WO2022144578A1

WO2022144578A1 - Method and composition for membrane cleaning

Info

Publication number: WO2022144578A1
Application number: PCT/IB2020/062582
Authority: WO
Inventors: Mehrdad DINIAN
Original assignee: Dinian Mehrdad
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-07-07

Abstract

An exemplary method for cleaning a membrane, such as a reverse osmosis (RO) membrane may include preparing an aphron-based cleaning fluid and pumping an exemplary aphron-based cleaning fluid into an exemplary RO membrane. In an exemplary embodiment, preparing an aphron-based cleaning fluid may include preparing a first mixture by mixing a surfactant and a cleaning chemical with water, preparing a second mixture by mixing pressurized air with an exemplary first mixture, and generating microbubbles in an exemplary second mixture by imparting shear stress to an exemplary second mixture in a stirred vessel.

Description

METHOD AND COMPOSITION FOR MEMBRANE CLEANING

TECHNICAL FIELD

[0001] The present disclosure relates to methods and compositions for cleaning membranes and particularly relates to methods and compositions for cleaning reverse osmosis membranes. More particularly, the present disclosure relates to a method for cleaning membranes utilizing an aphron-based cleaning composition.

BACKGROUND ART

[0002] Membranes that are utilized in membrane separation processes, such as in reverse osmosis (RO) water treatment processes, may become fouled by suspended solids, mineral scale, and microorganisms, over time. Such deposits may build up during operation and may cause increase in pressure drop, decrease in permeate recovery, and decrease in salt rejection. Consequently, membrane elements must be cleaned to remove such deposits. Specifically, in RO water treatment, any noticeable increase of salt content in the product water or in pressure drop may indicate that membrane elements are fouled and need to be cleaned.

[0003] A membrane cleaning process may include physical cleaning, chemical cleaning, or a combination of both. Physical cleaning may be performed to remove reversible fouling, such as deposited solids without utilizing any chemical reagents. Physical cleaning methods may generally include applying hydraulic or mechanical forces to dislodge foulants from the membrane surface. Chemical cleaning, on the other hand, may be used for irreversible fouling removal with the help of a combination of chemical agents such as acid solutions, bio-acid solutions, and alkaline solutions. Such chemical agents may dissolve foulants and this way a part of foulants may be removed. However, due to limited access of such chemical agents to all layers of foulants formed on the membrane surface and limited exposure time, a considerable portion of foulants may still remain on the membrane surfaces. The remaining portion of foulants may act as seeds for formation of new deposits on the membrane surfaces. [0004] There is, therefore, a need for a cleaning method for membranes, such as RO membranes, that may allow for performing both physical and chemical cleaning of the membrane surfaces. There is further a need for a method that may allow for performing a micro-scale physical cleaning of the membranes along with an effective chemical cleaning, which may remove both reversible and irreversible fouling, efficiently. SUMMARY OF THE DISCLOSURE

[0005] This summary is intended to provide an overview of the subject matter of the present disclosure and is not intended to identify essential elements or key elements of the subject matter, nor is it intended to be used to determine the scope of the claimed implementations. The proper scope of the present disclosure may be ascertained from the claims set forth below in view of the detailed description and the drawings.

[0006] According to one or more exemplary embodiments, the present disclosure is directed to a method for cleaning a membrane, such as a reverse osmosis (RO) membrane. An exemplary method may include preparing an aphron-based cleaning fluid and pumping an exemplary aphron-based cleaning fluid into an exemplary membrane. In an exemplary embodiment, preparing an aphron-based cleaning fluid may include preparing a first mixture by mixing a surfactant and a cleaning chemical with water, preparing a second mixture by mixing pressurized air with an exemplary first mixture, and generating microbubbles in an exemplary second mixture by imparting shear stress to an exemplary second mixture by a rotating disk stirrer disposed within an exemplary second mixture.

[0007] An exemplary cleaning chemical may include at least one of citric acid powder, a mixture of sodium tripolyphosphate (STPP) powder and sodium ethylenediaminetetraacetic acid (Na-EDTA), a mixture of STPP and sodium dodecylbenzene sulfonate (Na-DDBS), hydrochloric acid, sodium hydrosulfite powder, a mixture of sodium hydroxide (NaOH) powder and sodium dodecylsulfate (SDS), NaOH powder.

[0008] An exemplary surfactant may include anionic and non-ionic surfactants, such as at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkylphenol ethoxylates, cetyl trimethylammonium bromide, and polysorbate 20. An exemplary surfactant may have a concentration between 0.07 wt.% and 0.56 wt.% based on a total weight of the first mixture.

