A low toxicity membrane cleaning agent and method of use thereof

Abstract

The present application relates to the technical field of membrane cleaning, and particularly relates to a low-toxicity membrane cleaning agent and a use method thereof; the cleaning agent comprises the following components in parts by weight: 40-50 parts of persulfate, 10-20 parts of hydrochloride, and 30-40 parts of borax; the cleaning agent is dissolved in water to prepare a cleaning solution, which is used for soaking and cleaning a contaminated membrane module; the present application uses persulfate, hydrochloride and borax to prepare a high-ionic-strength cleaning solution; the persulfate can oxidize toxic halogenated products and precursors generated by active chlorine reaction; the borax and active chlorine form an inert intermediate product, so that the active chlorine generated in situ by the cleaning solution is kept at a low level, thereby ensuring that the active chlorine can only oxidize the membrane pollutants to make them fall off from the membrane surface, and cannot further participate in the subsequent reaction with the oxidation products of the membrane pollutants; the content of toxic by-products in the cleaning solution is further greatly reduced, the influence on the environment is reduced, and the subsequent treatment of the cleaning waste liquid is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of membrane cleaning, in particular to a low-toxicity membrane cleaning agent and a use method thereof. BACKGROUND

[0002] Membrane technology is widely used in seawater desalination, drinking water purification and wastewater recycling due to its simple process, high separation efficiency and energy saving and environmental protection. However, in the filtration process, inorganic matter, organic matter and microorganisms and other pollutants in the water will adhere to the membrane surface or block the membrane holes to form complex membrane pollution, causing problems such as membrane flux decline, filtration efficiency reduction and processing cost increase. Therefore, the membrane needs to be cleaned regularly to ensure normal operation of the membrane, prolong the service life of the membrane and reduce the use cost.

[0003] There are generally two kinds of existing membrane cleaning methods, one is physical cleaning, which removes membrane pollution by water flushing, gas pulse or ultrasonic impact; the other is chemical cleaning, which uses chemical agents to achieve the effect of loosening, dissolving dirt, oxidizing organic matter and inactivating microorganisms to remove membrane pollution. However, in the face of complex membrane pollution including humic acid (HA) and calcium ion (Ca 2+ ) complex, the existing cleaning agent has the problem of incomplete cleaning, in addition, common chemical agents such as sodium hypochlorite can also cause damage to the membrane material and generate toxic halogenated by-products to cause secondary pollution to the environment water. Therefore, a low-toxicity membrane cleaning agent and cleaning method are urgently needed to solve the above problems. SUMMARY

[0004] In order to solve the above problems, the present application provides a low-toxicity membrane cleaning agent and a use method thereof, which aims to simultaneously remove membrane pollution by using high ionic strength and active chlorine and singlet oxygen generated by the reaction of persulfate, hydrochloride and borax, and to control the generation of toxic halogenated by-products by persulfate and borax, thereby solving the problems of single cleaning substance, incomplete cleaning of complex pollution and generation of a large amount of toxic by-products in the existing cleaning of membrane pollution using sodium hypochlorite.

[0005] In one aspect, the present application provides a low-toxicity membrane cleaning agent, which comprises the following components by weight: 40-50 parts of persulfate, 10-20 parts of hydrochloride and 30-40 parts of borax.

[0006] Further, the persulfate is at least one of potassium peroxymonosulfate, sodium peroxymonosulfate, potassium peroxodisulfate and sodium peroxodisulfate.

[0007] Further, the hydrochloride is at least one of sodium chloride, potassium chloride, magnesium chloride, calcium chloride and aluminum chloride.

[0008] In another aspect, the application also provides a method for using the low-toxicity membrane cleaning agent as described above, first, adding a certain proportion of persulfate and borax into water according to the pH requirement, stirring uniformly to form a mixed solution, then adding hydrochloride into the mixed solution, stirring uniformly to obtain a cleaning solution, and finally using the cleaning solution for soaking and cleaning the contaminated membrane module.

[0009] Specifically, the contaminated membrane module is a membrane module contaminated by organic pollution, inorganic pollution, microbial pollution or metabolic product pollution, and is particularly suitable for a membrane module contaminated by humic acid and calcium ion complex.

