Method for preparing separation layer through in-situ electrooxidation of dynamic membrane bioreactor

Abstract

The invention discloses a method for preparing a separation layer by in-situ electrooxidation of a dynamic membrane bioreactor, which comprises the following steps: in the process of running the dynamic membrane bioreactor, when the transmembrane pressure difference is monitored to reach 40-60 kPa, stopping running; then performing in-situ electrooxidation treatment in the reactor by taking the conductive base membrane attached with the biological membrane as an anode and an equal-area stainless steel plate as a cathode, and synchronously recovering system operation; and when the transmembrane pressure difference is increased to 80-100 kPa, stopping, and cleaning to form a stable separation layer on the surface of the base membrane. According to the principle, corrosion sites are generated on the surface of a base membrane through the electrooxidation effect so as to enhance mechanical anchoring, meanwhile, loose components are degraded, a biological membrane network structure is strengthened in a cross-linking mode, and hydrophilic groups are introduced. The separation layer prepared by the method has the advantages of submicron interception precision, firm combination with the base membrane, good hydrophilicity, strong anti-pollution capability and the like, and can significantly improve the effluent quality and operation stability of the dynamic membrane bioreactor.

Description

Technical Field

[0001] This invention belongs to the field of membrane water treatment technology, and particularly relates to a method for preparing a separation layer by in-situ electro-oxidation in a dynamic membrane bioreactor. Background Technology

[0002] my country faces a very serious environmental situation, with water pollution being a particularly prominent issue. Pollutants in water bodies exhibit characteristics such as being difficult to degrade, mobile, and highly persistent in the environment. The continuous emergence of numerous new environmental pollutants poses a significant challenge to conventional water treatment technologies. Against this backdrop, next-generation water treatment technologies, represented by dynamic membrane bioreactors (MBRs), have demonstrated significant advantages in pollutant removal. Dynamic membrane separation technology uses large-pore materials as the base membrane, significantly reducing the manufacturing cost of membrane modules and offering good economic benefits. However, precisely because of the large pore size of the base membrane, dynamic membranes generally suffer from poor pollutant retention and insufficient effluent quality stability during operation, making it difficult to meet increasingly stringent standards for reclaimed water reuse or discharge. Furthermore, membrane fouling on the surface of the large-pore base membrane is particularly serious, directly affecting the long-term stable operation and economic viability of the process, and has become a major obstacle to the further promotion and application of this technology.

[0003] During the operation of a dynamic membrane bioreactor (MBR), its separation performance does not depend on the base membrane itself, but rather on the dynamic membrane layer that gradually accumulates on the base membrane surface. In the initial stage of operation, the macroporous base membrane physically traps flocculent sludge, causing it to accumulate on its surface and forming a sludge cake layer with a certain retention capacity, thereby improving the effluent quality. However, this process mainly relies on mechanical accumulation; the aggregation ability between microbial cells and their adhesion to the base membrane surface are weak, resulting in a loose dynamic membrane structure that is easily damaged by aeration or hydraulic shear forces within the reactor, leading to unstable performance. Simultaneously, in the sludge mixed liquor environment, a biofilm spontaneously forms on the base membrane surface and within its pores. The formation of this biofilm can be roughly divided into two stages: first, the initial adhesion and growth of microorganisms on the base membrane surface or within its pores lays the structural foundation for the biofilm; second, the continuous accumulation of extracellular polymeric substances (EPS) secreted by microorganisms and dissolved microbial metabolites (SMPs) on the base membrane surface provides the material conditions for the formation of a more dense and stable biofilm.

