WO2022167100A1 - Method and system for monitoring biofilms in household appliances - Google Patents

Method and system for monitoring biofilms in household appliances Download PDF

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Publication number
WO2022167100A1
WO2022167100A1 PCT/EP2021/052978 EP2021052978W WO2022167100A1 WO 2022167100 A1 WO2022167100 A1 WO 2022167100A1 EP 2021052978 W EP2021052978 W EP 2021052978W WO 2022167100 A1 WO2022167100 A1 WO 2022167100A1
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WO
WIPO (PCT)
Prior art keywords
biofilm
piezoelectric transducer
household appliance
appliance
test receptacle
Prior art date
Application number
PCT/EP2021/052978
Other languages
French (fr)
Inventor
Cristina Bertoni
Laura SQUARCIA
Orfeo SBAIZERO
Original Assignee
Electrolux Appliances Aktiebolag
Università Degli Studi Di Trieste
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Electrolux Appliances Aktiebolag, Università Degli Studi Di Trieste filed Critical Electrolux Appliances Aktiebolag
Priority to PCT/EP2021/052978 priority Critical patent/WO2022167100A1/en
Publication of WO2022167100A1 publication Critical patent/WO2022167100A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/036—Analysing fluids by measuring frequency or resonance of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/032—Analysing fluids by measuring attenuation of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/222—Constructional or flow details for analysing fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2437—Piezoelectric probes
    • G01N29/2443—Quartz crystal probes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
    • G01N29/4427—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with stored values, e.g. threshold values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/014—Resonance or resonant frequency
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02416—Solids in liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02466—Biological material, e.g. blood
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/025—Change of phase or condition
    • G01N2291/0256—Adsorption, desorption, surface mass change, e.g. on biosensors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/025—Change of phase or condition
    • G01N2291/0258—Structural degradation, e.g. fatigue of composites, ageing of oils

Definitions

  • the present invention generally relates to the field of household appliances. More particularly, the present invention relates to a method and a system for monitoring and treating biofilms forming in household appliances.
  • Most household appliances have one or more regions thereof comprising one or more walls configured to be at least temporally in contact with liquid.
  • refrigerators heat pump dryers and washer-dryers, air conditioners, air dehumidifiers, and heat pumps may comprise a container configured to collect condensation water.
  • dishwashers, clothes washers, and clothes iron appliances comprises a process liquid container configured to store a process liquid (e.g., water or water mixed with detergent).
  • a process liquid e.g., water or water mixed with detergent.
  • Another example comprises a beverage dispensing machine equipped with a water container.
  • These household appliance regions when containing liquid, are environments promoting the settling down of microorganisms, such as bacteria, generally coming from the external environment (e.g., clothes, dishes, air, food, etc.). Said microorganisms usually attach on wall(s) of said household appliance regions to form a microorganism aggregation, referred to as biofilm.
  • biofilm The biofilm growth on said household appliance regions is favored by static or stagnant liquid conditions. It is also appreciated that aerobic microorganism may also cause the formation of a biofilm at the interface between the liquid surface and air.
  • biofilms When biofilms are formed on wall(s) of a household appliance, undesired bad smells are generated, and the liquid in contact with the biofilm get contaminated, impairing the correct operation of the household appliance. If the biofilm grows to a sufficiently large extent, ducts of the household appliance may also get clogged. In case of beverage dispensing machine, the presence of a biofilm on the walls of the water container may also promote the presence of dangerous pathogenic organisms capable of compromising the quality of the beverages to be dispensed.
  • the Applicant has realized that in order to increase the efficiency and the operational life of household appliances that can be negatively affected by the formation of biofilms, an efficient method and a system for estimating a presence and/or a formation and/or a crumbling of biofilms in household appliances should be provided. In this way, by exploiting the knowledge about the presence/formation/crumbling of biofilms, proper actions can be advantageously undertaken for disinfecting and/or removing the bio films themselves.
  • An aspect of the present invention relates to a method for estimating a presence and/or a formation and/or a crumbling of a first biofilm on at least one wall of a household appliance region configured to be at least temporally in contact with a liquid.
  • the method comprises providing a test receptacle in fluid communication with said household appliance region and providing in the volume of said test receptacle a resonating mass- variation measuring device comprising a piezoelectric transducer configured to oscillate, said resonating mass-variation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of the properties, preferably of a mass and of viscoelasticity, of a second biofilm forming in said test receptacle.
  • said second biofilm is a biofilm growing on a sensing surface of the piezoelectric transducer exposed to the liquid within the test receptacle.
  • the method further comprises estimating said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
  • the presence and/or formation and/or crumbling of the first biofilm can be advantageously estimated in a stable, cost-effective and efficient way, without having to modify the household appliance region with the introduction of dedicated sensors, since the measure operations are performed in a separate location (the test receptacle).
  • the volume of said test receptacle is lower than 1 ml.
  • the volume of said test receptacle is lower than 100 pl, preferably about 50 pl.
  • a total surface inside the test receptacle in contact with said liquid is equal to a value comprised between 30% and 50%.
  • a volume of the test receptacle is equal to a value comprised between 7 and 10 mm 1 .
  • said resonating massvariation measuring device comprises a quartz crystal microbalance device.
  • said estimating said presence and/or formation and/or crumbling of said first biofilm comprises assessing, based on said measured variations of the piezoelectric transducer oscillation frequency, a first mass corresponding to a mass of a microorganism aggregation of said first biofilm plus a mass of microorganisms detached from and resting on said microorganism aggregation.
  • said estimating said presence and/or formation and/or crumbling of said first biofilm further comprises assessing a viscoelasticity of said microorganism aggregation of said first biofilm based on said measured piezoelectric transducer oscillation dissipation.
  • the method further comprises:
  • said monitoring said interaction of the injected disinfectant with said first biofilm comprises monitoring said interaction of the injected disinfectant with said first biofilm based on said assessed first mass and said assessed viscoelasticity.
  • the method further comprises causing a quasi-static liquid exchange between said household appliance region and said test receptacle.
  • said liquid is water.
  • said household appliance region comprises one of:
  • Another aspect of the present invention relates to a household appliance, comprising:
  • said household appliance region having at least one wall configured to be at least temporally in contact with a liquid;
  • Said system comprises:
  • test receptacle in fluid communication with said household appliance region
  • resonating mass- variation measuring device in the volume of said test receptacle, said resonating mass- variation measuring device comprising a piezoelectric transducer configured to oscillate, said resonating massvariation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of the properties, preferably, of a mass of a second biofilm forming in said test receptacle;
  • a processing unit configured to estimate said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
  • the volume of said test receptacle is lower than 1 ml.
  • the volume of said test receptacle is lower than 100 pl, preferably about 50 pl.
  • a total surface inside the test receptacle in contact with said liquid is equal to a value comprised between 30% and 50%.
  • a volume of the test receptacle is equal to a value comprised between 7 and 10 mm 1 .
  • said resonating mass- variation measuring device comprises a quartz crystal microbalance device.
  • said processing unit is configured to estimate said presence and/or formation and/or crumbling of said first biofilm by assessing, based on said measured variations of the piezoelectric transducer oscillation frequency, a first weight corresponding to a weight of a microorganism aggregation of said first biofilm plus a weight of microorganisms detached from and resting on said microorganism aggregation.
  • said processing unit is configured to estimate said presence and/or formation and/or crumbling of said first biofilm by further assessing a viscoelasticity of said microorganism aggregation of said first biofilm based on said measured piezoelectric transducer oscillation dissipation.
  • the household appliance further comprises a disinfectant injector device configured to inject a disinfectant into said household appliance region.
  • said disinfectant is configured to interact with said first biofilm for removing said first biofilm.
  • said processing unit is further configured to monitor the interaction of the injected disinfectant with said first biofilm for determining a sanitizing degree of said household appliance region based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
  • said processing unit is further configured to monitor the interaction of the injected disinfectant with said first biofilm based on said assessed first mass and said assessed viscoelasticity.
  • the household appliance further comprises a pump device configured to cause a quasi-static liquid exchange between said household appliance region and said test receptacle.
  • said pump device comprises a peristaltic pump.
  • said liquid is water.
  • said household appliance region comprises one of:
  • Figure 1A illustrates a household appliance comprising a system for estimating a presence and/or a formation and/or a crumbling of a biofilm according to embodiments of the invention
  • Figure IB is an enlarged view of a test receptacle of the system of Figure 1A according to an embodiment of the present invention
  • Figure 2 is a time diagram depicting exemplary experimental results about how a piezoelectric transducer oscillation frequency and a piezoelectric transducer oscillation dissipation variations measured using the system of Figure 1A according to an embodiment of the invention evolve over time;
  • Figures 3 and 4 are time diagrams depicting exemplary experimental results about how the piezoelectric transducer oscillation frequency and the piezoelectric transducer oscillation dissipation variations measured using the system of Figure 1A according to an embodiment of the invention evolve over time using three different kinds of disinfectant.
