Ultra Violet Disinfection

Ultra Violet Disinfection compliments our established range of products and services. This publication gives background and technical information to assist with understanding the UV concept and knowledge of the range that is offered.

What is Ultra Violet Disinfection?

There are four types of UV light within the electromagnetic spectrum and they all lie between X-Rays and visible light. The regions of energy that have a germicidal effect are known as UV-B and UV-C.
Increasing wavelength, decreasing frequency  →

Cosmic Rays

Gamma Rays


Ultra Violet

Visible Light

Infra Red

Radio Waves


Figure 1; The Electromagnetic Spectrum

Short-wave UV-C, where the main germicidal effects occur, lies between 200 and 280 nanometres (nm), nanometres being a measure of wavelength. Naturally occurring UV-C is rarely found at the earth’s surface because short-wave UV is screened out by the earth’s atmosphere.

The middle-wave UV-B, existing from 280 to 315nm, provides some germicidal effect if exposure is sufficient. To take advantage of UV’s germicidal potential however, a means of producing UV-C light must be used.
UV energy is typically produced by using electrical current to stimulate a mercury vapour in a fluorescent-like lamp. The most commonly used lamp is a low pressure mercury vapour lamp with an energy output of 253.7nm, close to the 265nm most effective at killing microbes.
Germicidal UV lamps are made with hard glass quartz, whereas standard fluorescent lamps are made from soft glass. Quartz transmits 92% of UV energy, far more than alternative materials.

How Effective is UV Disinfection?


Differing types of micro-organism can be more or less sensitive to UV light. This may be because of their cell wall structure, the presence of UV absorbing proteins or the structure of their nucleic acids.
The degree of destruction of microbes is a product of UV intensity multiplied by contact time. Intensity is the amount of UV energy per unit area measured in milliwatts per square centimetre (milliW/cm2). The contact time is the amount of time the solution is exposed to UV in the reactor, measured in seconds. The UV dose is expressed in millijoules per square centimetre (mJ/cm2).
The PWEL UV lamps kill at least 99.9% of the water borne contamination at the specified flow and transmission rates.



UV is a proven method of controlling microbiological contamination. Some of the features offered by UV as a process are;

  • Microbiological control can be achieved where chemicals cannot be used.
  • Very effective against planktonic bacteria
  • No residual left in the water
  • Non-corrosive
  • Low operating cost
  • Instantaneous in line treatment
  • Does not affect pH, odour or taste

These make UV an ideal process for;

  • Potable water, particularly stored potable water
  • Point of use applications such as showers
  • Spray systems such as environmental chambers
  • Vending machine make-up
  • Water features
  • Air handling units incorporating spray humidifiers*

*L8 recommends a full water treatment programme including traditional biocides in addition to a full maintenance programme of monitoring along with regular disinfection and cleaning for this type of system.

Ultra Violet

Figure 2; Typical UV Lamp



How Does Ultra Violet Disinfection Work?


Contamination found in water can be caused by a wide variety of pathogenic micro-organisms. Most are made up of a cell wall, a cytoplasmic membrane and DNA-bearing nucleic acid. Microbes are destroyed when UV light penetrates both the cell wall and cytoplasmic membrane and is then absorbed by the nucleic acids. The UV energy rearranges DNA molecules and prevents the cell from reproducing. The cell is then considered dead for all practical purposes.

Figure 3; Microbial Cell Structure


PWEL offers UV treatment as a microbial control process for humidifiers and air washers where the use of chemical biocides and disinfectants is usually precluded. However, this should only be in conjunction with filtration prior to the UV unit as part of a comprehensive service package which would encompass monitoring (of total bacterial counts, Legionella, and general water quality) and regular cleaning and disinfection, the latter at a frequency determined by the operating conditions. PWEL can provide this complete service on request.
PWEL can also provide an on-going maintenance programme for regular lamp cleaning and replacement.
UV is no guarantee against Legionella contamination of a water system. For this reason, and those stated above, along with the fact that UV offers no residual or control of biofilms, PWEL does not offer UV as a stand alone treatment for cooling towers.



A range of filters is available for effective removal of suspended solids from water entering the UV unit.
Circulating pumps, pressure gauges and flow indicators can be supplied as part of a complete system.

Please click icon to download Ultra Violet Disinfection Datasheet
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