrifying bacteria (AOB and NOB) on the membrane surface are significantly higher than those of traditional biofilm attachment methods, and the denitrification activity is high.

[0031] (3) Strong anti-competitiveness: By controlling the low C / N ratio and high DO aerobic activation and critical low DO hypoxia stress oscillation cycle, the excessive growth of heterotrophic bacteria is effectively inhibited, creating an exclusive ecological niche advantage for the directional enrichment of nitrifying bacteria on the MABR membrane surface, and ensuring the accuracy of the biofilm direction.

[0032] (4) Stable system operation: The combination of microbial biofilm formation and on-site acclimatization, and the precise control of tail gas oxygen content and ammonia nitrogen removal load as key indicators, ensures a smooth transition and long-term stability of the system from startup to full-load operation.

[0033] (5) Effectively prevent membrane fouling: The thickness of the biofilm is controlled by pulse scrubbing, which avoids the increase in mass transfer resistance and irreversible fouling caused by excessive biofilm thickness, and extends the membrane cleaning cycle and service life.

[0034] (6) Wide applicability: This method is particularly suitable for treating wastewater with high ammonia nitrogen or low carbon-nitrogen ratio, especially for the treatment of urban domestic sewage, rural decentralized sewage, livestock and poultry breeding wastewater, industrial wastewater, etc., and has strong universality. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 The diagram below is a flowchart illustrating the rapid microbial biofilm formation method based on dissolved oxygen stress according to the present invention.

[0037] Figure 2 This is a schematic flowchart of another method for rapid microbial biofilm formation based on dissolved oxygen stress according to an embodiment of the present invention.

[0038] Figure 3 This is an actual photograph of the MABR after it has attached to the substrate in Example 1.

[0039] Figure 4 This is a scanning electron microscope image of the MABR after it has attached to the membrane in Example 1.

[0040] Figure 5 This is a scanning electron microscope image of the MABR after it has attached to the membrane in Example 2. Detailed Implementation

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0042] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] like Figure 1 , Figure 2 As shown, this invention proposes a method for rapid microbial biofilm formation based on dissolved oxygen stress. In some specific embodiments, it includes the following steps:

[0046] A rapid microbial biofilm formation method based on dissolved oxygen stress includes the following steps:

[0047] S1. Inoculum preparation: Place the microbial raw material containing nitrifying bacteria in the inoculation tank, control the concentration of suspended solids in the mixed liquor to be greater than 8000 mg / L, and the ratio of the concentration of volatile suspended solids in the mixed liquor to the concentration of suspended solids in the mixed liquor to be greater than 55%;

[0048] S2. Dissolved oxygen stress cycle and targeted enrichment: The inoculation tank is alternately subjected to high dissolved oxygen aerobic activation treatment and critical low dissolved oxygen anoxic stress treatment to form a stress cycle; then, the MABR membrane module to be attached is immersed in the inoculation tank for targeted enrichment. After 4-6 stress cycles and targeted enrichment, preliminary membrane attachment is achieved. Figure 2 As shown, it specifically includes:

[0049] S2021, high DO aerobic activation, aeration treatment of sludge in the inoculation tank, so that dissolved oxygen in the inoculation tank is >3.0mg / L, and continuous aeration for 2~4 hours;

[0050] S2022, critical low DO anoxic stress, stop aeration, turn on stirring to prevent sludge deposition, let dissolved oxygen drop naturally to below 0.8 mg / L, and maintain this low oxygen state for 30~40 minutes;

[0051] S2023. Immerse the MABR membrane module to be attached in the inoculation tank, and control the gas supply to the MABR membrane module to be 0.005~0.02 Nm³. 3 / (m 2 • h) Under the conditions that the ammonia nitrogen concentration in the inoculation tank is 15~30 mg / L and the carbon-nitrogen ratio is less than 3:1, directional enrichment is carried out, and the immersion time is 2~4 hours each time;

[0052] S2024. Repeat steps 4 to 6 of S201-S203 alternately until a light brown biofilm is uniformly covered on the surface of the MABR membrane. The initial biofilm attachment is completed, and the membrane module with the initial biofilm attachment is obtained.

