Enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration system and preparation method of enzyme-containing acidic cleaning agent

Abstract

The invention relates to the technical field of water treatment, and particularly discloses an enzyme-containing acidic cleaning agent for a reverse osmosis and nanofiltration system and a preparation method of the enzyme-containing acidic cleaning agent. An enzyme-containing acidic cleaning agent for a reverse osmosis and nanofiltration system is composed of the following components in percentage by weight: 5-25% of organic acid, 1-5% of a chelating agent, 5% of a stabilizer, 1-5% of biological enzyme, 0.5-3% of a surfactant and the balance of deionized water. The stabilizer is prepared from alanine, trehalose, PEG (Polyethylene Glycol) and epsilon-polylysine, and the mass ratio of the alanine to the trehalose to the PEG to the epsilon-polylysine is 1 to (0.3 to 0.4) to (0.1 to 0.2) to (0.05 to 0.1). The cleaning agent provided by the invention can effectively remove various pollutants such as inorganic salt scales, combinations of iron, aluminum and organic matters, metal oxides, organic matters and microbial slime on the surface of the reverse osmosis membrane or the nanofiltration membrane, and remarkably recovers the flux and the desalination rate of the membrane.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems and its preparation method. Background Technology

[0002] Reverse osmosis (RO) and nanofiltration (NF) are two core pressure-driven membrane separation technologies in modern water treatment, widely used in seawater desalination, brackish water purification, industrial pure / ultrapure water production, municipal and industrial wastewater reuse, food and beverage processing, and pharmaceuticals. They achieve efficient separation of water molecules from dissolved salts, organic matter, colloids, microorganisms, and other contaminants through selective permeation of membranes under applied pressure. Currently, aluminum / iron flocculants (such as polyaluminum chloride PAC and ferric chloride FeCl3) are widely used in the pretreatment of reverse osmosis and nanofiltration systems. Membrane fouling in reverse osmosis and nanofiltration systems mainly includes inorganic scale, iron-aluminum-organic compounds, metal oxides, organic matter, and microbial slime, among other contaminants.

[0003] Currently, reverse osmosis cleaning agents on the market mainly include acidic cleaning agents, alkaline cleaning agents, and specialized bio-enzyme cleaning agents. Acidic cleaning agents are primarily used to remove inorganic contaminants such as carbonate scale and metal oxide scale, dissolving the scale layer into soluble salts through chemical reactions. Alkaline cleaning agents are commonly used to remove organic matter, colloids, and biofilms, utilizing their strong oxidizing components to kill microorganisms and decompose the molecular structure of contaminants. Specialized bio-enzyme cleaning agents utilize specific enzymes to specifically decompose proteins, polysaccharides, and other components in biological slime, making them environmentally friendly and causing minimal damage to the membrane, especially suitable for systems with severe microbial contamination.

[0004] However, existing cleaning agents have certain limitations: traditional acidic cleaning agents, while effective at removing inorganic scale, have limited ability to remove organic matter and biological contaminants, especially when iron and aluminum in the solution combine with serum proteins to cause contamination. Alkaline cleaning agents are ineffective at removing inorganic scale and may leave alkaline residues after cleaning, requiring additional rinsing steps, increasing cleaning costs and time. Specialized bio-enzyme cleaning agents are relatively expensive, and when used alone, their cleaning effect on some complex contaminants is not ideal. Furthermore, enzyme activity is easily affected by environmental factors (such as temperature and pH), leading to problems such as easy deactivation of the bio-enzymes. Summary of the Invention

[0005] To address the limitations of existing cleaning agents in terms of their limited cleaning effectiveness on reverse osmosis and nanofiltration membranes, as well as the ease with which biological enzymes can be deactivated, this application provides an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems, along with its preparation method.

[0006] In a first aspect, this application provides an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems, achieved through the following technical solution: An enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems, comprising the following components by weight percentage: 5-25% organic acid, 1-5% chelating agent, 5% stabilizer, 1-5% bio-enzyme, 0.5-3% surfactant, and the balance being deionized water.

[0007] Preferably, an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems comprises, by weight percentage: 20% organic acid, 5% chelating agent, 5% stabilizer, 5% bio-enzyme, 3% surfactant, and the balance being deionized water.

[0008] Preferably, the stabilizer includes alanine, trehalose, PEG and ε-polylysine, wherein the mass ratio of alanine, trehalose, PEG and ε-polylysine is 1:(0.3-0.4):(0.1-0.2):(0.05-0.1).

[0009] A significant synergistic effect exists among alanine, trehalose, PEG, and ε-polylysine. That is, the combination of alanine, trehalose, PEG, and ε-polylysine as stabilizers not only improves the storage stability of the enzyme, but also ensures that the cleaning agent still has a high cleaning ability after long-term storage.

[0010] Preferably, the stabilizer further includes N-acetylcysteine ​​and sodium ferulic acid, and the mass ratio of trehalose, ε-polylysine, N-acetylcysteine ​​and sodium ferulic acid is (0.3-0.4): (0.05-0.1): (0.2-0.3): (0.08-0.15).

[0011] More preferably, the stabilizer includes alanine, trehalose, PEG, ε-polylysine, N-acetylcysteine, and sodium ferulic acid.

[0012] This invention constructs a multi-level synergistic stabilizing system by combining alanine, trehalose, PEG, ε-polylysine, N-acetylcysteine, and sodium ferulic acid. This system not only improves the storage stability of enzymes but also ensures that the cleaning agent retains its high cleaning efficiency after long-term storage. Furthermore, it effectively inhibits the oxidative damage of free chlorine to biological enzymes and diethylenetriaminepentaacetic acid, significantly improving the cleaning effect of enzyme-containing acidic cleaning agents on both organic and inorganic substances and increasing the flux recovery rate.

