Membrane oil-water separation system integrated with photocatalytic self-cleaning function

Abstract

The application discloses a membrane oil-water separation system integrated with photocatalytic self-cleaning function, comprising a membrane separation unit, a light source module, a cleaning system and a control system. The membrane separation unit comprises at least one membrane assembly, the membrane assembly comprises a porous support and a photocatalytically active layer loaded on at least one side surface of the porous support; the light source module is integrated in the membrane separation unit or arranged adjacent to the membrane separation unit, and is used for generating light radiation capable of exciting the photocatalytically active layer; the control system is configured to switch to a self-cleaning mode when a preset cleaning condition is met, turn on the light source module and start the cleaning system, and remove pollutants on the membrane surface through the synergistic effect of photocatalytic reaction and fluid flushing. Compared with the prior art, the application can make timely, effective and persistent self-cleaning response to membrane pollution, and significantly improves the operation efficiency and long-term stability of the system in industrial application.

Description

Technical Field

[0001] This invention belongs to the field of separation system technology, specifically relating to a membrane oil-water separation system with integrated photocatalytic self-cleaning function. Background Technology

[0002] Membrane separation technology has been widely used in the treatment of oily wastewater. Microfiltration, ultrafiltration, or nanofiltration membranes trap oil droplets, offering advantages such as high separation efficiency and ease of operation. To mitigate membrane fouling, existing technologies attempt to introduce photocatalysis into the membrane separation process. For example, photocatalysts such as titanium dioxide are loaded onto the membrane surface, and the membrane surface is irradiated with an external ultraviolet light source. This photocatalytic reaction degrades oily pollutants, aiming to achieve membrane self-cleaning.

[0003] However, existing systems integrating photocatalytic self-cleaning with membrane separation processes generally face a fundamental technical problem: achieving deep and stable synergistic coordination among photoexcitation, catalytic degradation, and membrane cleaning under continuous industrial conditions. Specifically, the external irradiation method of the light source leads to significant light transmission losses and uneven illumination within the membrane module; the bonding strength between the photocatalytic active layer and the membrane substrate is insufficient to withstand long-term hydraulic operation; and the timing and method of photocatalytic degradation and hydraulic cleaning lack automatic synergistic control based on the membrane fouling state. The combined effect of these problems makes it difficult for existing systems to provide a timely, effective, and sustained self-cleaning response to membrane fouling, severely impacting the system's efficiency in practical applications.

[0004] Therefore, to address the aforementioned technical issues, it is necessary to provide a membrane-based oil-water separation system that integrates photocatalytic self-cleaning functionality. Summary of the Invention

[0005] The purpose of this invention is to provide a membrane-based oil-water separation system with integrated photocatalytic self-cleaning function, which can solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides a membrane-based oil-water separation system with integrated photocatalytic self-cleaning function, comprising: a membrane separation unit, a light source module, a cleaning system, and a control system. The membrane separation unit includes at least one membrane module, which comprises a porous support and a photocatalytic active layer loaded on at least one side surface of the porous support. The membrane separation unit has an inlet for inputting oily wastewater, a permeate outlet for outputting permeate, and a concentrate outlet for outputting retentate. The light source module is integrated within or adjacent to the membrane separation unit and is used to generate light radiation capable of exciting the photocatalytic active layer and to irradiate the photocatalytic active layer with the light radiation. The cleaning system includes a cleaning fluid source and a pipeline, which is connected to the membrane module and is used to supply cleaning fluid to the membrane module. The control system is used to control the membrane separation unit to operate in filtration mode for oil-water separation and to switch to self-cleaning mode when preset cleaning conditions are met. In the self-cleaning mode, the control system turns on the light source module and starts the cleaning system to remove contaminants from the membrane surface through photocatalytic reaction and fluid flushing.

[0007] In one or more embodiments of the present invention, the porous support is a flat plate, tubular or hollow fiber structure, and the material of the porous support is selected from ceramic, sintered metal, stainless steel mesh, polyvinylidene fluoride, polytetrafluoroethylene or polysulfone.

[0008] In one or more embodiments of the present invention, the photocatalytic active layer comprises at least one photocatalyst selected from TiO2, ZnO, WO3, Bi2, WO6, g-C3, N4, and BiOBr; the photocatalytic active layer is further doped with metal ions, non-metallic elements, or loaded with noble metal nanoparticles or quantum dots to extend the spectral response range to the visible light region; the photocatalytic active layer is fixed on a porous support by atomic layer deposition, hydrothermal synthesis, or chemical crosslinking, and the photocatalytic active layer and the porous support form a chemical bond or sintering bond.

