Ultraviolet sterilization is used to disinfect objects, surfaces, and air by breaking down the DNA and RNA of viruses and bacteria making them unable to reproduce. This is also known as UV germicidal irradiation.
It’s important to note that a UV sterilizer only affects microorganisms that are free-floating and won’t kill string algae or other organisms attached to rocks, substrate, or fish.
Biological Inactivation
UV radiation inactivates bacteria and viruses by damaging the DNA of the organism. DNA is responsible for the replication of cells, therefore damaging it renders the organism unable to reproduce and spread disease. When exposed to UV, DNA absorbs energy from incoming photons and forms pyrimidine dimers, which cause adjacent thymine and cytosine bases to bond with each other instead of across the normal double helix that contains the genetic information. The damage to DNA renders the organism unable to function and die, thus inactivating it.
UV sterilization has been shown to be effective in inactivating a wide range of microorganisms in both water (potable and wastewater) and air. The inactivation of these organisms is often measured using a dose-response model, which compares reductions in the concentration of bacterial or viral cells to the UV irradiation dosage.
A variety of methodologies can be used to evaluate inactivation, including plaque assays in bacterial cells, cytopathic effects in plants or embryo survival, and analysis of the integrity of viral nucleic acids. Regardless of the method used, it is important to verify that the results are comparable. This will enable laboratories to determine which inactivation methods are best suited for their specific research applications. For example, certain methods may only be suitable for evaluating the inactivation of a single virus isolate and may not be applicable to other isolates or to other applications.
Chemical Inactivation
UV rays penetrate the cells of disease-causing organisms, destroying their DNA. The damage to the DNA renders the organism unable to function or reproduce, which effectively stops it from spreading infection. This makes UV sterilization effective against a wide variety of microorganisms, including viruses.
However, the effectiveness of a UV sterilization process depends on the wavelength of the UV light emitted by the UV lamp used. UV-C, which has the shortest wavelength of the three UV rays, provides the greatest inactivation rate of bacteria and viruses.
Unlike chemical disinfectants, which can create toxic residues, UV treatment leaves no chemical byproducts or harmful materials behind. It also works quickly, and it is highly efficient against a range of organisms. This is why it is so popular in the field of water treatment, where it is used to sterilize potable and wastewater.
The way that UV sterilization works is very simple, as illustrated in the diagram below. The ultraviolet radiation emitted by the UV lamp pierces the cell of a microorganism, creating pyrimidine dimers in the DNA molecule. The pyrimidine dimers prevent two adjacent thymine or cytosine bases from bonding with each other across the DNA double-helix, as they would otherwise. When the DNA is damaged like this, the organism cannot replicate or spread disease. This is why UV sterilization is so effective at killing microorganisms.
Physical Inactivation
UV radiation disrupts the DNA of germs, preventing them from reproducing and causing disease. This process is highly effective in eradicating all bacteria, yeasts, molds and viruses. UV sterilization also eliminates many types of airborne pathogens, including dust mites and spores.
The disinfection effect of UV radiation depends on the irradiance and water quality parameters, with exposure times reported in terms of microwattsseconds per square centimeter (uWattsec/cm2). Most UV sterilization systems provide UV irradiance in the range of 30,000-50,000 uWatt*sec/cm2, which effectively inactivates a large variety of organisms and prevents the growth of fungus and mildew.
Unlike chemical disinfectants, UV treatment does not create harmful byproducts or leave any residue. It is also quick and easy to manage. Since the process is non-intrusive, it can be applied to surfaces that would not normally receive sterilization treatments.
UV sterilization is an excellent choice for any setting where microbial free, safe and pure water is required, especially in situations where there is a risk of contamination before the water reaches its final point of use. For example, UV sterilization can be used to disinfect the coils and drain pans of forced air cooling systems. UV sterilization is also a viable solution for reducing the spread of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus (VRE), common gram-positive bacteria that are resistant to many antibiotics.
Redundancy
UV radiation works to inactivate microorganisms by damaging the DNA that carries genetic information. This causes two adjacent thymine or cytosine bases to bond together instead of crossing over as they normally would, rendering the organism unable to replicate and thus unable to spread disease.
Waterborne pathogens have varying sensitivities to UV treatment, with bacteria and protozoa being more sensitive than viruses. Particulates and turbidity in the water can also shield microorganisms from UV, reducing disinfection effectiveness.
While the effectiveness of UV light in destroying microorganisms is proven, the actual performance of a germicidal UV sterilization system depends on the intensity and duration of the irradiation. Irradiation times and lamp intensity (measured as fluence rate) must be matched to the particular microorganisms being disinfected.
The ability of UVGI to inactivate viruses has led to a burgeoning market for airborne sanitizing devices that use far-UVC to destroy SARS-CoV-2 droplets as they leave symptomatic or asymptomatic carriers. These are marketed as an additional step to proven preventative controls like mask-wearing and social distancing. Laboratory technicians also rely on UVGI to disinfect equipment and surfaces in biological safety cabinets between uses. Finally, juice makers in the United States have recently begun using UVGI to sterilize their freshly pressed fruit and vegetable juices.