[0053] S3. On-site training and steady-state operation, such as Figure 2 As shown, it specifically includes:

[0054] S2031. Install the pre-formed MABR membrane module into the anoxic unit of the target wastewater treatment system, controlling the dissolved oxygen in this unit between 0.5 and 0.8 mg / L; adjust the influent flow rate and recirculation ratio to maintain the influent ammonia nitrogen concentration in this unit at 10-15 mg / L, with a hydraulic retention time of 2-5 hours; maintain the MABR aeration rate at 0.005-0.02 Nm³. 3 / (m 2 ·h);

[0055] S2032. When the oxygen volume concentration at the exhaust port of the MABR membrane module drops below 17%, and the ammonia nitrogen removal load reaches 0.8 gN / (m³),2 After d), the system enters a steady-state operation phase. Gradually reduce the reflux ratio or increase the influent flow rate by 15% to 30%.

[0056] In wastewater treatment, nitrifying bacteria, such as ammonia nitrogen oxidizing bacteria and nitrite oxidizing bacteria, exist within the concepts of critical dissolved oxygen (DO) concentration and critical time window. Within this range, nitrifying bacteria experience strong aerobic pressure, but this does not yet cause irreversible and significant damage to their activity. Specifically: First, an urgent aerobic state: as long as the DO concentration is below the level required for nitrifying bacteria to maintain their maximum rate (usually above 2-4 mg / L, varying depending on the system), they are in an "aerobic" state. When the DO drops even lower, this "aerobic" feeling becomes extremely "urgent." Second, an activity damage threshold: when the DO concentration is low enough, or the hypoxic state persists for a certain duration, the metabolic activity of nitrifying bacteria is significantly inhibited, the activity of key enzymes decreases, and even the bacteria begin to be damaged or die.

[0057] Dissolved oxygen (DO) concentrations of 0.5–0.8 mg / L: This is generally considered the range where the nitrification rate begins to decline sharply. Below DO 0.8 mg / L, nitrifying bacteria urgently require oxygen to maintain normal activity. At this concentration, although nitrifying bacteria urgently require oxygen and their activity is limited, they can maintain this low DO level for a considerable period (several hours or even longer) without causing significant long-term irreversible damage. Short-term exposure (30–40 minutes) within this range usually results in a relatively rapid recovery of activity after aeration is resumed.

[0058] At dissolved oxygen concentrations of 0.2-0.5 mg / L: This concentration represents the range where nitrification activity is significantly inhibited. At this level, nitrifying bacteria are severely "hypoxic," and their activity has drastically decreased, but they still strive to maintain minimal survival activities or metabolism. They are in a state of high oxygen urgency. However, even if dissolved oxygen is restored to above 2 mg / L, microbial nitrification activity is still difficult to recover. At this concentration, within a short period (<30-60 minutes): the bacteria will enter a state of severe metabolic slowdown or even partial stagnation. Once sufficient DO is restored, activity may gradually recover within a few hours to a day. This short-term shock is relatively reversible for mature, healthy nitrifying bacteria. At this concentration, after a longer period (>60 minutes, especially several hours or longer), the risk increases significantly. Nitrifying bacteria (especially slow-growing nitrite-oxidizing bacteria) may begin to die or suffer damage that is difficult to recover from quickly (such as degradation of key enzymes). After aeration is restored, nitrification capacity may take several days or even longer to rebuild, especially if low oxygen has led to bacterial loss. The risk and duration of increased ammonia nitrogen / nitrite nitrogen concentrations in the system effluent are both increased.

[0059] When dissolved oxygen concentration is <0.2 mg / L, nitrification usually approaches or ceases. Nitrifying bacteria metabolism is severely inhibited or even stops, entering a dormant or stress-induced survival mode. They are extremely in need of oxygen but cannot effectively utilize the remaining microaergy. Maintaining this concentration for a very short time (<15-30 minutes) is similar to the short-term effects at 0.2-0.5 mg / L, but under greater stress. Maintaining this concentration for more than 30-60 minutes: the risk of severe inhibition and damage is high, requiring a longer recovery period. Maintaining this concentration for a long time (several hours): is likely to cause significant irreversible damage and death, with a recovery period of several days to several weeks, or even requiring reculturing of the bacterial community.

