Method for preventing membrane system from being polluted by cationic surface active agent

Abstract

The invention discloses a method for preventing membrane system cationic surface active agent pollution, which comprises the following steps: risk assessment: detecting whether a membrane system inlet water sample is polluted by a cationic surface active agent through a test device, and if the water yield attenuation amplitude is greater than or equal to 30%, indicating that the inlet water sample has a pollution risk on a membrane element; the adding type and the adding amount are evaluated, after the risk is determined, a certain amount of anionic surfactant is added before the raw water enters the membrane system, and the type and the adding amount M of the added anionic surfactant need to be evaluated according to a small test result; step 2, determining an adding point, and adding the anionic surfactant before the raw water enters the membrane system according to the actual system anionic surfactant adding amount determined in the step 2; and preparing an anionic surfactant stock solution with required concentration and putting the anionic surfactant stock solution. A certain amount of anionic surfactant is added in the pretreatment stage of the membrane system to prevent performance degradation when the reverse osmosis or nanofiltration membrane system treats the cationic surfactant.

Description

Technical Field

[0001] The invention belongs to the technical field of permeable membranes, and in particular relates to a method for preventing cationic surfactant pollution of a membrane system. Background Art

[0002] As a popular water treatment method, reverse osmosis membrane and nanofiltration membrane have relatively strict requirements on the influent of the membrane system, including that no surfactant components can be detected in the influent. Therefore, reverse osmosis membrane and nanofiltration membrane are rarely used in the treatment of wastewater containing a certain concentration of cationic surfactants. With the substantial increase in the demand for wastewater reuse in various industries, reverse osmosis membrane and nanofiltration membrane are widely used in the treatment of wastewater containing surfactants. When used to treat wastewater containing cationic surfactants, the main problem is that it will cause the water output of the membrane system to decay and it is difficult to clean and restore.

[0003] Cationic surfactants are a type of surfactants with positive charges in the active part of the molecule. When they are dissolved in water, the hydrophilic group is positively charged. Cationic surfactants can be used as antistatic agents and softening finishing agents for fabrics; they can also be used as fungicides, anti-caking agents, ore flotation agents, cosmetic emulsifiers, metal corrosion inhibitors, etc. The application process of cationic surfactants may generate corresponding wastewater, such as the wastewater generated when cationic surfactants are used in the corrosion inhibition process of cold-rolled steel; the wastewater generated when cationic surfactants are used in the leather industry to remove preservatives on leather materials by immersion; the cleaning wastewater generated when they are used in the semiconductor industry for cleaning, etc.

[0004] Since cationic surfactants are positively charged in aqueous solution, while reverse osmosis membranes and nanofiltration membranes are generally negatively charged, cationic surfactants in wastewater are easily adsorbed on the membrane surface. Cationic surfactants are usually regarded as the source of organic pollutants in membrane systems. Conventional membrane systems generally remove them through flocculation filtration, ultrafiltration, activated carbon adsorption and other methods, but these methods have limited effects on the removal of surfactants, and even a small amount of surfactant entering the membrane system can cause irreversible performance degradation of the membrane system.

[0005] The Chinese invention patent with publication number CN102133505B discloses an enhanced cleaning method for reverse osmosis / nanofiltration membrane pollution, which introduces a functional material with pH response characteristics, allows the pH responsive functional material to enter the pollution layer through diffusion, and then changes the pH value of the solution to cause the material with pH response function in the pollution layer on the membrane surface to undergo molecular morphology transformation, thereby loosening the pollution layer, promoting the removal of pollutants from the membrane surface, and improving the cleaning efficiency of membrane pollution. It can effectively improve the cleaning effect of reverse osmosis / nanofiltration membrane pollution, thereby improving membrane separation efficiency and extending membrane service life, and the cleaning process is also relatively simple. However, this method is not perfect, and it is impossible to estimate whether there is a risk of pollution and accurately know the degree of pollution, and thus cannot solve the problem in a targeted manner. Summary of the invention

[0006] In order to solve the above problems, the present invention aims to provide a method for preventing cationic surfactant fouling of membrane systems.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme: a method for preventing cationic surfactant contamination of a membrane system, characterized in that it comprises the following steps:

[0008] Step 1: Assess the risk. Use a test device to test the membrane system to see if the influent water sample is contaminated by the cationic surfactant. If the water output attenuation is ≥30%, it indicates that the influent water sample has a risk of contaminating the membrane element.

