TWI855268B - Cleaning agent composition and clean-in-place method for biofilm of reverse osmosis membrane - Google Patents

Abstract

The present invention is related to a cleaning agent composition and a clean-in-place method for a reverse osmosis membrane. Prepared by specific amounts of anionic surfactant (A), non-ionic surfactant (B), organic phosphate (C), alkali (D) and a balance amount of water (E), the cleaning agent composition is highly compatible with the reverse osmosis membrane, and can effectively remove an organic foulant away from the surface of the reverse osmosis membrane, thereby can be used in clean-in-place cleaning of the reverse osmosis membrane.

Description

Reverse osmosis membrane biofilm cleaning agent composition and in-situ cleaning method

The present invention relates to a cleaning agent composition, in particular to a cleaning agent composition for a reverse osmosis membrane and an in-situ cleaning method.

Reverse osmosis system is a common technology for water treatment such as wastewater treatment and/or seawater desalination, in which the reverse osmosis membrane is the key to whether the reverse osmosis system can operate normally. When the reverse osmosis membrane is blocked, the pressure difference of the reverse osmosis membrane increases, and the water production decreases, resulting in a significant reduction in the efficiency of reverse osmosis. The fouling that blocks the reverse osmosis membrane includes inorganic scaleants and organic foulants. The cause of inorganic scaleants can be, for example, the precipitation of inorganic salts, and the cause of organic foulants can be, for example, the deposition and/or attachment of colloids, natural organic matter and/or microorganisms.

The fouling that blocks the reverse osmosis membrane is mainly organic fouling, among which microorganisms are one of the causes of serious blockage of the reverse osmosis membrane. This is because the extracellular polymeric substances (EPS) secreted by microorganisms can form a biofilm on the surface of the reverse osmosis membrane, which allows the microorganisms to attach more firmly to the surface of the reverse osmosis membrane and increase the tolerance of the microorganisms to chemicals and/or disinfectants, making it difficult to remove organic fouling from the reverse osmosis membrane by clean-in-place. Although there are cleaning agents on the market that can clean organic deposits in situ, they are not very effective in cleaning severely blocked reverse osmosis membranes. Off-line cleaning is still required to restore the pressure difference of the reverse osmosis membrane, thus affecting the water treatment process.

In view of this, there is an urgent need for a reverse osmosis membrane cleaning agent composition and an in-situ cleaning method to solve the above problems.

Therefore, one aspect of the present invention is to provide a reverse osmosis membrane cleaning agent composition, wherein the cleaning agent composition may include a non-ionic surfactant (A), an anionic surfactant (B), an organic phosphate (C), an alkali (D) and water (E). The cleaning agent composition excludes the use of a bactericide, has high compatibility with the reverse osmosis membrane, and can effectively remove organic deposits on the surface of the reverse osmosis membrane.

Another aspect of the present invention is to provide an in-situ cleaning method for a reverse osmosis membrane, comprising an alkaline washing step using the reverse osmosis membrane.

According to the above aspects of the present invention, a reverse osmosis membrane cleaning agent composition is provided, which may include but is not limited to 1.0 wt% to 5.0 wt% of a non-ionic surfactant (A), 0.5 wt% to 1.5 wt% of an anionic surfactant (B), 0.1 wt% to 1.0 wt% of an organic phosphate (C), 0.1 wt% to 0.5 wt% of an alkali (D) and a balance of water, but excludes the use of a bactericide. In one embodiment, the pH value of the cleaning agent composition may be, for example, 11 to 12.

In some embodiments, the hydrophilic-lipophilic balance (HLB) of the non-ionic surfactant (A) may be, for example, 10 to 15. In a specific example, the non-ionic surfactant (A) may optionally include: alkyl polyethylene glycol ether, alkylphenol polyethylene glycol ether, aromatic hydrocarbon polyethylene glycol ether, castor oil polyethylene glycol ether and/or polyethylene glycol fatty acid ester.

