System and method for measuring the concentration of microplastics in a water pipeline

Abstract

System and method for measuring the concentration of microplastics in a water pipeline. The system comprises: a microplastic (3) filtering membrane (2), fastened to a water pipe (14) and coated with plasmon resonance metal nanoparticles; a laser illumination source (4) that illuminates the membrane (2) at the plasmon resonance frequency; a Raman spectrometer (5) to obtain a surface-amplified Raman spectrum (7) of the membrane (2); a mechanical vibrator (8) to remove the microplastics (3) adhered to the membrane (2); a flow meter (10) to measure the water flow rate (11); and a data processing unit (13) to identify the chemical composition of the microplastics (3) using the Raman spectrum, to quantify microplastics (3) on the membrane (2) using the Raman spectrum and a pre-calibration of the Raman spectrometer (5) corresponding to the identified microplastics, and to obtain the concentration of microplastics (15) in the water using the water flow rate (11) and the quantification of microplastics.

Description

[0001] DESCRIPTION

[0002] SYSTEM AND METHOD FOR MEASURING THE CONCENTRATION OF MICROPLASTICS IN A WATER CONDUIT LINE

[0003] Field of invention

[0004] The present invention falls within the field of systems and methods for measuring the concentration of microplastics in water.

[0005] Background of the invention

[0006] In recent years, there has been growing concern about the impact of microplastics (synthetic polymers ranging in size from 0.1 m to 5 mm) on the environment and human health. Microplastics can be produced unintentionally from large pieces of plastic, such as tires or synthetic textiles, that wear down with use, or intentionally, as part of commercial products or raw materials (pellets).

[0007] Microplastics have now been found in freshwater, marine, and terrestrial ecosystems, as well as in food and drinking water. Once in the environment, microplastics do not biodegrade. Besides their high persistence, recent studies have shown that microplastics bioaccumulate in both aquatic and terrestrial species and have even been detected in human feces and the placenta. Undoubtedly, plastic materials, mostly polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyurethane (PU), and polyvinyl chloride (PVC), are the most widespread and abundant pollutants on our planet, and their impacts on ecosystems (including humans) are still largely unknown.

[0008] Recent studies point to synthetic fabrics and clothing (polyester and polyamide) as one of the main sources of fibers in the environment during washing processes throughout their lifespan. These fibers account for more than 35% of primary microplastics in aquatic systems.

[0009] Recent advances in our understanding of the potential health impacts of microplastics highlight the importance of identifying and reducing their presence in the environment, drinking water, and agri-food products. Furthermore, increased consumer awareness of food quality and the presence of toxins means that foods free of (or with minimal) microplastics increase their added value and perceived quality. In addition, the draft wastewater regulations include the analysis of microplastics as another emerging contaminant to be considered.

[0010] All of this has created great concern among water treatment plant managers and the agri-food industry, who see the need to adapt their processes to eliminate microplastics, as well as the need to include them as routine measurement parameters.

[0011] For all these reasons, monitoring microplastics in the environment, water supplies, and for food safety has become a necessity for science, consumers, and governments. While chemical analysis of these particles will soon be mandatory, a rapid and reliable method is needed to determine their size, shape, number, and composition in order to identify their origin and modify production processes to eliminate or minimize this contamination. Existing methods are inadequate for the routine analyses required by the agri-food industry because they are time-consuming and require personnel specifically trained in this methodology.

[0012] Currently, the only benchtop instruments on the market for determining microplastics in the laboratory (through water sample analysis) combine the determination of the shape, size, and quantity of microplastic particles using optical imaging technology with the composition of the microplastic particles through IR or Raman spectroscopy. Among these instruments, the most compact and fastest is the Agilent 8700 LDIR device, which incorporates a tunable laser source with IR emission. This makes the equipment prohibitively expensive for most companies in the water treatment and agri-food sectors.

[0013] Patent document WO2022119460-A1 describes a portable water quality analysis device that can be used to measure the size of microplastics present in a sample by image processing. This device captures the microplastics using different stackable mesh discs with varying mesh sizes to sieve the sample and visualizes them through a microscope connected to a camera.

