UNIQUE OXYGENATION TECHNOLOGY POISED TO TRANSFORM

AQUACULTURE WORLDWIDE

Since the launch of the technology last year, interest is burgeoning in a unique new low-

pressure oxygenation system that is poised to transform the world of aquaculture.

The uniqueness of the technology is based on its ability to perform three critical functions in

one system— dissolving oxygen in the water, producing the correct hydrodynamics and

stripping out potentially harmful inert gases like nitrogen — and all this via a very low energy

requirement. Moreover, the system is easily installed, including as a retrofit to existing fish

tanks, and is virtually maintenance-free.

SOLVOX® OxyStream, developed by Linde Gas, has been proven to improve the living

conditions of fish inside the tank, allowing for a significant increase in fish production volume,

optimise fish meat quality and considerably improve operations from an environmental

standpoint.

Aquaculture, also known as aquafarming, is the discipline of commercially farming aquatic

organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves

cultivating freshwater and saltwater populations under controlled conditions – in contrast to

commercial fishing, which is the harvesting of wild marine fish.

The Linde technology has been developed in response to a progressive trend that is seeing

aquaculture production being transferred from sea cages to land-based sites for the full

duration of a marine fish’s lifecycle. This change has confronted the industry with the

challenge of oxygenating large fish tanks that can accommodate fish stock from infancy to

maturity.

Ground-breaking patented SOLVOX® OxyStream is a combined oxygenation and flow

system which not only dissolves the optimal amount of oxygen in the inlet water flow, but

also distributes it evenly at an adjustable flow pattern through the tank, ensuring fish stock

benefit from the physical exercise involved in swimming against the current. The flow regime

can be fully tailored according to fish size, stock density and fish species, such as salmon or

cod. The system comprises a standalone unit and is installed individually in each tank, so

water flow and oxygen dosing can be individually controlled for each tank.

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The micro-bubbles created by SOLVOX® OxyStream create the additional benefit of helping

to reduce the concentration of dissolved inert gases such as nitrogen or argon. In particular,

oversaturation of nitrogen, even in relatively small quantities, can endanger the wellbeing of

fish stock, slowing growth and increasing the possibility of disease, and ultimately, even

mortality. With the installation of SOLVOX® OxyStream, external degassing units to prevent

inert gas build-up will, in many cases, become obsolete.

Depending on the application, pumping pressures as low as 0.05 to 0.2 bar are normally

sufficient to oxygenate the incoming water, strip nitrogen and create optimal tank

hydrodynamics. This low operating pressure makes the system very energy efficient.

OxyStream also requires very low maintenance, because it is not associated with any

ancillary equipment to manage water pressure.

Producing fish in captivity

“Aquaculture using sea cages came into its own as recently as the 1980s, when the fish

industry recognised that it would be more cost effective to produce fish in captivity in the

ocean than to trawl for wild fish,” says Stefan Dullstein, Head of Industrial Segment

Aquaculture & Water Treatment at Linde. “Today aquaculture is moving on-land, with the

biggest inroads being made in Norway, where there is a massive demand for salmon and

cod. This places an enormous burden on the farmers to produce fish more efficiently and

cost effectively.

“The limitation with a conventional on-land tank is the amount of oxygen available to the fish.

Water can only provide a certain amount of oxygen, which is quickly respired. There was

therefore a need to provide an additional source of oxygen. Linde has always played a

pioneering role in gas technology within the food production and processing market and

we’re delighted to be able to introduce such an effective and environmentally sustainable

solution to combat the challenges of dissolving a sufficient amount of oxygen in very large

tanks and distributing it evenly via an adjustable flow regime.”

SOLVOX® OxyStream is able to efficiently oxygenate sea water and can additionally be

used during the fresh water phase of salmon. This allows fish farmers to operate a single

oxygenation system in large tanks which can run on both fresh water and sea water. This

significantly reduces costs compared with running separate saline and fresh water

oxygenation systems.

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Dullstein says this capability was recently demonstrated during trials conducted at Marine

Harvest in Norway, the world’s largest salmon producer. Results showed that SOLVOX®

OxyStream was the only oxygenation source suitable for rearing young salmon hatched in

tanks running on fresh water, before gradually transitioning them to sea water. This creates

an optimum environment in which to rear salmon, ensuring the correct oxygen levels

throughout the entire production period and keeping fish stress levels to an absolute

minimum.