In the above embodiment, the anionic surfactant (B) may optionally include sodium dodecylbenzene sulfonate, sodium dodecyl sulfate and/or sodium α-olefin sulfonate. In one embodiment, the organic phosphate (C) may optionally include aminotrimethylene phosphonic acid, hydroxyethylene diphosphonic acid and/or ethylenediaminetetramethylene phosphonic acid. In one embodiment, the alkali (D) may include an alkali metal hydroxide.

According to another aspect of the present invention, a method for in-situ cleaning of a reverse osmosis membrane is provided. First, a diluent is prepared, wherein the diluent may include, but is not limited to, 2 vol% to 3 vol% of a cleaning agent composition and water. Then, an alkali washing step is performed at 30°C to 60°C, wherein the alkali washing step may include a soaking step to soak the reverse osmosis membrane in the diluent, and a circulating washing step to utilize the diluent to generate shear force on the reverse osmosis membrane. Then, an acid washing step is performed with a hydrochloric acid solution of pH 2 to 3. After the acid washing step, the pressure difference of the reverse osmosis membrane may be, for example, less than 2.2 kg/cm ² . In one embodiment, after the alkaline washing step and the acid washing step are repeated, the pressure difference may be, for example, no greater than 1.5 kg/cm ² . In one embodiment, the reverse osmosis membrane may be, for example, a polyamide (PA) membrane.

The cleaning agent composition and in-situ cleaning method for reverse osmosis membrane of the present invention comprises a specific content of non-ionic surfactant (A), anionic surfactant (B), organic phosphate (C), alkali (D) and water (E) to exclude the bactericide. The cleaning agent composition has high compatibility with the reverse osmosis membrane and can effectively remove organic foulants on the surface of the reverse osmosis membrane.

The making and using of embodiments of the present invention are discussed in detail below. However, it will be appreciated that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific contexts. The specific embodiments discussed are for illustration only and are not intended to limit the scope of the present invention.

The present invention provides a reverse osmosis membrane cleaning agent composition and an in-situ cleaning method thereof, wherein the reverse osmosis membrane cleaning agent composition comprises a specific composition but excludes the use of a bactericide. The cleaning agent composition has high compatibility with the reverse osmosis membrane and can effectively remove organic foulants from the reverse osmosis membrane.

The cleaning agent composition of the reverse osmosis membrane of the present invention can be applied to the in-situ cleaning method of the reverse osmosis membrane. In some embodiments, the reverse osmosis membrane can be, for example, a polyamide membrane (PA), specifically an aromatic polyamide, which is resistant to biological corrosion and is therefore often used at the front end of the reverse osmosis system to remove organic matter in the water body. However, the antioxidant capacity of the polyamide membrane is poor, so the cleaning agent composition used needs to exclude the use of strong oxidants. In some embodiments, the reverse osmosis membrane can be, for example, cellulose acetate, polysulfate and/or polyethersulfate. The cleaning agent composition of the reverse osmosis membrane of the present invention comprises a non-ionic surfactant (A), an anionic surfactant (B), an organic phosphate (C), an alkali (D) and water (E). In one embodiment, in order to facilitate storage and to accurately control the specific ratio of the cleaning agent composition, the cleaning agent composition can be prepared as a concentrated solution, and then diluted with water to 2 volume percent (vol%) to 3 vol% when used.

The non-ionic surfactant (A) has good dispersibility for organic foulants and good permeability for biofilms, so that the cleaning agent composition can quickly penetrate the biofilm and disperse the biofilm without agglomeration. In some embodiments, the hydrophilic lipophilic balance (HLB) of the non-ionic surfactant (A) can be, for example, 10 to 15, so as to have better permeability and higher compatibility with reverse osmosis membranes. In one embodiment, the non-ionic surfactant (A) comprises alkyl polyethylene glycol ether, alkylphenol polyethylene glycol ether, aromatic hydrocarbon polyethylene glycol ether, castor oil polyethylene glycol ether and/or polyethylene glycol fatty acid ester, wherein specific examples of the alkyl polyethylene glycol ether may be polyethylene glycol dodecyl ether, polyethylene glycol tridecyl ether, polyethylene glycol hexadecyl/oleyl ether and/or polyethylene glycol hexadecyl/octadecyl ether, but the present invention is not limited thereto.

