PVDF membrane pollution evaluation and cleaning method for MBR process

Abstract

The invention discloses an MBR (Membrane Bioreactor) process PVDF (Polyvinylidene Fluoride) membrane pollution evaluation and cleaning method, which comprises the following steps: carrying out pollution condition evaluation on a PVDF membrane with inorganic iron composite pollutants to obtain a pollution condition evaluation result of the PVDF membrane before cleaning; forming a chemical cleaning scheme based on the pollution condition evaluation result of the PVDF membrane before cleaning, and cleaning the PVDF membrane by adopting the chemical cleaning scheme; carrying out cleaning effect evaluation on the cleaned PVDF membrane; judging whether the cleaning effect reaches a preset standard or not based on the cleaning effect evaluation result; in response to the cleaning effect reaching the preset standard, judging that the cleaning is completed; and in response to the situation that the cleaning effect does not reach the preset standard, returning to the step of forming the chemical cleaning scheme, and adjusting the initial chemical cleaning scheme until the cleaning effect reaches the preset standard. By means of the scheme, the formed chemical cleaning scheme can be specially used for evaluating the result of the pollution condition, and membrane damage caused by blind cleaning is avoided. And meanwhile, the chemical cleaning scheme can be dynamically adjusted.

Description

Technical Field

[0001] The present application generally relates to the technical field of membrane pollutant cleaning, and more specifically, to a method for evaluating and cleaning PVDF membrane pollution in a MBR process. Background Art

[0002] It is said that membrane pollution and membrane aging problems are inevitable in the long-term operation of PVDF membranes in the membrane bioreactor (MBR) process, which leads to the decline of membrane mechanical properties and permeability, affecting the effluent water quality and water production. Therefore, regular ultrafiltration membrane restorative chemical cleaning is essential to restore membrane flux and extend membrane service life. Membrane pollution is usually divided into two categories: organic pollution and inorganic pollution. In the case of composite pollution of inorganic iron and organic protein, the reaction between the two produces composite pollutants that are more likely to foul the membrane filaments and reduce the membrane flux, which will lead to the irreversible pollution of the membrane filaments and increase the difficulty of chemical cleaning. In addition, iron, as a high-quality "base bed" for microbial growth, is more conducive to the growth of biofilms when protein provides sufficient nutrient sources, further increasing the filtration resistance of the membrane and greatly shortening the service life of the membrane. Therefore, when there is composite pollution with high iron content, it is particularly important to judge the degree of PVDF membrane pollution, adopt targeted restorative chemical cleaning methods, and evaluate the membrane cleaning effect.

[0003] However, in the prior art, there is a lack of cleaning agents and methods for inorganic iron composite pollutants, which makes the pollutant removal efficiency of the PVDF membrane insufficient and may increase the risk of secondary contamination of the PVDF membrane.

[0004] In view of this, there is an urgent need to provide a PVDF membrane pollution assessment and cleaning solution for the MBR process to achieve effective removal of inorganic iron composite pollutants. Summary of the invention

[0005] In order to at least solve one or more of the technical problems mentioned above, the present application proposes a MBR process PVDF membrane pollution assessment and cleaning solution in multiple aspects.

[0006] The present application provides a method for evaluating and cleaning PVDF membrane pollution in an MBR process, comprising: evaluating the pollution status of a PVDF membrane having inorganic iron composite pollutants to obtain a pollution status evaluation result of the PVDF membrane before cleaning; forming a chemical cleaning scheme based on the pollution status evaluation result of the PVDF membrane before cleaning, and using the formed chemical cleaning scheme to clean the PVDF membrane, wherein the chemical cleaning scheme includes: the type of cleaning agent, the concentration of each cleaning agent, the cleaning time of each cleaning agent, and the action sequence of various agents in the cleaning process based on the cleaning agent; evaluating the cleaning effect of the cleaned PVDF membrane; judging whether the cleaning effect reaches a preset standard based on the cleaning effect evaluation result; judging that the cleaning is completed in response to the cleaning effect reaching the preset standard; and returning to the step of forming the chemical cleaning scheme in response to the cleaning effect not reaching the preset standard, adjusting the initial chemical cleaning scheme until the cleaning effect reaches the preset standard.

[0007] In some embodiments, the pollution status assessment results include: inorganic pollution assessment results, organic pollution assessment results, mechanical property change assessment results, permeability change assessment results and iron elution situation assessment results; wherein, the inorganic pollution assessment results are obtained by scanning electron microscopy and energy spectrum analysis; the organic pollution assessment results are obtained by Fourier transform attenuated total reflection infrared spectroscopy; the mechanical property change assessment results are obtained by a tensile strength testing device; the permeability change assessment results are obtained by a clean water flux testing device; and the iron elution situation assessment results are obtained based on inductively coupled plasma emission spectroscopy.

[0008] In some embodiments, in the process of obtaining the iron elution evaluation result based on the inductively coupled plasma emission spectrum, the following steps are performed: based on the set immersion time, the set immersion temperature and the set liquid-to-solid ratio, the PVDF membrane is immersed in the solvent of the cleaning agent; the immersion liquid is filtered using a filter membrane of a set size to obtain a filtered immersion liquid; the filtered immersion liquid is introduced into an inductively coupled plasma mass spectrometer for measurement to obtain its corresponding emission spectrum intensity; the obtained emission spectrum intensity is substituted into the iron concentration-emission spectrum intensity standard curve to obtain the iron elution amount.

[0009] In some embodiments, the parameters used by the inductively coupled plasma mass spectrometer are: nebulizing gas flow rate is 0.85 L / min, auxiliary gas flow rate is 0.8 L / min, cooling gas flow rate is 13 L / min, and plasma power is 1350W.

[0010] In some embodiments, in the process of forming a chemical cleaning scheme based on the contamination status assessment results of the PVDF membrane before cleaning, the following steps are performed: based on the contamination status assessment results, an acidic cleaning agent is selected from all selectable acidic cleaning agents, an alkaline cleaning agent is selected from all selectable alkaline cleaning agents, a concentration is selected from all selectable concentrations corresponding to the selected cleaning agent, and a cleaning time is selected from all selectable cleaning times corresponding to the selected cleaning agent; by first using an acidic cleaning agent and then an alkaline cleaning agent, or first using an alkaline cleaning agent and then an acidic cleaning agent, so as to form an action sequence of various agents in the cleaning process based on the cleaning agents.

[0011] In some embodiments, during the process of cleaning the PVDF membrane using the formed chemical cleaning scheme, the following steps are performed: selecting an acidic cleaning agent from all selectable acidic cleaning agents, selecting a concentration value from the selectable concentrations of the acidic cleaning agent, mixing it with a solvent so that the pH value of the formed acidic cleaning solution is a first pH value; selecting a cleaning time from the selectable cleaning time of the acidic cleaning agent, soaking the PVDF membrane in the acidic cleaning solution for the selected cleaning time, and replenishing the selected acidic cleaning agent during the soaking process to make the pH value of the acidic cleaning solution constant; after the PVDF membrane is soaked in the acidic cleaning solution, rinsing the PVDF membrane with the solvent The method comprises the following steps: selecting an alkaline cleaning agent from among all selectable alkaline cleaning agents, selecting a concentration value from among the selectable concentrations of the alkaline cleaning agent, mixing the alkaline cleaning agent with a solvent, so that the pH value of the formed alkaline cleaning solution is a second pH value; selecting a cleaning time from among the selectable cleaning time of the alkaline cleaning agent, soaking the PVDF membrane in the alkaline cleaning solution for the selected cleaning time, and replenishing the selected alkaline cleaning agent during the soaking process, so that the pH value of the alkaline cleaning solution is constant; after the PVDF membrane is completely soaked in the alkaline cleaning solution, rinsing the PVDF membrane with the solvent, so that the pH value of the liquid on the PVDF membrane is neutral.

