Before the technical description of UV reactors for UV disinfection, we will briefly explain the physical relations of UV disinfection:
During an extensive R&D project of the German government a great number of germs (bacteria, virus, yeast, etc.) and their deactivation by UV light of the wave length 254 nm (main emission of a mercury low pressure lamp) was investigated. They focused on the incident UV dose dependent on the deactivation rate. This work lead to the fixing of the dose of UV at 400 J/m² for drinking water disinfection, because this dose showed a reliable reduction of germs for at least more than 99,99% of the relevant types of bacteria.
UV reactors have to be able to penetrate water with a given minimum dose.
The absorption of UV light in water, the geometrical construction of the irradiation chamber, the residence time in the irradiated area and the residence time distribution of the water are important parameters.
The law of Lambert-Beer describes the reduction of intensity of the UV light passing through the irradiated zone:
I0 is the initial intensity [in W] and I is the intensity at the location x.
SAC (Spectral Absorption Coefficient ) is an optical property of the liquid with the dimension [1/length]. For x1 this means:
The irradiance (Dosis) is a physical function of the intensity (Intensität), the residence time (Zeit) and the irradiated area (Fläche):
Relation of SAC and transmission at different path length for UV-light for sterilization (wavelength 254 nm).
|SAC in 1/m||T (1cm) in %||T (5cm) in %||T (10cm) in %|
The layout of UV reactors is the foundation of the design. The residence time in a conventional UV reactor is a very complex figure. This is why an exact calculation of the dose is not possible for conventional UV reactors. Therefore, enviolet only uses UV reactors with a rotational flow. A central quartz tube separates lamp and water, and in the ring space around this tube (and the horizontal axis) rotates the liquid (see Fig. below).
Exact calculations can be based on this design.
Visualization of the rotational flow typical for the UV disinfection reactors of enviolet. The narrow residence time behavior of the UV reactor leads to a well defined and calculable flow.
The advantages of the rotational flow are:
The integral monitoring of all UV lamps in one reactor leads to a reliable signal of the UV dose inside the enviolet MicroUV® reactor.