An electrochemical system for detecting bacterial growth in a duct

Abstract

An electrochemical system 200 for detecting bacterial growth, such as a biofilm, in a duct 205 comprises; one or more electrodes 210, 220, 230 and a measurement device 240 adapted to perform an electr

Description

Technical Field The present disclosure relates to an electrochemical system and method for detecting bacterial growth formation in a duct. Background Ducts of different size and shapes are used in a variety of applications that may include heating or cooling systems, water treatment and supply, food and drink manufacturing, to name a few. Bacterial growth formation, including the formation of biofilms in pipework requires regular maintenance. This may include inspection of the conduit followed by a cleaning procedure. Currently the detection of bacterial formation in pipework is performed using relatively complex techniques such as microscopy. It is an object of the disclosure to address one or more of the above mentioned limitations. Summary According to a first aspect of the disclosure, there is provided an electrochemical system for detecting bacterial growth in a duct, the system comprising: one or more electrodes, wherein each electrode is coupled to an electrolyte; and a measurement device adapted to perform an electrochemical measurement using the said one or more electrodes. For instance the duct may be made of a conducting material such as a metal or a metal alloy material. Alternatively the duct may be made of a non-conducting material, such as plastic. For instance, each electrode coupled to the electrolyte may form an electrode-electrolyte assembly. The electrode-electrolyte assembly may be implemented with different configurations. For example the electrode may form a first layer and the electrolyte a second layer in contact with the first layer. Alternatively, the electrode may be a rod, a wire or a plate surrounded at least partially by the electrolyte. Optionally, the measurement device comprises a potentiostat. Optionally, the electrochemical system comprises a mechanical arrangement adapted to attach the said one or more electrodes to the duct. For instance the mechanical arrangement may include a set of clamps for attaching the electrodes to the duct. Optionally, the said at least one electrodes are made of a metal or metal allow material. For instance, the electrode material may comprise stainless steel, silver, copper or platinum. Optionally, the electrolyte is a solid electrolyte. Optionally, the solid electrolyte comprises a conducting polymer mixed with metallic nanoparticles or carbon nanotubes CNTS. For instance multi-walled carbon nanotubes MWCNTs may be used. Optionally, the electrolyte is a quasi-solid electrolyte. Optionally, the quasi-solid electrolyte comprises a conducting hydrogel. For instance, the conducting hydrogel may comprise a natural or synthetic polymer and a conducting fluid. Optionally, a membrane may be provided on an active surface of the electrolyte. The membrane may be a protective membrane or filtration membrane. For instance, the membrane may be a polymer membrane. Optionally, the electrochemical system comprises a processor configured to process measurement data to identify bacterial growth formation. For instance the processor may be configured to execute a software or algorithm to analyse the measurement data. According to a second aspect of the disclosure, there is provided a method of detecting bacterial growth in a duct, the method comprising connecting one or more electrodes to the duct, wherein each electrode is coupled to an electrolyte; performing an electrochemical measurement using the said one or more electrodes; and identifying a level of bacterial growth based on the electrochemical measurement. Optionally, wherein connecting the one or more electrodes comprises attaching the one or more electrodes on an outer surface of the duct so that for each electrode the electrolyte is in contact with the outer surface of the duct. Optionally, wherein connecting the one or more electrodes comprises embedding the one or more electrodes within a wall of the duct. Optionally, the method comprises identifying formation of a biofilm based on the electrochemical measurement. Optionally, wherein the electrochemical measurement comprises at least one of an impedance, a current cycling, a chronoamperometry, a chronopotentiometry, a differential pulse voltammetry, a square wave voltammetry, and a cyclic voltammetry measurement. Optionally, wherein the electrochemical measurement comprises measuring a current, or a measuring a voltage between two electrodes or between the duct and at least one electrode. Optionally, wherein the electrochemical measurement comprises applying a voltage across the duct and the said one or more electrodes. According to a third aspect of the disclosure, there is provided the use of an electrochemical system according to the first aspect for detecting bacterial growth in a duct. According to a fourth aspect of the disclosure, there is provided