[0060] This invention combines the concepts of critical dissolved oxygen (DO) concentration and critical time window for nitrifying bacteria. It employs DO oscillation stress, and in step two, it creates a critical aerobic state by alternating between high DO aerobic conditions (greater than 3 mg / L) and low DO anoxic conditions (<0.8 mg / L) 4-6 times. Each aerobic period lasts 2-4 hours, and the anoxic period lasts 30-40 minutes, thereby enhancing the adhesion of aerobic nitrifying bacteria to the MABR membrane surface. Furthermore, it activates the stress metabolism of nitrifying bacteria, utilizing the characteristic that "sufficient DO bacteria are more sensitive to low DO" to enhance directional enrichment on the membrane surface. Functional bacterial colonization is completed in 2-3 days, solving the problem of long biofilm formation cycles in existing technologies.

[0061] Furthermore, the microbial raw material containing nitrifying bacteria is selected from at least one of the following: sludge from the aerobic tank of a municipal wastewater treatment plant, mature biological packing material of a moving bed biofilm reactor, or residual sludge from a secondary sedimentation tank.

[0062] Preferably, in step one, the concentration of suspended solids in the inoculation tank is greater than 8000 mg / L, and the ratio of the concentration of volatile suspended solids to the concentration of suspended solids in the mixture is greater than 55%.

[0063] Preferably, the nitrifying bacteria include ammonia nitrogen oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB).

[0064] The strains of this invention are derived from a composite inoculation source, which breaks through the limitations of single sludge and can enrich highly active nitrifying bacteria, shortening the biofilm formation time by more than 50%. Furthermore, by utilizing the low-oxygen sensitivity of long-term oxygen-enriched nitrifying bacteria, highly active strains are screened and weaker strains are eliminated, solving the problem of low nitrifying bacteria enrichment in the prior art.

[0065] This invention employs low C / N ratio control during the biofilm formation process, with ammonia nitrogen at 15-30 mg / L, C / N < 3, and MABR gas supply at 0.005-0.02 Nm³. 3 / m 2 / h, a low C / N ratio limits the proliferation of heterotrophic bacteria, and combined with DO shaking, it can further weaken their competitiveness, selectively inhibit heterotrophic bacteria, and increase the proportion of nitrifying bacteria to more than 35%.

[0066] Meanwhile, MABR membrane micro-oxygen supply (0.005-0.02 Nm) 3 / m 2 ( / h) induces the directed secretion of extracellular polysaccharides. Furthermore, it achieves gradient regulation from reversible attachment to stable transformation, which can solve the problem of easy detachment from biomembranes.

[0067] Optionally, during the acclimatization and steady-state operation, the ammonia nitrogen concentration in the influent of the unit containing the membrane module is controlled at 10~15 mg / L, the hydraulic retention time is 2~5 h, and the gas supply is 0.005~0.02 Nm³. 3 / m 2 / h; During the acclimatization and steady-state operation process, when the oxygen volume content in the tail gas of the membrane module drops to 17%, and the ammonia nitrogen removal load of this unit reaches 0.8 gN / m 2 After each day, the reflux ratio is gradually reduced by 15% to 30% or the influent flow rate is gradually increased. By gradually increasing the load after the conditions are met, a dynamic balance between biofilm activity and treatment load is achieved, avoiding biofilm detachment caused by sudden load changes. The pulse scrubbing frequency at the bottom of the membrane module is controlled to be 10-20 seconds at start and 100-120 seconds at stop, allowing the biofilm to be intermittently scrubbed while maintaining a biofilm thickness of 100-300 μm. Pulse scrubbing maintains an ideal membrane thickness of 100-300 μm, ensuring high mass transfer efficiency for the thin biofilm. The scrubbing frequency and DO stress cycle work together to prevent fouling, solving the problem of uncontrolled biofilm thickness.

[0068] This invention achieves the following innovations compared to existing technologies:

[0069] This invention is not a simple parameter optimization of existing microbial biofilm formation methods, but rather proposes an active regulation strategy based on the principles of microbial physiology and ecology. Its core innovation lies in the triple synergistic mechanism of "dissolved oxygen stress screening," "micro-oxygen niche construction," and "chemical selection pressure." Utilizing the sensitivity of long-term eutrophic bacterial communities to hypoxia, highly active strains are screened out while weaker communities are eliminated. Simultaneously, by employing an alternating aeration / hypoxia environment combined with MABR micro-oxygen supply, nitrifying bacteria are induced to directionally secrete extracellular polysaccharides on the MABR membrane surface, rapidly achieving enrichment on the MABR membrane surface.

