Preparation method and application of sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membrane

Abstract

The application discloses a preparation method and application of a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes, and belongs to the technical field of scale inhibitors.The application aims to solve the technical problems of existing protein source scale inhibitors, such as complex components, easy pollution of nanofiltration membranes or leakage to the water production side, and lack of a safe dosing control method considering scale inhibition effect, membrane pollution, water production leakage and enrichment on the concentrated water side.The scale inhibitor is prepared from sunflower seed meal through pretreatment, protein extraction, controlled enzymolysis, ultrafiltration grading and nanofiltration grading.The scale inhibitor can complex calcium, magnesium and other scale-forming ions through carboxyl groups, reduce the effective concentration of the scale-forming ions participating in scale formation reactions, and is adsorbed on crystal nucleus and crystal growth active sites to interfere with nucleation and crystal face growth of inorganic salts.The hydrophilic groups and steric hindrance of the peptide chain can also reduce the aggregation and membrane surface deposition of microcrystalline particles.The scale inhibitor can be continuously dosed before the membrane of an existing nanofiltration system.The scale inhibitor can be applied to the field of water treatment.

Description

Technical Field

[0001] This invention belongs to the field of scale inhibitor technology, specifically relating to the preparation method and application of a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes. Background Technology

[0002] Pressure-driven membrane separation technology has been widely applied in drinking water treatment and unconventional water resource development. Nanofiltration membranes, with their high water flux and selective separation capability for multivalent ions, play a crucial role in high-quality drinking water preparation and reverse osmosis pretreatment. However, during operation, scale-forming ions such as calcium and magnesium in the feed water gradually concentrate, easily forming inorganic scale layers such as calcium carbonate and calcium sulfate on the membrane surface. This leads to increased operating pressure and membrane performance degradation, severely impacting the long-term stable operation of the membrane system. Existing nanofiltration membrane antiscalants are mostly organophosphorus, polycarboxylic acid, or sulfonic acid-containing polymers. Some of these products have issues such as phosphorus content, poor biodegradability, or reliance on petrochemical raw materials, making it difficult to simultaneously meet the requirements of stable membrane system operation and environmental friendliness.

[0003] Agricultural by-product protein hydrolysates have the potential to act as green scale inhibitors by complexing with scale-forming ions such as calcium and magnesium, and adsorbing crystal nuclei and active sites for crystal growth. However, unselectively graded protein hydrolysates have complex compositions. When the degree of hydrolysis is insufficient, residual proteins, macropeptides, and aggregates are easily retained by nanofiltration membranes and deposited on the concentrate side, causing organic pollution. When the degree of hydrolysis is too high, more free amino acids and short peptides are generated. These components have limited multi-site complexing and crystal face adsorption capabilities and are prone to breakthrough fouling. Furthermore, existing protein hydrolysate scale inhibitors usually require modification before application to meet scale inhibition performance requirements, which undoubtedly increases costs. Although methods such as ion exchange, chromatographic separation, or electroporation can further purify the scale, their equipment investment and operating costs are high, making it difficult to meet the requirements for large-scale production of water treatment agents. In addition, after being retained by nanofiltration membranes, protein-derived scale inhibitors will continue to accumulate on the concentrate side as the system recovery rate increases, and may form higher local concentrations on the membrane surface due to concentration polarization. When the dosage is too low, it is difficult to effectively inhibit inorganic salt scaling, while when the dosage is too high, it may cause peptide aggregation or organic deposition on the membrane surface. Therefore, the existing technology lacks a method for preparing a green scale inhibitor with suitable membrane transfer characteristics that can remove easily fouled and leaky components at low cost, and also lacks a safe dosage control method that takes into account scale inhibition effect, membrane fouling, permeate leakage and concentrate enrichment. Summary of the Invention

[0004] The purpose of this invention is to address the technical problems of existing protein-derived scale inhibitors, such as complex compositions, susceptibility to nanofiltration membrane fouling or leakage to the permeate side, and the lack of a safe dosing control method that balances scale inhibition, membrane fouling, permeate leakage, and concentrate enrichment. This invention provides a method for preparing and applying an acidic functional peptide scale inhibitor from sunflower seed meal for nanofiltration membranes.