[0013] Preferably, the molecular weight of the ε-polylysine is 3500-4000 Daltons.

[0014] Preferably, the PEG is selected from one or more of PEG2000, PEG3000, and PEG4000; more preferably, the PEG is PEG2000.

[0015] Preferably, the chelating agent comprises diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, and hydrolyzed polymaleic anhydride; the mass ratio of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, and hydrolyzed polymaleic anhydride is 1:(0.2-0.3):(0.05-0.08):(0.03-0.05).

[0016] A complex of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, and hydrolyzed polymaleic anhydride was developed to construct an integrated "chelation-inhibition-dispersion" cleaning system. This system not only overcomes the limitations of diethylenetriaminepentaacetic acid alone in terms of chlorine resistance, lattice dissolution, and colloidal dispersion removal, but also demonstrates a significant synergistic effect in cleaning reverse osmosis membranes contaminated with inorganic substances and organic-inorganic composite colloidal fouling.

[0017] Preferably, the chelating agent further includes sodium phytate and polyaspartic acid, and the mass ratio of diethylenetriaminepentaacetic acid, hydrolyzed polymaleic anhydride, sodium phytate and polyaspartic acid is 1:(0.03-0.05):(0.06-0.08):(0.08-0.15).

[0018] The combination of diethylenetriaminepentaacetic acid, diethylenetriaminepentamide phosphonic acid, phosphonocarboxylic acid copolymer, hydrolyzed polymaleic anhydride, sodium phytate and polyaspartic acid not only overcomes the limitations of diethylenetriaminepentaacetic acid alone in terms of chlorine resistance and colloidal dispersion, but also achieves a further improvement in flux recovery rate, especially in working conditions with inorganic substances containing free chlorine and organic-inorganic composite colloidal contamination.

[0019] Preferably, the surfactant is a fatty alcohol polyoxyethylene ether.

[0020] Preferably, the organic acid is selected from one or more of citric acid, glycolic acid, and formic acid; more preferably, the organic acid is a mixture of citric acid and glycolic acid in a mass ratio of 1:1.

[0021] Preferably, the bioenzyme is selected from one or more of acidic protease, acidic cellulase, α-amylase, pectinase, and lipase.

[0022] Preferably, the bioenzyme is a mixture of acidic protease, α-amylase and lipase.

[0023] Preferably, the mass ratio of the acidic protease, α-amylase and lipase is 1:(0.2-0.3):(0.1-0.2); more preferably, the mass ratio of the acidic protease, α-amylase and lipase is 1:0.2:0.1.

[0024] Secondly, this application provides a method for preparing an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems, using the following technical solution: A method for preparing an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems includes the following steps: The biological enzyme, surfactant and stabilizer are mixed and stirred evenly to obtain mixture 1; Mix the organic acid and chelating agent, stir well, then add mixture 1 and stir well to obtain an enzyme-containing acidic cleaning agent.

[0025] In summary, this application has at least the following beneficial effects: 1. The enzyme-containing acidic cleaning agent provided in this application, through the synergistic effect of organic acids, chelating agents, surfactants, bio-enzymes, and stabilizers, can effectively remove various contaminants such as inorganic scale, iron-aluminum-organic compounds, metal oxides, organic matter, and microbial slime from the surface of reverse osmosis or nanofiltration membranes, significantly restoring membrane flux and desalination rate. Compared with using bio-enzyme cleaning agents alone, this application, through the synergistic effect of multiple components, reduces the amount of bio-enzyme used while ensuring cleaning effectiveness, thereby reducing costs.

[0026] 2. This application employs a stabilizer composed of alanine, trehalose, PEG, and ε-polylysine, and controls the mass ratio of these four components. This significantly improves the cleaning efficiency of biological and organic contaminants on reverse osmosis / nanofiltration membranes, restores membrane flux, extends membrane life, and enables bio-enzyme molecules to act efficiently on organic contaminants (such as proteins, polysaccharides, and lipids) on the membrane surface, rather than becoming inactive or adsorbed onto the reverse osmosis or nanofiltration membrane. Furthermore, the synergistic effect among alanine, trehalose, PEG, and ε-polylysine not only ensures that the bio-enzymes maintain their activity for extended periods in a liquid environment, giving the enzyme-containing acidic cleaning agent excellent long-term storage stability, but also ensures that the bio-enzymes maintain high activity under strong acidity, high salt conditions, and during subsequent dilution and cleaning processes. Among these components, alanine, as an amphoteric ion, provides excellent buffering capacity, stabilizing the acidic pH of the cleaning agent system and creating and maintaining the optimal working environment for bio-enzymes, preventing enzyme inactivation due to pH fluctuations. Trehalose effectively inhibits the thermal motion of bio-enzyme molecules, preventing enzyme extension, unfolding, and aggregation, thus significantly extending the shelf life of liquid enzyme preparations. During the cleaning cycle, the shear force of the liquid and the gas-liquid interface can denature proteins. The long chains of PEG prevent collisional aggregation between enzyme molecules through steric hindrance, while also reducing enzyme unfolding and inactivation at the interface. ε-polylysine neutralizes the negative charge on the surface of enzyme molecules or contaminant particles, reducing ineffective adsorption and self-aggregation caused by electrostatic interactions, allowing the enzyme to focus more effectively on the dirt on the membrane surface. Alanine, trehalose, PEG, and ε-polylysine address different pathways of enzyme inactivation, collectively forming a robust "defense line" to ensure that the bio-enzymes in the cleaning agent maintain high activity during storage and cleaning. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the embodiments.