[0009] In an exemplary embodiment, preparing an exemplary first mixture may further include mixing an exemplary polymer with an exemplary first mixture. An exemplary polymer may include at least one of anionic polymers, neutral polymers, and poly electrolytes. An exemplary polymer may further include at least one of polyacrylamide, Xanthan gum, and starch. An exemplary polymer may have a concentration between 0.14 wt.% and 1.42 wt.% based on the total weight of the first mixture. [0010] In an exemplary embodiment, preparing an exemplary first mixture may further include mixing exemplary nanoparticles with an exemplary first mixture. Exemplary nanoparticles may include nanoparticles of at least one of a biopolymer, magnesium oxide, polyacrylamide, polyvinyl alcohol, and ether sulfates. Exemplary nanoparticles may have a concentration between 0 and 0.28 wt.% based on the total weight of the first mixture.

[0011] In an exemplary embodiment, preparing an exemplary second mixture may include mixing an exemplary pressurized air with an exemplary first mixture, where a volume ratio of the pressurized air and the first mixture may be between 1:2.5 and 1:3 (volume of the first mixture: volume of the pressurized air).

[0012] In an exemplary embodiment, mixing the pressurized air with the first mixture may include mixing an exemplary first mixture at a first pressure with an exemplary pressurized air at a second pressure, where the second pressure may exceed the first pressure by 0.1 to 0.4 atmosphere.

[0013] In an exemplary embodiment, generating microbubbles in an exemplary second mixture may include stirring an exemplary second mixture in an exemplary stirred vessel. An exemplary stirred vessel may include an enclosed vessel, and at least one rotating disc impeller that may be disposed within an exemplary enclosed vessel. An exemplary rotating disc impeller may rotate at a rate between 8000 and 12000 rpm thereby imparting shear stress to an exemplary second mixture.

[0014] An exemplary rotating disc impeller may include a flat disk rotating at a rotational plane parallel with base ends of the cylindrical vessel. A diameter of an exemplary cylindrical vessel may be at most 3.5 times a diameter of an exemplary rotating disk stirrer.

[0015] An exemplary cylindrical vessel may further include at least one baffle. An exemplary baffle may include a flat plate that may be extended along a longitudinal axis of an exemplary cylindrical vessel and may be positioned adjacent an outer periphery of an exemplary rotating disc. An exemplary enclosed vessel may be pressurized to a pressure between 1 and 6 bars.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The novel features which are believed to be characteristic of the present disclosure, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the present disclosure will now be illustrated by way of example. It is expressly understood, however, that the drawings are for illustration and description only and are not intended as a definition of the limits of the present disclosure. Embodiments of the present disclosure will now be described by way of example in association with the accompanying drawings in which:

[0017] FIG. 1 illustrates a flowchart of a method for cleaning an RO membrane, consistent with one or more exemplary embodiments of the present disclosure;

[0018] FIG. 2 illustrates a flow diagram of a system for preparing an aphron fluid, consistent with one or more exemplary embodiments of the present disclosure; and

[0019] FIG. 3 illustrates a flow diagram of a system for cleaning an RO membrane, consistent with one or more exemplary embodiments of the present disclosure.

DESCRIPTION OF EMBODIMENTS

[0020] The novel features which are believed to be characteristic of the present disclosure, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.

[0021] The present disclosure is directed to exemplary embodiments of a method for cleaning membranes, specifically, reverse osmosis (RO) membranes. An exemplary cleaning method may utilize an aphron-based cleaning composition that may perform both physical and chemical cleaning of the membrane surfaces. An exemplary aphron-based cleaning composition may include aphrons, which are basically multi-layer bubbles, surrounded by a thin surfactant film. An exemplary aphron may be a colloidal gas aphron that may include tightly packed spherical bubbles with an average size of between 10 and 100 pm and may behave like a colloidal system. An exemplary aphron-based cleaning composition may include a gas aphron made of a gaseous core surrounded by a thin multi-layered aqueous surfactant shell. An exemplary colloidal gas aphron may be generated by stirring an aqueous surfactant solution in a baffled vessel by a disk impeller that may have a rotational speed of between 8000 and 12000 rpm. In addition to the aforementioned method, other methods such as homogenization and sonication may be used for producing colloidal gas aphrons, as well.