[0009] Step 2: Evaluate the type and amount of anionic surfactant to be added. After confirming the risk, add a certain amount of anionic surfactant before the raw water enters the membrane system. The type and amount of anionic surfactant to be added M need to be evaluated based on the results of a small test.

[0010] Step 3: Determine the dosing point. According to the actual system anionic surfactant dosage determined in step 2, add anionic surfactant before the raw water enters the membrane system. The dosing points include but are not limited to the pretreatment unit ultrafiltration water inlet pipe, ultrafiltration water production tank, pretreatment unit activated carbon treatment water inlet pipe, activated carbon treatment water outlet pipe, security filter water inlet pipe, and security filter water outlet pipe;

[0011] Step 4: prepare anionic surfactant stock solution of required concentration and add it;

[0012] Step 2 is as follows:

[0013] Step 21: Take 10 to 50 L of the influent water sample of the membrane system and put it into a bucket;

[0014] Step 22: Add different amounts of anionic surfactants into the barrel and run the small test device for multiple times. The running time is >30 min. Record the water production flow rate of the membrane element in L / min. Calculate and record the water production attenuation amplitude during the operation of the membrane element based on the initial water production flow rate F0 and the water production flow rate F1 at the end of the operation.

[0015] Step 23: Based on the above records, select the anionic surfactant dosage m with a water production attenuation amplitude of ≤15% during the test, and calculate the anionic surfactant dosage required for the actual system. The calculation formula is:

[0016]

[0017] in,

[0018] M: The amount of anionic surfactant required by the actual system, in g / min

[0019] m: dosage of anionic surfactant in small-scale test, unit: g

[0020] V: The volume of raw water in the small test, in L

[0021] Q: Actual water inlet flow rate of the membrane system, unit: m3 / h.

[0022] Furthermore, the actual pollution methods in step 1 include but are not limited to understanding the source of wastewater, water sample analysis, small-scale experiments, and analysis of previously polluted membranes.

[0023] Furthermore, the experimental device of step 1 includes a raw water barrel, a membrane element connected to the raw water barrel pipeline, the membrane element and the pressure gauge are arranged in the membrane shell, the membrane element is connected to two independent pipelines for wastewater and clean water, and a wastewater shut-off valve is arranged on the wastewater return pipeline of the membrane element, which is parallel to the wastewater return pipeline as a produced water return pipeline.

[0024] Furthermore, the steps of testing by the experimental device in step 1 are as follows:

[0025] Step 11: Take 10-50L of the membrane system's influent water sample and put it into the bucket

[0026] Step 12: Run the test device for >30 min, and record the water production flow rate of the membrane element at the beginning and end of the operation in L / min. Calculate the attenuation of water production during the operation of the membrane element based on the water production flow rate F0 at the beginning of the operation and the water production flow rate F1 at the end of the operation. The calculation formula is:

[0027]

[0028] Furthermore, the types of anionic surfactants added in step 3 include but are not limited to sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, fatty alcohol polyoxyethylene ether phosphate, and sodium N-acyl glutamate. The specific surfactant to be selected needs to be determined through small-scale test screening in step 2.

[0029] Furthermore, step 4 is specifically as follows: after steps 2 and 3 determine the dosage and addition site of the anionic surfactant before the raw water enters the membrane system, the anionic surfactant is added by metering with a dosing pump, that is, a certain concentration of anionic surfactant stock solution is prepared and added into the water inlet pipeline of the membrane system through a metering pump to ensure that the concentration added into the pipeline meets M in step 2.

[0030] Compared with the prior art, the present invention has the following advantages: the technology provided by the present invention adds a certain concentration of anionic surfactant before the wastewater containing cationic surfactant enters the reverse osmosis or nanofiltration membrane system, so as to react with the cationic surfactant in advance, generate products with less risk of contaminating the reverse osmosis membrane and the nanofiltration membrane, and remove the products in subsequent pretreatment units such as activated carbon filtration and ultrafiltration, so as to prevent the problem of water production attenuation that occurs when the reverse osmosis membrane or nanofiltration membrane treats the wastewater containing cationic surfactant. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 It is a flow chart of the small and medium-sized test device of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above-mentioned technical ideas of the present invention, various modifications, substitutions and changes made according to the common technical knowledge and customary means in the field are included in the scope of the present invention.