[0012] In some embodiments, during the process of cleaning the PVDF membrane using the formed chemical cleaning scheme, the following steps are performed: selecting an alkaline cleaning agent from all selectable alkaline cleaning agents, selecting a concentration value from the selectable concentrations of the alkaline cleaning agent, mixing it with a solvent so that the pH value of the formed alkaline cleaning solution is a third pH value; selecting a cleaning time from the selectable cleaning time of the alkaline cleaning agent, soaking the PVDF membrane in the alkaline cleaning solution for the selected cleaning time, and replenishing the selected alkaline cleaning agent during the soaking process so that the pH value of the alkaline cleaning solution is constant; after the PVDF membrane is soaked in the alkaline cleaning solution, using the solvent to rinse the PVDF membrane The invention relates to a method for washing the PVDF membrane so that the pH value of the liquid on the PVDF membrane is neutral; selecting an acidic cleaning agent from all the selectable acidic cleaning agents, selecting a concentration value from the selectable concentrations of the acidic cleaning agent, mixing it with a solvent, so that the pH value of the formed acidic cleaning solution is a fourth pH value; selecting a cleaning time from the selectable cleaning time of the acidic cleaning agent, soaking the PVDF membrane in the acidic cleaning solution for the selected cleaning time, and replenishing the selected acidic cleaning agent during the soaking process so that the pH value of the acidic cleaning solution is constant; after the PVDF membrane is soaked in the acidic cleaning solution, rinsing the PVDF membrane with the solvent so that the pH value of the liquid on the PVDF membrane is neutral.

[0013] In some embodiments, during the cleaning effect evaluation of the cleaned PVDF membrane, the following steps are performed: the contamination status of the cleaned PVDF membrane is evaluated to obtain a contamination status evaluation result of the cleaned PVDF membrane; the contamination status evaluation result of the cleaned PVDF membrane is compared with the contamination status evaluation result of the PVDF membrane before cleaning to obtain a comparison result.

[0014] In some embodiments, in the process of judging whether the cleaning effect reaches a preset standard based on the cleaning effect evaluation result, when the comparison result reaches a corresponding preset value, it is determined that the cleaning effect reaches the preset standard.

[0015] In some embodiments, during the adjustment of the initial chemical cleaning scheme, at least one of the following conditions is changed while other conditions remain unchanged: the type of cleaning agent, the order of action of various agents in the cleaning process based on the cleaning agent, the concentration of the cleaning agent, and the cleaning time of the cleaning agent.

[0016] Through the MBR process PVDF membrane pollution assessment and cleaning scheme provided above, the embodiment of the present application evaluates the pollution status of the PVDF membrane with inorganic iron composite pollutants, and forms a chemical cleaning scheme based on the pollution status assessment results of the PVDF membrane before cleaning, so that the formed chemical cleaning scheme is specifically targeted at the pollution status assessment results, avoiding membrane damage caused by blind cleaning. At the same time, by evaluating the cleaning effect of the PVDF membrane after cleaning, the chemical cleaning scheme is adjusted based on the cleaning effect evaluation results until the cleaning effect reaches the preset standard, and the chemical cleaning scheme can be dynamically adjusted to avoid the dissolution effect of excessive cleaning on the PVDF membrane caused by the use of a fixed chemical cleaning scheme, thereby reducing operation and maintenance costs.

[0017] Further, in some embodiments, based on the pollution status assessment result, an acidic cleaning agent is selected from all selectable acidic cleaning agents, an alkaline cleaning agent is selected from all selectable alkaline cleaning agents, a concentration is selected from all selectable concentrations corresponding to the selected cleaning agent, and a cleaning duration is selected from all selectable cleaning durations corresponding to the selected cleaning agent. By first using an acidic cleaning agent and then an alkaline cleaning agent, or first using an alkaline cleaning agent and then an acidic cleaning agent to form a sequence of actions of various agents in the cleaning process based on the cleaning agent, a limited number of chemical cleaning schemes can be formed, avoiding an infinite cycle caused by forming an unlimited number of chemical cleaning schemes. At the same time, by limiting the selectable range, the damage to the PVDF membrane can be limited to a minimum range when a chemical cleaning scheme is adopted. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By reading the detailed description below with reference to the accompanying drawings, the above and other purposes, features and advantages of the exemplary embodiments of the present application will become easy to understand. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0019] Figure 1 An exemplary flow chart of the MBR process PVDF membrane pollution assessment and cleaning method according to an embodiment of the present application is shown;

[0020] Figure 2 A schematic diagram showing the composition structure of a clean water flux testing device according to some embodiments of the present application is shown;

[0021] Figure 3 An exemplary flow chart of obtaining the evaluation result of the iron elution situation in an embodiment of the present application is shown;

[0022] Figure 4An exemplary flow chart of cleaning a PVDF membrane using an acidic cleaning agent first and then an alkaline cleaning agent according to some embodiments of the present application is shown;

[0023] Figure 5 An exemplary flow chart of cleaning a PVDF membrane using an alkaline cleaning agent first and then an acidic cleaning agent according to some embodiments of the present application is shown;

[0024] Figure 6 A schematic diagram of membrane flux corresponding to four chemical cleaning schemes in one embodiment of the present application is shown;

[0025] Figure 7 A schematic diagram of iron pollution removal corresponding to four chemical cleaning schemes in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0027] It should be understood that the terms "include" and "comprising" used in the specification and claims of the present application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0028] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in this application specification and claims, unless the context clearly indicates otherwise, the singular forms of "a", "an" and "the" are intended to include plural forms. It should also be further understood that the term "and / or" used in this application specification and claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0029] Figure 1 An exemplary flow chart of a method 100 for evaluating and cleaning PVDF membrane fouling in an MBR process according to an embodiment of the present application is shown.

[0030] like Figure 1 As shown, in step S110, the contamination status of the PVDF membrane with inorganic iron composite contaminants is evaluated to obtain the contamination status evaluation result of the PVDF membrane before cleaning.

[0031] In the embodiments of the present application, the aforementioned pollution status assessment results include: inorganic pollution assessment results, organic pollution assessment results, mechanical property change assessment results, permeability change assessment results and iron elution status assessment results.

[0032] In the embodiments of the present application, in the process of evaluating the pollution status of PVDF membranes with inorganic iron complex pollutants, scanning electron microscopy and energy spectrum analysis are used to obtain inorganic pollution assessment results, Fourier transform attenuated total reflection infrared spectroscopy is used to obtain organic pollution assessment results, a tensile strength testing device is used to obtain mechanical property change assessment results, a clean water flux testing device is used to obtain permeability change assessment results, and an iron elution situation assessment result is obtained based on inductively coupled plasma emission spectroscopy.

[0033] In some embodiments of the present application, in the process of obtaining the inorganic pollution assessment results by scanning electron microscopy and energy spectrum analysis, the 2 cm PVDF membrane filament is dried in a 50 ° C oven to constant weight and sprayed with gold before testing to enhance conductivity. The pollutants are found by scanning electron microscopy, and the average value data of the relative content of each element is obtained by energy spectrum analysis of multiple fixed points. The acceleration voltage used for the scanning electron microscope is 5kV, and the current used for the scanning electron microscope is 25pA. The composition of inorganic pollution elements within the surface scan range is determined by multi-point surface scanning through energy spectrum analysis, wherein the acceleration voltage used in the process of energy spectrum analysis is 15kV, the current used is 0.4nA, and the correction method used is ZAF. In other embodiments of the present application, the corresponding parameters used by the scanning electron microscope and the corresponding parameters used in the process of energy spectrum analysis can also be set according to actual needs, and this application is not limited here.

[0034] The surface morphology of PVDF membrane can be observed by scanning electron microscopy, and the elemental composition of inorganic pollutants on the membrane surface can be qualitatively and semi-quantitatively analyzed by energy spectrum analysis.