[0010] Further, the pH of the cleaning solution is 5-10.

[0011] Further, the pH of the cleaning solution is 6-8.

[0012] Further, the mass concentration of persulfate in the cleaning solution is 30-3000 mg / L, and the mass concentration ratio of hydrochloride to persulfate is 1:2-5.

[0013] Further, the membrane module is an organic membrane or an inorganic membrane, and is one of a polysulfone membrane, a polyether sulfone membrane, a polyethylene membrane, a polyvinyl chloride membrane, a polyvinylidene fluoride membrane and a ceramic membrane.

[0014] Further, the cleaning time of the cleaning solution for the membrane module is 0.5-24 hours.

[0015] The low-toxicity membrane cleaning agent provided by the application is configured into a high ionic strength cleaning solution by adding water, the persulfate itself can oxidize and modify the organic pollutants on the membrane surface, the hydrochloride can provide a high ionic strength to promote the desorption of the membrane pollutants from the membrane surface, and at the same time, the hydrochloride can also generate active chlorine with the persulfate: The borax can also provide a certain ionic strength and promote the decomposition of the persulfate to generate singlet oxygen: In addition, the borax also has the functions of buffering the pH of the solution and adjusting the dominant species of active chlorine in the solution, when the pH of the cleaning solution is less than 7.54, the active chlorine in the solution mainly exists in the form of hypochlorous acid molecules with an oxidation-reduction potential of 1.49 V, and when the pH of the cleaning solution is greater than 7.54, the active chlorine mainly exists in the form of hypochlorite ions with an oxidation-reduction potential of 0.94 V, therefore, under the combined action of the persulfate, active chlorine, singlet oxygen and high ionic strength, the pollutants are quickly detached from the membrane surface and channels, and the cleaning efficiency and effect of the cleaning agent are improved.

[0016] The low-toxicity membrane cleaning agent provided by the application adds a certain proportion of persulfate and borax into water according to pH requirements, stirs them uniformly to form a mixed solution, then adds hydrochloride into the mixed solution and stirs them uniformly to obtain a mixed solution, the persulfate can oxidize membrane pollutants so as to reduce the precursors of toxic halogenated by-products, in addition, the persulfate can directly oxidize toxic halogenated by-products so as to greatly reduce the content of the toxic halogenated by-products; the borax can react with active chlorine generated in-situ in the solution to generate an inert intermediate product: B4O7 2- + 4HClO + 5H2O → 4B(OH)3OCl - + 2H + , so that the concentration of active chlorine generated in-situ in the cleaning solution is maintained at a low level, at the concentration, the active chlorine can only oxidize membrane pollutants to make them fall off from the membrane surface and cannot further participate in subsequent reactions with membrane pollutant oxidation products, so that the generation of toxic by-product species with higher toxicity is avoided.

[0017] Compared with the prior art, the application has the following beneficial effects due to the above technical scheme:

[0018] 1) The low-toxicity membrane cleaning agent and the use method thereof provided by the application prepare a high-ionic-strength cleaning solution by using persulfate, hydrochloride and borax, the persulfate can oxidize toxic halogenated by-products and precursors thereof generated by active chlorine reaction, and the borax forms an inert intermediate product with active chlorine so that the concentration of active chlorine generated in-situ in the cleaning solution is maintained at a low level, thereby ensuring that the active chlorine can only oxidize membrane pollutants to make them fall off from the membrane surface and cannot further participate in subsequent reactions with membrane pollutant oxidation products, further greatly reducing the content of toxic by-products in the cleaning solution, reducing the impact on the environment, and facilitating subsequent treatment of cleaning waste liquid;

[0019] 2) The low-toxicity membrane cleaning agent and the use method thereof provided by the application, the persulfate, the hydrochloride and the borax are all solid powder reagents, the raw materials are easy to obtain and have more stable chemical properties, the reagents are convenient to transport and store, and the use method is simple and easy to operate;

[0020] 3) The low-toxicity membrane cleaning agent and the use method thereof provided by the application, the cleaning agent is a solid powder reagent, the dosage and the ratio of the reagent can be adjusted according to different pollution levels, the application range is wide, and the cleaning is more efficient. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical schemes in the embodiments of the application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creating laborious efforts.

