Method for preventing organic fouling of reverse osmosis membranes

Abstract

The application discloses a method for preventing organic matter from blocking reverse osmosis membranes, which comprises the following steps: precisely controlling the pH of the influent to the alkaline interval of 10.5-11.5, and relieving the organic blocking from the source by electrostatic repulsion. First, the organic-containing wastewater is pretreated, the pH is adjusted to 10.5-11.5 by adopting a double-alkali method to strengthen the hardness removal, the calcium hardness is reduced to below 100 mg / L in terms of CaCO3, and the precipitate is removed, and after filtration, the pH will naturally fall back. Then, a specific alkali-resistant scale inhibitor is added, a wide-channel alkali-resistant and pollution-resistant membrane assembly is selected, the influent pH is adjusted back to 10.5-11.5 through a high-precision pH sensor and a PLC controller, and the fluctuation is controlled within ±0.2. The system is operated at a pressure of 1.5-3.0 MPa, a recovery rate of 65-75%, and a temperature of below 35 DEG C. The application breaks through the conventional reverse osmosis operation limit of pH≤10, and realizes the long-term stable operation of the reverse osmosis system for high-organic wastewater under the alkaline working condition.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a reverse osmosis membrane treatment method that alleviates organic fouling by regulating alkaline feed water, and is particularly suitable for the stable operation of reverse osmosis in industrial wastewater with high organic content, such as coking plants. Background Technology

[0002] Reverse osmosis technology is a crucial technology in water treatment, achieving the separation of water and solutes through the selective permeability of semi-permeable membranes. However, when treating wastewater containing organic matter, reverse osmosis membranes are prone to fouling, leading to decreased membrane flux, increased frequency of chemical cleaning, reduced operating efficiency, and even system failure. The mechanisms of organic fouling of reverse osmosis membranes mainly include: physical adsorption, chemical bonding, and charge interactions of organic molecules on the membrane surface.

[0003] To alleviate organic fouling, existing technologies include adjusting the influent pH to 9-10. The principle is that increasing the pH causes acidic functional groups such as carboxyl groups in organic molecules to dissociate, giving the organic matter a negative charge. This negative charge then creates electrostatic repulsion on the negatively charged reverse osmosis membrane surface. Simultaneously, the solubility of organic matter increases under weakly alkaline conditions, thus reducing its deposition on the membrane surface. However, this technology remains significantly ineffective in removing fouling from high-concentration, highly polluted industrial wastewater.

[0004] Currently, it is generally believed in the field that the pH of reverse osmosis feed water should not exceed 10, and there are four major technical bottlenecks: 1. Limitations of membrane material tolerance: The amide bonds of conventional polyamide reverse osmosis membranes are prone to hydrolysis in alkaline environments with pH>10 during long-term operation, leading to membrane performance degradation, decreased desalination rate, and even membrane structure damage. This constitutes the primary obstacle to high pH applications. 2. Increased risk of inorganic salt scaling: When pH > 10, the alkalinity of water is converted into CO3²⁻ and OH⁻. - These inorganic salts react with divalent ions such as Ca²⁺ and Mg²⁺ in the water to form CaCO₃ and Mg(OH)₂ inorganic scale, leading to the risk of inorganic salt fouling of the reverse osmosis membrane. This type of scaling can be removed through regular chemical acid washing. For wastewater with high organic content, the damage to the membrane caused by inorganic salt scaling and the difficulty in treatment are far less than those caused by organic fouling. 3. Difficult to operate and control: It requires extremely precise pH control; if the pH is below the control range, the effect of alleviating organic fouling will be reduced; if the pH is above the control range, it will cause irreversible damage to the reverse osmosis membrane.

[0005] 4. High requirements for scale inhibitors: Conventional scale inhibitors are prone to decomposition and failure in high pH environments. Special membrane scale inhibitors suitable for organic wastewater should be selected to ensure that their scale inhibition performance decay rate is low under alkaline conditions.

