Nanobubble-enhanced reverse osmosis membrane system and method of use thereof

Abstract

The application discloses a nano-bubble enhanced reverse osmosis membrane system and an application method thereof, and belongs to the technical field of water treatment membrane separation. The system is composed of a nano-bubble generating and injecting module, a reverse osmosis membrane component and an online cleaning module. 10-200 nm negative nano-bubbles are prepared by ultrasonic cavitation or pressure dissolution method, and are uniformly injected into the water inlet end of the membrane after cyclone distribution. The functionalized membrane is modified by carbon nanotubes / metal organic framework and is decorated with a negative interface, and forms a double electrostatic repulsion layer with the nano-bubbles. Online cleaning is combined with ozone radical oxidation and gas-liquid pulse micro-jet physical peeling to realize drug-free membrane regeneration. The application solves the problems of traditional reverse osmosis membrane pollution, concentration difference polarization and high energy consumption through the synergistic effect of gas-liquid-membrane three phases, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of water treatment membrane separation technology, specifically involving a nanobubble-enhanced reverse osmosis membrane system and its application method, which is particularly suitable for scenarios such as high-salt seawater desalination, deep treatment of highly polluted industrial wastewater, preparation of ultrapure water in the medical industry, and resource reuse of municipal sewage. Background Technology

[0002] Reverse osmosis (RO) membrane separation is a physical separation technology that uses pressure difference as the driving force to efficiently separate water molecules from pollutants such as dissolved salts, organic matter, colloids, and microorganisms through a semi-permeable membrane. In the global process of water resource utilization, reverse osmosis technology occupies a core position. However, traditional reverse osmosis membrane systems suffer from four major technical defects in practical engineering applications, which have become the main constraints on the industry's development: 1. Membrane fouling is a prominent issue, resulting in poor system operational stability. Membrane fouling refers to the process by which organic pollutants, inorganic colloids, microorganisms, metal ions, and other substances in raw water adsorb, deposit, and accumulate on the membrane surface, forming a dense fouling layer. Based on the type of fouling, it can be divided into four main categories: organic fouling (humic acid, proteins, oils), inorganic fouling (calcium carbonate, calcium sulfate, silicate scaling), biological fouling (bacteria, algae forming biofilms), and colloidal fouling (suspended particulate matter, inorganic colloids). Membrane fouling directly leads to a rapid decline in membrane flux, a decrease in desalination rate, and an increase in transmembrane pressure. To maintain system operation, frequent chemical cleaning is necessary, which not only significantly increases operating costs but also damages the membrane material structure and shortens the lifespan of membrane modules. According to industry statistics, the chemical cleaning cycle of traditional reverse osmosis membrane systems is only 1-2 months, and the lifespan of membrane modules is only 2-3 years. The maintenance costs caused by membrane fouling account for more than 40% of the total operating costs of water treatment systems.

[0003] 2. Significant concentration polarization and low mass transfer efficiency. Traditional reverse osmosis membrane systems operate in a single-phase liquid flow mode. Under pressure, water molecules permeate through the membrane, while contaminants are trapped and accumulate on the membrane surface, forming a high-concentration boundary layer, a phenomenon known as concentration polarization. Concentration polarization increases membrane separation resistance, reduces the water molecule permeation rate, and leads to a decrease in system water flux. Simultaneously, the high-concentration boundary layer accelerates contaminant crystallization and deposition, further exacerbating membrane fouling. To overcome concentration polarization and membrane resistance, traditional systems must operate under high pressure (typically 5.5-6.5 MPa for seawater desalination and 1.5-2.5 MPa for brackish water), resulting in high energy consumption. Energy costs account for more than 50% of the total operating cost of reverse osmosis systems, which is inconsistent with the development trend of low-carbon water treatment.

[0004] 3. High dependence on chemical reagents and significant risk of secondary environmental pollution. To control membrane fouling, traditional reverse osmosis systems require the regular addition of chemical agents such as antiscalants, bactericides, and acid / alkali cleaning agents. While antiscalants can delay inorganic scaling, they increase the chemical oxygen demand (COD) of the water; acid / alkali cleaning agents damage the functional groups on the membrane surface, reducing membrane stability; and bactericides can easily cause excessive residual chlorine in the water, corroding membrane modules and piping equipment. The use of large amounts of chemical agents not only increases water treatment costs but also leads to the discharge of cleaning wastewater, causing secondary environmental pollution.

