Construction and operation method of hydrophobic membrane MABR biological membrane based on biphasic regulation and control

Abstract

The invention discloses a construction and operation method of a hydrophobic membrane MABR biological membrane based on biphase regulation and control, and belongs to the technical field of sewage treatment. The invention develops a novel MABR biofilm culturing method, which can effectively reconcile the interface contradiction between a hydrophobic membrane material and hydrophilic microorganisms, not only can utilize heterotrophic bacteria to improve the microenvironment on the surface of the membrane, but also can prevent the heterotrophic bacteria from being excessively proliferated and blocking mass transfer through accurate process control; therefore, rapid, stable and function-oriented biological membrane construction on the surface of the durable hydrophobic membrane is realized.

Description

TECHNICAL FIELD

[0001] The application relates to a method for constructing and operating a hydrophobic membrane MABR biofilm based on two-phase regulation, and belongs to the technical field of wastewater treatment. BACKGROUND

[0002] The amount of domestic wastewater, industrial wastewater and agricultural non-point source pollution has increased significantly, and the nitrogen substances contained in these polluted wastewater are continuously discharged into water bodies, causing serious eutrophication problems in rivers, lakes and other water areas. This situation not only leads to significant degradation of the ecological system, but also greatly reduces the ecological service function.

[0003] Therefore, it is an urgent need in the current environmental protection field to develop efficient and low-cost wastewater treatment technologies, especially for the deep removal of ammonia nitrogen and total nitrogen. Existing wastewater treatment methods, such as oxidation ditch and SBR, can remove pollutants in wastewater to some extent, but have limitations in treatment efficiency, operating cost and operation complexity. In particular, when treating high-concentration ammonia nitrogen and total nitrogen wastewater, a long treatment period and high energy consumption are often required, and the treatment effect is unstable, which is difficult to meet the increasingly stringent environmental protection emission standards.

[0004] In a membrane-aerated biofilm reactor (MABR), the biofilm is one of the key technologies that determines the performance of the reactor. The formation process of the biofilm usually includes the attachment, colonization, reproduction and metabolism of microorganisms. MABR, as a new and efficient wastewater treatment technology, uses a gas-permeable membrane module (such as a hollow fiber membrane) to achieve bubble-free oxygen supply. Oxygen is directly transferred to the inner layer of the biofilm attached to the membrane surface, while pollutants diffuse from the outside of the water body into the biofilm. This unique "counter-current mass transfer" mechanism makes MABR have significant energy-saving and process advantages in simultaneous nitrification and denitrification (SND) and high-ammonia-nitrogen wastewater treatment. The gas-permeable membrane module is both a gas mass transfer channel and a carrier for microbial attachment, and its performance directly determines the start-up speed and running stability of the reactor.

[0005] In engineering applications, in order to ensure the service life of the membrane module under long-term hydraulic scouring and chemical cleaning, polyvinylidene fluoride (PVDF), polypropylene (PP) and other high molecular materials are usually selected. These materials have excellent mechanical strength and corrosion resistance, but their surfaces have strong hydrophobicity (low surface energy). However, the key to the start-up of MABR is the rapid colonization of functional bacteria (especially slow-growing autotrophic nitrifying bacteria) on the membrane surface. Autotrophic nitrifying bacteria have weak ability to secrete extracellular polymeric substances (EPS), and it is difficult for them to form initial biofilms on the originally smooth and hydrophobic membrane surface. This leads to a very long start-up period of conventional MABR, and the initial biofilm is prone to fall off, which seriously limits the engineering popularization of the technology.

[0006] Therefore, it is urgent to develop a new MABR biofilm formation method, which can effectively reconcile the interface contradiction between hydrophobic membrane material and hydrophilic microorganisms, utilize heterotrophic bacteria to improve the microenvironment on the membrane surface, prevent excessive proliferation and block mass transfer through precise process control, and thus realize the rapid, stable and function-oriented biofilm construction on the surface of durable hydrophobic membrane. SUMMARY

[0007] To solve the above problems, the application develops a new MABR biofilm formation method, which can effectively reconcile the interface contradiction between hydrophobic membrane material and hydrophilic microorganisms, utilize heterotrophic bacteria to improve the microenvironment on the membrane surface, prevent excessive proliferation and block mass transfer through precise process control, and thus realize the rapid, stable and function-oriented biofilm construction on the surface of durable hydrophobic membrane.