[0014] These devices and equipment can only be used in ex situ mode, in the laboratory, and do not allow for real-time or continuous measurements in a water pipeline, as sample preparation requires pre-treatment before analysis.

[0015] The present invention provides a solution to this problem.

[0016] Description of the invention

[0017] The invention relates to a system and method for measuring the concentration of microplastics in a water pipeline.

[0018] The system comprises a microplastic filter membrane, attached to a water conduit and coated with plasmonic-resonant metallic nanoparticles; a laser light source configured to illuminate the membrane at a frequency compatible with the plasmonic resonance of the metallic nanoparticles; a Raman spectrometer coupled to the laser light source and configured to obtain a surface-amplified Raman spectrum from the membrane; a mechanical vibrator coupled to the water conduit and configured to remove microplastics adhering to the membrane; and a flow meter to measure the flow rate of water circulating through the water conduit.and a data processing unit configured to identify the chemical composition of microplastics using surface-amplified Raman spectroscopy, quantify microplastics on the membrane using surface-amplified Raman spectroscopy and a prior calibration of the Raman spectrometer corresponding to the identified microplastics, and obtain the concentration of microplastics in the water using the water flow rate and the quantification of microplastics.

[0019] The method comprises repeatedly performing the following steps: illuminating, using a laser light source, a microplastic filter membrane attached to a water conduit and coated with plasmonic-resonant metallic nanoparticles, where the illumination is carried out at a frequency compatible with the plasmonic resonance of the metallic nanoparticles; obtaining, using a Raman spectrometer coupled to the laser light source, a surface-amplified Raman spectrum from the membrane; measuring, using a flow meter, a flow rate of water circulating through the water conduit; identifying the chemical composition of the microplastics using the surface-amplified Raman spectrum; quantifying microplastics in the membrane using the surface-amplified Raman spectrum and a prior calibration of the Raman spectrometer corresponding to the identified microplastics;to obtain the concentration of microplastics in the water using the water flow rate and the quantification of microplastics; to activate a mechanical vibrator coupled to the water conduit to remove the microplastics adhered to the membrane; and to deactivate the mechanical vibrator.

[0020] The invention allows for the capture of microplastics at specific measurement points in the plant using chemically modified filter membranes, preferably with gold metallic particles exhibiting plasmonic resonance around 785 nm, although the nanoparticles could be made of other metals that exhibit plasmonic resonance at a specific frequency coinciding with the laser light source (e.g., silver or copper). Advantageously, it has been found that the 785 nm wavelength does not generate luminescence from the microplastics that could mask the Raman signal, whereas other commonly used wavelengths, such as 532 nm, do generate luminescence interference. However, other wavelengths besides 785 nm can be used, provided they do not generate luminescence interference from the microplastics. The flow meter allows for the measurement of the amount of water passing through the filter membrane at any given time.

[0021] The detection of the chemical composition and concentration of microplastics is performed using fiber optic Raman spectrophotometry, with the signal amplified by the plasmonic effect generated by the gold metallic particles. The Raman effect is excited by illumination with a diode laser (e.g., emission at 785 nm), also coupled to a fiber optic cable. The libraries available in the Raman instrument software allow for rapid identification of the different plastics present on the membrane. Furthermore, through prior calibration with standards of the most frequently identified plastics in water samples, it is possible to quantify their concentration, also taking into account the amount of water that has passed through the filter membrane, measured with a flow meter.

[0022] The filtration membrane is regenerated by mechanical vibration to remove trapped microplastics and prepare it for further analysis.

[0023] Optionally, the system allows the identification of the size and shape of the microplastics on the filter membrane, and their quantification, by microscopic observation through an endoscopic camera coupled to fiber optics and modified with a miniaturized long focal length lens, and the use of image recognition software that identifies the contours of the particles, quantifies their size and performs the count.