[0005] 4. Nanobubble coupling technology faces application bottlenecks and has not yet been industrialized. Nanobubble technology, due to its unique physicochemical properties, has become a research hotspot for membrane fouling control and mass transfer enhancement. Existing research shows that nanobubbles can inhibit membrane fouling through interfacial charge repulsion, microjets, and oxidative degradation, while simultaneously enhancing mass transfer and reducing concentration polarization through turbulence. However, existing nanobubble-reverse osmosis membrane coupling technologies suffer from three major drawbacks: first, nanobubble generation devices cannot achieve stable, large-scale, and uniform bubble preparation, resulting in uneven bubble size distribution and poor concentration controllability; second, nanobubbles cannot achieve directional and uniform distribution at the reverse osmosis feed end, easily leading to bubble aggregation and escape, preventing sufficient contact with the membrane surface; and third, functional matching between membrane materials and nanobubbles has not been achieved, resulting in a mismatch between the membrane surface interfacial properties and the charge characteristics of nanobubbles, failing to maximize synergistic effects. These shortcomings have kept nanobubble technology confined to the laboratory research stage, hindering its large-scale application in industrial reverse osmosis systems.

[0006] In summary, the technical shortcomings of traditional reverse osmosis membrane systems and the application bottlenecks of existing coupling technologies urgently require an integrated, systematic, and industrialized innovative solution. This invention addresses these industry pain points by innovating three core technologies: nanobubble generation and precise injection, membrane surface functionalization modification, and online adaptive cleaning. It constructs an enhanced reverse osmosis membrane system with gas-liquid-membrane three-phase synergy, solving the problems of membrane fouling, concentration polarization, and high energy consumption at the mechanistic level, thus achieving efficient, low-consumption, green, and long-term operation of the reverse osmosis system. Summary of the Invention

[0007] The purpose of this invention is to overcome the technical shortcomings of traditional reverse osmosis membrane systems, such as severe membrane fouling, low mass transfer efficiency, high operating energy consumption, frequent chemical cleaning, and difficulty in the coupled application of nanobubbles. This invention provides a nanobubble-enhanced reverse osmosis membrane system and its application method. Through the system integration of stable nanobubble generation and uniform injection, functional modification of membrane materials, and online composite cleaning, this invention achieves a synergistic effect between the gas, liquid, and membrane phases.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: The nanobubble-enhanced reverse osmosis membrane system includes the following modules. Nanobubble generation and injection module: Nanobubbles are generated using ultrasonic aeration or pressure dissolution generators, and then injected into the nanobubbles via a vortex distributor; Reverse osmosis membrane module: with polyamide membrane as the substrate, the active layer is embedded with hydrophobic carbon nanotubes or metal-organic framework materials to form nanoscale water molecule permeation channels, and its water inlet end is connected to the nanobubble generation and injection module. Online cleaning module: It adopts a composite cleaning method of ozone nanobubble oxidation and gas-liquid pulse micro-jet, which physically removes dirt from the membrane surface through the micro-jet generated by the rupture of nanobubbles.

[0009] As a preferred embodiment, the nanobubble generation and injection module generates nanobubbles with a particle size of 10-200 nm, and the bubble medium is one or more of oxygen, ozone, air or hydrogen peroxide.

[0010] As a preferred embodiment, the nanobubble particle size is preferably 30-80 nm, the interfacial ζ-potential is ≤-30 mV, and the bubble concentration at the inlet water end is stably controlled at 10. 6 -10 8 per mL.

[0011] As a preferred embodiment, the surface of the reverse osmosis membrane module is coated with negatively charged silica nanoparticles or grafted with negatively charged functional groups, so that the ζ potential of the membrane surface is ≤-30mV, forming a double electrostatic repulsion layer with the nanobubbles.

