WO2024186202A1

WO2024186202A1 - Wastewater pollution measurement device

Info

Publication number: WO2024186202A1
Application number: PCT/NL2024/050097
Authority: WO
Inventors: Peyman TAHERI; Majid Ahmadi
Original assignee: Hypersoniq B.V.; Technische Universiteit Delft
Priority date: 2023-03-03
Filing date: 2024-03-01
Publication date: 2024-09-12

Abstract

Aqueous-liquid measurement device for measuring pollution in an aqueous-liquid comprising an electrochemical impedance spectroscopy module arranged to determine the electrochemical impedance of a sample of aqueous-liquid, preferably wastewater, comprising an electrochemical impedance spectroscopy sensor comprising a plurality of electrodes, wherein the electrodes are substantially evenly spaced from each other for performing electrochemical impedance spectroscopy measurements a frequency response analyzer arranged to determine an impedance profile of the sample of aqueous-liquid a microprocessor arranged to compare the impedance profile to a database of impedance profiles to determine pollution in the aqueous-liquid sample.

Description

Title: Wastewater pollution measurement device

The invention relates to an aqueous-liquid measurement device and a method of determining a pollutant in an aqueous-liquid.

In industry, in particular the chemical industry, a large amount of water is used for various processes. For example, water may be used to cool equipment or other liquids via a heat exchanger, or may be used as a process liquid itself. As a result, water may be polluted, e.g. with chemicals, heavy metal ions, or petrochemical components. Since the polluted water may have adverse effects on the environment, e.g. plants, animals, or humans, it needs to be treated before it can be disposed to open water or transported away from the production site. Such a treatment can be done in a separate processing unit, called a wastewater treatment plant. During the treatment of the wastewater, the polluted water may pass various processing stages before finally coming to a storage tank. The wastewater in the storage tank needs to be analyzed in a laboratory to see if the water was treated sufficiently, i.e. to determine if the pollutants have been sufficiently removed to safely release the wastewater on the open water or transport it off-site.

Such an analysis can take a relatively long time. A sample is taken, e.g. by a process operator, and handed over to a laboratory. While some production sites may have a laboratory suitable for the analysis of wastewater samples on-site, it may very well be that the samples need to be taken off-site for analysis. This, in combination with an analysis time of sometimes up to a day, may result that it takes a relatively long time before it is determined if there are any pollutants in the wastewater. If this is the case, and the wastewater in the storage tank is considered to be sufficiently clean, the wastewater can be released to open water or transported off-site, thereby freeing up the storage tank. While this is a reliable method of testing wastewater, it is a relatively time-consuming and labor-intensive process. Due to the relatively long time, it takes for the analysis to finish and the pollutant content in the wastewater is determined, storage equipment is occupied for a relatively long time. Therefore, it may happen that production facilities require additional storage tanks to allow for continuous operation. As a result, the long analysis times may cost significant resources.

The invention aims to counteract the above disadvantages, preferably while retaining the advantages. More specifically, the invention aims to provide an aqueous-liquid measurement device and a method of determining a pollutant in an aqueous-liquid that makes it possible to provide a relatively quick and reliable analysis of the pollutants present in the aqueous-liquid. In particular, at least two pollutants can be determined simultaneously from a single measurement, thereby greatly speeding up the detection of pollutants.

Therefore, the invention provides an aqueous-liquid measurement device, for measuring pollutants in an aqueous-liquid comprising an electrochemical impedance spectroscopy (EIS) module arranged to determine the electrochemical impedance of a sample of aqueous-liquid, preferably wastewater. The EIS module comprises an EIS sensor, a frequency response analyzer arranged to determine an impedance profile of the sample of aqueous-liquid, and a microprocessor arranged to compare the impedance profile to a database of impedance profiles to determine pollution in the aqueous-liquid sample. The frequency response analyzer is generally provided by a potentiostat equipped with the frequency response analyzer. In particular, the invention provides an aqueous-liquid measurement device according to claim 13-25 of the application as filed.

In the context of the invention ‘pollutants’ should be understood as a plurality of pollutants, i.e. at least two pollutants. The EIS sensor comprises a plurality of electrodes. The electrodes are substantially evenly spaced from each other (at least adjacent working and counter electrodes defining a measurement zone for holding a sample exposed to a measurement). This is advantageous to provide uniform electric fields during EIS measurement; thus the (at least adjacent counter and working electrodes defining a measurement zone) are typically at least substantially parallel at the space at which the sample is exposed to the electrodes during the measurement; in other words, the electrodes comprise surface areas that are substantially evenly spaced from each other. The electrodes can have substantially the same or precisely constant surface area for performing reliable and reproducible electrochemical impedance spectroscopy measurements; thus at least the surface areas to which the sample is exposed during the measurement can be substantially the same. However, it advantageously a counter electrode’s surface area to which the sample is exposed during the measurement can be larger than its corresponding (adjacent) working electrode’s surface area to which the sample is exposed during the measurement. In particular, the surface areas of counter electrode(s) and working electrode(s) together defining a measurement zone for a sample may have a ratio counter electrode(s) surface are to working electrodes surface area in the range of 1:1 to 2:1, more in particular 1.2:1 to 2:1.

The aqueous-liquid measurement device can be a microelectromechanical system (MEMS) based device.