[0070] 1. Dissolved oxygen stress screening – physiological domestication and natural selection based on microbial physiology.

[0071] Traditional biofilm formation is a passive, indiscriminate adsorption process. The core of this patent lies in introducing a oscillating cycle of "high DO aerobic activation - critical low DO hypoxia stress," which is an active screening and acclimatization mechanism for nitrifying bacteria. Specifically, this includes:

[0072] "High DO aerobic activation": Under the condition of DO > 3.0 mg / L, all aerobic microorganisms (including heterotrophic bacteria and nitrifying bacteria) are in a state of maximum activity, carrying out vigorous metabolism and proliferation, and reserving a large number of active bacterial groups for subsequent stress screening.

[0073] "Critical low DO stress": This involves precisely controlling DO levels below 0.8 mg / L, a critical point. Under this condition, all aerobic bacteria face hypoxic stress. However, the tolerance and response mechanisms of different bacterial species vary significantly: For heterotrophic bacteria, most grow rapidly but are highly sensitive to sudden hypoxia, especially under low C / N conditions, where metabolic activity rapidly declines, and some species may even enter dormancy or detach from the membrane surface. For nitrifying bacteria (AOB / NOB), although strictly aerobic, their unique enzyme systems (such as ammonia monooxygenase AMO) elicit a stronger stress response when faced with brief hypoxic stress. By adjusting their metabolic strategies, they secrete large amounts of extracellular polymeric substances (EPS), particularly proteins and polysaccharides, to enhance substrate adsorption and intercellular cohesion.

[0074] This invention employs 4-6 alternating cycles of biofilm formation, essentially performing multiple rounds of targeted "survival of the fittest" screening of the microbial community. This enriches highly active nitrifying strains that are tolerant of dissolved oxygen (DO) fluctuations and possess strong recovery capabilities, while eliminating less competitive heterotrophic and weaker nitrifying bacteria. This effectively achieves targeted evolution of the microbial community in a short period.

[0075] 2. Micro-aerobic gas supply and targeted enrichment – ​​a synergistic mechanism for constructing a “nitrifying bacteria-specific ecological niche”

[0076] (1) After each critical low DO hypoxia stress, the MABR membrane module was introduced and micro-oxygen supply was applied to provide a stable and dedicated oxygen source for the screened nitrifying bacteria that were in a state of "urgent oxygen demand".

[0077] Due to the inherent characteristics of MABR, the thickness of the micro-oxygen zone (DO>0.5 mg / L) formed on the membrane surface is limited, which effectively isolates the competition between nitrifying bacteria and heterotrophic bacteria in space, promoting the preferential and firm colonization of nitrifying bacteria on the membrane surface.

[0078] The present invention controls the extremely low gas supply to the MABR, aiming to precisely create a "micro-aerobic zone" that is only a few hundred micrometers thick and closely adheres to the membrane surface. The dissolved oxygen (DO) in this zone is just enough to meet the oxygen requirements of nitrifying bacteria, but not enough to diffuse far beyond the MABR membrane.

[0079] Niche isolation: The selected nitrifying bacteria are in a state of urgent need following "hypoxia stress." Once they sense a stable micro-oxygen source on the MABR membrane surface, they strongly tend to colonize it and firmly attach to the MABR membrane surface using EPS secreted during the hypoxia stress period. This ingeniously achieves spatial niche separation of functional bacterial communities, with nitrifying bacteria occupying the optimal position on the membrane wall, fundamentally avoiding competition with heterotrophic bacteria.

[0080] 3. Low C / N ratio (less than 3) control – applying chemical selection pressure

[0081] By controlling the carbon-to-nitrogen ratio to be less than 3, the growth and reproduction of heterotrophic bacteria that feed on organic matter were greatly inhibited. This, in synergy with the microaerobic niche on the MABR membrane surface, created a selective enrichment environment of "low carbon, microaerobic" that is highly favorable to nitrifying bacteria and extremely inhibits heterotrophic bacteria, ensuring the accuracy of the biofilm attachment direction.