[0012] As a preferred embodiment, the gas-liquid pulse frequency in the online cleaning module is 10-50Hz, and the pressure is 0.2-0.5MPa.

[0013] The application method of the nanobubble-enhanced reverse osmosis membrane system includes the following steps: S1: After pretreatment to remove suspended solids, colloids and residual chlorine, the raw water enters the nanobubble generation and injection module to prepare a uniform gas-liquid two-phase flow. S2: The gas-liquid two-phase flow enters the reverse osmosis membrane module after passing through the swirling distribution, achieving the separation of water molecules and pollutants under low pressure; S3: Periodically introduce rinsing solution containing ozone nanobubbles to degrade organic pollutants and inhibit biofilm formation using their free radical oxidation ability. Combined with gas-liquid pulse technology, the micro-jet generated by the rupture of nanobubbles physically removes dirt from the membrane surface, thereby completing the physical-chemical composite cleaning of the fouling layer on the membrane surface. S4: The separated permeate is collected and stored, and the concentrate is discharged or reused after meeting the standards.

[0014] As a preferred embodiment, the raw water is one of seawater, industrial wastewater, municipal sewage, or medical ultrapure water preparation raw water; seawater desalination uses air nanobubbles, industrial wastewater uses H2O2 nanobubbles, and medical ultrapure water uses oxygen nanobubbles.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. The turbulence effect of nanobubbles can completely destroy the concentration polarization boundary layer on the membrane surface, reducing mass transfer resistance; the nanochannels of functionalized membranes enhance the water molecule permeation rate, increasing water flux by 30%-50% compared to traditional reverse osmosis membranes, resulting in a significant increase in water production under the same equipment scale; 2. With the improvement of mass transfer efficiency, the transmembrane pressure required by the system is significantly reduced. Under the same water production capacity, the operating pressure is reduced by 20%-30% compared with the traditional system, and the energy consumption cost is reduced by more than 25%, which meets the development requirements of low-carbon water treatment. 3. The dual electrostatic repulsion layer inhibits membrane fouling at its source. Online composite cleaning requires no chemical agents, and there is no chemical corrosion or structural damage to the membrane surface. The chemical cleaning cycle is extended by more than 3 times, and the service life of the membrane module is increased from the traditional 2-3 years to 5-8 years, significantly reducing equipment depreciation costs. Detailed Implementation

[0016] The technical solution of this application will be further described and illustrated below through embodiments.

[0017] The nanobubble-enhanced reverse osmosis membrane system of the present invention consists of a nanobubble generation and injection module, a reverse osmosis membrane assembly, and an online cleaning module. The modules work together to achieve efficient and stable operation of the system.

[0018] 1. Nanobubble generation and injection module The nanobubble generation and precise injection module is the core enhancement unit of the system. It is responsible for preparing nanobubbles with uniform particle size, controllable concentration, and strong stability, and injecting them into the reverse osmosis membrane feed end in a directional and uniform manner to form a stable gas-liquid two-phase flow.

[0019] S1: Nanobubble generation technology Ultrasonic cavitation or pressure dissolution nanobubble generators are used, with oxygen, ozone, air, hydrogen peroxide, etc., preferred bubble generating media, which can be flexibly selected according to different water treatment scenarios. By adjusting the ultrasonic power, pressure parameters, and gas flow rate, monodisperse nanobubbles with a particle size of 10-200 nm are precisely prepared, with a preferred particle size of 30-80 nm. Bubbles in this particle size range can have a residence time in water of over 720 hours and a specific surface area as high as 10. 5 -10 8 With a surface area of ​​m² / m³ and a stable interfacial ζ-potential of ≤-30mV, it exhibits optimal mass transfer enhancement and anti-fouling effects.

[0020] S2: Precise control of bubble concentration By using an online concentration sensor to provide real-time feedback on bubble concentration, the generator's operating parameters are adjusted to stably control the bubble concentration at the inlet water at 10. 6 -10 8 The preferred concentration is 5 × 10⁻⁶ cells / mL. 7 The concentration range of particles / mL can form a uniform gas-liquid two-phase flow, which avoids insufficient synergistic effect due to too low a concentration, and prevents bubble aggregation and flow turbulence caused by too high a concentration.

