Basics
The UV technology is both the oldest and one of the very latest technologies used to disinfect fluids.The method is based on the natural disinfectant action of the sun’s rays. Low-pressure UV lamps imitate the disinfecting rays of the sun.

The reaction time between the UV irradiation and the organism to be killed is very short and does not create any by-products at all. The water quality, both physical and chemical, remains identical before and after treatment using the low-pressure UV technique. UV disinfection can therefore take place at any conceivable and necessary place in a system.

Due to the low operating costs, these installations are very efficient economically. Their compact structure allows the installations to be set up in the smallest spaces.

No chemicals need to be stored. The system operates without problems and is completely hazard-free. There are no undesirable by-products.

Before examining the technologies and methods used, we will first look at the underlying concepts.

Transmission
When light shines through water, the water stops part of the radiation. This also means that the disinfectant effect is reduced as the radiation lessens.

Transmission is the capacity of a substance to allow UV light (± 254 nm) to pass through it, as measured across 1 cm of liquid.

Here are transmission values for a few types of water (transmission through 1 cm):
   

Type	Transmissionvalue (%)
Spring water	96
Osmoses water	96
Mains water	90-96
Rain water	80-96
Ditch water	60-80
Waste water after biological	60
Horticultural water
Vegetables	15-30
Flowers	15-45
Ornamental plants	25-40
Chicory	20-55

  

Radiation doses
The radiation dose is a measure of the biological effect of the UV irradiation.

The effect depends on the organism needing to be killed.
The measurement is expressed in mJ/cm2 and/or J/m2.

The disinfectant capacity is dependent on:

• The capacity of the UV lamp
• The soiling of the quartz tube
• The transmission of the fluid
  * The thickness of the fluid layer
• The fluid flow rate
  

What UV dose is needed?

	mJ/cm²
Coliform bacteria, legionella, faecal bacteria, streptococci, nematodes (eelworms) and yeasts, etc.	3 tot 40
Pathogenic fungi, such as fusarium, pithium,Phytophtora, etc.	30 tot 120
Viruses such as cucumber virus, olpidium, cholera, etc.	60 tot 250

What is UV?
UV rays are energy-rich electromagnetic rays that occur in the natural spectrum of sunlight. They are in the invisible shortwave light band. UV rays are divided into the following categories :

The radiation range below 200 nm consists of ionising ozone-generating or hard rays.

 

Basic principle
The low intensity lamps used for UV disinfection have their maximum
capacity at 254 nm and therefore cover almost the entire absorption curve of DNA.

UV radiation gives rise to a photochemical reaction in the DNA, which leads to the information of dimers, prefarably at the level of the thymine bases. This prevents the naturation (= bonding) of the adenine bases and as a result,

further cell multiplication and metabolism is interrupted.

In this way micro-organisms are deactivated and rendered harmless.

No by-products are formed in this process which could give rise to a change in the water or have a negative impact on the taste of drinking water.