[0008] The first object of the application is to provide a MABR-based biofilm formation method, comprising the steps of: Inoculating aerobic tank activated sludge in the reactor to an initial suspended sludge concentration of 2500-3000 mg / L, adding MABR, adding sewage in the reactor, continuously adding basic nutrient solution containing signal molecule C8-HSL, injecting sodium acetate at the beginning of each cycle to make the initial instantaneous COD concentration of the mixed liquor in the reactor reach 200-210 mg / L, and obtaining MABR with mature biofilm by running the reactor; Wherein, the running of the reactor includes water inlet, circulation and water outlet, and the running cycle is 11-12 h.

[0009] In an embodiment, the MABR is a polyvinylidene fluoride hollow fiber membrane, each membrane filament has an inner diameter of 200 microns, an outer diameter of 280 microns, and a length of 30 cm, the membrane module is packaged by 70 hydrophobic PVDF hollow fiber membranes, the specific surface area of the membrane module is about 154 m² / m³, the effective length of the membrane bundle is 30 cm, and the aeration pressure is 0.02-0.03 Mpa.

[0010] In an embodiment, the basic nutrient solution contains 50-55 mg / L NH4 + , 10-11 mg / L PO4 3- , and 800-900 mg / L NaHCO3.

[0011] In an embodiment, the concentration of signal molecule C8-HSL in the basic nutrient solution is 100-110 nmol / L.

[0012] In an embodiment, the concentration of sodium acetate is 256-270 mg / L.

[0013] A second object of the present application is to provide a method for shortening the MABR biofilm formation period and avoiding blockage, comprising the steps of: Inoculating the aerobic tank activated sludge in the reactor to an initial suspended sludge concentration of 2500-3000 mg / L, adding the MABR, adding sewage to the reactor, continuously adding the basic nutrient solution containing the signal molecule C8-HSL, injecting sodium acetate at the beginning of each cycle to make the initial instantaneous COD concentration of the mixed liquor in the reactor reach 200-210 mg / L, and obtaining the MABR with mature biofilm by operating the reactor. Wherein, the operation of the reactor includes water inlet, circulation and water outlet, and the operation cycle is 12 h.

[0014] In an embodiment, the MABR is a polyvinylidene fluoride hollow fiber membrane, each membrane filament has an inner diameter of 200 microns, an outer diameter of 280 microns, and a length of 30 cm, the membrane module is packaged by 70 hydrophobic PVDF hollow fiber membranes, the specific surface area of the membrane module is about 154 m² / m³, the effective length of the membrane bundle is 30 cm, and the aeration pressure is 0.02-0.03 Mpa.

[0015] In an embodiment, the basic nutrient solution contains 50-55 mg / L NH4 + -N, 10-11 mg / L PO4 3- -P, and 800-900 mg / L NaHCO3.

[0016] In an embodiment, the concentration of the signal molecule C8-HSL in the basic nutrient solution is 100-110 nmol / L.

[0017] In an embodiment, the concentration of sodium acetate is 256-270 mg / L.

[0018] Advantages of the present application The present application effectively solves the technical bottlenecks of the conventional MABR reactor, such as difficulty in biofilm formation on the surface of durable hydrophobic membranes, long start-up period, blockage of flow channels caused by excessive proliferation of heterotrophic bacteria, and oxygen transfer obstruction, by introducing a pulse-type carbon source dosing strategy. (1) The present application breaks through the interface affinity bottleneck of hydrophobic membrane materials and realizes "biologically induced" rapid biofilm formation.