[0034] The present invention provides a method for preventing cationic surfactant pollution of a membrane system. A certain amount of anionic surfactant is added in the pretreatment stage of the membrane system to prevent the performance degradation of a reverse osmosis or nanofiltration membrane system when treating a cationic surfactant. Cationic surfactant pollution refers to the fact that the raw water treated by the membrane system may contain cationic surfactants such as quaternary ammonium salts, which are very easy to adsorb on the surface of the reverse osmosis membrane or nanofiltration membrane, causing membrane system pollution and membrane system performance degradation.

[0035] The method for preventing cationic surfactant contamination in a membrane system according to the present invention mainly comprises the following steps:

[0036] Step 1: First, determine whether the membrane system is at risk of cationic surfactant contamination. By understanding the source of wastewater, water sample analysis, small-scale experiments, and previous contaminated membrane analysis, determine whether there are cationic surfactants in the water source, or determine whether there is a risk of cationic surfactant contamination when the water source is treated by membrane method. Taking the small-scale test as an example, the steps to verify whether the membrane system is at risk of cationic surfactant contamination include:

[0037] Step 11: Take about 10 to 50L of the membrane system’s influent water sample and put it into a bucket;

[0038] Step 12: Take a 1812 size RO membrane element and install it into the membrane housing. Figure 1 , is the flow chart of the small test device. The main components of the pump, membrane housing, pressure gauge, and wastewater shut-off valve are connected through pipelines to build a simple small test device. The above simple test device is run for a running time of >30min. At the beginning and end of the operation, the water production flow rate of the membrane element is recorded in L / min. The water production flow rate F0 at the beginning of the operation and the water production flow rate F1 at the end of the operation are used to calculate the water production attenuation amplitude during the operation of the membrane element. The calculation formula is:

[0039]

[0040] If the water production attenuation is ≥30%, it indicates that the inlet water sample has a high risk of contamination to the membrane element.

[0041] Step 2: Add a certain amount of anionic surfactant before the raw water enters the membrane system to prevent cationic surfactant contamination in the membrane system. The type and amount of anionic surfactant added need to be evaluated based on the results of the small test. The specific steps of the small test are as follows:

[0042] Step 21: Take about 10 to 50L of the influent water sample of the membrane system and put it into a bucket;

[0043] Step 22: Take a 1812 size RO membrane element and install it into the membrane housing. Figure 1 As shown, the main components of the pump, membrane housing, pressure gauge, and wastewater shut-off valve are connected through pipelines to construct a simple small-scale test device; a certain amount of anionic surfactant is added to the raw water bucket, and the above simple test device is operated for a running time of >30min, which is the same as the running time in step 1, and the water production flow rate of the membrane element is recorded at the beginning and end of the operation, in units of L / min, and the water production flow rate F0 at the beginning of the operation and the water production flow rate F1 at the end of the operation are used to calculate the water production attenuation amplitude during the operation of the membrane element;

[0044] Take 10-50L of membrane system inlet water sample again and put it into the original water barrel. Add different amounts of anionic surfactant into the barrel. Repeat step 22. Calculate the attenuation of water production during the above small test process when adding different concentrations of anionic surfactant, and record it in the following table:

[0045] Anionic surfactant dosage m1 m2 m3 m... Water production attenuation

[0046] Through the above small-scale test, the anionic surfactant dosage m with a water production attenuation amplitude of ≤15% during the test was selected to calculate the anionic surfactant dosage required for the actual system. The calculation formula is:

[0047]

[0048] in,

[0049] M: The amount of anionic surfactant required by the actual system, in g / min

[0050] m: dosage of anionic surfactant in small-scale test, unit: g

[0051] V: The volume of raw water in the small test, in L

[0052] Q: Actual water flow rate of the membrane system, unit: m3 / h

[0053] Step 3: According to the actual system anionic surfactant dosage determined in step 2, anionic surfactant is added before the raw water enters the membrane system. The addition site can be the ultrafiltration water inlet pipe and ultrafiltration water production tank of the pretreatment unit; the activated carbon treatment water inlet pipe and activated carbon treatment water outlet pipe of the pretreatment unit; the safety filter water inlet pipe and safety filter water outlet pipe, etc.