[0022] An exemplary aphron-based cleaning composition may further include chemical cleaning agents. Since an exemplary RO membrane may experience both fouling by organic substances and fouling by inorganic substances, a combination of two or more reagents, such as acid reagents and alkali reagents may be utilized for preparation of an exemplary aphron- based cleaning composition. Such combination of an exemplary colloidal gas aphron and chemical cleaning agents may have similar flow properties to those of pure water. In an exemplary embodiment, bursting of tightly packed micro bubbles of an exemplary aphron- based cleaning composition next to fouling and contamination deposits on a membrane surface may create a force that may dislodge foulants from the membrane surface, while chemical agents present in the composition of an exemplary aphron-based cleaning composition may dissolve the foulants. Consequently, an exemplary aphron-based cleaning composition may perform both physical and chemical cleanings on the membrane surface with a relatively higher efficiency compared to water-based cleaning compositions. In addition, such simultaneous physical and chemical cleaning of an RO membrane may reduce the amount of chemical agents utilized for cleaning and may make cleaning more feasible.

[0023] FIG. 1 illustrates a flowchart of a method 100 for cleaning a membrane, such as an RO membrane, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, method 100 may include a step 102 of preparing an aphron-based cleaning fluid and a step 104 of pumping the aphron-based cleaning fluid into the membrane. As used herein, pumping an aphron-based cleaning fluid into a membrane may refer to pumping an aphron-based cleaning fluid into an inlet of a membrane. In an exemplary embodiment, step 102 of preparing the aphron-based cleaning fluid may include a step 120 of preparing a first mixture by mixing a surfactant and a cleaning chemical with water, a step 122 of preparing a second mixture by mixing pressurized air with the first mixture, and a step 124 of generating microbubbles in the second mixture by imparting shear stress to the second mixture in a stirred vessel by a rotating disk stirrer.

[0024] In an exemplary embodiment, step 120 of preparing the first mixture may include mixing the surfactant and the cleaning chemical with water in a stirred vessel. In an exemplary embodiment, the cleaning chemical may include at least one of citric acid powder, a mixture of sodium tripolyphosphate (STPP) powder and sodium ethylenediaminetetraacetic acid (Na- EDTA), a mixture of STPP and sodium dodecylbenzene sulfonate (Na-DDBS), hydrochloric acid, sodium hydrosulfite powder, a mixture of sodium hydroxide (NaOH) powder and sodium dodecylsulfate (SDS), and NaOH powder. In an exemplary embodiment, the cleaning chemical may be selected based on the type of contamination that needs to be removed. For example, the cleaning chemical may include citric acid that may be mixed with water with a concentration of 0.17 pounds per gallon of water. In an exemplary embodiment, the cleaning chemical may include a mixture of STPP and Na-EDTA powders that may be mixed with water with a concentration of STPP equal to approximately 17 pounds per 100 gallon of water and a concentration of Na-EDTA equal to approximately 7 pounds per 100 gallon of water. In an exemplary embodiment, the cleaning chemical may include a mixture of STPP and Na-DDBS powders that may be mixed with water with a concentration of STPP equal to approximately 17 pounds per 100 gallon of water and a concentration of Na-DDBS equal to approximately 0.21 pounds per 100 gallon of water. In an exemplary embodiment, the cleaning chemical may include hydrochloric acid that may be mixed with water with a concentration of 0.47 gallons of hydrochloric acid per 100 gallon of water. In an exemplary embodiment, the cleaning chemical may include sodium hydrosulfite powder that may be mixed with water with a concentration of approximately 8.5 pounds per 100 gallon of water. In an exemplary embodiment, the cleaning chemical may include a mixture of NaOH and SDS powders that may be mixed with water with a concentration of NaOH equal to approximately 0.83 pound per 100 gallons of water and a concentration of SDS equal to approximately 0.25 pounds per 100 gallon of water. In an exemplary embodiment, the cleaning chemical may include NaOH powder that may be mixed with water with a concentration of approximately 0.83 pounds per 100 gallons of water.

[0025] In an exemplary embodiment, the surfactant may be an anionic or non-ionic surfactant such as at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkylphenol ethoxylates, cetyl trimethylammonium bromide, and polysorbate 20. In an exemplary embodiment, step 120 of preparing the first mixture may include mixing the surfactant and the cleaning chemical with water, such that the surfactant may have a concentration of between 0.07 wt.% and 0.56 wt.% based on a total weight of the first mixture. [0026] In an exemplary embodiment, step 120 of preparing the first mixture may further include mixing a polymer with the first mixture. In an exemplary embodiment, the polymer may include at least one of anionic polymers, neutral polymers, and poly electrolytes. For example, the polymer may include at least one of polyacrylamide, Xanthan gum, and starch. In an exemplary embodiment, step 120 of preparing the first mixture may further include mixing the polymer with the surfactant, the cleaning chemical, and water, such that the polymer may have a concentration of between 0.14 wt.% and 1.42 wt.% based on the total weight of the first mixture. As used herein mixing the components of the first mixture may refer to mixing the components in a stirred vessel utilizing a mechanical stirrer. [0027] In an exemplary embodiment, step 120 of preparing the first mixture may further include mixing nanoparticles with the first mixture, where the nanoparticles may include nanoparticles of at least one of a biopolymer, magnesium oxide, polyacrylamide, polyvinyl alcohol, and ether sulfates. In an exemplary embodiment, step 120 of preparing the first mixture may include mixing the nanoparticles with the surfactant, the cleaning chemical, the polymer, and water such that the nanoparticles may have a concentration of between 0 and 0.28 wt.% based on the total weight of the first mixture.