[0019] For the problem that the surface energy of durable membrane materials such as PVDF and PP is low and hydrophobic, which leads to the difficulty of direct colonization of autotrophic nitrifying bacteria, the present application creates a short 'rich nutrition' window period in the initial start-up stage by 'pulse carbon addition'. The strategy induces the pioneer heterotrophic bacteria with strong adhesion ability to rapidly secrete extracellular polymeric substances (EPS) on the membrane surface, and the polysaccharides and proteins rich in these EPS construct a layer of hydrophilic 'biological scaffold' on the hydrophobic membrane surface. This in-situ modification method avoids chemical damage to the membrane material, significantly reduces the interfacial energy barrier of subsequent autotrophic nitrifying bacteria attachment, and shortens the start-up period of MABR by 40%-50%.

[0020] (2) The present application establishes a'spatial and temporal partitioning' regulation mechanism, which solves the problems of 'oxygen shielding' and blockage of MABR from the root, and the present application initiates an 'alternating pulse starvation-satiety' operation mode, which utilizes the differences in growth kinetics and tolerance of autotrophic bacteria and heterotrophic bacteria for niche selection: Spatial optimization: During the'satiety period', the appropriate amount of heterotrophic bacteria improves the membrane surface environment; during the'starvation period', the suspended heterotrophic bacteria with weak starvation tolerance undergo endogenous respiration or disintegration, preventing the blockage of the flow channel between the membrane filaments.

[0021] Oxygen shielding is removed: The pulse carbon source cut-off forcibly peels off the over-proliferated outer loose heterotrophic biofilm, ensuring that the oxygen transferred in the membrane can be preferentially supplied to the inner layer nitrifying bacteria close to the membrane surface. This enables the reactor to maintain a high ammonia nitrogen removal rate (>90%) while successfully constructing a stable double-layer structure of 'inner layer aerobic / outer layer anoxic', realizing simultaneous nitrification and denitrification (SND).

[0022] (3) The mechanical stability and impact load capacity of the biofilm are strengthened by using QS signal molecules. In view of the problem that the biofilm is prone to fall off under pulse hydraulic conditions, the present application activates the quorum sensing system of the microorganisms in the biofilm by adding exogenous signal molecule C8-HSL. C8-HSL specifically up-regulates the expression of genes related to EPS synthesis, significantly increases the proportion of proteins and polysaccharides in EPS, and enhances the internal cohesion of the biofilm and the adhesion to the membrane matrix. This makes the formed biofilm structure more dense and compact, which can withstand the environmental fluctuations and hydraulic shear caused by pulse operation, ensuring the long-term stability of the effluent water quality.

[0023] (4) The low-cost, long-life membrane module is efficiently applied in engineering. The application enables the direct application of inexpensive and durable general-purpose polymer microporous membranes (such as ordinary PVDF hollow fiber membranes) to a high-performance MABR system without the need for expensive surface hydrophilic modification pretreatment. The biofilm cultivated by the method has a significant "self-renewal" ability, effectively prolongs the cleaning cycle and service life of the membrane module, significantly reduces the capital investment and operation and maintenance cost of the MABR process, and has extremely high engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a membrane hanging effect diagram for Example 1.

[0025] Figure 2 It is a membrane hanging effect diagram for Comparative Example 1. DETAILED DESCRIPTION

[0026] The preferred embodiments of the application are described below, and it should be understood that the embodiments are for better explanation of the application and are not used to limit the application.

[0027] 1. Raw materials involved in the following examples and comparative examples: The membrane filaments are purchased from Mitsubishi Chemical Corporation, Japan; The signal molecule C8-HSL is purchased from Aladdin; The aerobic tank sludge is derived from Yixing Concept Factory.

[0028] 2. Composition of activated sludge in the aerobic tank: Aerobic bacteria Aerobic bacteria oxidize and degrade organic and inorganic matter in an aerobic environment. They usually use organic matter as a carbon source and oxygen as an electron acceptor for aerobic respiration, playing a core role in removing pollutants.

[0029] Main types: Heterotrophic bacteria (Heterotrophic Bacteria): These bacteria use organic matter as a carbon source and utilize oxygen for respiration to degrade organic pollutants in water. They are the main force in degrading organic matter in the aerobic tank and can decompose carbon sources (such as COD and BOD) in water into carbon dioxide and water, reducing organic pollutants in water.

