Which pathogens is the target for a recirculator? What is its efficiency against these pathogens?

Each microorganism requires a specific UV dose due to their individual sensitivity to UV radiation. For a different disinfection level (disinfection efficiency), different UV doses are required. To achieve the higher disinfection level you need to deliver a higher UV dose.

Microorganism Required UV dose (mJ/cm2) at disinfection efficiency level
90% 99,9%
Staphylococcus aureus 4,9 6,6
Escherichia coli 3,0 6,6
Pseudomonas aeruginosa 5,5 10,5
Salmonella sp. 2 – 8 6 – 15
Influenza virus 3,6 6,6
COVID-19 (SARS-CoV-2) 10 – 20*
Poliovirus 11 21
Rotavirus 13 24
Klebsiella pneuomoniae 12 17,5
Acinetobacter baumannii 3,3
Penicillum fungi (Penicillium sp.) 12 – 14 22 – 26

* according to the International Ultraviolet Association (IUVA) on 28-04-2020.

It follows from these data that the 99.9% effectiveness against Staphylococcus aureus (provided by a certain UV unit) may not be enough for other microorganisms:

Microorganism 99.9% efficiency
Staphylococcus aureus +
Escherichia coli +
Pseudomonas aeruginosa -
Salmonella sp. -
Influenza virus +
COVID-19 (SARS-CoV-2) -
Poliovirus -
Rotavirus -
Klebsiella pneuomoniae -
Acinetobacter baumannii -
Penicillum (Penicillum sp.) -

For this reason it is necessary to make sure that the given recirculator provides a high disinfection level against this specific pathogen.

Based on the above, the recirculator should provide a UV dose not less than 25-30 mJ/cm2 to be efficient against a wide range of pathogens.

Total bacterial count (TBC) – that indicates how many microorganisms are present in a certain volume – is easy to use for evaluation of recirculator performance.

It is the TBC indicator, along with other sanitary indicator microorganisms (Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella and Escherichia coli bacteria) that is used to analyze microbial contamination in medical facilities. And if your recirculator reduces TBC (by at least 99%), then it is effective. The only thing you need is to select the correct capacity

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Ultraviolet technology for water, air and surface disinfection is based on germicidal effect of UV-C radiation. 

UV radiation is electromagnetic radiation between x-rays and visible light. UV wavelengths range from 100 to 400 nanometer.

The UV wavelengths are divided in 4 groups, each with a different germicidal effect – UV-A (315–400 nm), UV-B (280–315 nm), UV-C (200–280 nm) and Vacuum UV (100–200 nm).

Ultraviolet in

Within the UV spectrum, UV-C range is considered the strongest UV radiation, which is easily absorbed by DNA, RNA and proteins. This range is often called germicidal due to its high disinfection efficiency against bacteria and viruses. The highest germicidal effect occurs at 205-280 nm and the maximum germicidal sensitivity of microorganisms at 265 nm. 

The germicidal effect is based on photon absorption by DNA and RNA molecules. Photochemical reaction provokes dimerization of DNA and RNA bonds, which inhibits the ability of microorganisms to replicate. This process is known as inactivation of microorganisms.

Mechanism of
UV disinfection

UV disinfection technology can be applied for potable water supply, wastewater treatment as well as for air and surface disinfection applications.

The major advantages of this technology:

  • high efficiency against a wide range of microorganisms including chlorine resistant ones (viruses and protozoa oocysts);
  • no impact on physical, chemical and organoleptic properties of water and air; no by-products; no dangerous overdosing;
  • low capital costs, power consumption and operational costs;
  • UV systems are compact and easy to operate; no need for special operational safety precautions.

Main industrial available sources of UV radiation are low pressure amalgam lamps and mercury medium pressure lamps. Medium pressure lamp technology have higher power per lamp (several kW) but significant lower efficiency (9-12%) in comparison to low pressure lamp technology with efficiencies between of 35-40% and power per lamp up to 1000 watt.

UV systems equipped with amalgam lamp technology generally have a little larger physical footprint but they are significantly more energy efficient.

The design of UV application depends on the required UV dose, flow rate and physical and chemical parameters of media to be disinfected. The facility design criteria, flexible, economical and sustainable operation are also the decisive design parameters.