Microorganism rapid biofilm culturing method based on dissolved oxygen stress

Abstract

The invention discloses a rapid microbial biofilm culturing method based on dissolved oxygen stress, and belongs to the technical field of sewage treatment. The core of the method is as follows: active physiological domestication and screening are performed on microbial communities through alternate circulation of high dissolved oxygen aerobic activation and critical low dissolved oxygen anoxic stress, and directional enrichment is performed by utilizing micro-aerobic air supply of an MABR membrane module and a low C / N ratio environment after each stress cycle; therefore, a biological membrane which is rich in high-activity nitrifying bacteria and compact in structure is rapidly constructed on the surface of the MABR membrane within a short time. The method breaks through the technical bottlenecks of long biofilm culturing period, fierce flora competition and easy falling of a biofilm in the traditional method, realizes efficient, rapid and stable starting of the MABR system, and is especially suitable for treatment of sewage with high ammonia nitrogen and low carbon nitrogen ratio.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment, and particularly relates to a method for quickly forming a biofilm based on dissolved oxygen stress, in particular, a method for quickly and directionally enriching nitrifying bacteria on the surface of a MABR membrane based on dissolved oxygen stress and ecological niche regulation. BACKGROUND

[0002] In the current ammonia-nitrogen wastewater treatment technology, the activated sludge process is generally used, which has the advantages of large treatment capacity, high treatment efficiency and good effluent quality. Its various modified processes have good denitrification and phosphorus removal performance, and have been widely used in municipal wastewater treatment. The disadvantage is that it is difficult to obtain a high amount of aerobic microorganisms in the activated sludge system, the nitrification efficiency is low, which leads to weak impact resistance of the nitrification system, incomplete nitrification, and the need for a large amount of aeration and long retention time, and the operation maintenance and management are difficult. In recent years, with the continuous improvement of biological wastewater treatment technology, the biofilm method has begun to be applied in biological denitrification technology. It has the advantages of stable operation, less excess sludge, simple management, strong removal capacity for ammonia-nitrogen and refractory pollutants, and can adapt to large changes in water quality. It has been widely used in domestic wastewater and industrial wastewater treatment.

[0003] The biofilm method refers to adding microorganisms (nitrifying bacteria and denitrifying bacteria) in wastewater treatment to make them adhere or fix on the surface of biological fillers to form a layer of biofilm. Through the contact between wastewater and the biofilm, mass transfer of solid-liquid two phases is realized to achieve the biological degradation of ammonia-nitrogen and other pollutants in wastewater. According to different operation modes, it can be divided into biological filter, biological rotating disc, biological contact oxidation method, etc. Although their structures are quite different, their basic principles are the same.

[0004] Membrane aeration biofilm reactor (MABR) is a new wastewater treatment technology. It realizes the simultaneous nitrification and denitrification process by bubbleless oxygen supply through hollow fiber membranes, and oxygen directly diffuses into the biofilm attached to the membrane surface. It has the advantages of high oxygen mass transfer efficiency, low energy consumption, and good denitrification effect. However, the slow start-up phase (i.e. "microbial biofilm formation" phase) of MABR technology seriously restricts its wide application. The existing biofilm formation methods usually use direct immersion natural biofilm formation or low load continuous operation biofilm formation, which mainly has the following defects: 1. Long biofilm formation period: Because the growth rate of nitrifying bacteria (including ammonia-oxidizing bacteria AOB and nitrite-oxidizing bacteria NOB) is slow, natural biofilm formation usually takes 20-40 days or even longer, which seriously affects the commissioning progress and economic benefits of the project.

[0005] 2. Competitive disadvantage of microbial community: In the early stage of biofilm formation, fast-growing heterotrophic bacteria will preferentially occupy the surface niche of the membrane, compete for oxygen and space, inhibit the attachment and growth of nitrifying bacteria, and result in low proportion of nitrifying bacteria in the final biofilm, poor activity, and limited denitrification capacity.

[0006] 3. Unstable biofilm structure: The biofilm formed by traditional methods is loose and has weak binding force with the membrane surface, and is easily detached in large areas under hydraulic flushing and load impact, resulting in unstable system treatment efficiency.

[0007] 4. Rough process control: Lack of fine and dynamic control of key parameters such as dissolved oxygen (DO) and carbon-nitrogen ratio (C / N), and the success rate and efficiency of biofilm formation depend on experience and have poor repeatability.