The invention further provides an electrochemical impedance spectroscopy sensor comprising a plurality of electrodes, wherein the surface of each electrode of said plurality of electrodes comprises a covered section that is covered with an insulating material and an uncovered section that is free of the insulating material such that the uncovered section of each electrode is exposed to a sample during use, wherein the surface of the uncovered section has a surface roughness (Ra) of less than 7nm, preferably less than 6nm or less than 5nm; and wherein the electrodes are substantially evenly spaced from each other, at least at the uncovered sections of said electrodes.

In particular, the sensor according to the invention is a sensor according to claim 26, 27 or 28 of the application as filed.

The sensor according to the invention is in particular useful in the aqueous-liquid measurement device or method according to the invention. The sensor according to the invention is in particular useful in a aqueous- liquid measurement device according to the invention or a method of determining one or more pollutants in an aqueous-liquid. Said method comprising the use of the sensor according to the invention can be based on the method according to the invention, with the proviso that it is sufficient that a single component, in particular a single metal ion or a single metalloid ion, is determined. With a measurement device and with a sensor according to the invention it has been found possible to carry out EIS measurements with a very good accuracy. Figs. 6A and 6B illustrate a measurement ((100 mg/L Zn(NOs)2 in pure water)) with an average error of less than 1.4% during two days of measurements on one solution with a sensor according to the invention.

In the context of the invention, the aqueous-liquid, preferably a liquid used during industrial processes, is liquid around its operating point. More specifically, the aqueous-liquid can be wastewater.

The aqueous-liquid may be stored in a storage container, for example, a storage tank or hold-up tank of a wastewater treatment facility. The wastewater can contain various forms of pollution that may have adversary effects when released into the environment. To prevent such adversary effects, the wastewater may be tested on the presence of said pollution. When the amount of pollution present in the aqueous-hquid is below threshold values, for example, a threshold value imposed by environmental regulations, the wastewater can be released into open water or transported off the production site.

Electrochemical impedance spectroscopy (EIS) may be used to determine the presence of pollution. EIS is a frequency domain measurement made by applying a sinusoidal voltage to a sample. The sinusoidal voltage may have a relatively small amplitude, such that the perturbations by the voltage on the sample are relatively small. An impedance profile of the sample is generated using a frequency response analyzer, which can be used to determine the type and amount of pollution of the sample. Preferably, a single impedance profile can be used to track and/or determine multiple types of pollution present in the sample.

By evenly spacing the electrodes highly reproducible results may be achieved, thereby increasing operational reliability. Preferably, the distance between electrodes (at the space where measurement is to take place between a working electrode and adjacent working electrode) may be the same between electrodes. The distance between electrodes (at the space where measurement is to take place between a working electrode and adjacent working electrode) is called the pitch. Usually the pitch is in the range of 100 nm to 10 mm, or in the range of 200 nm to 5 mm. A relatively large pitch, in particular of 0.5-10 mm or about 1 to about 5 mm, e.g. about 3 mm, can in particular be used when relatively limited information suffices. A relatively large pitch can facilitate cleaning.

The pitch preferably is relatively small, e.g. from a 0.1 um to lOOum, more preferably in the range of 0.5 um to 50 um, more preferably in the range of about 1 to about 30 um, in particular in the range of about 2 to about 25 um, as reducing the pitch results in more information from the double-layer (DL) at the interface of the electrodes. The DL may vary from 20nm to a few micron, in particular from 20 nm to 500 nm, 200 nm to 400 nm or 20 nm to 200 nm. The exact thickness can depend on the conditions at the interface, such as the type of solution and dissolved components. Placing the electrodes closely in the EIS module increases the signal-to- noise ratio, in particular in a polluted sample in which the resistance may be relatively high and the measured current would be relatively low, e.g. in the pico-Ampere range. Fabrication of such chips can be done mainly using photolithography, e.g. UV, deep-UV, laser writing, and e-beam lithography may be used for fabrication of the chips containing the electrodes with the small pitches and lateral resolutions. A reliable and accurate EIS module is important to determine two or more pollutants simultaneously in the same sample. Figure 5 illustrates a phase diagram (Fig 5B) at high frequencies (1kHz to 100 MHz) for three different chip designs (interdigitated design) with different pitches ‘f (50um, 25um and lOum; electrode thicknesses ‘e’ and ‘g’ 50 um in each case, Fig. 5A). At higher frequencies, the EIS provides information from interfaces at the electro de/electrolyte and very fast electrochemical reactions. By reducing the pitch size, more detailed information (wo peaks are more clear for (interdigitated) ID4 (f=25 um) and ID 5 designs (f=10 um)).