[0028] In an exemplary embodiment, step 122 of preparing the second mixture may include mixing pressurized air with the first mixture in a static mixer. In an exemplary embodiment, a volume ratio of the pressurized air and the first mixture is between 1:2.5 and 1:3 (volume of the first mixture: volume of the pressurized air). In an exemplary embodiment, the first mixture may enter an exemplary static mixture at a first pressure and the pressurized air may enter the static mixer at a second pressure. In an exemplary embodiment, the second pressure may be 0.1 to 0.4 atm more than the first pressure.

[0029] In an exemplary embodiment, step 124 of generating microbubbles in the second mixture may include sending the second mixture into a stirred vessel and then stirring the second mixture utilizing a flat disk impeller disposed within the stirred vessel at a high rotational speed between 8000 and 12000 rpm. In an exemplary embodiment, rotational movement of the flat disk impeller within the second mixture may lead to generation of micro bubbles within the second mixture. In an exemplary embodiment, the pressure within the enclosed vessel may be between 1 and 6 bars.

[0030] FIG. 2 illustrates a flow diagram of a system 200 for preparing an aphron-based cleaning fluid, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, system 200 may include a stirred tank 202 that may be equipped with a mechanical stirrer 204, a static mixer 206 that may be utilized for mixing a pressurized air stream 208 with a first mixture stream 210 from stirred tank 202, and an aphron generating device 212 that may be configured to generate micro-bubbles within a received fluid. In an exemplary embodiment, system 200 may further include an air compressor 214 that may be utilized for compressing air to obtain pressurized air stream 208.

[0031] In an exemplary embodiment, system 200 may be configured to perform a method for preparing an aphron-based cleaning fluid similar to step 102 of method 100. For example, step 120 of preparing a first mixture by mixing a surfactant and a cleaning chemical with water may be carried out in a stirred tank similar to stirred tank 202. In an exemplary embodiment, a base cleaning fluid stream 216 and a surfactant stream 218 may enter stirred tank 202, where base cleaning fluid stream 216 and surfactant stream 218 may be mixed utilizing mechanical stirrer 204 to obtain first mixture stream 210. In an exemplary embodiment, base cleaning fluid stream 216 may include a mixture of the cleaning chemical and water. For example, base cleaning fluid stream 216 may include citric acid mixed with water with a concentration of 0.17 pounds per gallon of water. In an exemplary embodiment, base cleaning fluid stream 216 may include a mixture of STPP and Na-EDTA powders mixed with water with a concentration of STPP equal to approximately 17 pounds per 100 gallon of water and a concentration of Na-EDTA equal to approximately 7 pounds per 100 gallon of water. In an exemplary embodiment, base cleaning fluid stream 216 may include a mixture of STPP and Na-DDBS powders mixed with water with a concentration of STPP equal to approximately 17 pounds per 100 gallon of water and a concentration of Na-DDBS equal to approximately 0.21 pounds per 100 gallon of water. In an exemplary embodiment, base cleaning fluid stream 216 may include hydrochloric acid mixed with water with a concentration of 0.47 gallons of hydrochloric acid per 100 gallon of water. In an exemplary embodiment, base cleaning fluid stream 216 may include sodium hydrosulfite powder mixed with water with a concentration of approximately 8.5 pounds per 100 gallon of water. In an exemplary embodiment, base cleaning fluid stream 216 may include a mixture of NaOH and SDS powders mixed with water with a concentration of NaOH equal to approximately 0.83 pound per 100 gallons of water and a concentration of SDS equal to approximately 0.25 pounds per 100 gallon of water. In an exemplary embodiment, base cleaning fluid stream 216 may include NaOH powder mixed with water with a concentration of approximately 0.83 pounds per 100 gallons of water.