a system comprising a duct fitted with and an electrochemical system according to the first aspect for detecting bacterial growth in the duct. For instance the system may be a temperature conditioning system, or a water treatment system, or a food and drink manufacturing system. According to a fifth aspect of the disclosure, there is provided a method of removing bacterial growth from a duct, the method comprising providing the duct with an electrochemical system according to the first aspect; filling at least partially the duct with a salt solution; applying a voltage across the duct and the said at least one electrodes; and rinsing the duct with an aqueous solution. Optionally, the method comprises performing an electrochemical measurement. Description of the drawings The disclosure is described in further detail below by way of example and with reference to the accompanying drawings, in which: figure 1 is a flow chart of a method for detecting bacterial growth in a duct; figure 2 is a diagram of an electrochemical system for detecting bacterial growth in a duct; figure 3A is a cross section of an electrode / electrolyte assembly fitted onto the surface of a conducting duct; figure 3B is a cross section of another electrode / electrolyte assembly fitted onto the surface of a conducting duct; figure 3C is a cross section of an electrode / electrolyte assembly fitted on a non-conducting duct; figure 4A is a plot showing several impedance spectra obtained with a copper working electrode in waste water using an open circuit potential configuration; figure 4B is a model for fitting the impedance spectra of figure 4A; figure 4C is a plot of the resistance of the biofilm as a function of time; figure 5 is a plot showing several impedance spectra obtained with a copper working electrode waste water using open circuit potential configuration; figure 6A is a plot showing open circuit potential evolution of a copper electrode in waste water; figure 6B is a plot showing the open circuit potential evolution of a copper electrode in distilled water; figure 7 A is an atomic force microscopy profile image of untreated copper; figure 7B is an atomic force microscopy profile image of copper in wate water after 15 days using a closed circuit potential of -0.3 V; figure 7C is an atomic force microscopy profile image of copper in wate water after 15 days using an open circuit potential (0V); figure 7D is a plot of the roughness factor profile of the image of figure 7C; figure 7E is an atomic force microscopy profile image of copper in distilled water after 15 days using an open circuit potential (0V); figure 7F is a plot of the roughness factor profile of the image of figure 7E; figure 8A is a plot of the current measured as a function of time between a stainless steel working electrode and a platinum counter electrode in waste water using closed circuit potential of -0.3V; figure 8B is a plot showing the impedance spectra obtained using the setup of figure 8A at 0 days, 4 days, 8 days, and 11 days; figure 8C is a plot showing the capacitance measurements obtained using the setup of figure 8A at 0 days, 4 days, 8 days, and 11 days; figure 9 is a plot of the current measured as a function of time between a stainless steel WE and a stainless steel CE, obtained in both a duct without water and with water, respectively; figure 10 is a plot showing the cyclic voltammetry measurements of water contaminated with bacteria obtained before and after biofilm formation; figure 11 is a plot showing the differential pulse voltammetry of water contaminated with bacteria obtained before and after biofilm formation; figure 12 is another plot showing the cyclic voltammetry measurements of water contaminated with bacteria obtained before and after biofilm formation; figure 13 is a plot showing the differential pulse voltammetry of water contaminated with bacteria obtained before and after biofilm formation; figure 14 is a plot showing the cyclic voltammetry measurements of tap water obtained before and after biofilm formation; figure 15 is a plot showing the differential pulse voltammetry of tap water obtained before and after biofilm formation; figure 16 is a plot showing the OCP evolution of a stainless steel electrode in 10 ml of water contaminated with bacteria and tap water, respectively; figure 17 is a flow chart of a method for removing bacterial growth from a duct; figure 18A is a plot showing the OCP evolution of a stainless steel electrode in 10 ml of water contaminated with bacteria; figure 18B is a plot showing the contaminated water as in figure 18A but after applying a voltage between the duct and the electrode to remove the biofilm. Description Figure 1 is a flow chart of a method for detecting bacterial growth in a duct. For instance, the duct may be made of a conducting material such as a metal or a metal alloy material. Alternatively the duct may be made of a non-conducting material, such as plastic. At step 110 one or more electrodes are connected to the metallic duct. Each electrode is coupled to an electrolyte. When