Summary of main findings

UV-C light destroys pathogens by inactivating its DNA. When the DNA absorbs a high photon energy, such as that of UV-C, its peptide and disulfide bonds break and become permanently damaged.[21] UV-C irradiation is effective in the reduction of different microorganisms including different hospital endemic strains particularly C. difficile, MRSA, and VRE,[14,16,17,20-24] as well as different fungi and virus such as Ebola virus, influenza, rhinovirus, enterovirus, and human metapneumovirus.[15,19] It is safe to consider that UV-C light disinfection is an effective germicidal agent against different microorganisms, reducing infection rates, and contamination. However, there are no studies in disinfection using UV-C against SARS-CoV-2 found in the literature. It is important to note that pathogen concentration does not significantly affect the efficacy of UV-C and different surfaces have similar reduction rates with the use of UV-C, except for steel.[31] In addition, there is reduction in efficacy when distance is increased between target surface and UV-C light device, when the surface is not in-line-of-sight of the UV-C light device and when there is the presence of organic matter. On the other hand, an increased efficacy is noted in the reduction of different microorganisms when the inoculum is spread out on a larger surface area.[31] These factors can be considered to create strategies to increase efficacy and efficiency of the UV-C disinfection process.

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The use of UV-C light as a disinfecting tool seems to be most effective as an adjunct to already existing terminal cleaning standard operating procedures. This disinfecting process even outperformed active hydrogen peroxide in the removal of MRSA, VRE, and C. difficile.[18] UV-C disinfection is especially useful as an adjunct in the disinfection process of surfaces with a high microbial burden where there is frequent occupant use. These places may be harder to clean manually as it takes a longer time and disinfection may be harder. In addition, UV-C as an adjunct has the upper hand compared to manual terminal cleaning as this is dependent on cleaner&#;s education and efficiency. Moreover, purely manual terminal cleaning presents a risk of contamination through cleaning materials used and potential transfer of micro-organisms. It also poses a risk for microbial resistance and increased labor.[20]

Some considerations that may arise with the use of UV-C as a disinfecting tool are its efficacy as a stand-alone procedure seeing as some studies have not seen significant results without the isolated use of UV-C in the reduction of infections.[14] This suggests that other factors are at play and that UV-C is most helpful as a supplement to the standard manual terminal cleaning practices. Other concerns include, largely, the lack of standardization in irradiation dose (irradiance and exposure time) and the distance between surfaces for different UV-C light devices such as automated UVGI and hand-held UV-C light devices.

The effects of the use of UV-C light devices beyond its proven germicidal function include a slew of damages such as erythema, tanning, missing desmosomes, and changes in the stratum corneum. Exceptional findings include DNA damage, formation of lacunae and cytoplasmic debris, thickening of the stratum corneum, increase in keratohyalin, and vacuole formation in stratum granulosum.[25-27] These effects depend on exposure time lengths, number of cycles, and irradiance intensity. Current guidelines for exposure to UV-C radiation should not exceed 30 J/m2 at 270 nm for the eyes and skin. At 254 nm, the maximum exposure limit is set at 60 J/m2.[28]

In general, conventional UV-C light devices used as a disinfecting tool utilize 254 nm UV-C. Findings show that this particular wavelength induces cellular damage in the DNA of microorganisms, effectively killing it and reducing surface and air bioburden. This occurs specifically by inducing CPD formation in cells. In humans, this wavelength induces the formation of mutagenic and cytotoxic damages to the DNA, possibly leading to photocarcinogenesis. DNA lesions may cause epidermal hyperplasia which is a strong correlator of UV-B effects rather than chronic irradiation, regardless of wavelength.[29,30] This suggests that conventional 254 nm UV-C light devices do not produce isolated UV-C light. In fact, <10% of light emitted by conventional germicidal lamps are not at the 254 nm wavelength.[29,30]

On the other hand, newer studies suggest that the 222 nm wavelength has the same bactericidal effects as the conventional 254 nm UV-C without the hazardous effects. The 222 nm irradiation causes apoptotic cell death that has a protective function against photocarcinogenesis. However, this mechanism is not yet well understood, and its chronic effects are not yet explored.[29,30] The safe use of the 222 nm UV-C in disinfection is largely because it cannot penetrate mammalian nuclei and does not even reach the stratum corneum because of its short wavelength.[30] Furthermore, the presence of melatonin seems to have a protective function against UV-C irradiation, whether that melatonin protects against UV-C or possibly UV-B emitted in germicidal lamps is something to be explored.[27]

This review was carried out to determine whether the use of UV-C light in the disinfecting processes is effective and whether it poses risks. UV-C light, indeed, is effective in the reduction of infections from both surfaces and the air. Single and chronic irradiation from these devices, however, pose a risk through photocarcinogenesis and other dermal damages.[32] To maximize the positive effects of UV-C germicidal light devices, current terminal end manual cleaning should be supplemented with a standard effective dose of UV-C. In addition, UV-C disinfecting processes should explore the use of isolated 222 nm UV-C to reduce safety issues.