  • a household appliance in which embodiments of the present invention can be applied is globally identified with reference 100.
  • the household appliance 100 comprises one or more household appliance regions 110 (only one illustrated in Figure 1A) each including at least one wall 115 configured to be at least temporally in contact with a liquid, identified in Figure 1A with reference 120.
  • the household appliance region 110 is a liquid container of the household appliance 100 and the at least one wall 115 comprises the bottom wall and the side walls of said liquid container.
  • the at least one wall 115 comprises a different set of walls of the container, such as for example only the bottom wall of the container.
  • the concepts of the present invention directly apply to other kinds of household appliance regions 110, such as for example tanks, reservoirs, basins, ducts, pipes, comprising one or more walls configured to be at least temporally in contact with a liquid.
  • the household appliance 100 may be a refrigerator appliance, a heat pump dryer or washer-dryer appliance, an air conditioner appliance, an air dehumidifier appliance or a heat pump appliance
  • the liquid 120 may be condensation water produced by the household appliance 100 during its operation
  • the household appliance region 110 may be or may comprise a condensation water container.
  • the household appliance 100 may be a dishwasher appliance or a clothes washer appliance
  • the liquid 120 may be a process liquid (e.g., water or water mixed with detergents or other chemical agent(s))
  • the household appliance region 110 may be or may comprise a process liquid container.
  • the household appliance 100 may be a clothes iron appliance
  • the liquid 120 may be water used to generate steam
  • the household appliance region 110 may be or may comprise a process liquid container.
  • the household appliance 100 may be a beverage dispensing machine, the liquid 120 may be water and the household appliance region 110 may be or may comprise a water container.
  • microorganisms e.g., bacteria
  • biofilm a microorganism aggregation biofilm
  • the household appliance 100 comprises a system 150 for estimating a presence and/or a formation and/or a crumbling of the biofilm 125.
  • the system 150 comprises a test receptacle 155 in fluid communication with the household appliance region 110.
  • test receptacle 155 An enlarged view of the test receptacle 155 according to an embodiment of the present invention is illustrated in Figure IB.
  • the test receptacle 155 is used as a test chamber for performing analysis operations on samples of the liquid 120 taken from the household appliance region 110 and estimating a presence and/or a formation and/or a crumbling of the biofilm 125 on the walls 115 of the household appliance region 110 based on the results of these analysis operations.
  • the test receptacle 155 has a first port 158 in fluid communication with the household appliance region 110 through a first pipe element 160 and a second port 162 in fluid communication with the household appliance region 110 through a second pipe element 164.
  • the system 150 is configured to cause a liquid 120 exchange between the test receptacle 155 and the household appliance region 110, so that the test receptacle 155 receives an amount of the liquid 120 contained in the household appliance region 110.
  • the system 150 is further equipped with a pump 170 configured to cause:
  • the liquid 120 exchange between the test receptacle 155 and the household appliance region 110 is of the quasistatic type, a liquid exchange that happens slowly enough for the liquid contained in the system comprising the household appliance region 110 and the test receptacle 155 to remain in internal equilibrium. In this way, liquid inside the test receptacle 155 replicates quasi-static and water quality conditions including bacterial contamination occurring inside the household appliance region 110.
  • quasi-static liquid exchange can be realized with by setting the flow rate of the pump 170 within the interval 200 p L/h - 1 mL/h.
  • the flow rate can also be stopped completely for periods of time.
  • the pump 170 is a peristaltic pump.
  • test receptacle 155 and the household appliance region 110 are in fluid communication by means of other kind of hydraulic and electric components.
  • test receptacle 155 may be configured as a sub-chamber included in the household appliance region 110 and in fluid communication with the latter.
  • a resonating massvariation measuring device 175 is provided in the test receptacle 155.
  • resonating mass- variation measuring device it is herein intended a device configured to measure mass variations by exploiting a resonator element.
  • the resonating massvariation measuring device 175 is located inside the volume enclosed by the test receptacle 155.
  • the resonating massvariation measuring device 175 comprises a piezoelectric transducer 178 configured to oscillate.
  • the resonating mass- variation measuring device 175 is positioned in the test receptacle 155 in such a way that at least one face of the piezoelectric transducer 178 is in direct contact with the liquid 120 inside the test receptacle 155.
  • the piezoelectric transducer 178 comprises an active sensing surface 179 that is in direct contact with the liquid 120 inside the test receptacle 155.
  • test receptacle 155 and the household appliance region 110 are in fluid communication so as to share the same liquid 120, and therefore are subjected to a same or at least a very similar environmental condition, when a biofilm 125 is formed on the walls 115 of the household appliance region 110, a corresponding biofilm 180 grows on:
  • the surface(s) of the piezoelectric transducer 178 (and particularly the active sensing surface 179), in direct contact with the liquid 120.
  • the resonating mass-variation measuring device 175 is configured to measure variations of a piezoelectric transducer oscillation frequency fm caused by variations of the mass of the biofilm 180 on the active sensing surface 179 of the piezoelectric transducer 178.
  • the resonating massvariation measuring device 175 is configured to measure variations of a piezoelectric transducer oscillation dissipation Dm caused by variations of the viscoelasticity of the biofilm 180 on the active sensing surface 179 of the piezoelectric transducer 178.
  • the resonating massvariation measuring device 175 is a Quartz Crystal Microbalance (QCM) device.
  • QCM Quartz Crystal Microbalance
  • the active sensing surface of the piezoelectric transducer 178 of the resonating mass- variation measuring device 175 comprises a piezoelectric quartz crystal surface coated with gold.
  • the piezoelectric transducer 178 of the resonating mass-variation measuring device 175 oscillates at a piezoelectric transducer oscillation frequency fm having a value corresponding to its fundamental frequency value.
  • the actual value of the piezoelectric transducer oscillation frequency fm is influenced by the properties of the piezoelectric material of the piezoelectric transducer 178 itself as well as by geometric factors, such as the thickness of the piezoelectric material of the piezoelectric transducer 178, the size of the active sensing area 179, the thickness of metal electrodes, as well as by factors depending on the liquid 120 in contact with the piezoelectric transducer 178 and on the biofilm 180 formed on the active sensing surface 179, such as biofilm thickness, density or viscosity, viscoelasticity.
  • the resonating mass-variation measuring device 175 is therefore capable of obtaining information about the biofilm 180 based on variations of the piezoelectric transducer oscillation frequency fm and of the piezoelectric transducer oscillation dissipation Dm.
  • the processing and control unit 185 of the system 150 is configured to estimate the presence and/or formation and/or crumbling of the biofilm 125 based on at least one between:
  • the volume of test receptacle 155 is substantially lower than the volume of the household appliance region 110.
  • the volume of test receptacle 155 is lower than 1 ml.
  • the volume of test receptacle 155 is lower than 100 pl, preferably about 50 pl.
  • a volume of the test receptacle 155 is equal to a value comprised between 7 and 10 mm 1 .
  • the diameter of the active surface 179 is equal to 14 mm;
  • the volume of the test receptacle 155 is equal to 47 pl;
  • the ratio between the active sensing surface 179 in contact with the liquid and the surfaces inside the test receptacle 155 that are in contact with the liquid is equal to 50%
  • the ratio between the surfaces inside the test receptacle 155 that are in contact with the liquid and the volume of the test receptacle 155 is equal to 7 mm 1 .
  • test receptacle 155 with a substantially reduced volume and/or having a substantially high ratio between the inner surfaces of the test receptacle 155 subjected to the potential formation of the biofilm 180 and the volume of the test receptacle 155 has the effect that if dead microorganisms are detached from the biofilm 180, for example following the administration of proper disinfectant agents - provided that quasi-static or static flow condition between the test receptacle 155 and the household appliance region 110 is obtained- said dead microorganisms remains trapped inside the volume of the test receptacle 155, and precipitates on the active sensing surface 179 of the piezoelectric transducer 178 (and possibly on any still alive microorganism aggregation of the biofilm 180 on the active sensing surface 179) because of gravity.
  • the processing and control unit 185 of the system 150 is configured to estimate the presence and/or formation and/or crumbling of the biofilm 125 by assessing, based on said measured variation of the piezoelectric transducer oscillation frequency fm, a mass value W corresponding to a mass VV7 of the microorganism aggregation of the biofilm 180 plus a mass VV2 of microorganisms detached from and resting on said microorganism aggregation of the biofilm 180.
  • the processing and control unit 185 of the system 150 is configured to estimate the presence and/or formation and/or crumbling of the biofilm 125 by further assessing a viscoelasticy of the microorganism aggregation of the biofilm 180 based on said measured variations of the piezoelectric transducer oscillation dissipation Dm.