[0021] S3: Uniform Swirl Distribution Technology A multi-stage vortex distributor is installed at the inlet of the reverse osmosis membrane module. After being cut and dispersed by the vortex, the nanobubbles are evenly distributed in the raw water, which avoids the local aggregation of bubbles or their escape along the pipe wall. This ensures that the nanobubbles are in uniform contact with the entire cross-section of the membrane surface, maximizing their synergistic effect.

[0022] 2. Reverse osmosis membrane module Functionalized reverse osmosis membrane modules are the core separation unit of the system. Through membrane surface modification and interface regulation, they achieve efficient synergy with nanobubbles, thereby improving the membrane's separation performance and antifouling ability.

[0023] S1: Selection of membrane material substrate Using traditional polyamide reverse osmosis membranes as the substrate, while retaining their core advantage of high desalination rate, nanoscale functionalization modification is carried out on the polyamide active layer. The thickness of the modified layer is controlled at 50-200nm, without damaging the original membrane structure and separation performance.

[0024] S2: Hydrophobic nanomaterial embedding modification Hydrophobic carbon nanotubes (CNTs) or metal-organic frameworks (MOFs) are embedded in the polyamide active layer. The diameter of the carbon nanotubes is controlled at 2-10 nm, and the pore size of the MOF material is 0.3-0.8 nm, forming continuous nanoscale water molecule rapid permeation channels. These channels can reduce water molecule permeation resistance, increase water flux, and at the same time, utilize the hydrophobic interface to repel organic pollutants and reduce pollutant adsorption.

[0025] S3: Anti-fouling regulation of negatively charged interface Negatively charged silica (SiO2) nanoparticles are coated onto the membrane surface using the sol-gel method, or negatively charged functional groups (-COOH, -SO3H) are grafted using plasma, stabilizing the membrane surface zeta potential to ≤-30mV. The nanobubbles themselves carry a negative charge, forming a double electrostatic repulsion layer with the membrane surface, effectively repelling positively charged pollutants such as Ca²⁺, Mg²⁺, colloidal particles, and microorganisms in the water, thus inhibiting the adsorption and deposition of pollutants on the membrane surface at the source.

[0026] 3. Online cleaning module The online adaptive cleaning and regeneration system eliminates the need to disassemble membrane modules or use large amounts of chemical agents. It achieves efficient removal and degradation of the fouling layer on the membrane surface through a composite cleaning method of ozone nanobubble oxidation and gas-liquid pulse microjet, thus extending the membrane's service life.

[0027] S1: Oxidative degradation cleaning Ozone nanobubbles are periodically introduced, and the ozone nanobubbles burst on the membrane surface, releasing strong oxidizing free radicals such as OH and O3. These free radicals can efficiently degrade organic pollutants on the membrane surface, destroy the biofilm structure, and kill bacteria and algae. The TOC removal rate can reach more than 90%, thoroughly eliminating organic and biological pollution.

[0028] S2: Physical microfluidic cleaning By combining gas-liquid pulse technology and adjusting the pulse frequency (10-50Hz) and pressure (0.2-0.5MPa), nanobubbles are directionally broken on the membrane surface to generate high-speed microjets (velocities up to 100-300m / s), which physically remove inorganic scale and colloidal deposits from the membrane surface without mechanical damage or disruption to the membrane structure.

[0029] S31: Adaptive adjustment of cleaning parameters The system intelligently judges the degree of membrane fouling by monitoring parameters such as membrane flux, transmembrane pressure, and effluent water quality online, and automatically adjusts the cleaning frequency, ozone concentration, and pulse parameters to achieve on-demand cleaning, avoid over-cleaning or under-cleaning, and maximize cleaning efficiency.

[0030] Example 1: Application of Seawater Desalination System System Composition Raw water pretreatment unit (sand filtration + activated carbon adsorption + security filtration), pressure dissolution nanobubble generator, CNT-MOF reverse osmosis membrane module, and ozone nanobubble online cleaning module.