the duct is made of a conducting material various means (for instance mechanical arrangements) may be used to attach the electrodes on the surface of the duct. When the duct is made of a non-conducting material the electrodes may be inserted in the duct's wall. The electrodes may be distributed along the length of the duct as appropriate depending on the size and shape of the duct. At step 120 an electrochemical measurement is performed using the said one or more electrodes. The electrochemical measurement may be performed over an extended period of time, for instance a few hours or a few days. At step 130 a level of bacterial growth is identified based on the electrochemical measurement. For instance various phases of biofilm formation may be identified. Figure 2 is a diagram of an electrochemical system for detecting bacterial growth in a duct. The duct 205 may be made of different metallic materials, including metal alloys. For instance the duct 205 may be made of stainless steel or copper. The system 200 includes one or more electrodes. In this example three electrodes are connected to the duct 205 at different locations along its length, labelled 210, 220 and 230. The electrodes can be attached on the external surface of the duct 205. As a result the electrodes 210, 220 and 230 are not in direct contact with the fluid present in the duct 205. Each electrode is coupled to an electrolyte to form an electrode-electrolyte assembly. The electrode 210 is in contact with the electrolyte 211 to form the electrode-electrolyte assembly 210’. Similarly the electrode 220 is in contact with the electrolyte 212 to form the electrode-electrolyte assembly 220', and the electrode 230 is in contact with the electrolyte 213 to form electrode-electrolyte assembly 230'. The electrodes can be made of metallic, or metal allow materials such as stainless steel, silver (Ag), copper (Cu) or Platinum (Pt). It will also be appreciated that the electrodes may be functionalised, for instance with nanoparticles. The electrolyte may be a solid electrolyte, also referred to as solid-state electrolyte. The solid electrolyte could be made of a conducting polymer such as Polyaniline (PANI). The conducting polymer may be mixed with metallic nanoparticles or carbon nanotubes CNTS. Multi-walled nanotubes, for instance multi-walled carbon nanotubes MWCNTs may also be used. MWCNTs are a special form of carbon nanotubes in which multiple singlewalled carbon nanotubes are nested inside one another. Alternatively, the electrolyte may be a quasi-solid electrolyte, also referred to as gel polymer electrolyte (GPE). For instance, the gel polymer electrolyte may be made of a conducting hydrogel made of a natural or synthetic polymer and a conducting fluid. The conducting fluid may include a saline solution, a buffer solution or hard water (i.e water with a high mineral content). A measurement device 240 is provided to perform an electrochemical measurement using the electrodes 210, 220 and 230. For instance, the measurement device 240 may be a potentiostat. The measurement device 240 may also be configured to communicate with a user device 250 such as a computer, a server, or a mobile phone. A processor configured to process the measurement data may be provided to identify bacterial growth formation. The processor may be implemented as part of the measurement device 240 or as part of the user device 250. The processor may be configured to execute a software program to analyse the data. The software program may be used to identify a particular feature in the measurement data indicative of biofilm formation. The processor may also be configured to generate a warning signal upon identification of bacterial growth formation. The system 200 can be installed or retrofitted on existing pipework without having to penetrate through the pipes / conduits. The electrode-electrolyte assemblies may be fitted on the external surface of the duct using various techniques. For instance a mechanical arrangement such as a clamp may be used to attach each electrode-electrolyte assembly onto the duct. The system 200 may be used to perform various types of electrochemical measurements including impedance measurements, current cycling measurements, chronoamperometry, chronopotentiometry, differential pulse voltammetry, square wave voltammetry, or cyclic voltammetry, to name a few. The measurements may be performed in a closed circuit potential CCP configuration or in an open circuit potential OCP configuration. When using the closed circuit potential configuration, a voltage is applied across the metallic duct and the electrodes. For instance, the measurement device 240 may be used to apply a negative voltage to the duct 205 and a positive voltage to the electrodes 210, 220 and 230. The measurement device 240 is used to measure a current. The current response can then be analysed to identity bacterial growth. Depending on the electrochemical measurement chosen, the metallic duct itself can act as one electrode, for instance as a working electrode (WE) or a counter