  • the household appliance 100 further comprises a disinfectant injector system, globally illustrated in Figure 1A with reference 190, configured to inject a disinfectant into (the liquid 120 of) the household appliance region 110.
  • Said disinfectant is a chemical substance configured to interact with the biofilms 125, 180 for the removal thereof.
  • the disinfectant may be a substance capable of killing bacteria by physical and/or chemical interaction with the bacteria aggregation forming the biofilms.
  • the disinfectant injector system 190 preferably comprises a disinfectant reservoir 192 configured to store the disinfectant.
  • the capacity of the disinfectant reservoir 192 is sufficient to allow a number of disinfectant injections before requiring to be recharged.
  • the disinfectant injector system 190 preferably comprises a delivery pump 194 configured to be activated (for example by the processing and control unit 185) to cause the injection of a disinfectant dose taken from the disinfectant reservoir 192 into the liquid 120 contained in the household appliance region 110 through a corresponding pipe element 196.
  • the fluid communication between the household appliance region 110 and the test receptacle 155 is controlled by setting the flow rate of the pump 170 to a value within the range 200 pL/h - 1 mL/h, and/or by stopping the pump 170 for some time periods.
  • Having a null flow rate during some time periods allows to assess signals generated by the resonating mass- variation measuring device 175 when no liquid exchange occurs between the the household appliance region 110 and the test receptacle 155.
  • the ratio between the inner surfaces of the test receptacle 155 subjected to the potential formation of the biofilm 180 and the volume of the test receptacle 155 can be increased in order to enhance the sensitivity to the crumbling of the biofilm forming on the internal surface of the test receptacle.
  • the design of the test receptacle 155 can be optimized to enhance said two phenomena by increasing the internal surfaces of the test receptacle 155 while keeping constant its volume (z.e., by increasing the ratio between the inner surfaces of the test receptacle 155 subjected to the potential formation of the biofilm 180 and the volume of the test receptacle 155).
  • the processing and control unit 185 of the system 150 is configured to monitor the interaction of the injected disinfectant with the biofilm 125 for determining a sanitizing degree of the household appliance region 110 based on at least one between:
  • the processing and control unit 185 of the system 150 is configured to monitor the interaction of the injected disinfectant with the biofilm 125 so as to estimate a crumbling of the biofilm 125 based on:
  • the mass value W (corresponding to the mass W1 of the microorganism aggregation of the biofilm 180 plus the mass VV2 of microorganisms detached from and resting on said microorganism aggregation of the biofilm 180), assessed using said measured variations of the membrane oscillation frequency fm, and
  • Figure 2 is a time diagram depicting exemplary experimental results about how the piezoelectric transducer oscillation frequency fm and the membrane oscillation dissipation Dm variations measured using the system 150 of Figure 1A according to an embodiment of the invention evolve over time.
  • the time diagram illustrated in Figure 2 covers a time interval corresponding to three consecutive days DI, D2, D3, wherein: - the starting condition provides for walls 115 of the household appliance region 110 that is clean, z.e., no biofilm 125 is formed yet;
  • a bacteria suspension (Escherichia coli) dose is injected in the liquid 120 contained in the household appliance region 110, for promoting the formation of the biofilm 125 on the walls 115 of the household appliance region 110;
  • a dose of disinfectant - in the considered exemplary case, Aniosept Activ® (Paracetic acid production in solution having a concentration of 1% in MilliQ) is injected in the liquid 120 contained in the household appliance region 110 for disinfecting the latter by causing the biofilm 125 crumble.
  • the processing and control unit 185 of the system 150 measures:
  • the processing and control unit 185 of the system 150 can expediently assess the presence of the biofilm 125 and follow in real-time the formation of the latter.
  • the processing and control unit 185 of the system 150 can expediently assess the crumbling of the biofilm 125 for example caused by the interaction of the disinfectant with the biofilm 180 (and therefore with the biofilm 125).
  • the piezoelectric transducer oscillation frequency fm After an increase in the piezoelectric transducer oscillation frequency fm caused by the crumbling of the biofilm 180 (and therefore in the biofilm 125) due to the diffusion of the disinfectant in the biofilm, the piezoelectric transducer oscillation frequency fm starts again to fall down. This is caused by dead microorganisms, previously detached from the biofilm because of the disinfectant, that detach from the test receptacle 155 internal surfaces as well as from the active sensing surface 179 of the piezoelectric transducer 178 and get suspended in the liquid medium. This translates in a progressive increase in particulate concentration in the liquid which is enhanced by the surface-to-volume ratio of the test receptacle (e.g.
  • Figures 3 and 4 are time diagrams depicting exemplary experimental results about how the piezoelectric transducer oscillation frequency fm ( Figure 3) and the piezoelectric transducer oscillation dissipation Dm ( Figure 4) variations measured using the system 150 of Figure 1A according to an embodiment of the invention evolve over time using three different kinds of disinfectant, i.e., Amuchina® 0.45% (Sodium Hypochlorite having a 0.45% concentration in PBS - 50ppm of Sodium Hypochlorite), Amuchina® 0.9% (Sodium Hypochlorite having a 0.9% concentration in PBS - lOOppm of Sodium Hypochlorite) and Aniosept Activ® (Paracetic acid production in solution having a concentration of 1% in MilliQ).
  • a disinfectant i.e., Amuchina® 0.45% (Sodium Hypochlorite having a 0.45% concentration in PBS - 50ppm of Sodium Hypochlorite), Amuchina® 0.9% (Sodium
  • the piezoelectric transducer oscillation frequency fm variation corresponding to the case in which the disinfectant is Amuchina® 0.45% is identified with reference 310
  • the one corresponding to the case in which the disinfectant is Amuchina® 0.9% is identified with reference 320
  • the case in which the disinfectant is Aniosept Activ® is identified with reference 330.
  • the piezoelectric transducer oscillation dissipation Dm corresponding to the case in which the disinfectant is Amuchina® 0.45% is identified with reference 340
  • the one corresponding to the case in which the disinfectant is Amuchina® 0.9% is identified with reference 350
  • the case in which the disinfectant is Aniosept Activ® is identified with reference 360.
  • the system 150 for estimating a presence and/or a formation and/or a crumbling of the biofilm 125 can be advantageously exploited to efficiently test the effectiveness of different disinfectants in removing biofilms.
  • each disinfectant following the introduction of each disinfectant, an increase in the piezoelectric transducer oscillation frequency fm is observed, until a corresponding piezoelectric transducer oscillation frequency fm peak is reached.
  • the piezoelectric transducer oscillation frequency fm is caused by the progressive detaching of microorganisms from the microorganism aggregation of the biofilm 180 on the active sensing surface 179 of the piezoelectric transducer 178 due to the disinfectant injection.
  • Each disinfectant corresponds to a different piezoelectric transducer oscillation frequency fm peak.
  • the time needed to reach the piezoelectric transducer oscillation frequency fm peak depends on the different diffusion rate and action of each disinfectant.
  • the peak occurs after about 2 hours from the injection of disinfectant, while for Aniosept Activ® the peak occurs after about 12 hours from the injection of disinfectant.
  • the time needed to reach the piezoelectric transducer oscillation frequency fm peak can be recognized through sensor data fusion techniques.
  • the subsequent decrease in the piezoelectric transducer oscillation frequency fm after the peak even in presence of disinfectant is due to an equilibrium between microorganisms cells removal operated by the disinfectant and the increase in the microorganisms mass that is suspended in the liquid which is followed over the time by the slow gravimetric precipitation of suspended dead microorganisms cells and aggregates of dead microorganisms cells on the active sensing surface 179 of the piezoelectric transducer 178 of the resonating mass-variation measuring device 175.
  • the piezoelectric transducer oscillation dissipation Dm tends to reach a value corresponding to a situation before the formation of the biofilm 180, and enables to estimate the efficacy of the biofilm removal that is the amount of soft deposit still attached on the active sensing surface 179 of the piezoelectric transducer 178 of the resonating mass- variation measuring device 175, providing complementary index to the estimation of the disinfectant penetration in the biofilm.

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Abstract

A method for estimating a presence and/or a formation and/or a crumbling of a first biofilm (125) on at least one wall (115) of a household appliance region (110) configured to be at least temporally in contact with a liquid. The method comprises: - providing a test receptacle (155) in fluid communication with said household appliance region and providing in the volume of said test receptacle a resonating mass-variation measuring device (175) comprising a piezoelectric transducer (178) configured to oscillate, said resonating mass- variation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of properties of a second biofilm (180) forming in said test receptacle, and - estimating said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.

Description

METHOD AND SYSTEM FOR MONITORING BIOFILMS IN HOUSEHOLD APPLIANCES
DESCRIPTION
Field of the invention
The present invention generally relates to the field of household appliances. More particularly, the present invention relates to a method and a system for monitoring and treating biofilms forming in household appliances.
Background of the invention
Most household appliances have one or more regions thereof comprising one or more walls configured to be at least temporally in contact with liquid.