[0054] Step 4: After the dosage and dosing location of the anionic surfactant before the raw water enters the membrane system are determined in steps 2 and 3, the anionic surfactant is added by metering with a dosing pump, that is, a certain concentration of anionic surfactant stock solution is prepared and added into the water inlet pipeline of the membrane system through a metering pump to ensure that the concentration added into the pipeline meets M in step 2;

[0055] The types of anionic surfactants added include but are not limited to sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, fatty alcohol polyoxyethylene ether phosphate, sodium N-acyl glutamate, etc. The specific surfactant to be selected needs to be screened and determined through the pilot test in step 2.

[0056] Example 1

[0057] The reverse osmosis membrane element was run for a long time in a non-polluting sodium chloride solution, and the performance of the membrane element was tested after the operation:

[0058] Table 1. Changes in water production after membrane elements were operated in non-polluted sodium chloride solution (unit: GPD)

[0059]

[0060] After running in a non-polluted sodium chloride solution for 72 hours, the water output of 1# and 2# membrane elements decreased by about 7-8%, indicating that the performance of membrane elements changes little in the absence of pollution.

[0061] Example 2

[0062] Prepare a 15ppm dodecyltrimethylammonium bromide solution with pure water, run the reverse osmosis membrane in the solution, and test the performance of the membrane element after running:

[0063] Table 2. Changes in water production after membrane element operation and cleaning in a dodecyltrimethylammonium bromide cationic surfactant solution (unit: GPD)

[0064]

[0065]

[0066] In the solution containing cationic surfactants, the water production of 3# and 4# membrane elements decreased by about 50-55% after running for about 6 hours, and recovered by about 62-67% after alkali washing, indicating that the performance of membrane elements will be significantly attenuated in the presence of cationic surfactant pollutants.

[0067] Example 3

[0068] Prepare a 15ppm dodecyltrimethylammonium bromide solution with pure water, run the reverse osmosis membrane in the solution, and add different concentrations of sodium dodecylbenzene sulfonate before running. Test the performance of the membrane element after running:

[0069] Table 3. Changes in water production after membrane element operation and cleaning in a solution containing dodecyltrimethylammonium bromide cationic surfactant (unit: GPD)

[0070]

[0071] After the 5# membrane element was operated in a solution containing a cationic surfactant for 6 hours, the water production decreased by 52%, and the water production recovered by 72% after alkaline washing; after the 6#~8# membrane elements were operated in a solution containing a cationic surfactant + an anionic surfactant of different concentrations for 6 hours, the water production decreased by 12%~42%, and the water production recovered by 80%~95% after alkaline washing. After the anionic surfactant was added, the attenuation of the water production of the membrane element was reduced, and the recovery after alkaline washing was increased. This shows that adding a certain amount of anionic surfactant to a solution containing a cationic surfactant can reduce the cationic surfactant pollution to a certain extent.

[0072] Example 4

[0073] The reverse osmosis membrane was run in wastewater containing cationic surfactants (cold rolling line finishing liquid of steel mills) and solutions with different concentrations of anionic surfactants. The performance of the membrane element was tested after the operation:

[0074] Table 4. Changes in water production after operation and cleaning of membrane elements in a solution containing cationic surfactants + anionic surfactants of varying concentrations (unit: GPD)

[0075]

[0076] After the 9# membrane element was operated in a solution containing a cationic surfactant for 3 hours, the water production decreased by 57%, and the water production recovered by 85% after alkaline washing; after the 10#~12# membrane elements were operated in a solution containing a cationic surfactant + an anionic surfactant of different concentrations for 3 hours, the water production decreased by 15%~42%, and the water production recovered by 89%~95% after alkaline washing. After the anionic surfactant was added, the attenuation of the water production of the membrane element was reduced, and the recovery after alkaline washing was increased. This shows that adding a certain amount of anionic surfactant to a solution containing a cationic surfactant can reduce the cationic surfactant pollution to a certain extent.

[0077] The present invention provides a method for preventing cationic surfactant contamination of a membrane system. A certain amount of anionic surfactant is added in the pretreatment stage of the membrane system to prevent the performance degradation of a reverse osmosis or nanofiltration membrane system when treating a cationic surfactant. The cationic surfactant contamination refers to the fact that the raw water treated by the membrane system may contain cationic surfactants such as quaternary ammonium salts, which are very easy to adsorb on the surface of the reverse osmosis membrane or the nanofiltration membrane, causing membrane system contamination and membrane system performance degradation.