[0006] Therefore, although theoretically raising the pH to above 10 could further dissociate weaker acidic groups in organic matter, such as phenolic hydroxyl groups, and change their molecular conformation in the aqueous phase, thereby maximizing the electrostatic repulsion effect, the aforementioned limiting factors have not been effectively resolved. As a result, pH > 10 has long been regarded as a technical taboo for reverse osmosis processes, and there is still no technical solution that can stably raise the pH value to above 10 and achieve industrial application while avoiding the risks of membrane hydrolysis and scaling. Summary of the Invention

[0007] The purpose of this invention is to provide a method to prevent organic matter from clogging reverse osmosis membranes. This method uses alkaline feed water with a pH of 10.5 to 11.5 as a means, combined with deep hardening removal, alkali-resistant membranes, reverse osmosis antiscalants, and precise pH control, to solve the problems of membrane hydrolysis, inorganic salt scaling, and poor reagent compatibility under high pH conditions, thereby achieving long-term stable operation of the reverse osmosis system.

[0008] The technical solution adopted in this invention is as follows: To alleviate organic fouling, the electrostatic repulsion is enhanced by adjusting the pH of the reverse osmosis feed water to the alkaline range of 10.5–11.5. This includes the following steps: S1. Pretreatment for Hardness and Turbidity Reduction: Wastewater containing organic matter is pretreated using a dual-alkali method to reduce its calcium hardness (CaCO3) to below 100 mg / L, preferably less than 50 mg / L, and remove any generated precipitate particles, with suspended solids less than 1 mg / L. After sedimentation and filtration, the wastewater pH will naturally decrease, requiring precise readjustment of the alkali in subsequent steps. This reduces the risk of inorganic salt scaling in high pH environments at its source; sterilization and reduction steps are also included. S2, Two-stage precise alkali adjustment: A two-stage adjustment method is adopted to compensate for the pH drop after pretreatment, and adjust the pH value of the pretreated wastewater to 10.5-11.5, so that the acidic functional groups such as carboxyl groups and phenolic hydroxyl groups in organic matter are fully dissociated, maximizing the electrostatic repulsion between organic molecules and the surface of the reverse osmosis membrane, and achieving efficient anti-organic fouling. S3. High-alkali stable scale inhibition: Add reverse osmosis scale inhibitor to the wastewater after pH adjustment. After standing at a constant temperature of 25°C for 72 hours under pH 10.5-11.5 conditions, the scale inhibition performance decay rate is less than 10%, ensuring that it can still play a stable scale inhibition effect in a high-alkali environment. S4. Reverse Osmosis Treatment: The wastewater after the addition of reagents is sent to a reverse osmosis system for treatment. The reverse osmosis system includes an anti-fouling reverse osmosis membrane module and an automatic control unit. The anti-fouling reverse osmosis membrane module adopts a wide flow channel structure, which has a wider feed screen, reducing the deposition of suspended solids and colloids on the membrane surface and reducing concentration polarization. The automatic control unit includes a pH sensor and a PLC controller for real-time monitoring and adjustment of the feed water pH value, controlling pH fluctuations within ±0.2. The operating pressure of the reverse osmosis system is 1.5–3.0 MPa, the recovery rate is 65–75%, and the operating temperature is less than 35°C, which can slow down the hydrolysis rate of the membrane material.

[0009] A more specific technical solution for the above-mentioned method to prevent organic matter from clogging the reverse osmosis membrane can be: In S1, a dual-alkali method is used to reduce the calcium hardness of wastewater. The specific steps are: adding NaOH and Na2CO3 to the wastewater, controlling the molar ratio of Na2CO3 to Ca²⁺ to be 1.2–1.5:1, and maintaining the pH of the reaction system at 10.5–11.5 to enhance calcium hardness removal. This pH is the process condition for the hardness removal reaction. After precipitation and filtration, the pH of the wastewater will naturally decrease, requiring precise readjustment in S2. The reaction temperature is 20–30℃, and the reaction time is 30–60 minutes. By optimizing the dual-alkali reaction conditions, the calcium hardness removal efficiency is improved.

[0010] Furthermore, in S1, the calcium hardness in the wastewater is reduced to less than 50 mg / L as CaCO3; and precipitated particles are removed by a multi-media filter or ultrafiltration device, so that the suspended solids concentration in the pretreated wastewater is less than 1 mg / L, further reducing the risk of scaling and particulate fouling.