In order to further increase reliability, in particular, if multiple sensor chips are used, the sensor chips should be relatively identical. In order to achieve relatively identical electrodes, and thereby sensor chips, robust fabrication techniques may be applied in for example in a clean room, contrary to screen-printed disposable chips. Such devices can be used many times with or without surface cleaning and the electrodes stay intact even by applying voltage (for better selectivity the proper applied potential for specific components, such as oxidation or reduction potential of that component, can be chosen for EIS measurement). Preferably, the fabrication process for producing the measurement device allows for nanometer scale accuracy. In order to facilitate identifying the pollution type and quantity, a microprocessor is provided that is arranged to compare the impedance profile to a database of impedance profiles. The microprocessor may contain an algorithm, preferably a machine learning algorithm, e.g. a deep learning neural network that may be trained by supervised or unsupervised learning, that can compare the impedance profile from a measurement to a database of stored impedance profiles for such wastewater solutions. The database may be filled with lab-measured impedance profiles of known compositions. A further advantage of using a microprocessor to identify the type and amount of pollution via the impedance profile is that it may be possible to quickly establish that the pollution is below the threshold values. This, in its turn, may result in faster disposal of the wastewater, thereby freeing up the storage facility faster, thereby also providing a significant economic advantage.

The aqueous-liquid measurement device can be arranged to perform the electrochemical impedance spectroscopy measurement directly on a source of the sample of aqueous-liquid, e.g. by providing a wireless connection between the measurement device and the microprocessor arranged to compare the impedance profiles to the database of impedance profiles. Preferably, the measurements can be taken ‘on-line’, meaning that the measurement device can be provided directly on the storage facility, e.g. on the storage tank, or on piping close to the storage tank. More generally, the measurement device allows for the measurement to be taken on the production site, as opposed to e.g. an off-site lab facility. Preferably, the measurement results can also be shown on the production site, e.g. on a display of the measurement device or on a computer that is communicatively connected to the measurement device.

In order to facilitate reproducible and accurate results by the measurement device, the ElS-sensor may have minimum exposure to outside interference. For example, the aqueous-liquid measurement device can further comprise a water jacket cell surrounding the aqueous-liquid sample during use and a thermal bath, wherein the water-jacked cell can be in fluid connection with the thermal bath. This may allow for the sample to maintain a substantially constant temperature during each measurement, thereby limiting the effect of temperature swings on the sample. Preferably, the thermal bath may be of the same temperature of as the source of the sample, e.g. bulk temperature of the waste water in the storage tank. Alternatively, the temperature of the thermal bath may be of a different temperature, e.g. lower or higher than the bulk temperature of the wastewater in the storage tank. In such a situation, the sample may be stored and exposed sufficiently long to the thermal bath, such that the sample may reach a constant temperature for EIS measurements, which is highly desirable for accuracy of measurement. Adjusting the temperature of the sample, e.g. via the thermal bath, may improve measurement results.

In order to shield the EIS module against electromagnetic interference/radiation, e.g. leaking of electricity from nearby devices, the measurement device can further comprise a Faraday cage. The EIS module can be substantially closed by said Faraday cage. This is particularly advantageous when the distance (pitch) between electrodes of the EIS module is relatively small (such as 100 um or less, 50 um or less, 30 um or less, or 25 um or less) to collect reliable and reproducible data. Additionally, electrical leakage from the sample to the surroundings can be minimized to further increase the accuracy of the measurement. For instance, it is advantageous that the sample is electrically isolated during measurement in view of accuracy of the EIS data. In order to reduce the effect of vibrations surrounding the EIS module, e.g. a truck passing by or vibrations caused by the use of nearby production facilities, the EIS module can be substantially insulated from vibrations of the surrounding, for example via dampers, e.g. O-rings or other dampers 11, 21 (e.g., rubbers or if needed the passive and active stages) provided at locations where the device is in physical contact with its surrounding.

The aqueous-liquid measurement device can comprise a sampling system arranged to provide a fluid sample to the EIS module and a source from which the sample is to be taken. The sampling system can be in fluid connection to a source from which the sample can be taken, preferably as a parallel bypass connection. A sampling system can facilitate providing a sample easily to the EIS module. This may allow for the sample to be kept isolated from the source of the aqueous-liquid, e.g. the wastewater storage tank. Isolating the sample may facilitate the accuracy and reproducibility of the measurement results. Such a sampling system may be a bypass connection provided on the storage tank or piping in fluid connection with the storage tank. Such a bypass may comprise a plurality of valves that may facilitate for isolating the sample. Furthermore, a sampling system that is in fluid connection to the source from which the sample is taken may allow for intermittent sampling, i.e. the taken sample in the bypass may be kept stationary, and non-flowing, while the rest of the system may still be in use. More specifically, a wastewater sample may be taken and isolated in the bypass. While the sample is kept stationary and for example is being analyzed, the storage system and/or the connected piping may still be in use. The measurement device may further comprise a filtering system having filters to remove solid particles/components and/or membrane-based filters to remove unnecessary components for detection purposes (e.g., organic materials or slats which make the detection of required pollutants more complicated).