[0032] In an exemplary embodiment, step 122 of preparing a second mixture by mixing pressurized air with the first mixture may involve pumping first mixture stream 210 into static mixer 206 utilizing a pump 217, where first mixture stream 210 may be mixed with pressurized air stream 208 to obtain a second mixture stream 220. In an exemplary embodiment, static mixer 206 may include non-moving baffles contained in a housing, where first mixture stream 210 and pressurized air stream 208 may move through the non-moving baffles, thereby pressurized air stream 208 may be dispersed into first mixture stream 210. In an exemplary embodiment, first mixture stream 210 and pressurized air stream 208 may be mixed with a ratio of between 1:2.5 and 1:3. Here, the ratio is defined as the volume flow rate of first mixture stream 210 to the volume flow rate of pressurized air stream 208.

[0033] In an exemplary embodiment, step 124 of generating microbubbles in the second mixture may involve utilizing aphron generating device 212 to generate microbubbles within second mixture stream 220. In an exemplary embodiment, aphron generating device 212 may include an enclosed vessel 222, in which at least one rotating disk stirrer may be housed. For example, aphron generating device 212 may include a first rotating disk stirrer 224 and a second rotating disk stirrer 226 that may be coaxially disposed within enclosed vessel 222. In an exemplary embodiment, aphron generating device 212 may further include a motor 228 that may be mounted on enclosed vessel 222 and may further be coupled with first rotating disk stirrer 224 and second rotating disk stirrer 226 via a drive shaft 230. In an exemplary embodiment, motor 228 may be configured to drive a rotational movement of first rotating disk stirrer 224 and second rotating disk stirrer 226 about a longitudinal axis of drive shaft 230, which is parallel with a longitudinal axis of enclosed vessel 222. As used herein, a longitudinal axis may refer to an axis of an object associated with the longest dimension of that object. In an exemplary embodiment, aphron generating device 212 may further include a first set of baffles 223 mounted adjacent first rotating disk stirrer 224 and a second set of baffles 234 mounted adjacent second rotating disk stirrer 226. In an exemplary embodiment, first rotating disk stirrer 224 and second rotating disk stirrer 226 may be structured as flat discs that may be rotatable about their normal axes. As used herein, a normal axis of an object may refer to an axis perpendicular to the largest surface of that object.

[0034] In an exemplary embodiment, enclosed vessel 222 may be a box-shaped or cylindrical vessel. In case of a cylindrical vessel, a diameter of enclosed vessel 222 may be at most 3.5 times a diameter of either first rotating disk stirrer 224 or second rotating disk stirrer 226. In case of a box-shaped vessel, an equivalent diameter of enclosed vessel 222 may be at most 3.5 times a diameter of either first rotating disk stirrer 224 or second rotating disk stirrer 226. As used herein, an equivalent diameter may refer to the diameter of a circle with the same area as the area of the cross-section of the boxed-shaped vessel.

[0035] In an exemplary embodiment, first set of baffles 223 may include at least one flat plate baffle that may be mounted in an upright position extended along the longitudinal axis of enclosed vessel 222. In an exemplary embodiment, an edge-to-edge lateral distance between the at least one flat plate and first rotating disk stirrer 224 may be between 1 and 3 cm. Similarly, in an exemplary embodiment, second set of baffles 234 may include at least one flat plate baffle that may be mounted in an upright position extended along the longitudinal axis of enclosed vessel 222. In an exemplary embodiment, an edge-to-edge lateral distance between the at least one flat plate and second rotating disk stirrer 226 may be between 5 to 10 cm. In an exemplary embodiment, motor 228 may drive a rotational movement of first rotating disk stirrer 224 or second rotating disk stirrer 226 at a rotational speed of between 8000 and 12000 rpm.

[0036] In an exemplary embodiment, second mixture stream 220 may enter enclosed vessel 222 from a bottom portion of enclosed vessel 222. As used herein, bottom portion may refer to a portion of an outer periphery of enclosed vessel 222, which is close to a lower end 236 of enclosed vessel 222. In an exemplary embodiment, enclosed vessel 222 may be filled with the second mixture. Here, aphron generating device 212 may be operated in a continuous process. In an exemplary embodiment, second mixture stream 220 may continuously be fed into enclosed vessel 222 and first rotating disk stirrer 224 and second rotating disk stirrer 226 may continuously agitate the contents of enclosed vessel 222 to produce a continuous stream of an aphron-based cleaning fluid. Here, the continuous stream of the aphron-based cleaning fluid may be continuously discharged from enclosed vessel 222 via aphron-based cleaning fluid stream 238. In exemplary embodiments, aphron-based cleaning fluid stream 238 may later be utilized for cleaning RO membranes. In an exemplary embodiment, an internal pressure of enclosed vessel 222, which may be determined by the pressure of second mixture stream 220, may be between 1 and 6 bars.

[0037] In an exemplary embodiment, surfactant stream 218 may include a stream of at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkylphenol ethoxylates, cetyl trimethylammonium bromide, and polysorbate 20.

