Research trials demonstrate low doses of UV are effective and keep cost down

Recent research conducted by Nofima partaking in the CrtlAQUA project, have shown that there are several benefits from adapting the ultraviolet light (UV) dose to the pathogen being dealt with. 

By disinfecting water with UV, the lamps involved in this process emit light of a certain wavelength, and of low or medium pressure. The light waves are capable of interfering with the DNA found in harmful microorganisms. The harder a pathogen is to kill, the higher the UV dose is required.

Utilising UV light is costly and requires further examination of applying high doses on harmful pathogens.

Master students Kari Justad from the Arctic University of Norway and Miguel Guerreiro from the University of Algarve, Portugal, conducted research at Nofima's Tromso laboratories. In collaboration with Nofima technicians and researchers they used two UV Collimated Beam Apparatus to investigate six different pathogens.

Two different UVC technologies of distinct wavelength lengths were used: low pressure and medium pressure, and seawater for the trials was collected at varying depths at two different sites. One was near to a salmon farm, while the other wasn't nearby to fish farmers.

Results showed that in all trials, 99 percent of pathogens were eliminated by using a lower dose and therefore low cost than required.

"The IPNV is the only one of the five virus and bacteria we have tested that required a very high dose, luckily there is a vaccine against it. All the other pathogens were eliminated using UV doses typically below 10 mj/cm2," says Nofima scientist Vasco Mota.

"These results may indicate that there is a need to assess the UV doses that are required to disinfect the intake water of aquaculture facilities, which could potentially reduce energy costs regarding UV disinfection," explains Mota. "The exception in our trials was the IPN virus which required a high UV dose, but the existence of a vaccine for this virus reduces the need to eliminate it. All the other pathogens were eliminated using much lower doses."

Water disinfection utilising UV technology has applications in land-based farms, including both flow-through systems and RAS, as well as semi-closed containment facilities at sea.

"Facilities at sea pose a challenge because of the enormous volumes of water that are used," says Mota. "It is not possible to use low pressure UV when working with these amounts of water."

With medium pressure UV being best placed to scale up as aquaculture facilities increase in size, Mota explains the benefits of it:

"Medium pressure UV also attacks the proteins and enzymes, the machinery that the harmful microorganisms use to repair cell damage. As a result, UV disinfection efficiency is further strengthened."

New trials will be carried out at four commercial fish farms this year. UV disinfection will be tested using clear seawater, which happens during summer and winter, and more murky sweater, which occurs as a consequence of algae growth during spring and autumn.

"We will not be adding pathogens in these trials. Instead, we will treat what is naturally found in the water," Mota concludes.

For more information on Nofima visit their website, HERE.

For more information on the CtrlAQUA project visit their website, HERE.

The Aquaculturists

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