As Pierre Kwan discussed in his October 2016 blog, the HDR Water Institute has been developing ultraviolet systems for years. Now let’s examine how UV disinfection can improve the lives of those creatures who breathe water. Mark Hassebrock shares his experience.
Something that all fish hatcheries have in common is the constant battle to keep fish healthy. Because hatcheries are built to accommodate a quantity of fish in a space typically much smaller than what those fish would occupy in the wild, disease organisms can propagate rapidly throughout a fish population.
One way to control diseases in hatcheries is to reduce or eliminate the threat of disease-causing organisms entering the hatchery through its water supply. Hatcheries that use surface water supply sources, such as lakes and rivers, tend to be the most susceptible to disease from organisms in the water supply.
As with treatment of water for human consumption and wastewater, one powerful tool for treatment is ultraviolet (UV) disinfection. It’s often a favorable option for hatchery operators because it doesn’t involve handling or applying chemicals.
UV treatment system we designed for Leadville National Fish Hatchery in Leadville, CO
The keys to successful control of fish diseases using UV disinfection involve identifying the disease organisms that are expected to be present, and then determining the ability of the source water to transmit UV light.
Research has helped to define the UV doses required to inactivate various protozoa, viruses, fungi, and bacteria that cause fish diseases. Since not all pathogens are present in all water sources, careful identification of which target organisms are present is critical to economical UV design. And, it’s only necessary to provide the dose required to inactivate the toughest organism present in the source water.
We must also consider contaminants that can reduce the dose to be delivered to disease organisms. Particulate matter suspended in the water reduces the effective dose by physically blocking the light energy from reaching organisms for the required time. Even if the water appears very clear, dissolved contaminants common in surface water, such as iron and certain acids, can also absorb UV light. The designed intensity of UV light must be increased to compensate for these effects—to deliver the minimum dose required for inactivation of the target organisms.
An additional consideration for hatchery UV systems involves developing strategies to prevent partially treated or untreated water from reaching the fish, if the UV system becomes impaired or completely disabled. If the UV light intensity is reduced due to failure of one or more lamps in the treatment vessel, or is completely interrupted by a power failure, the flow of water to the fish must be stopped until the light intensity is restored.
UV technology is a proven treatment to keep our hatchery fish healthy. Tell us how you use UV treatment in your work.
Images courtesy of Mark Hassebrock.