Reverse osmosis membrane chemical cleaning method aiming at organic and microorganism composite sewage plugging

Abstract

The invention discloses a reverse osmosis membrane chemical cleaning method aiming at organic and microorganism composite sewage plugging. According to the method, the cleaning sequence of'alkali first, sterilization second and acid second 'is adopted, organic sewage blocking substances and biological membranes serving as pollution matrixes are removed preferentially, wrapped inorganic scales and microorganisms are fully exposed, and the reaction efficiency of subsequent sterilization and descaling agents is remarkably improved. The method provided by the invention can effectively recover the membrane flux and desalination rate, significantly reduce the system operation pressure difference and prolong the service life of the membrane element, and is especially suitable for reverse osmosis systems such as urban reclaimed water, closed lake water and the like which are easy to generate organic and microorganism composite sewage blockage.

Description

A chemical cleaning method for reverse osmosis membranes resistant to organic and microbial fouling. Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a chemical cleaning method for reverse osmosis membranes that are clogged by a combination of organic and microbial fouling. Background Technology

[0002] As a core component of water treatment systems, reverse osmosis membranes are susceptible to the combined effects of organic matter, microorganisms, and inorganic scale during long-term operation, leading to decreased membrane flux, reduced desalination rate, and increased transmembrane pressure. In systems using complex water sources such as urban reclaimed water or closed lakes, organic and biofouling problems are particularly severe, often resulting in complex fouling. Current conventional cleaning methods often employ single acid-base cleaning or simple alternating cleaning, failing to fully consider the interactions and hierarchical distribution characteristics of different pollutants. In actual fouling structures, organic pollutants (such as biofilms, grease, and colloids) often act as a matrix, encapsulating inorganic scale and microbial cells to form a dense composite layer. This hinders the effective penetration and reaction of cleaning agents, resulting in incomplete cleaning, insufficient bactericidal efficacy, and consequently affecting the long-term stable operation of the system and membrane lifespan.

[0003] Therefore, there is an urgent need to develop a chemical cleaning method that can effectively deal with the combined fouling of organic and microbial contaminants, and has a clear cleaning sequence and parameter control, so as to achieve thorough cleaning and ensure system recovery. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a chemical cleaning method for reverse osmosis membranes that addresses complex fouling by organic and microbial contamination.

[0006] This invention proposes a chemical cleaning method for reverse osmosis membranes that are fouled by a combination of organic and microbial fouling, comprising the following steps: (1) flushing the membrane system with reverse osmosis permeate and draining the raw water; (2) pumping alkaline cleaning solution into the system, circulating and displacing the residual water in the system and then turning it back to the source, closing the valve and soaking before circulating and cleaning again, and after the circulation operation, flushing with reverse osmosis permeate until the pH of the discharged water is neutral and clear without foam; (3) pumping non-oxidizing bactericidal cleaning solution into the system, circulating and displacing before turning it back to the source, closing the valve and soaking before circulating and cleaning again, discharging the cleaning solution, and flushing with reverse osmosis permeate or demineralized water; (4) pumping acidic cleaning solution into the system, circulating and displacing before turning it back to the source, closing the valve and soaking before circulating and cleaning again, and flushing with reverse osmosis permeate until the pH of the discharged water is neutral; (5) flushing with a large flow of reverse osmosis permeate to restore the normal operation of the system, and discharging the initially generated permeate.

[0007] Furthermore, in step (1), the membrane system is flushed with reverse osmosis permeate at a low pressure of 0.3-0.5 MPa for 15-30 minutes.

[0008] Furthermore, the concentration of the alkaline cleaning solution is 1%-2%, and the pH is adjusted to 12.0±0.5.

[0009] Furthermore, the alkaline cleaning agent used in the alkaline cleaning solution is selected from one or more of sodium hydroxide, sodium ethylenediaminetetraacetate, and sodium dodecylbenzenesulfonate.