The electrodes may be made of different materials such as, but not limited to, Au, Pt, Bi, and glassy carbon or alloys. The electrodes may be covered by nanoparticles, or organic compounds on their surface to increase the selectivity and sensitivity of EIS measurements for specific pollutants in wastewater solutions. Different materials for an electrode may result in different operating conditions, which may affect the double layer (DL). This may be advantageous as this may increase the selectivity and sensitivity of the EIS module to specific pollutants. Additionally or alternatively, the surface of the electrodes is relatively smooth, advantageously a surface roughness equal or less than 7 nm, more advantageously equal to or less than 5nm or equal to or less than 4 nm, or even equal to or less than 1 nm, according to the arithmetic average profile height deviation from the mean line (Ra). Such a low roughness can for instance be obtained using a deposition technique in a clean room, such as sputtering or vapor deposition, in particular physical vapor deposition (PVD). Electrodes with a very low roughness can for instance be deposited on (highly) polished Si-wafers, which can be atomically smooth. A relatively low roughness is in particular also advantageous for improved reproducibility. In practice, the Ra can be about 0.1 nm or more, about 0.2 nm or more, about 0.5 nm or more, or about 1 nm or more. Surface roughness can be determined using a generally known standard method, such as by atomic force microcopy (AFM), as applicable on the filing date of the present disclosure; profile roughness parameters are included in BS EN ISO 4287:2000 British standard, identical to the ISO 4287:1997 standard.

The electrodes may be partially covered with one or more insulating high band gap semiconductor materials, such as SiO2, A2O3, SiC, or Si_xNy. Only predetermined and specific areas (precisely constant) of the electrodes are not covered and will be exposed to the sample for the EIS measurement. Additionally or alternatively, at least one of the electrodes can comprise a coating arranged to improve measurement accuracy. In order to further facilitate measurement accuracy and sensitivity, coating or nanoparticles can be provided on the electrodes. Said coatings or nanoparticles may be provided on one or more electrodes, and various types of materials may be used, e.g. oxide nanoparticles (e.g., NiO, TiO2), bimetallic nanoparticles or organic (mono)layer as a receptor for specific components/pollutants. A protection layer (such as Cr, Ni) can be used to protect the surface of the electrodes during the opening of the insulating layers, for instance in the case of using dry reactive ion etching. This layer can be chemically etched away from the surface of the electrodes.

The aqueous-liquid measurement device can further comprise an electrode cleaning arrangement arranged to clean the electrode. Accuracy and longevity of the sensors may be increased when the sensor, and in particular, the electrodes, are cleaned. Due to the exposure to the aqueous- liquid, pollutants and a voltage, a layer of dirt, e.g. oxidation, may form on the electrodes. Such a deposited lay er/p articles may reduce the effectiveness of the electrodes, thereby resulting in reduced accuracy and sensitivity of the sensor after consecutive uses. The electrodes may be cleaned by chemical cleaning, e.g. exposing them to a cleaning product/methods or DI- water. Additionally or alternatively, a cleaning agent may be provided in the sample bypass, thereby reducing the amount of times the sensor needs to be taken from the measurement device. Preferably, the electrode cleaning arrangement can be arranged to change the polarity of the electrode and provide a DC-current to the electrode. This polarity of the electrodes and providing the DC-current may cause the layer deposited on the electrode to detach (e.g., electrochemical etching of deposited metals or oxidation of deposited organic layer on the surface of electrodes) from the electrodes, such that they are washed away during conventional use. As an advantage, this does not require the addition or manual labor associated to with introducing them to mechanical or chemical cleaning.

The aqueous-liquid measurement device can further comprise a thermopile arranged to measure the temperature of the aqueous-liquid sample in contact with electrodes on the chip. As the temperature may affect the EIS measurement, knowing the temperature at the time of may allow for the correction of the data resulting from the EIS measurement. In addition, the invention provides a method of determining at least two pollutants in an aqueous-hquid, preferably using the aqueous- liquid measurement device respectively the sensor described above, the method comprising:

- providing a stationary, non-flowing, sample of the aqueous- liquid;

- performing electrochemical impedance spectroscopy at a high frequency range on the sample using at least one sensor;

- determining the presence or content of the at least two pollutants in the sample based on data obtained from the electrochemical impedance spectroscopy at high frequency;

- using an algorithm for simultaneous detection of two or more pollutants by one sensor; and

- in response to successfully determining the presence or content of at least two pollutants in the sample, storing and processing the data obtained from the electrochemical impedance spectroscopy on a digital medium via a microprocessor or otherwise performing electrochemical impedance spectroscopy at a medium frequency and an additional step of determining the presence or content of the at least two pollutants based on data obtained from the electrochemical impedance spectroscopy at the medium frequency. In particular, the a method of determining at least two pollutants in an aqueous-liquid in accordance with the invention is a method according to any of claims 1-12 of the application as filed.

An EIS measurement in accordance with the invention is generally carried out using two or more different frequencies, in particular two or more different ranges of frequencies (at least said high frequency and said medium frequency). The two or more different (ranges of) frequencies are usually selected in the general frequency range of ImH to 1GHz, in particular 500 MHz or less, more in particular 100 MHz or less or 1MHz or less. At least the high(est) frequency (or high(est) range of frequencies) is usually at least 0.01Hz, in particular at least 1Hz, more in particular at least 10 Hz. Herein after when referring to a high, medium respectively low frequency this is meant to include a high range of frequencies, a medium range of frequencies respectively a low range of frequencies, unless specified otherwise or unless it follows from the context that a single frequency is meant. Such range may also be referred to as the high frequency range, medium frequency range respectively low frequency range.