[0005] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing an acidic functional peptide scale inhibitor from sunflower seed meal for nanofiltration membranes, the method comprising the following steps: Step 1: Crush and sieve the sunflower seed meal, and then wash it to remove residual oil, phenolic substances, pigments, soluble salts and crude fiber to obtain pretreated sunflower seed meal. Step 2: Mix the pretreated sunflower seed meal with water and extract the protein under alkaline conditions to obtain a protein extract. Step 3: Add alkaline protease or a complex protease including alkaline protease to the protein extract for enzymatic hydrolysis. The amount of enzyme added is 0.5-2% of the soluble protein in the protein extract. Under controlled conditions of pH 7-8.5 and temperature 40-60℃ with stirring, hydrolyze for 1-4 h. After hydrolysis, inactivate the enzyme, centrifuge, and microfilter to obtain a clear hydrolysate. Step 4: The clarified enzymatic hydrolysate is fractionated using an ultrafiltration membrane to retain residual proteins, macropeptides, hydrophobic aggregates, and colloidal particles, resulting in an ultrafiltration permeate containing oligopeptides and small peptides. Step 5: The ultrafiltration permeate is fractionated using a nanofiltration membrane to allow inorganic salts, free amino acids, and short peptides to enter the nanofiltration permeate. The nanofiltration retentate rich in acidic functional peptides is collected. The nanofiltration retentate is replenished with water or washed at least once. Then, one or more of the following methods are used in combination: end filtration, concentration, and drying to obtain a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes.

[0006] Further specifying, the cleaning in step 1 uses one or more of the following methods in combination: water washing, acid washing, or salt washing.

[0007] Further specified, the material-to-liquid mass ratio in step 2 is 1:(8-12), the pH is adjusted to 9.0 using sodium hydroxide solution in step 2, and the extraction is carried out at 45℃ with stirring at 300 r / min for 60 min.

[0008] Further specifying, the complex protease in step 3 consists of alkaline protease and neutral protease.

[0009] Further specifying, in step 3, the enzyme is inactivated by raising the temperature or adjusting the pH to deactivate the protease.

[0010] Further specifying, the molecular weight cutoff of the ultrafiltration membrane in step 4 is 3-10 kDa.

[0011] Further specifying, the molecular weight cutoff of the nanofiltration membrane in step 5 is 300-500 Da.

[0012] The second objective of this invention is to provide an application of the sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes prepared by the above method in the field of water treatment based on nanofiltration membrane systems.

[0013] Further specifying, the scale inhibitor is added to the feed water to be treated before the nanofiltration membrane module.

[0014] Further specify that the dosage of scale inhibitor is 5-10 mg / L based on the influent volume.

[0015] The advantages of this invention compared to existing technologies are: (1) This invention uses sunflower seed meal as raw material and obtains acidic functional peptides rich in carboxyl sites through controlled enzymatic hydrolysis, thereby realizing the resource utilization of agricultural by-product protein and reducing dependence on phosphorus-containing scale inhibitors and petrochemical-derived polymer raw materials. The controlled enzymatic hydrolysis does not target the maximum degree of hydrolysis, thus avoiding excessive hydrolysis that produces too many free amino acids and excessively short peptides. This is beneficial for reducing the residual protein content while retaining the multi-site complexing, crystal face adsorption, and steric hindrance effects of the peptides.

[0016] (2) This invention employs a combined membrane fractionation method of "ultrafiltration permeation-nanofiltration retention". The ultrafiltration step removes residual proteins, macromolecular peptides, hydrophobic aggregates, and suspended particles. Then, nanofiltration fractionation is performed using the differences in molecular size and charge characteristics of different components, allowing some inorganic salts, free amino acids, and excessively short peptides to enter the permeate, thereby obtaining acidic functional peptide-enriched components with specific membrane transfer windows. Compared with ion exchange or chromatographic fine purification, this method is relatively simple and suitable for continuous and large-scale production.

