Aquaculture is a growing and increasingly important industry in many parts of the world, including Scotland, Chile, Norway, Greece and Turkey. It helps to sustain economic growth in rural and coastal communities which are often isolated from the more developed and industrialised areas of these countries.
UV Water Disinfection for Fish Farms and Hatcheries
The modern aquaculture industry faces a number of issues:
Disease
High rates of water extraction and increased reliance on recirculated water can lead to poor water quality, resulting in increased outbreaks of viral, bacterial and parasitic fish diseases which can decimate fish stocks. Due to the intensive nature of fish farming, fish stock is also highly susceptible to infection from natural fish populations in the feed water to the farm.
Regulation
Fish reared and released back into the wild, as well as those endorsed by the regulatory bodies such as the UK’s Marine Stewardship Council, must be disease-free.
Water Quality
To minimise the chance of infection and disease, the water used in fish farms and hatcheries needs to be of a minimum quality. Ensuring this quality is not easy – chemical treatment is not appropriate as it harms the fish and cannot be released into open waters.
To ensure water quality and to break the infection cycle between fish farms and natural fish populations, a disinfection system is needed to treat water entering and circulating within fish farms.
The advantages of UV disinfection
UV is ideally suited for treating incoming and recirculated water in fish farms and hatcheries as it uses no chemicals and does not create by-products which would harm the fish stock, or other aquatic life, on discharge. Unlike other treatment methods, UV also avoids the expense of complex monitoring systems required for adding and removing chemicals before the water reaches the fish. In addition, it does not alter the pH of the water. In fact, UV is now widely regarded to be the most effective and economical disinfection technique for use in fish aquaculture.
UV applications in aquaculture
The applications for UV include treatment of water in hatcheries, shell-fish purging tanks and fry rearing tanks. It is also used in fish processing plants and well boats. UV is even used to disinfect recirculation water in marine parks and aquaria.
Some considerations
• When installing UV systems, operators need to be aware of which viruses, bacteria or parasites are posing a problem and size the UV systems accordingly. Hanovia usually recommends a UV dose of between 120 – 150mJ/cm2, but the final dose always depends on a number of factors, including whether the water is single-pass or recirculated.
• Water needs to be treated at all stages in the process, from the egg stage right through to full maturity
• All effluent water from hatcheries, processing plants and well boats must also be treated so as to protect the environment and stop the possible transmission of disease to wild fish populations
UV technology
UV technology is surprisingly simple to install and use. A UV disinfection chamber can usually be retrofitted to existing pipework and circulation systems with minimum disruption to the process.
All controls are automatic and maintenance of the systems is usually restricted to the replacement of the UV lamp every 12-18 months, depending on use. This is a simple operation that can be carried out by on-site staff. An automatic or manual wiper fitted over the quartz sleeve surrounding the UV lamp prevents the build-up of any deposits, ensuring maximum levels of UV irradiation at all times.
A significant feature of modern UV systems is the control mechanism which displays a range of useful functions such as flow rate, UV dose and intensity. The systems are usually capable of logging up to one year’s performance data, which can be downloaded to a PC through an RS232 port. Linked into a central computer, the control panel can also be operated remotely, and allows the system to operate around the clock.
Case studies
Cultivos Huacamalal Ltda., Chile
Cultivos Huacamalal Ltda. of Chile is using a Hanovia UV disinfection system for its salmon hatchery in Rio Ignao in the south of the country. The UV system is part of a US$1.1 million water recirculation and effluent treatment system provided by Atlantech Chile Ltda. of Puerto Montt, Chile.
The UV unit treats well water used for make-up supply in the water recirculation system to control against Infectious Pancreatic Necrosis (IPN) RNA-virus. IPN is found in wild salmon populations on the Pacific coasts of both North and South America and can cause severe mortality (up to 80%) in fish up to two years old. It is a common disease in hatcheries and is also capable of transmitting epizootic conditions back to wild populations.
Chile is one of the three major salmon farming countries in the world, along with Norway and Scotland. Cultivos Huacamalal is a new player in the Chilean salmon aquaculture industry. The company was formed by a number of experienced partners in the fish production and shipbuilding industry in Chile and has signed an agreement to supply product to one of the largest salmon exporters in the country.
Loch Fyne Oysters Ltd, Scotland
Loch Fyne Oysters Ltd in Scotland is using two Hanovia UV disinfection systems for its oyster farm in Loch Fyne, Cairndow, Scotland. The UV systems, which were installed by Barr and Wray, destroy harmful E.Coli bacteria from its oyster and mussel depuration tanks. Each UV chamber treats up to 150 m3 water per hour.
According to a spokesperson from Loch Fyne Oysters, “The Hanovia units were recommended to us by Barr and Wray because of their 99.99% log reduction of E.Coli, their robust, stainless steel construction, their ease of installation and easy maintenance – including easy UV lamp replacement and daily cleaning with a manual wiper – and low running costs. We also find the digital run-time read-out very useful.”
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