[0009] In one or more embodiments of the present invention, the light source module includes at least one light-emitting diode light source, wherein the light-emitting diode is an ultraviolet LED, a near-ultraviolet LED, or a visible LED, and the emission wavelength of the light source module matches the absorption band edge of the photocatalytic active layer; the light source module is installed inside the housing of the membrane assembly and is isolated from the membrane surface by a transparent sealing window.

[0010] In one or more embodiments of the present invention, a light-reflecting layer is provided on the inner surface of the membrane assembly housing. The light-reflecting layer is a polished metal layer or a coating with a high-reflectivity film, used to reflect the light emitted by the light source to the membrane surface.

[0011] In one or more embodiments of the present invention, the cleaning system includes a backwashing subsystem and a cross-flow flushing subsystem. The backwashing subsystem injects cleaning fluid into the permeate side in the reverse direction through the product water port, and the cross-flow flushing subsystem makes the cleaning fluid flow at high speed along the membrane surface through the feed port or a dedicated flushing port.

[0012] In one or more embodiments of the present invention, an online membrane fouling monitoring unit is further included. The monitoring unit includes a pressure sensor for detecting transmembrane pressure difference and a flow meter for detecting permeate flow. The control system receives the monitoring signal and determines that the preset cleaning conditions are met when the transmembrane pressure difference exceeds a preset threshold or the permeate flow decreases to a preset percentage, thereby triggering a self-cleaning mode.

[0013] In one or more embodiments of the present invention, the light source module includes at least one light guide element. The light guide element is made of a light-transmitting material and has a light-incident end face and a light-emitting side face. The light radiation generated by the light source is coupled into the light guide element from the light-incident end face, and after internal transmission, it is uniformly radiated to the photocatalytic active layer from the light-emitting side face.

[0014] In one or more embodiments of the present invention, the light guide element is a side-emitting optical fiber, a light guide rod, or a light guide plate, and the material of the light guide element is selected from quartz glass, borosilicate glass, or a high-transmittance polymer; the light-emitting side of the light guide element is provided with microstructures or nano-scattering points; the membrane assembly is a hollow fiber membrane assembly or a flat membrane assembly, and the light guide element is interspersed in the gaps between the membrane fibers or arranged parallel to the membrane surface at intervals, such that the distance between the light-emitting side of the light guide element and the photocatalytic active layer of the membrane surface is 0.1 to 10 mm; the surface of the light guide element is hydrophilically modified to reduce the adhesion of oily substances in oily wastewater to its surface.

[0015] In one or more embodiments of the present invention, the LED light source of the light source module is installed outside the membrane assembly or located in the sealed cavity of the housing, and the light radiation is introduced into the membrane assembly only through the light guide element, thereby achieving physical isolation between the light source and the fluid.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: by integrating the light source module inside the membrane separation unit and using a light guide element to achieve uniform illumination, the photocatalytic active layer and the porous support are stably bonded by atomic layer deposition or chemical cross-linking, and the control system automatically triggers the synergistic cleaning program of photocatalytic degradation and hydraulic flushing according to the online monitoring signal. This solves the fundamental technical problem that existing systems are unable to achieve deep, stable and intelligent online synergy of photoexcitation, catalytic degradation and membrane cleaning under continuous operation conditions. As a result, the system can make a timely, effective and long-lasting self-cleaning response to membrane fouling, significantly improving the operating efficiency and long-term stability of the system in industrial applications. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a membrane oil-water separation system with integrated photocatalytic self-cleaning function in one embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the concealed installation of the LED light source and its cooperation with the light reflection layer in one embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram showing the interlaced arrangement of light guide elements and film assemblies in one embodiment of the present invention;

[0021] Figure 4 This is a control flowchart of the self-cleaning mode in one embodiment of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0023] Example 1:

[0024] like Figures 1-4As shown, an embodiment of the present invention discloses a membrane-based oil-water separation system with integrated photocatalytic self-cleaning function, comprising a membrane separation unit, a light source module, a cleaning system, and a control system. The membrane separation unit can intercept oil droplets, emulsified oil, and suspended impurities in oily wastewater under pressure. The membrane separation unit includes at least one membrane module, which is typically configured as a shell structure. The shell houses a porous support and its surface photocatalytic active layer. The porous support serves as both a load-bearing framework and a fluid channel. The pore structure of the load-bearing framework must ensure sufficient mechanical strength while providing a low-resistance channel for aqueous phase permeation. To adapt to different device sizes and installation spaces, the porous support can be designed as a flat plate, tubular, or hollow fiber structure. Flat plate structures are easy to maintain and replace, and suitable for modular integration; tubular structures facilitate the formation of higher shear flow rates, which helps reduce concentration polarization; hollow fiber structures have the advantages of large membrane area per unit volume, making them suitable for integrating lighting and light guide elements.

[0025] The material of the porous support can be selected according to the wastewater properties and operating conditions, such as ceramics, sintered metals, stainless steel mesh, polyvinylidene fluoride, polytetrafluoroethylene, or polysulfone. Ceramic or sintered metal supports are resistant to high temperatures and corrosion, making them suitable for long-term operation and strong chemical cleaning; polymer supports have the advantages of being lightweight, easy to process, and low in cost. To further enhance the bonding stability between the photocatalytic active layer and the support, the support surface can be roughened, plasma activated, or treated with coupling agents to form reactive hydroxyl, carboxyl, or metal active sites, thus providing a chemical bonding basis for the subsequent fixation of the catalytic layer. After such treatment, the photocatalytic layer is not easily peeled off during long-term hydraulic scouring and cleaning cycles, and can maintain stable photocatalytic activity.

[0026] A photocatalytic active layer is loaded onto at least one surface of a porous support and disposed on the feed side surface of the membrane, so that pollutants can be partially degraded by photocatalysis before entering the membrane pores, reducing the adhesion and accumulation of organic oil on the membrane surface. This photocatalytic active layer may contain at least one of TiO2, ZnO, WO3, Bi2, WO6, g-C3N4, and BiOBr.

[0027] To enhance the response to visible light, the photocatalytic active layer can be doped with metal ions, non-metallic elements, or loaded with co-catalytic components such as noble metal nanoparticles and quantum dots, thereby expanding the absorption band edge and improving carrier separation efficiency. For example, TiO2 can be modified with nitrogen doping or silver nanoparticles to maintain a certain level of activity under visible light; g-C3N4 can form a heterojunction with BiOBr to promote the separation of photogenerated electrons and holes, thereby improving the oxidative decomposition efficiency of oily organic matter.

[0028] The photocatalytic active layer can be constructed using atomic layer deposition, hydrothermal synthesis, or chemical cross-linking. Atomic layer deposition can achieve uniform coating at the nanoscale, making it suitable for precise coating of complex pores and fiber surfaces; hydrothermal synthesis is suitable for in-situ growth of plate-like or flower-like catalytic crystals on a support, which is beneficial for increasing the specific surface area; chemical cross-linking is suitable for firmly fixing pre-fabricated nanoparticles to the surface of a support through a cross-linking network.

[0029] To further improve mechanical stability, chemical bonding or sintering can be formed between the photocatalytic active layer and the porous support. For example, a strong bonding interface can be formed on a ceramic support through high-temperature sintering, while on a polymer support, interfacial bonding can be achieved through silane coupling or epoxy crosslinking. This avoids the active layer from detaching due to shear force, backwashing, or temperature fluctuations during long-term operation, fundamentally improving the self-cleaning lifespan.

[0030] Preferably, the photocatalytic active layer can be designed as a gradient structure, where the layer closest to the support enhances adhesion and force transfer, while the outer layer consists of high specific surface area nanoparticles to provide reaction sites. This gradient structure balances robustness and catalytic efficiency, making it suitable for high-pollution-load conditions.

[0031] Furthermore, the surface of the photocatalytic layer can be modified to be hydrophilic / superhydrophilic to reduce the adhesion energy of oil droplets on the film surface. Combined with photocatalytic decomposition, this can significantly delay the formation of the contamination layer.

[0032] The light source module provides light radiation to the photocatalytic active layer to stimulate its reaction, unlike the traditional method of placing the light source outside the membrane module and irradiating it from a distance through air or the shell wall. In this solution, the light source module is integrated into or adjacent to the membrane separation unit, which significantly shortens the optical path distance between the light source and the membrane surface, reduces light energy transmission loss, and improves the problem of uneven illuminance distribution inside the membrane module.