[0004] In dynamic membrane bioreactor systems, extracellular polymeric substances (EPS) play a crucial role as "bioglue," closely related to the filtration properties of the biofilm. The three-dimensional network structure formed by EPS effectively enhances the biofilm's ability to retain large organic molecules in water, promoting the enrichment of most dissolved organic matter within the biofilm. Recent research further reveals that the extracellular components in EPS play a vital role in maintaining the three-dimensional spatial structure of the biofilm. Therefore, how to fully utilize and enhance this spatial network structure of the biofilm on the base membrane surface, and construct a functionalized separation layer with high retention performance and high stability based on it, has become a core issue in improving the overall operational efficiency of dynamic membrane bioreactors. Currently, existing technologies lack effective means to directly and efficiently enhance the biofilm structure within the reactor and transform it into a stable separation layer. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical shortcomings of existing dynamic membrane bioreactor technologies, such as poor pollutant retention, unstable effluent quality, and severe membrane fouling caused by large-pore base membranes, and to provide a simple, efficient, and in-situ feasible method for preparing a separation layer. This method modifies naturally formed biofilms in situ on the surface of a conductive base membrane using electrochemical oxidation technology, thereby constructing a stable separation layer with high retention accuracy, strong interfacial bonding, and excellent antifouling properties.

[0006] To achieve the above objectives, the present invention provides a method for preparing a separation layer in situ using electro-oxidation in a dynamic membrane bioreactor, comprising the following steps: (1) The dynamic membrane bioreactor with conductive material as conductive base membrane is operated normally, and the transmembrane pressure difference of the dynamic membrane is monitored in real time; when the transmembrane pressure difference reaches the first preset threshold of 40-60 kPa, the aeration of the reactor and the operation of water inlet and outlet are stopped. (2) Using the conductive base film described in step (1) as the anode, a cathode plate with the same area as the conductive base film is placed parallel to the dynamic membrane bioreactor, and the distance between the anode and the cathode plate is 8-15 mm; the anode and the cathode are respectively connected to the positive and negative terminals of a DC power supply. (3) Turn on the DC power supply, set the output voltage to 15-40 V and maintain constant voltage output mode, and restart the operation of the dynamic membrane bioreactor; continue to monitor the transmembrane pressure difference, and when the transmembrane pressure difference rises to the second preset threshold of 80-100 kPa, turn off the DC power supply and the dynamic membrane bioreactor. (4) Remove the anode and cathode plates, clean the loose biofilm residues on the surface of the anode base film, thereby obtaining an in-situ formed separation layer with high retention performance on the surface of the conductive base film.

[0007] The core concept of this method is to fully utilize the biofilm spontaneously formed on the surface of the conductive base membrane during the operation of the dynamic membrane bioreactor as "raw material." Inside the reactor, a controllable DC electric field is applied to trigger a series of electrochemical oxidation reactions and physicochemical changes, transforming the originally loose and easily detached biofilm into a dense and stable functional separation layer. The entire process requires no external reactor or additional chemical reagents, achieving in-situ, green, and intelligent preparation of the separation layer.

[0008] In step (1), the selection of transmembrane pressure difference as the trigger signal has a clear physical significance. When the TMP value is in the range of 40-60 kPa, it indicates that a biofilm of sufficient thickness has accumulated on the surface of the base membrane but has not yet become overly dense. At this time, the biofilm still contains abundant microbial active components and extracellular polymers, providing an ideal material basis for subsequent electro-oxidative modification.

[0009] Steps (2) and (3) constitute the core of electro-oxidation modification. Using the conductive substrate film with attached biofilm as the anode, after applying a DC voltage of 15-40 V, the following effects mainly occur: First, the electrochemical corrosion on the anode surface generates micron or nanoscale corrosion sites, which greatly enhances the surface roughness of the substrate and provides a strong mechanical anchoring point for the separation layer. Second, the anodic oxidation reaction generates reactive oxygen species such as hydroxyl radicals. These strong oxidants can effectively degrade the loosely structured and weakly adhesive soluble microbial products in the biofilm, while selectively retaining and crosslinking the components that act as "scaffolding" in EPS (such as extracellular DNA and proteins), thereby strengthening the strength and stability of the biofilm network structure and promoting its chemical bonding with the substrate surface. Furthermore, the electro-oxidation process can introduce a large number of hydrophilic functional groups such as hydroxyl and carboxyl groups on the biofilm macromolecules, significantly improving the surface hydrophilicity of the separation layer, which is the key to its enhanced anti-fouling ability. Limiting the electrode spacing to 8-15 mm is to obtain a sufficiently strong and uniform electric field strength within the limited space of the reactor.