[0010] Further, in step (2), under the condition of 30-40°C, the alkaline cleaning solution is pumped into the system at a low inlet water pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate, and then circulated and discharged for 5-10 minutes before being turned back; the valve is closed and the system is soaked for 30-60 minutes, then circulated and cleaned for 60-90 minutes, and this process is repeated 2-3 times.

[0011] Furthermore, the concentration of the non-oxidizing bactericidal cleaning solution is 0.1%-0.5%.

[0012] Furthermore, the bactericide used in the non-oxidizing bactericidal cleaning solution is selected from one or more of isothiazolinone, glutaraldehyde, dodecyl dimethyl benzyl ammonium chloride, and 2,2-dibromo-3-azapropionamide.

[0013] Further, in step (3), under conditions of 30-40°C, the non-oxidizing bactericidal cleaning solution is pumped into the system at a low inlet water pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate. After circulating and discharging for 15-30 minutes, it is switched to reflux. The valve is closed and the system is soaked for 4-8 hours. After circulating and cleaning for 30-60 minutes, the cleaning solution is discharged. Finally, the system is rinsed with a large flow rate of reverse osmosis permeate or demineralized water.

[0014] Furthermore, the concentration of the acidic cleaning solution is 0.5%-1.0%, and the pH is adjusted to 2.0±0.5.

[0015] Furthermore, the cleaning agent used in the acidic cleaning solution is selected from hydrochloric acid, citric acid, or oxalic acid.

[0016] Further, in step (4), under conditions of 30-40°C, the acidic cleaning solution is pumped into the system at a low inlet pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate, and then circulated and discharged for 5-10 minutes before being turned into reflux; the valve is closed and soaked for at least 30 minutes, then circulated and cleaned for at least 60 minutes, and finally rinsed with reverse osmosis permeate until the pH of the discharged water is neutral.

[0017] Furthermore, in step (5), a high flow rate of reverse osmosis permeate is used to flush the system for 5-10 minutes to ensure that there are no chemical residues in the system; the system is restored to normal operation, and the permeate generated in the initial 15-30 minutes is discharged.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention adopts the cleaning sequence of "alkali first - sterilization then acid", which prioritizes the removal of organic dirt and biofilm as the contaminant matrix, so as to fully expose the encapsulated inorganic scale and microorganisms, and significantly improve the reaction efficiency of subsequent sterilization and descaling agents.

[0019] This invention achieves effective killing of deep microorganisms inside the membrane and biofilm disintegration through the synergistic effect of prolonged immersion and non-oxidizing bactericides, thereby inhibiting the regeneration of biological pollution.

[0020] The present invention optimizes key parameters such as pressure, flow rate, pH and temperature during the cleaning process to ensure uniform and stable cleaning and avoid secondary damage to membrane elements.

[0021] The method of the present invention can effectively restore membrane flux and desalination rate, significantly reduce system operating pressure difference, and extend the service life of membrane elements. It is especially suitable for reverse osmosis systems that are prone to organic and microbial fouling, such as urban greywater and closed lake water. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which: Figure 1 is a flowchart of the chemical cleaning method for reverse osmosis membranes of the present invention for organic and microbial complex fouling; Figure 2 is a state diagram of the reverse osmosis membrane before and after cleaning in Example 1 of the present invention; Figure 3 is a scanning electron microscope image of the reverse osmosis membrane before and after cleaning in Example 1 of the present invention. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] The following description, in conjunction with the accompanying drawings, describes the chemical cleaning method for reverse osmosis membranes proposed in this invention, targeting complex fouling by organic and microorganisms.