[0008] Therefore, there is an urgent need in the art for a biofilm formation method that can break through the limitations of natural microbial growth, actively, quickly and directionally enrich high-activity nitrifying bacteria on the surface of MABR membrane. SUMMARY

[0009] The present application aims to overcome the shortcomings of the prior art, and proposes an alternating shock cycle of high-DO aerobic activation treatment and critical low-DO anoxic stress, which utilizes the sensitivity difference of nitrifying bacteria to sudden anoxia to realize the competitive selection of high-activity strains, breaks through the biological selection blind area of traditional submerged natural static biofilm formation, and provides a microbial rapid biofilm formation method with extremely short biofilm formation period, uniform biofilm formation, high nitrifying bacteria enrichment efficiency and stable system operation. In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: The present application proposes a microbial rapid biofilm formation method based on dissolved oxygen stress, comprising: Step one, preparing inoculum: placing microbial raw materials containing nitrifying bacteria in an inoculum pool; Step two, dissolved oxygen stress cycle and directional enrichment: alternately performing high-DO aerobic activation treatment and critical low-DO anoxic stress treatment on the inoculum pool to form a stress cycle, and immersing the MABR membrane assembly to be formed in the inoculum pool for directional enrichment after each cycle, and achieving preliminary biofilm formation after 4-6 stress cycles and directional enrichment; 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 anoxic stress step, the dissolved oxygen is reduced to below 0.8 mg / L and maintained for 30-40 minutes; In the directional enrichment step, the gas supply amount of the MABR membrane assembly is controlled to be 0.005-0.02 Nm 3 / (m 2 ·h), the ammonia nitrogen concentration in the inoculum pool is 15-30 mg / L, and the carbon-nitrogen ratio is less than 3:1, and the directional enrichment is carried out under the condition that the immersion time is 2-4 hours. Step three, field domestication and steady operation: placing the MABR membrane assembly with completed preliminary biofilm into the anoxic unit of the actual sewage treatment system for field domestication and steady operation.

[0010] Optionally, the microorganism raw material containing nitrifying bacteria in the step one is selected from at least one of sludge in an aerobic tank of a municipal sewage treatment plant, mature biological filler of a moving bed biofilm reactor, or residual sludge in a secondary sedimentation tank. Preferably, the mixed liquor suspended solid concentration in the inoculation tank in the step one is greater than 8000 mg / L, and the ratio of the mixed liquor volatile suspended solid concentration to the mixed liquor suspended solid concentration is greater than 55%. Preferably, the nitrifying bacteria include ammonia-oxidizing bacteria and nitrite-oxidizing bacteria.

[0011] Optionally, in the critical low-dissolved-oxygen anoxic stress treatment of the step two, the inoculation tank is stirred at a stirring speed of 20-60 rpm.

[0012] Optionally, in the steady operation stage of the step three, an intermittent pulse scrubbing mode is adopted to control the biofilm thickness to be between 100-300 μm.

[0013] Optionally, the pulse scrubbing is started when the biofilm thickness is greater than 200 μm, works for 10-20 seconds, and stops for 100-120 seconds.

[0014] Optionally, in the step three, after entering the steady operation stage, the reflux ratio is gradually reduced or the influent quantity is gradually increased at a proportion of 15-30% to improve the treatment load.

[0015] Optionally, the sewage treated by the actual sewage treatment system in the step three is high-ammonia-nitrogen or low-carbon-nitrogen-ratio sewage; preferably, the sewage is at least one of urban domestic sewage, rural decentralized sewage, livestock and poultry breeding wastewater, and industrial wastewater.

[0016] In the step three, during the field domestication, the dissolved oxygen is controlled to be 0.5-0.8 mg / L; the influent flow and the 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 amount is maintained at 0.005-0.02 Nm 3 / (m 2 ·h); when the oxygen volume concentration at the exhaust port of the membrane assembly is reduced to below 17% and the ammonia-nitrogen removal load reaches 0.8 gN / (m 2 ·d) or above, the steady operation stage is entered.

[0017] The application further provides a MABR membrane assembly enriched with a high-activity nitrifying bacteria group and prepared by the above method.

[0018] Compared with the prior art, the present application has the following outstanding beneficial effects: (1) The biofilm formation speed is extremely fast: through the alternating shock cycle strategy of "high DO aerobic activation and critical low DO anoxic stress", the directional screening of high-activity strains is realized by using the sensitivity difference of nitrifying bacteria to sudden anoxia, and the directional enrichment of high-activity nitrifying bacteria on the surface of the MABR membrane is realized by using the characteristics of high oxygen transmission efficiency and high oxygen concentration on the surface of the MABR membrane, thereby shortening the biofilm formation period from several weeks to 2-3 days and greatly improving the biofilm formation efficiency.

[0019] (2) The quality of the biofilm is high: the biofilm structure formed is dense and uniform, and is firmly combined with the membrane surface and 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 the traditional biofilm formation method, and the denitrification activity is high.

[0020] (3) The competition resistance is strong: by controlling the low C / N ratio and the alternating shock cycle of high DO aerobic activation and critical low DO anoxic stress, the overgrowth of heterotrophic bacteria is effectively inhibited, a special ecological niche advantage is created for the directional enrichment of nitrifying bacteria on the surface of the MABR membrane, and the accuracy of the biofilm formation direction is ensured.

