The term “bactericidal” includes, in addition to bacteria, the ability to destroy and inactivate viral pathogens, while “disinfection” is understood to include the process that destroys or inactivates 99.9% of harmful microorganisms.
UV radiation has been used successfully in the disinfection of water, air and surfaces for over 70 years (mainly the wavelength of 253.4 nm), and its effectiveness in deactivating bacterial and viral pathogens leaves no doubt. It has been scientifically proven that far ultraviolet UVC is the most effective bactericidal band of UV radiation.
The disinfection method of germicidal UV radiation, called GUV (Germicidal UV), is officially recommended by the World Health Organization (WHO) and the International Commission on Illumination ( CIE Position Statement on the use of Ultraviolet (UV) Radiation to Manage the Risk of COVID-19 Transmission of May 12, 2020 ).
UVC radiation causes an immediate photochemical reaction in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), modifying its molecular structure, which causes the formation of the so-called dimers and other pyrimidine photoproducts, which inhibit the process of genetic replication and transcription. As a result, pathogenic microorganisms lose their ability to reproduce.
Over the past 80 years, many studies have been carried out around the world on the effectiveness of photoinactivation – the destruction of bacteria, viruses, molds, fungi and other potentially harmful microorganisms with UV radiation.
The intensity of germicidal ultraviolet radiation (UVGI) is the energy of radiation reaching the surface from all front angles per unit area. In the SI system, it is expressed in watts per square centimeter [W/cm²], milliwatts per square centimeter [mW/cm²] and in microwatt per square centimeter [μW/cm²]. For the purposes of designing and working on GUV-related devices, most recently the unit “μW/cm²” is the most common.
The most effective wavelength range of UV radiation for disinfection is 250-280nm, with a peak of 264nm. Interestingly, some studies conducted on the HCoV-OC43 virus as a surrogate for the SARS-CoV-2 coronavirus, show 286 nm as the most effective UV wavelength recommended for combating this pathogen.
When conducting laboratory tests, for each tested pathogen, it is possible to determine the effective dose of energy (deactivating-destructive) of UVC radiation, expressed in the SI system in J/m² (in joules per square meter), i.e., W*s/m² (watt multiplied by second per meter square). The standard assumption is to determine the effective radiation dose (Eeff) for inactivation of 90% of pathogens (D90).
The amount of radiation dose required in practice may depend on the following factors:
- wavelength of the UVC light
- the angle of attack of the UVC rays
- concentration of pathogens in the tested sample
- the type of substrate, the environment in which the irradiated microorganisms arrive and the ambient temperature
- the size and characteristics of the micro-organism
- the type of genetic material making up the microorganism (ssRNA, ssDNA, dsRNA, dsDNA) and the properties of the genome
- ambient temperature and humidity