The cleaning agent composition may contain 1.0 wt% to 5.0 wt% of the non-ionic surfactant (A), and preferably 0.75 wt% to 1.25 wt%. When the content of the non-ionic surfactant (A) is less than 1.0 wt%, the cleaning agent composition has insufficient permeability and dispersibility, and thus cannot quickly penetrate the biofilm, nor can it effectively disperse organic foulants, thereby reducing the efficiency of the cleaning agent composition in removing organic foulants. When the content of the non-ionic surfactant (A) is greater than 5.0 wt%, the cleaning agent composition is prone to generate excessive foam, thereby affecting the subsequent treatment of the in-situ cleaning method.

The anionic surfactant (B) may have good emulsification and dispersion effects to prevent organic deposits from reattaching to the surface of the reverse osmosis membrane during the cleaning process. In one embodiment, the anionic surfactant (B) may include but is not limited to sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfonate, sodium dodecyl sulfate and/or sodium α-olefin sulfonate.

The cleaning agent composition may contain 0.5 wt% to 1.5 wt% of anionic surfactant (B), and preferably 0.75 wt% to 1.25 wt%. When the content of the anionic surfactant (B) is less than 0.5 wt%, the emulsification and dispersibility of the cleaning agent composition are insufficient, and the organic fouling cannot be effectively removed. When the content of the anionic surfactant (B) is greater than 1.5 wt%, the cleaning agent composition is prone to generate excessive foam, thereby affecting the subsequent treatment of the in-situ cleaning method.

In one embodiment, the weight ratio of the non-ionic surfactant (A) to the anionic surfactant (B) may be, for example, 0.67 to 10, preferably 2 to 4. When the weight ratio of the two is within the aforementioned range, the non-ionic surfactant (A) can accelerate the penetration of the anionic surfactant (B) into the biofilm, thereby effectively emulsifying and dispersing organic foulants, thereby improving the cleaning performance of organic foulants.

Organic phosphate (C) can make the particles of inorganic scale have the same charge, and can stably disperse the inorganic scale in the water body, thereby preventing the inorganic scale from re-depositing on the reverse osmosis membrane. Secondly, organic phosphate (C) can also destroy the bond between inorganic ions (such as calcium) and extracellular polymers in the biofilm, making the biofilm loose and easier to remove. In one embodiment, the organic phosphate (C) can optionally include amino trimethylene phosphonic acid (ATMP), 1-diphosphonic acid (HEDP) and/or ethylenediamine tetra(methylene phosphonic acid), EDTMP.

It is worth noting that, since organic phosphate (C) has a good threshold inhibition effect, that is, there is no chemical dosage relationship between organic phosphate and inorganic scale and/or organic scale, only a small amount of organic phosphate (C) (e.g., 0.1 wt% to 1.0 wt%) is required in the cleaning agent composition to effectively prevent the scaling of inorganic scale and/or organic scale. However, when the amount of organic phosphate (C) used increases (e.g., greater than 1.0 wt%), the above-mentioned scale inhibition effect is not significantly improved.

The alkali (D) is used to adjust the pH value of the cleaning agent composition, wherein the alkali (D) may include an alkali metal hydroxide, specifically sodium hydroxide and/or potassium hydroxide. The cleaning agent composition contains 0.1 wt% to 0.5 wt% of the alkali (D), so that the pH value of the cleaning agent composition may be, for example, 11 to 12. If the content of the alkali (D) is less than 0.1 wt%, the cleaning agent composition cannot effectively hydrolyze and/or dissolve the biofilm, but if the content of the alkali (D) is greater than 0.5 wt%, the cleaning agent composition will destroy the structure of the reverse osmosis membrane.