The high frequency (range) is preferably selected in the range of between 100 hertz and 10 megahertz or between IKHz and 1 GHz, in particular between 100 Hz and 30 MHz. In a specific embodiment, the high frequency is up to 10 MHz, in particular in the range of 100Hz to 10 MHz. Performing the electrochemical impedance spectroscopy at a high frequency has the advantage that the spectroscopy can be finished relatively fast comparable to lower frequencies. For example, an EIS performed at a frequency between 1 KHz and 30 megahertz can be finished within a minute, while an EIS performed at a frequency below 0.1 Hz may take an hour to complete.

The medium frequency (range) electrochemical impedance spectroscopy can be performed on the sample using at least one sensor. The medium frequency is a frequency lower than the high frequency, preferably in the range of between 1 Hz and 0.1 KHz. In a specific embodiment, the medium frequency is up to 100 Hz, in particular in the range of 1Hz to 1 KHz. The additional step of determining the presence or content of pollutants at least two pollutants can be done based on data obtained from the medium frequency electrochemical impedance spectroscopy. The method can further comprise the step of:

- in response to successfully determining the presence or content of the at least two pollutants in the sample storing the determined presence or content; or otherwise performing a low frequency electrochemical impedance spectroscopy and an additional step of determining the presence or content of the at least two pollutants based on data obtained from the low frequency electrochemical impedance spectroscopy. The low frequency (range) is a frequency (range) lower than the high frequency (range)and the medium frequency (range), preferably a frequency (range) selected in the range of between 0.1 mHz and 10 Hz. In a specific embodiment, the low frequency is up to 1 Hz, in particular in the range of 0.001 Hz to 1 Hz. While a lower frequency EIS may take relatively long compared to a high frequency EIS, a lower frequency EIS may yield results that can be successfully used to determine the presence or content of the at least two pollutants in the sample. Additionally or alternatively, if the low frequency electrochemical impedance spectroscopy did not yield data that could be used to determine the presence or content of the at least two pollutants, the sample may be brought to a lab for analysis. This data can then be used to further train the trained model.

Storing and processing the data obtained by the EIS on a digital medium, for example in a computer, may facilitate forming a database that can be used by the algorithm on the microprocessor to determine the quantity and type of pollutant in the sample.

The method according to the invention can further comprise the step of executing a program on a processor of a computer to train an algorithm to relate data obtained from electrochemical impedance spectroscopy to pollutions as required measuring components in the wastewater, preferably heavy metal ions.

The sample can be taken from a storage facility. If the at least two pollutants determined in the sample are below a lower threshold, preferably each pollutant individually, the aqueous-liquid in the storage facility can be released into open water. The algorithm may be a machine learning algorithm, e.g. a binary classification, multiclass classification, regression, deep neural network learning, or any combination thereof. Preferably, the measurement device is used to determine the presence and quantity of at least one metal ion and/or metalloid ion, preferably arsenic (As). Preferably, a metal ion is determined and selected from the group consisting of mercury (Hg), cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copper (Cu), iron (Fe), silver (Ag), and nickel (Ni), in particular lead and/or zinc.

The stationary sample can be provided via a bypass provided on a pipe in fluid communication with a storage facility containing the aqueous- liquid. The EIS can be performed in the bypass.

Further advantageous aspects of the invention are set out in the description and appended claims.

The technical features described in the paragraphs and sentences above can be isolated from the context, and the isolated technical features from the different paragraphs and sentences can be combined. Such combinations are herewith specifically disclosed in this description.

The invention will further be elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention.

In the drawings:

Fig. 1 shows a schematic overview of an aqueous-liquid measurement device for measuring pollution in an aqueous-liquid;

Fig. 2 A shows an overview of the sensor electrodes of the measurement device;

Fig. 2B shows a detail B from Fig. 2A;

Fig. 3 shows a flow chart of method of determining a pollutant in an aqueous-liquid according to the invention;

Fig 4A, 4B, 4C, and 4D show the results of an experiment using the measurement device and using the method of determining a pollutant in an aqueous-liquid according to the invention.

Fig 5A and Fig 5B schematically shows three different chip designs (interdigitated design) with different pitches ‘f (50um, 25um and lOum; electrode thicknesses ‘e’ and ‘g’ 50 um in each case and a phase diagram in each case).

Figs. 6A and 6B illustrate a measurement with a sensor according to the invention.

Referring to Fig. 1, an aqueous-liquid measurement device 1 for measuring pollution in an aqueous-liquid 2 is depicted. The measurement device 1 comprises an electrochemical impedance spectroscopy (EIS) module 3 arranged to determine the electrochemical impedance of a sample of wastewater 2. The device 1 further comprises a potentiostat equipped with a frequency response analyzer 5 arranged to determine an impedance profile of the sample of wastewater 2 and a microprocessor 6 arranged to compare the impedance profile to a database of impedance profiles to determine pollution in the wastewater 2. The measurement device 1 is a so- called microelectromechanical system (MEMS)-based chip.

During use, wastewater 2 can be taken from the wastewater treatment storage tank 7. At least one of the valves 15 can be opened, such that the measurement device 1 fills up with a wastewater sample 2. The valves 15 can be closed, thereby physically separating the wastewater sample 2 from the storage tank 7 and the live piping 16. When the analysis is finished, and the pollution content of the wastewater sample 2 is below the environmental threshold, the wastewater from the storage tank 7 can be disposed via an opening 14 in open water.