[0028] All raw materials used in this application are commercially available, and there is no limitation on the purchasing company for raw materials not mentioned in the embodiments and comparative examples.

[0029] Example Examples 1-13 provide an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems. The following description uses Example 1 as an example.

[0030] Example 1 provides an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems, which, by weight percentage, consists of the following components: 20% organic acid, 5% chelating agent, 5% stabilizer, 5% bio-enzyme, 3% surfactant, and 62% deionized water; The organic acid is composed of citric acid and glycolic acid mixed in a mass ratio of 1:1. The chelating agent is diethylenetriaminepentaacetic acid (CAS No. 67-43-6). The stabilizer is a mixture of alanine, trehalose, PEG2000 and ε-polylysine (molecular weight 3500 Daltons) in a mass ratio of 1:0.3:0.1:0.05; The biological enzyme is composed of acidic protease, α-amylase and lipase in a mass ratio of 1:0.2:0.1; The surfactant is isotridecyl alcohol polyoxyethylene ether (specification 1309 TO-9, purchased from Guangzhou Dute Chemical Co., Ltd.).

[0031] The preparation steps for enzyme-containing acidic cleaning agents used in reverse osmosis and nanofiltration systems are as follows: The biological enzyme, surfactant and stabilizer are mixed and stirred evenly to obtain mixture 1; Mix the organic acid and chelating agent, stir well, then add mixture 1 and stir well to obtain an enzyme-containing acidic cleaning agent.

[0032] Comparative Example 1 differs from Example 1 only in that the stabilizer is replaced by deionized water. The preparation steps for enzyme-containing acidic cleaning agents used in reverse osmosis and nanofiltration systems are as follows: Mix the biological enzyme and surfactant, stir until homogeneous, to obtain mixture 1; Mix the organic acid and chelating agent, stir well, then add mixture 1 and stir well to obtain an enzyme-containing acidic cleaning agent.

[0033] Comparative Example 2 differs from Example 1 only in that the stabilizer is alanine.

[0034] Comparative Example 3 differs from Example 1 only in that the stabilizer is a mixture of alanine and trehalose in a mass ratio of 1:0.3.

[0035] Comparative Example 4 differs from Example 1 only in that the stabilizer is a mixture of alanine, trehalose and PEG2000 in a mass ratio of 1:0.3:0.1.

[0036] Comparative Example 5 differs from Example 1 only in that the stabilizer is a mixture of alanine, trehalose and ε-polylysine (molecular weight 3500 Daltons) in a mass ratio of 1:0.3:0.05.

[0037] Comparative Example 6 differs from Example 1 only in that the stabilizer is a mixture of alanine, PEG2000 and ε-polylysine (molecular weight 3500 Daltons) in a mass ratio of 1:0.1:0.05.

[0038] Comparative Example 7 differs from Example 1 only in that the stabilizer is a mixture of trehalose, PEG2000 and ε-polylysine (molecular weight 3500 Daltons) in a mass ratio of 0.3:0.1:0.05.

[0039] The enzyme-containing acidic cleaning agents prepared in Example 1 and Comparative Examples 1-9 were placed at 25°C and normal pressure for 1 day, 10 days, and 100 days, respectively. They were then diluted with deionized water to a concentration of 3 wt% to obtain a diluted solution. Concentrated hydrochloric acid was added dropwise to the diluted solution to adjust the pH to 2-3, thus obtaining a cleaning solution. The cleaning solution was used to clean the reverse osmosis membranes contaminated with organic matter. The cleaning time was 2 hours for all cases. After cleaning, the flux recovery rate of the reverse osmosis membrane was measured. The test results are shown in Table 1.

[0040] The test steps for the flux recovery rate of reverse osmosis membranes include: S1. Determine the initial flux of the new membrane: Take a new, unused reverse osmosis membrane (Dow reverse osmosis membrane element BW30-400FR), install it in the test cell, seal it well, rinse it with deionized water for 10 min, apply a pressure of 0.6 MPa, keep the temperature constant at 25℃, and run it stably for 60 min; record the permeate volume and calculate the flux, which is the initial flux of the new membrane. The flux calculation formula is: Flux = Permeate volume / (Effective membrane area × Time).

[0041] S2, Prepare a fouled reverse osmosis membrane.

[0042] S3. Cleaning the fouled reverse osmosis membrane: Inject the prepared cleaning solution into the fouled side of the reverse osmosis membrane and soak it at 35℃ for 2 hours. Then, apply a pressure of 0.4 MPa and a flow rate of 1 m / s to the water on the permeate side of the reverse osmosis membrane for circulation cleaning. The process includes forward rinsing for 10 minutes, circulation cleaning for 40 minutes, and reverse rinsing for 10 minutes. After cleaning, drain the enzyme-containing acidic cleaning agent. Use deionized water as the rinsing water until the pH is neutral and the conductivity is stable. The total rinsing time should not be less than 30 minutes. After rinsing, drain the rinsing water.

[0043] S4. Determine the pure water flux after cleaning: Reinstall the cleaned and rinsed reverse osmosis unit into the test cell, seal it well, rinse with deionized water for 10 min, apply a pressure of 0.6 MPa, keep the temperature at 25℃, circulate for 30 min, and wait for the flux to stabilize; record the permeate volume and calculate the flux, which is the pure water flux after cleaning.

[0044] S5. Calculate the flux recovery rate, where the flux recovery rate = pure water flux after cleaning / initial flux of new membrane × 100%.

[0045] A higher flux recovery rate indicates a better cleaning effect on the reverse osmosis membrane.