[0010] In step (4), the loose parts that are still not firmly bonded after electro-oxidation are removed by simple physical cleaning, leaving behind a high-precision separation layer that is firmly bonded to the base film and has an optimized structure. The termination point is set at 80-100 kPa TMP because the densification of the separation layer has reached an ideal state at this point; continuing to apply current may lead to excessive oxidation or energy waste. This threshold control ensures that the formation process of the separation layer is precise, controllable, and repeatable.

[0011] Furthermore, the conductive base film is a stainless steel mesh with a mesh count of 400-600.

[0012] Further, in step (3), restarting the operation of the dynamic membrane bioreactor includes: restoring the membrane effluent pump to maintain membrane flux and restoring aeration to provide hydraulic shear.

[0013] Furthermore, the cathode plate is made of stainless steel.

[0014] Furthermore, in step (4), a physical cleaning method is used to remove loose biofilm residues on the surface of the anode base film.

[0015] Further, the first preset threshold is 40 kPa, 45 kPa, 50 kPa, 55 kPa or 60 kPa; the second preset threshold is 80 kPa, 85 kPa, 90 kPa, 95 kPa or 100 kPa.

[0016] Furthermore, the output voltage is 15 V, 20 V, 25 V, 30 V, 35 V or 40 V.

[0017] Furthermore, the distance between the anode and the cathode plate is 8 mm, 10 mm, 12 mm or 15 mm.

[0018] Furthermore, the method is used to treat domestic sewage or industrial wastewater containing organic pollutants, by periodically implementing steps (1) to (4) during the operation of the dynamic membrane bioreactor to achieve the regeneration and performance restoration of the separation layer.

[0019] A separation layer is prepared by in-situ electro-oxidation in a dynamic membrane bioreactor, using the method described above.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The separation layer on the surface of the conductive base membrane is prepared in situ in the dynamic membrane bioreactor, without the need for an additional electro-oxidation reactor and chemical reagents. The separation layer preparation process is simple and controllable.

[0021] (2) The TMP index during the operation of the dynamic membrane bioreactor can reflect the thickness and porosity of the biofilm on the base membrane surface. The control of the TMP index during the preparation process can regulate the retention accuracy of the separation layer on the one hand, and strengthen the bonding strength between the separation layer and the base membrane on the other hand.

[0022] (3) The separation layer formed in situ on the base membrane surface is homologous to the sludge mixture in the dynamic membrane bioreactor. The electro-oxidation reaction enhances the hydrophilicity of the separation layer, which is beneficial to the separation layer in mitigating membrane fouling. Attached Figure Description

[0023] Figure 1This describes the pore size distribution of the separation layer prepared using different electro-oxidation parameters in Examples 1 to 4 of the present invention. Detailed Implementation

[0024] 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.

[0025] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0026] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0027] In the embodiments, unless otherwise specified, the conductive base membrane used is a commercially available stainless steel mesh, and the dynamic membrane bioreactor is a laboratory-scale aerobic reactor.

[0028] Example 1 This embodiment uses a dynamic membrane bioreactor with an effective volume of 20 L. The sludge concentration in the reactor is maintained at approximately 8.7 g / L, and the hydraulic retention time and sludge retention time are set to 10 h and 30 d, respectively. The influent is simulated domestic sewage with a chemical oxygen demand (COD) of [missing information]. Cr The concentration is 300~430 mg / L. The membrane module operating flux is 20 L / (m²). 2 The bottom aeration rate is 450 L / h to provide shear force and prevent sludge deposition. The dynamic membrane operation adopts an intermittent suction mode. In each working cycle, the suction time is 13 min, followed by a 2 min aeration period after suction stops.