[0033] The light source module preferably includes at least one light-emitting diode (LED) light source, which can be an ultraviolet LED, a near-ultraviolet LED, or a visible LED, and its emission wavelength matches the absorption band edge of the photocatalytic active layer. If the active layer is a TiO2-based material, a near-ultraviolet LED with a wavelength around 365nm, 385nm, or 395nm is preferred; if it is a visible light-responsive catalytic layer, a blue, green, or broadband white LED can be selected. Through wavelength matching, the utilization efficiency of photons is higher, and ineffective irradiation is avoided.

[0034] In terms of structural arrangement, the LED light source can be installed inside the membrane module housing and isolated from the membrane surface by a transparent sealing window. The transparent sealing window is preferably made of quartz glass, sapphire glass, or high-transmittance engineering plastic to balance light transmittance and chemical resistance. An oil- and corrosion-resistant sealing ring can be used to seal the window and the housing, preventing leakage between the light source cavity and the fluid cavity. This allows the light source to operate in a closed and stable environment, while the fluid side of the membrane module maintains normal hydraulic operation. This avoids direct contact between the lamp and oily wastewater, preventing contamination or short circuits, and also allows the light radiation to be as close as possible to the catalyst layer surface, significantly enhancing the self-cleaning response.

[0035] A light-reflecting layer can also be provided on the inner surface of the membrane module housing. This layer can be a polished metal layer or a coating with a high-reflectivity film, such as an aluminum film, silver film, or a high-reflectivity oxide coating. The function of the light-reflecting layer is not merely simple reflection, but rather to redirect light that might otherwise be absorbed or scattered by the housing back to the membrane surface or the surface of the light guide element, thereby improving the uniformity of the light field within the housing. For hollow fiber membrane modules, the reflective layer can also improve the problem of insufficient illumination in the shadow areas between fiber bundles, ensuring that the inner fibers also receive effective light.

[0036] The light source module may also include at least one light guide element. This light guide element is made of a light-transmitting material and has an incident light facet and an exit light facet. Light radiation emitted by the light source is coupled into the light guide element from the incident light facet, transmitted internally, and then uniformly radiated from the exit light facet to the photocatalytic active layer. In other words, the LED light source does not need to be directly placed near the film surface; instead, the light guide element can deliver light to various locations within the film assembly, achieving physical isolation between the light source and the fluid, while simultaneously solving the problem of uneven illumination over a large film surface.

[0037] The light guide element can be a side-emitting optical fiber, a light guide rod, or a light guide plate. The material can be quartz glass, borosilicate glass, or a high-transmittance polymer to ensure low light loss and good mechanical strength.

[0038] Specifically, the light-emitting side of the light guide element can be provided with microstructures or nano-scattering points, such as microprisms, laser-etched scattering points, or surface roughening textures, to release axially propagating light in segments on the side, achieving a more uniform surface light source effect. If the light guide element is used in a hollow fiber membrane module, it can be interspersed between the membrane fibers; if it is used in a flat sheet membrane module, it can be arranged parallel to the membrane surface at intervals. The spacing between the light-emitting side of the light guide element and the photocatalytic active layer of the membrane surface is preferably controlled between 0.1 and 10 mm to ensure light coverage while avoiding mechanical interference with the membrane surface.

[0039] The surface of the light guide element can also be modified with hydrophilic treatment, such as grafting hydrophilic polymers, coating with a hydrophilic silica layer, or undergoing oxygen plasma treatment, to reduce the adhesion of oily substances in oily wastewater to its surface and prevent the light guide element from being affected by adhering contaminants.

[0040] The cleaning system supplies cleaning fluid to the membrane module in self-cleaning mode to work in conjunction with the photocatalytic reaction to remove contaminants. The cleaning system includes at least a cleaning fluid source and piping connected to the membrane module. The cleaning fluid can be clean water, backwash solution, a cleaning solution containing a weak alkali or surfactant, or a low-concentration oxidant solution depending on the nature of the fouling. To balance cleaning effectiveness and membrane material tolerance, the cleaning solution formulation can be controlled within a range that does not significantly corrode the membrane substrate.