[0017] (3) The method of this invention enables control over indicators such as molecular weight distribution, carboxyl equivalent, free amino acid ratio, turbidity, ash content, hard water compatibility, and target nanofiltration membrane rejection rate of the product, which is beneficial to improving the batch stability of the product. The obtained functional peptides can be effectively retained by the target nanofiltration membrane, and continuously exert their functions of complexing scale ions, inhibiting crystal nucleus formation, interfering with crystal growth, and dispersing microcrystalline particles on the concentrate side, while reducing the leakage of scale inhibitor to the product water side.

[0018] (4) This invention determines the safe dosing window based on the minimum effective scale inhibition concentration, the critical concentration of autonomous organic fouling, the permeate leakage limit, and the concentrate enrichment limit, and incorporates the effects of membrane retention, system recovery rate, and concentration polarization on the local concentration of the scale inhibitor into the control. As a result, while ensuring the scale inhibition effect, it can reduce the risk of peptide self-aggregation, calcium bridge aggregation, and organic deposition on the membrane surface, and can be implemented using the existing nanofiltration system's pre-membrane continuous dosing method. Attached Figure Description

[0019] Figure 1 This is a comparison chart of the calcium sulfate scale inhibition rates of the samples obtained in Examples 1-12 and Comparative Examples 1-4; Figure 2 This is a schematic diagram of the cross-flow nanofiltration membrane test system used in the dynamic scale inhibition performance test of the nanofiltration membrane of the present invention; Figure 3 This is a graph showing the normalized membrane flux of the blank group and the preferred sample A7 as a function of operating time in the dynamic scale inhibition experiment of the nanofiltration membrane of the present invention. Figure 4 This is a comparison chart of the membrane flux decrease rate and membrane flux recovery rate between the blank group and the preferred sample A7 in the dynamic scale inhibition experiment of the nanofiltration membrane of the present invention. Figure 5 The graph shows the changes in membrane flux decline rate, membrane flux recovery rate, and total organic carbon concentration in the effluent corresponding to the dosage of the preferred sample A7 in Application Example 1. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0022] Example 1: The preparation method of the sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes in this example is carried out according to the following steps: Step 1: Weigh 100 g of defatted sunflower seed meal, crush it and pass it through a 60-mesh sieve. Add 1000 mL of deionized water and wash it at 300 r / min for 20 min at 25℃. After filtration, repeat the washing process once under the same conditions. After solid-liquid separation, obtain pretreated sunflower seed meal. Step 2: Mix the pretreated sunflower seed meal and deionized water at a mass ratio of 1:10. Adjust the pH to 9.0 using a 10% sodium hydroxide solution. Extract at 45℃ with stirring at 300 r / min for 60 min. After extraction, centrifuge at 6000 r / min for 10 min, collect the supernatant to obtain the protein extract, and determine the soluble protein concentration using the Coomassie Brilliant Blue method. Calculate the amount of soluble protein based on the total volume of the protein extract and the soluble protein concentration. Step 3: Adjust the pH of the protein extract to 8.5 and the temperature to 50℃. Add alkaline protease at 1.0% of the soluble protein in the protein extract and hydrolyze for 120 min under stirring at 300 r / min to obtain protein hydrolysate. Heat the protein hydrolysate to 90℃ and keep it at that temperature for 10 min to inactivate the alkaline protease. After cooling to 25℃, adjust the pH to 7.0 and centrifuge at 8000 r / min for 15 min. Collect the supernatant and filter it through a microfiltration membrane with a pore size of 0.45 μm to obtain a clear enzymatic hydrolysate. Step 4: Cross-flow ultrafiltration of the clarified enzyme hydrolysate was performed using an ultrafiltration membrane with a molecular weight cutoff of 5 kDa. The operating temperature was 25℃ and the transmembrane pressure was 0.15 MPa. The ultrafiltration permeate containing oligopeptides and small peptides was collected. Step 5: The ultrafiltration permeate was fractionated using a nanofiltration membrane with a molecular weight cutoff of 300 Da. The operating temperature was 25℃ and the transmembrane pressure was 1.5 MPa. The ultrafiltration permeate was concentrated to one-quarter of its initial volume. Then, an equal volume of deionized water was added to the obtained nanofiltration retentate, and the volume was concentrated again to the volume before water replenishment. This completed one water replenishment and filtration cycle. The nanofiltration retentate was collected, and the pH was adjusted to 7.0±0.2. It was then filtered through a 0.45 μm pore size membrane for final filtration. The solid content was then adjusted to 10% by concentration to obtain a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes, denoted as sample A1.