[0038] In an exemplary embodiment, stirred tank 202 may further be utilized for mixing a polymer stream with base cleaning fluid stream 216 and surfactant stream 218, where the polymer stream may be a stream of at least one of anionic polymers, neutral polymers, and poly electrolytes. As used herein, a stream of a substance may also refer to a dose of that substance injected into a vessel. In an exemplary embodiment, stirred tank 202 may further be utilized for mixing a stabilizer stream with the polymer stream, base cleaning fluid stream 216, and surfactant stream 218, where the stabilizer stream may include a stream of at least one of a biopolymer, magnesium oxide, polyacrylamide, polyvinyl alcohol, and ether sulfates. [0039] FIG. 3 illustrates a flow diagram of a system 300 for cleaning an RO membrane 302, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, system 300 may include an aphron generating subsystem 304 that may be connected in fluid communication with a membrane cleaning cycle, where cleaning chemicals from the membrane cleaning cycle may be fed into aphron generating subsystem 304 to produce a continuous flow of an aphron-based cleaning fluid. In an exemplary embodiment, aphron generating subsystem 304 may include a first stirred tank 340 similar to stirred tank 202 that may be equipped with a mechanical stirrer 342 similar to mechanical stirrer 204, a static mixer 344 similar to static mixer 206 that may be utilized for mixing a pressurized air stream 346 with a first mixture stream 348, and an aphron generating device 350 similar to aphron generating device 212 that may be configured to generate micro-bubbles within a received fluid. In an exemplary embodiment, aphron generating subsystem 304 may further include an air compressor 352 similar to air compressor 214 that may be utilized for compressing air to obtain pressurized air stream 346.

[0040] In an exemplary embodiment, one or more additive streams 354 may enter first stirred tank 340, where additive streams 354 may be mixed utilizing mechanical stirrer 342 to obtain an additive mixture stream 356. In an exemplary embodiment, one or more additive streams 354 may include a surfactant, where an exemplary surfactant may include at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkylphenol ethoxylates, cetyl trimethylammonium bromide, and polysorbate 20. In an exemplary embodiment, one or more additive streams 354 may further include a polymer, where an exemplary polymer may include at least one of anionic polymers, neutral polymers, and poly electrolytes. In an exemplary embodiment, one or more additive streams 354 may further include nanoparticles, where exemplary nanoparticles may include nanoparticles of at least one of a biopolymer, magnesium oxide, polyacrylamide, polyvinyl alcohol, and ether sulfates.

[0041] In an exemplary embodiment, additive mixture stream 356 that may include at least one of an exemplary surfactant, an exemplary polymer, and exemplary nanoparticles may be mixed with a stream of a base cleaning fluid stream 306 to obtain first mixture stream 348. In an exemplary embodiment, base cleaning fluid stream 306 may include a mixture of diluting water and at least one of citric acid powder, a mixture of sodium tripolyphosphate (STPP) powder and sodium ethylenediaminetetraacetic acid (Na-EDTA), a mixture of STPP and sodium dodecylbenzene sulfonate (Na-DDBS), hydrochloric acid, sodium hydrosulfite powder, a mixture of sodium hydroxide (NaOH) powder and sodium dodecylsulfate (SDS), and NaOH powder.

[0042] As mentioned before, in an exemplary embodiment, first mixture stream 348 may be mixed with pressurized air stream 346 in static mixer 344 to obtain a second mixture stream 358. In an exemplary embodiment, second mixture stream 358 may continuously be fed into aphron generating device 350, where the second mixture may be stirred utilizing at least one disk impeller to generate micro bubbles within the second mixture and obtain an aphron-based cleaning stream 360 that may be continuously discharged from aphron generating device 350. In an exemplary embodiment, second mixture stream 358 may include pressurized air dispersed into first mixture stream 348, where first mixture stream 348 may be basically a mixture of a base cleaning fluid and additives, such as surfactants, polymers, and stabilizers.

[0043] In an exemplary embodiments, system 300 may further include a second stirred vessel 308 that may be equipped with a mechanical stirrer and may be utilized for mixing cleaning chemicals with a water stream 310 to obtain base cleaning fluid stream 306. In an exemplary embodiment, base cleaning fluid stream 306 may be discharged from second stirred vessel 308 and may either be pumped directly into RO membrane 302 or may be partially pumped into aphron generating subsystem 304 to be mixed with additive mixture stream 356.

[0044] In an exemplary embodiment, the cleaning chemicals may include at least one of citric acid powder, a mixture of sodium tripolyphosphate (STPP) powder and sodium ethylenediaminetetraacetic acid (Na-EDTA), a mixture of STPP and sodium dodecylbenzene sulfonate (Na-DDBS), hydrochloric acid, sodium hydrosulfite powder, a mixture of sodium hydroxide (NaOH) powder and sodium dodecylsulfate (SDS), and NaOH powder.