[0041] The cleaning system specifically includes a backwashing subsystem and a cross-flow flushing subsystem. The backwashing subsystem injects cleaning fluid in the reverse direction into the permeate side through the permeate inlet to push out clogging particles and loose fouling layers from inside the membrane pores. The cross-flow flushing subsystem allows cleaning fluid to flow at high speed along the membrane surface through the feed inlet or a dedicated flushing port, using shear force to peel off attached contaminants. Photocatalytic reaction chemically decomposes the organic adhesive layer, while hydraulic flushing physically removes and carries the degradation products away from the membrane surface. These two functions complement each other, forming a complete self-cleaning process.

[0042] The control system controls the membrane separation unit to operate in filtration mode for oil-water separation and switches to self-cleaning mode when preset cleaning conditions are met. In filtration mode, the control system maintains the set feed flow rate, transmembrane pressure difference, and recovery rate to ensure stable water production; in self-cleaning mode, the light source module is activated and the cleaning system is driven, so that photocatalysis and fluid flushing are performed simultaneously.

[0043] To achieve refined control based on fouling conditions, an online membrane fouling monitoring unit can be set up. The monitoring unit includes a pressure sensor for detecting the transmembrane pressure difference and a flow meter for detecting the permeate flow. If necessary, a turbidity sensor, conductivity sensor, oil content sensor or optical transmittance sensor can also be added to more comprehensively reflect the membrane fouling condition.

[0044] After receiving monitoring signals, the control system determines whether to enter self-cleaning mode based on preset thresholds. For example, when the transmembrane pressure difference rises to 1.2 to 2.0 times the initial value, or the permeate flow rate decreases to 70% to 90% of the initial value, the system determines that the preset cleaning conditions are met and triggers the self-cleaning program. After triggering, the control system can first briefly reduce the feed pressure to make the membrane fouling layer easier to peel off, then turn on the LED light source and backwash pump, and then switch to cross-flow flushing for a certain period of time to form a staged cleaning process. After self-cleaning, the system re-enters filtration mode and judges whether the cleaning is sufficient based on the recovered pressure difference and flow rate data. If the recovery rate is lower than the preset value, the control system can perform secondary cleaning or extend the illumination time. This control method makes cleaning no longer dependent on manual experience, but dynamically adjusted according to the actual degree of fouling, which can reduce energy waste caused by over-cleaning and avoid fouling accumulation caused by insufficient cleaning.

[0045] The control system can be implemented using a PLC, embedded controller, or industrial computer, and establish a comprehensive judgment logic based on time, differential pressure, flow rate decay rate, and the number of cleaning cycles. For example, when cleaning is frequently triggered within a short cycle, the system can automatically increase the cleaning flow rate or extend the illumination time; when the contamination is light, only short-term illumination-assisted flushing is performed.

[0046] To achieve more precise control, the system can also incorporate pulsed illumination control, which involves intermittently lighting LEDs with a certain duty cycle to reduce heat accumulation and improve the migration efficiency of photogenerated carriers. Alternatively, synchronous control linked to the flow rate can be used to vary the illumination intensity according to the cleaning flow rate, adapting to different stages of contamination.

[0047] During operation, oily wastewater enters the membrane separation unit through the feed inlet. Under pressure, it passes through the photocatalytic active layer on the membrane surface and enters the membrane pores. Oil droplets, colloids, and suspended particles in the multiphase mixture are trapped on the membrane surface or at the pore inlet. Simultaneously, the light source module emits light continuously or intermittently. Under illumination, the photocatalytic active layer generates electron-hole pairs, which in turn produce reactive species such as hydroxyl radicals and superoxide radicals. These reactive species oxidize and degrade oily pollutants on the membrane surface, transforming them from large, hydrophobic fouling layers into smaller molecules or loose fragments that are more easily carried away by the water flow. This process prevents the fouling layer from becoming denser, alleviating membrane pore blockage at its source. Because the light source is positioned close to the membrane surface or directly transmits light through a light guide element, the light energy utilization rate is significantly higher than that of traditional externally illuminated structures. Therefore, even at lower input power, effective catalytic cleaning can be maintained.