[0021] (4) The system runs stably: the microbial biofilm formation is combined with the on-site acclimation, and the tail gas oxygen content and ammonia nitrogen removal load are used as key indicators for precise regulation and control, thereby ensuring the smooth transition and long-term stability of the system from start-up to full load operation.

[0022] (5) The membrane pollution is effectively prevented: the biofilm thickness is controlled by pulse scrubbing, thereby avoiding the increase of mass transfer resistance and irreversible pollution caused by the over-thickness of the biofilm, and prolonging the membrane cleaning period and service life.

[0023] (6) The applicability is wide: the method is especially suitable for treating high-ammonia-nitrogen or low-carbon-nitrogen-ratio sewage, and is especially suitable for treating urban domestic sewage, rural decentralized sewage, livestock and poultry breeding wastewater, industrial wastewater and the like, and has strong universality. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the following specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0025] Figure 1 It is a flowchart of the rapid microbial biofilm formation method based on dissolved oxygen stress according to the present application.

[0026] Figure 2This 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.

[0027] Figure 3 This is an actual photograph of the MABR after it has attached to the substrate in Example 1.

[0028] Figure 4 This is a scanning electron microscope image of the MABR after it has attached to the membrane in Example 1.

[0029] Figure 5 This is a scanning electron microscope image of the MABR after it has attached to the membrane in Example 2. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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: A rapid microbial biofilm formation method based on dissolved oxygen stress includes the following steps: 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%; 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: 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; 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; 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; 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.

[0035] S3. On-site training and steady-state operation, such as Figure 2 As shown, it specifically includes: 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); 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%.

[0036] In wastewater treatment, there is a concept of critical dissolved oxygen (DO) concentration and critical time window for nitrifiers such as ammonia oxidizers and nitrite oxidizers. Within this range, nitrifiers will experience a strong need for oxygen, but not yet significant damage to their activity that is irreversible. This is manifested in two ways: First, a state of urgent need for oxygen: as long as the DO concentration is below the level required for nitrifiers to maintain maximum rate (usually above 2-4 mg / L, depending on the system), they are in a state of "need for oxygen". When DO drops to a lower level, this "need for oxygen" becomes very "urgent". Second, a threshold of activity damage: that is, when DO concentration is low enough, or low oxygen state lasts long enough, to cause significant inhibition of metabolic activity of nitrifiers, key enzyme activity decreases, and even the bacteria begin to be damaged or die.

[0037] DO concentration of 0.5-0.8 mg / L: This is the range of DO concentration at which the rate of nitrification is usually considered to start to decline sharply. When DO is below 0.8 mg / L, nitrifiers are in urgent need of oxygen to maintain normal activity. At this concentration, nitrifiers are in urgent need of oxygen and their activity is limited, but they can maintain a relatively long time (hours or even longer) at this lower DO level without causing significant long-term irreversible damage. Short time (30-40 min) in this range, after restoring aeration, the activity can usually recover quickly.

[0038] DO concentration of 0.2-0.5 mg / L: This concentration is the range at which nitrification activity is significantly inhibited. At this time, nitrifiers are in a state of severe "hypoxia" and their activity has been greatly reduced, but they still try to maintain the minimum level of survival activity or metabolism. They are in a state of high urgent need for oxygen. But at this concentration, if the dissolved oxygen is restored to 2 mg / L or more, the microbial nitrification activity is still difficult to recover. At this concentration, for a short time (<30-60 minutes): the bacteria will enter a state of severe metabolic slowdown or even partial arrest. Once sufficient DO is restored, the activity may gradually recover within a few hours to a day. The reversibility of this short-term shock to a mature and healthy nitrifier population is relatively high. At this concentration, for a longer period of time (> 60 minutes, especially hours or longer), the risk will increase significantly. Nitrifiers (especially slow-growing nitrite oxidizers) may start to die or be damaged (such as key enzyme degradation) that is difficult to recover quickly. After restoring aeration, it may take several days or even longer to rebuild nitrification capacity, especially if low oxygen has caused a loss of bacterial population. The risk and time of increasing ammonia nitrogen / nitrite nitrogen concentration in the effluent of the system are increased.

[0039] When the dissolved oxygen concentration is <0.2 mg / L, nitrification is usually close to or enters a state of stagnation. Nitrifying bacteria metabolism is severely inhibited or even stopped, and enters a dormant or stress survival mode. Oxygen is extremely urgent, but the remaining micro-oxygen cannot be effectively utilized. Maintaining this concentration for a very short time (<15-30 minutes) is similar to a short-term effect at 0.2~0.5 mg / L, but the stress is greater. Maintaining this concentration for more than 30-60 minutes: there is a high risk of severe inhibition and damage, and a longer recovery period is required. Maintaining this concentration for a long time (several hours): it is very likely to cause significant irreversible damage and death, and the recovery period requires several days to several weeks, or even requires re-cultivation of the bacterial population.