For example, refrigerators, heat pump dryers and washer-dryers, air conditioners, air dehumidifiers, and heat pumps may comprise a container configured to collect condensation water. Moreover, dishwashers, clothes washers, and clothes iron appliances comprises a process liquid container configured to store a process liquid (e.g., water or water mixed with detergent). Another example comprises a beverage dispensing machine equipped with a water container.
These household appliance regions, when containing liquid, are environments promoting the settling down of microorganisms, such as bacteria, generally coming from the external environment (e.g., clothes, dishes, air, food, etc.). Said microorganisms usually attach on wall(s) of said household appliance regions to form a microorganism aggregation, referred to as biofilm. The biofilm growth on said household appliance regions is favored by static or stagnant liquid conditions. It is also appreciated that aerobic microorganism may also cause the formation of a biofilm at the interface between the liquid surface and air.
When biofilms are formed on wall(s) of a household appliance, undesired bad smells are generated, and the liquid in contact with the biofilm get contaminated, impairing the correct operation of the household appliance. If the biofilm grows to a sufficiently large extent, ducts of the household appliance may also get clogged. In case of beverage dispensing machine, the presence of a biofilm on the walls of the water container may also promote the presence of dangerous pathogenic organisms capable of compromising the quality of the beverages to be dispensed.
Summary of invention
The Applicant has realized that in order to increase the efficiency and the operational life of household appliances that can be negatively affected by the formation of biofilms, an efficient method and a system for estimating a presence and/or a formation and/or a crumbling of biofilms in household appliances should be provided. In this way, by exploiting the knowledge about the presence/formation/crumbling of biofilms, proper actions can be advantageously undertaken for disinfecting and/or removing the bio films themselves.
One or more aspects of the present invention are set out in the independent claims, with advantageous features of the same invention that are indicated in the dependent claims.
An aspect of the present invention relates to a method for estimating a presence and/or a formation and/or a crumbling of a first biofilm on at least one wall of a household appliance region configured to be at least temporally in contact with a liquid.
The method comprises providing a test receptacle in fluid communication with said household appliance region and providing in the volume of said test receptacle a resonating mass- variation measuring device comprising a piezoelectric transducer configured to oscillate, said resonating mass-variation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of the properties, preferably of a mass and of viscoelasticity, of a second biofilm forming in said test receptacle. Preferably, said second biofilm is a biofilm growing on a sensing surface of the piezoelectric transducer exposed to the liquid within the test receptacle.
The method further comprises estimating said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
In this way, the presence and/or formation and/or crumbling of the first biofilm can be advantageously estimated in a stable, cost-effective and efficient way, without having to modify the household appliance region with the introduction of dedicated sensors, since the measure operations are performed in a separate location (the test receptacle).
According to an embodiment of the present invention, the volume of said test receptacle is lower than 1 ml.
According to an embodiment of the present invention, the volume of said test receptacle is lower than 100 pl, preferably about 50 pl.
According to an embodiment of the present invention, a ratio between:
- an active surface of said piezoelectric transducer in contact with said liquid, and
- a total surface inside the test receptacle in contact with said liquid, is equal to a value comprised between 30% and 50%.
According to an embodiment of the present invention, a ratio between:
- the total surface inside the test receptacle in contact with said liquid, and
- a volume of the test receptacle, is equal to a value comprised between 7 and 10 mm 1.
Having a test receptacle with a substantially reduced volume and/or having a substantially high ratio between the inner surfaces of the test receptacle subjected to the potential formation of the biofilm and the volume of the test receptacle has the effect that if dead microorganisms are detached from the biofilm, if quasi- static or static flow condition between the test receptacle and the household appliance region is obtained, said dead microorganisms remains trapped inside the volume of the test receptacle, and precipitates on the active sensing surface of the piezoelectric transducer (and possibly on any still alive microorganism aggregation of the biofilm on the active sensing surface) because of gravity. According to an embodiment of the present invention, said resonating massvariation measuring device comprises a quartz crystal microbalance device.
According to an embodiment of the present invention, said estimating said presence and/or formation and/or crumbling of said first biofilm comprises assessing, based on said measured variations of the piezoelectric transducer oscillation frequency, a first mass corresponding to a mass of a microorganism aggregation of said first biofilm plus a mass of microorganisms detached from and resting on said microorganism aggregation.
According to an embodiment of the present invention, said estimating said presence and/or formation and/or crumbling of said first biofilm further comprises assessing a viscoelasticity of said microorganism aggregation of said first biofilm based on said measured piezoelectric transducer oscillation dissipation.
According to an embodiment of the present invention, the method further comprises:
- injecting a disinfectant into said household appliance region, said disinfectant being configured to interact with said first biofilm for removing said first biofilm;
- monitoring the interaction of the injected disinfectant with said first biofilm for determining a sanitizing degree of said household appliance region, said monitoring the interaction comprising:
- monitoring said interaction of the injected disinfectant with said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
Thanks to the improved monitoring of the interaction of the injected disinfectant with the biofilm, more efficient disinfection operations can be carried out, optimizing the disinfectant consumption.
According to an embodiment of the present invention, said monitoring said interaction of the injected disinfectant with said first biofilm comprises monitoring said interaction of the injected disinfectant with said first biofilm based on said assessed first mass and said assessed viscoelasticity. In this way, the effectiveness of different disinfectants in removing biofilms can be efficiently tested.
According to an embodiment of the present invention, the method further comprises causing a quasi-static liquid exchange between said household appliance region and said test receptacle.
By quasi-static liquid exchange it is herein intended a liquid exchange that happens slowly enough for the liquid contained in the system comprising the household appliance region and the test receptacle to remain in internal equilibrium so that the liquid inside the test receptacle replicates quasi-static and water quality conditions including bacterial contamination occurring inside the household appliance region.
According to an embodiment of the present invention, said liquid is water.
According to an embodiment of the present invention, said household appliance region comprises one of:
- a condensation water container of a refrigerator appliance;
- a condensation water container of a heat pump dryer appliance;
- a condensation water container of a heat pump washer-dryer appliance;
- a condensation water container of an air conditioner appliance;
- a condensation water container of an air dehumidifier appliance;
- a condensation water container of a heat pump appliance;
- a process liquid container of a dishwasher appliance;
- a process liquid container of a clothes washer appliance;
- a process liquid container of a clothes iron appliance;
- a water container of a beverage dispensing machine.
Another aspect of the present invention relates to a household appliance, comprising:
- a household appliance region, said household appliance region having at least one wall configured to be at least temporally in contact with a liquid;
- a system for estimating a presence and/or a formation and/or a crumbling of a first biofilm on said at least one wall.
Said system comprises:
- a test receptacle in fluid communication with said household appliance region;
- a resonating mass- variation measuring device in the volume of said test receptacle, said resonating mass- variation measuring device comprising a piezoelectric transducer configured to oscillate, said resonating massvariation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of the properties, preferably, of a mass of a second biofilm forming in said test receptacle;
- a processing unit configured to estimate said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
According to an embodiment of the present invention, the volume of said test receptacle is lower than 1 ml.
According to an embodiment of the present invention, the volume of said test receptacle is lower than 100 pl, preferably about 50 pl.
According to an embodiment of the present invention, a ratio between:
- an active surface of said piezoelectric transducer in contact with said liquid, and
- a total surface inside the test receptacle in contact with said liquid, is equal to a value comprised between 30% and 50%.
According to an embodiment of the present invention, a ratio between:
- the total surface inside the test receptacle in contact with said liquid, and
- a volume of the test receptacle, is equal to a value comprised between 7 and 10 mm 1.
According to an embodiment of the present invention, said resonating mass- variation measuring device comprises a quartz crystal microbalance device.
According to an embodiment of the present invention, said processing unit is configured to estimate said presence and/or formation and/or crumbling of said first biofilm by assessing, based on said measured variations of the piezoelectric transducer oscillation frequency, a first weight corresponding to a weight of a microorganism aggregation of said first biofilm plus a weight of microorganisms detached from and resting on said microorganism aggregation.
According to an embodiment of the present invention, said processing unit is configured to estimate said presence and/or formation and/or crumbling of said first biofilm by further assessing a viscoelasticity of said microorganism aggregation of said first biofilm based on said measured piezoelectric transducer oscillation dissipation.
According to an embodiment of the present invention, the household appliance further comprises a disinfectant injector device configured to inject a disinfectant into said household appliance region.
According to an embodiment of the present invention, said disinfectant is configured to interact with said first biofilm for removing said first biofilm.
According to an embodiment of the present invention said processing unit is further configured to monitor the interaction of the injected disinfectant with said first biofilm for determining a sanitizing degree of said household appliance region based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
According to an embodiment of the present invention, said processing unit is further configured to monitor the interaction of the injected disinfectant with said first biofilm based on said assessed first mass and said assessed viscoelasticity.