[0082] 4. The transformation from reversible to irreversible adhesion – based on interface chemistry and biomembrane science.

[0083] MABR biofilm formation is not merely the attachment of microorganisms, but a process that transitions from reversible to irreversible attachment, ultimately leading to the formation of a mature biofilm. This invention achieves the transformation from initial attachment to irreversible attachment:

[0084] "High DO aerobic activation - critical low DO hypoxia stress - MABR directional enrichment" induces initial attachment: Under hypoxia stress, EPS secreted by nitrifying bacteria increases cell hydrophobicity and surface charge, enhancing the probability of its migration and reversible attachment to the MABR membrane surface.

[0085] Microaerobic environment promotes irreversible adhesion: When bacteria reach the membrane surface and sense a stable microaerobic environment, they continuously secrete more EPS, permanently and chemically "anchoring" themselves to the membrane surface, transforming into irreversible adhesion. This invention actively induces and accelerates this key transformation process by precisely controlling the timing of stress and gas supply.

[0086] 5. Pulse scrubbing and biofilm thickness control – steady-state maintenance based on mass transfer kinetics.

[0087] This invention does not aim for an infinitely thick biofilm, but rather controls the thickness of the MABR membrane within the optimal range of 100-300 μm through pulse scrubbing.

[0088] Optimizing substrate mass transfer: Ammonia nitrogen and oxygen require anisotropic diffusion through the biofilm. Excessively thick biofilms create significant mass transfer resistance, causing internal microorganisms to become dormant or die due to lack of substrate, resulting in no increase in actual biomass and a decrease in treatment efficiency. Controlling the thickness ensures that both oxygen and ammonia nitrogen can effectively diffuse to the deepest parts of the biofilm, achieving efficient utilization of the entire biofilm cross-section.

[0089] Preventing endogenous decay and pore blockage: Excessively thick biofilms can lead to endogenous respiration due to substrate scarcity, causing the biofilm structure to become loose and prone to generating biodebris that can clog gas channels on the membrane surface. Controlling the thickness avoids this problem.

[0090] Preventing irreversible fouling: In excessively thick biofilms, the internal microbial community secretes excessive amounts of viscous polysaccharides to maintain the structure, but these substances can easily cause irreversible blockage of the membrane pores. Intermittent pulse scrubbing (10s on / 110s off) can periodically remove the loose outermost structure of the biofilm before it excessively secretes these substances, keeping the biofilm thin, dense, and highly active, thereby fundamentally extending the membrane's operating cycle.

[0091] In summary, this invention transcends the traditional passive biofilm formation approach of submerged MABR membrane modules. Through the synergistic effect of multiple processes—aerobic activation-hypoxia stress (physiological selection), microaerobic aeration (niche construction), low C / N ratio (chemical selection), and pulsed scrubbing (mass transfer optimization)—it decomposes the MABR biofilm formation process into a series of steps: "pre-screening-critical stimulation-directional attachment-stable transformation," actively intervening in and accelerating the succession of the microbial community. It is not merely a "biofilm formation method," but rather a set of "regulatory strategies" based on microbiology.

[0092] Example 1

[0093] S1: Place the aerobic MBBR packing material or aerobic suspended sludge in the inoculation tank. The packing material and suspended sludge can be derived from suspended sludge from the aerobic tank of a municipal wastewater treatment plant, or mature biological packing material and suspended sludge containing nitrifying bacteria from other biofilm reactors (such as moving bed biofilm reactors, MBBRs), or excess sludge containing nitrifying bacteria discharged from the secondary sedimentation tank. The sludge concentration in the inoculation tank is 8500 mg / L, and the MLVSS / MLSS ratio is 58%. The nitrifying bacteria include ammonia nitrogen oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB).