In a hospital setting, UV-C can be employed to disinfect the air of bacterial particles with the use of the upper room UV-C lights. This strategy may be useful for reducing HAIs. However, studies pertaining to the efficacy of air decontamination decreasing HAIs outside laboratory testing are still to be explored.[18] Another strategy using UV-C is to install them in shared toilet rooms, especially in wards as toilet flushing may produce bioaerosols.[13] Furthermore, the use of UV-C in hospital rooms, particularly in operating rooms where there is a rapid bed turnover rate, may create an efficient disinfecting system, decreasing time, and labor needed to prepare rooms for the next patient especially in times of emergencies.[15] Along with reducing incidence of different pathogens on patient room surfaces, the use of UV-C also shows a sustained reduction of bioburden on surfaces even before cleaning[14] and a reduction in developing drug resistance.[16,17] These may explain the reduction of HAIs in rooms where previous occupants were infected with multi-drug resistant organisms.[24] These studies focus only on hospital room surfaces, toilets and the air and were not able to test the efficacy of UV-C on medical instruments and equipment that may also have a high bioburden. Its efficacy on different surfaces including medical instruments and equipment as well as possible damages to the integrity of materials is something to be explored.

In the context of the COVID-19 global pandemic, the use of UV-C disinfection for surfaces and air should be explored as only sterilization of personal protective equipment reuse has been studied.[33-35] However, it seems that UV-C has the potential to effectively inactivate SARS-CoV-2. Studies on UV-C inactivating SARS-CoV-1 present the possibility because of its close genomic identity with SARS-CoV-2.[36,37] Leveraging on this possibility, upper room UV-C light devices may be installed in COVID-19 isolation rooms to provide a no-touch disinfecting system and portable UV-C light devices may also be employed to disinfect isolation rooms after occupancy. Strategies like these may reduce time and labor in cleaning and disinfecting. Most importantly, it may reduce the risk of disease transmission from patient to health workers.

For the main interest of this review, several evidence of varying methodological quality across different outcomes was identified. Although a number of studies addressing the efficacy of UV-C irradiation in reducing hospital associated infection rates were included, the overall certainty of evidence collected was low, with the highest quality of evidence coming from a single RCT that studied the efficacy of mercury UV-C disinfection in reducing HAIs and colonization. The reasons for downgrading the certainty of the evidence were due to limitations in study design, imprecision due to wide confidence intervals, and high risk of bias among studies. In this review, there was considerable uncertainty as the majority of the included studies were before and after studies that had inconsistent effects on different hospital acquired infection rates. Limitations with this type of study include difficulty in controlling confounding variables that may influence both the pre- and post-intervention periods which could lead to an overestimation of the efficacy of UV-C irradiation. In addition, there was high risk of bias across studies, predominantly attributable to non-randomized methods of allocation. Insufficient randomization or allocation concealment put studies at risk of selection bias.[38] The unpredictability of conditions occurring in a live setting like a hospital is high, thus, it is important to blind the evaluating observers to treatment allocation and treatment supervision. Blinding is important in disqualifying confounders that may sweep in after the allocation has taken place; the lack thereof may result in an overestimation of the effects. It is also important to note that sample sizes of some of the included studies were generally small, which might compromise the value of the outcomes resulting in an underpowered study. Unlike the studies on the efficacy of UV-C irradiation, limited studies regarding its safety were included in this review. Similarly, overall certainty of the evidence collected was low due to limitations in study design.

How Does a UV Disinfection System Work?

With an all-time high demand for cost-efficient and sustainable solutions to provide clean water, UV disinfection systems have taken on an increasingly important role. It is especially the global sustainability focus that has made choosing the right solution for water disinfection challenges ever more important. The growing environmental awareness combined with stricter regulations for effluent discharge standards continues to fill the agenda in this regard.

Since UV technology was discovered well over 100 years ago, it has undergone huge technological improvements, which today has made it impossible to ignore when it comes to water treatment processes.

UV systems are a globally accepted solution for water disinfection due to being a chemical-free sustainable solution, combined with being able of inactivating bacteria, viruses, and protozoa, which makes the technology vital for the future of water disinfection.