[0023] Example 2 The difference between this embodiment and Example 1 is that the mass of alkaline protease added in step 3 is 0.5% of the soluble protein mass. Other steps and parameters are the same as in Example 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A2.

[0024] Example 3 The difference between this embodiment and Example 1 is that the mass of alkaline protease added in step 3 is 2.0% of the soluble protein mass. Other steps and parameters are the same as in Example 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A3.

[0025] Example 4 The difference between this embodiment and Example 1 is that the enzymatic hydrolysis time in step 3 is adjusted from 120 min to 60 min. Other steps and parameters are the same as in Example 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A4.

[0026] Example 5 The difference between this embodiment and Example 1 is that the enzymatic hydrolysis time in step 3 is adjusted from 120 min to 240 min. Other steps and parameters are the same as in Example 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A5.

[0027] Example 6 The difference between this embodiment and Example 1 is that in step 3, the pH of the protein extraction solution is adjusted to 7.0, the protease is replaced by a neutral protease instead of an alkaline protease, and the amount of protease added, as well as other steps and parameters, are the same as in Example 1. Finally, a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is obtained, denoted as sample A6.

[0028] Example 7 The difference between this embodiment and Example 1 is as follows: In step 3, the pH of the protein extract is first adjusted to 8.5, the temperature is adjusted to 50°C, and 0.5% alkaline protease (based on the soluble protein content) is added. Enzymatic hydrolysis is then performed for 60 min under stirring at 300 r / min. Subsequently, the pH is adjusted to 7.0, and 0.5% neutral protease (based on the soluble protein content) is added. Enzymatic hydrolysis continues for 60 min under stirring at 50°C and 300 r / min to obtain a composite enzymatically hydrolyzed protein solution. Other steps and parameters are the same as in Example 1. Finally, an acidic functional peptide scale inhibitor from sunflower seed meal for nanofiltration membranes is obtained, designated as sample A7.

[0029] Example 8 The difference between this embodiment and Example 1 is that the molecular weight cutoff of the ultrafiltration membrane in step 4 is changed from 5 kDa to 3 kDa. Other steps and parameters are the same as in Example 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A8.

[0030] Example 9 The difference between this embodiment and Embodiment 1 is that the molecular weight cutoff of the ultrafiltration membrane in step 4 is changed from 5 kDa to 10 kDa. Other steps and parameters are the same as in Embodiment 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A9.

[0031] Example 10 The difference between this embodiment and Embodiment 1 is that the molecular weight cutoff of the nanofiltration membrane in step 5 is changed from 300 Da to 500 Da. Other steps and parameters are the same as in Embodiment 1. The resulting sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is designated as sample A10.

[0032] Example 11 The difference between this embodiment and Embodiment 1 is that in step 5, the ultrafiltration permeate is concentrated to one-quarter of its initial volume. After concentration, deionized water is not added for makeup water washing; instead, the nanofiltration retentate is directly collected for subsequent end-stage filtration. Other steps and parameters are the same as in Embodiment 1. Finally, a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is obtained, denoted as sample A11.