In order to insulate the measurement device 1 from its direct surroundings, and thereby improving the quality of measurements done by the device, various insulation measures have been taken. For thermal isolation, a water jacket cell 8 surrounding the wastewater sample 2 during use is provided. The water jacket cell 8 is in fluid connection with a thermal bath 9, which thermal bath 9 can be used to influence the temperature of the sample 2, e.g. keeping it constant during measurement. A static cooling/heating chamber 22 may be present between the water jacket cell 8 and the sample vessel 2. Furthermore, to provide isolation against electromagnetic radiation, the ElS-module 3 is substantially enclosed by a Faraday cage 10. Additionally, the ElS-module 2 is substantially insulated from vibrations via dampers 11, 21, such as O-rings.

In order to further improve measurement quality, the electrodes 4 comprise a coating that is arranged to improve measurement accuracy.

The measurement device 1 further comprises an electrode cleaning arrangement 13 arranged to clean at least one of the electrodes 4, preferably wherein the electrode cleaning arrangement 13 is arranged to reverse polarity of the at least one electrode 4 and provide a DC-current to the at least one electrode 4.

The device 1 is arranged to perform the EIS measurement directly on a source 7 of the sample of waste water 2. In addition, a sampling system 12 arranged to provide the fluid sample 2 to the ElS-module 3 is provided. To isolate the sample from the source 7 and corresponding piping 16, two valves 15 have been provided to form a parallel by-pass connection.

Turning to Figs. 2A and 2B a layout of the electrodes 4 of an EIS- sensor 17. The electrodes 4 have contact pads 18 and an ElS-electrode 19 can be seen, which are opened electrodes with a surface area A. The surface areas A are substantially the same and the distance D between the electrodes; i.e. the pitch is substantially the same for different devices for accurate and reproducible EIS data. Preferably, one of the electrodes is a working electrode and the other electrode is the counter electrode. Also, a reference electrode 20 is provided adjacent to the workin g/counter electrode. The reference electrode 20 can be an inert deposited electrode on the chip (e.g., Pt, Au, or glassy carbon). The reference electrode 20 can be monitored and calibrated during measurement by a standard reference electrode 20 (e.g., calomel, silver chloride electrode) The pitch preferably is relatively small, e.g. from lum to 25um, as reducing the pitch results in more information from the double-layer at the interface of the electrode/electrolyte. In the shown example, the pitch is 10 um. Placing the electrodes as close as possible in the EIS module increases the signal-to- noise ratio, in particular in a polluted sample in which the resistance may be relatively high and the measured current would be relatively low, e.g. in the pico-Ampere range.

The electrodes 4 can be made of different materials such as, but not limited to, Au, Pt, Bi, and glassy carbon. In the shown example, the electrode is made of Pt. Different materials for an electrode may result in different operating conditions, which may affect the double layer. The surface of the electrodes may modified by nanoparticles or receptors to increase the selectivity and sensitivity of the EIS measurements for certain pollutants. This may be advantageous as this may increase the selectivity and sensitivity of the EIS module to specific pollutants. The surface of electrodes 4 is relatively smooth having a surface roughness of 5nm or even less based on the quality of the silicon wafer used for fabrication of such MEMS-based devices, e.g. in the clean room.

The electrodes 4 are partially covered with an insulating semiconductor material, such as SiO2, A2O3 , SiC or Si_xN_y. In the shown example, the insulating material is A12O3. Only predetermined and specific areas of the electrodes 4 are not covered and will be exposed to the sample for the EIS measurement.

Referring to Fig. 3, a flowchart of an exemplary method of determining at least two pollutants in an aqueous-liquid is depicted. A measurement device, preferably the measurement device 1 described above is provided. A stationary, non-flowing, sample of the aqueous-liquid is provided to the measurement device. A high frequency electrochemical impedance spectroscopy, between 3 megahertz and 30 megahertz, is performed using at least one sensor. The high frequency spectroscopy can be performed relatively fast, for example in less than a minute. The obtained data is used to determine the presence or content of the at least two pollutants in the sample, using the trained model in combination with stored EIS data. Preferably, the stored EIS data will contain imaginary and real impedance for a large range of frequencies for different types of pollutants and concentrations of pollutants, for each pollutant individually and/or for a combination of pollutants. The measured high frequency EIS data will be compared to the stored EIS data, for example, using a trained model, preferably a deep neural network, and more preferably a neural network in a probabilistic Bayesian setting, in order to determine the presence and content of the sample.

