FISH FARMING TECHNOLOGY #3 UV TECHNOLOGY IN AQUACULTURE When designed, installed and maintained properly, UV systems are extremely robust, reliable and effective. Pentair Aquatic Eco-Systems (PAES) is a leading manufacturer of UV water treatment systems for use in a range of industries.
by Michael Annett, Sales/ Business Manager UV Systems, Pentair Aquatic EcoSystems
PAES has particular expertise in designing and supporting UV systems in aquaculture field applications. In addition to new installations, PAES also provides consulting and support for UV systems that are installed in existing aquaculture facilities. UV treatment has been used successfully for approximately six decades to treat and sanitise water in many critical applications. In this article, we will describe the array of UV system configurations along with their associated lamp technologies, to serve as a high-level guide to important design and operating considerations for UV systems.
UV process discussion
Ultraviolet or UV energy is located in the electromagnetic spectrum with a wavelength shorter than that of visible light and longer than x-rays. When UV systems are deployed to treat water, the reactions are instantaneous, taking only a few seconds to occur, without the creation of disinfection by-products. Chemicals are not required and the associated hazards of chemical handling and storage are not present. UV treatment does not alter colour, odour, taste or pH. As such, UV processes are environmentally safe and are considered ecologically-responsible technology. The science behind UV technology is well-established; and its efficacy is well-proven. UV systems are trusted in a wide range of industries including drinking water production, aquaculture farming and other applications. UV light is comprised of electromagnetic radiation of wavelengths ranging from 100nm to 400nm: UV-A (long wave UV): 315-400nm UV-B (middle wave UV): 280-315nm UV-C (short wave UV): 200-280nm Vacuum UV: 100-200nm
When a UV system is used to treat water, UV light at the 254nm wavelength penetrates the cell wall of microorganisms that are present in the treatment water. The amount of UV delivered to the organism is called the dose. The UV energy permanently alters the DNA structure of the microorganism in a process called thymine dimerisation. The microorganism is not destroyed, rather it is ‘inactivated’ and rendered unable to reproduce or infect.
Another useful way that UV can be utilised is in the
Enclosed UV reactors
destruction of oxidants that are present in post-treatment water in the form of residuals. Ozone (and some other oxidant chemicals) can be eliminated by the application of UVC radiation. UV energy in the wavelength of 254nm has the ability to catalyse ozone into harmless oxygen and water. UV is very effective at destroying ozone (O3). O3 molecules absorb 254nm UV radiation and this absorption causes decomposition of the O3 molecule. O3 concentrations at less than 0.5mg/l can be eliminated with a UV dose of 60mJ/cm2. 1.0mg/l ozone concentrations require a minimum UV dose of 90mJ/ cm² for complete destruction.
UV reactor types
UV reactors for processing fluids are generally either enclosed or oriented in channels without an enclosure. UV reactors can be in-line in a pressurised piping system or fed by gravity without requiring pumps.
Enclosed reactors can be installed vertically or horizontally, in an “L” shape or “U” shape, or with the inlet and outlet on opposing sides. They are cylindrical and can be manufactured from stainless steel, various plastics and polymers such as PVC, HDPE and others.
Open channel and gravity-fed reactors
Open channel reactors are either installed in concrete channels or in pre-manufactured troughs, typically stainless steel or fiberglass reinforced plastic (FRP). The lamps can be oriented horizontally in racks or mounted vertically, perpendicular to the flow. Open channel systems can treat very large flows and are economical if gravity feed is available. Gravity fed reactors can also be offered in enclosed FRP vessels with the lamps mounted vertically.
UV lamp technology
UV lamps used in disinfection and photolysis applications are categorised into two basic types: low
48 | July | August 2016 - International Aquafeed