[0024] The use of surface-amplified Raman scattering (SERS) by the plasmonic effect of metallic nanoparticles present in the filter membrane allows for the detection of much smaller quantities of plastic. This, combined with the fact that this technique is coupled to fiber optics, allows the Raman detector to be placed far from the point of microplastic collection, and therefore does not impede the flow of water in the water supply system, typically through bypasses in the inlet or outlet pipes of the industrial plant.

[0025] The present invention provides a real-time, in-situ, and continuous measurement of microplastic concentration in a water pipe. It is a modular system to which different modules and functionalities can be optionally added (independently, according to the end user's needs), such as a camera for detecting the size and shape characteristics of the microplastics.

[0026] Optical images for determining the size, shape, and number of particles are taken through a miniaturized lens and transmitted via fiber optics, which does not impede the passage of water while preserving the endoscopic camera device.

[0027] All of this represents the advantages of enabling on-site measurement at the branch lines located in the inlet or outlet water pipes of the industrial plant, real-time measurement through data processing (e.g., via cloud computing), and obtaining the measurement in terms of concentration by incorporating a flow meter that allows for continuous monitoring of the amount of water that has passed through the filter membrane, as well as easy reading on a computer, tablet, mobile phone, or any other electronic device. Furthermore, the system allows for continuous measurement through the filter membrane regeneration system using mechanical vibration.

[0028] In one embodiment, the system combines Raman scattering, excited by a laser light source (e.g., at 785 nm), which allows for the identification of plastics and the measurement of their concentration, with an endoscopic camera coupled to a miniaturized long-focal-length lens to capture images of the membrane where the microplastics are collected. This allows for the characterization of the size and shape of the microplastics and the quantification of their number. The optical images are then analyzed using appropriate image recognition software to determine their characteristics.

[0029] Microplastics are collected via a membrane that filters and accumulates them, preferably in branch lines of main water supply or aqueous product lines in food processing plants or water treatment facilities. The membrane contains metallic nanoparticles that, through the plasmonic effect, act as antennas to enhance the spectroscopic signals from the microplastics, providing reliable signals for surface-enhanced Raman spectroscopy (SERS). The combined use of these two techniques allows for a modular system design, enabling it to independently measure either the size, shape, and quantity of microplastic particles using the endoscopic camera, identify their chemical nature and concentration through plasmonic-enhanced Raman scattering, or perform all measurements simultaneously.

[0030] The system also incorporates a flow meter that allows for the continuous determination of the amount of water passing through the filter membrane, enabling the quantification of microplastics in terms of concentration. Finally, the filter membrane is regenerated through mechanical vibration, eliminating accumulated microplastics and preparing the filter for subsequent analyses, thus allowing for the continuous monitoring of microplastic concentration in the water supply.

[0031] Although the system is designed for on-site use in water inlet lines or in the outlet lines of aqueous end products in the industries of interest, it can be easily adapted for off-site use, allowing it to be used in the laboratory if the end user deems it necessary. Therefore, the system's design is highly flexible, enabling it to be adapted to the end user's needs.

[0032] The collected data is processed in the data processing unit, which can be located locally at the facility where the water pipeline containing the membrane is located (e.g., a computer) or remotely (e.g., cloud computing via a remote server). The results can then be read in the appropriate format on a computer, tablet, mobile phone, or any other electronic device. The proposed system is suitable for measuring microplastics in water used for both human consumption and industrial purposes.The system identifies the chemical nature of the plastics detected through their characteristic Raman spectrum (each Raman spectrum is like a fingerprint of a specific substance, unique to that substance), and determines their concentration through the intensity of this signal (taking into account a prior calibration corresponding to the identified compound) and by quantifying the liters of water that have passed through the filter membrane using a flow meter. Furthermore, by combining this technology with an optical image taken with an endoscopic camera coupled to fiber optics and modified with a miniaturized long-focal-length lens, the system determines the shape and size of these microplastic particles and quantifies their number.

[0033] The present invention can be applied to different types of industries, including:

[0034] Water purification plants: to be able to analyze the level of microplastics in the water entering their plants, but also to analyze it at the plant's outlet, and to introduce, if necessary, a stage for the removal of these substances during the plant's treatment, thus being able to offer their clients clear and verified information.