[0033] Example 12 The difference between this embodiment and Embodiment 1 is that in step 5, the ultrafiltration permeate is concentrated to one-quarter of its initial volume. An equal volume of deionized water is added to the resulting nanofiltration retentate, and the concentration is repeated to the volume before replenishment, completing one replenishment filtration. Then, an equal volume of deionized water is added again in the same manner, and the concentration is repeated to the volume before replenishment, completing two replenishment filtrations in total. Other steps and parameters are the same as in Embodiment 1. Finally, a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes is obtained, designated as sample A12.

[0034] Comparative Example 1 This comparative example provides a sunflower seed meal protein hydrolysate without ultrafiltration and nanofiltration fractionation. The preparation method differs from that of Example 1 in that: the clarified enzymatic hydrolysate obtained in step 3 is not subjected to ultrafiltration and nanofiltration fractionation, but is directly concentrated under reduced pressure at a temperature not exceeding 45°C, and the pH is adjusted to 7.0±0.2. It is then filtered at the end through a filter membrane with a pore size of 0.45 μm, and the solid content is adjusted to 10% to obtain sunflower seed meal protein hydrolysate without membrane fractionation, which is denoted as sample B1.

[0035] Comparative Example 2 This comparative example provides a sunflower seed meal protein hydrolysate that has undergone only ultrafiltration fractionation. The preparation method differs from that of Example 1 in that: the ultrafiltration permeate obtained in step 4 is not subjected to nanofiltration fractionation, but is directly concentrated under reduced pressure at a temperature not exceeding 45°C. The pH of the concentrate is adjusted to 7.0±0.2, and then filtered at the end through a filter membrane with a pore size of 0.45 μm. The solid content is then adjusted to 10% to obtain the sunflower seed meal protein hydrolysate that has undergone only ultrafiltration fractionation, which is designated as sample B2.

[0036] Comparative Example 3 This comparative example provides a sunflower seed meal protein hydrolysate that undergoes direct nanofiltration fractionation without ultrafiltration fractionation. The preparation method differs from Example 1 in that the clarified enzymatic hydrolysate obtained in step 3 is not subjected to ultrafiltration fractionation in step 4, but directly proceeds to step 5. The resulting sunflower seed meal protein hydrolysate that undergoes direct nanofiltration fractionation without ultrafiltration fractionation is designated as sample B3.

[0037] Comparative Example 4 This comparative example provides a sunflower seed meal protein hydrolysate obtained through excessive enzymatic hydrolysis and combined membrane fractionation. The preparation method differs from Example 1 in that: the pH of the protein extract obtained in step 2 is adjusted to 8.5, the temperature is adjusted to 50°C, and 3.0% (by weight of soluble protein) of alkaline protease is added. Enzymatic hydrolysis is carried out at 300 r / min for 360 min with stirring to obtain an over-hydrolyzed protease hydrolysate. Subsequent enzymatic hydrolysis steps are the same as in Example 1. The sunflower seed meal protein hydrolysate obtained through excessive enzymatic hydrolysis and combined membrane fractionation is designated as sample B4.

[0038] Performance verification To evaluate the scale inhibition performance of the sunflower seed meal acidic functional peptide scale inhibitor prepared in this invention and its application effect in nanofiltration membrane systems, static scale inhibition tests, nanofiltration membrane dynamic scale inhibition tests, and safe dosing window determinations were conducted on the samples obtained in Examples 1-12 and Comparative Examples 1-4, respectively. Unless otherwise stated, the actual dosage of each sample was calculated based on the solids content, and each test was performed in triplicate, with the average value of the test results taken.

[0039] I. Static scale inhibition performance of calcium sulfate The static scale inhibition performance of calcium sulfate was tested on the samples obtained in Examples 1-12 and Comparative Examples 1-4. Calcium chloride and sodium sulfate solutions were prepared, and the two test solutions were mixed to ensure that the concentrations of calcium ions and sulfate ions in the final test solution were both 250 mg / L. The samples were then added separately to achieve an effective dosage concentration of 5 mg / L.

