UV TREATMENT

Context

For many years, protecting our water has been a necessity..

Water is exposed to various sources of pollution which are difficult to control and therefore it becomes essential to improve the quality of consumed and discharged water

The presence of pathogenic microorganisms presents a significant health risk for consumers. Thus agriculture, animal breeding and other industries also need solutions to improve the quality of their water.

History

The process of water sterilisation by means of UV first appeared in 1910, but it wasn’t until the 1970’s that it really developed. This physical treatment does not modify the organoleptic properties of water.

The basic principle, known since the start of the twentieth century, today benefits from new materials (lamps with high germicidal effect, irradiation chambers with high reflection coefficient) and from total control of the parameters surrounding the operation (environment, flow rate, application). As a finger has often been pointed at water quality during recent years, the principle of disinfection by means of UV has greatly advanced.

How its works

Ultra-violet radiation consists of electromagnetic waves, the spectrum of which can be divided into three distinct bands. The rays have a photochemical effect on the body. This effect manifests itself through different reactions.

  • UUVA: from 315 to 400 nm – pigmentation of the skin
  • UVB: from 280 to 315 nm – production of vitamin D
  • UVC: from 180 to 280 nm – destruction of microorganisms

Ultraviolet rays with a wavelength of exactly 253.7 nanometres instantly inactivate microorganisms by causing photochemical reactions in their DNA. An abnormal liaison is created in the DNA chain and the microorganism thus loses its capacity to reproduce. Cell division stops and the microorganism becomes inoffensive.

The minimum UVC energy intensity (or dose) recommended by the French Ministry of Health, following its recommendation of October 18th 2012, is 40mJ/cm2 for water destined for consumption.
UVGERMI already applies this dose to all its equipment.

Our technology

The UVC–rays are produced by mercury vapour lamps, which could be either of the low pressure or medium pressure type.

As the maximum sensitivity to UVC radiation of microorganisms is situated at a wavelength of 260 nm, we have chosen to work with low pressure lamps emitting at a monochromatic wavelength of 253.7 nm (usually, though not quite accurately, referred to as 254 nm). Because this wavelength is closest to 260 nm, it is most effective in the destruction of microorganisms.

Because low pressure technology has many advantages, UVGERMI has decided to focus mainly on this activity. But we are flexible and can respond equally well to clients requiring medium pressure technology.

The UV treatment device consists of one or more lamps placed in quartz sleeves so they are thermally and electrically insulated from the water.

These lamps can be assembled in a cylindrical tube (closed reactor) or in canalisation (open reactor). In both cases, the water circulates around the lamps in thin layers so the UV radiation is rapidly absorbed by the components dissolved in water.

The energy needed for disinfection varies with regard to:

• The absorption of the radiation by the water to be treated (turbidity, presence of metals, organic materials, etc.)

• The germicidal effectiveness targeted

The germicidal effectiveness itself varies between 90 and 99.99%, depending on the duration of the exposure of the water to the radiation. It depends on various factors: the quality of the water, the flow rate, the UVC dose delivered (UVC intensity of the lamp multiplied by the duration of the contact around the lamp).

The UV treatment advantages

>> No modification to the chemical composition of the water
>> No modification to organoleptic qualities
>> No addition of chemical products
>> No formation of toxic by-products
>> Safe to use, no handling of dangerous products
>> No dosage problems

>> Very short contact time (a few seconds)
>> Modest costs: the only operating costs are the changing of lamps and electricity consumption.
>> Maintenance reduced to lamp replacement and cleaning of quartz sleeves
>> Not dependent on PH
>> PNo corrosion linked to reagent overdosing
>> No risk of secondary reactions
>> More effective than chlorine on some viruses and protozoa