[0040] The present application combines the concept of critical dissolved oxygen (DO) concentration and critical time window of nitrifying bacteria, and uses DO shock stress. In step two, the amount of dissolved oxygen is alternately cycled (4~6 times) from high DO aerobic (greater than 3 mg / L) to low DO anoxic (<0.8 mg / L), with each aerobic maintaining 2~4 hours and anoxic maintaining 30~40 minutes, to create a critical oxygen demand state, and to strengthen the nitrifying bacteria's tendency to adhere to the surface of the MABR membrane. And activate the stress metabolism of nitrifying bacteria, take advantage of the "sufficient DO bacterial population is more sensitive to low DO" characteristics, and strengthen the directional enrichment of the membrane surface. The functional bacteria colonization is completed in 2-3 days, solving the problem of long biofilm formation period in the prior art.

[0041] Further, the microorganism raw material containing nitrifying bacteria is selected from at least one of the sludge in the aerobic tank of a municipal sewage treatment plant, the mature biological filler of a moving bed biofilm reactor, or the excess sludge in the secondary sedimentation tank; Preferably, the mixed liquor suspended solids concentration in the inoculation tank in step one is greater than 8000 mg / L, and the ratio of the mixed liquor volatile suspended solids concentration to the mixed liquor suspended solids concentration is greater than 55%; Preferably, the nitrifying bacteria include ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB).

[0042] The strain source of the present application is inoculated from a composite bacterial source, breaking through the limitation of single sludge, and can enrich a high-activity nitrifying bacterial population, shorten the biofilm formation time by more than 50%, and take advantage of the low-oxygen sensitivity of long-term oxygen-rich nitrifying bacteria to screen high-activity strains and eliminate weak bacterial populations, solving the problem of low nitrifying bacteria enrichment in the prior art.

[0043] In the present application, low carbon-nitrogen ratio control is used during the biofilm formation process, ammonia nitrogen is 15~30 mg / L, C / N is <3, and the MABR gas supply is 0.005-0.02 Nm 3 / m 2 / h, the low C / N ratio limits the proliferation of heterotrophic bacteria, and the DO shock can further weaken their competitiveness and selectively inhibit heterotrophic bacteria, so that the proportion of nitrifying bacteria is increased to more than 35%.

[0044] 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.

[0045] 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.

[0046] This invention achieves the following innovations compared to existing technologies: 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.

[0047] 1. Dissolved oxygen stress screening – physiological domestication and natural selection based on microbial physiology.

[0048] 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: "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.

[0049] "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.

[0050] 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.

[0051] 2. Micro-aerobic gas supply and targeted enrichment – ​​a synergistic mechanism for constructing a “nitrifying bacteria-specific ecological niche” (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".

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 3. Low C / N ratio (less than 3) control – applying chemical selection pressure 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.

[0056] 4. The transformation from reversible to irreversible adhesion – based on interface chemistry and biomembrane science.

[0057] 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: "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.

[0058] 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.

[0059] 5. Pulse scrubbing and biofilm thickness control – steady-state maintenance based on mass transfer kinetics.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] Example 1 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).

[0066] 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.

[0067] The above cycle of "aerobic activation-hypoxia stress-directional enrichment" was repeated 5 times, lasting a total of 1.35 days.

[0068] 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 (15s on, 105s off) to stabilize the biofilm thickness at approximately 200 μm.

[0069] 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.

[0070] 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.

[0071] Example 2: Treatment of a high ammonia nitrogen chemical wastewater (ammonia nitrogen = 150 mg / L, C / N = 2.5).

[0072] 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.

[0073] S2: Turn on aeration to maintain DO at 3.5 mg / L for 4 hours.

[0074] Stop aeration, turn on stirring (45 rpm), and maintain this hypoxic stress state for 40 minutes when DO drops to 0.7 mg / L.

[0075] 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.

[0076] The above cycle of "aerobic activation-hypoxia stress-directional enrichment" was repeated 6 times, lasting 2.16 days.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Comparative Example 1 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.

[0083] Comparative Example 2 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.

[0084] Comparative Example 3 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.

[0085] Comparative Example 4 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.

[0086] Comparative Example 5 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.

[0087] Comparative Example 6 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.

[0088] Comparative Example 7 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.

[0089] The detailed comparison results of the above embodiments and comparative examples are summarized in Table 1 below: Table 1

[0090] 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.

[0091] 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, the initial membrane attachment is achieved. 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, an intermittent pulse scrubbing mode is used to control the biofilm thickness between 100-300 μm.

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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