Let&#;s take a deeper look at how UV systems work.

Watch the video below for a full overview of the UV system disinfection process &#; or continue reading below.

How a UV disinfection system disinfects water

Disinfecting water with UV systems is a very straightforward, yet extremely efficient method to ensure disinfected water.

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As seen on the image below, the water flows through the piping system and through the UV chamber. In this chamber, the water is exposed to ultraviolet light, that is emitted from the UV lamps. The UV light from the lamps has a specific wavelength in the UV-C spectrum (around 254nm), that enables microorganism inactivation if exposed with the right intensity.

In technical terms, when the water comes into contact with UV light, the chemical bonds are broken down, which changes the DNA structure. It is this change in the DNA structure that disables the pathogens&#; ability to perform vital cellular functions, including reproducing or causing infection.

As the video above shows, bacteria such as E. coli reproduce extremely rapidly. This is where the UV lamps come into action to damage the DNA or RNA of the microorganisms, which disrupts their ability to function and replicate.

Make sure that the right UV system is selected

Dependent on the efficiency of the lamps and the microorganism to be inactivated &#; the contaminated water that has gone into the system will come out disinfected. This is why it is essential to make sure that the right UV system is selected for the specific water to be treated. In other words &#; If the UV system is too small for the task, it will not be able to inactivate the microorganisms, as the rays emitted from the lamps will not be powerful enough. All factors for ensuring proper water treatment conditions for the specific challenge are naturally assessed and considered when a UV system from ULTRAAQUA is inquired.

As a notable advantage, the disinfected water coming out of the reactor will have no altering of taste, odor, or color of the water. This means that both the physical and chemical properties of the water remain identical both before and after the treatment.

While there are averages for the different water treatment applications such as drinking water facilities, it is always considered to be best practice to test and measure the water before selecting the UV system to make sure the targeted microorganisms are inactivated.

The benefits of using UV systems

Even though water can visually appear to be clean, there is no guarantee that it does not contain significant levels of harmful bacteria, viruses, and parasites. UV disinfection has a vital role in many water treatment processes worldwide to solve this biosecurity issue. While UV disinfection can not always stand alone in water treatment processes, there are several benefits of including the technology.

This includes benefits such as:

• A lower carbon footprint in comparison to alternative disinfection methods
• Low maintenance, administration, and OPEX costs
• No dangerous chemicals involved (storage, handling, and residuals)
• No by-products being created in the disinfection process
• No change in the water properties such as pH and temperature
• Instant treatment with no processing time
• Simple and safe implementation

It is especially a beneficial alternative to chlorine disinfection, which can potentially result in health complications such as respiratory diseases, as well as being incapable of inactivating Cryptosporidium and Giardia.

What components are a UV disinfection system made of?

Understanding the components included in a common UV disinfection system can be beneficial in regard to getting a full understanding of how UV systems work. Each of these parts has an important role to carry out in the disinfection process.

• UV lamps

The UV lamps are the heart of the UV system, which emits UV-C ultraviolet light to inactivate the microorganisms. With enough UV light exposure, microorganism inactivation will be achieved. Dependent on the water treatment challenge, either low-pressure or medium-pressure lamps can be used.

• Quartz Sleeves

The quartz sleeves allow the UV lamps to do their job by protecting the lamp from water. To prevent fouling over time, quartz sleeve wiping can be integrated to consistently keep the quartz sleeves clean, allowing the UV lamps to stay close to full performance.

• Reactor

The reactor is where the UV disinfection process takes place. As the water flows through the chamber, the UV lamps are doing their job to inactivate the microorganisms. Dependent on the water treatment challenge, the reactor material can consist of either stainless steel (SS), polypropylene (PP), or high-density polyethylene (PEHD).

• Ballast

The ballasts ensure that the system is provided with the accurate electrical input it needs to maintain a stable operation.

• Control Cabinet

The control cabinet is what controls the disinfection behind the scenes, by offering the operator control over the state of the system. Besides advanced functions, it is usually capable of sending out alerts if the lamps are not working correctly and providing info about the disinfection performance.

All these main components are a necessity for any operational UV disinfection system. The amount of them will however vary dependent on the disinfection challenge, where specific cases might require more lamps than others. For one closed vessel reactor, the UV systems from ULTRAAQUA can range from 1 lamp up to 56 UV lamps per unit.

If you are interested in learning more about our UV disinfection systems, you are always welcome to reach out to our sales engineers at  &#; or use the contact formula below.

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