[0035] In the embodiments of the present application, during the pollution status assessment of the PVDF membrane with inorganic iron composite pollutants, Fourier transform attenuated total reflection infrared spectroscopy was used to obtain the organic pollution assessment result.

[0036] In some embodiments of the present application, in the process of obtaining the organic pollution assessment results by Fourier transform attenuated total reflection infrared spectroscopy, the corresponding parameter conditions are: the wave number range is 4000cm -1 -400cm -1 , the number of scans is 32 times, the resolution is 4cm -1 In other embodiments of the present application, in the process of obtaining the organic pollution assessment result by using Fourier transform attenuated total reflection infrared spectroscopy, the corresponding parameter conditions can also be set according to actual needs, and the present application does not limit this.

[0037] In the embodiments of the present application, during the contamination status assessment of a PVDF membrane having inorganic iron composite contaminants, a tensile strength testing device is used to obtain the evaluation results of mechanical property changes.

[0038] In the examples of the present application, tensile strength and tensile strain at break are used to characterize the evaluation results of mechanical property changes. The tensile strength is calculated as follows: tensile strength = maximum force (N) / effective cross-sectional area of ​​membrane filament (mm 2 The calculation formula of the tensile strain at break is: tensile strain at break (%) = (total length at break - original length) / original length × 100%.

[0039] In some embodiments of the present application, the tensile strength test device adopts a microcomputer-controlled electronic universal testing machine. In the process of obtaining the mechanical property change evaluation results by using the tensile strength test device, the corresponding parameter conditions are: the ambient temperature is 22.3°C, the humidity is 35%, the test sample length is 10cm, and the test speed is 5mm / min. In other embodiments of the present application, the tensile strength test device may also adopt other devices. In the process of obtaining the mechanical property change evaluation results by using the tensile strength test device, the corresponding parameter conditions may also be set according to actual needs, and the present application does not limit this.

[0040] In the examples of the present application, during the pollution status assessment of the PVDF membrane with inorganic iron composite pollutants, a clean water flux testing device is used to obtain the permeability performance change assessment results.

[0041] In some embodiments of the present application, the specific composition structure of the clean water flux testing device can be found in Figure 2 .

[0042] Figure 2 A schematic diagram of the composition structure of a clean water flux testing device according to some embodiments of the present application is shown.

[0043] like Figure 2 As shown, the clean water flux test device 200 includes a water bucket 210, a hose 220, a pressure gauge 230, a peristaltic pump 240 and a measuring cylinder 250. Deionized water is added to the water bucket 210, and a PVDF membrane 260 is arranged in the water bucket 210. The beginning end of the hose 220 is connected to the PVDF membrane 260, and the end of the hose 220 is arranged in the measuring cylinder 250. The water bucket 210 is connected to the pressure gauge 230 through the hose 220, and the pressure gauge 230 is connected to the peristaltic pump 240 through the hose 220.

[0044] Before obtaining the permeability change evaluation result, the water is passed through for 5 minutes to stabilize the pressure. Next, by starting the peristaltic pump 240 and setting a suitable speed to control the flow rate of the water flow, the peristaltic pump 240 draws water from the water bucket 210 and enters the pressure gauge 230 through the hose 220. The pressure is monitored by the pressure gauge 230 to ensure that the pressure reaches the set value. Then, under the set pressure, the water passes through the PVDF membrane 260, and the water passing through the PVDF membrane 260 continues to enter the measuring cylinder 250 through the hose 220. The permeation liquid volume and measurement time are obtained in the measuring cylinder 250 to obtain the permeability change evaluation result. Specifically, the permeability change evaluation result is the membrane flux.

[0045] Specifically, the calculation formula of membrane flux is: J = V / (A×t), where J is the membrane flux, the unit is L / (m 2 h), V is the volume obtained by measuring the measuring cylinder 250, in L, and A is the effective membrane area of ​​the PVDF membrane 260, in m 2 ; t is the measurement time, in h.

[0046] In other embodiments of the present application, the specific composition of the clean water flux testing device can also be the same as the above Figure 2 The specific composition of the clean water flux test device described in is different, and this application is not limited thereto.

[0047] In the embodiments of the present application, a clean water flux test device is used to test the membrane flux under different transmembrane pressure differences to form a membrane flux-transmembrane pressure difference curve, and the slope of the membrane flux-transmembrane pressure difference curve is the specific flux.

[0048] In the embodiments of the present application, during the contamination assessment of a PVDF membrane having inorganic iron composite contaminants, an iron elution assessment result is obtained based on inductively coupled plasma emission spectroscopy.

[0049] In the embodiments of the present application, the specific process involved in obtaining the iron elution evaluation result based on inductively coupled plasma emission spectroscopy can be found in Figure 3 .

[0050] Figure 3 An exemplary flow chart for obtaining the evaluation result of the iron elution situation according to an embodiment of the present application is shown.

[0051] like Figure 3As shown, in step S310, the PVDF membrane is soaked with the solvent of the cleaning agent based on the set soaking time, the set soaking temperature and the set liquid-to-solid ratio. In step S320, the soaking liquid is filtered using a filter membrane of a set size to obtain a filtered soaking liquid. In step S330, the filtered soaking liquid is introduced into an inductively coupled plasma mass spectrometer for measurement to obtain the corresponding emission spectrum intensity. In step S340, the obtained emission spectrum intensity is substituted into the iron concentration-emission spectrum intensity standard curve to obtain the iron elution amount.

[0052] In an embodiment of the present application, the aforementioned iron concentration-emission spectrum intensity standard curve can be obtained by the following steps: First, the high-purity iron standard solution of the solvent being the solvent of the cleaning agent is diluted as needed to prepare a standard solution of at least 5 concentration gradients. Secondly, the optimal emission wavelength of the inductively coupled plasma mass spectrometer is selected according to the element to be measured (such as the optimal emission wavelength of iron is 238.204nm), and the standard solution is introduced into the inductively coupled plasma mass spectrometer for measurement to obtain the emission spectrum intensity corresponding to the standard solution of each concentration. Then, with the standard solution concentration as the horizontal coordinate and the emission spectrum intensity corresponding to the standard solution of each concentration as the vertical coordinate, an iron concentration-emission spectrum intensity standard curve is established.

[0053] In the embodiments of the present application, the aforementioned soaking time, soaking temperature and liquid-to-solid ratio can be set according to actual needs, and the present application does not limit them here.

[0054] By filtering the soaking liquid with a filter membrane of a set size, insoluble impurities can be removed to ensure that the soaking liquid is clear and transparent, avoiding clogging of the nebulizer in the inductively coupled plasma mass spectrometer.

[0055] In an embodiment of the present application, the size of the filter membrane can be set according to the type of impurities in the soaking liquid, and the present application does not limit this. For example, in an embodiment of the present application, the size of the filter membrane is set to 0.45 μm.

[0056] In the embodiment of the present application, when the filtered soaking solution is introduced into the inductively coupled plasma mass spectrometer for measurement, the parameters used by the aforementioned inductively coupled plasma mass spectrometer are the same as the parameters used by the inductively coupled plasma mass spectrometer when the standard solution is introduced into the inductively coupled plasma mass spectrometer for measurement. Thus, the error introduced by the instrument fluctuation is reduced, and the accuracy and reliability of the evaluation results of the iron elution situation are ensured.

[0057] In some implementations of the present application, the parameters used by the inductively coupled plasma mass spectrometer are: nebulizing gas flow rate is 0.85 L / min, auxiliary gas flow rate is 0.8 L / min, cooling gas flow rate is 13 L / min, and plasma power is 1350 W.