[0046] The steps for preparing an organically fouled reverse osmosis membrane are as follows: Dow reverse osmosis membrane element BW30-400FR was selected as the experimental membrane. At a water temperature of 25℃, a salt solution with a total salt content of 4000 mg / L was prepared using sodium chloride and deionized water as the raw water. The influent pressure was controlled at 0.8 MPa, and the influent flow rate was 1 m³ / s. 3 / h, When the membrane element is operating normally, the permeate flow rate is 0.71 m³ / h. 3 The permeate salt content was 6 mg / L. Organic pollutants were added to the raw water to make the concentrations of humic acid, bovine serum albumin, and activated sludge supernatant in the raw water 5 mg / L, 5 mg / L, and 10 mL / L, respectively (i.e., 5 mg of humic acid, 5 mg of bovine serum albumin, and 10 mL of activated sludge supernatant were added per L of raw water). After 2 hours of operation, the influent pressure rose to 1.2 MPa, and the influent flow rate was 1 m³ / h. 3 / h, product water flow rate 0.3m 3 The permeate salt content was 35 mg / L, indicating that the reverse osmosis membrane had been fouled. Specifically, the permeate flow rate decreased by approximately 57% compared to the initial value, and the desalination rate decreased to approximately 99.1%. The preparation steps of activated sludge supernatant are as follows: Take 100 mL of activated sludge from the aerobic tank of an urban wastewater treatment plant (the microbial community of activated sludge includes Proteobacteria, Bacteroidetes, and Ascomycota), let it stand for 30 min, and then collect the supernatant, which is the activated sludge supernatant.

[0047] Table 1 As shown in Table 1, the enzyme-containing acidic cleaning agent provided in Example 1 of this invention exhibits excellent long-term storage stability. Even after 100 days at room temperature, its flux recovery rate remains as high as 89.0%, indicating that the activity of the biological enzymes is effectively protected and the cleaning performance hardly diminishes. In Comparative Example 1, where deionized water was used instead of the stabilizer, the flux recovery rate of the cleaning agent after 100 days was only 10.5%, and the enzyme was essentially inactivated, indicating that the enzyme is easily denatured and degraded in an acidic environment without a stabilizer. The flux recovery rate of Comparative Example 2 (alanine only) after 100 days was 50.8%; that of Comparative Example 3 (alanine + trehalose) was 63.5%, indicating that relying solely on alanine and / or trehalose is insufficient to maintain the long-term activity of the enzyme. Comparative Examples 4 (deficient in ε-polylysine) and 5 (deficient in PEG2000) showed flux recovery rates of 74.2% and 74.8% after 100 days, respectively, while Comparative Examples 6 (deficient in trehalose) and 7 (deficient in alanine) showed rates of 72.3% and 64.1%, respectively. This indicates that the absence of any key component significantly reduces the protective effect. Therefore, there is a significant synergistic effect among alanine, trehalose, PEG2000, and ε-polylysine. The combination of alanine, trehalose, PEG2000, and ε-polylysine as stabilizers not only improves the storage stability of the enzyme but also ensures that the cleaning agent retains its high cleaning efficiency even after long-term storage. This may be because alanine provides pH buffering and osmotic protection in an acidic environment, trehalose inhibits protein unfolding through a "water substitution" mechanism, PEG2000 prevents enzyme molecule aggregation through steric hindrance, and ε-polylysine reduces ineffective adsorption of enzymes on the membrane surface through electrostatic shielding, thereby increasing the concentration of free enzymes. The four components work together to construct a multi-level protection network of "buffering-structural stability-anti-aggregation-anti-adsorption", which makes the performance of Example 1 significantly better than any combination of missing components, demonstrating non-linear synergistic gains.

[0048] During their research, the inventors discovered that surface water or municipal tap water is typically disinfected with chlorination, which may leave residual free or combined chlorine. Although the system is equipped with dechlorination measures such as activated carbon and sodium bisulfite, trace amounts of free chlorine may still enter the reverse osmosis system during malfunctions. Because polyamide membranes are highly sensitive to oxidants, such residues can cause irreversible oxidative damage to the membrane material, leading to a decrease in desalination rate and a shortened lifespan. Therefore, the concentration of free chlorine in the feed water must be strictly controlled below 0.1 ppm. While free chlorine below 0.1 ppm meets the requirements of a reverse osmosis system, it is still sufficient to cause oxidative inactivation of biological enzymes. Furthermore, diethylenetriaminepentaacetic acid (DTA) contains multiple amine and carboxyl groups; the amine groups are easily attacked and oxidized to imines or broken by free chlorine, which can impair the chelating effect of DTA and reduce the cleaning effect of enzyme-containing acidic cleaning agents.

[0049] Example 2 differs from Example 1 only in that the stabilizer is composed of alanine, trehalose, PEG2000, ε-polylysine (molecular weight of 3500 Daltons) and N-acetylcysteine ​​in a mass ratio of 1:0.3:0.1:0.05:0.2.

[0050] Example 3 differs from Example 1 only in that the stabilizer is composed of alanine, trehalose, PEG2000, ε-polylysine (molecular weight 3500 Daltons) and sodium ferulic acid in a mass ratio of 1:0.3:0.1:0.05:0.08.

[0051] Example 4 differs from Example 1 only in that the stabilizer is composed of alanine, trehalose, PEG2000, ε-polylysine (molecular weight 3500 Daltons), N-acetylcysteine ​​and sodium ferulic acid in a mass ratio of 1:0.3:0.1:0.05:0.2:0.08.

[0052] Comparative Example 8 differs from Example 4 only in that the stabilizer is a mixture of alanine, PEG2000, ε-polylysine (molecular weight 3500 Daltons), N-acetylcysteine ​​and sodium ferulic acid in a mass ratio of 1:0.1:0.05:0.2:0.08.