[0030] Autotrophic bacteria (Autotrophic Bacteria): Use inorganic matter (such as ammonia nitrogen and nitrate) as a carbon source for oxidation-reduction reactions. The most common are nitrifying bacteria, which participate in the nitrogen cycle.

[0031] Nitrifying bacteria: such as Nitrosomonas and Nitrobacter. Nitrifying bacteria convert ammonia nitrogen (NH3) into nitrite (NO2 -), and then further converted into nitrate (NO3 - ). It is involved in nitrogen removal, and the nitrification reaction is an important way for ammonia nitrogen removal in wastewater.

[0032] Denitrifying bacteria: such as Pseudomonas, Bacillus, etc., are bacteria that can reduce nitrate (NO3 - ) to nitrogen (N2) under anoxic conditions, usually active in the transition zone between the aerobic tank and the anoxic tank or under certain specific conditions. It reduces nitrate to nitrogen, participates in nitrogen removal (denitrification process), and plays an important role in the nitrogen reflux process in wastewater treatment.

[0033] 4. Test methods used in the following examples and comparative examples: (1) Determination method and calculation method of ammonia nitrogen removal rate: Nessler's reagent colorimetry: Nessler's reagent (containing mercuric chloride and sodium chloride) reacts with ammonia nitrogen to form a yellow complex. The higher the concentration of ammonia nitrogen, the darker the color. By measuring the absorbance of the sample, the concentration of ammonia nitrogen can be calculated.

[0034] Ammonia nitrogen removal rate (%) = (influent ammonia nitrogen concentration - effluent ammonia nitrogen concentration) / influent ammonia nitrogen concentration × 100% (3) Determination method and calculation method of total nitrogen removal rate: Persulfate digestion method: persulfate reacts with nitrogen in the water sample at high temperature to form nitrate, and then the absorbance is measured by a specific reagent reaction (such as diazomethane reagent).

[0035] Total nitrogen removal rate (%) = (influent total nitrogen concentration - effluent total nitrogen concentration) / influent total nitrogen concentration × 100% (4) Determination method of biofilm micro-morphology: Scanning electron microscope (SEM) method Sample sampling: The biofilm on the filler is taken off and cut into samples suitable for SEM observation.

[0036] Drying treatment: The biofilm sample is treated and dried by freezing or air drying to avoid deformation of the membrane structure.

[0037] Gold plating treatment: In order to improve the clarity of the image, the sample needs to be plated with a thin metal film (such as gold or platinum) in a vacuum.

[0038] SEM observation: Observe the surface morphology of the biofilm under a scanning electron microscope.

[0039] Example 1 A method for constructing and operating a hydrophobic membrane MABR biofilm based on dual-phase regulation, comprising the steps of: The reactor was continuously fed with base nutrient solution 50 mg / L NH4 + -N, 10 mg / L PO4 3- -P, 850 mg / L NaHCO3 (total volume 650 mL); a hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membrane was used, each membrane filament had an inner diameter of 200 microns, an outer diameter of 280 microns, and a length of 30 cm, a membrane module was packaged by bundling 70 hydrophobic PVDF hollow fiber membranes, the specific surface area of the membrane module was about 154 m² / m³, the effective length of the membrane bundle was 30 cm, air was introduced into the membrane, the aeration pressure was 0.02-0.03 Mpa, and the outside of the membrane was a sewage flow area; aerobic tank activated sludge was inoculated, the initial suspended sludge concentration (MLSS) was 2500 mg / L, and the inoculated sludge was used as the source of the biofilm; The running cycle was set to 12 h (T=12 h), at the beginning of each cycle, a high-concentration sodium acetate solution (256 mg / L) was instantaneously injected into the reactor, so that the initial instantaneous COD concentration of the mixed liquor in the reactor reached 200 mg / L; at the remaining time, only the continuous flow of the base nutrient solution was maintained (100 nmol / L of the signal molecule C8-HSL, N-octanoyl-homoserine lactone).