According to an embodiment of the present invention, the household appliance further comprises a pump device configured to cause a quasi-static liquid exchange between said household appliance region and said test receptacle.
According to an embodiment of the present invention, said pump device comprises a peristaltic pump.
According to an embodiment of the present invention, said liquid is water.
According to an embodiment of the present invention, said household appliance region comprises one of:
- a condensation water container of a refrigerator appliance;
- a condensation water container of a heat pump dryer appliance;
- a condensation water container of a heat pump washer-dryer appliance;
- a condensation water container of an air conditioner appliance;
- a condensation water container of an air dehumidifier appliance;
- a condensation water container of a heat pump appliance;
- a process liquid container of a dishwasher appliance;
- a process liquid container of a clothes washer appliance;
- a process liquid container of a clothes iron appliance;
- a water container of a beverage dispensing machine.
Brief description of the annexed drawings
These and other features and advantages of the present invention will be made apparent by the following description of some exemplary and non-limitative embodiments thereof; for its better intelligibility, the following description should be read by making reference to the attached drawings. On this regard, it is explicitly intended that the drawings are not necessarily drawn to scale (with some details thereof that can be exaggerated and/or simplified) and that, unless otherwise stated, they are simply used for conceptually illustrating the described structures and procedures. Particularly:
Figure 1A illustrates a household appliance comprising a system for estimating a presence and/or a formation and/or a crumbling of a biofilm according to embodiments of the invention;
Figure IB is an enlarged view of a test receptacle of the system of Figure 1A according to an embodiment of the present invention; Figure 2 is a time diagram depicting exemplary experimental results about how a piezoelectric transducer oscillation frequency and a piezoelectric transducer oscillation dissipation variations measured using the system of Figure 1A according to an embodiment of the invention evolve over time;
Figures 3 and 4 are time diagrams depicting exemplary experimental results about how the piezoelectric transducer oscillation frequency and the piezoelectric transducer oscillation dissipation variations measured using the system of Figure 1A according to an embodiment of the invention evolve over time using three different kinds of disinfectant.
Detailed description of preferred embodiments of the invention
By making reference to Figure 1A, a household appliance in which embodiments of the present invention can be applied is globally identified with reference 100.
The household appliance 100 comprises one or more household appliance regions 110 (only one illustrated in Figure 1A) each including at least one wall 115 configured to be at least temporally in contact with a liquid, identified in Figure 1A with reference 120.
In the exemplary embodiment illustrated in Figure 1A, the household appliance region 110 is a liquid container of the household appliance 100 and the at least one wall 115 comprises the bottom wall and the side walls of said liquid container. However, similar considerations apply in case the at least one wall 115 comprises a different set of walls of the container, such as for example only the bottom wall of the container.
Moreover, the concepts of the present invention directly apply to other kinds of household appliance regions 110, such as for example tanks, reservoirs, basins, ducts, pipes, comprising one or more walls configured to be at least temporally in contact with a liquid. For example, the household appliance 100 may be a refrigerator appliance, a heat pump dryer or washer-dryer appliance, an air conditioner appliance, an air dehumidifier appliance or a heat pump appliance, the liquid 120 may be condensation water produced by the household appliance 100 during its operation, and the household appliance region 110 may be or may comprise a condensation water container.
As another example, the household appliance 100 may be a dishwasher appliance or a clothes washer appliance, the liquid 120 may be a process liquid (e.g., water or water mixed with detergents or other chemical agent(s)), and the household appliance region 110 may be or may comprise a process liquid container.
Furthermore, the household appliance 100 may be a clothes iron appliance, the liquid 120 may be water used to generate steam, and the household appliance region 110 may be or may comprise a process liquid container.
Moreover, the household appliance 100 may be a beverage dispensing machine, the liquid 120 may be water and the household appliance region 110 may be or may comprise a water container.
The concepts of the present invention may however apply to other kind of household appliances not included in the list above.
Because of the prolonged presence of - possibly stagnant - liquid 120 in the household appliance region 110, microorganisms (e.g., bacteria) may grow on the walls 115, causing the formation of a microorganism aggregation biofilm, hereinafter briefly referred to as “biofilm” and identified in Figure 1A with reference 125.
According to an embodiment of the present invention, the household appliance 100 comprises a system 150 for estimating a presence and/or a formation and/or a crumbling of the biofilm 125.
According to an embodiment of the present invention, the system 150 comprises a test receptacle 155 in fluid communication with the household appliance region 110.
An enlarged view of the test receptacle 155 according to an embodiment of the present invention is illustrated in Figure IB. According to an embodiment of the present invention, the test receptacle 155 is used as a test chamber for performing analysis operations on samples of the liquid 120 taken from the household appliance region 110 and estimating a presence and/or a formation and/or a crumbling of the biofilm 125 on the walls 115 of the household appliance region 110 based on the results of these analysis operations.
According to an exemplary embodiment of the present invention, the test receptacle 155 has a first port 158 in fluid communication with the household appliance region 110 through a first pipe element 160 and a second port 162 in fluid communication with the household appliance region 110 through a second pipe element 164.
According to an embodiment of the invention, the system 150 is configured to cause a liquid 120 exchange between the test receptacle 155 and the household appliance region 110, so that the test receptacle 155 receives an amount of the liquid 120 contained in the household appliance region 110.
For this reason, according to an embodiment of the present invention, the system 150 is further equipped with a pump 170 configured to cause:
- liquid located in the household appliance region 110 to reach the test receptacle 155 through the first pipe element 160 and the first port 158, and
- liquid located in the test receptacle 155 to return back to the household appliance region 110 through the second port 162 and the second pipe element 164.
According to an embodiment of the present invention, the liquid 120 exchange between the test receptacle 155 and the household appliance region 110 is of the quasistatic type,
Figure imgf000013_0001
a liquid exchange that happens slowly enough for the liquid contained in the system comprising the household appliance region 110 and the test receptacle 155 to remain in internal equilibrium. In this way, liquid inside the test receptacle 155 replicates quasi-static and water quality conditions including bacterial contamination occurring inside the household appliance region 110.
According to an embodiment of the present invention, quasi-static liquid exchange can be realized with by setting the flow rate of the pump 170 within the interval 200 p L/h - 1 mL/h.
According to an embodiment of the present invention, the flow rate can also be stopped completely for periods of time.
According to an embodiment of the present invention, the pump 170 is a peristaltic pump.
Similar considerations apply in case the test receptacle 155 and the household appliance region 110 are in fluid communication by means of other kind of hydraulic and electric components.
Moreover, the concepts of the present invention apply in case the liquid exchange between the test receptacle 155 and the household appliance region 110 is carried out by exploiting gravimetric and/or precipitation phenomena and/or the communicating vessels principle, such as through a proper positioning of the test receptacle 155 with respect to the household region 110. For example, according to an embodiment of the invention not illustrated in the figures, the test receptacle 155 may be configured as a sub-chamber included in the household appliance region 110 and in fluid communication with the latter.
According to an embodiment of the present invention, a resonating massvariation measuring device 175 is provided in the test receptacle 155.
By resonating mass- variation measuring device it is herein intended a device configured to measure mass variations by exploiting a resonator element.
According to an embodiment of the present invention, the resonating massvariation measuring device 175 is located inside the volume enclosed by the test receptacle 155.
According to an embodiment of the present invention, the resonating massvariation measuring device 175 comprises a piezoelectric transducer 178 configured to oscillate. The resonating mass- variation measuring device 175 is positioned in the test receptacle 155 in such a way that at least one face of the piezoelectric transducer 178 is in direct contact with the liquid 120 inside the test receptacle 155. Particularly, the piezoelectric transducer 178 comprises an active sensing surface 179 that is in direct contact with the liquid 120 inside the test receptacle 155.
Since the test receptacle 155 and the household appliance region 110 are in fluid communication so as to share the same liquid 120, and therefore are subjected to a same or at least a very similar environmental condition, when a biofilm 125 is formed on the walls 115 of the household appliance region 110, a corresponding biofilm 180 grows on:
- the wall(s) of the test receptacle, and
- the surface(s) of the piezoelectric transducer 178 (and particularly the active sensing surface 179), in direct contact with the liquid 120.
According to an embodiment of the invention, the resonating mass-variation measuring device 175 is configured to measure variations of a piezoelectric transducer oscillation frequency fm caused by variations of the mass of the biofilm 180 on the active sensing surface 179 of the piezoelectric transducer 178.
According to an embodiment of the present invention, the resonating massvariation measuring device 175 is configured to measure variations of a piezoelectric transducer oscillation dissipation Dm caused by variations of the viscoelasticity of the biofilm 180 on the active sensing surface 179 of the piezoelectric transducer 178.