[0053] Comparative Example 9 differs from Example 4 only in that the stabilizer is a mixture of alanine, trehalose, PEG2000, N-acetylcysteine ​​and sodium ferulic acid in a mass ratio of 1:0.3:0.1:0.2:0.08.

[0054] The enzyme-containing acidic cleaning agents prepared in Examples 1-4 and Comparative Examples 4, 6, and 8-9 were placed at 25°C and normal pressure for 1 day and then used to clean reverse osmosis membranes contaminated with organic matter, reverse osmosis membrane 2 contaminated with organic matter, and reverse osmosis membrane 2 contaminated with inorganic matter. After cleaning, the flux recovery rate of the reverse osmosis membranes was measured, and the test results are shown in Table 2.

[0055] The preparation steps for the organically fouled reverse osmosis membrane 2 are the same as those for the organically fouled reverse osmosis membrane, except that a salt solution with a total salt content of 4000 mg / L is prepared using sodium chloride and deionized water as the raw water. NaClO is then added to the salt solution to release free chlorine (ClO₂). - The content is 0.05 ppm, and the free chlorine (ClO) - The raw water was a salt solution with a salt content of 0.05 ppm and a total salt content of 4000 mg / L.

[0056] The preparation steps of the inorganically fouled reverse osmosis membrane 2 are as follows: Dow reverse osmosis membrane element BW30-400FR was selected as the experimental membrane. A salt solution with a total salt content of 2000 mg / L was prepared using sodium chloride and deionized water at a water temperature of 25℃. NaClO was then added to the salt solution to release free chlorine (ClO₂). - The content of free chlorine is 0.05 ppm. A salt solution with a free chlorine content of 0.05 ppm and a total salt content of 2000 mg / L is used as the raw water. Calcium chloride (CaCl2·2H2O) is added to the raw water to make Ca... 2 ⁺ A concentration of 100 mg / L, barium chloride (BaCl2·2H2O) makes Ba 2 ⁺ A concentration of 10 mg / L, strontium chloride (SrCl2·6H2O) causes Sr 2 ⁺ At a concentration of 5 mg / L, sodium sulfate (Na₂SO₄) causes SO₄²⁻ to form SO₄²⁻. 2 The concentration is 200 mg / L, and the alkalinity is adjusted to 150 mg / L (calculated as CaCO3) with sodium bicarbonate (NaHCO3). The inlet water pressure is controlled at 0.8 MPa, and the inlet water flow rate is 1 m³ / s. 3 The system recovery rate is controlled at 75% per hour, and the permeate flow rate is 0.25 m³ / h when the membrane element is operating normally. 3 / h, product water salt content 6mg / L; After 48 hours of continuous operation, the inlet water pressure rose to 1.1 MPa, while the inlet water flow rate remained at 1 m³ / h. 3 / h, the permeate flow rate decreased to 0.13m 3 The permeate salt content increased to 30 mg / L per hour, indicating that the reverse osmosis membrane had become fouled. Specifically, the permeate flow rate decreased by approximately 48% compared to the initial value, and the desalination rate decreased to approximately 98.6%. Simultaneously, ferric chloride (FeCl3·6H2O) was added to the feed water to reduce the Fe... 3 ⁺ A concentration of 2 mg / L, aluminum chloride (AlCl3·6H2O) makes Al 3 ⁺ A concentration of 1 mg / L, manganese chloride (MnCl2·4H2O) makes Mn 2 ⁺ A concentration of 0.5 mg / L, copper chloride (CuCl2·2H2O) makes Cu 2 ⁺ Concentration of 0.2 mg / L, zinc chloride (ZnCl2) makes Zn 2 When the concentration of ⁺ was 0.2 mg / L, after 24 hours of operation, reddish-brown to brownish-black deposits formed on the membrane surface.