[0048] When the monitoring unit determines that the contamination level exceeds the threshold, the system automatically enters self-cleaning mode. First, it maintains continuous irradiation through the light source module, then applies backwashing and cross-flow rinsing through the cleaning system. At this time, photocatalysis weakens the adhesion between oil and the membrane surface, while fluid rinsing quickly removes loosened contaminants, creating a synergistic effect. Compared to using backwashing alone, this method significantly reduces backwashing pressure and cleaning fluid consumption; simultaneously, it solves the problem that photocatalysis can only decompose but cannot effectively remove residual contaminants in a timely manner.

[0049] To further enhance the system's continuous operation capability, auxiliary cooling structures, such as air-cooled heat sinks or circulating water-cooled jackets, can be added to the outside of the membrane module housing to control the temperature rise of the LED light source and the interior of the housing, preventing high temperatures from causing a decline in photocatalytic performance or aging of the membrane material. A replaceable protective lens can also be installed at the front end of the light source module for localized maintenance after long-term operation. Furthermore, the system can be configured with a backup light source circuit, automatically switching to the backup circuit when a group of LEDs decays or fails, ensuring uninterrupted self-cleaning functionality.

[0050] In summary, this invention integrates the photocatalytic active layer, membrane separation unit, light source module, cleaning system, and control system into a unified design, enabling the membrane separation process and the in-situ photocatalytic self-cleaning process to work synergistically. Compared with existing technologies, this invention no longer relies on an external light source for inefficient irradiation of the membrane surface, nor does it treat photocatalytic cleaning and hydraulic cleaning as independent processing steps. Instead, it links photoexcitation, pollutant degradation, fluid flushing, and pollution status monitoring within the same membrane separation system, thereby improving the timeliness, stability, and continuity of the self-cleaning response.

[0051] Specifically, this invention integrates the light source module within the membrane separation unit or adjacent to the membrane module, and matches the light source wavelength with the absorption characteristics of the photocatalytic active layer. This shortens the light radiation transmission path, reduces light energy loss, and improves the problem of uneven illumination within the membrane module, enabling the photocatalytic active layer to obtain more sufficient and stable excitation conditions. By fixing the photocatalytic active layer to the surface of the porous support through chemical bonding, sintering, or other robust methods, the adhesion stability of the active layer under long-term filtration, backwashing, and cross-flow scouring conditions is improved, reducing the risk of catalyst detachment and activity degradation.

[0052] Simultaneously, this invention utilizes a control system to automatically trigger a self-cleaning mode based on membrane fouling parameters such as transmembrane pressure difference and permeate flow rate, enabling photocatalytic degradation and cleaning processes such as backwashing and cross-flow scouring to proceed simultaneously or in stages. The photocatalytic reaction weakens and decomposes the oil-based fouling layer on the membrane surface, while the cleaning fluid promptly removes loose contaminants from the membrane surface. This method avoids excessive energy consumption caused by fixed-cycle cleaning and also prevents the problem of flux recovery being difficult after excessive fouling accumulation.

[0053] Therefore, this invention can effectively delay membrane flux decay, reduce the rate of increase in transmembrane pressure difference, improve the flux recovery rate after membrane module cleaning, reduce the frequency of chemical cleaning and downtime for maintenance, and enhance the continuity and operational stability of the oily wastewater treatment process. Especially in industrial applications with high oil loads, long operating cycles, or complex internal lighting conditions of the membrane module, this invention balances separation efficiency, self-cleaning efficiency, equipment reliability, and ease of maintenance, demonstrating significant engineering application value.

[0054] Example 2:

[0055] Unlike Example 1, the membrane separation unit is not limited to a single membrane material system. Depending on the oil phase viscosity, emulsification degree, temperature, salt content, and treatment scale of the oily wastewater, polymer membranes, inorganic ceramic membranes, or carbon-based composite membranes can be selected. Polymer membranes can be made of polyvinylidene fluoride, polysulfone, or polyethersulfone, suitable for treating conventional industrial oily wastewater, offering advantages such as low cost, ease of processing, and suitability for hollow fiber or spiral wound modules. Inorganic ceramic membranes can be made of alumina, zirconium oxide, silicon carbide, or titanium dioxide ceramics, suitable for wastewater systems with high temperature, high salt, high viscosity, or corrosive components, and capable of withstanding high backwashing pressure and cross-flow scouring intensity. Carbon-based composite membranes can employ graphene oxide, reduced graphene oxide, graphene nanonets, or carbon nanotubes to enhance aqueous phase transport efficiency, surface antifouling ability, and recycling stability. Through this multi-material approach, the present invention can balance flux, strength, durability, and cost in different application scenarios.