[0035] The agri-food, cosmetic, and pharmaceutical industries that use water in their processes can analyze the level of microplastics in both the input water and the wastewater at the end of the process, indicating the level of microplastics in the final products and ensuring that they do not contribute to the contamination of the environment by these pollutants.

[0036] Water treatment plants: to be able to analyze the level of microplastics in the incoming and outgoing water at their plants, and introduce if necessary a stage of removal of these contaminants during the purification process, ensuring that the plant does not contribute to the dispersion of these contaminants in the environment.

[0037] Laundries and hotels with their own laundries: to prevent synthetic microfibers, which make up a large part of the microplastics present in the environment, from reaching it.

[0038] The paint industry, where international regulations prohibiting the intentional use of microplastics have been applied.

[0039] Water analysis laboratories can substantially reduce the measurement time for these contaminants, currently a minimum of three days from sample collection to preparation and analysis. With the proposed system, measurements are taken in real time, without prior sample preparation, greatly simplifying the analysis and eliminating the need for specialized personnel.

[0040] The main advantage of the proposed system is that it allows for on-site measurement, a feature that no other device currently on the market can offer.

[0041] Furthermore, the system allows for real-time measurements (or measurements with minimal delay) through the reading and analysis of the Raman signal (e.g., by processing this signal in the cloud and reading it on an electronic device). Other equipment currently on the market requires prior sample preparation and subsequent analysis, which precludes this real-time measurement capability. This feature is crucial for end users, as it allows them to determine whether the water quality they are using meets their standards and to ensure that wastewater (or treated water) leaving their plants does not contribute to the spread of these contaminants.

[0042] The proposed system also allows for continuous measurement. Through a membrane regeneration system using a mechanical vibration process, which eliminates all microplastic particles present on the membrane at any given time, the sample can be recollected during the user-defined period, and measurements can continue without having to stop the process or the entire plant to perform the analysis and receive the results. Furthermore, the system is modular, allowing for design flexibility to adapt it to the user's specific needs.

[0043] Finally, an additional advantage is the device's small size and the fact that, apart from the filter membrane required for sample collection, the connections made in the plant's water pipes contain nothing more than optical fibers with diameters of less than 500 micrometers to excite and collect the Raman signal and capture the optical image of the membrane surfaces. This does not substantially alter the water flow through these pipes during measurements, allowing the plant to operate normally.

[0044] Brief description of the drawings

[0045] Next, a series of drawings are briefly described that help to better understand the invention and that are expressly related to an embodiment of said invention which is presented as a non-limiting example thereof.

[0046] Figure 1 represents a system for measuring the concentration of microplastics in a water pipeline according to a possible embodiment.

[0047] Figure 2 shows, as an example, the installation point of the system of the present invention in a water treatment plant.

[0048] Figures 3A and 3B show, respectively, a front view and a side view of the water conduit and the membrane installed inside it, with the different elements that make up the present invention.

[0049] Figure 4 shows a flow diagram of a method for measuring the concentration of microplastics in a water pipeline according to one embodiment.

[0050] Figure 5 represents the SERS spectra obtained for different types of plastic and quantities of plastic used in the previous calibration.

[0051] Figure 6A shows an assembly of microlenses and Figure 6B shows a schematic of the operation of the microlens assembly in the system of the present invention, according to one embodiment.

[0052] Detailed description of the invention

[0053] Figure 1 represents an embodiment of a system (1) for measuring the concentration of microplastics in a water pipeline. The system comprises a microplastic-filtering membrane 2 3, attached to a water conduit 14 and coated with plasmonic-resonant metallic nanoparticles. The arrows inside the water conduit 14 represent the flow of water 9 in a specific direction indicated by the arrow. The system 1 further comprises a laser illumination source 4 configured to illuminate the membrane 2 at a frequency compatible with the plasmonic resonance of the metallic nanoparticles. A Raman spectrometer 5, coupled to the laser illumination source 4, is configured to obtain a surface-amplified Raman spectrum 7 (SERS spectrum) from the membrane 2.Through an optical fiber 6, the laser light source 5 excites the metallic nanoparticles of the membrane 2, and the Raman spectrometer 4 acquires the spectroscopic signals derived from the microplastics 3 and obtains the surface-amplified Raman spectrum 7.