[0057] Table 2 As shown in Table 2, this invention constructs a multi-level synergistic stabilizing system through the compounding of alanine, trehalose, PEG2000, ε-polylysine, N-acetylcysteine, and sodium ferulic acid, effectively inhibiting 0.05 ppm free chlorine (ClO).- The oxidative damage to biological enzymes and diethylenetriaminepentaacetic acid significantly improved the cleaning effect of enzyme-containing acidic cleaning agents on organic and inorganic matter, increasing flux recovery rate. Specifically, Example 1, using a stabilizer composed of alanine, trehalose, PEG2000, and ε-polylysine, achieved a flux recovery rate of 93.2% for organically fouled membranes under chlorine-free conditions, indicating that this basic formulation has good enzyme stabilization capabilities. However, the introduction of 0.05 ppm free chlorine (ClO) into the raw water... - After (i.e., "reverse osmosis membrane 2 with organic fouling"), its flux recovery rate significantly decreased to 75.8%; similarly, the introduction of 0.05 ppm free chlorine (ClO) into the raw water... - After (i.e., "reverse osmosis membrane 2 with inorganic fouling"), the flux recovery rate significantly decreased to 72.4%. This indicates that the stabilizer composed of alanine, trehalose, PEG2000, and ε-polylysine cannot effectively resist the oxidative damage of trace amounts of chlorine to enzymes and the oxidative attack on diethylenetriaminepentaacetic acid. Example 4, using a stabilizer composed of alanine, trehalose, PEG2000, ε-polylysine, N-acetylcysteine, and sodium ferulic acid, achieved a flux recovery rate of 90.2% on membranes fouled by chlorine-containing organic matter and 89.8% on membranes fouled by chlorine-containing inorganic matter, significantly higher than Example 1 (without N-acetylcysteine ​​and sodium ferulic acid), Example 2 (without N-acetylcysteine), Example 3 (without sodium ferulic acid), Comparative Example 8 (without trehalose), and Comparative Example 9 (without ε-polylysine). Example 4 corresponds to a chlorine-containing (ClO) - Flux recovery rate on organic-contaminated membranes and on membranes containing chlorine (ClO) - The flux recovery rate on the inorganic fouling membrane was significantly higher than that of the other groups. This is due to N-acetylcysteine ​​(strong reducing agent, protects -SH groups), sodium ferulic acid (free radical scavenging, broad-spectrum antioxidant), and trehalose, which not only provide structural stability but also reduce the exposure of oxidative sites caused by protein conformation unfolding. ε-polylysine, although it can chelate Fe through multiple ε-amino groups on its molecular chain... 2 ⁺、Cu 2 ε-polylysine, containing transition metal ions such as ⁺, inhibits the generation of hydroxyl radicals in the Fenton reaction, thereby effectively reducing the oxidation potential of the system. Furthermore, ε-polylysine reduces the adsorption and inactivation of enzymes on container walls or contaminant surfaces, preventing the exposure of oxidation sites due to protein conformation unfolding. When used in combination with N-acetylcysteine, sodium ferulic acid, and trehalose, ε-polylysine significantly enhances the stability and durability of the overall antioxidant system through source oxygen control and structural protection, maintaining the activity of enzymes and diethylenetriaminepentaacetic acid in environments containing 0.05 ppm free chlorine (ClO₂). -ε-Polylysine exhibits synergistic effects with N-acetylcysteine, sodium ferulic acid, and trehalose, achieving a comprehensive six-in-one protection system encompassing structural stability, anti-aggregation, anti-adsorption, anti-oxidation, metal inhibition, and chelation protection, thus protecting low-chlorine (ClO) compounds. - The activity of biological enzymes in enzyme-containing acidic cleaning agents under certain environmental conditions is effectively protected, thus preserving the chelating function of diethylenetriaminepentaacetic acid.

[0058] During their research, the inventors discovered that diethylenetriaminepentaacetic acid (DTPA) is a potent multidentate chelating agent for Ca2+. 2 ⁺、Ba 2 ⁺、Sr 2 ⁺、Fe 3 Metal ions such as ⁺ have high complexation constants, but diethylenetriaminepentaacetic acid, as a chelating agent, is not only affected by free chlorine in the influent (such as ClO) - Due to the influence of [unclear], its cleaning effect is significantly limited in complex pollution systems. For example, it has limited ability to dissolve calcium sulfate deposits and is difficult to completely remove the crystal structure; it has slow chelation kinetics for iron / aluminum-based hydroxides and oxides and cannot effectively disperse organic-inorganic composite colloidal pollutants.

[0059] Example 5 differs from Example 4 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid and diethylenetriaminepentamethylenephosphonic acid (CAS No. 15827-60-8) in a mass ratio of 1:0.2.

[0060] Example 6 differs from Example 4 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, and phosphonocarboxylic acid copolymer in a mass ratio of 1:0.2:0.05. The phosphonocarboxylic acid copolymer is model BP-8W28 and was purchased from Bangpu Chemical (Shandong) Co., Ltd.

[0061] Example 7 differs from Example 4 only in that the chelating agent is composed of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer and hydrolyzed polymaleic anhydride in a mass ratio of 1:0.2:0.05:0.03. The hydrolyzed polymaleic anhydride is of model GN-19025 and was purchased from Shandong Huayou Water Treatment Technology Co., Ltd.

[0062] Example 8 differs from Example 4 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, and hydrolyzed polymaleic anhydride in a mass ratio of 1:0.2:0.03.

[0063] Example 9 differs from Example 4 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid, phosphonocarboxylic acid copolymer and hydrolyzed polymaleic anhydride in a mass ratio of 1:0.05:0.03.

[0064] Example 10 differs from Example 7 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, hydrolyzed polymaleic anhydride, and sodium phytate (CAS No. 14306-25-3) in a mass ratio of 1:0.2:0.05:0.03:0.06.

[0065] Example 11 differs from Example 7 only in that the chelating agent is composed of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, hydrolyzed polymaleic anhydride, and polyaspartic acid in a mass ratio of 1:0.2:0.05:0.03:0.08. The polyaspartic acid has a CAS number of 25608-40-6 and a molecular weight of 6000, and was purchased from Shanghai Kanglang Biotechnology Co., Ltd.

[0066] Example 12 differs from Example 7 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, hydrolyzed polymaleic anhydride, sodium phytate and polyaspartic acid in a mass ratio of 1:0.2:0.05:0.03:0.08.

[0067] Example 13 differs from Example 7 only in that the chelating agent is a mixture of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, sodium phytate and polyaspartic acid in a mass ratio of 1:0.2:0.03:0.08.

[0068] The enzyme-containing acidic cleaning agents prepared in Examples 4-13 were placed at 25°C and normal pressure for 1 day and then used to clean inorganically fouled reverse osmosis membranes, inorganically fouled reverse osmosis membrane 2, and organic-inorganic composite colloidal fouled reverse osmosis membranes. The cleaning time for inorganically fouled reverse osmosis membranes and inorganically fouled reverse osmosis membrane 2 was 2 hours, and the cleaning time for organic-inorganic composite colloidal fouled reverse osmosis membranes was 3 hours. After cleaning, the flux recovery rate of the reverse osmosis membranes was measured, and the test results are shown in Table 3.

[0069] The preparation steps for the inorganically fouled reverse osmosis membrane are the same as those for the inorganically fouled reverse osmosis membrane 2, except that the raw water is a salt solution with a total salt content of 2000 mg / L, and does not contain free chlorine (ClO₂). - ).