[0029] The specific steps for preparing the separation layer are as follows: (1) The reactor is started and continuously operated with a 400-mesh stainless steel mesh as the conductive base membrane. The change of the transmembrane pressure difference (TMP) of the system is monitored in real time. When the TMP rises to 40 kPa (indicating that a biofilm layer of a certain thickness has been formed on the base membrane surface), the aeration and influent / effluent of the reactor are stopped.

[0030] (2) The conductive substrate membrane with attached biofilm is used as the anode, and a stainless steel plate of equal area is used as the cathode, and both are placed parallel to each other in the reactor. The distance between the anode and cathode plates is adjusted to 8 mm. The anode is connected to the positive terminal of the DC regulated power supply through a wire, and the cathode is connected to the negative terminal.

[0031] (3) Turn on the DC power supply and set the output voltage to 15 V, maintaining constant voltage output mode. Simultaneously with power on, run the dynamic membrane bioreactor to allow it to continue operating under electro-oxidation conditions. During this process, continuously monitor TMP changes.

[0032] (4) When the TMP value continues to rise to 80 kPa, it indicates that the electro-oxidation modification process has been completed and the separation layer has been densified. Turn off the DC power supply and the dynamic membrane bioreactor. Take out the anode and cathode plates, clean the anode surface to remove the loose biofilm residue that is still bound after electro-oxidation, and finally obtain a firmly attached separation layer on the base membrane surface.

[0033] Implementation results are as follows Figure 1 As shown in Figure 1, this figure illustrates the pore size distribution of the separation layer prepared under different operating conditions. Figure 1 As can be seen in working condition 1, the separation layer prepared by the method of this embodiment has a nominal diameter (i.e., the main pore size) of about 0.82 μm, which is more than two orders of magnitude higher than the original 400 mesh base film (about 38 μm).

[0034] To evaluate the long-term operational performance of the separation layer, after preparation, the membrane module was placed back into the reactor and subjected to five consecutive performance tests under the same simulated domestic wastewater and operating conditions. At the end of each operating cycle (i.e., when TMP reached approximately 50 kPa), the membrane was cleaned by reverse flushing with clean water before starting the next cycle.

[0035] Table 1 summarizes the comparative data of the original stainless steel mesh base film and the separation layer prepared in this embodiment on several key performance indicators.

[0036] Table 1. Comparison of operational performance between the separation layer prepared in Example 1 and the original base membrane. As shown in Table 1, the separation layer prepared in this embodiment significantly improved the removal rates of COD and turbidity by 18.4% and 25.1%, respectively, compared to the original base membrane, resulting in a fundamental improvement in effluent quality. Simultaneously, the membrane fouling rate, characterizing the rate of membrane fouling development, decreased dramatically from 5.3 kPa / d to 1.2 kPa / d, indicating that the separation layer possesses excellent anti-fouling properties. Although the flux recovery rate slightly decreased after backwashing (from 93.2% to 85.2%), it remained at a high level, and the retention rate of pollutants by the separation layer fluctuated by less than 5% over five operating cycles, demonstrating its structural stability and ability to withstand periodic physical cleaning, making it fully suitable for long-term online operation and maintenance of dynamic membrane bioreactors.

[0037] Example 2 The reactor structure, influent water quality, and operating mode used in this embodiment are exactly the same as in Embodiment 1, with only the base membrane specifications and some electro-oxidation parameters changed. The sludge concentration in the reactor is approximately 8.3 g / L, and the influent COD is... Cr The concentration is 320~380 mg / L.

[0038] The separation layer preparation steps are as follows: (1) The dynamic membrane bioreactor is operated with 500 mesh stainless steel mesh as the base membrane. When the TMP reaches 45 kPa, the aeration and influent / effluent of the dynamic membrane bioreactor are stopped. (2) A conductive base membrane is used as the anode and an equal area stainless steel plate is used as the cathode. They are arranged in parallel in the dynamic membrane bioreactor. The distance between the anode and cathode plates is set to 10 mm. The plates are connected to the positive and negative terminals of a DC power supply respectively. (3) Turn on the DC power supply and set the voltage to 25 V constant voltage output. Simultaneously run the dynamic membrane bioreactor. When TMP reaches 85 kPa, turn off the DC power supply and the dynamic membrane bioreactor, remove the anode and cathode plates, clean the loose biofilm on the anode surface, and obtain the separation layer.