[0054] A mechanical vibrator 8 coupled to the water conduit 14, when activated, removes microplastics 3 adhered to the membrane 2 through vibration. For a greater vibration effect, the membrane 2 preferably comprises a rigid metal support 19. A flow meter 10 measures the flow rate of water 11 circulating through the water conduit 14.

[0055] System 1 also comprises a data processing unit 13 configured to identify the chemical composition of microplastics 3 using surface-amplified Raman spectrum 7, quantify microplastics 3 on membrane 2 using surface-amplified Raman spectrum 7 and a prior calibration of the Raman spectrometer 5 performed for the identified microplastics, and obtain the concentration of microplastics 15 in water using water flow rate 11 and microplastic quantification.

[0056] In one embodiment, the system may optionally comprise a camera 16 configured to acquire at least one image 17 of the membrane 2 through an optical fiber 18. The data processing unit 13 may be configured to detect the size and number of microplastics 3 adhered to the membrane 2 using the at least one image 17 acquired by the camera 16.

[0057] Figure 2 illustrates, as an example of the application of the present invention, a general diagram of a water treatment plant, showing the points (ag) where branch line 20 could be installed to the main water circulation pipes in the plant. Through these branches, the microplastic content could be analyzed using system 1, allowing for detailed monitoring of the water treatment process and its influence on the removal of microplastics. The figure illustrates, as an example, branch line 20 at point g, that is, at the outlet of the water treatment plant (connection to the main network). The water pipe 14 and the membrane 2 would be located at this branch line 20. This branch line 20 can be established in the same way at the other points (af).

[0058] Figures 3A and 3B show, respectively, a front view and a side view of the water conduit 14 and the membrane 2 installed inside the conduit, as well as the other elements that make up the invention (for simplicity, the data processing unit 13 and the signals / data exchanged with it are not shown). Figure 3A shows the accumulation on the membrane 2 of microplastic particles 3 carried by the water 9 circulating through the water conduit 14, with the mechanical vibrator 8 deactivated. Figure 3B shows the trajectory of the microplastic particles 3 when the mechanical vibrator 8 is activated, as they are pushed by the water flow 9 circulating through the pipe.

[0059] In one embodiment, membrane 2 is flexible, preferably made of polytetrafluoroethylene (PTFE) modified with gold nanoparticles. The main advantage of using a flexible membrane for liquid filtration and microplastic particle collection is that the filtration process itself is pressure-controlled. This pressure, in this case hydrostatic, generates mechanical resistance on membrane 2. If membrane 2 were rigid, its mechanical resistance would be very limited to a small pressure range, such that exceeding this range would cause it to rupture, limiting its lifespan. In contrast, by using a flexible membrane 2, this pressure range is wider. Given that the measurements will be carried out in a moving liquid medium, this medium will exert pressure on membrane 2.Furthermore, at certain times, this liquid can carry a load of solid elements (inorganic particles, sludge, organic matter, etc., hundreds of micrometers in diameter or even a few millimeters) that can impact membrane 2, exerting, at specific moments, a pressure higher than the average pressure produced by the liquid circulation. These peak pressures can be withstood by a flexible membrane, while they would cause a rigid membrane to rupture. Since these processes cannot be controlled, it is advisable to use a flexible membrane.

[0060] In the embodiment shown in Figures 3A and 3B, the membrane 2 is fixed to the water conduit 14 by means of fastening, preferably elastic radial supports 22, although other types of fastening could be used. In Figure 3A, the mechanical vibrator 8 is deactivated, while in Figure 3B, the mechanical vibrator 8 is operating, which causes the membrane 2 to vibrate and move in different directions (permitted by the fastening means) to remove the microplastics 3 accumulated on the membrane 2. The activation and deactivation of the mechanical vibrator 8 can be performed, for example, by a control unit 23 or the data processing unit 13 itself.

