A closer look at UV technology

The Evac Evolution BWMS automatically adjusts to different qualities of sea water, compensating where necessary for changes in the levels of sediment. The key factor that differentiates the system is the relationship between the UV Transmission (UVT) sensors and the UV Intensity (UVI) meters which create a ‘feedback’ loop ensuring that the correct UV dosage is applied.

  • Precise dosing for different sea water qualities
  • Optimised UV chamber design
  • Medium pressure lamps for greater effectiveness
  • The Evac Evolution is the only BWMS to have UV Transmission sensors as standard. With other systems they are charged as extras

UVI meters

UV intensity meters are mounted on the walls of the UV reactors and measure the intensity of UV light actually received during irradiation. This relationship creates a feed-back loop in which the calculated does is continuously compared with the actual dose. If the actual dose is within the prescribed range, ballast water treatment continues as normal. However, if the dose is less, the automation control unit indicates a cleaning cycle is required or that lamp renewal is necessary.
Maximum power is only used occasionally, when the conditions demand. The readings from the UV Transmission sensor are automatically recorded. This provides the owner with proof that the system is working according to specification.

Enhanced UV chamber design

The reactor has been designed to meet the level of irradiation required by the U.S. Coast Guard ‘live/dead’ standard, whilst other features extend the exposure time with the sea water. In addition to creating a helix flow as the water enters the chamber, its path is interrupted to cause a lateral movement. This brings organisms from the edge of the flow into closer contact with the light emitted from the UV lamps in a repeating cycle as the water passes along the chambers.

UVT sensors

UVT sensors measure the UV light transmittance through a sample of sea water before it reaches the UV reactors. This is measured at the same wavelength (UVC 254nm) as the biocidal light emitted by the UV lamps. From this data, the automation control unit calculates the correct UV dosage.

Medium pressure UV lamps for greater effectiveness

The Evac Evolution system uses medium pressure UV lamps because of their superior disinfection potential. The broader UV spectrum of these lamps allows for a more effective inactivation of organisms across a wide range of water qualities, particularly in the more demanding fresh water and brackish water conditions.

Medium pressure lamps have multiple peaks of UV-C, the biocidal spectrum which renders organisms and pathogens harmless.

Low pressure lamps have far fewer peaks and therefore the ballast water is not as thoroughly irradiated.

The quartz sleeves surrounding the UV lamps are doped during manufacture to filter out the lower wavelengths in the UV spectrum. This eliminates the production of ozone and other chemical pollutants in the treated water, ensuring the system is entirely chemical free.

The UV lamps can be easily removed from the quartz sleeves by releasing the snap-tight electrical connections and withdrawing them. Access is only required from one end of the chamber in order to do this. As the chambers are relatively short, the length of the lamps (1175mm) is equally compact and therefore less space is required in order to carry out maintenance.