electrode (CE). The electrode and electrolyte may be arranged using different configurations. Figure 3A is a cross section of an electrode / electrolyte assembly fitted onto the surface of a conducting duct. The electrode 310 forms a first layer provided on top the electrolyte 311 which forms a second layer. The electrolyte 311 is in contact with the wall surface 305 of the duct. A liquid 301 is provided inside the duct. The nature of the liquid would depend on the application. The liquid can be any fluid medium that is capable of allowing bacteria to grow, such as water, liquid and viscous food stuffs, sugar solutions, milky fluids, beverages among many other types of liquids. Figure 3B is a cross section of another electrode / electrolyte assembly fitted onto the surface of a conducting duct. In this example the electrode 310’ is a rod or wire provided within the electrolyte 311’. The electrolyte 311’ surrounds the electrode 310’ so that only the electrolyte 311’ is in contact with the surface of the duct 305. As mentioned above when the duct is made of a non-conductive material, the electrode / electrolyte assembly may be inserted within a wall portion of the duct. Figure 3C is a cross section of an electrode / electrolyte assembly fitted on a non-conducting duct. The same reference numerals have been used as in figure 3B for labelling corresponding components. In this example, an aperture or hole is formed within the duct’ wall 305. The electrode / electrolyte assembly 310' / 311' is inserted within the aperture, so that electrolyte 311’ has an active surface that can come into contact with the liquid 301. Optionally, a membrane 312’ may be provided on the active surface of the electrolyte 311’. The membrane 312’ may be a protective or filtration membrane used to prevent contamination between the liquid and the electrolyte. For instance, the membrane 312' may be a polymer membrane. Examples of polymer membranes may include a sulfonated tetrafluoroethylene based fluoropolymer-copolymer membrane, such as a Nafion membrane. To illustrate the principle of operation of the proposed system, various electrochemical measurements are described with reference to figures 4 to 19 and 21. Figure 4A is a plot showing impedance spectra obtained with a copper working electrode (WE) dipped in in 11 ml of waste water, using a platinum counter electrode (CE) and a Platinum reference electrode (RE). Measurements are provided after 1 hour (waveform 410), 11 days (waveform 420) and 14 days (waveform 430) using the closed circuit potential configuration. Depending on the ionic strength of the solution and the temperature, the voltage applied between the WE and CE can range from about -0.2 V to about -10 V. It is also possible to apply a current at about -100 mA . For example in saline water at 0.1 M it is 2V , in 0.01 M it is 0.5 V at RT. Figure 4B is a model for fitting the impedance spectra of figure 4A. The model shows the charge transfer resistance Ret and the biofilm resistance Rbiofilm which can be extracted from the model. Figure 4C is a plot of the resistance of the biofilm as a function of time. Once the biofilm has matured the resistance Rbiofilm drops sharply around day 14. The sharp drop in resistance value may be used as an indicator of biofilm formation. Figure 5 is a plot showing impedance spectra obtained with a copper working electrode (WE) dipped in 5 ml of waste water, using a platinum counter electrode (CE) and a Platinum reference electrode (RE). Measurements are provided after 1 hour (waveform 510), 6 days (waveform 520), 9 days (waveform 530), 12 days (waveform 540), 13 days (waveform 550) using the open circuit potential OCP configuration (no voltage applied). Figure 6A is a plot showing the OCP evolution of a copper electrode in waste water. In this experiment a potential also referred to as OCP potential is measured between the WE and the RE. The Y axes shows the open circuit potential OCP in volts. Figure 6B is a plot showing the OCP evolution of a copper electrode in distilled water. Figure 7A shows the atomic force microscopy (AFM) profile image of a piece of untreated copper. Figure 7B shows the AFM profile image of copper in wate water after 15 days using a closed circuit potential of -0.3 V. The globular features confirm the presence of the biofilm. Figure 7C shows the AFM profile image of copper in wate water after 15 days using an open circuit potential (OV). Figure 7D is a plot of the roughness factor profile of the image of figure 7C. The globular features confirm the presence of the biofilm. Figure 7E shows the AFM image of copper in distilled water after 15 days using an open circuit potential (OV). Figure 7F is a plot of the roughness factor profile of the image of figure 7E. Figure 8A is a plot showing the electrochemical signal (current) measured as a function of time between a stainless steel working electrode (WE) and a platinum counter electrode (CE). Measurements were obtained by dipping a Platinum reference electrode (RE) in 100 ml of waste water and using a closed circuit