According to an embodiment of the present invention, the resonating massvariation measuring device 175 is a Quartz Crystal Microbalance (QCM) device. For example, the active sensing surface of the piezoelectric transducer 178 of the resonating mass- variation measuring device 175 comprises a piezoelectric quartz crystal surface coated with gold. When an alternating voltage is applied to the piezoelectric transducer 178 via metal electrodes (preferably gold), for example supplied under the control of a processing and control unit 185 of the system 150, and no biofilm 180 is formed on the active sensing surface 178, the piezoelectric transducer 178 of the resonating mass-variation measuring device 175 oscillates at a piezoelectric transducer oscillation frequency fm having a value corresponding to its fundamental frequency value.
Generally, the actual value of the piezoelectric transducer oscillation frequency fm is influenced by the properties of the piezoelectric material of the piezoelectric transducer 178 itself as well as by geometric factors, such as the thickness of the piezoelectric material of the piezoelectric transducer 178, the size of the active sensing area 179, the thickness of metal electrodes, as well as by factors depending on the liquid 120 in contact with the piezoelectric transducer 178 and on the biofilm 180 formed on the active sensing surface 179, such as biofilm thickness, density or viscosity, viscoelasticity.
Information about the biofilm 180 can be obtained from:
- variations of the piezoelectric transducer oscillation frequency fm due to the formation of the biofilm 180 (the higher the mass of microorganism corresponding to the biofilm, the lower the piezoelectric transducer oscillation frequency fm), and
- variations of a piezoelectric transducer oscillation damping Dam caused by the viscoelasticity of the biofilm 180 (a viscoelastic biofilm being not capable of oscillating fully coupled to the piezoelectric transducer 178).
As it is known to those skilled in the art, the following relationship exists between the piezoelectric transducer oscillation damping Dam and the piezoelectric transducer oscillation dissipation Dm:
Dm = 2* Dam / fr, \\i\\cvc fr is the fundamental frequency value of the piezoelectric transducer oscillation frequency fm.
The development of the biofilm 180 on the piezoelectric transducer 178 leads to a decrease in the piezoelectric transducer oscillation frequency fm due to an increase of the mass of microorganisms of the biofilm 180, and to an increase of the piezoelectric transducer oscillation dissipation Dm due to an increase of dumping caused by the growing biofilm 180. According to an embodiment of the invention, the resonating mass-variation measuring device 175 is therefore capable of obtaining information about the biofilm 180 based on variations of the piezoelectric transducer oscillation frequency fm and of the piezoelectric transducer oscillation dissipation Dm.
Since the test receptacle 155 and the household appliance region 110 are in fluid communication so as to share the same liquid 120, and therefore the biofilm 180 formed on the piezoelectric transducer 178 of the resonating mass-variation measuring device 175 has the same or very similar features of the biofilm 125 formed on the walls 115 of the household appliance region 110, the processing and control unit 185 of the system 150 is configured to estimate the presence and/or formation and/or crumbling of the biofilm 125 based on at least one between:
- the measured variations of the piezoelectric transducer oscillation frequency fm and
- the measured variations of the piezoelectric transducer oscillation dissipation Dm.
According to an embodiment of the present invention the volume of test receptacle 155 is substantially lower than the volume of the household appliance region 110.
According to an embodiment of the present invention, the volume of test receptacle 155 is lower than 1 ml.
According to an embodiment of the present invention, the volume of test receptacle 155 is lower than 100 pl, preferably about 50 pl.
According to an embodiment of the present invention, the ratio between:
- the active sensing surface 179 of the piezoelectric transducer 178 of the resonating mass-variation measuring device 175 in contact with the liquid, and
- the surfaces inside the test receptacle 155 that are in contact with the liquid (defining the total useful surface subjected to the potential formation of the biofilm 180), is between 30 and 50%. According to an embodiment of the present invention, the ratio between:
- the surfaces inside the test receptacle 155 that are in contact with the liquid, and
- a volume of the test receptacle 155, is equal to a value comprised between 7 and 10 mm 1.
For example, according to an exemplary embodiment of the present invention:
- the diameter of the active surface 179 is equal to 14 mm;
- the volume of the test receptacle 155 is equal to 47 pl;
- the ratio between the active sensing surface 179 in contact with the liquid and the surfaces inside the test receptacle 155 that are in contact with the liquid is equal to 50%, and
- the ratio between the surfaces inside the test receptacle 155 that are in contact with the liquid and the volume of the test receptacle 155 is equal to 7 mm 1.
Having a test receptacle 155 with a substantially reduced volume and/or having a substantially high ratio between the inner surfaces of the test receptacle 155 subjected to the potential formation of the biofilm 180 and the volume of the test receptacle 155 has the effect that if dead microorganisms are detached from the biofilm 180, for example following the administration of proper disinfectant agents - provided that quasi-static or static flow condition between the test receptacle 155 and the household appliance region 110 is obtained- said dead microorganisms remains trapped inside the volume of the test receptacle 155, and precipitates on the active sensing surface 179 of the piezoelectric transducer 178 (and possibly on any still alive microorganism aggregation of the biofilm 180 on the active sensing surface 179) because of gravity.
According to an embodiment of the present invention, the processing and control unit 185 of the system 150 is configured to estimate the presence and/or formation and/or crumbling of the biofilm 125 by assessing, based on said measured variation of the piezoelectric transducer oscillation frequency fm, a mass value W corresponding to a mass VV7 of the microorganism aggregation of the biofilm 180 plus a mass VV2 of microorganisms detached from and resting on said microorganism aggregation of the biofilm 180.
According to an embodiment of the present invention, the processing and control unit 185 of the system 150 is configured to estimate the presence and/or formation and/or crumbling of the biofilm 125 by further assessing a viscoelasticy of the microorganism aggregation of the biofilm 180 based on said measured variations of the piezoelectric transducer oscillation dissipation Dm.
According to an embodiment of the present invention, the household appliance 100 further comprises a disinfectant injector system, globally illustrated in Figure 1A with reference 190, configured to inject a disinfectant into (the liquid 120 of) the household appliance region 110. Said disinfectant is a chemical substance configured to interact with the biofilms 125, 180 for the removal thereof. For example, the disinfectant may be a substance capable of killing bacteria by physical and/or chemical interaction with the bacteria aggregation forming the biofilms.
According to an embodiment of the present invention, the disinfectant injector system 190 preferably comprises a disinfectant reservoir 192 configured to store the disinfectant. Preferably, the capacity of the disinfectant reservoir 192 is sufficient to allow a number of disinfectant injections before requiring to be recharged.
According to an embodiment of the present invention, the disinfectant injector system 190 preferably comprises a delivery pump 194 configured to be activated (for example by the processing and control unit 185) to cause the injection of a disinfectant dose taken from the disinfectant reservoir 192 into the liquid 120 contained in the household appliance region 110 through a corresponding pipe element 196.
Since the household appliance region 110 and the test receptacle 155 are in fluid communication, disinfectant injected into the household appliance region 110 reaches also the test receptacle 155, so that the injected disinfectant interact with both the biofilms 125 and 180 for causing crumbling thereof.
As already mentioned above, according to an embodiment of the present invention, the fluid communication between the household appliance region 110 and the test receptacle 155 is controlled by setting the flow rate of the pump 170 to a value within the range 200 pL/h - 1 mL/h, and/or by stopping the pump 170 for some time periods.
Having a null flow rate during some time periods allows to assess signals generated by the resonating mass- variation measuring device 175 when no liquid exchange occurs between the the household appliance region 110 and the test receptacle 155.
According to an embodiment of the present invention, the ratio between the inner surfaces of the test receptacle 155 subjected to the potential formation of the biofilm 180 and the volume of the test receptacle 155 can be increased in order to enhance the sensitivity to the crumbling of the biofilm forming on the internal surface of the test receptacle.
According to an embodiment of the present invention, the higher the ratio between the surfaces inside the test receptacle 155 that are in contact with the liquid, and the volume of the test receptacle 155, the higher the amount of biofilm 180 growing on the surfaces inside the test receptacle 155, and consequently the higher the amount of biofilm 180 that can detach from the surfaces inside the test receptacle 155 upon disinfectant administration.
Having a liquid 120 exchange between the test receptacle 155 and the household appliance region 110 of the quasi-static type, the following two phenomena may happen after the administration of disinfectant:
- a liquid density increasing caused by dead microorganism cells and/or aggregates of dead microorganism cells which remain suspended in the liquid, and
- a local mass increasing caused by gravimetric precipitation of dead microorganism cells and/or aggregates of dead microorganism cells.
According to an embodiment of the present invention, the design of the test receptacle 155 can be optimized to enhance said two phenomena by increasing the internal surfaces of the test receptacle 155 while keeping constant its volume (z.e., by increasing the ratio between the inner surfaces of the test receptacle 155 subjected to the potential formation of the biofilm 180 and the volume of the test receptacle 155).