[0070] Organic-inorganic composite colloids refer to stable colloidal particles (1nm-1μm in diameter) formed by the combination of inorganic particle cores (such as metal oxides, silicates, and carbonates) and organic shells or bridging agents (such as humic acid, proteins, and polysaccharides) through electrostatics, hydrogen bonds, complexation, or physical encapsulation. They carry a negative charge on their surface, are easily adsorbed on membrane surfaces, have a "gel-like" structure, block membrane pores, and are more difficult to clean than single inorganic or organic colloids.

[0071] The preparation steps for reverse osmosis membranes fouled by organic-inorganic composite colloids are the same as those for reverse osmosis membranes fouled by organic matter, except that the organic pollutants are replaced with organic-inorganic composite colloidal pollutants. Specifically, the steps for adding organic-inorganic composite colloidal pollutants to the raw water are as follows: add 100 mL of humic acid-ferric hydroxide colloidal stock solution with a concentration of 50 mg / L (calculated as Fe), 100 mL of protein-ferric oxide colloidal stock solution with a concentration of 50 mg / L (calculated as Fe), 5 mg / L of humic acid-ferric hydroxide colloid, 100 mL of polysaccharide-ferric hydroxide colloidal stock solution with a concentration of 50 mg / L (calculated as Al), 100 mL of humic acid-aluminum hydroxide colloidal stock solution with a concentration of 50 mg / L (calculated as Si), and 100 mL of silicate-humic acid composite colloidal stock solution with a concentration of 50 mg / L (calculated as Si) to 1 L of raw water. The preparation steps of humic acid-ferric hydroxide colloid are as follows: 0.75 mg FeCl3·6H2O is dissolved in 90 mL of raw water, the pH is adjusted to 7.0 with 0.1 mol / L NaOH aqueous solution, and hydrolyzed under stirring to generate ferric hydroxide colloid; then 3.0 mg sodium humate is added, stirring is continued for 2 h, and the volume is adjusted to 100 mL with the above raw water to obtain a humic acid-ferric hydroxide colloid stock with a concentration of 50 mg / L (calculated as Fe); The preparation steps of protein-iron oxide colloid are as follows: Dissolve 0.75 mg FeCl3·6H2O in 90 mL of raw water, adjust the pH to 8.0 to generate Fe(OH)3 precipitate, and further oxidize it to Fe2O3 colloid nucleus; add 3.0 mg bovine serum albumin, stir for 2 h to allow the protein to be adsorbed on the particle surface, and make up the volume to 100 mL with raw water to obtain a protein-iron oxide colloid stock solution with a concentration of 50 mg / L (calculated as Fe); The preparation steps of polysaccharide-ferric hydroxide colloid are as follows: dissolve 0.75 mg FeCl3·6H2O in 90 mL of raw water, adjust the pH to 7.0 to generate ferric hydroxide colloid; add 3.0 mg sodium alginate, stir for 2 h, and make up to 100 mL with raw water to obtain a polysaccharide-ferric hydroxide colloid stock solution with a concentration of 50 mg / L (calculated as Fe); The preparation steps of humic acid-aluminum hydroxide colloid are as follows: Dissolve 0.65 mg AlCl3·6H2O in 90 mL of raw water, adjust the pH to 6.5 to generate Al(OH)3 colloid; add 3.0 mg sodium humate, stir for 2 h, and make up to 100 mL with raw water to obtain a humic acid-aluminum hydroxide colloid stock solution with a concentration of 50 mg / L (calculated as Al); The preparation steps of the silica-humic acid composite colloid are as follows: Dissolve 10 mg Na2SiO3·9H2O in 100 mL of raw water, adjust the pH to 8.5, and let it stand for 24 h to form a silica sol; take 90 mL of the sol, add 3.0 mg sodium humate, stir for 2 h, and you will get a silica-humic acid composite colloid stock solution with a concentration of 50 mg / L (calculated as Si).

[0072] Table 3 Comparing the experimental data of Example 7 with Examples 4-6 and 8-9 in Table 3, it can be seen that Example 7, by adding diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylphosphonic acid, phosphonocarboxylic acid copolymer, and hydrolyzed polymaleic anhydride to diethylenetriaminepentaacetic acid, significantly improved the flux recovery rate of all three fouled membranes, indicating a significant synergistic effect of the components. In the cleaning of inorganic fouled membranes, Example 7 achieved a flux recovery rate of 98.0%, significantly higher than the 95.0% of Example 4 (diethylenetriaminepentaacetic acid alone); in the presence of 0.05 ppm free chlorine (ClO₂), the flux recovery rate was also significantly improved. - Under the operating conditions described above, Example 7 still maintained a high recovery rate of 95.0%, significantly better than the 89.8% of Example 4, indicating that diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, and hydrolyzed polymaleic anhydride jointly enhanced the antioxidant stability of the system. In the cleaning of organic-inorganic composite colloidal fouling, the flux recovery rate of Example 7 increased from 60.0% to 85.3%, highlighting the key role of phosphonocarboxylic acid copolymer in disrupting metal-organic crosslinks and hydrolyzed polymaleic anhydride in efficiently dispersing colloids. Therefore, Example 7 constructed an integrated "chelation-inhibition-dispersion" cleaning system by compounding diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, and hydrolyzed polymaleic anhydride. This system not only overcomes the limitations of diethylenetriaminepentaacetic acid alone in terms of chlorine resistance, lattice dissolution, and colloidal dispersion, but also exhibits a significant synergistic effect in cleaning inorganically fouled reverse osmosis membrane 2 and organic-inorganic composite colloidal fouling reverse osmosis membranes. This is likely because diethylenetriaminepentaacetic acid (DTI) acts as the base chelating agent, primarily functioning to chelate Ca. 2 ⁺、Ba 2 ⁺、Sr 2 ⁺、Fe 3 ⁺ and other metal ions; diethylenetriaminepentamethylenephosphonic acid enhances the chelating power of metal ions, especially Fe. 3 ⁺、Al 3High-valence metal ions such as ⁺ have stronger complexing ability and are resistant to oxidation; phosphonocarboxylic acid copolymers have both chelating and dispersing functions, can destroy organic-inorganic crosslinking points, and inhibit polymerization reactions, making them particularly suitable for treating organic-inorganic composite colloidal contamination; hydrolyzed polymaleic anhydride has excellent dispersing properties, prevents particle redeposition, and is particularly suitable for treating contaminants in already formed colloidal networks.