[0022] Figure 1 A diagram for the membrane flux recovery rate and the membrane resistance removal rate in the embodiment 1 of the present application;

[0023] Figure 2 A diagram for the membrane flux recovery rate and the membrane resistance removal rate in the embodiment 2 of the present application;

[0024] Figure 3 A diagram for the membrane flux recovery rate and the membrane resistance removal rate in the comparative examples 1-3 of the present application;

[0025] Figure 4 A comparison diagram for the partial toxic halogenated by-product generation effect in the embodiment 3 and the comparative examples 4-5 of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0027] The present application provides a low-toxicity membrane cleaning agent, which comprises the following components by weight parts: 40-50 parts of persulfate, 10-20 parts of hydrochloride, and 30-40 parts of borax.

[0028] As one of the embodiments, the persulfate can be permonosulfate or perdisulfate. Specifically, the persulfate is at least one of potassium permonosulfate, sodium permonosulfate, potassium perdisulfate, and sodium perdisulfate. The persulfate can be one or a mixture of two or more thereof, which can be selected according to actual needs.

[0029] As one of the embodiments, the hydrochloride is at least one of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, and aluminum chloride. The hydrochloride can be one or a mixture of two or more thereof, which can be selected according to actual needs.

[0030] The present application also provides a use method of the low-toxicity membrane cleaning agent. First, a certain proportion of persulfate and borax is added to water according to pH requirements, stirred uniformly to form a mixed solution, then the hydrochloride is added to the mixed solution and stirred uniformly to obtain a cleaning solution, and finally the cleaning solution is used for soaking and cleaning the contaminated membrane assembly. Specifically, after the contaminated membrane assembly is soaked and cleaned in the cleaning solution for a period of time, it is taken out, rinsed with clean water to remove the residual medicament on the surface, dried, and the cleaning operation is completed.

[0031] As one of the embodiments, the membrane assembly is one of an organic membrane or an inorganic membrane, one of a polysulfone membrane, a polyethersulfone membrane, a polyethylene membrane, a polyvinyl chloride membrane, a polyvinylidene fluoride membrane, and a ceramic membrane.

[0032] The high ionic strength cleaning agent with low toxicity provided by the application can oxidize and modify the organic pollutants on the membrane surface by itself, the hydrochloride can provide high ionic strength to promote the desorption of the membrane pollutants from the membrane surface, at the same time, the hydrochloride can also react with the persulfate to generate active chlorine, the borax can promote the decomposition of the persulfate to generate singlet oxygen and buffer the pH of the solution to adjust the dominant species of the active chlorine in the solution, under the combined action of the persulfate, the active chlorine, the singlet oxygen and the high ionic strength, the pollutants are quickly removed from the membrane surface and the channel, the cleaning efficiency and the cleaning effect of the cleaning agent are improved. The borax and the active chlorine form an inert intermediate product, so that the active chlorine generated by the cleaning solution is kept at a low level, thereby ensuring that the active chlorine can only oxidize the membrane pollutants to make them fall off from the membrane surface and cannot further participate in the subsequent reaction with the oxidation products of the membrane pollutants, greatly reducing the generation of toxic by-products in the cleaning solution.

[0033] In the application, in order to ensure the consistency of the test, the polluted membrane is prepared by the following method: humic acid and calcium chloride are dissolved in ultrapure water, and a 50kDa polyether sulfone ultrafiltration membrane is used to filter to obtain the polluted membrane assembly in the following examples and comparative examples, and the membrane flux of the polluted membrane assembly is reduced to 53% of the initial flux.