[0011] Furthermore, pH adjustment in S2 employs a two-stage adjustment: the first stage adjusts the wastewater pH to 10.0–10.5; the second stage finely adjusts the wastewater pH to 10.5–11.5 at the reverse osmosis system inlet, compensating for the natural pH drop after S1's removal of hard sediment filtration, avoiding excessive pH fluctuations caused by single-stage adjustment, ensuring that the pH value entering the reverse osmosis system remains stable within the target range, and achieving stable alkali control of the reverse osmosis feed water.

[0012] Furthermore, the S1 pretreatment includes a sterilization step, where an oxidizing bactericide is added to control the residual chlorine at 0.3–0.5 mg / L, and a reducing agent is added before the reverse osmosis feed water to reduce the ORP to below 300 mV. The oxidizing bactericide can effectively kill microorganisms in the wastewater and prevent biofouling of the reverse osmosis membrane.

[0013] In some possible implementations, the reverse osmosis antiscalant in S3 is a phosphorus-free reverse osmosis antiscalant. Phosphorus-free antiscalants avoid introducing phosphorus nutrients into the water, reducing the risk of microbial growth within the reverse osmosis system. Furthermore, phosphorus-free antiscalants typically exhibit better chemical stability under high pH conditions. The antifouling reverse osmosis membrane module is a polyamide composite membrane, whose separation layer has undergone alkali-resistant modification. Through surface grafting, cross-linking, and other modification techniques, the polyamide composite membrane's tolerance to alkaline environments can be effectively improved, enabling it to maintain good separation performance and structural stability even at pH > 10. The modification treatment significantly inhibits the hydrolysis of amide bonds in the polyamide membrane under high alkaline conditions, thereby ensuring long-term stable operation of the membrane module under harsh operating conditions and significantly extending its service life.

[0014] In some possible implementations, the pH sensor is a high-precision pH sensor with a measurement error ≤ ±0.02; the automatic control unit achieves precise feedback adjustment of the pH value through a fuzzy PID algorithm. The PLC controller automatically adjusts the alkali dosage based on the feedback signal from the pH sensor, realizing closed-loop control of the pH value. The fuzzy PID algorithm combines the advantages of fuzzy control and PID control, and is suitable for the precise control of nonlinear, time-varying systems such as pH values.

[0015] In some possible implementations, the operating parameters of the reverse osmosis system described in S4 are: operating pressure 2.5–3.0 MPa, recovery rate 72–75%, and operating temperature 25–30°C. This preferred range ensures stable system operation, guarantees water production efficiency, and also achieves better economic efficiency.

[0016] In some possible implementations, the COD concentration of the organic wastewater is 200–300 mg / L.

[0017] The test method for scale inhibition performance degradation rate is as follows: The scale inhibitor is allowed to stand for 72 hours under specified pH and temperature conditions. The scale inhibition rate before and after standing is then tested, and the degradation rate is calculated as: (Initial scale inhibition rate - Scale inhibition rate after standing) / Initial scale inhibition rate × 100%. The scale inhibition rate can be tested using the conventional calcium carbonate deposition method or the static scale inhibition method. Scale inhibitors that meet this performance requirement are considered high-alkali compatible scale inhibitors suitable for high-pH environments.

[0018] By adopting the above technical solution, the present invention has the following advantages compared with the prior art: 1. Significant effect: With alkaline influent pH 10.5-11.5 as the control condition, the organic fouling rate is reduced by more than 70%, and the flux decay rate is significantly reduced; 2. Stable system: Alkali-resistant membrane inhibits hydrolysis, deep hardening is combined with phosphorus-free reverse osmosis antiscalant to prevent scaling, and it can operate continuously for a long time; 3. Cost reduction: Reduced cleaning frequency and extended membrane life result in annual operating costs that are 10% to 30% lower than conventional processes; 4. Improved efficiency: The system recovery rate increases by 5 to 10 percentage points, resulting in higher water resource utilization. Detailed Implementation