[0094] S2: Control the dissolved oxygen in the inoculation tank to 3.5 mg / L through aeration for 3 hours; then stop aeration and turn on the agitator (40 rpm) to prevent sludge from settling at the bottom and causing anaerobic conditions. Once the dissolved oxygen drops to 0.7 mg / L, start timing and maintain this for 35 minutes to ensure the nitrifying bacteria in the inoculation tank are in a state of urgent oxygen demand and limited activity. After the anoxic stress ends, the MABR membrane module (membrane area 100 m²) is then installed. 2 Immerse the membrane module in the tank. Control the air supply to the membrane module to 0.01 Nm³. 3 / (m 2 • h), by adding NH4Cl and a trace amount of methanol, the ammonia nitrogen concentration in the tank was controlled to be 20 mg / L and the C / N ratio to be 2.8. Immersion for 3 hours.

[0095] The above cycle of "aerobic activation-hypoxia stress-directional enrichment" was repeated 5 times, lasting a total of 1.35 days.

[0096] S3: Move the membrane module to the anoxic zone (DO = 0.6 mg / L) of the target wastewater treatment system. Control the influent ammonia nitrogen at 12 mg / L and HRT = 4.5 hours. After 3 days of operation, the tail gas oxygen concentration was monitored to be 16.5%, and the ammonia nitrogen removal load was 0.85 gN / (m³). 2 •d). Subsequently, the influent load was gradually increased by 20% per day. During operation, pulse scrubbing was initiated (operating for 15 seconds and stopping for 105 seconds) to stabilize the biofilm thickness at approximately 200 μm.

[0097] like Figure 3 As shown, as the attached biofilm gradually densifies, its color changes from brown to gray, and finally to brown. The biofilm thickness also becomes more uniform with the scouring, scrubbing, and proliferation of the water flow, and its pollutant removal capacity gradually increases. A unique biological community characteristic of the biofilm gradually forms, as observed by scanning electron microscopy. Figure 4 The biofilm formation on the MABR membrane surface is relatively good and the biofilm formation is relatively uniform.

[0098] Testing showed that the system completed microbial biofilm formation on day 1.35, reached full-load operation in 10 days, with effluent ammonia nitrogen consistently below 0.5 mg / L and simultaneous denitrification load reaching 1.8 gN / m³. 2 / d.

[0099] Example 2: Treatment of a high ammonia nitrogen chemical wastewater (ammonia nitrogen = 150 mg / L, C / N = 2.5).

[0100] S1: Take sludge from the aerobic tank of a municipal wastewater treatment plant and biological packing material from the MBBR reactor as inoculum, and prepare a mixed solution with MLSS of 9000 mg / L and MLVSS / MLSS = 60% in the inoculation tank.

[0101] S2: Turn on aeration to maintain DO at 3.5 mg / L for 4 hours.

[0102] Stop aeration, turn on stirring (45 rpm), and maintain this hypoxic stress state for 40 minutes when DO drops to 0.7 mg / L.

[0103] After the hypoxia stress ended, the MABR membrane module (membrane area 100m²) was used. 2 Immerse the membrane module in the tank. Control the air supply to the membrane module to 0.01 Nm³. 3 / (m 2 • h), by adding NH4Cl and a trace amount of methanol, the ammonia nitrogen concentration in the tank was controlled to be 20 mg / L and the C / N ratio to be 2.8. Immersion time was 4 hours.

[0104] The above cycle of "aerobic activation-hypoxia stress-directional enrichment" was repeated 6 times, lasting 2.16 days.

[0105] After 2.16 days of operation, a light brown, slightly sticky biofilm was observed to be evenly covered on the surface of the membrane filaments. Microscopic observation revealed a large number of bacterial flocs and filamentous bacteria, indicating that biofilm attachment was initially successful.

[0106] S3: Transfer the membrane module to the anoxic tank (DO=0.6 mg / L) of the target chemical wastewater treatment system. Control the influent ammonia nitrogen concentration at 12 mg / L and HRT=4.5h. Maintain the MABR gas supply.

[0107] After 4 days of operation, the oxygen content in the exhaust gas was measured to be 16.4%, and the ammonia nitrogen removal load was calculated to be 1.25 gN / (m³). 2 ·d). Then, gradually increase the influent load by 20% per day.

[0108] During stable system operation, pulse scrubbing was initiated (10 seconds on, 110 seconds off), and periodic sampling was performed to monitor the biofilm thickness, which remained at approximately 200 μm. Observation was conducted using a scanning electron microscope. Figure 5 MABR membranes exhibit good biofilm attachment on their surface.