“Importantly, we can precisely predict flow velocity and are able to adjust this velocity in the

circular on-land tanks,” he explains. “The fish, depending on their age and size, need a

certain water velocity for optimum growth conditions. If the velocity is incorrect, the fish won’t

exercise, so it’s important to apply the correct water velocity in each application to keep them

‘working out’ against a robust current.”

Parallel development

Typically, aquaculture farmers have grown salmon from eggs to about 100 grams in weight

in small to mid-sized tanks. Once acclimatising the fish to sea water conditions they are

usually transferred to sea cages.

“This method has been constrained by some major challenges,” says Dullstein. “There is

always the potential for break-outs, allowing valuable stock to escape, while the high density

of fish in this natural environment has the potential to foster diseases. So it makes sense to

govern the entire lifecycle on land, where the health of the fish and the environment can be

managed with more control.

“Although the method was mooted as far back as ten years ago, at that time the costs were

inhibitive owing to the high energy required to pump water through the dissolvers operated at

higher pressure into land tanks and dissolve oxygen in the water. Today SOLVOX®

OxyStream, with its unprecedented low energy demand, makes this possible. And, with new

legislation imminent in Norway that will allow farmers to develop fish to a size of 1 000 grams

on land, a whole new market has opened for us. Research is already underway to

investigate the on-land development of fish up to 4 to 5 kg, harnessing our technology.”

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The largest tank equipped so far with SOLVOX® OxyStream is 15 m in diameter, but

aquaculture farmers are looking to increase the size of tanks – up to around 20 to 25 m in

diameter.

Immense interest

The industry has responded to the introduction of this system with immense interest and the

Linde team currently has about 20 units piloting at customer sites, with many more proposals

out there. It has fielded enquiries from North America, the UK, Norway, France and even

from Saudi Arabia.

“In fact, interest levels are so high that we’re having to accelerate our activities to meet

customer demand,” he comments. “This is a customised solution and it’s not a simple matter

of ‘plug and play’. Each customer application is unique and needs our professional input.”

Dullstein says Linde’s latest customers are thrilled with the quality of the fish product being

achieved. With the longstanding quality competitiveness between companies farming fish

and those harvesting wild fish, he says it’s impossible to tell the difference wherever

SOLVOX® OxyStream has been used.

To showcase its technology in action, Linde is constructing a brand new test centre in

Norway where customers will be able to see SOLVOX® OxyStream in action as it operates in

windowed tanks. Training and equipment testing will also be carried out using the new

centre as a base.

Environment

Dullstein says with the ocean’s reserves of fish steadily depleting and the demand for fish

products on the increase, adding more sea cages on the world’s coastlines is not an

adequate solution.

“In this scenario not all the fish feed deployed to the sea cages is converted to fish meat —

there is a lot of wastage,” he says. “At the same time, a large amount of fish excrement

released in a specific area tends to over-fertilise the ecosystem. By comparison, the

producing from infancy to maturity in on-land tanks has significant environmental benefits.

The water flowing through fish tanks can be recycled to a high extent with excrement and

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feed residues filtered out effectively. As such, pollution to the marine environment and the

possible spread of disease to wild fish is prevented.

“Diseases can be properly handled in land based tanks. Fish farmers using sea cages may

need to chemically treat the fish to get rid of sea-lice and this is prejudicial both to the

environment and to the fish themselves. Sea-lice are not an issue in recirculation tanks, as

these parasites cannot get into the system in the first place.

“There are other advantages. Fish being bred in aquaculture are, in many cases, genetically

different to wild fish, so when there is a break-out and fish escape into the ocean, this could

have an impact on the genetics of natural fish population.

“A technology like SOLVOX® OxyStream was unquestionably needed to ensure the future

success of the growing land-based aquaculture industry. However, it’s not the end of the

story for us. Although it is the most advanced equipment available to this industry at this

time, I’m convinced that we can improve it even further and research and development will

be ongoing to maintain our position as a leader in this field.”

The future

Dullstein envisages a very bright future for SOLVOX® OxyStream. He believes the vigorous

interest being shown by aquaculture farmers is just the tip of the iceberg.

“Norway’s fish farming industry, which is the most industrialised in the world, but by no

means the biggest, produces about one million tons of salmon a year, but global tonnage –

including all fish species, molluscs, croustades, etc., is as high as 50 million tons per year,”

he says. “The largest aquaculture industry is in China, which produces about 70% of the

world’s farmed fish. However, the industry in China tends to comprise many small, family

owned companies, using a low level of technology. Therefore, from a cost perspective alone,

sooner or later China will begin to industrialise its aquaculture industry.”

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