[0019] The technical concept of this invention originates from groundbreaking thinking in engineering practice: conventional alkaline washing is a staged treatment and cannot completely solve the problem of fouling. This application maintains an alkaline environment of pH 10.5 to 11.5 throughout the process to achieve a continuous weak alkaline washing effect, thereby solving the problem of high COD fouling from the root. This technical approach has been successfully applied in the treatment of coking wastewater and landfill leachate. The present invention will be further described in detail below with reference to embodiments: The experimental wastewater used in the embodiments and comparative examples of this invention is simulated high-concentration organic industrial wastewater with a COD concentration of 200-300 mg / L, a pH value of 7.0-7.5, and a Ca²⁺ concentration of 200-300 mg / L. The high-precision pH sensor used in these embodiments has a measurement error ≤ ±0.02, and the reverse osmosis antiscalant is a phosphorus-free reverse osmosis antiscalant. Under pH conditions of 10.5-11.5 and after standing at a constant temperature of 25°C for 72 hours, the antiscaling performance degradation rate is less than 10%. The reverse osmosis system includes an antifouling reverse osmosis membrane module and an automatic control unit. The antifouling reverse osmosis membrane module is an alkali-resistant modified polyamide composite membrane with a wide flow channel structure. The automatic control unit includes a pH sensor and a PLC controller, and is equipped with a fuzzy PID algorithm for real-time monitoring and adjustment of the feed water pH value, controlling pH fluctuations within ±0.2, while simultaneously achieving real-time monitoring of the transmembrane pressure difference.

[0020] Experimental equipment: Single-stage RO, flow rate 1 m³ / h; membrane material: antifouling RO membrane. Experimental period: 30 consecutive days of operation, with daily monitoring of parameters such as membrane flux, desalination rate, pH value, conductivity, transmembrane pressure difference, and frequency of chemical cleaning.

[0021] Example 1 The method for preventing organic matter from clogging the reverse osmosis membrane in this embodiment includes the following steps: S1. Pretreatment for Hardness and Turbidity Reduction: Simulated coking wastewater with a COD concentration of 200 mg / L and a Ca²⁺ concentration of 200 mg / L is pretreated. A dual-alkali method is used to reduce calcium hardness by adding NaOH and Na₂CO₃ to the wastewater, controlling the molar ratio of Na₂CO₃ to Ca²⁺ at 1.25:1. The pH of the reaction system is 10.8, the reaction temperature is 20℃, and the reaction time is 30 minutes, reducing the calcium hardness in the wastewater to 60 mg / L (calculated as CaCO₃). A multi-media filter is used to remove the precipitated particles generated during pretreatment, reducing the suspended solids concentration in the wastewater to 0.8 mg / L. Simultaneously, sterilization is performed by adding an oxidizing bactericide to the wastewater, controlling the residual chlorine content to 0.3–0.5 mg / L. A reducing agent is added before the reverse osmosis feed water to reduce the ORP to below 300 mV, ensuring the safe operation of the reverse osmosis membrane. In this embodiment, the reducing agent is sodium bisulfite.

[0022] S2, Two-stage Precise Alkalinity Adjustment: A two-stage adjustment method is adopted. The first stage adjusts the pH of the wastewater to 10.0, and the second stage finely adjusts the pH of the wastewater to 10.5 at the inlet of the reverse osmosis system to compensate for the natural pH drop after S1 filtration to remove hard sediment.

[0023] S3. High-alkali stabilized scale inhibition: Add a phosphorus-free reverse osmosis scale inhibitor to the pH-adjusted wastewater at a dosage of 3–5 mg / L, preferably 4 mg / L. The scale inhibitor exhibits an 8% scale inhibition performance degradation rate after standing at 25°C for 72 hours at pH 10.5.

[0024] S4. Reverse osmosis treatment: The wastewater after adding scale inhibitor is sent to the reverse osmosis system for treatment. The operating parameters of the reverse osmosis system are: operating pressure 1.5MPa, recovery rate 65%, and operating temperature 25℃.

[0025] Example 2 The method for preventing organic matter from clogging the reverse osmosis membrane in this embodiment includes the following steps: S1. Pretreatment for Hardness and Turbidity Reduction: Simulated coking wastewater with a COD concentration of 250 mg / L and a Ca²⁺ concentration of 225 mg / L was pretreated. A dual-alkali method was used to reduce calcium hardness. NaOH and Na₂CO₃ were added to the wastewater, controlling the molar ratio of Na₂CO₃ to Ca²⁺ at 1.35:1. The pH of the reaction system was 11.0, the reaction temperature was 25℃, and the reaction time was 45 minutes, reducing the calcium hardness in the wastewater to 45 mg / L (calculated as CaCO₃). A multi-media filter was used to remove the precipitated particles generated during pretreatment, reducing the suspended solids concentration in the wastewater to 0.5 mg / L. Sterilization and reduction were performed as in Example 1.

