5Principle of microbial particle detection (sensor unit)Onboard potable water monitoring system incorporating a microbial particle counterPotable water is passed through a deep UV irradiation device and fed to a high-sensitivity microbial particle counter. The system configuration consists of a flow controller for adjusting the water flow rate and a PC for monitoring the measurement results.Kazuma SekimotoAdvanced Technology Development Section, Particle Counter Development Department, Particle Counter Division. Joined Rion in 2007 and has been involved with the research and development of microbial particle counters since the time of the former R&D Center. He is among the leading experts on counting technology using the autofluorescence emitted by microbial particles.The principle of microbial detection in microbial particle counters is based on the detection of autofluorescence emitted by metabolically active substances (riboflavin) contained in microbes. When violet laser light is irradi-ated onto a sample, the light scattered by the particles is received by a scattered light detection element and converted to an electrical signal. The size of the particles is calculated from the signal strength. The number of particles is calculated from how many times scattered light is detected. Of the particles detected, those for which autofluorescence is detected by the fluorescence detection element are identified as microbial particles.Expecting Rion and JAXA to maintain their relationshipinto the distant futuremercury lamp.Rion’s microbial particle counter uses a mercury lamp, which emits deep UV light and irradiates the sample to enable accu-rate quantification. This is a major feature of our counter. But the mercury lamp, essential to emitting high-output deep UV light, can’t be used on the space station for safety reasons. This is a problem that needs to be resolved in the future. “Various ideas have been presented that rely on different UV irradiation methods besides the mercury lamp—for example, LEDs,” says Minakami. “Unfortunately, none has yet achieved the same level of irradiance as what we’re currently using. But the development of detection devices has been driven by inno-vations in laser or other technologies. One day, as newer compo-nents become available to replace mercury lamps, I believe it will become possible to achieve this.”Measurements were carried out three times: in 2021, 2022, and 2023. The results of all three measurements pointed to the superiority of the microbial control method based on microbial particle counting technology. Continuously monitoring the number of microbes will allow detection of changes in real time, making it possible to issue early warnings of microbial outbreaks in potable water by analyzing the trends.“The fact that we were able to demonstrate that the microbial particle counting technology can be applied to assess potable water on the ISS is a significant achievement,” says Professor Yamazaki. “On the other hand, we’ve also found a problem we need to solve to achieve real-time monitoring in space.”“The quality of potable water is being inspected by someone somewhere, whether it’s water in a PET bottle or tap water. It’s the same in space as here on Earth. We can drink water with peace of mind because someone guarantees it’s safe.”What Rion plans to work on with JAXA going forward is research on a method of onboard monitoring of microbes to ensure the safety of water from dispensers used in future manned space activities. We’re hoping that microbial particle counting technology can be optimized for use in space and be applied as a new technology for potable water management that doesn’t rely on conventional culturing methods.“The concept of the microbial particle counter is to automate measurements of water,” explains Sekimoto, who developed the microbial particle counter, a core of this project. “But I think we can contribute to solving certain social issues. Some predict that issues involving water will become an even more pressing matter in the future and that the world will eventually be locked in a struggle over access to fresh water. While Japan is relatively blessed in terms of water, many countries aren’t so fortunate. That’s why methods like sewage reuse and seawater desali-nation are being considered. The complete reuse of water may eventually become a necessity. At the moment, water is not yet an urgent issue on Earth. But there’s already demand for water management in space. I think there’s definitely significance to being involved in research in this field from now on.”After ISS, next in line will be the Gateway lunar orbit station. After that, we’ll build a lunar base. In the not-so-distant future, humans will go on to build a base on Mars. Rion’s microbial particle counting technology might end up being essential there.Violet laser(405 nm)Scattered light detectorScattered lightFluorescenceFluorescence detectorMicrobial particlesNon-microbial particlesFlow cell
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