[0031] process parameters (1) Pretreatment: Seawater is filtered by sand to remove large suspended solids, activated carbon adsorption to remove residual chlorine and some organic matter, and security filtration (5μm) to remove small colloids. After pretreatment, the turbidity of the effluent is ≤0.1NTU and the residual chlorine is ≤0.01mg / L.

[0032] (2) Nanobubble injection: Air nanobubbles with a particle size of 50 nm and a concentration of 10 were prepared using a pressure dissolution generator. 7 The sample is injected evenly into the membrane inlet end via a cyclone distributor at a density of 1 / mL.

[0033] (3) Membrane separation operation: CNT-MOF composite modified polyamide membrane is used, with membrane surface ζ potential = -35mV, operating pressure 1.5MPa, temperature 25℃, and recovery rate 45%.

[0034] (4) Online cleaning: Cleaning is started every 48 hours, with ozone nanobubbles (concentration 5mg / L) introduced, gas-liquid pulse frequency 30Hz, and cleaning time 10 minutes.

[0035] Running effect The system operated continuously for 180 days, with membrane flux stabilizing at 40 L / (m²・h), a 45% increase compared to traditional seawater desalination reverse osmosis membranes; product water salinity <500 ppm, desalination rate ≥99.5%; TOC removal rate >90%, microbial rejection rate 100%; operating pressure reduced by 60% compared to traditional systems (traditional seawater desalination pressure 5.5-6.5 MPa), energy consumption reduced by 55%; chemical cleaning cycle extended to over 12 months, and membrane lifespan expected to reach 8 years.

[0036] Example 2: Application of Industrial Wastewater Reuse System System Composition Raw water pretreatment unit (coagulation sedimentation + ultrafiltration), ultrasonic cavitation nanobubble generator, SiO2 negative charge modified reverse osmosis membrane module, and H2O2 nanobubble online cleaning module.

[0037] process parameters (1) Pretreatment: Highly polluted industrial wastewater (dyeing and printing wastewater, COD=1500mg / L, color=500 times) is treated by coagulation and sedimentation to remove suspended pollutants, and ultrafiltration (0.01μm) is used to remove colloidal and macromolecular organic matter. After pretreatment, COD≤100mg / L and color≤50 times.

[0038] (2) Nanobubble injection: H2O2 nanobubbles with a particle size of 80 nm and a concentration of 8 × 10⁻⁶ were prepared by ultrasonic cavitation. 7 Cells / mL, directionally injected into the inlet end of the membrane.

[0039] (3) Membrane separation operation: SiO2 negatively charged modified membrane is used, ζ potential = -30mV, operating pressure 1.2MPa, recovery rate 60%.

[0040] (4) Online cleaning: Cleaning is started every 24 hours, with a gas-liquid pulse pressure of 0.4MPa and a cleaning time of 15 minutes.

[0041] Running effect After 120 days of continuous operation, the membrane flux decay rate is less than 5%, which is 35% higher than that of traditional industrial wastewater reverse osmosis systems; the product water COD is ≤10mg / L and the color is ≤5 times, meeting the industrial reuse standards; CaCO3 scaling is completely inhibited, with no inorganic pollution; the amount of chemical reagents used is reduced by 100%, and the operation and maintenance costs are reduced by 40%; the membrane lifespan is expected to reach 6 years.

[0042] Example 3: Application of Medical Ultrapure Water Preparation System System Composition Raw water pretreatment unit (activated carbon + ultrafiltration + ultraviolet sterilization), pressure dissolution nanobubble generator, MOF functionalized reverse osmosis membrane module, and ozone nanobubble online cleaning module.

[0043] process parameters (1) Pretreatment: Municipal tap water is decomposed by activated carbon adsorption to remove organic matter, ultrafiltration to remove microorganisms, and ultraviolet sterilization to kill bacteria. The total number of colonies after pretreatment is ≤10 CFU / mL.

[0044] (2) Nanobubble injection: Oxygen nanobubbles were prepared with a particle size of 30 nm and a concentration of 5 × 10⁻⁶. 7 per mL.