[0026] S2, Two-stage Precision Alkalinity Adjustment: A two-stage adjustment method is adopted. The first stage adjusts the pH of the wastewater to 10.3, and the second stage finely adjusts the pH of the wastewater to 11.0 at the inlet of the reverse osmosis system to compensate for the natural pH drop after S1 filtration to remove hard sediment.

[0027] S3. High-alkali stabilized scale inhibition: Add a phosphorus-free reverse osmosis scale inhibitor to the pH-adjusted wastewater at a dosage of 3–5 mg / L, preferably 4 mg / L. The scale inhibitor exhibits a 5% scale inhibition performance degradation rate after standing at 25°C for 72 hours at pH 11.0.

[0028] S4. Reverse osmosis treatment: The wastewater after adding scale inhibitor is sent to the reverse osmosis system for treatment. The operating parameters of the reverse osmosis system are: operating pressure 2.5MPa, recovery rate 72%, and operating temperature 28℃.

[0029] Example 3 The method for preventing organic matter from clogging the reverse osmosis membrane in this embodiment includes the following steps: S1. Pretreatment for Hardness and Turbidity Reduction: Simulated coking wastewater with a COD concentration of 300 mg / L and a Ca²⁺ concentration of 280 mg / L was pretreated. A dual-alkali method was used to reduce calcium hardness. NaOH and Na₂CO₃ were added to the wastewater, controlling the molar ratio of Na₂CO₃ to Ca²⁺ at 1.5:1. The pH of the reaction system was 11.5, the reaction temperature was 30℃, and the reaction time was 60 minutes, reducing the calcium hardness in the wastewater to 40 mg / L (calculated as CaCO₃). A multi-media filter was used to remove the precipitated particles generated during pretreatment, reducing the suspended solids concentration in the wastewater to 0.4 mg / L. Sterilization and reduction were performed as in Example 1.

[0030] S2, Two-stage Precise Alkalinity Adjustment: A two-stage adjustment method is adopted. The first stage adjusts the pH of the wastewater to 10.5, and the second stage finely adjusts the pH of the wastewater to 11.5 at the inlet of the reverse osmosis system to compensate for the natural pH drop after S1 filtration to remove hard sediment.

[0031] S3. High-alkali stabilized scale inhibition: Add a phosphorus-free reverse osmosis scale inhibitor to the pH-adjusted wastewater at a dosage of 3–5 mg / L, preferably 4 mg / L. The scale inhibitor exhibits a 7% scale inhibition performance degradation rate after standing at 25°C for 72 hours at pH 11.5.

[0032] S4. Reverse osmosis treatment: The wastewater after adding scale inhibitor is sent to the reverse osmosis system for treatment. The operating parameters of the reverse osmosis system are: operating pressure 3.0MPa, recovery rate 75%, and operating temperature 30℃.

[0033] Comparative Example 1 The same water quality as in Example 1 was used, but the pH was not adjusted, no deep hardness pretreatment was performed, and the water was conventionally softened to a calcium hardness of 200 mg / L. A conventional polyamide composite membrane and a conventional scale inhibitor were used.

[0034] Comparative Example 2 The same water quality as in Example 1 was used, with the pH adjusted to 9.8, and the water hardness removed to a calcium hardness of 150 mg / L. A conventional polyamide composite membrane and a conventional scale inhibitor were used.

[0035] Comparative Example 3 The pH is only increased to 10.5–11.5, without deep hardening pretreatment, the calcium hardness is maintained at 200 mg / L, no alkali-resistant modified membrane is used, and conventional scale inhibitors are used.

[0036] Comparative Example 4 The pH is only increased to 10.5–11.5, without deep hardening pretreatment, the calcium hardness is maintained at 200 mg / L, an alkali-resistant modified membrane is used, and a high-alkali stabilizer scale inhibitor is not used.

[0037] Comparative Example 5 Simply raise the pH to 10.5–11.5, do not perform deep hardening pretreatment, maintain calcium hardness at 200 mg / L, use an alkali-resistant modified membrane, and use a high-alkali stabilizer scale inhibitor.