[0034] Example 1

[0035] 10mM of potassium hydrogen persulfate and 3mM of borax are added to the cleaning tank, and different concentrations of sodium chloride are added to the cleaning tank, respectively, wherein the temperature of the ultrapure water in the cleaning tank is kept at 25℃, the addition of sodium chloride is 0mM (first group), 5mM (second group), 10mM (third group), 15mM (fourth group) and 20mM (fifth group), respectively, and the cleaning solution is prepared after stirring uniformly, the pH of the cleaning solution is 7, the polluted membrane assembly is soaked for 1 hour and cleaned, after the soaking and cleaning are completed, the cleaning solution is removed from the membrane surface by rinsing with clean water, and the cleaned membrane assembly is obtained after drying, the cleaned membrane assembly is detected, the membrane flux and the membrane resistance removal rate are detected, as shown in the drawings, the detection results show that the membrane flux recovery rates after adding 0mM, 5mM, 10mM, 15mM and 20mM of sodium chloride are 52%, 54%, 78%, 94% and 124%, respectively, and the membrane resistance removal rates are 64%, 70%, 88%, 96% and 112%, respectively. Figure 1

[0036] Example 2

[0037] ​In the cleaning tank, 10 mM of oxone, 3 mM of borax and 15 mM of sodium chloride were added, the temperature of the ultrapure water in the cleaning tank was kept at 25 °C, and the mixture was stirred uniformly to prepare four groups of cleaning solutions. The pH of the cleaning solutions was adjusted to 6, 7, 8 and 9 respectively using sodium hydroxide and sulfuric acid. The contaminated membrane module was soaked in the cleaning solution for 1 hour and cleaned. After the soaking and cleaning were completed, the membrane module was rinsed with clean water to remove the residual cleaning solution on the surface of the membrane, dried, and the cleaned membrane module was obtained. The cleaned membrane module was detected to detect the membrane flux and the membrane resistance removal rate. As shown in the drawings, the detection results showed that when the pH of the cleaning solution was 6, 7, 8 and 9, the membrane flux recovery rate of the cleaned membrane module was 99%, 94%, 44% and 38% respectively, and the membrane resistance removal rate was 100%, 96%, 61% and 56% respectively. Figure 2 The test results showed that when the pH of the cleaning solution was 6-7, the cleaning effect was best, and the borax could buffer the pH of the cleaning solution, so that the pH of the cleaning solution was maintained at about 6-7, and the best cleaning effect was maintained.

[0038] The test results showed that when the pH of the cleaning solution was 6-7, the cleaning effect was best, and the borax could buffer the pH of the cleaning solution, so that the pH of the cleaning solution was maintained at about 6-7, and the best cleaning effect was maintained.

[0039] Comparative Example 1

[0040] In the cleaning tank, 10 mM of oxone, 3 mM of borax and 15 mM of sodium chloride were added, the temperature of the ultrapure water in the cleaning tank was kept at 25 °C, and the mixture was stirred uniformly to prepare four groups of cleaning solutions. The pH of the cleaning solutions was adjusted to 6, 7, 8 and 9 respectively using sodium hydroxide and sulfuric acid. The contaminated membrane module was soaked in the cleaning solution for 1 hour and cleaned. After the soaking and cleaning were completed, the membrane module was rinsed with clean water to remove the residual cleaning solution on the surface of the membrane, dried, and the cleaned membrane module was obtained. The cleaned membrane module was detected to detect the membrane flux and the membrane resistance removal rate. As shown in the drawings, the detection results showed that when the pH of the cleaning solution was 6, 7, 8 and 9, the membrane flux recovery rate of the cleaned membrane module was 99%, 94%, 44% and 38% respectively, and the membrane resistance removal rate was 100%, 96%, 61% and 56% respectively. Figure 3 The test results showed that when the pH of the cleaning solution was 6-7, the cleaning effect was best, and the borax could buffer the pH of the cleaning solution, so that the pH of the cleaning solution was maintained at about 6-7, and the best cleaning effect was maintained.