[0061] When the mechanical vibrator 8 is activated, the vibration is transmitted to the fixing means, which allow the membrane 2 to move and / or rotate. This, along with the vibration, removes the microplastics 3 adhered to it (Figure 3B). When the mechanical vibrator 8 is deactivated, the membrane 2 returns, by the action of the fixing means, to its initial position perpendicular to the direction of water flow 9 (Figure 3A). Then, after a certain time has elapsed to allow for a new accumulation of microplastics 3 on the membrane 2, the microplastic concentration measurement process is repeated. The waiting time will determine the frequency of the measurements.

[0062] Figure 4 shows a flow diagram of a method for measuring the concentration of microplastics in a water pipeline. The method involves repeatedly performing the following steps:

[0063] Illuminate 110, using a laser light source 4, a microplastic filter membrane 2 3 attached to a water pipe 14 and coated with metallic nanoparticles with plasmonic resonance, where the illumination is carried out at a frequency compatible with the plasmonic resonance of the metallic nanoparticles.

[0064] Obtain 120, using a Raman spectrometer 5 coupled to the laser illumination source 4, a surface-amplified Raman spectrum 7 from the membrane 2.

[0065] Measure 130, using a flow meter 10, a flow rate of water 11 that circulates through the water conduit 14.

[0066] Identify 140 the chemical composition of microplastics 3 using surface-amplified Raman spectrum 7.

[0067] Quantify 150 microplastics 3 on membrane 2 using surface amplified Raman spectrum 7 and a prior calibration of the Raman spectrometer 5 corresponding to the identified microplastics.

[0068] Obtain 160 the concentration of microplastics 15 in the water using the water flow rate 11 and the quantification of microplastics 3.

[0069] - Activate 170 a mechanical vibrator 8 coupled to the water conduit 14 to remove the microplastics 3 adhered to the membrane 2.

[0070] Deactivate 180 the mechanical vibrator 8.

[0071] Wait 190 a certain time T to perform a new measurement of the microplastic concentration 15.

[0072] The preliminary calibration of the Raman spectrometer 5 is performed by measuring initial SERS 24 spectra in the laboratory of selected plastics (e.g., the ten plastic types defined by the European Commission: polyethylene, polypropylene, polyethylene terephthalate, polystyrene, polyvinyl chloride, polyamide, polyurethane, polymethyl methacrylate, polytetrafluoroethylene, and polycarbonate) on membrane 2 modified with metallic nanoparticles. Figure 5 shows, as an example, the first SERS 24 spectrum obtained for N plastics during the preliminary calibration process for a specific quantity of plastic (Qu, Q12,... , QNI) accumulated on the membrane, where Qij represents the quantity of plastic j for plastic i.

[0073] From each of these initial SERS spectra, one or more key regions are selected for the identification of each type of plastic (these do not necessarily coincide with the complete spectrum, although the complete spectrum could be considered). To identify the chemical composition of the microplastics, the data processing unit acquires the surface-amplified Raman spectrum of the sample under analysis and compares it with the initial SERS spectra of the N plastic types, considering the regions used for identification. This comparison allows the identification / classification of the type of each of the microplastics collected on the filter membrane modified with metallic nanoparticles. Any state-of-the-art technique can be used to classify the type of plastic (e.g., using a classifier based on neural networks).

[0074] In the preliminary calibration, initial SERS spectra 24 and additional SERS spectra 26 are obtained from different quantities (Qu, Q12, ... , QI R; Q21 , Q22, ... , Q2R; ... ; QNI , QN2, . . . , QNR) deposited on membrane 2 of each of the N plastics, to measure the variation of the Raman signal as a function of the quantity of each of these microplastics on membrane 2. By graphically representing the variation of the intensity (vertical axis) of the surface-amplified Raman signal with the quantity of plastics, a calibration curve 27 is derived for each of the plastic types. The calibration curve 27 for each plastic can relate, for example, a specific intensity parameter (e.g., a local maximum value, an average intensity value) of the SERS spectrum obtained for that plastic to a quantity value (measured, for example, in mg) of that plastic on membrane 2.