According to an embodiment of the present invention, the processing and control unit 185 of the system 150 is configured to monitor the interaction of the injected disinfectant with the biofilm 125 for determining a sanitizing degree of the household appliance region 110 based on at least one between:
- the measured variations of the piezoelectric transducer oscillation frequency fm and
- the measured variations of the membrane oscillation dissipation Dm.
According to an embodiment of the present invention, the processing and control unit 185 of the system 150 is configured to monitor the interaction of the injected disinfectant with the biofilm 125 so as to estimate a crumbling of the biofilm 125 based on:
- the mass value W (corresponding to the mass W1 of the microorganism aggregation of the biofilm 180 plus the mass VV2 of microorganisms detached from and resting on said microorganism aggregation of the biofilm 180), assessed using said measured variations of the membrane oscillation frequency fm, and
- the viscoelasticy of the microorganism aggregation of the biofilm 180, assessed using said measured variations of the piezoelectric transducer oscillation dissipation Dm.
In order to better show how the system 150 for estimating a presence and/or a formation and/or a crumbling of the biofilm 125 operates according to an embodiment of the invention, reference will be now made to Figure 2.
Figure 2 is a time diagram depicting exemplary experimental results about how the piezoelectric transducer oscillation frequency fm and the membrane oscillation dissipation Dm variations measured using the system 150 of Figure 1A according to an embodiment of the invention evolve over time.
The time diagram illustrated in Figure 2 covers a time interval corresponding to three consecutive days DI, D2, D3, wherein: - the starting condition provides for walls 115 of the household appliance region 110 that is clean, z.e., no biofilm 125 is formed yet;
- at the beginning of day DI, and at the beginning of day D2, a bacteria suspension (Escherichia coli) dose is injected in the liquid 120 contained in the household appliance region 110, for promoting the formation of the biofilm 125 on the walls 115 of the household appliance region 110;
- at the beginning of day D3, a dose of disinfectant - in the considered exemplary case, Aniosept Activ® (Paracetic acid production in solution having a concentration of 1% in MilliQ) is injected in the liquid 120 contained in the household appliance region 110 for disinfecting the latter by causing the biofilm 125 crumble.
The horizontal axis of the time diagram corresponds to the time t, with the beginning of the first day DI that corresponds to time t = 0.
The vertical axis on the left of the time diagram corresponds to the measured variation 210 of the piezoelectric transducer oscillation frequency fm with respect to a starting value 210(0) equal to 0 at time t = 0 (this starting value is equal to the fundamental frequency value corresponding to the piezoelectric transducer 178).
The vertical axis on the right of the time diagram corresponds to the measured variation 220 of the piezoelectric transducer oscillation dissipation Dm with respect to a starting value 220(0) equal to 0 at time t = 0.
Following the injection of bacteria nutrient doses, the processing and control unit 185 of the system 150 measures:
- a decrease in the piezoelectric transducer oscillation frequency fm, due to an increase of the mass of microorganisms of the biofilm 180 (which is in turn indicative of a corresponding increase of the mass of microorganisms of the biofilm 125), and
- an increase in the piezoelectric transducer oscillation dissipation Dm due to the viscoelasticity of the biofilm 180 growing on the sensing surface of the piezoelectric transducer (which is in turn indicative of a corresponding evolution in the biofilm 125 viscoelesticity along the growth process). By detecting a decrease in the piezoelectric transducer oscillation frequency fm and an increase in the piezoelectric transducer oscillation dissipation Dm, the processing and control unit 185 of the system 150 can expediently assess the presence of the biofilm 125 and follow in real-time the formation of the latter.
Moreover, when the processing and control unit 185 of the system 150 detects an increase in the piezoelectric transducer oscillation frequency fm and a decrease in the piezoelectric transducer oscillation dissipation Dm, the processing and control unit 185 of the system 150 can expediently assess the crumbling of the biofilm 125 for example caused by the interaction of the disinfectant with the biofilm 180 (and therefore with the biofilm 125).
After an increase in the piezoelectric transducer oscillation frequency fm caused by the crumbling of the biofilm 180 (and therefore in the biofilm 125) due to the diffusion of the disinfectant in the biofilm, the piezoelectric transducer oscillation frequency fm starts again to fall down. This is caused by dead microorganisms, previously detached from the biofilm because of the disinfectant, that detach from the test receptacle 155 internal surfaces as well as from the active sensing surface 179 of the piezoelectric transducer 178 and get suspended in the liquid medium. This translates in a progressive increase in particulate concentration in the liquid which is enhanced by the surface-to-volume ratio of the test receptacle (e.g. the higher the surface-to-volume ratio of the cell and the higher is the amount of dead microorganisms cells and/or aggregates that can detach from the test receptacle internal surfaces including the sensing surface). Moreover, due to quasi-static down to null exchange flow conditions between the household appliance region 110 and the test receptacle 155, dead microorganisms in the form of single cells or aggregates can precipitate over time toward the active sensing surface 179 because of gravity.
Figures 3 and 4 are time diagrams depicting exemplary experimental results about how the piezoelectric transducer oscillation frequency fm (Figure 3) and the piezoelectric transducer oscillation dissipation Dm (Figure 4) variations measured using the system 150 of Figure 1A according to an embodiment of the invention evolve over time using three different kinds of disinfectant, i.e., Amuchina® 0.45% (Sodium Hypochlorite having a 0.45% concentration in PBS - 50ppm of Sodium Hypochlorite), Amuchina® 0.9% (Sodium Hypochlorite having a 0.9% concentration in PBS - lOOppm of Sodium Hypochlorite) and Aniosept Activ® (Paracetic acid production in solution having a concentration of 1% in MilliQ).
Particularly, in Figure 3 the piezoelectric transducer oscillation frequency fm variation corresponding to the case in which the disinfectant is Amuchina® 0.45% is identified with reference 310, the one corresponding to the case in which the disinfectant is Amuchina® 0.9% is identified with reference 320, and the case in which the disinfectant is Aniosept Activ® is identified with reference 330.
In Figure 4, the piezoelectric transducer oscillation dissipation Dm corresponding to the case in which the disinfectant is Amuchina® 0.45% is identified with reference 340, the one corresponding to the case in which the disinfectant is Amuchina® 0.9% is identified with reference 350, and the case in which the disinfectant is Aniosept Activ® is identified with reference 360.
Since, as can be seen from Figures 3 and 4, each disinfectant causes different variations in the piezoelectric transducer oscillation frequency fm and in the piezoelectric transducer oscillation dissipation Dm, the system 150 for estimating a presence and/or a formation and/or a crumbling of the biofilm 125 according to the embodiments of the invention can be advantageously exploited to efficiently test the effectiveness of different disinfectants in removing biofilms.
As can be seen in Figure 3, following the introduction of each disinfectant, an increase in the piezoelectric transducer oscillation frequency fm is observed, until a corresponding piezoelectric transducer oscillation frequency fm peak is reached. The piezoelectric transducer oscillation frequency fm is caused by the progressive detaching of microorganisms from the microorganism aggregation of the biofilm 180 on the active sensing surface 179 of the piezoelectric transducer 178 due to the disinfectant injection. Each disinfectant corresponds to a different piezoelectric transducer oscillation frequency fm peak. Moreover, the time needed to reach the piezoelectric transducer oscillation frequency fm peak depends on the different diffusion rate and action of each disinfectant. The later the occurrence of the peak, the longer is the disinfectant diffusion through the biofilm and the consequent disinfection operation efficacy. For example, for Amuchina® 0.45% and Amuchina® 0.9%, the peak occurs after about 2 hours from the injection of disinfectant, while for Aniosept Activ® the peak occurs after about 12 hours from the injection of disinfectant. The time needed to reach the piezoelectric transducer oscillation frequency fm peak can be recognized through sensor data fusion techniques.
The subsequent decrease in the piezoelectric transducer oscillation frequency fm after the peak even in presence of disinfectant is due to an equilibrium between microorganisms cells removal operated by the disinfectant and the increase in the microorganisms mass that is suspended in the liquid which is followed over the time by the slow gravimetric precipitation of suspended dead microorganisms cells and aggregates of dead microorganisms cells on the active sensing surface 179 of the piezoelectric transducer 178 of the resonating mass-variation measuring device 175.
Making reference to Figure 4, after the injection of disinfectant, the piezoelectric transducer oscillation dissipation Dm tends to reach a value corresponding to a situation before the formation of the biofilm 180, and enables to estimate the efficacy of the biofilm removal that is the amount of soft deposit still attached on the active sensing surface 179 of the piezoelectric transducer 178 of the resonating mass- variation measuring device 175, providing complementary index to the estimation of the disinfectant penetration in the biofilm.
Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many logical and/or physical modifications and alterations. More specifically, although the present invention has been described with a certain degree of particularity with reference to preferred embodiments thereof, it should be understood that various omissions, substitutions and changes in the form and details as well as other embodiments are possible. In particular, different embodiments of the invention may even be practiced without the specific details set forth in the preceding description for providing a more thorough understanding thereof; on the contrary, well-known features may have been omitted or simplified in order not to encumber the description with unnecessary details. Moreover, it is expressly intended that specific elements and/or method steps described in connection with any disclosed embodiment of the invention may be incorporated in other embodiments.
Figure imgf000026_0001

Claims

1. A method for estimating a presence and/or a formation and/or a crumbling of a first biofilm (125) on at least one wall (115) of a household appliance region (110) configured to be at least temporally in contact with a liquid, the method comprising:
- providing a test receptacle (155) in fluid communication with said household appliance region and providing in the volume of said test receptacle a resonating mass-variation measuring device (175) comprising a piezoelectric transducer (178) configured to oscillate, said resonating massvariation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of properties of a second biofilm (180) forming in said test receptacle, and
- estimating said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
2. The method of claim 1, wherein the volume of said test receptacle (155) is lower than 1 ml.
3. The method of any of the preceding claims, wherein the volume of said test receptacle (155) is lower than 100 pl, preferably about 50 pl.
4. The method of any of the preceding claims, wherein a ratio between:
- an active surface (179) of said piezoelectric transducer (178) in contact with said liquid, and
- a total surface inside the test receptacle (155) in contact with said liquid, is equal to a value comprised between 30% and 50%.
25
5. The method of claim 4, wherein a ratio between:
- the total surface inside the test receptacle (155) in contact with said liquid, and
- a volume of the test receptacle, is equal to a value comprised between 7 and 10 mm 1.
6. The method of any of the preceding claims, wherein said resonating massvariation measuring device (175) comprises a quartz crystal microbalance device.
7. The method of any of the preceding claims, wherein said estimating said presence and/or formation and/or crumbling of said first biofilm (125) comprises assessing, based on said measured variations of the piezoelectric transducer (178) oscillation frequency, a first mass corresponding to a mass of a microorganism aggregation of said first biofilm plus a mass of microorganisms detached from and resting on said microorganism aggregation.
8. The method of claim 7, wherein said estimating said presence and/or formation and/or crumbling of said first biofilm (125) further comprises assessing a viscoelasticity of said microorganism aggregation of said first biofilm based on said measured piezoelectric transducer (178) oscillation dissipation.
9. The method of any of the preceding claims, further comprising:
- injecting a disinfectant into said household appliance region (110), said disinfectant being configured to interact with said first biofilm (125) for removing said first biofilm;
- monitoring the interaction of the injected disinfectant with said first biofilm for determining a sanitizing degree of said household appliance region, said monitoring the interaction comprising:
- monitoring said interaction of the injected disinfectant with said first biofilm based on said measured variations of the piezoelectric transducer (178) oscillation frequency and of the piezoelectric transducer oscillation dissipation.
10. The method of claim 9 when depending on claim 8, wherein said monitoring said interaction of the injected disinfectant with said first biofilm (125) comprises monitoring said interaction of the injected disinfectant with said first biofilm based on said assessed first mass and said assessed viscoelasticity.
11. The method of any of the preceding claims, further comprising causing a quasi-static liquid exchange between said household appliance region (110) and said test receptacle (155).
12. The method of any of the preceding claims, wherein said liquid is water.
13. The method of any of the preceding claims, wherein said household appliance region (110) comprises one of:
- a condensation water container of a refrigerator appliance;
- a condensation water container of a heat pump dryer appliance;
- a condensation water container of a heat pump washer-dryer appliance;
- a condensation water container of an air conditioner appliance;
- a condensation water container of an air dehumidifier appliance;
- a condensation water container of a heat pump appliance;
- a process liquid container of a dishwasher appliance;
- a process liquid container of a clothes washer appliance;
- a process liquid container of a clothes iron appliance;
- a water container of a beverage dispensing machine.
14. A household appliance (100), comprising:
- a household appliance region (110), said household appliance region having at least one wall (115) configured to be at least temporally in contact with a liquid;
- a system (150) for estimating a presence and/or a formation and/or a crumbling of a first biofilm (125) on said at least one wall, the system comprising:
- a test receptacle (155) in fluid communication with said household appliance region;
- a resonating mass-variation measuring device (175) in the volume of said test receptacle, said resonating mass- variation measuring device comprising a piezoelectric transducer (178) configured to oscillate, said resonating mass- variation measuring device being configured to measure variations of a piezoelectric transducer oscillation frequency and of a piezoelectric transducer oscillation dissipation caused by variations of properties of a second biofilm (180) forming in said test receptacle;
- a processing unit (185) configured to estimate said presence and/or formation and/or crumbling of said first biofilm based on said measured variations of the piezoelectric transducer oscillation frequency and of the piezoelectric transducer oscillation dissipation.
15. The household appliance (100) of claim 13, wherein the volume of said test receptacle (155) is lower than 1 ml.
16. The household appliance (100) of claim 13 or claim 14, wherein the volume of said test receptacle (155) is lower than 100 pl, preferably about 50 pl.
17. The household appliance (100) of any of claims 14 to 16, wherein a ratio between:
- an active surface (179) of said piezoelectric transducer (178) in contact with said liquid, and
- a total surface inside the test receptacle (178) in contact with said liquid, is equal to a value comprised between 30% and 50%.
28
18. The household appliance (100) of claim 17, wherein a ratio between:
- the total surface inside the test receptacle (155) in contact with said liquid, and
- a volume of the test receptacle, is equal to a value comprised between 7 and 10 mm 1.
19. The household appliance (100) of any of claims 14 to 18, wherein said resonating mass- variation measuring device (175) comprises a quartz crystal microbalance device.
20. The household appliance (100) of any of claims 14 to 19, wherein said processing unit (185) is configured to estimate said presence and/or formation and/or crumbling of said first biofilm (125) by assessing, based on said measured variations of the piezoelectric transducer (178) oscillation frequency, a first mass corresponding to a mass of a microorganism aggregation of said first biofilm plus a mass of microorganisms detached from and resting on said microorganism aggregation.
21. The household appliance (100) of claim 20, wherein said processing unit (185) is configured to estimate said presence and/or formation and/or crumbling of said first biofilm (125) by further assessing a viscoelasticity of said microorganism aggregation of said first biofilm based on said measured piezoelectric transducer (178) oscillation dissipation.
22. The household appliance (100) of any of claims 14 to 21, further comprising a disinfectant injector device (190) configured to inject a disinfectant into said household appliance region (110), said disinfectant being configured to interact with said first biofilm (125) for removing said first biofilm, said processing unit (185) is further configured to monitor the interaction of the injected disinfectant with said
29 first biofilm for determining a sanitizing degree of said household appliance region based on said measured variations of the piezoelectric transducer (178) oscillation frequency and of the piezoelectric transducer oscillation dissipation.
23. The household appliance (100) of claim 22 when depending on claim 21, wherein said processing unit (185) is further configured to monitor the interaction of the injected disinfectant with said first biofilm (125) based on said assessed first mass and said assessed viscoelasticity.
24. The household appliance (100) of any of claims 14 to 23, further comprising a pump device (170) configured to cause a quasi-static liquid exchange between said household appliance region (110) and said test receptacle (155).
25. The household appliance (100) of claim 24, wherein said pump device (170) comprises a peristaltic pump.
26. The household appliance (100) of any of claims 14 to 25, wherein said liquid is water.
27. The household appliance (100) of any of claims 14 to 26, wherein said household appliance region (110) comprises one of:
- a condensation water container of a refrigerator appliance;
- a condensation water container of a heat pump dryer appliance;
- a condensation water container of a heat pump washer-dryer appliance;
- a condensation water container of an air conditioner appliance;
- a condensation water container of an air dehumidifier appliance;
- a condensation water container of a heat pump appliance;
- a process liquid container of a dishwasher appliance;
- a process liquid container of a clothes washer appliance;
30 - a process liquid container of a clothes iron appliance;
- a water container of a beverage dispensing machine.
31
PCT/EP2021/052978 2021-02-08 2021-02-08 Method and system for monitoring biofilms in household appliances WO2022167100A1 (en)

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Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
GABRIEL OHLSSON ET AL: "A miniaturized flow reaction chamber for use in combination with QCM-D sensing", MICROFLUIDICS AND NANOFLUIDICS, SPRINGER, BERLIN, DE, vol. 9, no. 4-5, 6 March 2010 (2010-03-06), pages 705 - 716, XP019811160, ISSN: 1613-4990 *
REIPA V ET AL: "Long-term monitoring of biofilm growth and disinfection using a quartz crystal microbalance and reflectance measurements", JOURNAL OF MICROBIOLOGICAL METHODS, ELSEVIER, AMSTERDAM, NL, vol. 66, no. 3, 1 September 2006 (2006-09-01), pages 449 - 459, XP027926922, ISSN: 0167-7012, [retrieved on 20060901] *

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