[0078] The above is a detailed introduction to a method for preventing cationic surfactant contamination of a membrane system provided by the present invention. The structure and working principle of the present invention are described in detail using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, the present invention can also be improved and modified without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preventing cationic surfactant contamination of a membrane system, characterized in that: The following steps are included: Step 1: Assess the risk. Use a test device to detect whether the membrane system influent water sample is contaminated by cationic surfactants. If the water output attenuation is ≥30%, it indicates that the influent water sample has a risk of contaminating the membrane element. Step 2: Evaluate the type and amount of anionic surfactant to be added. After confirming the risk, add a certain amount of anionic surfactant before the raw water enters the membrane system. The type and amount of anionic surfactant to be added M need to be evaluated based on the results of a small test. Step 3: Determine the dosage point, and add anionic surfactant to the actual system anionic surfactant dose determined in step 2, and add anionic surfactant before the raw water enters the membrane system; Step 4: Prepare the required concentration of anionic surfactant stock solution and place it; Step 2 is as follows: Step 21: Take the inlet water sample of the 10-50L membrane system and put it into the barrel; Step 22: Add different amounts of anionic surfactants into the barrel and run the small test device for multiple times. The running time is >30 min. Record the water production flow rate of the membrane element in L / min. Calculate and record the water production attenuation amplitude during the operation of the membrane element based on the initial water production flow rate F0 and the water production flow rate F1 at the end of the operation. Step 23: Based on the above records, select the anionic surfactant dosage m with a water production attenuation amplitude of ≤15% during the test, and calculate the anionic surfactant dosage required for the actual system. The calculation formula is: in, M: The amount of anionic surfactant required for the actual system, unit g / min m: the amount of anionic surfactant added in small test test, unit g V: The volume of test raw water in the small test test, unit L Q: The actual water inlet flow of the membrane system, unit m3 / h.

2. The method of preventing cationic surfactant contamination of membrane system according to claim 1, characterized in that: The actual contamination methods of step 1 include but are not limited to understanding the source of wastewater, water sample analysis, small test experiments, and previous contaminated membrane analysis.

3. The method of preventing cationic surfactant contamination of membrane system according to claim 1, characterized in that: The experimental device of step 1 includes a raw water barrel, a membrane element connected to the raw water barrel pipeline, the membrane element and the pressure gauge are arranged in the membrane shell, the membrane element is connected to two independent pipelines for wastewater and clean water, and a wastewater stop valve is arranged on the pipeline for wastewater return of the membrane element, which is parallel to the wastewater return pipeline as a produced water return pipeline.

4. The method of preventing cationic surfactant contamination of membrane system according to claim 1, characterized in that: The steps for testing through the experimental device in Step 1 are as follows: Step 11: Take the inlet water sample of the 10-50L membrane system and put it into the barrel; Step 12: Run the test device for >30 min, and record the water production flow rate of the membrane element at the beginning and end of the operation in L / min. Calculate the attenuation of water production during the operation of the membrane element based on the water production flow rate F0 at the beginning of the operation and the water production flow rate F1 at the end of the operation. The calculation formula is:

5. The method of preventing cationic surfactant contamination of membrane system according to claim 1, characterized in that: The types of anionic surfactants added in step 3 include but are not limited to sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, fatty alcohol polyoxyethylene ether phosphate, and sodium N-acyl glutamate. The specific surfactant to be selected needs to be determined through small-scale test screening in step 2.

6. The method for preventing membrane system cationic surfactant contamination according to claim 1, characterized in that: The anionic surfactant addition points before the raw water in step 3 enters the membrane system include but are not limited to the pretreatment unit ultrafiltration inlet pipe, the ultrafiltration water production tank, the pretreatment unit activated carbon treatment inlet pipe, the activated carbon treatment outlet pipe, the safety filter inlet pipe, and the safety filter outlet pipe.

7. The method for preventing membrane system cationic surfactant contamination according to claim 1, characterized in that: The specific details of step 4 are as follows: after steps 2 and 3 determine the dosage and addition site of the anionic surfactant before the raw water enters the membrane system, the anionic surfactant is added by metering with a dosing pump, that is, a certain concentration of anionic surfactant stock solution is prepared and added into the water inlet pipeline of the membrane system through a metering pump to ensure that the concentration added into the pipeline meets M in step 2.

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