[0040] The pH of each test solution was adjusted to 8.5±0.1, and the solutions were kept at 80±1℃ for 6 h. After the incubation period, the solutions were cooled to room temperature, filtered using medium-speed quantitative filter paper, and the concentration of residual calcium ions in the filtrate was measured. A blank group without scale inhibitor and an initial group without incubation were also included.

[0041] The scale inhibition rate of calcium sulfate is calculated according to the following formula: η(%)=(ρ1-ρ0) / (ρ2-ρ0)×100% In the formula, η is the scale inhibition rate of calcium sulfate, ρ1 is the calcium ion concentration in the filtrate after adding scale inhibitor and constant temperature treatment, ρ0 is the calcium ion concentration in the filtrate of the blank test solution without scale inhibitor after constant temperature treatment, and ρ2 is the calcium ion concentration in the initial test solution without constant temperature treatment.

[0042] The scale inhibition rate results are as follows Figure 1As shown, to facilitate comparison of the effects of different preparation conditions on scale inhibition performance, Example 1 was used as a common baseline, and the implementations were divided into different parameter groups. Examples 1, 2, and 3 were used to compare the effect of alkaline protease addition; Examples 1, 4, and 5 were used to compare the effect of enzymatic hydrolysis time; Examples 1, 6, and 7 were used to compare the effect of enzymatic hydrolysis method; Examples 1, 8, and 9 were used to compare the effect of ultrafiltration membrane molecular weight cutoff; Examples 1 and 10 were used to compare the effect of nanofiltration membrane retention characteristics; and Examples 1, 11, and 12 were used to compare the effect of the number of water replenishment and filtration cycles. Comparative Examples 1-4 were used to illustrate the role of process steps such as combined membrane fractionation, ultrafiltration pre-fractionation, and controlled enzymatic hydrolysis.

[0043] Table 1 Scale inhibition rate test results

[0044] Depend on Figure 1 As shown in Table 1, the calcium sulfate scale inhibition rate of the acidic functional peptide scale inhibitors obtained in Examples 1-12 was 81.63%-94.18%, which was higher than that of Comparative Examples 1-4 (66.24%-83.57%). This indicates that the raw material pretreatment, protein extraction, controlled enzymatic hydrolysis, clarification, and ultrafiltration-nanofiltration combined fractionation process required by this invention can effectively obtain acidic functional peptide components with scale inhibition activity. The amount of alkaline protease added, the hydrolysis time, the hydrolysis method, the membrane retention characteristics, and the number of water washing cycles all affect the scale inhibition effect. Increasing the amount of enzyme added, extending the hydrolysis time, or increasing the degree of washing does not necessarily lead to a continuous increase in the scale inhibition rate. Among them, sample A7, obtained by staged compound enzymatic hydrolysis, had the highest scale inhibition rate, reaching 94.18%, indicating that appropriate adjustment of the hydrolysis conditions and membrane fractionation process is beneficial to obtaining acidic functional peptide components with high scale inhibition activity.

[0045] II. Dynamic scale inhibition performance of nanofiltration membranes To evaluate the actual scale inhibition effect of sample A7 prepared in the preferred embodiment in the nanofiltration membrane system, a cross-flow nanofiltration membrane test apparatus (see...) was used. Figure 2 Dynamic scale inhibition tests were conducted. The tests included a control group and a scale inhibitor group. The control group received no scale inhibitor, while the scale inhibitor group received 5 mg / L of sample A7. An NF270 nanofiltration membrane with an effective membrane area of ​​140 cm² was used in the tests. 2 The membrane was pre-pressurized with deionized water at 0.6 MPa for 2 hours until the membrane flux stabilized. Calcium-containing and sulfate-containing solutions were prepared using calcium chloride and sodium sulfate and mixed before entering the nanofiltration membrane unit. The concentrations of calcium and sulfate ions in the mixed test feed water were 250 mg / L. The nanofiltration experiment was conducted at 0.4 MPa with a cross-flow velocity of 0.20 m / s at the membrane surface.