[0058] Based on the inorganic pollution assessment results and the organic pollution assessment results, the type of cleaning agent in the subsequent chemical cleaning process can be accurately matched. According to the inorganic pollution assessment results, the organic pollution assessment results and the mechanical property change assessment results, the cleaning time in the subsequent chemical cleaning process can be matched to avoid membrane breakage caused by excessive cleaning. According to the permeability change assessment results and the iron elution situation assessment results, they can be used as core indicators of the cleaning effect, and real-time feedback and optimization of the subsequent chemical cleaning process can be obtained. Therefore, by obtaining the pollution status assessment results of the PVDF membrane before cleaning, including the inorganic pollution assessment results, the organic pollution assessment results, the mechanical property change assessment results, the permeability change assessment results and the iron elution situation assessment results, it is possible to match a scientific and efficient chemical cleaning plan to achieve the dual goals of pollution control and membrane performance maintenance.

[0059] After executing step S110, in step S120, a chemical cleaning scheme is formed based on the contamination status evaluation result of the PVDF membrane before cleaning, and the PVDF membrane is cleaned using the formed chemical cleaning scheme.

[0060] Specifically, the chemical cleaning scheme includes: the type of cleaning agent, the concentration of each cleaning agent, the cleaning time of each cleaning agent, and the action sequence of various agents in the cleaning process based on the cleaning agent.

[0061] In the embodiment of the present application, in the process of forming a chemical cleaning scheme based on the pollution status evaluation result of the PVDF membrane before cleaning, first, based on the pollution status evaluation result, an acidic cleaning agent is selected from all selectable acidic cleaning agents, an alkaline cleaning agent is selected from all selectable alkaline cleaning agents, a concentration is selected from all selectable concentrations corresponding to the selected cleaning agent, and a cleaning duration is selected from all selectable cleaning durations corresponding to the selected cleaning agent. Then, the action sequence of various agents in the cleaning process based on the cleaning agents is formed by first using an acidic cleaning agent and then an alkaline cleaning agent, or first using an alkaline cleaning agent and then an acidic cleaning agent.

[0062] In the embodiments of the present application, all selectable acidic cleaning agents, all selectable alkaline cleaning agents, the selectable concentrations of the cleaning agents, and the selectable cleaning times of the cleaning agents are set according to actual needs and historical experience, and the present application does not impose any restrictions thereon.

[0063] In some embodiments of the present application, the specific process of first using an acid cleaning agent and then using an alkaline cleaning agent to clean the PVDF membrane can be found in Figure 4 .

[0064] Figure 4An exemplary flow chart of some embodiments of the present application for cleaning a PVDF membrane using an acidic cleaning agent first and then an alkaline cleaning agent is shown.

[0065] like Figure 4 As shown, in step S410, an acidic cleaning agent is selected from all the selectable acidic cleaning agents, and a concentration value is selected from the selectable concentrations of the acidic cleaning agent, and it is mixed with a solvent so that the pH value of the formed acidic cleaning solution is a first pH value. In step S420, a cleaning time is selected from the selectable cleaning time of the acidic cleaning agent, and the PVDF membrane is soaked in the acidic cleaning solution for the selected cleaning time, and the selected acidic cleaning agent is supplemented during the soaking process to make the pH value of the acidic cleaning solution constant. In step S430, after the PVDF membrane is soaked in the acidic cleaning solution, the PVDF membrane is rinsed with a solvent so that the pH value of the liquid on the PVDF membrane is neutral.

[0066] Next, in step S440, an alkaline cleaning agent is selected from all the selectable alkaline cleaning agents, and a concentration value is selected from the selectable concentrations of the alkaline cleaning agent, and the alkaline cleaning agent is mixed with a solvent so that the pH value of the formed alkaline cleaning solution is a second pH value. In step S450, a cleaning time is selected from the selectable cleaning time of the alkaline cleaning agent, and the PVDF membrane is soaked in the alkaline cleaning solution for the selected cleaning time, and the selected alkaline cleaning agent is supplemented during the soaking process to make the pH value of the alkaline cleaning solution constant. In step S460, after the PVDF membrane is soaked in the alkaline cleaning solution, the PVDF membrane is rinsed with a solvent so that the pH value of the liquid on the PVDF membrane is neutral.

[0067] In other embodiments of the present application, the specific process of first using an alkaline cleaning agent and then using an acidic cleaning agent to clean the PVDF membrane can be found in Figure 5 .

[0068] Figure 5 An exemplary flow chart of some embodiments of the present application for cleaning a PVDF membrane using an alkaline cleaning agent first and then an acidic cleaning agent is shown.

[0069] like Figure 5As shown, in step S510, an alkaline cleaning agent is selected from all the selectable alkaline cleaning agents, and a concentration value is selected from the selectable concentrations of the alkaline cleaning agent, and it is mixed with a solvent so that the pH value of the formed alkaline cleaning solution is a third pH value. In step S520, a cleaning time is selected from the selectable cleaning time of the alkaline cleaning agent, and the PVDF membrane is soaked in the alkaline cleaning solution for the selected cleaning time, and the selected alkaline cleaning agent is supplemented during the soaking process to make the pH value of the alkaline cleaning solution constant. In step S530, after the PVDF membrane is soaked in the alkaline cleaning solution, the PVDF membrane is rinsed with a solvent so that the pH value of the liquid on the PVDF membrane is neutral.

[0070] Next, in step S540, an acidic cleaning agent is selected from all the selectable acidic cleaning agents, and a concentration value is selected from the selectable concentrations of the acidic cleaning agent, and the acidic cleaning agent is mixed with a solvent so that the pH value of the formed acidic cleaning solution is a fourth pH value. In step S550, a cleaning time is selected from the selectable cleaning time of the acidic cleaning agent, and the PVDF membrane is soaked in the acidic cleaning solution for the selected cleaning time, and the selected acidic cleaning agent is supplemented during the soaking process to make the pH value of the acidic cleaning solution constant. In step S560, after the PVDF membrane is soaked in the acidic cleaning solution, the PVDF membrane is rinsed with a solvent so that the pH value of the liquid on the PVDF membrane is neutral.

[0071] In the above-mentioned embodiment, in the process of cleaning the PVDF membrane with an acidic cleaning agent first and then an alkaline cleaning agent, after cleaning with the acidic cleaning agent, the PVDF membrane is rinsed with a solvent so that the pH value of the liquid on the PVDF membrane is neutral, and then the PVDF membrane is cleaned with an alkaline cleaning agent. In the process of cleaning the PVDF membrane with an alkaline cleaning agent first and then an acidic cleaning agent, after cleaning with the acidic cleaning agent, the PVDF membrane is rinsed with a solvent so that the pH value of the liquid on the PVDF membrane is neutral, and then the PVDF membrane is cleaned with an alkaline cleaning agent. This can completely remove the residue of the cleaning agent (acidic or alkaline) in the previous step, avoid direct contact between different agents (acidic and alkaline) to produce a neutralization reaction, thereby reducing ineffective chemical consumption. By eliminating cross-interference between agents, it is ensured that the alkaline / acidic cleaning agents work within their respective optimal pH ranges (such as alkaline cleaning is more effective in removing organic pollutants, and acidic cleaning is targeted at pollutants), and targeted pollutant removal is achieved. At the same time, prevent acidic and alkaline agents from mixing directly to produce salt precipitation or gas (such as CO 2) and other byproducts to prevent such byproducts from clogging the membrane pores of the PVDF membrane or damaging the membrane surface structure of the PVDF membrane. In addition, although the PVDF membrane is resistant to acid and alkali, the rapid switching of extreme pH values ​​may cause swelling or shrinkage stress in the microstructure of the PVDF membrane material. Neutral flushing buffers the pH mutation and reduces the risk of material fatigue of the PVDF membrane.

[0072] After executing step S120, in step S130, the cleaning effect of the cleaned PVDF membrane is evaluated.

