ISH 2021

•••4••• Innovationen Water disinfection with ozone New hygiene system avoids residues from disinfectants W hile chlorine and ultra- violet light are the stand- ard means of disinfecting water, ozone is equally effective in killing germs. To date, ozone has only been used as an oxidation agent for treating water in large plants. Now, however, a project consor- tium from Schleswig-Holstein is developing a miniaturized ozone generator for use in smaller ap- plications such as water dispens- ers or small domestic appliances. The Fraunhofer Institute for Sili- con Technology ISIT has provided the sensor chip and electrode sub- strates for the electrolysis cell. Compared to conventional means of disinfection such as chlorine or ultraviolet, ozone dissolved in wa- ter has a number of advantages: it is environmentally friendly, re- mains active beyond its immedi- ate place of origin, has only a short retention time in water and is sub- sequently tasteless. Due to its high oxidation potential, ozone is very effective at combating germs. It breaks down the cell membrane of common pathogens. In Germa- ny, ozone is chiefly used to disin- fect swimming pools and drinking water and to purify wastewater. Yet it is rarely used to disinfect water in domestic appliances such as ice machines and beverage dis- pensers or in other fixtures such as shower-toilets. MIKROOZON, a project funded by the State of Schleswig-Holstein and the EU, aims to change this. Researchers from Fraunhofer ISIT have teamed up with the Itzehoe-based com- pany CONDIAS GmbH, which was founded in 2001 as a spin-off from the Fraunhofer Institute for Sur- face Engineering and Thin Films IST, and CONDIAS partner Go Sys- temelektronik GmbH, from Kiel. The three partners are developing a miniaturized ozone generator with integrated sensor technol- ogy and microprocessor control system. Direct production of ozone via water electrolysis “The ozone generator is very com- pact and can be integrated in sys- tems and appliances that require regular disinfection,” says Norman Laske, researcher at Fraunhofer ISIT. “You simply connect it up to the water line, and it will produce the right amount of ozonized water whenever required.” The ozone generator is only a couple of cubic centimeters in size and comprises an electrolysis cell, a sensor chip, control electronics to regulate current and voltage, and electronics to read the sensor signals. “The two electrodes are separated by an ion-conducting separator membrane,” Laske ex- plains. “When a voltage is applied across the electrodes, the water is split by a process of electroly- sis. Because of the diamond layer coating the electrodes, this pro- cess first forms hydroxyl radicals, which then react to form primar- ily ozone (O3) as well as oxygen (O2).” Diamond-coated silicon elec- trodes How the electrodes with their boron-doped diamond layer are made is the know-how that has given CONDIAS GmbH its name. The company already uses a chemical vapor deposition pro- cess to coat large-scale electrodes required to disinfect the ballast water of marine vessels. Howev- er, the electrodes required for the MIKROOZON generator are much smaller. They are made of silicon and have finely etched trenches that run through the electrodes to form narrow slits on the re- verse side. In order to be able to etch these trenches with the re- quired precision, the researchers from Fraunhofer ISIT had to have wafer material manufactured to their own specifications. To build an ozone generator, pairs of these electrodes are mounted back to back, with a separator membrane between them. The gases are released at the inter- face to the separator membrane and then escape through the trenched structure to the other side of the electrode, where the turbulence of the water flow en- sures that they are efficiently dis- solved and dispersed. The sensor chip from Fraunhofer ISIT is equipped with three sensors to measure conductivity, mass flow and temperature. These pa- rameters need to be monitored in order to control the electrolytic process. The sensor chip provides the data that is required to con- trol ozone production in line with the quality and the amount of wa- ter used. “In order to ensure that there is enough ozone available over the period required, the tem- perature has to be monitored,” Laske explains. “This is because ozone decomposes more quickly at higher temperatures.” Conduc- tivity correlates to the degree of water hardness: the harder the water, the higher the conductivity – meaning that more current must flow in order to achieve the de- sired effect. When equipped with a system to monitor these param- eters, the ozone generator should be capable of processing up to 6 liters of water per minute – with- out the sensor chip, it is currently specified for 0.5 to 1.5 liters. CONDIAS is marketing the mini- generator under the brand name of MIKROZON®. “Each partner has contributed years of experi- ence from their own area of spe- cialization,” says Volker Hollinder, CEO of CONDIAS GmbH. “This has created a product that can now be manufactured on an industrial scale. The spread of the coronavi- rus has underlined the importance of disinfection. The use of chemi- cal disinfectants is often problem- atic, because they leave harmful residues. Our system uses electro- lytically generated ozone to elimi- nate germs. It therefore does not produce any residues from disin- fectants.” The electrodes for the ozone generator are made of si- licon wafers with precisely etched trenches. Foto: Fraunhofer ISIT BDH legt Positionspapier zur Diskussion vor Nachbesserungsbedarf im aktuellen Gesetzesentwurf des SteuVerG Der Bundesverband der Deut- schen Heizungsindustrie (BDH) nimmt in seinem neuen Positi- onspapier Stellung zur Einbin- dung von flexiblen Lasten wie Wärmepumpen und Elektroau- tos in das Stromnetz. „Die Erwei- terung der regulatorischen Rah- menbedingungen zur Nutzung der Flexibilität von steuerbaren Verbrauchern ist zwingend erfor- derlich, um den Hochlauf der Elektromobilität zu ermögli- chen“ erklärt Andreas Lücke, Hauptgeschäftsführer des BDH. Die gesetzlichen Änderungen müssten jedoch so gestaltet wer- den, dass sie auf die Akzeptanz der Investoren stoßen. Hier sieht der Verband Nachbesserungsbe- darf im aktuellen Gesetzesent- wu r f de s St eue r ba r e - Ve r- brauchseinrichtungen-Gesetz (SteuVerG). Die Wärmepumpe wird hier in der Regelbarkeit mit der Ladestation für Elektroautos im Wesentlichen gleichgesetzt. Eine Wärmepumpe kann jedoch beispielsweise nicht beliebig oft über den Tag ein- und ausge- schaltet oder gar stufenlos gere- gelt werden. Lastverschiebung: Zentrales Ins- trument für die Elektrifizierung von Wärmeerzeugung und Ver- kehr Das Verschieben von Lasten ist ein zentrales Element im zu- künftigen Energiesystem: bei gleichbleibendem Komfort für den Kunden soll ein flexibler Verbraucher Energie möglichst dann verbrauchen, wenn erneu- erbarer Strom zur Verfügung steht und auch durch das Strom- netz transportiert werden kann. Die beiden wichtigsten Flexibili- tätsquellen auf der Verbrauchs- seite sind dabei Wärmepumpen und Elektroautos. Für beide muss die Nutzung ihrer Flexibi- lität so gestaltet werden, dass beim Endkunden Komfort, Wirt- schaftlichkeit und Versorgungs- sicherheit erhalten bleiben. „Dies ist erforderlich, um die gegenwärtig hohen Wachstums- raten der Wärmepumpe nicht zu gefährden und damit letztlich die Wärmewende voranzutrei- ben“ führt Dieter Kehren, Leiter der Fachabteilung Energiema- nagementsysteme im BDH aus. „Hierzu müssen bei der Gestal- tung der Rahmenbedingungen auch die technologiespezifi- schen Eigenschaften der Wärme- pumpe Berücksichtigung finden. Solche Punkte können nur im Di- alog mit der Heizungsindustrie identifiziert und behandelt wer- den“. Der BDH und seine Mit- gliedsunternehmen stehen für diesen Dialog zur Verfügung.