[0075] The intensity of the Raman signal collected for each type of microplastic identified is compared with the calibration curve 27 previously established for each type of plastic. From this comparison, the quantity of each type of microplastic present in the sample can be determined. Thus, in this embodiment, to quantify 150 microplastics 3 on membrane 2, the surface-amplified Raman spectrum 7 obtained and a calibration curve 27 corresponding to the identified microplastics, previously determined with the Raman spectrometer 5, are used.

[0076] Finally, by dividing the amount of microplastics obtained by the liters of water that have passed through the membrane during the measurement time, you can obtain the concentration of each type of microplastic per liter of water.

[0077] In one embodiment, the method further comprises acquiring, by means of a camera 16, at least one image 17 of the membrane 2 through an optical fiber 18; and detecting the size and number of microplastics 3 adhered to the membrane 2 using at least one image 17 acquired by the camera 16.

[0078] In one embodiment, an array of microlenses is used to focus the Raman spectrometer laser. The optical system can therefore be supplemented with an ordered two-dimensional array of microlenses with a lattice parameter of tens or hundreds of micrometers, which are positioned at the end of the Raman system's optical fiber 6 by means of an adapted mechanical support. This array of microlenses is located between (i) the optical fiber 6, which carries the excitation laser and the Raman signal to the detector, and (ii) the membrane 2.

[0079] Figure 6A shows an overview 30 and a microscopic view 31 of a microlens assembly 32. Figure 6B depicts a schematic of the operation of the microlens assembly 32 used to focus the light beams 34 emerging from the optical fiber 6. The light beams 34 strike the microlens assembly 32, are focused onto the flexible membrane 2 modified with gold nanoparticles and microplastics 3 on its surface, and return along the same path to the detector. Figure 6B also shows the excitation wavefront 35 emerging from the optical fiber 6. The distance at which the microlens assembly 32 is positioned corresponds to the focal distance required to refocus the beam exiting the optical fiber 6, as well as to align the maximum intensity of these refocused light beams with the surface of the membrane 2 where the microplastics 3 are embedded.As shown in Figure 6B, the microlens array 32 divides the excitation light beam emerging from the optical fiber 6 into multiple conical light beams (as many as there are microlenses in the system, which can be on the order of thousands) that are focused onto the surface of the membrane 2. In addition, once the Raman signal is generated, the same microlenses collect it and focus it onto the optical fiber 6, which sends it to the Raman detector.

[0080] The advantages of using an ordered, two-dimensional array of 32 microlenses are numerous:

[0081] On the one hand, the excitation beam and the signal generated by the microplastics 3 travel through the same channel, minimizing the number of optical components required by the system and simultaneously facilitating their alignment. On the other hand, as reported in the scientific literature (Yang et al., Spectrochimica Acta A 287 (2023) 122129, DOI: 10.1016 / j.saa.2022.122129), the use of microlenses in Raman spectroscopy can amplify the Raman SERS signal by up to a factor of 10. 7 , which allows the detection of even microplastic particles 3 of smaller sizes or with much smaller concentrations.

[0082] It should also be noted that the microlens array 32 collimates the incident light beam, allowing for the correction of variations in light intensity or irregularities in the system. This corrects the incidence of the light beam 34 and the wavefront 35 on the membrane 2, making it homogeneous across the entire assembly. This advantage is important in the liquid environment where the measurements will be performed, which can cause the intensity of the wavefront 35 to fluctuate due to localized variations in the refractive index. This system effectively incorporates adaptive optical correction.

[0083] • Another noteworthy aspect is the fact that the same microlenses are used as a collection system, which makes the collection of light more efficient, while at the same time increasing the intensity of the collected signal.

[0084] • Finally, there are currently optical fibers that at their end already incorporate a set of 32 two-dimensional and ordered microlenses, making the system even more compact.