[0073] In the embodiment of the present application, in the process of evaluating the cleaning effect of the cleaned PVDF membrane, first, the contamination status of the cleaned PVDF membrane is evaluated to obtain the contamination status evaluation result of the cleaned PVDF membrane. Then, the contamination status evaluation result of the cleaned PVDF membrane is compared with the contamination status evaluation result of the PVDF membrane before cleaning to obtain a comparison result.

[0074] In the embodiments of the present application, the pollution status assessment results of the cleaned PVDF membrane also include: inorganic pollution assessment results, organic pollution assessment results, mechanical property change assessment results, permeability change assessment results and iron elution assessment results.

[0075] The specific process involved in obtaining the contamination status assessment result of the PVDF membrane after cleaning is consistent with the specific process involved in obtaining the contamination status assessment result of the PVDF membrane before cleaning, and will not be repeated in this application.

[0076] By obtaining the inorganic pollution assessment results of the PVDF membrane after cleaning and comparing them with the inorganic pollution assessment results of the PVDF membrane before cleaning, it is possible to determine whether there are changes in the morphology of the outer surface, inner surface and cross section of the PVDF membrane, as well as the iron removal effect. If the cleaning effect is significant, the inner surface, cross section and outer surface of the membrane filament will not contain iron or the iron content will be greatly reduced, the microporous structure of the membrane cross section can be seen and the support layer will be broken and damaged, there will be no large amount of blocky or paste-like deposits attached to the inner and outer surfaces of the membrane, and the membrane structure is intact.

[0077] By obtaining the organic contamination evaluation results of the PVDF membrane after cleaning and comparing them with the organic contamination evaluation results of the PVDF membrane before cleaning, it is possible to determine the changes in the peak intensity of organic matter such as protein on the surface of the PVDF membrane and the changes in the intensity of the characteristic peaks of the PVDF membrane structure. If the peak intensity of the characteristic peak of protein in the cleaned PVDF membrane is significantly reduced, the PVDF membrane CF 2 and CH 2 The peak intensity of the characteristic peak was significantly enhanced, indicating that the membrane performance was restored, the organic pollution removal effect was obvious, and the cleaning method was properly selected.

[0078] By obtaining the evaluation results of the mechanical property changes of the PVDF membrane after cleaning and comparing them with the evaluation results of the mechanical property changes of the PVDF membrane before cleaning, the tensile strength and tensile strain at break of the PVDF membrane before and after cleaning can be compared. If the cleaning method is appropriate, the PVDF membrane's anti-fracture ability and ductility should be restored. Thus, the changes in the mechanical properties of the PVDF membrane can be determined, and the cleaning conditions and cleaning methods can be judged.

[0079] By obtaining the evaluation results of the permeability change of the PVDF membrane after cleaning and comparing it with the evaluation results of the permeability change of the PVDF membrane before cleaning, it is possible to determine whether the chemical cleaning has caused damage to the membrane structure, resulting in membrane damage, breakage or other performance degradation. By comparing the membrane flux data of the PVDF membrane before cleaning and the membrane flux data of the PVDF membrane after cleaning, it is helpful to select the best cleaning solution and evaluate the chemical cleaning effect.

[0080] By obtaining the evaluation results of the iron elution of the PVDF membrane after cleaning and comparing them with the evaluation results of the iron elution of the PVDF membrane before cleaning, it is possible to compare the surface iron content of the PVDF membrane before cleaning and the surface iron content of the PVDF membrane after cleaning. If the cleaning method is selected properly, the iron elution amount after cleaning should be greatly increased compared with the iron elution amount before cleaning, and the comparison of the removal amount can clarify the best cleaning method for iron contamination.

[0081] After executing step S130, in step S140, it is determined whether the cleaning effect reaches a preset standard based on the cleaning effect evaluation result.

[0082] In an embodiment of the present application, in the process of judging whether the cleaning effect reaches a preset standard based on the cleaning effect evaluation result, when the comparison result reaches a corresponding preset value, it is judged that the cleaning effect reaches the preset standard.

[0083] In the embodiments of the present application, the aforementioned preset values ​​can be set according to actual needs and historical experience, and the present application does not limit this.

[0084] In response to the cleaning effect reaching the preset standard, in step S150 , it is determined that the cleaning is completed.

[0085] In response to the cleaning effect not reaching the preset standard, in step S160 , the process returns to the step of forming a chemical cleaning scheme, and the initial chemical cleaning scheme is adjusted until the cleaning effect reaches the preset standard.

[0086] In an embodiment of the present application, during the adjustment of the initial chemical cleaning scheme, at least one of the following conditions is changed while other conditions remain unchanged: the type of cleaning agent, the order of action of various agents in the cleaning process based on the cleaning agent, the concentration of the cleaning agent, and the cleaning time of the cleaning agent. For example, the current chemical cleaning scheme uses the first cleaning agent among the acidic cleaning agents. During the adjustment of the initial chemical cleaning scheme, the first cleaning agent among the acidic cleaning agents used in the current chemical cleaning scheme can be changed to the second cleaning agent among the acidic cleaning agents, and other conditions remain unchanged to form a new chemical cleaning scheme.

[0087] By adjusting the chemical cleaning scheme based on the cleaning effect evaluation results until the cleaning effect reaches the preset standard, the chemical cleaning scheme can be dynamically adjusted to avoid the dissolution of the PVDF membrane caused by excessive cleaning due to the use of a fixed chemical cleaning scheme, thereby reducing operation and maintenance costs.

[0088] In summary, through the MBR process PVDF membrane pollution assessment and cleaning scheme provided above, the embodiment of the present application evaluates the pollution status of the PVDF membrane with inorganic iron composite pollutants, and forms a chemical cleaning scheme based on the pollution status assessment results of the PVDF membrane before cleaning, so that the formed chemical cleaning scheme is specifically targeted at the pollution status assessment results, avoiding membrane damage caused by blind cleaning. At the same time, by evaluating the cleaning effect of the PVDF membrane after cleaning, the chemical cleaning scheme is adjusted based on the cleaning effect evaluation results until the cleaning effect reaches the preset standard, and the chemical cleaning scheme can be dynamically adjusted to avoid the dissolution effect of excessive cleaning on the PVDF membrane caused by the use of a fixed chemical cleaning scheme, thereby reducing operation and maintenance costs.

[0089] Further, in some embodiments, based on the pollution status assessment result, an acidic cleaning agent is selected from all selectable acidic cleaning agents, an alkaline cleaning agent is selected from all selectable alkaline cleaning agents, a concentration is selected from all selectable concentrations corresponding to the selected cleaning agent, and a cleaning duration is selected from all selectable cleaning durations corresponding to the selected cleaning agent. By first using an acidic cleaning agent and then an alkaline cleaning agent, or first using an alkaline cleaning agent and then an acidic cleaning agent to form a sequence of actions of various agents in the cleaning process based on the cleaning agent, a limited number of chemical cleaning schemes can be formed, avoiding an infinite cycle caused by forming an unlimited number of chemical cleaning schemes. At the same time, by limiting the selectable range, the damage to the PVDF membrane can be limited to a minimum range when a chemical cleaning scheme is adopted.

[0090] In one embodiment of the present application, the aforementioned MBR process PVDF membrane pollution assessment and cleaning method 100 is used to assess the PVDF membrane pollution and during the cleaning process, all the selectable acidic cleaning agents include agent a and agent b, and the selectable alkaline cleaning agent is agent c. Agent a is oxalic acid, and its selectable concentration range is 0.05%-0.1%. Agent b is citric acid, and its selectable concentration range is 0.3%-1%. Agent c is sodium hypochlorite, and its selectable concentration range is 0.1%-0.3%. At the same time, the selectable cleaning time ranges corresponding to agents a, b and c are all 6-8h. By successively forming a chemical cleaning scheme based on the pollution status assessment results of the PVDF membrane before cleaning, using the formed chemical cleaning scheme to clean the PVDF membrane, evaluating the cleaning effect of the cleaned PVDF membrane, and adjusting the initial chemical cleaning scheme based on the cleaning effect evaluation results, a total of four chemical cleaning schemes are obtained before the cleaning effect reaches the preset standard.