[0109] Ultimately, the system completed microbial biofilm formation on day 2.16, and after reaching full load operation on day 12, the effluent ammonia nitrogen level stabilized below 0.3 mg / L, with a simultaneous denitrification load of 1.5 g N / m³. 2 / d, far exceeding the effect that traditional methods require 40 days to achieve.

[0110] Comparative Example 1

[0111] Compared to Example 1, this comparative example did not subject to low DO hypoxia stress; inoculation was performed directly after aeration. All other steps were the same as in Example 1. In this comparative example, there was no low DO hypoxia stress, resulting in a biofilm formation time of 20 days and full-load operation achieved in 32 days.

[0112] Comparative Example 2

[0113] Compared to Example 1, the dissolved oxygen content for reducing dissolved oxygen stress in this comparative example was 1.5 mg / L, and inoculation was performed directly after aeration. All other steps were the same as in Example 1. In this comparative example, the DO value under hypoxic stress was too high, resulting in a prolonged biofilm formation period of 25 days, reaching full-load operation after 45 days.

[0114] Comparative Example 3

[0115] Compared to Example 1, this comparative example involved three stress cycles and directional enrichment. The remaining steps were the same as in Example 1. In this comparative example, because only three stress cycles were performed, the biofilm formation period was extended to 15 days, and full-load operation was achieved in 36 days.

[0116] Comparative Example 4

[0117] Compared with Example 1, the low dissolved oxygen stress time in this comparative example was 50 min, and the remaining steps were the same as in Example 1. The low DO stress time in this comparative example was too long, resulting in the biofilm formation period being extended to 10 days, and full-load operation was reached in 27 days. The proportion of nitrifying bacteria on the MABR membrane surface was low.

[0118] Comparative Example 5

[0119] Compared to Example 1, in this comparative example, the carbon-to-nitrogen ratio of the wastewater in the inoculation tank was adjusted to be greater than 4 during the initial biofilm formation. All other steps were the same as in Example 1. In this comparative example, low C / N ratios were not controlled, resulting in a longer biofilm formation period of 15 days, reaching full-load operation in 32 days. Heterotrophic bacteria proliferated on the MABR membrane surface, forming a thick and viscous biofilm, leading to increased gas supply resistance of the membrane module, low nitrification activity, and ammonia nitrogen removal load consistently below 0.3 g N / (m³). 2 ·d), the proportion of nitrifying bacteria on the surface of the MABR membrane is low.

[0120] Comparative Example 6

[0121] Compared to Example 1, in this comparative example, the membrane micro-oxygen supply was adjusted to 0.025 Nm during the acclimatization and steady-state operation process. 3 / m 2 / h. The remaining steps are the same as in Example 1. In this comparative example, the membrane micro-oxygen supply was too high, resulting in a biofilm formation period of 17 days and full-load operation in 38 days. The biofilm thickness of 310 μm was too high, and membrane fouling was serious.

[0122] Comparative Example 7

[0123] Compared to Example 1, no pulse scrubbing was performed on the membrane module during the acclimatization and steady-state operation in this comparative example. All other steps were the same as in Example 1. The absence of pulse scrubbing in this comparative example resulted in a prolonged biofilm formation period of 12 days, reaching full-load operation in 48 days, an excessively high biofilm thickness of 350 μm, and severe membrane fouling.

[0124] The detailed comparison results of the above embodiments and comparative examples are summarized in Table 1 below:

[0125] Table 1

[0126]

[0127] In summary, this invention represents a breakthrough in biofilm formation efficiency, shortening the initial biofilm formation cycle to 3 days (compared to 10-25 days traditionally), and increasing the proportion of nitrifying bacteria by 3 times; the simultaneous nitrogen removal load reaches 1.5~1.8 g N / m³. 2 / d (traditional MABR < 0.8g N / m 2 / d). This invention has the advantage of enhanced stability: highly stress-resistant nitrifying bacteria are obtained through "high DO aerobic activation - critical low DO anoxic stress - targeted enrichment screening"; this invention has the advantage of cost savings, with energy consumption reduced by 40% during the biofilm formation stage; only a lower C / N ratio is required during biofilm formation, reducing reagent costs by 60%. This invention has compatibility and universality, applicable to municipal / rural / industrial wastewater (especially high ammonia nitrogen wastewater with C / N < 3); it supports microbial biofilm formation in mainstream MABRs such as hollow fiber membranes and flat sheet membranes.

