Specialised Aquaculture Applications Require Specialised Products & SolutionsSalmon Aquaculture and the use of sea pens to farm salmon is a booming segment of the food industry. Profit margins are ever high, as is consumer demand. This has led to the increasing use of technology by the Aquaculture industry, much of which relies on the use of compressed air and low-pressure air. Salmon feeding has been a pneumatic procedure for over 12 years, whereby the feed is directed from the feed silo into the pens by a low-pressure air stream. This tried-and-tested technique is now leading to feed barges being designed with machine rooms beside the feed silos in which the blowers and any ancillary equipment can be housed to protect them from the outside elements. In recent years, higher pressure compressed air applications have increasingly found their way into the Aquaculture industry. Operating in the 7-bar range, compressors – either diesel or electric powered – are used to provide the compressed air for important tasks such as removing dead fish from the pens (mort removal) or to raise the level of oxygen in the sea pens (a procedure known as ‘Sea Pen Aeration - SPA’).
Prior to the innovative technique of automating mort removal, divers were dispatched to the pens to manually place the dead fish in baskets which then had to be lifted out of the water by hand. Now, using compressed air to do the job instead, a cone is installed in the deepest part of the sea pens. This is connected to a tube through which compressed air is blown, forcing the dead fish up from the bottom of the pen to the top, owing to the “airlift pump” principle. Here they are separated from the water so that skilled staff can assess the condition of the carcasses and conduct statistical analyses on them.
One of the most important uses for compressed air in Aquaculture is ‘Sea Pen Aeration - SPA’, a process whereby compressed air is blown into the pens through diffusers. As bubbles rise to the surface, a gas exchange takes place between the water and the gases in the bubbles, raising the oxygen levels in the water. Even more importantly, it results in an artificial upwelling, which forces oxygen-rich, cold water from deeper down in the water column up into the pens. This has several effects:
- firstly, because colder, deep waters can hold more oxygen, the oxygen levels in the pens are raised. This is particularly important in the summer months when environmental factors such as algal blooms can be a major concern. Cold, deep waters also mitigate the effects of temperature peaks, which are dangerous for the salmon and have become increasingly common during the summer months in recent years.
- A further effect of the upwelling is that, thanks to the water at the upper levels flowing outwards, less of the oxygen-poor surface water enters the pens. Moreover, algae drifting in upper water layers is kept out of the sea pens by the outwards flow. This effect is most important during algae blooms and prevent the algae from reaching the Salmon.
The SPA concept described above is currently most commonly used in Canada and Norway. In other countries, including Scotland and Chile, bubble curtains are the usual method for protecting the fish from swarms of jellyfish (Scotland) and algal blooms (Chile). In the past, these two blights have been responsible for wiping out entire fish stocks in some farms and resulted in financial losses totalling millions. Such compressor applications are relatively new, so most feed barges have nowhere to house the associated necessary equipment. This means that the compressors tend either to be installed at the farms themselves or on rafts specially designed and built to accommodate them.
Author: Adrian Feiler, KAESER Business Development Manager – Aquaculture