[0091] In the first chemical cleaning scheme, the PVDF membrane with inorganic iron composite pollutants is soaked in agent c for 6-8 hours, the initial pH is measured, and agent c is added in time during the soaking process to maintain a constant pH to ensure that the agent fully penetrates the inner and outer pores of the membrane fibers of the PVDF membrane. After the soaking, the membrane fibers are rinsed with deionized water until the pH is neutral. Then, the PVDF membrane is placed in agent b for 6-8 hours, the initial pH is measured, and agent b is added in time during the soaking process to maintain the solution pH. After the soaking, the PVDF membrane fibers are rinsed with deionized water until the pH is neutral, and the cleaned PVDF membrane fibers are placed in deionized water for storage and testing, which is recorded as cleaned membrane fibers 1.

[0092] The inorganic contamination evaluation result of the cleaned membrane filament 1 is obtained and compared with the inorganic contamination evaluation result of the contaminated membrane filament before cleaning. The obtained analysis results are shown in Table 1:

[0093] Table 1 Analysis of the results of the evaluation of inorganic pollution of cleaning membrane 1

[0094]

[0095] According to Table 1, no iron was detected in the cross section and outer surface of the cleaned membrane filament 1, but iron was present on the inner surface of the membrane.

[0096] The organic contamination evaluation results of the cleaned membrane filament 1 were obtained and compared with the organic contamination evaluation results of the contaminated membrane filaments before cleaning. -1 、1549cm -1 The characteristic absorption peak of protein amino group is 2870cm -1 The peak intensity of the protein saturated CH stretching vibration peak at the contaminated membrane was lower than that of the contaminated membrane.2 and CF 2 The characteristic peak increased relative to the intensity of the polluted membrane filaments, indicating that the organic pollution was effectively removed and the PVDF properties of the PVDF membrane were restored.

[0097] The evaluation results of the changes in mechanical properties of the cleaned membrane filament 1 were obtained and compared with the evaluation results of the changes in mechanical properties of the contaminated membrane filament before cleaning. The tensile strength and tensile strain at break of the cleaned membrane filament 1 were 93.2 MPa and 21%, respectively; the tensile strength of the contaminated membrane filament was 89.9 MPa, and the tensile strain at break was 24%. The cleaned membrane filament 1 had enhanced anti-fracture ability compared with the contaminated membrane filament, but its ductility was deteriorated.

[0098] The permeability change evaluation results of the cleaned membrane filament 1 were obtained and compared with the permeability change evaluation results of the contaminated membrane filament before cleaning. The specific flux of the cleaned membrane filament 1 was 3.93 L / m 2 h·kPa, the specific flux of the fouled membrane is 1.84L / m 2 h·kPa, the specific flux of clean membrane filament 1 is 2.09L / m higher than that of contaminated membrane 2 ·h·kPa. Since the specific flux is the slope of the membrane flux-transmembrane pressure difference curve, the higher the specific flux, the better the membrane permeability.

[0099] The evaluation results of iron elution of cleaned membrane filament 1 were obtained and compared with the evaluation results of iron elution of contaminated membrane filament before cleaning. The analysis results are shown in Table 2:

[0100] Table 2 Evaluation and analysis of iron elution from cleaning membrane filament 1

[0101] Sample name Iron mg / L Deionized water cleaning solution for contaminated membrane 0.03 Cleaning membrane filament 1 cleaning solution 0.1

[0102] According to Table 2, the iron elution amount corresponding to the cleaned membrane filament 1 is 0.1 mg / L, which is greater than the iron elution amount of the contaminated membrane filament.

[0103] In summary, the comparison results were compared with the corresponding preset values. The first chemical cleaning scheme had a good effect on the recovery of PVDF membrane permeability and the removal of protein and organic matter, but the removal of iron pollution was not ideal, and the mechanical properties of the membrane fibers were affected. Therefore, the cleaning effect of the PVDF membrane by the first chemical cleaning scheme did not meet the preset standard.

[0104] In the second chemical cleaning scheme, compared with the problem of poor iron pollution removal effect in the first chemical cleaning scheme, the first chemical cleaning scheme is improved, and the cleaning order is adjusted to acid first and then alkali. Specifically, the PVDF membrane with inorganic iron composite pollutants is soaked in agent b for 6-8 hours, the initial pH is determined, and agent b is supplemented in time during the soaking process to maintain a constant pH, ensuring that the agent fully penetrates the inner and outer pores of the membrane silk of the PVDF membrane, and the membrane silk is rinsed with deionized water to a neutral pH after the soaking. Then, the PVDF membrane is placed in agent c and soaked for 6-8 hours, the initial pH is determined, and agent c is supplemented in time during the soaking process to maintain the solution pH. After the soaking, the PVDF membrane silk is rinsed with deionized water to a neutral pH, and the cleaned PVDF membrane silk is placed in deionized water for storage and testing, which is recorded as cleaning membrane silk 2.

[0105] The inorganic contamination evaluation result of the cleaned membrane filament 2 is obtained and compared with the inorganic contamination evaluation result of the contaminated membrane filament before cleaning. The obtained analysis results are shown in Table 3:

[0106] Table 3 Analysis of the results of the evaluation of inorganic pollution of cleaning membrane filament 2

[0107]

[0108] According to Table 3, no iron was detected in the cross section and outer surface of the cleaned membrane filament 2, but iron was present on the inner surface of the membrane.

[0109] The organic contamination evaluation result of the cleaned membrane filament 2 was obtained and compared with the organic contamination evaluation result of the contaminated membrane filament before cleaning. The peak intensity of the protein characteristic absorption peak of the cleaned membrane filament 2 was lower than that of the contaminated membrane filament. The PVDF membrane CH 2 and CF 2 The characteristic peak increases relative to the intensity of the polluted membrane filaments. As a result, the performance of the membrane filaments is effectively restored and the organic matter removal effect is good.

[0110] The evaluation results of the changes in the mechanical properties of the cleaned membrane filament 2 were obtained and compared with the evaluation results of the changes in the mechanical properties of the contaminated membrane filament before cleaning. The tensile strength and tensile strain at break of the cleaned membrane filament 2 were 95.6 MPa and 26%, respectively; the tensile strength of the contaminated membrane filament was 89.9 MPa, and the tensile strain at break was 24%. The cleaned membrane filament 2 had enhanced anti-fracture ability compared with the contaminated membrane filament, and its mechanical property recovery effect was good.

[0111] The permeability change evaluation result of the cleaned membrane filament 2 is obtained and compared with the permeability change evaluation result of the contaminated membrane filament before cleaning. The specific flux of the cleaned membrane filament 2 is 4.54 L / m 2 ·h·kPa, 0.61L / m higher than the cleaning membrane filament 1 2 h·kPa, 2.7L / m higher than the specific flux of the fouled membrane2 ·h·kPa.

[0112] The evaluation results of iron elution of cleaned membrane filament 2 were obtained, and compared with the evaluation results of iron elution of contaminated membrane filament before cleaning, and the obtained analysis results are shown in Table 4:

[0113] Table 4 Evaluation and analysis of iron elution from cleaning membrane filament 2

[0114] Sample name Iron mg / L Deionized water cleaning solution for contaminated membrane 0.03 Cleaning membrane filament 2 cleaning solution 0.05

[0115] According to Table 4, the iron elution amount corresponding to the cleaning membrane filament 2 is 0.05 mg / L.

[0116] In summary, the comparison results were compared with the corresponding preset values. The second chemical cleaning scheme had good effects on the recovery of PVDF membrane permeability and the removal of protein and organic matter, but poor removal of iron pollution. Therefore, the cleaning effect of the PVDF membrane by the second chemical cleaning scheme did not meet the preset standard.