[0041] Comparative Example 2

[0042] In the cleaning tank, 10 mM of oxone, 3 mM of borax and 15 mM of sodium chloride were added, the temperature of the ultrapure water in the cleaning tank was kept at 25 °C, and the mixture was stirred uniformly to prepare four groups of cleaning solutions. The pH of the cleaning solutions was adjusted to 6, 7, 8 and 9 respectively using sodium hydroxide and sulfuric acid. The contaminated membrane module was soaked in the cleaning solution for 1 hour and cleaned. After the soaking and cleaning were completed, the membrane module was rinsed with clean water to remove the residual cleaning solution on the surface of the membrane, dried, and the cleaned membrane module was obtained. The cleaned membrane module was detected to detect the membrane flux and the membrane resistance removal rate. As shown in the drawings, the detection results showed that when the pH of the cleaning solution was 6, 7, 8 and 9, the membrane flux recovery rate of the cleaned membrane module was 99%, 94%, 44% and 38% respectively, and the membrane resistance removal rate was 100%, 96%, 61% and 56% respectively. Figure 3 The test results showed that when the pH of the cleaning solution was 6-7, the cleaning effect was best, and the borax could buffer the pH of the cleaning solution, so that the pH of the cleaning solution was maintained at about 6-7, and the best cleaning effect was maintained.

[0043] Comparative Example 3

[0044] Add 10 mM potassium persulfate, 3 mM sodium hydroxide, and 15 mM sodium chloride to the cleaning tank, maintaining the ultrapure water temperature at 25°C. Stir until homogeneous to prepare the cleaning solution. Immerse the contaminated membrane module in the solution for 1 hour and clean it. After immersion and cleaning, rinse with clean water to remove residual cleaning solution from the membrane surface. Dry to obtain the cleaned membrane module. Test the cleaned membrane module to determine its membrane flux and membrane resistance removal rate, as per the attached instruction manual. Figure 3 As shown, the test results indicate that the membrane flux recovery rate after cleaning was 12%, and the membrane resistance removal rate was 21%. These are significantly lower than the membrane flux and membrane resistance removal rate of the membrane module after cleaning in the fourth group of Example 1.

[0045] Example 3

[0046] Add 10 mM potassium persulfate, 3 mM borax, and 15 mM sodium chloride to the cleaning tank, maintaining the ultrapure water temperature at 25°C. Stir until homogeneous to prepare the cleaning solution, which has a pH of 7. Immerse the contaminated membrane module in the solution for 1 hour and clean it. After immersion and cleaning, rinse with clean water to remove residual cleaning solution from the membrane surface. Dry the membrane module to obtain the cleaned membrane module. Detect the toxic byproducts in the cleaning solution. As shown in Figure 4 of the instruction manual, the concentrations of hydrated trichloroacetaldehyde (CH), dichloroacetonitrile (DCAN), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) in the cleaning solution were 0.1 μg / L, 1.0 μg / L, 2.9 μg / L, and 23.9 μg / L, respectively.

[0047] Comparative Example 4

[0048] To investigate the effectiveness of borax in controlling toxic byproducts, the same toxic byproduct monitoring conditions as in Example 3 were used. 9.7 mM potassium persulfate, 3 mM borax, and 0.3 mM sodium hypochlorite were added to a cleaning tank. The ultrapure water temperature in the cleaning tank was maintained at 25°C. The mixture was stirred thoroughly to prepare a cleaning solution with a pH of 7. The contaminated membrane module was then immersed in the solution for 1 hour and cleaned. After immersion and cleaning, the membrane module was rinsed with clean water to remove residual cleaning solution from the membrane surface. It was then dried to obtain the cleaned membrane module. The toxic byproducts in the cleaning solution were then detected as shown in the attached instructions. Figure 4 As shown, the concentrations of hydrated trichloroacetaldehyde (CH), dichloroacetonitrile (DCAN), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in the cleaning solution were 0.1 μg / L, 1.3 μg / L, 20.1 μg / L and 170.5 μg / L, respectively. The levels of toxic byproducts generated in the cleaning solution were significantly higher than those in Example 3.