[0040] The high-concentration carbon source can promote the rapid metabolic activity of heterotrophic denitrifying bacteria, cause substrate starvation environment, inhibit the proliferation of suspended sludge, and restore the inner nitrification activity.

[0041] The treated sewage was detected for ammonia nitrogen and total nitrogen removal rates and the morphology of the biofilm was observed. The ammonia nitrogen removal rate was stably above 90%, the total nitrogen removal rate was stably above 80%, the suspended sludge concentration (MLSS) in the reactor gradually decreased from the initial 2500 mg / L and finally stabilized at 300-500 mg / L, the biofilm rapidly grew in the first 20 days, stabilized at 400-600 microns after 30 days, and then maintained a dynamic balance, the efficient and synchronous removal of ammonia nitrogen and total nitrogen confirmed that under the cooperation of pulse and QS, the functional double-layer biofilm structure of inner-layer aerobic and outer-layer anoxic was successfully constructed on the membrane surface.

[0042] Figure 1 For the biofilm formation effect of Example 1, the scanning electron microscope image showed that the surface of the hydrophobic PVDF membrane filament was completely covered by a layer of dense, continuous and uniform biofilm. The biofilm surface presented a rough porous structure, and no obvious membrane filament substrate bare area was seen. Although there were microcracks on the surface produced during the SEM sample preparation (dehydration and drying) process, the overall skeleton of the biofilm remained intact without large area peeling.

[0043] Comparative Example 1 On the basis of Example 1, no signal molecule C8-HSL is added in the continuous flow influent, and the influent COD concentration and other conditions remain the same as in Example 1.

[0044] The sewage treatment condition is detected, and the results show that in the initial stage of operation, only a patchy and discontinuous biofilm is formed on the surface of the hydrophobic PVDF membrane; under the condition of entering the "starvation period" and hydraulic flushing, it is observed that the biofilm repeatedly peels off and falls off, and the thickness cannot be stabilized and hovers at 50-150 μm for a long time, and the distribution is extremely uneven. Benefiting from the pulse operation, the MLSS also decreases to below 500 mg / L; the ammonia nitrogen removal rate fluctuates between 30% and 70%, and the total nitrogen removal rate is less than 40%.

[0045] Figure 2 For the biofilm formation effect of Comparative Example 1, the scanning electron microscope image shows that the biofilm on the membrane surface presents a discontinuous "patchy" or "island-like" distribution, and a large area of smooth PVDF membrane substrate is directly exposed. The edge of the attached biofilm is clear, showing obvious layered peeling and curling characteristics, indicating that the adhesion between the biofilm and the substrate is very weak.

[0046] Comparative Example 2 On the basis of Example 1, no signal molecule C8-HSL is added in the continuous flow influent, and the pulse carbon source is changed to continuous flow input of carbon source, and the influent COD concentration and other conditions remain the same as in Example 1.

[0047] The sewage treatment condition is detected, and the results show that due to the lack of "starvation period" substrate limitation, the heterotrophic bacteria grow in an unordered isotropic manner in the suspension and the membrane gap. The MLSS in the reactor does not decrease but increases, and is maintained at a high level of 2500-3000 mg / L for a long time, resulting in serious blockage, and the membrane filaments also adhere and harden.

[0048] The ammonia nitrogen removal rate is greater than 80% in the first 5 days of operation, and then due to the thick suspended sludge layer outside hindering the diffusion of ammonia nitrogen to the membrane surface and the outward transmission of oxygen, there is a cliff-like drop, and on the 12th day, it drops to below 20%. The total nitrogen removal rate is less than 30% due to the collapse of the nitrification reaction.

[0049] Comparative Example 3 On the basis of Example 1, the pulse carbon source is changed to continuous flow input of carbon source, and the influent COD concentration and other conditions remain the same as in Example 1.

[0050] The sewage treatment condition is detected, and the results show that under the induction of the signal molecule, the microorganisms secrete a large amount of high-viscosity extracellular polymeric substance, and under the sufficient supply of continuous carbon source, these high-viscosity biomass not only rapidly covers the membrane surface, but also captures a large amount of suspended sludge like "glue".