[0073] Comparing the experimental data of Example 12 with Examples 7, 10-11, and 13 in Table 3, it can be seen that Example 12, which combines diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer, hydrolyzed polymaleic anhydride, sodium phytate, and polyaspartic acid, not only overcomes the limitations of diethylenetriaminepentaacetic acid alone in terms of chlorine resistance and colloidal dispersion, but also achieves a further improvement in flux recovery rate. Especially under the conditions of inorganic matter containing free chlorine and organic-inorganic composite colloidal contamination, the flux recovery rate of Example 12 reaches 99.0% and 92.4%, respectively, which is significantly better than that of Examples 7, 10-11, and 13. Further analysis revealed a significant synergistic effect among hydrolyzed polymaleic anhydride, sodium phytate, and polyaspartic acid, particularly in their combined performance of anti-redeposition, interfacial protection, and colloidal decomposition. This is attributed to the following: hydrolyzed polymaleic anhydride provides bulk dispersion; sodium phytate adsorbs onto the membrane surface, forming a charge barrier and inhibiting pollutant adsorption; and polyaspartic acid, with its strong hydrophilicity, penetrates and dissociates the composite structure. The complementary mechanisms of these three components result in a synergistic effect in organic-inorganic composite colloidal cleaning. Furthermore, although hydrolyzed polymaleic anhydride, sodium phytate, and polyaspartic acid are not direct antioxidants, they significantly enhance the chlorine resistance of the cleaning system under conditions containing free chlorine (0.05 ppm ClO⁻) through a synergistic mechanism. Sodium phytate, in particular, chelates Fe... 3 ⁺ By inhibiting free radical oxidation, polyaspartic acid forms a hydration protective layer on the membrane surface, while hydrolyzed polymaleic anhydride reduces the adsorption of oxidizing substances through electrostatic repulsion. These three mechanisms complement each other. Example 12 achieved a flux recovery rate of 99.0% under chlorine-containing conditions, an increase of 1.2% compared to Example 7, indicating the construction of a three-pronged chlorine-resistant protection system of "inhibition-protection-dispersion," further effectively mitigating the oxidative damage of free chlorine to diethylenetriaminepentaacetic acid.

[0074] The specific embodiments are merely explanations of this application and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems, characterized in that, The raw materials for its preparation, by weight percentage, include: 5-25% organic acid, 1-5% chelating agent, 5% stabilizer, 1-5% biological enzyme, 0.5-3% surfactant, and the balance being deionized water; the stabilizer includes alanine, trehalose, PEG and ε-polylysine, and the mass ratio of alanine, trehalose, PEG and ε-polylysine is 1:(0.3-0.4):(0.1-0.2):(0.05-0.1).

2. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 1, characterized in that, The stabilizer also includes N-acetylcysteine ​​and sodium ferulic acid, wherein the mass ratio of trehalose, ε-polylysine, N-acetylcysteine ​​and sodium ferulic acid is (0.3-0.4): (0.05-0.1): (0.2-0.3): (0.08-0.15).

3. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 1, characterized in that, The PEG is selected from one or more of PEG2000, PEG3000, and PEG4000.

4. An enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to any one of claims 1-3, characterized in that, By weight percentage, it consists of the following components: 20% organic acid, 5% chelating agent, 5% stabilizer, 5% bio-enzyme, 3% surfactant, and the balance deionized water.

5. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 1, wherein the chelating agent comprises diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer and hydrolyzed polymaleic anhydride; wherein the mass ratio of diethylenetriaminepentaacetic acid, diethylenetriaminepentamethylenephosphonic acid, phosphonocarboxylic acid copolymer and hydrolyzed polymaleic anhydride is 1:(0.2-0.3):(0.05-0.08):(0.03-0.05).

6. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 5, characterized in that, The chelating agent further includes sodium phytate and polyaspartic acid, and the mass ratio of diethylenetriaminepentaacetic acid, hydrolyzed polymaleic anhydride, sodium phytate and polyaspartic acid is 1:(0.03-0.05):(0.06-0.08):(0.08-0.15).

7. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 1, characterized in that, The surfactant is a fatty alcohol polyoxyethylene ether.

8. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 1, characterized in that, The organic acid is selected from one or more of citric acid, glycolic acid, and formic acid.

9. The enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to claim 1, characterized in that, The bioenzyme is selected from one or more of acidic protease, acidic cellulase, α-amylase, pectinase, and lipase.

10. A method for preparing an enzyme-containing acidic cleaning agent for reverse osmosis and nanofiltration systems according to any one of claims 1-9, characterized in that, Includes the following steps: The biological enzyme, surfactant and stabilizer are mixed and stirred evenly to obtain mixture 1; Mix the organic acid and chelating agent, stir well, then add mixture 1 and stir well to obtain an enzyme-containing acidic cleaning agent.

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