If the relatively fast high frequency EIS measurement did not yield data that can be used with the trained model, e.g. due to a new type of pollutant or combination of pollutants, to determine the presence or content of the at least two pollutants in the sample, a medium frequency EIS measurement may be performed. Such a medium frequency EIS measurement is preferably in the range of 300 kilohertz and 3 megahertz, and may take a few minutes to complete. The obtained data can then again be used with the trained model to determine the presence or content of the at least two pollutants. If from the data of a medium frequency EIS measurement also not sufficiently the presence and content of the at least pollutants in the sample can be determined, a low-frequency EIS measurement can be performed. Such a low-frequency EIS measurement is performed at a frequency between 30 and 300 KHz. Such a measurement may take between a few minutes and an hour, and may result in more accurate data that can be used to determine the presence of a pollutant in the sample. Finally, if still there is no successful determination of the at least two pollutants contents of the sample, the sample can be sent to a lab for analysis. When the results return from, e.g. after a few hours, the results and measurement data can be stored and used to further train the trained model. In Figs 4A, 4B, 4C and 4D experimental results of the measurement device and the method for determining a pollutant in an aqueous-liquid are shown. Figs 4A and 4B show depict various concentrations of zinc sulfate and lead nitrate in DI water respectively. In Fig. 4A three dashed hnes are depicted, denoting the low-frequency, medium-frequency, and high frequency measurements, from left to right. In Figs 4A and 4B, various concentrations of pollutants are plotted from top to bottom, with the top most graph being showing the EIS measurement results from DI water with no pollutants, while the bottom most graph shows the EIS measurement for a concentration of 100 parts per million (ppm) zinc sulfate and lead nitrate in Figs 4A and 4B respectively. This data is used to develop and train the trained algorithm.

The trained algorithm, together with the measurement device, where tested on a sample of DI water containing a pollution of both zinc sulfate and lead nitrate. Figs 4C and 4D show the results for the detection of the content of zinc sulfate. Fig. 4C shows the results for a total pollution of 5 ppm, Fig. 4D shows the results for a total pollution of 50 ppm. For both total pollution contents, the amount of zinc sulfate and lead nitrate was varied relative to each other while maintaining the same total amount of pollution. In other words, in Fig. 4C multiple measurements were taken with a total pollution of 5 ppm pollution in DI water, starting with 0 ppm zinc sulfate and 5 ppm lead nitrate and ending with 5 ppm zinc sulfate and 0 ppm lead nitrate. The dashed line depicts the lab results, while the dots, including the error bars, depict the results measured by the high frequency measurements performed by the measurement device according to the invention. From these results, it can be concluded that the measurement device and the method according to the invention can be used to determine the content of a specific pollution (e.g. zinc sulfate) from DI water containing an additional pollution (e.g. lead nitrate) with an accuracy that is comparable to lab results. It is noted that the figures are only schematic representations that are given by way of non-limited examples. In the figures, the same or corresponding parts are designated with the same reference numerals.

Many variations will be apparent to the skilled person in the art. Such variations are understood to be comprised within the scope of the invention as defined in the appended claims.

Claims

1. Method of determining at least two pollutants in an aqueous- liquid, the method comprising:

- providing a stationary, non-flowing, sample of the aqueous- liquid;

- performing electrochemical impedance spectroscopy at a high frequency, on the sample using at least one sensor;

- determining the presence or content of the at least two pollutants in the sample based on data obtained from the electrochemical impedance spectroscopy at the high frequency;

- in response to successfully determining the presence or content of the at least two pollutants in the sample storing and processing the data obtained from the electrochemical impedance spectroscopy on a digital medium via a microprocessor or otherwise performing electrochemical impedance spectroscopy at a medium frequency (i.e. a lower frequency than the high frequency) and an additional step of determining the presence or content of the at least two pollutants based on data obtained from the electrochemical impedance spectroscopy at the medium frequency.

2. Method of determining at least two pollutants in an aqueous- liquid according to claim 1, wherein the high frequency is selected in the range of 100 mHz to 1GHz, preferably in the range of 100 mHz to 500 MHz, more preferably in the range of 1 Hz to 100 MHz.

3. Method of determining at least two pollutants in an aqueous- liquid according to claim 2, wherein the high frequency is selected in the range of between 100 Hz and 10 MHz.

4. Method of determining at least two pollutants in an aqueous- liquid according to claim 2, wherein the high frequency is selected in the range of between IKHz and 1 GHz, in particular between 1 KHz and 30 MHz.

5. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein the medium frequency is selected in the range of ImHz to 100 MHz, preferably in the range of lOmHz to 1MHz, 100 mHz to IKHz or 1 Hz to 100 Hz.

6. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein the medium frequency electrochemical impedance spectroscopy is performed on the sample using at least one sensor, and the additional step of determining the presence or content of the at least two pollutants is done based on data obtained from the medium frequency electrochemical impedance spectroscopy; and wherein the method further comprises the step of:

- in response to successfully determining the presence or content of the at least two pollutants in the sample storing the determined presence or content; or otherwise performing electrochemical impedance spectroscopy at a low frequency (i.e. a lower frequency than the medium frequency), preferably at a frequency of 1 Hz or less, such as selected in the range of 0.001-1 Hz; and an additional step of determining the presence or content of the at least two pollutants based on data obtained from the low frequency electrochemical impedance spectroscopy.

7. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, further comprising:

- executing a program on a processor of a computer to train an algorithm to relate data obtained from electrochemical impedance spectroscopy to pollutants, preferably heavy metal ions or metalloid ions.

8. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein the sample is taken from a storage facihty, and wherein if the at least two pollutants determined in the sample are below a lower threshold, the aqueous-liquid in the storage facility is released to open water.

9. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein at least one metal ion pollutant is determined or at least two metal ions, preferably at least one metal ion or at least two metal ions selected from the group consisting of mercury (Hg), cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copp .

10. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein at least one metalloid ion pollutant is determined, preferably arsenic (As).

11. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein the stationary sample is provided via a by-pass provided on a pipe in fluid communication with a storage facility containing the aqueous-liquid; and wherein the electrochemical impedance spectroscopy is performed in the bypass.

12. Method of determining at least two pollutants in an aqueous- liquid according to any of the preceding claims, wherein the aqueous liquid is waste water.

13. Aqueous-liquid measurement device for measuring pollutants in an aqueous liquid, preferably suitable for measuring pollutants using a method according to any of the preceding claims, comprising: an electrochemical impedance spectroscopy module arranged to determine the electrochemical impedance of a sample of aqueous-liquid, preferably wastewater, comprising: an electrochemical impedance spectroscopy sensor comprising a plurality of electrodes, wherein the electrodes at least comprises areas that are substantially evenly spaced from each other; a frequency response analyzer arranged to determine an impedance profile of the sample of aqueous-liquid; a microprocessor arranged to compare the impedance profile to a database of impedance profiles to determine/track the pollutants in the aqueous-liquid sample, wherein the pollutants are at least two pollutants.

14. Aqueous-liquid measurement device according to claim 13, wherein the frequency response analyzer is provided by a potentiostat equipped with the frequency response analyzer.

15. Aqueous-liquid measurement device according to claim 13 or 14, whereby the device is arranged to perform the electrochemical impedance spectroscopy measurement directly on a source of the sample of aqueous- liquid.

16. Aqueous-liquid measurement device according to claim 13, 14 or 15, comprising a water jacket cell surrounding the aqueous-liquid sample during use and a thermal bath, wherein the water jacket cell is in fluid connection with the thermal bath.

17. Aqueous-liquid measurement device according to any of the claims 13-16, further comprising a Faraday cage, wherein the electrochemical impedance spectroscopy module is substantially enclosed by the Faraday cage.

18. Aqueous-liquid measurement device according to any of the claims 13-17, wherein the electrochemical impedance spectroscopy module is substantially insulated from vibrations of the surrounding of the electrochemical impedance spectroscopy module, for example via dampers.

19. Aqueous-liquid measurement device according to any of the claims 13-18, comprising a sampling system arranged to provide a fluid sample to the electrochemical impedance spectroscopy module and a source from which the sample is to be taken, which sampling system is in fluid connection to the source, preferably as a parallel bypass connection.

20. Aqueous-liquid measurement device according to any of the claims 13-19, wherein the device is a microelectromechanical system (MEMS).

21. Aqueous-liquid measurement device according to any of the claims 13-20, wherein at least one of the electrodes comprises a coating or surface modification arranged to improve measurement accuracy.

22. Aqueous-liquid measurement device according to any of the claims 13-21, further comprising an electrode cleaning arrangement arranged to clean at least one of the electrodes, preferably wherein the electrode cleaning arrangement is arranged to reverse polarity of the at least one electrode and provide a DC-current to the at least one electrode.

23. Aqueous-liquid measurement device according to any of the claims 13-22, wherein at least two or more adjacent electrodes of said electrodes are substantially evenly spaced from each other (at least in a measurement zone for holding a sample), at a distance in the range of 100 nm to 10 mm .

24. Aqueous-liquid measurement device according to claim 23, wherein said adjacent electrodes are substantially evenly spaced from each other (at least in a measurement zone for holding a sample) at a distance in the range of 100 nm to 100 micrometer (um), preferably at a distance in the range of 2-25 micrometer.

25. Aqueous-liquid measurement device according to claim 23, wherein said adjacent electrodes are substantially evenly spaced from each other (at least in a measurement zone for holding a sample) at a distance in the range of 0.5-10 mm, preferably at a distance in the range of 1-5 mm.

26. Electrochemical impedance spectroscopy sensor comprising a plurality of electrodes, said plurality of electrodes having a surface area comprising a covered section that is covered with an insulating material and an uncovered section that is free of the insulating material such that the uncovered section of each electrode is exposable to an aqueous-liquid sample, which sensor preferably is for use in the aqueous-liquid measurement device according to any of the claims 13-25 or for use in a method according to any of the claims 1-12, , wherein the uncovered section of said surface area of said plurality of electrodes has a surface roughness (Ra) of 7 nm or less, preferably of 5 nm or less; and wherein the uncovered sections of the electrodes or parts thereof are substantially evenly spaced from each other.

27. Electrochemical impedance spectroscopy sensor according to claim 26, wherein said substantially even spaced surface areas of at least two adjacent electrodes of said electrodes are at a distance in the range of 100 nm to 100 micrometer, more preferably at a distance in the range of 1-50 micrometer or 2-25 micrometer.

28. Electrochemical impedance spectroscopy sensor according to claim 26 or 27, wherein, during use, a double layer forms on the uncovered section that has a thickness between 20nm and lOOOnm, preferably between 20 nm and 400 nm or between 20 nm and 200 nm.

29. Use of an electrochemical impedance spectroscopy sensor according to claim 26, 27 or 28 in an electrochemical impedance spectroscopy method of determining one or more components in an aqueous- liquid, preferably one or more metal ions or metalloid ions, more preferably one or ions selected from the group consisting of ions of mercury (Hg), cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copper (Cu), iron (Fe), silver (Ag), and nickel (Ni), and arsenic (As), in particular lead ions and/or zinc ions and/or arsenic (As) ions.