potential of -0.3V between the WE and the CE. After 5 days the current signal increases sharply indicating biofilm formation. Figure 8B is a plot showing the impedance spectra obtained using the setup of figure 8A at 0 days (waveform 810), 4 days (waveform 811), 8 days (waveform 812), and 11 days (waveform 813). Figure 8C is a plot showing the capacitance measurements obtained using the setup of figure 8A at 0 days (waveform 820), 4 days (waveform 821), 8 days (waveform 822), and 11 days (waveform 823). Figure 9 is a plot showing the electrochemical signal (current) measured as a function of time between a stainless steel WE (provided by the duct itself) and a stainless steel CE. Measurements were obtained in both a duct without water and with water using the electrode arrangement described in figure 3A. The electrolyte is provided by a PAN1 / MWCNT solid electrolyte with an electrode / electrolyte arrangement as shown in figure 3A. Figure 10 is a plot showing the cyclic voltammetry (CV) measurements of water contaminated with bacteria obtained at 0 hours (waveform 1010 before after biofilm formation) and after 20 hours ( waveform 1020 after biofilm formation). The CV measurements were obtained using stainless steel electrodes. Figure 11 is a plot showing the differential pulse voltammetry (DPV) measurements of water contaminated with bacteria obtained at 0 hours (waveform 1110 before after biofilm formation) and after 20 hours ( waveform 1120 after biofilm formation). The CV measurements were obtained using stainless steel electrodes. Figure 12 is a plot showing the cyclic voltammetry (CV) measurements of water contaminated with bacteria obtained at 0 hours (waveform 1210 before after biofilm formation) and after 72 hours ( waveform 1220 after biofilm formation). The CV measurements were obtained using carbon electrodes. Figure 13 is a plot showing the differential pulse voltammetry (DPV) measurements of water contaminated with bacteria obtained at 0 hours (waveform 1310 before after biofilm formation) and after 72 hours ( waveform 1320 after biofilm formation). The CV measurements were obtained using carbon electrodes. Figure 14 is a plot showing the cyclic voltammetry (CV) measurements of tap water obtained at 0 hours (waveform 1410 before after biofilm formation) and after 20 hours (waveform 1420 after biofilm formation). The CV measurements were obtained using carbon electrodes. Figure 15 is a plot showing the differential pulse voltammetry (DPV) measurements of tap water at 0 hours (waveform 1510 before after biofilm formation) and after 20 hours ( waveform 1520 after biofilm formation). The CV measurements were obtained using carbon electrodes. Figure 16 is a plot showing the OCP evolution of a stainless steel electrode in 10 ml of water contaminated with bacteria with 0.1M NaCl (waveform 1620), and tap water with 0.1M NaCl (waveform 1610). In this experiment, a potential also referred to as OCP potential is measured between the WE and the RE. The Y axes shows the open circuit potential OCP in volts. The electrochemical system of the disclosure can also be used to remove bacterial growth in the duct. Figure 17 is a flow chart of a method for removing bacterial growth from a duct. At step 1710, the duct is provided with an electrochemical system. The electrochemical system comprises one or more electrodes, each electrode being coupled to an electrolyte; and a measurement device to perform an electrochemical measurement using the said one or more electrodes. For instance the electrochemical system described in figure 2 maybe used. At step 1720, the duct is filled at least partially with a salt solution. Various concentrations of NaCl may be used, for example 0.1 g / lOOml ; or 0.01 g / 100ml. Alternatively an electrolyte may be used. At step 1730 a voltage is applied between the duct and the one or more electrodes. The voltage applied may vary depending on the NaCl concentration. For instance a voltage of +0.2V may be applied for an NaCl concentration of 0.1 g / lOOml and a voltage of +0.5 V may be applied for an NaCl concentration of 0.01 g / 100ml. Various solutions may be used. To improve reproducibility a constant ionic strength and temperature should preferably be used. At step 1740, the duct is rinsed with an aqueous solution. Figure 18A is a plot showing the OCP evolution of a stainless steel electrode in 10 ml of water contaminated with bacteria with 0.1M NaCl. In this experiment, a potential also referred to as OCP potential is measured between the WE and the RE. The Y axes shows the open circuit potential OCP in volts. The plot shows the attachment of bacteria . Figure 18B is a plot showing the same contaminated water as in Figure 18A but after applying a voltage between the duct and the electrode to remove the biofilm (Step 1730 of figure 17). The plot shows that the biofilm has been removed. A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the disclosure. Accordingly, the above description of the specific embodiments is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims

1. An electrochemical system for detecting bacterial growth in a duct, the system comprisingone or more electrodes, wherein each electrode is coupled to an electrolyte; anda measurement device adapted to perform an electrochemical measurement using the said one or more electrodes.

2. The electrochemical system as claimed in claim 1, wherein the measurement device comprises a potentiostat.

3. The electrochemical system as claimed in claim 1 or 2, comprising a mechanical arrangement adapted to attach the said one or more electrodes to the duct.

4. The electrochemical system as claimed in any of the preceding claims, wherein the said at least one electrodes are made of a metal or metal allow material.

5. The electrochemical system as claimed in any of the preceding claims, wherein the electrolyte is a solid electrolyte.

6. The electrochemical system as claimed in claim 5, wherein the solid electrolyte comprises a conducting polymer mixed with metallic nanoparticles or carbon nanotubes CNTS.

7. The electrochemical system as claimed in any of claims 1 to 4,wherein the electrolyte is a quasi-solid electrolyte.

8. The electrochemical system as claimed in claim 7, wherein the quasi-solid electrolyte comprises a conducting hydrogel.

9. The electrochemical system as claimed in any of the preceding claims comprising a processor configured to process measurement data to identify bacterial growth formation.

10. A method of detecting bacterial growth in a duct, the method comprisingconnecting one or more electrodes to the duct, wherein each electrode is coupled to an electrolyte;performing an electrochemical measurement using the said one or more electrodes; andidentifying a level of bacterial growth based on the electrochemical measurement.

11. The method as claimed in claim 10, wherein connecting the one or more electrodes comprises attaching the one or more electrodes on an outer surface of the duct so that for each electrode the electrolyte is in contact with the outer surface of the duct.

12. The method as claimed in claim 10, wherein connecting the one or more electrodes comprises embedding the one or more electrodes within a wall of the duct.

13. The method as claimed in any of the claims 10 to 12, comprising identifying formation of a biofilm based on the electrochemical measurement.

14. The method as claimed in any of the claims 10 to 13, wherein the electrochemical measurement comprises at least one of an impedance, a current cycling, a chronoamperometry, a chronopotentiometry, a differential pulse voltammetry, a square wave voltammetry, and a cyclic voltammetry measurement.

15. The method as claimed in any of the claims 10 to 13, wherein the electrochemical measurement comprises measuring a current or measuring a voltage between two electrodes or between the duct and at least one electrode.

16. The method as claimed in claim 14, wherein the electrochemical measurement comprises applying a voltage across the duct and the said one or more electrodes.

17. Use of an electrochemical system as claimed in any of the claims 1 to 9 for detecting bacterial growth in a duct.

18. A system comprising a duct fitted with and an electrochemical system as claimed in any of the claims 1 to 9 for detecting bacterial growth in the duct.

19. A method of removing bacterial growth from a duct, the method comprising providing the duct with an electrochemical system as claimed in claim 1; filling at least partially the duct with a salt solution; applying a voltage across the duct and the said at least one electrodes; and rinsing the duct with an aqueous solution.

20. The method as claimed in claim 19, comprising performing an electrochemical measurement.

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