[0117] In the third chemical cleaning scheme, compared with the problem of poor iron pollution removal effect in the first chemical cleaning scheme, the first chemical cleaning scheme is improved by changing the acidic cleaning agent from b to a. Specifically, the PVDF membrane with inorganic iron complex pollutants is soaked in agent c for 6-8 hours, the initial pH is measured, and agent c is supplemented in time during the soaking process to maintain a constant pH to ensure that the agent fully penetrates the inner and outer pores of the membrane filaments of the PVDF membrane. After the soaking, the membrane filaments are rinsed with deionized water to a neutral pH. Then, the PVDF membrane is placed in agent a and soaked for 6-8 hours, the initial pH is measured, and agent a is supplemented in time during the soaking process to maintain the solution pH. After the soaking, the PVDF membrane filaments are rinsed with deionized water to a neutral pH, and the cleaned PVDF membrane filaments are placed in deionized water for storage and testing, which is recorded as cleaning membrane filaments 3.

[0118] The inorganic contamination evaluation result of the cleaned membrane filament 3 was obtained and compared with the inorganic contamination evaluation result of the contaminated membrane filament before cleaning. The obtained analysis results are shown in Table 5:

[0119] Table 5 Analysis of the results of the evaluation of inorganic pollution of cleaning membrane filament 3

[0120]

[0121]

[0122] According to Table 5, no iron element was detected in the cross section, inner surface and outer surface of the cleaned membrane filament 3.

[0123] The organic contamination evaluation results of the cleaned membrane filament 3 were obtained and compared with those of the contaminated membrane filament before cleaning. The peak intensity of the protein characteristic absorption peak of the cleaned membrane filament 3 was significantly lower than that of the contaminated membrane filament. 2 and CF 2 The characteristic peak increases relative to the intensity of the polluted membrane filaments. As a result, the performance of the membrane filaments is effectively restored and the organic matter removal effect is good.

[0124] The evaluation results of the changes in the mechanical properties of the cleaned membrane filaments 3 were obtained and compared with the evaluation results of the changes in the mechanical properties of the contaminated membrane filaments before cleaning. The tensile strength and tensile strain at break of the cleaned membrane filaments 3 were 89.6 MPa and 21%, respectively; the tensile strength of the contaminated membrane filaments was 89.9 MPa, and the tensile strain at break was 24%. The degree of recovery of the mechanical properties of the cleaned membrane filaments 3 was relatively weak.

[0125] The permeability change evaluation result of the cleaned membrane filament 3 is obtained and compared with the permeability change evaluation result of the contaminated membrane filament before cleaning. The specific flux of the cleaned membrane filament 3 is 3.37 L / m 2 h·kPa, 0.56L / m lower than that of cleaning membrane 1 2 h·kPa, 1.53L / m higher than the specific flux of the fouled membrane 2 ·h·kPa. The membrane permeability of the cleaned membrane filament 3 is weak.

[0126] The evaluation results of iron elution of cleaned membrane filament 3 were obtained, and compared with the evaluation results of iron elution of contaminated membrane filament before cleaning, and the obtained analysis results are shown in Table 6:

[0127] Table 6 Evaluation and analysis of iron elution from cleaning membrane filament 3

[0128] Sample name Iron mg / L Deionized water cleaning solution for contaminated membrane 0.03 Cleaning membrane filament 3 cleaning solution 0.16

[0129] According to Table 6, the iron elution amount corresponding to cleaning membrane filament 3 is 0.16 mg / L, which is increased compared with cleaning membrane filament 1.

[0130] In summary, the comparison results were compared with the corresponding preset values. The third chemical cleaning scheme had a good effect on the removal of organic matter and iron pollution, but the recovery of membrane fiber permeability and mechanical properties was weak. Therefore, the cleaning effect of the PVDF membrane by the third chemical cleaning scheme did not meet the preset standard.

[0131] In the fourth chemical cleaning scheme, compared with the first chemical cleaning scheme, the acidic cleaning agent is changed from b to a, and the cleaning order is adjusted to acid first and then alkali. Specifically, the PVDF membrane with inorganic iron complex pollutants is soaked in agent a for 6-8 hours, the initial pH is measured, and agent a is replenished in time during the soaking process to maintain a constant pH to ensure that the agent fully penetrates the inner and outer pores of the membrane filaments of the PVDF membrane. After the soaking, the membrane filaments are rinsed with deionized water to a neutral pH. Then, the PVDF membrane is placed in agent c and soaked for 6-8 hours, the initial pH is measured, and agent c is replenished in time during the soaking process to maintain the solution pH. After the soaking, the PVDF membrane filaments are rinsed with deionized water to a neutral pH, and the cleaned PVDF membrane filaments are placed in deionized water for storage and testing, which is recorded as cleaning membrane filaments 4.

[0132] The inorganic contamination evaluation result of the cleaned membrane filament 4 was obtained and compared with the inorganic contamination evaluation result of the contaminated membrane filament before cleaning. The obtained analysis results are shown in Table 7:

[0133] Table 7 Analysis of the results of the evaluation of inorganic pollution of cleaning membrane filament 4

[0134]

[0135] According to Table 7, no iron element was detected in the cross section, inner surface and outer surface of the cleaned membrane filament 4.

[0136] The organic contamination evaluation results of the cleaned membrane filament 4 were obtained and compared with the organic contamination evaluation results of the contaminated membrane filaments before cleaning. -1 、1549cm -1 The characteristic absorption peak of protein amino group at 1405cm -1 、1205cm -1 PVDF membrane CH 2 and CF 2 The intensity of the characteristic peak is greatly improved compared with the contaminated membrane filaments, indicating that the removal effect of protein organic contamination is obvious and the performance of the membrane filaments has been restored.

[0137] The evaluation results of the changes in the mechanical properties of the cleaned membrane filament 4 were obtained and compared with the evaluation results of the changes in the mechanical properties of the contaminated membrane filament before cleaning. The tensile strength and tensile strain at break of the cleaned membrane filament 4 were 93.4 MPaPa and 25%, respectively; the tensile strength of the contaminated membrane filament was 89.9 MPa, and the tensile strain at break was 24%. The cleaned membrane filament 4 showed good membrane fracture resistance and ductility.

[0138] The permeability change evaluation result of the cleaned membrane filament 4 is obtained and compared with the permeability change evaluation result of the contaminated membrane filament before cleaning. The specific flux of the cleaned membrane filament 4 is 7.4 L / m 2h·kPa, 3.47L / m higher than the cleaning membrane filament 1 2 h·kPa, 5.56L / m higher than the specific flux of the fouled membrane 2 ·h·kPa. The permeability recovery degree of membrane filament 4 after cleaning is the best.

[0139] The evaluation results of iron elution of cleaned membrane filament 4 were obtained, and compared with the evaluation results of iron elution of contaminated membrane filament before cleaning, and the obtained analysis results are shown in Table 8:

[0140] Table 8 Evaluation and analysis of the elution of 4 iron from the cleaning membrane

[0141] Sample name Iron mg / L Deionized water cleaning solution for contaminated membrane 0.03 Cleaning membrane filament 4 cleaning solution 0.88

[0142] According to Table 8, the iron elution amount corresponding to the cleaning membrane filament 4 is 0.88 mg / L, and the iron elution effect is significant.

[0143] The membrane fluxes corresponding to the four chemical cleaning schemes are compared. Figure 6 As shown in the figure, the membrane flux corresponding to the cleaning membrane filament 4 under the corresponding transmembrane pressure difference is much higher than that of other membrane filaments. At the same time, the iron elution amounts corresponding to the four chemical cleaning schemes are compared, as shown in the figure. Figure 7 As shown, the iron elution amount corresponding to the cleaning membrane filament 4 is much higher than that of the other membrane filaments.