[0056] For polymer membranes, a porous support can be prepared first through phase inversion, thermally induced phase separation, or wet spinning. Then, its surface can be treated with plasma, UV grafting, dopamine deposition, or silane coupling to form hydroxyl, amino, carboxyl, or catechol groups. Subsequently, photocatalytic materials such as TiO2, ZnO, g-C3N4, or BiOBr can be immobilized via sol-gel, chemical crosslinking, or low-temperature in-situ deposition. This treatment method can improve the bonding strength between the photocatalytic active layer and the polymer substrate membrane, reduce coating detachment during backwashing or long-term cross-flow operation, and simultaneously reduce oil droplet adhesion through a hydrophilic interface, alleviating membrane pore blockage caused by high-viscosity oil contamination.

[0057] For ceramic membranes, tubular, planar, or multi-channel honeycomb structures can be employed, and a photocatalytic active layer can be formed on the ceramic pore walls or membrane surface through impregnation-coating, hydrothermal growth, spray sintering, or sol-gel processes. For example, TiO2 nanoparticles, nanorods, or sheet-like catalytic structures can be grown in situ on the surface of alumina or silicon carbide supports, and a robust bonding interface can be formed after appropriate heat treatment. Due to the high mechanical strength and chemical stability of ceramic supports, they can be used in conjunction with high-flow-rate cross-flow scouring and high-pressure backwashing, allowing oily contaminants that have been photocatalytically degraded and loosened to detach from the membrane surface in a timely manner, thereby improving flux recovery and long-term operational stability.

[0058] For graphene-based composite membranes, ultrathin reinforcing layers of graphene oxide, reduced graphene oxide, graphene nanonetworks, or carbon nanotubes can be constructed on the surface of polymer or ceramic supports. These reinforcing layers can be formed through spraying, blade coating, vacuum filtration, layer-to-layer self-assembly, or roll-to-roll continuous coating, and can be cross-linked and fixed using dopamine, polyethyleneimine, polyvalent metal ions, or silane coupling agents. Graphene sheets or carbon nanotube networks provide low-resistance water transport channels and a reinforcing framework, while nanopores or interlayer spacing serve as selective channels for the preferential passage of the aqueous phase. By controlling the carbon-based materials to ultrathin layers at the nanometer to micrometer scale, the amount of high-cost materials used can be reduced, flux reduction due to excessive coating thickness can be avoided, and the membrane's antifouling properties and mechanical stability can be improved.

[0059] Molecularly imprinted layers or smart-response layers can also be deposited on the membrane surface to improve the selective separation capability of complex oil-water systems. Molecularly imprinted layers are formed by surface polymerization using specific hydrocarbons, surfactants, or oily contaminants as template molecules. Removing the template leaves recognition holes, which are used to improve the retention or repulsion of specific oily components. Smart-response layers can use temperature-responsive, pH-responsive, light-responsive, or electro-responsive polymers, allowing the membrane surface wettability or pore state to adjust according to changes in the operating environment.

[0060] To meet the demands of large-scale applications, photocatalytic active layers, graphene-based reinforcing layers, or carbon nanotube layers can be fabricated using continuous processes. For example, flat sheet or spiral-wound membranes can be continuously formed using roll-to-roll coating, spraying, dip coating, or slot coating methods, coupled with online thickness detection, machine vision defect detection, contact angle detection, or throughput sampling to control coating uniformity and batch stability. Hollow fiber membranes can undergo continuous surface activation, functional slurry impregnation, crosslinking curing, and winding processes after spinning to achieve online construction of functional layers. Through ultra-thin coatings, localized functionalization, and continuous production, it is possible to reduce material consumption and manufacturing costs while simultaneously ensuring anti-fouling properties, throughput, mechanical strength, and industrial scale-up feasibility.