It is worth noting that the cleaning agent composition of the reverse osmosis membrane of the present invention excludes the use of bactericides, because if the bactericide cannot completely remove the microorganisms in the biofilm, it will cause the microorganisms to secrete more extracellular polymers, thereby increasing the difficulty of removal. The above-mentioned bactericide may include but is not limited to oxidizing bactericides (such as sodium hypochlorite) or non-oxidizing bactericides [such as isothiazolinone or tributyl tetradecyl phosphonium chloride (TTPC). In addition, the cleaning agent composition of the reverse osmosis membrane of the present invention does not need to add additional metal chelating agents and/or biological surfactants (such as rhamnolipids) to effectively remove organic deposits without destroying the structure of the reverse osmosis membrane.

The present invention also provides an in-situ cleaning method for a reverse osmosis membrane. The cleaning method uses a dilution of the above-mentioned cleaning agent composition. Specifically, the dilution contains 2 vol% to 3 vol% of the cleaning agent composition and a balance of water. Then, an alkaline washing step is performed at 30°C to 60°C, wherein the alkaline washing step includes a soaking step and a circulating washing step. The soaking step may, for example, soak the reverse osmosis membrane in a diluent so that the diluent fully penetrates, emulsifies and disperses the organic and/or inorganic foulants on the surface of the reverse osmosis membrane, and the circulating cleaning step utilizes the diluent to generate shear force on the reverse osmosis membrane to flush the organic and/or inorganic foulants on the surface of the reverse osmosis membrane.

The aforementioned soaking step and circulation cleaning step are both performed in the reverse osmosis column. In other words, the soaking step and circulation cleaning step are to introduce the dilute solution into the reverse osmosis column to soak and circulate the reverse osmosis membrane therein. The reverse osmosis membrane is soaked in the dilute solution for 3 to 5 hours, and during the circulation cleaning step, the dilute solution is circulated in the reverse osmosis column for 0.5 to 2 hours.

Next, reverse osmosis water is introduced into the reverse osmosis column to wash away the diluent, and then a hydrochloric acid solution with a pH of 2 to 3 is used for an acid washing step. After the acid washing step, the hydrochloric acid solution in the column is washed away with reverse osmosis water.

The in-situ cleaning method can effectively remove organic fouling on the reverse osmosis membrane, and its cleaning effect can be evaluated by the pressure difference after cleaning, where "pressure difference" refers to the difference between the pressure before the membrane and the pressure after the membrane when the water passes through the reverse osmosis membrane. Taking a two-stage reverse osmosis system as an example, the upper limit of the operating pressure difference of each vessel is 3.5 kg/ ^cm2 , but in order to avoid damaging the reverse osmosis membrane, reverse osmosis is usually operated at a pressure difference of less than 1.5 kg/ ^cm2 , and it is considered that when the pressure difference is greater than 1.5 kg/ ^cm2 , it means that the reverse osmosis membrane is blocked, and when the pressure difference is greater than 2.5 kg/ ^cm2 , it means that the reverse osmosis membrane is seriously blocked.

It is particularly noted that the cleaning agent composition has a high compatibility with the reverse osmosis membrane, so it will not destroy the structure of the reverse osmosis membrane, and will not affect the reverse osmosis efficiency of the reverse osmosis membrane. The reverse osmosis efficiency can be evaluated, for example, by the desalination rate, wherein the desalination rate refers to the relative salt content of the water after passing through the reverse osmosis membrane relative to the water before passing through the reverse osmosis membrane.

Experiments have shown that using the above cleaning agent composition to clean the reverse osmosis membrane once can reduce the pressure difference of a severely blocked reverse osmosis membrane (e.g., the pressure difference is greater than 2.5 kg/cm ² ) to less than 2.2 kg/cm ² . If another in-situ cleaning is performed, the pressure difference of the reverse osmosis membrane can be reduced to no more than 1.5 kg/cm ² .

Several embodiments are used below to illustrate the application of the present invention, but they are not intended to limit the present invention. Those with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Embodiment 1

First, prepare the cleaning solution of Example 1, wherein the cleaning solution comprises 3 wt% of polyethylene glycol tridecyl ether, 1 wt% of sodium dodecylbenzene sulfonate, 0.5 wt% of aminotrimethylenephosphonic acid and 0.3 wt% of sodium hydroxide. Then, add water to dilute the cleaning solution to 2 vol% to 3 vol%.