[0045] (3) Membrane separation operation: MOF modified membrane, ζ potential = -38mV, operating pressure 0.8MPa, recovery rate 70%.

[0046] (4) Online cleaning: Cleaning is started every 72 hours with an ozone concentration of 3 mg / L and a cleaning time of 5 minutes.

[0047] Running effect The resistivity of the produced water is ≥18.2MΩ・cm, meeting the medical ultrapure water standard; the microbial rejection rate is 100%, with no biological contamination; the system operates at low pressure, reducing energy consumption by 30%; the membrane flux is stable with no flux decay, and the service life is expected to reach 7 years.

[0048] This invention achieves the industrial-scale application of nanobubble technology in reverse osmosis water treatment systems through gas-liquid-membrane three-phase synergistic innovation, covering water treatment needs in all scenarios such as seawater desalination, industrial wastewater reuse, municipal sewage resource utilization, medical / electronic ultrapure water preparation, and drinking water purification.

[0049] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A reverse osmosis membrane system based on nanobubbles, characterized in that: It includes the following modules Nanobubble generation and injection module: Nanobubbles are generated using ultrasonic aeration or pressure dissolution generators, and then injected into the nanobubbles via a vortex distributor; Reverse osmosis membrane module: with polyamide membrane as the substrate, the active layer is embedded with hydrophobic carbon nanotubes or metal-organic framework materials to form nanoscale water molecule permeation channels, and its water inlet end is connected to the nanobubble generation and injection module. Online cleaning module: It adopts a composite cleaning method of ozone nanobubble oxidation and gas-liquid pulse microjet, which physically removes dirt from the membrane surface through the microjet generated by the rupture of nanobubbles.

2. The nanobubble-enhanced reverse osmosis membrane system according to claim 1, characterized in that: The nanobubble generation and injection module generates nanobubbles with a particle size of 10-200 nm, and the bubble medium is one or more of oxygen, ozone, air or hydrogen peroxide.

3. The nanobubble-enhanced reverse osmosis membrane system according to claim 1, characterized in that: The nanobubble particle size is preferably 30-80 nm, the interfacial ζ-potential is ≤-30 mV, and the bubble concentration at the inlet water end is stably controlled at 10. 6 -10 8 per mL.

4. The nanobubble-enhanced reverse osmosis membrane system according to claim 1, characterized in that: The surface of the reverse osmosis membrane module is coated with negatively charged silica nanoparticles or grafted with negatively charged functional groups, so that the ζ potential of the membrane surface is ≤-30mV, forming a double electrostatic repulsion layer with the nanobubbles.

5. The nanobubble-enhanced reverse osmosis membrane system according to claim 1, characterized in that: The gas-liquid pulse frequency in the online cleaning module is 10-50Hz, and the pressure is 0.2-0.5MPa.

6. The application method of the nanobubble-enhanced reverse osmosis membrane system according to any one of claims 1-5, characterized in that, It includes the following steps: S1: After pretreatment to remove suspended solids, colloids and residual chlorine, the raw water enters the nanobubble generation and injection module to prepare a uniform gas-liquid two-phase flow. S2: The gas-liquid two-phase flow enters the reverse osmosis membrane module after passing through the swirling distribution, achieving the separation of water molecules and pollutants under low pressure; S3: Periodically introduce rinsing solution containing ozone nanobubbles to degrade organic pollutants and inhibit biofilm formation using their free radical oxidation ability. Combined with gas-liquid pulse technology, the micro-jet generated by the rupture of nanobubbles physically removes dirt from the membrane surface, thereby completing the physical-chemical composite cleaning of the fouling layer on the membrane surface. S4: The separated permeate is collected and stored, and the concentrate is discharged or reused after meeting the standards.

7. The application method of the nanobubble-enhanced reverse osmosis membrane system according to claim 6, characterized in that: The raw water is one of the following: seawater, industrial wastewater, municipal sewage, or medical ultrapure water preparation raw water; seawater desalination uses air nanobubbles, industrial wastewater uses H2O2 nanobubbles, and medical ultrapure water uses oxygen nanobubbles.