[0039] See implementation results Figure 1 Condition 2. As shown in the figure, the nominal diameter of the separation layer prepared in this embodiment is 0.78 μm, and the pore size of the base membrane is approximately 25 μm with a 500-mesh pore size, indicating that the separation layer prepared in this embodiment significantly improves the retention accuracy of the base membrane.

[0040] After five cycles of testing, the same as in Example 1, the performance comparison data is shown in Table 2.

[0041] Table 2 Comparison of operational performance between the separation layer prepared in Example 2 and the original base membrane Data shows that applying the method of this invention to a finer base membrane can also form an ultrafine separation layer, achieving a significant improvement in pollutant removal rate and effective control of membrane fouling.

[0042] Example 3 This embodiment aims to explore the application effect under higher influent loads. The reactor structure and operation mode are the same as in Embodiment 1, the sludge concentration is approximately 7.8 g / L, and the influent COD is... Cr Increase to 430~480 mg / L.

[0043] The separation layer preparation steps are as follows: (1) The dynamic membrane bioreactor is operated with 600 mesh stainless steel mesh as the base membrane. When the TMP reaches 55 kPa, the aeration and influent / effluent of the dynamic membrane bioreactor are stopped. (2) A conductive base membrane is used as the anode and an equal area stainless steel plate is used as the cathode. They are arranged in parallel in the dynamic membrane bioreactor. The distance between the anode and cathode plates is set to 12 mm. The plates are connected to the positive and negative terminals of a DC power supply respectively. (3) Turn on the DC power supply and set the voltage to 35 V constant voltage output. Simultaneously run the dynamic membrane bioreactor. When TMP reaches 90 kPa, turn off the DC power supply and the dynamic membrane bioreactor, remove the anode and cathode plates, clean the loose biofilm on the anode surface, and obtain the separation layer.

[0044] See implementation results Figure 1 In the medium working condition 3, the nominal diameter of the separation layer prepared in this embodiment is 0.57 μm, and the pore size of the base membrane is approximately 23 μm with a 600-mesh pore size. The separation layer prepared in this embodiment significantly improves the retention accuracy of the base membrane.

[0045] The performance comparison is shown in Table 3.

[0046] Table 3 Comparison of operational performance between the separation layer prepared in Example 3 and the original base membrane The results show that even under high organic loads, the separation layer prepared by the method of the present invention still exhibits excellent and stable retention and antifouling performance.

[0047] Example 4 This embodiment further verifies the effectiveness of the upper limit of the electro-oxidation parameters. The reactor conditions are the same as in Example 1, with a sludge concentration of approximately 8.8 g / L and an influent COD of [missing value]. Cr The concentration is 280~310 mg / L.

[0048] The separation layer preparation steps are as follows: (1) The dynamic membrane bioreactor is operated with 600 mesh stainless steel mesh as the base membrane. When the TMP reaches 60 kPa, the aeration and influent / effluent of the dynamic membrane bioreactor are stopped. (2) A conductive base membrane is used as the anode and an equal area stainless steel plate is used as the cathode. They are arranged in parallel in the dynamic membrane bioreactor. The distance between the anode and cathode plates is set to 15 mm. The plates are connected to the positive and negative terminals of a DC power supply respectively. (3) Turn on the DC power supply and set the voltage to 40 V constant voltage output. Simultaneously run the dynamic membrane bioreactor. When TMP reaches 100 kPa, turn off the DC power supply and the dynamic membrane bioreactor, remove the anode and cathode plates, clean the loose biofilm on the anode surface, and obtain the separation layer.