[0045] In an exemplary embodiment, a first portion of base cleaning fluid stream 306 as first stream 314 may be mixed with additive mixture stream 356 by an ejector 315 and may eventually be utilized for generating aphron-based cleaning fluid stream 360. In an exemplary embodiment, a second portion of base cleaning fluid stream 306 as second stream 316 may be mixed with aphron-based cleaning fluid stream 360 with a predetermined ratio. In an exemplary embodiment, an exemplary predetermined ratio may be adjusted by a valve 318 that may be adjusted between a fully closed position and a fully opened position. In an exemplary embodiment, aphron-based cleaning fluid stream 360 may either be sent directly into RO membrane 302 or may first be partially mixed with base cleaning fluid stream 306 and then be injected into RO membrane 302. [0046] In an exemplary embodiment, RO membrane 302 may include a pressure vessel with a reverse osmosis membrane element or reverse osmosis membrane elements that may be connected in series by a water collection tube. During a cleaning cycle that may go one for 30 to 60 minutes, aphron-based cleaning fluid may circulate within RO membrane 302. In other words, aphron-based cleaning fluid may enter RO membrane 302 via inlet line 301 and may exit through permeate stream 320 and a reject line 324 and may be sent back into second stirred vessel 308 via stream 312 to complete a cleaning cycle. In exemplary embodiments, such configuration of aphron generating subsystem 304 and second stirred vessel 308 and how aphron generating subsystem 304 may be in fluid communication with second stirred vessel 308 may allow for generating an aphron-based cleaning fluid with a wide range of pH and utilizing such aphron-based fluid in a cleaning cycle of a membrane, such as RO membrane 302. As mentioned before, an exemplary aphron-based fluid may allow for both physical and chemical cleaning of an RO membrane, which ensures a thorough cleaning process.

[0047] The embodiments have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0048] The foregoing description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

[0049] The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments but should be defined only in accordance with the following claims and their equivalents.

[0050] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not to the exclusion of any other integer or step or group of integers or steps.

[0051] Moreover, the word "substantially" when used with an adjective or adverb is intended to enhance the scope of the particular characteristic, e.g., substantially planar is intended to mean planar, nearly planar and/or exhibiting characteristics associated with a planar element.

Further use of relative terms such as “vertical”, “horizontal”, “up”, “down”, and “side-to-side” are used in a relative sense to the normal orientation of the apparatus.

Claims

WHAT IS CLAIMED IS:

1. A method for cleaning a membrane, the method comprising: preparing an aphron-based cleaning fluid by: preparing a first mixture by mixing a surfactant and a cleaning chemical with water; preparing a second mixture by mixing pressurized air with the first mixture; and generating microbubbles in the second mixture by imparting shear stress to the second mixture by at least one rotating disk stirrer disposed within the second mixture; and pumping the cleaning fluid into the membrane.

2. The method of claim 1, wherein preparing the first mixture comprises mixing the surfactant and the cleaning chemical with water, the cleaning chemical comprising at least one of citric acid powder, a mixture of sodium tripolyphosphate (STPP) powder and sodium ethylenediaminetetraacetic acid (Na-EDTA), a mixture of STPP and sodium dodecylbenzene sulfonate (Na-DDBS), hydrochloric acid, sodium hydrosulfite powder, a mixture of sodium hydroxide (NaOH) powder and sodium dodecylsulfate (SDS), NaOH powder.

3. The method of claim 1, wherein preparing the first mixture comprises mixing the surfactant and the cleaning chemical with water, the surfactant comprising at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkylphenol ethoxylates, cetyl trimethylammonium bromide, and polysorbate 20.