[0038] Comparative Example 6 The pH was adjusted to 11.6–12.0, and a deep hardening pretreatment was performed to reduce the calcium hardness to 40 mg / L. An alkali-resistant modified membrane was used, along with a high-alkali stabilizer scale inhibitor.

[0039] Scale inhibitor performance verification examples Commercially available conventional scale inhibitors and the preferred phosphorus-free reverse osmosis scale inhibitor of this invention were selected and allowed to stand for 72 hours at pH 10.5, pH 11.0, pH 11.5, and 25℃, respectively, to test their scale inhibition performance before and after standing. Test conditions: Ca²⁺ concentration was 200 mg / L, and HCO₃⁻ concentration was 300 mg / L. The scale inhibition performance was tested using the calcium carbonate deposition method: hard water containing Ca²⁺ and HCO₃⁻ was prepared, the scale inhibitor was added, and the mixture was heated in an 80℃ water bath for 10 hours. After filtration, the Ca²⁺ concentration in the filtrate was measured, and the scale inhibition rate was calculated.

[0040] Test results: The initial scale inhibition rate of conventional reverse osmosis antiscalant was 92%, but after standing for 72 hours, the scale inhibition rate dropped to 68%, with a decay rate of 26.1%. The preferred phosphorus-free reverse osmosis antiscalant of this invention: pH 10.5: Initial scale inhibition rate 94%, scale inhibition rate after standing 86%, and degradation rate 8.5%; pH 11.0: Initial scale inhibition rate 94%, scale inhibition rate after standing 87%, and degradation rate 7.4%; pH 11.5: Initial scale inhibition rate 94%, scale inhibition rate after standing 87%, and attenuation rate 7.4%.

[0041] The results show that the scale inhibitor selected in this invention meets the requirement of a decay rate of less than 10% in the entire pH range of 10.5 to 11.5, while conventional scale inhibitors suffer severe performance degradation in high pH environments.

[0042] The phosphorus-free reverse osmosis antiscalant used in the above embodiments is the antiscalant disclosed in the patent application filed by the applicant, entitled "Phosphorus-free reverse osmosis antiscalant and its preparation method," with publication number CN120736700A. The automatic control unit adopts a Siemens PLC control system.

[0043] Comparison of effects between the examples and the comparative examples The effects of Examples 1-3 and Comparative Examples 1-2 were compared. The test indicators included membrane flux decline rate, desalination rate retention rate, transmembrane pressure difference increase, chemical cleaning frequency, and membrane module condition. The specific results are shown in the table below: Experimental conclusion: (1) Under pH>10 conditions, the organic fouling rate can be reduced by more than 70%, and the membrane flux decay rate is reduced from 60% in the traditional process to 15%, which is 50% lower than 30% under pH 9.5-10 conditions.

[0044] (2) This invention maximizes the charge repulsion between organic matter and membrane surface by using the theory of changes in the molecular structure of organic matter under pH>10 conditions. Under pH conditions of 10.5 to 11.5, acidic functional groups such as carboxyl groups in organic matter are completely dissociated, and the degree of negative charge is increased compared with pH=10.

[0045] (3) Under high pH conditions, the structure of organic molecules is more stable and less likely to undergo chemical cross-linking reaction with the polyamide layer on the membrane surface. The flux attenuation rate is reduced by more than 50% compared with conventional polyamide composite membranes and by 25% compared with pH control at 9.5-10.

[0046] (4) The high-alkali environment and the alkali-resistant modified membrane material are well matched, which effectively inhibits the hydrolysis of the polyamide layer; the effective control of organic fouling significantly reduces the frequency of chemical cleaning and reduces the repeated impact of cleaning agents on the membrane layer. The synergistic effect of the two significantly extends the overall service life of the membrane module.

[0047] (5) When treating organic wastewater with COD of 200-300 mg / L, by reducing the frequency of chemical cleaning and the number of membrane replacements, the annual operating cost of the system is reduced by about 30% compared with the process without adjusting the pH value of the influent, and by about 10% compared with the process of controlling the pH at 9.5-10.

[0048] (6) While effectively controlling fouling, the system recovery rate can be increased by 5 to 10 percentage points, significantly increasing water production and improving water resource utilization efficiency and system economy.

