Fish consumption is rising. With the increase of the world population and the need for nutritious food, health-conscious are looking for alternatives to “a nice slice of meat”. And they end up eating more fish or vegetarian food.
Specific species of wild fish are getting more and more scarce in open water due to the huge impact of industrialized fishing fleets and over-fishing. The sea can not provide the increasing demand. Fortunately, in a trend towards sustainable food production, fish farming is gaining increasingly in interest.
Fish Farming
Fish farming is the aquatic peer of farming cows, sheep, or chicken. For many years we as humans have been farming our main food. We have it grown in greenhouses, stables, or in the fields. We try to fulfill our demands, in a more sustainable way, with respect for natural resources. Fish farming appears to be moving in that same direction.
When people hear about fish farms, images of aquariums, ponds, and floating nets, flood the mind. In Norway, fish farming is performed on a much larger scale. A typical fish cage near the Norwegian coast has a diameter of tens of meters containing 200,000 to 300,000 salmon. In the near future, these designs will be scaled to 1 or 2 million salmon. Only in Norway, at the beginning of 2018 more than 3500 cages for fish farming were floating in the sea. And ‘Norway’ is expanding their knowledge and technology across the world, where people are interested in large scale harvesting of fish in the sea- or maybe also on land.
Salmon is a great example of a fish that can be farmed. They need cold water- seven to nine degrees Celsius is what they like most- which is why this aquaculture is taking place in the Northern hemisphere, off-shore in the fjords. Moreover: salmon is a very popular fish, often found on the menu all around the world- so there is a high demand.
Aeration
In fish farming, aeration is vitally important. In addition to food, the fish need oxygen that is supplied in the form of tiny air bubbles (‘aerated’) to the water. But aeration has more advantages.
In the early days, lice were a major disease that impacted salmon. Salmon lice had an impact on harvest, because of this fish farmers had to look for solutions. For one reason or another they started to purge air from the bottom of the cage. They observed that the movement of the fish started to change. Instead of circling day in and day out – as salmon normally do- they started to move around the cage and became more agile. If the salmon are more agile, the muscles have to work more, and meat from moving animals has a better quality. At the same time, the fish farmers detected the aeration helped them to create a more thermal friendly water environment, with an advantageous temperature, conditions, and amount of oxygen. The occurrence of salmon lice was reduced. There are 2 advantages of aeration, improving the salmon quality, and reducing the unwanted lice. By the way: the words purging and aeration have the same meaning. ‘Aeration’ has the word air inside.
Aeration of fish farms using mass flow controllers
The process of aeration is very simple- like in any aquarium you have at home- and yet you can lead to very nice results as we saw above. The air bubbles can be generated by natural water currents ( off-shore, down-hill), pumps, impellers, variable area flow meters or – as we do at Bronkhorst – by mass flow controllers and compressors. Here, a compressor generates compressed air from the surrounding atmosphere, and feeds this to the mass flow controller for controlled aeration of the water in the fish cages.
To run fish farms remotely controlled and without manpower, as much automation as possible is required. This also involves automated feeding. When the fish are fed, the air purging needs to be interrupted to give the fish the opportunity to hunt for the food before it floats out of the cage. In the between the feeding periods, the aeration improves the condition of the water and the salmon. Here, it helps that mass flow controllers are remotely controlled from the control room at land. The aeration is stopped when the feeding starts, and when the feeding is over, the previous set point will automatically return and the water condition is as stable as it was before.
But there is more: mass flow controllers provide a potential for saving energy due to better conditions in the cage. The accuracy of the devices is important here. Every cubic meter of air you save by being more accurate- faster control or opening of valves- is of direct influence to your costs for running the compressor. Moreover, in stormy weather you can reduce the aeration, but during a long dry period without water movement, more air bubbles are needed. So essentially, this accuracy and flexibility leads to a better controlled environment.
With MASS-STREAM mass flow controllers we have a robust instrument, which is performing well in the harsh northern surroundings. By Bronkhorst standards, this kind of aeration is a ‘high flow’. Typical air flows for a fish cage are in the range between 600 and 1400 liters per minute.
Mass flow controllers for other types of aeration
Mass flow controllers are suitable for other types of aeration – also again in aquaculture and agriculture. If you grow salmon, you need to breed the fish, which normally occurs on land. Fish eggs and young fish are even more vulnerable to changes, so the environment has to be more stable than for grown fish. Depending on the type of fish, the balance of oxygen in the water is delicate and has to be controlled accurately.
In algae farming, carbon dioxide gas is one of the food components for these species to grow, which needs to be supplied under defined conditions.
A very well-known application of aeration is in food & beverage industry. As you might know, every soda or carbonated drink is a liquid purged with carbon dioxide gas. Related to that: when packaging food, the packaging is purged with nitrogen to remove the oxygen before the food enters the packaging, as one of the steps to prolong the shelf of the food.
“Fish farming with controlled aeration by mass flow controllers will support the focus on good fish quality, control of diseases and increase of the yield” according to Nicolaus Dirscherl, Managing Director of M+W instruments GmbH.