[0061] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A membrane-based oil-water separation system integrating photocatalytic self-cleaning function, characterized in that, include: A membrane separation unit includes at least one membrane module, the membrane module comprising a porous support and a photocatalytic active layer supported on at least one side surface of the porous support, the membrane separation unit having an inlet for inputting oily wastewater, a permeate outlet for outputting permeate and a concentrate outlet for outputting retentate. A light source module, integrated within or adjacent to the membrane separation unit, is used to generate light radiation capable of exciting the photocatalytic active layer and to irradiate the photocatalytic active layer with the light radiation. A cleaning system includes a cleaning fluid source and piping, the piping being connected to a membrane module for supplying cleaning fluid to the membrane module; The control system is used to control the membrane separation unit to operate in filtration mode for oil-water separation, and to switch to self-cleaning mode when preset cleaning conditions are met. In the self-cleaning mode, the control system turns on the light source module and starts the cleaning system to remove contaminants from the membrane surface through photocatalytic reaction and fluid flushing.

2. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 1, characterized in that, The membrane substrate of the membrane separation unit is selected from one or more of polyvinylidene fluoride, polysulfone, polyethersulfone, inorganic ceramic membrane or graphene-based composite membrane. An ultrathin antifouling reinforcement layer is provided on the surface of the membrane substrate. The ultrathin antifouling reinforcement layer is one or more of TiO2 modified layer, reduced graphene oxide layer, graphene nanomesh layer or carbon nanotube reinforcement layer, and is formed by roll-to-roll continuous coating, spraying, dip coating or in-situ growth, so as to reduce the amount of material used while taking into account antifouling performance, separation flux and mechanical strength.

3. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 1, characterized in that, The photocatalytic active layer contains at least one photocatalyst selected from TiO2, ZnO, WO3, Bi2, WO6, g-C3, N4, and BiOBr; the photocatalytic active layer is also doped with metal ions, non-metallic elements, or loaded with noble metal nanoparticles or quantum dots to extend the spectral response range to the visible light region. The photocatalytic active layer is fixed on the porous support by atomic layer deposition, hydrothermal synthesis or chemical cross-linking, and the photocatalytic active layer and the porous support are chemically bonded or sintered together.

4. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 1, characterized in that, The light source module includes at least one light-emitting diode light source, which is an ultraviolet LED, a near-ultraviolet LED, or a visible LED. The emission wavelength of the light source module matches the absorption band edge of the photocatalytic active layer. The light source module is installed inside the housing of the membrane assembly and is isolated from the membrane surface through a transparent sealing window.

5. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 4, characterized in that, The inner surface of the membrane module housing is provided with a light-reflecting layer, which is a polished metal layer or a coating with a high-reflectivity film, used to reflect the light emitted by the light source to the membrane surface.

6. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 1, characterized in that, The cleaning system includes a backwashing subsystem and a cross-flow flushing subsystem. The backwashing subsystem injects cleaning fluid into the permeate side in the reverse direction through the product water port. The cross-flow flushing subsystem makes the cleaning fluid flow at high speed along the membrane surface through the feed port or a dedicated flushing port.

7. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 1, characterized in that, It also includes an online membrane fouling monitoring unit, which includes a pressure sensor for detecting transmembrane pressure difference and a flow meter for detecting permeate flow. The control system receives the monitoring signal and determines that the preset cleaning conditions are met when the transmembrane pressure difference exceeds a preset threshold or the permeate flow decreases to a preset percentage, and triggers the self-cleaning mode.

8. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 1, characterized in that, The light source module includes at least one light guide element, which is made of a light-transmitting material and has a light-incident end face and a light-emitting side face. The light radiation generated by the light source is coupled into the light guide element from the light-incident end face, and after internal transmission, it is uniformly radiated to the photocatalytic active layer from the light-emitting side face.

9. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 8, characterized in that, The light guide element is a side-emitting optical fiber, a light guide rod, or a light guide plate. The material of the light guide element is selected from quartz glass, high borosilicate glass, or a high-transmittance polymer. The light-emitting side of the light guide element is provided with microstructures or nano-scattering points. The membrane module is a hollow fiber membrane module or a flat sheet membrane module, and the light guide element is inserted between the membrane fibers or arranged parallel to the membrane surface at intervals, so that the distance between the light-emitting side of the light guide element and the photocatalytic active layer of the membrane surface is 0.1 to 10 mm. The surface of the light guide element is hydrophilically modified to reduce the adhesion of oily substances from oily wastewater to its surface.

10. The membrane oil-water separation system with integrated photocatalytic self-cleaning function according to claim 8, characterized in that, The LED light source of the light source module is installed outside the membrane assembly or inside the sealed cavity of the housing. The light radiation is introduced into the membrane assembly only through the light guide element, so as to achieve physical isolation between the light source and the fluid.

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