[0049] The method for preventing organic fouling of reverse osmosis membranes according to the present invention is applicable not only to the aforementioned coking wastewater, but also to the treatment of landfill leachate, pharmaceutical wastewater, dyeing and printing wastewater, and other types of industrial wastewater with high organic content. Any technical solution that uses alkaline conditions of pH 10.5 to 11.5, combined with deep hardening removal, alkali-resistant membranes, high-alkali-stability antiscalants, and precise pH control to achieve reverse osmosis membrane anti-organic fouling falls within the protection scope of the present invention.

Claims

1. A method for preventing organic matter from clogging a reverse osmosis membrane, characterized in that, To alleviate organic fouling, the electrostatic repulsion is enhanced by adjusting the pH of the reverse osmosis feed water to the alkaline range of 10.5–11.

5. This includes the following steps: S1. Pre-treat the wastewater containing organic matter by using the double alkali method to reduce the calcium hardness in the wastewater to below 100 mg / L (calculated as CaCO3) and remove the generated precipitate particles. S2. A two-stage adjustment method is adopted to adjust the pH value of the pretreated wastewater to 10.5-11.5; S3. Add reverse osmosis antiscalant to the pH-adjusted wastewater. After standing at a constant temperature of 25°C for 72 hours under pH conditions of 10.5–11.5, the antiscalant's scale inhibition performance degradation rate is less than 10%. S4. The wastewater after the addition of reagents is sent to a reverse osmosis system for treatment; the reverse osmosis system includes an anti-fouling reverse osmosis membrane module and an automatic control unit; the anti-fouling reverse osmosis membrane module adopts a wide flow channel structure; the automatic control unit includes a pH sensor and a PLC controller, used to monitor and adjust the pH value of the feed water in real time, and control the pH fluctuation within ±0.2; the operating pressure of the reverse osmosis system is 1.5~3.0MPa, the recovery rate is 65~75%, and the operating temperature is less than 35℃.

2. The method for preventing organic fouling of the reverse osmosis membrane according to claim 1, characterized in that: In S1, the double alkali method is used to reduce the hardness of wastewater. The specific steps are as follows: NaOH and Na2CO3 are added to the wastewater, the molar ratio of Na2CO3 to Ca²⁺ is controlled at 1.2 to 1.5:1, the pH value of the reaction system is controlled at 10.5 to 11.5, the reaction temperature is 20 to 30℃, and the reaction time is 30 to 60 minutes.

3. The method for preventing organic matter from clogging the reverse osmosis membrane according to claim 2, characterized in that: In S1, the hardness of the wastewater is reduced to less than 50 mg / L as CaCO3; and precipitated particles are removed by a multi-media filter or ultrafiltration device, so that the suspended solids concentration of the pretreated wastewater is less than 1 mg / L.

4. The method for preventing organic fouling of the reverse osmosis membrane according to claim 3, characterized in that: In S2, pH adjustment is carried out in two stages: the first stage adjusts the wastewater pH to 10.0-10.5; the second stage finely adjusts the wastewater pH to 10.5-11.5 at the inlet of the reverse osmosis system.

5. The method for preventing organic fouling of the reverse osmosis membrane according to claim 1, characterized in that: S1 pretreatment includes a sterilization step, adding an oxidizing bactericide to control residual chlorine at 0.3-0.5 mg / L, and adding a reducing agent before reverse osmosis feed water to reduce ORP to below 300 mv.

6. The method for preventing organic fouling of the reverse osmosis membrane according to claim 1, characterized in that: The reverse osmosis antiscalant mentioned in S3 is a phosphorus-free reverse osmosis antiscalant; the antifouling reverse osmosis membrane module is a polyamide composite membrane, and its separation layer has been modified to be alkali-resistant.

7. The method for preventing organic fouling of the reverse osmosis membrane according to claim 1, characterized in that: The pH sensor is a high-precision pH sensor with a measurement error of ≤±0.02; the automatic control unit achieves precise feedback adjustment of pH value through a fuzzy PID algorithm.

8. The method for preventing organic fouling of the reverse osmosis membrane according to claim 1, characterized in that: The operating parameters of the reverse osmosis system described in S4 are: operating pressure 2.5~3.0MPa, recovery rate 72~75%, and operating temperature 25~30℃.

9. The method for preventing organic fouling of the reverse osmosis membrane according to claim 1, characterized in that: The COD concentration of the wastewater containing organic matter is 200–300 mg / L.

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