[0046] Nanofiltration membrane flux is calculated using the following formula: J = V / (A × t) In the formula, J is the nanofiltration membrane flux, with units of L / (m²). 2 (·h); V is the volume of permeate collected within time t, in L; A is the effective membrane area, in m². 2 t represents the water collection time, in hours (h).

[0047] Standardized membrane flux is calculated using the following formula: F (%) = J t / J0×100% In the formula, F is the standardized membrane flux, J0 is the initial membrane flux at the start of the experiment, and J t This represents the membrane flux after t hours of operation.

[0048] After the experiment, the membranes were rinsed with deionized water. Membranes of the same area were taken and dried at 45°C to constant weight. The mass of deposit per unit membrane area was calculated based on the mass difference before and after the experiment. Simultaneously, the pure water flux after rinsing was measured, and the membrane flux decline rate (FDR) and membrane flux recovery rate (FRR) were calculated using the following formulas: FDR (%) = (J t - J0) / J0×100% FRR (%) = J c ÷ J0 × 100% In the formula, J c This represents the pure water flow rate after cleaning.

[0049] Depend on Figure 3 It can be seen that without scale inhibitor, the normalized membrane flux decreases rapidly due to the supersaturation of calcium sulfate. However, when sample A7 of the preferred embodiment is added, the membrane flux remains basically unchanged within 100 min and then decreases slowly. Figure 4 The results showed that the FDR was 89.55% and the FRR was 33.2% without the scale inhibitor, while the FDR was 7.11% and the FRR was 90.5% when the preferred embodiment A7 sample was added. This indicates that the acidic functional peptide scale inhibitor not only effectively prevented the formation and growth of calcium sulfate crystals, but also controlled membrane fouling to reversible fouling, which is beneficial to maintaining the cleaning and recovery performance and operational stability of the nanofiltration membrane.

[0050] Application Example 1: Dynamic scale inhibition tests were conducted using the aforementioned cross-flow nanofiltration device. The simulated influent calcium sulfate concentration was 250 mg / L, and the pH was 7.0±0.2. The test temperature was 25±1 ℃, the transmembrane pressure was 0.4 MPa, and the cross-flow velocity was 0.20 m / s. The dosage concentrations of sample A7 were set to 0, 1, 2, 5, 10, 20, and 30 mg / L, respectively.

[0051] The determination of the safe dosing window considers the following conditions: in simulated feedwater containing calcium sulfate, the membrane flux decline rate after 24 hours of operation is no higher than 10%, and the membrane flux recovery rate after cleaning is no less than 95%; in simulated feedwater without scale-forming ions, the membrane flux decline rate caused by the reagent itself is no higher than 5%; and the total organic carbon concentration in the permeate is no higher than 0.50 mg / L. The dosing concentration range that simultaneously meets the above conditions is determined as the safe dosing window under the conditions of this experiment.

[0052] With a fixed system recovery rate of 70%, the dynamic scale inhibition performance, the risk of autonomous membrane fouling, and permeate leakage were investigated at different dosage concentrations. The initial membrane flux, the membrane flux after 120 min of operation, and the pure water flux after cleaning were recorded. The FDR and FRR were calculated according to the aforementioned formulas, and the total organic carbon (TOC) concentration in the effluent was measured.

[0053] Depend on Figure 5 It was found that when the dosage of sample A7 was 1-2 mg / L, the FDR was still higher than 10% after 120 min of operation, indicating that this dosage was insufficient to effectively control the nucleation and deposition of calcium sulfate on the membrane surface. When the dosage was increased to 5-20 mg / L, the FDR decreased to below 10%, and the FRR reached above 90%, indicating that this dosage range could significantly slow down the membrane flux decline caused by calcium sulfate scaling. When the dosage was further increased to 30 mg / L, the FDR increased to 13.99%, and the FRR decreased to below 90%, indicating that excessive accumulation of acidic functional peptides on the concentrate side may have an adverse effect on the operation and cleaning recovery of the nanofiltration membrane.