[0049] See implementation results Figure 1 In the medium working condition 4, the nominal diameter of the separation layer prepared in this embodiment is 0.48 μm, and the pore size of the base membrane is approximately 23 μm with a 600-mesh pore size. The separation layer prepared in this embodiment significantly improves the retention accuracy of the base membrane.

[0050] The performance comparison is shown in Table 4.

[0051] Table 4 Comparison of operational performance between the separation layer prepared in Example 4 and the original base membrane This embodiment demonstrates that, under the upper limits of the TMP trigger point and voltage parameters, a separation layer with the highest retention accuracy can be formed, resulting in near-complete removal of turbidity in the effluent and the lowest membrane fouling rate.

[0052] In summary, as demonstrated in Examples 1-4, the method of this invention can produce, in situ, a high-performance separation layer with a nominal diameter in the range of 0.48-0.82 μm that is firmly bonded to the substrate membrane, on stainless steel conductive substrates with different pore sizes (400-600 mesh). This is achieved by adjusting the TMP trigger point (40-60 kPa), electro-oxidation voltage (15-40 V), and TMP termination point (80-100 kPa). This separation layer significantly improves the pollutant rejection rate, substantially reduces the membrane fouling rate, and maintains good physical cleaning and recovery capabilities. The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a separation layer in situ using electro-oxidation in a dynamic membrane bioreactor, characterized in that, Includes the following steps: (1) The dynamic membrane bioreactor with conductive material as conductive base membrane is operated normally, and the transmembrane pressure difference of the dynamic membrane is monitored in real time; when the transmembrane pressure difference reaches the first preset threshold of 40-60 kPa, the aeration of the reactor and the operation of water inlet and outlet are stopped. (2) Using the conductive base film described in step (1) as the anode, a cathode plate with the same area as the conductive base film is placed parallel to the dynamic membrane bioreactor, and the distance between the anode and the cathode plate is 8-15 mm; the anode and the cathode are respectively connected to the positive and negative terminals of a DC power supply. (3) Turn on the DC power supply, set the output voltage to 15-40 V and maintain constant voltage output mode, and restart the operation of the dynamic membrane bioreactor; continue to monitor the transmembrane pressure difference, and when the transmembrane pressure difference rises to the second preset threshold of 80-100 kPa, turn off the DC power supply and the dynamic membrane bioreactor. (4) Remove the anode and cathode plates, clean the loose biofilm residues on the surface of the anode base film, thereby obtaining an in-situ formed separation layer with high retention performance on the surface of the conductive base film.

2. The method according to claim 1, characterized in that, The conductive base film is a stainless steel mesh with a mesh size of 400-600.

3. The method according to claim 1, characterized in that, In step (3), restarting the operation of the dynamic membrane bioreactor includes: restoring the membrane effluent pump to maintain membrane flux and restoring aeration to provide hydraulic shear.

4. The method according to claim 1, characterized in that, The cathode plate is made of stainless steel.

5. The method according to claim 1, characterized in that, In step (4), physical cleaning is used to remove loose biofilm residues on the surface of the anode base film.

6. The method according to claim 1, characterized in that, The first preset threshold is 40 kPa, 45 kPa, 50 kPa, 55 kPa or 60 kPa; the second preset threshold is 80 kPa, 85 kPa, 90 kPa, 95 kPa or 100 kPa.

7. The method according to claim 1, characterized in that, The output voltage is 15 V, 20 V, 25 V, 30 V, 35 V or 40 V.

8. The method according to claim 1, characterized in that, The distance between the anode and the cathode plate is 8 mm, 10 mm, 12 mm or 15 mm.

9. The method according to claim 1, characterized in that, The method is used to treat domestic sewage or industrial wastewater containing organic pollutants. Steps (1) to (4) are periodically implemented during the operation of the dynamic membrane bioreactor to achieve the regeneration and performance restoration of the separation layer.

10. A method for preparing a separation layer in situ using electro-oxidation in a dynamic membrane bioreactor, characterized in that, It is prepared by the method described in any one of claims 1-9.

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