Claims

CLAIMS 1. A system for measuring the concentration of microplastics in a water pipeline, comprising: a microplastic filter membrane (2) (3) attached to a water pipeline (14) and coated with plasmonic-resonant metallic nanoparticles; a laser light source (4) configured to illuminate the membrane (2) at a frequency compatible with the plasmonic resonance of the metallic nanoparticles; a Raman spectrometer (5) coupled to the laser light source (4) and configured to obtain a surface-amplified Raman spectrum (7) from the membrane (2); a mechanical vibrator (8) coupled to the water pipeline (14) and configured to remove microplastics (3) adhering to the membrane (2); a flow meter (10) for measuring a water flow rate (11) circulating through the water pipeline (14); and a data processing unit (13) configured to: - identify the chemical composition of microplastics (3) using surface-amplified Raman spectrum (7); - quantify microplastics (3) on the membrane (2) using the surface-amplified Raman spectrum (7) and a prior calibration of the Raman spectrometer (5) corresponding to the identified microplastics; and - obtain the concentration of microplastics (15) in the water using the water flow rate (11) and the quantification of microplastics.

2. The system according to claim 1, comprising a camera (16) configured to acquire at least one image (17) of the membrane (2) through an optical fiber (18); and wherein the data processing unit (13) is configured to detect the size and number of microplastics (3) adhered to the membrane (2) using at least one image (17) acquired by the camera (16).

3. The system according to any of the preceding claims, comprising an optical fiber (6) for illuminating the membrane (2) and acquiring the spectroscopic signals from the microplastics (3).

4. The system according to claim 3, comprising a set of microlenses (32) arranged between the optical fiber (6) and the membrane (2).

5. The system according to any of the preceding claims, comprising a control unit (23) configured to activate the mechanical vibrator (8) to remove the microplastics (3) from the membrane (2), and to deactivate the mechanical vibrator (8) in order to perform a new measurement of the microplastic concentration (15).

6. The system according to any of the preceding claims, wherein the membrane (2) is flexible.

7. The system according to any of the preceding claims, wherein the membrane (2) is fixed to the water conduit (14) by means of elastic radial supports 22.

8. The system according to any of the preceding claims, wherein the membrane (2) comprises a rigid metallic support (19).

9. The system according to any of the preceding claims, wherein the metallic nanoparticles are gold, silver, or copper nanoparticles.

10. The system according to any of the preceding claims, wherein the laser light source (4) is configured to illuminate the membrane (2) with a wavelength of 785 nm.

11. The system according to any of the preceding claims, wherein the water conduit (14) is located in a branch (20) of a main pipe of an industrial plant.

12. A method for measuring the concentration of microplastics in a water pipeline, comprising repeatedly performing the following steps: illuminate (110), by means of a laser light source (4), a microplastic filter membrane (2) (3) fixed to a water conduit (14) and coated with plasmonic resonance metallic nanoparticles, wherein the illumination is carried out at a frequency compatible with the plasmonic resonance of the metallic nanoparticles; obtain (120), by means of a Raman spectrometer (5) coupled to the laser light source (4), a surface-amplified Raman spectrum (7) from the membrane (2); measure (130), using a flow meter (10), a flow rate of water (11) circulating through the water conduit (14); identify (140) the chemical composition of the microplastics (3) using the surface-amplified Raman spectrum (7); quantify (150) microplastics (3) on the membrane (2) using the surface-amplified Raman spectrum (7) and a prior calibration of the Raman spectrometer (5) corresponding to the identified microplastics; obtain (160) the concentration of microplastics (15) in the water using the water flow rate (11) and the quantification of microplastics; activate (170) a mechanical vibrator (8) coupled to the water conduit (14) to remove the microplastics (3) adhering to the membrane (2); and deactivate (180) the mechanical vibrator (8).

13. The method according to claim 12, comprising: acquiring, by means of a camera (16), at least one image (17) of the membrane (2) through an optical fiber (18); detecting the size and number of microplastics (3) adhered to the membrane (2) using at least one image (17) acquired by the camera (16).

14. The method according to any of claims 12 to 13, wherein the water conduit (14) is located in a branch (20) of a main pipe of an industrial plant.

15. The method according to any of claims 12 to 14, wherein the membrane (2) is coated with gold nanoparticles, and the laser light source (4) illuminates the membrane (2) with a wavelength of 785 nm.

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