[0049] Comparative Example 5

[0050] To investigate the effect of potassium hydrogen persulfate on controlling toxic by-products, the same toxic by-product monitoring conditions as in Example 3 were used. 10 mM sodium hypochlorite was added to the cleaning tank, the temperature of the ultrapure water in the cleaning tank was kept at 25°C, and the cleaning solution was prepared by stirring uniformly. The pH of the cleaning solution was 7, the contaminated membrane module was soaked for 1 hour and cleaned, after the soaking and cleaning were completed, the cleaning solution was removed from the surface of the membrane by rinsing with clean water, and the cleaned membrane module was dried. The toxic by-products in the cleaning solution were detected, as shown in the accompanying drawings, the concentrations of hydrated trichloroacetaldehyde (CH), dichloroacetonitrile (DCAN), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) in the cleaning solution were 13.3 μg / L, 1.9 μg / L, 8.1 μg / L, and 108.6 μg / L, respectively, and the generation level of toxic by-products in the cleaning solution was obviously higher than that in Example 3. Figure 4

[0051] To verify the effect of reducing the toxicity of the cleaning solution, the cleaning solutions after cleaning in Example 3 and Comparative Example 5 were subjected to acute toxicity determination according to the “Determination of Acute Toxicity of Water by Luminescent Bacteria Method (GB / T 15441-1995)”. The results showed that the luminescence inhibition rates of the cleaning solutions in Comparative Example 5 and Example 3 on Photobacterium were 27% and 13%, respectively. The results showed that the use of persulfate, hydrochloride, and borax as cleaning agents after cleaning the contaminated membrane resulted in lower toxicity.

[0052] Comparative Example 6

[0053] 10 mM potassium hydrogen persulfate and 15 mM sodium chloride were added to the cleaning tank, the temperature of the ultrapure water in the cleaning tank was kept at 25°C, and the cleaning solution was prepared by stirring uniformly. The pH of the cleaning solution was adjusted to 7 with sodium hydroxide, and 0.96 mM hypochlorite was generated in the cleaning solution after one hour.

[0054] In the above Example 3, under the same conditions as in Comparative Example 6, 0.26 mM hypochlorite was generated in the cleaning solution after one hour. It was obviously lower than the hypochlorite generated in Comparative Example 6, indicating that borax would react with hypochloric acid to form an inert intermediate product, so that more active chlorine could not be monitored.

[0055] It will be understood by those skilled in the art that the present application can be implemented in many other specific forms without departing from the spirit and scope of the present application. Although an embodiment of the present application has been described, it should be understood that the present application should not be limited to this embodiment, and those skilled in the art can make changes and modifications within the spirit and scope of the present application as defined in the appended claims.​

Claims

1. A method for using a low-toxicity membrane cleaning agent, characterized in that: The cleaning agent comprises the following components by weight: 40-50 parts persulfate, 10-20 parts hydrochloride, and 30-40 parts borax. The cleaning agent is used as follows: first, according to the pH requirement, a certain proportion of persulfate and borax are added to water and stirred evenly to form a mixed solution; then, hydrochloride is added to the mixed solution and stirred evenly to obtain a cleaning solution; finally, the cleaning solution is used to soak and clean the contaminated membrane module.

2. The method of using the low-toxicity membrane cleaning agent according to claim 1, characterized in that, The persulfate is at least one of potassium persulfate, sodium persulfate, potassium persulfate, and sodium persulfate.

3. The method of using the low-toxicity membrane cleaning agent according to claim 1, characterized in that, The hydrochloride is at least one of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, and aluminum chloride.

4. The method of using the low-toxicity membrane cleaning agent according to claim 1, characterized in that, The pH of the cleaning solution is 5 to 10.

5. The method of using the low-toxicity membrane cleaning agent according to claim 4, characterized in that, The pH of the cleaning solution is 6 to 8.

6. The method of using the low-toxicity membrane cleaning agent according to claim 1, characterized in that, The mass concentration of persulfate in the cleaning solution is 30–3000 mg / L, and the mass concentration ratio of hydrochloride to persulfate is 1:2–5.

7. The method of using the low-toxicity membrane cleaning agent according to claim 1, characterized in that, The membrane module is an organic membrane or an inorganic membrane.

8. The method of using the low-toxicity membrane cleaning agent according to claim 1, characterized in that, The cleaning time for the membrane assembly is 0.5 to 24 hours.

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