[0128] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for rapid microbial biofilm formation based on dissolved oxygen stress, characterized in that, include: Step 1: Prepare inoculum: Place the microbial raw material containing nitrifying bacteria into the inoculation tank; Step 2, Dissolved Oxygen Stress Cycling and Targeted Enrichment: The inoculation tank is alternately subjected to high DO aerobic activation treatment and critical low DO anoxic stress treatment to form a stress cycle. After each cycle, the MABR membrane module to be attached is immersed in the inoculation tank for targeted enrichment. After 4 to 6 stress cycles and targeted enrichment, a biofilm is evenly covered on the surface of the MABR membrane, and the MABR membrane module with preliminary biofilm attachment is obtained. In the high-DO aerobic activation step, the dissolved oxygen concentration is greater than 3.0 mg / L, and the duration is 2-4 hours. In the critical low DO hypoxia stress step, dissolved oxygen drops below 0.8 mg / L and is maintained for 30-40 minutes; In the directional enrichment step, the gas supply to the MABR membrane module is controlled to be 0.005~0.02 Nm³. 3 / (m 2 •h) Targeted enrichment was carried out under the conditions that the ammonia nitrogen concentration in the inoculation tank was 15~30 mg / L and the carbon-nitrogen ratio was less than 3:1, with each immersion time being 2~4 hours; Step 3: On-site acclimatization and steady-state operation: The MABR membrane module that has completed the initial membrane attachment is placed in the anoxic unit of the actual wastewater treatment system for on-site acclimatization and stable operation.

2. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, The microbial raw material containing nitrifying bacteria in step one is selected from at least one of the following: sludge from the aerobic tank of a municipal wastewater treatment plant, mature biological packing material of a moving bed biofilm reactor, or residual sludge from a secondary sedimentation tank. The nitrifying bacteria include ammonia nitrogen oxidizing bacteria and nitrite oxidizing bacteria.

3. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, In step one, the concentration of suspended solids in the mixed solution in the inoculation pool is greater than 8000 mg / L, and the ratio of the concentration of volatile suspended solids in the mixed solution to the concentration of suspended solids in the mixed solution is greater than 55%.

4. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, In the critical low dissolved oxygen hypoxia stress treatment in step two, the inoculation tank is stirred at a speed of 20-60 rpm.

5. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, In the steady-state operation phase of step three, the biofilm thickness is controlled between 100-300 μm using an intermittent pulse scrubbing mode.

6. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 5, characterized in that, The pulse scrubbing is initiated when the biofilm thickness is greater than 200 μm, operates for 10-20 seconds, and stops for 100-120 seconds.

7. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, In step three, after entering the steady-state operation stage, the reflux ratio is gradually reduced or the influent flow rate is increased by 15% to 30% to improve the treatment load.

8. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, In step three, the on-site acclimatization includes: controlling dissolved oxygen at 0.5~0.8 mg / L; adjusting the influent ammonia nitrogen concentration to 10~15 mg / L; maintaining a hydraulic retention time of 2~5 hours; and maintaining the MABR aeration rate at 0.005~0.02 Nm³. 3 / (m 2 •h); When the oxygen volume concentration at the membrane module exhaust port drops below 17% and the ammonia nitrogen removal load reaches 0.8 gN / (m 2 When ·d) or above, it enters the steady-state operation stage.

9. The rapid microbial biofilm formation method based on dissolved oxygen stress according to claim 1, characterized in that, The wastewater treated by the actual wastewater treatment system in step three is wastewater with high ammonia nitrogen or low carbon-to-nitrogen ratio. The wastewater is at least one of the following: urban domestic sewage, rural decentralized sewage, livestock and poultry breeding wastewater, and industrial wastewater.

10. A MABR membrane module enriched with highly active nitrifying bacteria, prepared by the microbial rapid biofilm formation method based on dissolved oxygen stress as described in any one of claims 1 to 8.

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