[0025] As shown in Figure 1, the chemical cleaning method for reverse osmosis membranes targeting organic and microbial complex fouling of the present invention includes the following steps: (1) flushing the membrane system with reverse osmosis permeate and draining the raw water; (2) pumping alkaline cleaning solution into the system, circulating and displacing the residual water in the system and then turning it back to the source, closing the valve and soaking before circulating and cleaning again, and after the circulation operation, flushing with reverse osmosis permeate until the pH of the discharged water is neutral and clear without foam; (3) pumping non-oxidizing bactericidal cleaning solution into the system, circulating and displacing before turning it back to the source, closing the valve and soaking before circulating and cleaning again, discharging the cleaning solution, and flushing with reverse osmosis permeate or demineralized water; (4) pumping acidic cleaning solution into the system, circulating and displacing before turning it back to the source, closing the valve and soaking before circulating and cleaning again, and flushing with reverse osmosis permeate until the pH of the discharged water is neutral; (5) flushing with a large flow of reverse osmosis permeate to restore the normal operation of the system, and discharging the initially generated permeate.

[0026] Step (1) is a low-pressure flushing process, in which the membrane system is flushed with reverse osmosis permeate at a low pressure of 0.3-0.5 MPa for 15-30 minutes.

[0027] Step (2) is the alkaline cleaning process. Under conditions of 30-40°C, the alkaline cleaning solution is pumped into the system with low inlet water pressure and high flow rate. After circulating and discharging for 5-10 minutes to replace the residual water in the system, it is switched to reflux, so that the concentrate and permeate flow back to the cleaning tank together. The valve is closed and the system is soaked for 30-60 minutes, and then circulated and cleaned for 60-90 minutes. The above circulation operation can be repeated 2-3 times. Finally, the system is rinsed with reverse osmosis permeate until the pH of the discharged water is close to neutral and clear without foam. Among them, pumping the alkaline cleaning solution into the system with low inlet water pressure and high flow rate means pumping the alkaline cleaning solution into the system with a low inlet water pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate.

[0028] In some embodiments, the concentration of the alkaline cleaning solution is 1%-2%, and the pH is adjusted to 12.0±0.5. The alkaline cleaning agent used in the alkaline cleaning solution is mainly used to remove biofilms, organic matter, grease, and colloidal contaminants, and may be one or more of sodium hydroxide, sodium ethylenediaminetetraacetate, and sodium dodecylbenzenesulfonate.

[0029] Step (3) is a non-oxidizing disinfectant cleaning process. Under conditions of 30-40°C, the cleaning solution is pumped into the system at low pressure, circulated and discharged for 15-30 minutes, then switched to reflux, and the valve is closed for soaking for 4-8 hours; the system is then circulated and cleaned again for 30-60 minutes, and the cleaning solution is discharged; finally, a high-flow-rate rinse is performed with reverse osmosis permeate or demineralized water to ensure no disinfectant residue remains. Pumping the cleaning solution into the system at low pressure means pumping the cleaning solution into the system at a low inlet pressure of 0.3-0.5 MPa and a flow rate of 1.5 to 2 times the design flow rate. A high-flow-rate rinse refers to rinsing at a flow rate of 1.5 to 2 times the design flow rate.

[0030] In some embodiments, the concentration of the non-oxidizing bactericidal cleaning solution is 0.1%-0.5%.

[0031] In some embodiments, the bactericide used in the non-oxidizing bactericidal cleaning solution is mainly used to kill microorganisms and break down the biofilm structure, and can be one or more of isothiazolinone, glutaraldehyde, dodecyl dimethyl benzyl ammonium chloride, and 2,2-dibromo-3-azapropionamide.

[0032] Step (4) is an acidic cleaning process. Under conditions of 30-40°C, the solution is pumped into the system at low pressure and high flow rate. After circulating and discharging for 5-10 minutes, it is switched to reflux. The valve is closed and the solution is soaked for at least 30 minutes, followed by circulation and cleaning for at least 60 minutes. Finally, the solution is rinsed with reverse osmosis permeate until the pH of the discharged water is close to neutral. The low pressure and high flow rate method of pumping the solution into the system means pumping the cleaning solution into the system at a low inlet water pressure of 0.3-0.5 MPa and a flow rate of 1.5 to 2 times the design flow rate.

[0033] In some embodiments, the concentration of the acidic cleaning solution is 0.5%-1.0%, and the pH is adjusted to 2.0±0.5. The cleaning agent used in the acidic cleaning solution is mainly used to kill microorganisms and break down biofilm structures, and can be one of hydrochloric acid, citric acid, or oxalic acid.

