International Aquafeed Article: Oxygenation Technology

Oxygenation is a concern for most fish farmers. In the May/June 2012 issue of International Aquafeed magazine, Stefan Dullstein of Linde outlines a new low-pressure technology.

The full text follows but you can also view the article as it appears in the magazine  here 
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Oxygenation technology poised to transform aquaculture worldwide

by Stefan Dullstein, Head of Industrial Segment Aquaculture & Water Treatment, Linde Gases Division, Germany

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 — 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 and launched in August 2011, 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.

The 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.

The micro-bubbles created by SOLVOX^® OxyStream have 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 it would be more cost effective to produce fish in captivity in the ocean rather than to trawl for wild fish. Today aquaculture is moving to on-land farming, with the most significant inroads being made in Norway, where there is a massive demand for salmon and cod. This places an enormous burden on 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, so there is a need to provide an additional source of oxygen. 

 

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.

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. 

 

By precisely predicting flow velocity SOLVOX^® OxyStream is able to adjust this velocity in the circular on-land tanks. The fish, depending on their age and size, need a certain water velocity for optimum growth conditions, so 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 100g in weight in small to mid-sized tanks. Once the fish are acclimatised to sea water conditions, they are usually transferred to sea cages. 

 

This method has been constrained by some major challenges as 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 prohibitive 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.

Furthermore, new legislation imminent in Norway will allow farmers to develop fish to a size of 1000g on land, meaning a whole new market has opened for us. Research is already underway to investigate the on-land development of fish up to 4 to 5kg, harnessing our technology.

The largest tank equipped so far with SOLVOX^® OxyStream is 15m in diameter, but aquaculture farmers are looking to increase the size of tanks – up to around 20 to 25m 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. 

 

With interest levels so high, Linde has had to accelerate its activities to meet customer demand. As a customised solution, it is not a simple matter of ‘plug and play’. Each customer application needs to be approached from a unique perspective, needing professional, tailored input. 

 

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

With the ocean’s reserves of fish steadily depleting and the demand for fish products on the increase, adding more sea cages along 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. 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 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 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. Although it is the most advanced equipment available to this industry at this time, Linde is convinced that it can improve the technology even further and research and development will be ongoing to maintain their position as a leader in the field.

The future

Envisaging a bright future for SOLVOX^® OxyStream, Linde 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, and others, is as high as 50m tons per year. The largest aquaculture industry is in China, which produces about 70 per cent 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.