[0051] Compared with Comparative Example 2, the plugging of Comparative Example 3 occurred earlier and more completely. After only 7 days of operation, the membrane module was completely filled with dense gelatinous biomass, with MLSS as high as 4000 mg / L and biofilm thickness exceeding 2000 μm. Due to the extremely thick and dense bio-layer, an impermeable "heterotrophic barrier layer" was formed, completely blocking the oxygen transfer to the outside. The ammonia nitrogen removal rate was almost zero, and the system completely lost the MABR function, and the experiment was forced to terminate prematurely Table 1 Sewage treatment effect

[0052] Although the present application has been disclosed with reference to the preferred embodiments, it is not intended to limit the application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the application, and therefore the protection scope of the present application should be defined by the claims.

Claims

1. A method for attaching a biofilm based on a MABR, characterized in that, Including the following steps: The reactor is inoculated with activated sludge from an aerobic tank until the initial suspended sludge concentration reaches 2500-3000 mg / L, then MABR is added. Wastewater is added to the reactor, and a basic nutrient solution containing the signaling molecule C8-HSL is continuously fed in. Sodium acetate is injected instantaneously at the beginning of each cycle to bring the initial instantaneous COD concentration of the mixture in the reactor to 200-210 mg / L. Running the reactor yields an MABR with a mature biofilm. The operating reactor includes influent, circulation, and effluent, with an operating cycle of 11-12 hours.

2. The biofilm attachment method according to claim 1, characterized in that, MABR is a polyvinylidene fluoride hollow fiber membrane. Each membrane fiber has an inner diameter of 200 micrometers, an outer diameter of 280 micrometers, and a length of 30 cm. The membrane module is composed of 70 hydrophobic PVDF hollow fiber membranes bundled together. The specific surface area of ​​the membrane module is 154 m² / m³, the effective length of the membrane bundle is 30 cm, and the aeration pressure is 0.02~0.03 MPa.

3. The biofilm attachment method according to claim 1, characterized in that, The basic nutrient solution contains 50-55 mg / L NH4. + -N, 10~11 mg / L PO4 3— P, 800~900 mg / L NaHCO3.

4. The film-attaching method according to claim 1, characterized in that, The concentration of the signaling molecule C8-HSL in the basal nutrient solution was 100~110 nmol / L.

5. The method for attaching a biofilm according to claim 1, characterized in that, The concentration of sodium acetate is 256~270 mg / L.

6. A method for shortening the MABR biofilm formation cycle and avoiding clogging, characterized in that, Including the following steps: The reactor is inoculated with activated sludge from an aerobic tank until the initial suspended sludge concentration reaches 2500-3000 mg / L, then MABR is added. Wastewater is added to the reactor, and a basic nutrient solution containing the signaling molecule C8-HSL is continuously fed in. Sodium acetate is injected instantaneously at the beginning of each cycle to bring the initial instantaneous COD concentration of the mixture in the reactor to 200-210 mg / L. Running the reactor yields an MABR with a mature biofilm. The operating reactor includes influent, circulation, and effluent, with an operating cycle of 11-12 hours.

7. The film-attaching method according to claim 6, characterized in that, MABR is a polyvinylidene fluoride hollow fiber membrane. Each membrane fiber has an inner diameter of 200 micrometers, an outer diameter of 280 micrometers, and a length of 30 cm. The membrane module is composed of 70 hydrophobic PVDF hollow fiber membranes bundled together. The specific surface area of ​​the membrane module is approximately 154 m² / m³, the effective length of the membrane bundle is 30 cm, and the aeration pressure is 0.02~0.03 MPa.

8. The biofilm attachment method according to claim 6, characterized in that, The basic nutrient solution contains 50-55 mg / L NH4. + -N, 10~11 mg / L PO4 3- -P, 800~900 mg / L NaHCO3.

9. The method for attaching a film according to claim 6, characterized in that, The concentration of the signaling molecule C8-HSL in the basal nutrient solution was 100~110 nmol / L.

10. The biofilm attachment method according to claim 6, characterized in that, The concentration of sodium acetate is 256~270 mg / L.

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