Feb 2 2021
While ultraviolet light and chlorine are the routine ways of disinfecting water, ozone is just as effective in destroying microorganisms.
The electrodes for the ozone generator are made of silicon wafers with precisely etched trenches. Image Credit: © Fraunhofer ISIT.
So far, scientists have only used ozone as an oxidation agent for treating water in large-scale plants. But now a project consortium from Schleswig-Holstein is designing a tiny ozone generator that can be used in smaller applications, like small domestic appliances or water dispensers.
The electrode substrates and the sensor chip for the electrolysis cell were provided by the Fraunhofer Institute for Silicon Technology ISIT.
When compared to traditional methods of disinfection, like ultraviolet or chlorine, ozone dissolved in water offers several benefits: for example, it is eco-friendly, has just a short retention time in water, continues to remain active further than its immediate place of origin, and is subsequently tasteless.
Ozone is highly effective at fighting germs because of its high oxidation potential. It decomposes the cell membrane of typical germs. In Germany, ozone is mainly utilized to disinfect drinking water and swimming pools and also to disinfect wastewater.
But despite this fact, ozone is seldom used to purify water in domestic appliances, including beverage dispensers or ice machines, or in other fixtures, like shower-toilets.
MIKROOZON is a new project financially supported by the State of Schleswig-Holstein and the EU and is now aiming to change this situation.
Scientists from Fraunhofer ISIT have now collaborated with the Itzehoe-based firm CONDIAS GmbH, which was established back in 2001 as a spin-off from the Fraunhofer Institute for Surface Engineering and Thin Films IST, and CONDIAS associate, Go Systemelektronik GmbH, from Kiel. All three associates are designing a tiny ozone generator with the built-in microprocessor control system and sensor technology.
Direct Production of Ozone via Water Electrolysis
The ozone generator is very compact and can be integrated in systems and appliances that require regular disinfection. You simply connect it up to the water line, and it will produce the right amount of ozonized water whenever required.
Norman Laske, Researcher, Fraunhofer ISIT
The miniaturized ozone generator measures just 2 cm3 in size and features a sensor chip, an electrolysis cell, electronics to read the sensor signals and control electronics to regulate voltage and current.
The two electrodes are separated by an ion-conducting separator membrane. When a voltage is applied across the electrodes, the water is split by a process of electrolysis. Because of the diamond layer coating the electrodes, this process first forms hydroxyl radicals, which then react to form primarily ozone (O3) as well as oxygen (O2).
Norman Laske, Researcher, Fraunhofer ISIT
Diamond-Coated Silicon Electrodes
CONDIAS GmbH received its name by its know-how on the manufacturing process of the electrodes with their boron-doped diamond layer. A chemical vapor deposition process is already being used by CONDIAS GmbH to coat large-scale electrodes needed to sterilize the ballast water of marine vessels. But the electrodes needed for the MIKROOZON generator are relatively smaller.
They are composed of silicon and have delicately etched trenches running via the electrodes to create narrow slits on the opposite side. To etch these trenches with the needed accuracy, the Fraunhofer ISIT team needed to manufacture the wafer material according to their own specifications.
To construct a miniaturized ozone generator, pairs of these electrodes are placed in a back-to-back fashion, with a separator membrane positioned between them.
The gases are discharged at the interface to the separator membrane and subsequently allowed to escape via the trenched structure to the other part of the electrode, in which the turbulence of the water flow makes sure that the gases are efficiently dissolved and distributed.
The new sensor chip developed by the Fraunhofer ISIT team is integrated with three sensors to quantify temperature, mass flow, and conductivity. Such parameters should be tracked to regulate the electrolytic process. The solve sensor chip offers the information needed to regulate the production of ozone in line with the amount and the quality of water utilized.
In order to ensure that there is enough ozone available over the period required, the temperature has to be monitored. This is because ozone decomposes more quickly at higher temperatures.
Norman Laske, Researcher, Fraunhofer ISIT
Conductivity corresponds to the level of water hardness: harder water translates to higher conductivity, which means that additional current should flow to obtain the required effect.
When fitted with a system to track these parameters, the miniaturized ozone generator must be able to process up to 6 L of water every minute—but without the sensor chip, it is presently specified for 0.5 to 1.5 L.
CONDIAS GmbH is now marketing the new mini generator under the brand name of MIKROZON®.
According to Volker Hollinder, the CEO of CONDIAS GmbH, “Each partner has contributed years of experience from their own area of specialization. This has created a product that can now be manufactured on an industrial scale. The spread of the coronavirus has underlined the importance of disinfection. The use of chemical disinfectants is often problematic, because they leave harmful residues.”
“Our system uses electrolytically generated ozone to eliminate germs. It therefore does not produce any residues from disinfectants,” Hollinder concluded.