4. The method of claim 3, wherein the surfactant has a concentration between 0.07 wt.% and 0.56 wt.% based on a total weight of the first mixture. The method of claim 3, wherein preparing the first mixture further comprises mixing a polymer with the first mixture, the polymer comprising at least one of anionic polymers, neutral polymers, and poly electrolytes. The method of claim 5, wherein the polymer comprises at least one of polyacrylamide, Xanthan gum, and starch. The method of claim 5, wherein the polymer has a concentration between 0.14 wt.% and 1.42 wt.% based on the total weight of the first mixture. The method of claim 5, wherein preparing the first mixture further comprises mixing nanoparticles with the first mixture, the nanoparticles comprising nanoparticles of at least one of a biopolymer, magnesium oxide, polyacrylamide, polyvinyl alcohol, and ether sulfates. The method of claim 5, wherein the nanoparticles have a concentration between 0 and 0.28 wt.% based on the total weight of the first mixture. The method of claim 8, wherein preparing the second mixture comprises mixing the pressurized air with the first mixture, wherein a volume ratio of the pressurized air and the first mixture is between 1:2.5 and 1:3 (volume of the first mixture: volume of the pressurized air). The method of claim 9, wherein mixing the pressurized air with the first mixture comprises mixing the first mixture at a first pressure with the pressurized air at a second pressure, the second pressure exceeding the first pressure by 0.1 to 0.4 atmosphere. The method of claim 9, wherein generating microbubbles in the second mixture comprises stirring the second mixture in a stirred vessel, the stirred vessel comprising an enclosed vessel, wherein the at least one rotating disc stirrer disposed within the enclosed vessel, the at least one rotating disc stirrer rotating at a rate between 8000 and 12000 rpm. The method of claim 12, wherein generating microbubbles in the second mixture comprises stirring the second mixture in the stirred vessel, wherein the enclosed vessel comprises a cylindrical vessel, the at least one rotating disc stirrer comprising a flat disk rotating at a rotational plane parallel with base ends of the cylindrical vessel. The method of claim 13, wherein generating microbubbles in the second mixture comprises stirring the second mixture in the stirred vessel, wherein a diameter of the cylindrical vessel is at most 3.5 times a diameter of the at least one rotating disk stirrer. The method of claim 14, wherein generating microbubbles in the second mixture comprises stirring the second mixture in the stirred vessel, the cylindrical vessel further comprising at least one baffle, the at least one baffle comprising a flat plate extended along a longitudinal axis of the cylindrical vessel, positioned adjacent an outer periphery of the rotating disc. The method of claim 15, wherein generating microbubbles in the second mixture comprises stirring the second mixture in the stirred vessel, the enclosed vessel pressurized to a pressure between 1 and 6 bars. A method for cleaning a membrane, the method comprising: preparing an aphron fluid by: preparing a first mixture by mixing a surfactant and a cleaning chemical with water, the cleaning chemical comprising at least one of citric acid powder, a mixture of sodium tripolyphosphate (STPP) powder and sodium ethylenediaminetetraacetic acid (Na-EDTA), a mixture of STPP and sodium dodecylbenzene sulfonate (Na- DDBS), hydrochloric acid, sodium hydrosulfite powder, a mixture of sodium hydroxide (NaOH) powder and sodium dodecylsulfate (SDS), NaOH powder, the

17 surfactant comprising at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkylphenol ethoxylates, cetyl trimethylammonium bromide, and polysorbate 20, the surfactant has a concentration between 0.07 wt.% and 0.56 wt.% based on a total weight of the first mixture; preparing a second mixture by mixing pressurized air at a first pressure with the first mixture at a second pressure, wherein a volume ratio of the pressurized air and the first mixture is between 1:2.5 and 1:3 (volume of the first mixture: volume of the pressurized air), the first pressure exceeding the second pressure by 0.1 to 0.4 atmosphere; and generating microbubbles in the second mixture by imparting shear stress to the second mixture in a stirred vessel, the stirred vessel comprising at least one rotating disk impeller disposed within an enclosed cylindrical vessel, the at least one rotating disc stirrer comprising a flat disk rotating at a rotational plane parallel with base ends of the cylindrical vessel at a rotational speed of between 8000 and 12000, wherein a diameter of the cylindrical vessel is at most 3.5 times a diameter of the at least one rotating disk impeller; and pumping the cleaning fluid into the membrane. The method of claim 17, wherein preparing the first mixture further comprises mixing a polymer with the first mixture, the polymer comprising at least one of anionic polymers, neutral polymers, and polyelectrolytes, wherein the polymer has a concentration between 0.14 wt.% and 1.42 wt.% based on the total weight of the first mixture. The method of claim 18, wherein preparing the first mixture further comprises mixing nanoparticles with the first mixture, the nanoparticles comprising nanoparticles of at least one of a biopolymer, magnesium oxide, polyacrylamide, polyvinyl alcohol, and ether sulfates, wherein the nanoparticles have a concentration between 0 and 0.28 wt.% based on the total weight of the first mixture. The method of claim 19, wherein the cylindrical vessel further comprising at least one baffle, the at least one baffle comprising a flat plate extended along a longitudinal axis of the cylindrical vessel, positioned adjacent an outer periphery of the rotating disc.

18 The method of claim 20, wherein generating microbubbles in the second mixture comprises stirring the second mixture in the stirred vessel, the enclosed vessel pressurized to a pressure between 1 and 6 bars.

19