Next, the severely clogged (pressure difference not less than 2.5kg/ ^cm2 ) reverse osmosis membrane was immersed in a 40°C dilute solution for 4 hours, and the dilute solution was circulated to clean the reverse osmosis membrane for 1 hour. Then, after the dilute solution on the reverse osmosis membrane was washed away with reverse osmosis water, an acid washing step was performed with a hydrochloric acid solution of pH 2 to 3, and the hydrochloric acid solution was washed away with reverse osmosis water. Afterwards, the pressure difference and desalination rate of the reverse osmosis membrane after cleaning were measured, and the results were recorded in Table 1. Comparative Examples 1 to 5

The cleaning methods of Comparative Examples 1 to 5 are the same as those of Example 1, except that the cleaning solution of Comparative Example 1 is a sodium hydroxide aqueous solution with a pH of 11 to 12, the cleaning solution of Comparative Example 2 is a sodium hydroxide aqueous solution (pH of 11 to 12) containing 1 wt% of sodium dodecyl sulfate aqueous solution, the cleaning solution of Comparative Example 3 is a sodium hydroxide aqueous solution (pH of 11 to 12) containing 2.5 vol% of butyltetradecylphosphonium chloride, the cleaning solution of Comparative Example 4 is a 7 wt% sodium chloride aqueous solution, and the cleaning solution of Comparative Example 5 is a sodium hydroxide aqueous solution (pH of 11 to 12) containing 1 wt% of sodium dodecyl sulfate and 0.5 wt% of aminotrimethylenephosphonic acid. When used, water was added to dilute the cleaning solution of Comparative Examples 1 to 5 to a dilution of 2 vol% to 3 vol%. The measurement results of the pressure difference and desalination rate of the reverse osmosis membrane after cleaning of Comparative Examples 1 to 5 are recorded in Table 1. Table 1 Group Embodiment Comparison Example 1 1 2 3 4 5 Pressure difference (kg/cm ² ) Before cleaning 2.8 2.5 2.8 3.1 2.8 2.7 After cleaning 1.8 2.4 2.2 2.2 2.8 2.3 Desalination rate (%) After cleaning 95.2 95.2 Not tested

As shown in Table 1, the cleaning solution of Example 1 includes anionic surfactant (A), non-ionic surfactant (B), organic phosphate (C), alkali (D) and water (E), and after in-situ cleaning with the cleaning solution of Example 1, the pressure difference of the reverse osmosis membrane can be changed from 2.8 kg/ ^cm2 to 1.8 kg/ ^cm2 .

The cleaning solution of Comparative Example 1 is the cleaning solution recommended in the user manual of a commercially available reverse osmosis membrane. However, after in-situ cleaning with the cleaning solution of Comparative Example 1, the pressure difference of the reverse osmosis membrane was 2.4 kg/cm ² , indicating that the conventional cleaning method cannot effectively remove organic foulants.

The cleaning solution of Comparative Example 2 contains anionic surfactant, and the cleaning solution of Comparative Example 3 contains bactericide. However, after in-situ cleaning with the cleaning solution of Comparative Example 2 or Comparative Example 3, the pressure difference of the reverse osmosis membrane is still as high as 2.2 kg/cm ² .

High concentration sodium chloride can change the cross-linking structure of colloidal organic foulants and destroy the bond between calcium ions and organic foulants by ion exchange. However, the cleaning solution of Comparative Example 4 (high concentration sodium chloride aqueous solution) cannot effectively reduce the pressure difference of the blocked reverse osmosis membrane.

The anionic surfactant used in Comparative Example 5 is sodium dodecyl sulfate, and no non-ionic surfactant is used. Therefore, when the cleaning solution of Comparative Example 5 is used for in-situ cleaning, the pressure difference of the reverse osmosis membrane is still as high as 2.3 kg/cm ² .