[0054] When the dosage of sample A7 was no higher than 10 mg / L, the total organic carbon concentration in the permeate was no higher than 0.50 mg / L, indicating that sample A7 did not cause significant autonomous membrane fouling within this dosage range, and the leakage on the permeate side was also low. When the dosage was increased to 20 mg / L and 30 mg / L, the total organic carbon concentration in the permeate increased to 0.86 mg / L and 1.42 mg / L, respectively, indicating that excessive acidic functional peptides may undergo peptide self-aggregation, membrane adsorption, or organic deposition after enrichment on the concentrate side, increasing the risk of leakage to the permeate side.

[0055] Based on the above results, under the experimental conditions of a calcium sulfate concentration of 250 mg / L, a system recovery rate of 70%, and a transmembrane pressure of 0.4 MPa, the dosage of sample A7 below 5 mg / L could not sufficiently inhibit calcium sulfate scaling, while the risk of autonomous membrane fouling and permeate leakage gradually increased when the dosage exceeded 10 mg / L. Therefore, 5-10 mg / L was determined to be the safe dosage window for sample A7 in the nanofiltration membrane system described above.

[0056] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes, characterized in that, The method described: Step 1: Crush and sieve the sunflower seed meal, and then wash it to remove residual oil, phenolic substances, pigments, soluble salts and crude fiber to obtain pretreated sunflower seed meal. Step 2: Mix the pretreated sunflower seed meal with water and extract the protein under alkaline conditions to obtain a protein extract. Step 3: Add alkaline protease or a complex protease including alkaline protease to the protein extract for enzymatic hydrolysis. The amount of enzyme added is 0.5-2% of the soluble protein in the protein extract. Under controlled conditions of pH 7-8.5 and temperature 40-60℃ with stirring, hydrolyze for 1-4 h. After hydrolysis, inactivate the enzyme, centrifuge, and microfilter to obtain a clear hydrolysate. Step 4: The clarified enzymatic hydrolysate is fractionated using an ultrafiltration membrane to retain residual proteins, macropeptides, hydrophobic aggregates, and colloidal particles, resulting in an ultrafiltration permeate containing oligopeptides and small peptides. Step 5: The ultrafiltration permeate is fractionated using a nanofiltration membrane to allow inorganic salts, free amino acids, and short peptides to enter the nanofiltration permeate. The nanofiltration retentate rich in acidic functional peptides is collected. The nanofiltration retentate is replenished with water or washed at least once. Then, one or more of the following methods are used in combination: end filtration, concentration, and drying to obtain a sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes.

2. The preparation method according to claim 1, characterized in that, In step 1, the cleaning process uses one or more of the following methods in combination: water washing, acid washing, or salt washing.

3. The preparation method according to claim 1, characterized in that, In step 2, the material-to-liquid mass ratio is 1:(8-12). In step 2, the pH is adjusted to 9.0 using sodium hydroxide solution, and the mixture is extracted at 45℃ with stirring at 300 r / min for 60 min.

4. The preparation method according to claim 1, characterized in that, In step 3, the complex protease consists of alkaline protease and neutral protease.

5. The preparation method according to claim 1, characterized in that, In step 3, the enzyme is inactivated by raising the temperature or adjusting the pH.

6. The preparation method according to claim 1, characterized in that, In step 4, the ultrafiltration membrane has a molecular weight cutoff of 3-10 kDa.

7. The preparation method according to claim 1, characterized in that, In step 5, the nanofiltration membrane has a molecular weight cutoff of 300-500 Da.

8. The application of the sunflower seed meal acidic functional peptide scale inhibitor for nanofiltration membranes prepared by the method according to any one of claims 1-7, characterized in that, The scale inhibitor is used in the field of water treatment based on nanofiltration membrane systems.

9. The application according to claim 8, characterized in that, The scale inhibitor is added to the feed water to be treated before the nanofiltration membrane module.

10. The application according to claim 8, characterized in that, The dosage of scale inhibitor is 5-10 mg / L based on the influent volume.

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