[0144] In summary, the comparison results were compared with the corresponding preset values. The fourth chemical cleaning scheme did not cause damage to the membrane structure, the membrane fracture resistance and ductility were good, the permeability recovery was the best, and the removal efficiency of composite pollution was the highest. Therefore, this cleaning method was effective. Therefore, the PVDF membrane was cleaned by the fourth chemical cleaning scheme, and the cleaning effect reached the preset standard.

[0145] Although multiple embodiments of the present application have been shown and described herein, it is obvious to those skilled in the art that such embodiments are provided only by way of example. Those skilled in the art can think of many changes, modifications and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein can be adopted. The attached claims are intended to limit the scope of protection of the present application, and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A method for evaluating and cleaning PVDF membrane pollution in a MBR process, characterized in that: include: The contamination status of the PVDF membrane with inorganic iron composite contaminants is evaluated to obtain the contamination status evaluation result of the PVDF membrane before cleaning; A chemical cleaning scheme is formed based on the pollution status evaluation result of the PVDF membrane before cleaning, and the PVDF membrane is cleaned by using the formed chemical cleaning scheme, wherein the chemical cleaning scheme includes: the type of cleaning agent, the concentration of each cleaning agent, the cleaning time of each cleaning agent, and the action order of various agents in the cleaning process based on the cleaning agent; Evaluate the cleaning effect of the cleaned PVDF membrane; Based on the cleaning effect evaluation results, determine whether the cleaning effect meets the preset standards; In response to the cleaning effect reaching a preset standard, determining that the cleaning is completed; In response to the cleaning effect not reaching the preset standard, the process returns to the step of forming a chemical cleaning scheme, and the initial chemical cleaning scheme is adjusted until the cleaning effect reaches the preset standard.

2. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 1, characterized in that, The pollution status assessment results include: inorganic pollution assessment results, organic pollution assessment results, mechanical property change assessment results, permeability change assessment results and iron elution assessment results; Among them, scanning electron microscopy and energy spectrum analysis were used to obtain the inorganic pollution assessment results; Fourier transform attenuated total reflectance infrared spectroscopy was used to obtain organic pollution assessment results; The tensile strength test device was used to obtain the evaluation results of mechanical property changes; A clean water flux test device was used to obtain the results of the permeability performance change assessment; Iron elution assessment was obtained based on inductively coupled plasma optical emission spectroscopy.

3. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 2, characterized in that, To obtain an assessment of iron elution based on ICP-EOS, perform the following steps: Soaking the PVDF membrane with the solvent of the cleaning agent based on a set soaking time, a set soaking temperature, and a set liquid-to-solid ratio; Using a filter membrane of a set size to filter the soaking liquid to obtain a filtered soaking liquid; The filtered soaking liquid is introduced into an inductively coupled plasma mass spectrometer for measurement to obtain the corresponding emission spectrum intensity; The obtained emission spectrum intensity was substituted into the standard curve of iron concentration-emission spectrum intensity to obtain the iron elution amount.

4. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 3, characterized in that, The parameters adopted by the inductively coupled plasma mass spectrometer are: atomizing gas flow rate of 0.85 L / min, auxiliary gas flow rate of 0.8 L / min, cooling gas flow rate of 13 L / min, and plasma power of 1350 W.

5. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 2, characterized in that, In the process of forming a chemical cleaning plan based on the results of the contamination assessment of the PVDF membrane before cleaning, the following steps are performed: Selecting an acid cleaning agent from all selectable acid cleaning agents, selecting an alkaline cleaning agent from all selectable alkaline cleaning agents, selecting a concentration from all selectable concentrations corresponding to the selected cleaning agent, and selecting a cleaning duration from all selectable cleaning durations corresponding to the selected cleaning agent based on the pollution status assessment result; The action sequence of various agents in the cleaning process based on the cleaning agents is formed by first using an acidic cleaning agent and then an alkaline cleaning agent, or first using an alkaline cleaning agent and then an acidic cleaning agent.

6. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 5, characterized in that: In the process of cleaning the PVDF membrane using the formed chemical cleaning scheme, the following steps are performed: Selecting an acid cleaning agent from all selectable acid cleaning agents, selecting a concentration value from selectable concentrations of the acid cleaning agent, and mixing it with a solvent so that the pH value of the formed acid cleaning solution is a first pH value; Selecting a cleaning time from the selectable cleaning time of the acid cleaning agent, soaking the PVDF membrane in the acid cleaning solution for the selected cleaning time, and replenishing the selected acid cleaning agent during the soaking process to make the pH value of the acid cleaning solution constant; After the PVDF membrane is immersed in the acidic cleaning solution, the PVDF membrane is rinsed with the solvent so that the pH value of the liquid on the PVDF membrane is neutral; Selecting an alkaline cleaning agent from all selectable alkaline cleaning agents, selecting a concentration value from selectable concentrations of the alkaline cleaning agent, and mixing it with a solvent so that the pH value of the formed alkaline cleaning solution is a second pH value; Selecting a cleaning time from the selectable cleaning time of the alkaline cleaning agent, soaking the PVDF membrane in the alkaline cleaning solution for the selected cleaning time, and replenishing the selected alkaline cleaning agent during the soaking process to make the pH value of the alkaline cleaning solution constant; After the PVDF membrane is immersed in the alkaline cleaning solution, the PVDF membrane is rinsed with the solvent so that the pH value of the liquid on the PVDF membrane is neutral.

7. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 5, characterized in that: In the process of cleaning the PVDF membrane using the formed chemical cleaning scheme, the following steps are performed: Selecting an alkaline cleaning agent from all selectable alkaline cleaning agents, selecting a concentration value from selectable concentrations of the alkaline cleaning agent, and mixing it with a solvent so that the pH value of the formed alkaline cleaning solution is a third pH value; Selecting a cleaning time from the selectable cleaning time of the alkaline cleaning agent, soaking the PVDF membrane in the alkaline cleaning solution for the selected cleaning time, and replenishing the selected alkaline cleaning agent during the soaking process to make the pH value of the alkaline cleaning solution constant; After the PVDF membrane is immersed in the alkaline cleaning solution, the PVDF membrane is rinsed with the solvent so that the pH value of the liquid on the PVDF membrane is neutral; Selecting an acid cleaning agent from all selectable acid cleaning agents, selecting a concentration value from selectable concentrations of the acid cleaning agent, and mixing the acid cleaning agent with a solvent so that the pH value of the formed acid cleaning solution is a fourth pH value; Selecting a cleaning time from the selectable cleaning time of the acid cleaning agent, soaking the PVDF membrane in the acid cleaning solution for the selected cleaning time, and replenishing the selected acid cleaning agent during the soaking process to make the pH value of the acid cleaning solution constant; After the PVDF membrane is immersed in the acidic cleaning solution, the PVDF membrane is rinsed with the solvent so that the pH value of the liquid on the PVDF membrane is neutral.

8. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 1 or 2, characterized in that, In the process of evaluating the cleaning effect of the cleaned PVDF membrane, the following steps are performed: Performing pollution status evaluation on the cleaned PVDF membrane to obtain a pollution status evaluation result of the cleaned PVDF membrane; The contamination status evaluation result of the PVDF membrane after cleaning is compared with the contamination status evaluation result of the PVDF membrane before cleaning to obtain a comparison result.

9. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 8, characterized in that: In the process of judging whether the cleaning effect reaches the preset standard based on the cleaning effect evaluation result, when the comparison result reaches the corresponding preset value, it is judged that the cleaning effect reaches the preset standard.

10. The MBR process PVDF membrane pollution assessment and cleaning method according to claim 1, characterized in that: In the process of adjusting the initial chemical cleaning scheme, while other conditions remain unchanged, at least one of the following conditions is changed: the type of cleaning agent, the order of action of various agents in the cleaning process based on the cleaning agent, the concentration of the cleaning agent, and the cleaning time of the cleaning agent.

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