It is additionally noted that after repeated in-situ cleaning with the cleaning solution of Example 1, the pressure difference of the reverse osmosis membrane can be further reduced to 1.4 kg/cm ² , reaching the standard of a pressure difference of no more than 1.5 kg/cm ^2. However, after the second in-situ cleaning with the cleaning solutions of Comparative Examples 1 to 5, the pressure difference of the reverse osmosis membrane is still almost the same as that after the first cleaning, and is still greater than 2.0 kg/cm ² , and there is no improvement after multiple cleanings.

It is worth noting that after in-situ cleaning using the cleaning solutions of Example 1 and Comparative Example 1, the desalination rates of the reverse osmosis membranes were both 95.2%, indicating that the cleaning solution of Example 1 is highly compatible with the reverse osmosis membrane and will not affect the reverse osmosis performance of the reverse osmosis membrane.

As can be seen from the above embodiments, the reverse osmosis membrane cleaning agent composition and the in-situ cleaning method of the present invention have the advantages of comprising specific components, having high compatibility with the reverse osmosis membrane, and being able to effectively remove organic deposits on the surface of the reverse osmosis membrane, and thus being applicable to the cleaning and/or maintenance of the reverse osmosis system for wastewater treatment and/or seawater purification.

Although the present invention has been disclosed as above with several specific embodiments, various modifications, changes and substitutions may be made to the above disclosed contents, and it should be understood that, without departing from the spirit and scope of the present invention, certain features of the embodiments of the present invention will be adopted in certain situations but other features will not be used accordingly. Therefore, the spirit and scope of the claims of the present invention should not be limited to the above exemplary embodiments.

without

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Claims (8)

A cleaning agent composition for biofilm of reverse osmosis membrane, wherein the cleaning agent composition is formulated to remove biofilm, comprising: 1.0wt% to 5.0wt% of polyethylene glycol tridecyl ether; 0.5wt% to 1.5wt% of anionic surfactant (B); 0.1wt% to 1.0wt% of aminotrimethylenephosphonic acid; 0.1wt% to 0.5wt% of alkali (D); and a balanced amount of water (E), wherein the cleaning agent composition excludes the use of a bactericide, and a weight ratio of the polyethylene glycol tridecyl ether to the anionic surfactant (B) is 2 to 3. The reverse osmosis membrane biofilm cleaning agent composition as described in claim 1, wherein the hydrophilic-lipophilic balance value of the polyethylene glycol tridecyl ether is 10 to 15. The cleaning agent composition for the biofilm of the reverse osmosis membrane as described in claim 1, wherein the anionic surfactant (B) comprises sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate and/or sodium α-olefin sulfonate. The cleaning agent composition for the biofilm of the reverse osmosis membrane as described in claim 1, wherein the alkali agent (D) comprises an alkali metal hydroxide. A cleaning agent composition for a biofilm of a reverse osmosis membrane as described in claim 1, wherein the pH value of the cleaning agent composition is 11 to 12. A method for in-situ cleaning of a biofilm of a reverse osmosis membrane comprises: preparing a dilution solution, wherein the dilution solution comprises: 2 vol% to 3 vol% of a cleaning agent composition as described in any one of claims 1 to 5; and a balance amount of water; performing an alkali washing step at 30°C to 60°C, wherein the alkali washing step comprises: performing an immersion step to immerse the reverse osmosis membrane in the dilution solution; and performing a circulation washing step to generate a shear force on the reverse osmosis membrane using the dilution solution; and performing an acid washing step with a hydrochloric acid solution of pH 2 to 3, and after the acid washing step, a pressure difference of the reverse osmosis membrane is less than 2.2 kg/ ^cm2 . In the in-situ cleaning method of a biofilm of a reverse osmosis membrane as described in claim 6, after the alkaline washing step and the acid washing step are repeated, the pressure difference is no more than 1.5 kg/cm ² . An in-situ cleaning method for a biofilm of a reverse osmosis membrane as described in claim 6, wherein the reverse osmosis membrane is a polyamide membrane.