How does UVC disinfection work? What are the key benefits of disinfecting air and surfaces with UV light, as opposed to chemical cleaning methods?
UVC disinfection technology works by damaging the DNA of microorganisms, so that they either die or lose their ability to replicate. UVC radiation can be delivered by mercury lamps, LED or also, now, UVC chips; the optimum frequency of radiation to ensure that the radiation is adequately absorbed by the DNA of the microorganisms is around 264nm. UVC can be used to disinfect surfaces and air: UVC air disinfection is quite safe for the people using it, because UVC systems are architectured in such a way that there is no direct exposure to UVC sources; but when you use UVC to disinfect surfaces, you have to be aware that the effects of direct radiation on the skin and eyes can be damaging.
Because UVC disinfection is entirely physical, the development of resistance of microorganisms in human habitats is unlikely. In fact, there is no potential for microorganisms to develop resistance to it in the same way that they do to chemicals: over time, microorganisms can build a resistance to chemical disinfectants, because they are able to change rapidly to adapt to their surroundings. The example that I typically use when explaining the difference between UVC and chemical disinfection to students is that UVC radiation is similar to ‘burning’: regardless of a microorganism’s DNA makeup, if you burn it, it will die. With chemicals, because microorganisms can make those little changes, they can become less susceptible to the disinfectant over time; and then the microorganisms which are least affected by chemicals will thrive and build an increased level of resistance.
Chemical disinfectants are more complex to regulate, in part due to the multitude of ways chemical products can interact with each other. UVC is more direct and does not lead to these types of problems. In addition to this, UVC is definitely a greener approach in comparison to chemical disinfection, particularly when LEDs are used – traditional UVC lamps do still contain mercury, which is not particularly environment-friendly – but it is only a matter of time before those mercury lamps are entirely replaced by LEDs. Because of the pandemic, there are several devices already on the market which make use of UVC LEDs: there are still some barriers in place, such as high prices and the relatively low output power of these energy sources, but as these devices become more common they will increase in power and decrease in cost.
Are there any significant limitations or challenges associated with UVC disinfection?
There is no single perfect method for disinfection. It is always important to establish the correct context in which any technology should be used. For example, when UVC is used to disinfect surfaces, any areas which are in shadow will not be disinfected by the radiation; so it is necessary to place the sources of radiation in several locations in order to be sure to reach all the surfaces in the area. Another aspect which has to be carefully estimated is the fluid dynamic of the UV reactors, because that fluid dynamic is a key influence on the exposure of the air which passes through the reactor: it is important to make the right calculations to ensure that the appropriate dose is delivered through the reactor into the air, otherwise the desired effect will not take place.