[0034] The present invention will now be described in detail with reference to specific embodiments.

[0035] Example 1: A reverse osmosis membrane system using urban wastewater as its source experienced severe fouling due to a combination of organic and microbial fouling during operation, resulting in a decrease in permeate flow rate from the initial 120 m³ / h. 3 / h dropped to 78m 3 / h, the inter-section pressure difference increased from 0.32MPa to 0.58MPa. The cleaning method of this invention is as follows: Step 1: Rinse the system with RO permeate at low pressure for 20 minutes, then drain the raw water; Step 2: Prepare a 1% compound alkaline cleaning solution, adjust the pH to 12.0 with NaOH, heat to 30°C, and then apply at 0.3MPa pressure and 240m... 3 Pump the system at a flow rate of / h, circulate and discharge for 5 minutes, then switch to reflux; soak for 45 minutes, circulate and clean for 75 minutes, repeat twice; rinse with RO permeate until the effluent pH=7 and is clear; third step: prepare a 0.2% compound non-oxidizing bactericide cleaning solution, heat to 30°C, and then pump at 240m 3 Pump the solution into the system at a flow rate of / h, circulate for 20 minutes, soak for 6 hours, then circulate for another 45 minutes before discharging; rinse with RO permeate at a high flow rate; Step 4: Prepare a 0.8% hydrochloric acid cleaning solution, adjust the pH to 2.0, heat to 30°C, and then pump at 240m... 3Pump the system at a flow rate of / h, soak for 30 minutes, and circulate for 60 minutes, monitoring and maintaining the pH at 2-3 during the process; rinse with RO permeate until the effluent pH=7; Step 5: Rinse with high flow rate for 10 minutes, restore system operation, and discharge permeate for the first 20 minutes.

[0036] After cleaning, the system's water production capacity was restored to 113m³. 3 / h, the inter-stage pressure difference drops to 0.34MPa, and the desalination rate recovers to the design level.

[0037] In Experiment 1, the state of the reverse osmosis membrane before and after cleaning was observed and recorded, as shown in Figure 2. Figure 2 shows that before cleaning, the surface of the reverse osmosis membrane was covered with unevenly distributed sludge, with localized flocculent and particulate contaminants, accompanied by a distinct fishy odor; after cleaning, the sludge and particulate matter on the membrane surface were largely removed, and visual observation showed that it had returned to cleanliness.

[0038] In Experiment 2, scanning electron microscopy (SEM) tests were performed on the reverse osmosis membranes before and after cleaning. The results are shown in Figure 3. As can be seen from Figure 3, before cleaning, the membrane surface was covered by a continuous and dense amorphous capping layer, and the membrane structure was not visible. The fouling material was in the form of a gel-like biofilm / extracellular polymer. After cleaning, the capping layer was basically removed, and the fibrous structure on the membrane surface was clearly visible. Only trace amounts of contaminants remained, which did not affect the overall performance.

[0039] In Experiment 3, energy dispersive spectroscopy (EDS) analysis was performed on the reverse osmosis membrane before and after cleaning. The results are shown in Table 1 below.

[0040] Table 1:

[0041] As shown in Table 1, before cleaning, the carbon content on the membrane surface was as high as 90.10%, and the carbon-oxygen ratio was about 9.10, indicating that the fouling mainly originated from organic matter and biofilm. After cleaning, the carbon content dropped to 77.14%, the oxygen content rose to 22.86%, and the carbon-oxygen ratio dropped to 3.4, which is close to the theoretical range of clean polyamide membranes, confirming that the organic fouling was effectively removed.

[0042] The above results show that after cleaning by the method of the present invention, the key performance indicators of the reverse osmosis membrane system, such as permeate flow, pressure difference and desalination rate, are significantly restored. This confirms that the sequential cleaning strategy of "alkali first - sterilization then acid" can effectively peel off and remove the composite fouling layer, fundamentally restoring membrane performance. This verifies the high efficiency and reliability of the method in treating organic and microbial composite fouling.

[0043] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A chemical cleaning method for reverse osmosis membranes clogging by a combination of organic and microbial fouling, characterized in that, Includes the following steps: (1) Use reverse osmosis permeate to flush the membrane system and drain the raw water; (2) Pump alkaline cleaning solution into the system, circulate and discharge to replace the residual water in the system and then turn to reflux, close the valve to soak and then circulate and clean again. After the circulation operation, use reverse osmosis permeate to flush until the pH of the discharged water is neutral and clear without foam; (3) Pump non-oxidizing bactericidal cleaning solution into the system, circulate and discharge and then turn to reflux, close the valve to soak and then circulate and clean again, discharge the cleaning solution, and flush with reverse osmosis permeate or demineralized water; (4) Pump acidic cleaning solution into the system, circulate and discharge and then turn to reflux, close the valve to soak and then circulate and clean again, and flush with reverse osmosis permeate until the pH of the discharged water is neutral; (5) Use reverse osmosis permeate to flush with a large flow rate to restore the normal operation of the system and discharge the initially generated permeate.

2. The method as described in claim 1, characterized in that, In step (1), the membrane system is flushed with reverse osmosis permeate at a low pressure of 0.3-0.5 MPa for 15-30 minutes.

3. The method as described in claim 1, characterized in that, The concentration of the alkaline cleaning solution is 1%-2%, and the pH is adjusted to 12.0±0.5; and / or, the alkaline cleaning agent used in the alkaline cleaning solution is one or more of sodium hydroxide, sodium ethylenediaminetetraacetate, and sodium dodecylbenzenesulfonate.

4. The method as described in claim 1, characterized in that, In step (2), at 30-40°C, the alkaline cleaning solution is pumped into the system at a low inlet pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate. After circulating and discharging for 5-10 minutes, it is switched to reflux. The valve is closed and the solution is soaked for 30-60 minutes, then circulated and cleaned for 60-90 minutes. This process is repeated 2-3 times.

5. The method as described in claim 1, characterized in that, The concentration of the non-oxidizing bactericidal cleaning solution is 0.1%-0.5%; and / or, the bactericide used in the non-oxidizing bactericidal cleaning solution is selected from one or more of isothiazolinone, glutaraldehyde, dodecyl dimethyl benzyl ammonium chloride, and 2,2-dibromo-3-azapropionamide.

6. The method as described in claim 1, characterized in that, In step (3), at 30-40°C, the non-oxidizing bactericidal cleaning solution is pumped into the system at a low inlet pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate. After circulating and discharging for 15-30 minutes, it is switched to reflux. The valve is closed and the system is soaked for 4-8 hours. After circulating and cleaning for 30-60 minutes, the cleaning solution is discharged. Finally, the system is rinsed with a large flow rate of reverse osmosis permeate or demineralized water.

7. The method as described in claim 1, characterized in that, The concentration of the acidic cleaning solution is 0.5%-1.0%, and the pH is adjusted to 2.0±0.

5.

8. The method as described in claim 1, characterized in that, The cleaning agent used in the acidic cleaning solution is selected from hydrochloric acid, citric acid, or oxalic acid.

9. The method as described in claim 1, characterized in that, In step (4), at 30-40°C, the acidic cleaning solution is pumped into the system at a low inlet pressure of 0.3-0.5MPa and a flow rate of 1.5 to 2 times the design flow rate. After circulating and discharging for 5-10 minutes, it is switched to reflux. The valve is closed and the solution is soaked for at least 30 minutes, then circulated and cleaned for at least 60 minutes. Finally, it is rinsed with reverse osmosis permeate until the pH of the discharged water is neutral.

10. The method as described in claim 1, characterized in that, In step (5), the reverse osmosis permeate is flushed at a high flow rate for 5-10 minutes to ensure that there are no chemical residues in the system; the system is restored to normal operation, and the permeate generated in the initial 15-30 minutes is discharged.

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