Oxygen Generation, containers solutions onsite

As Sterner approaches its 20th year in the UK and Ireland market place the industry desire for solutions to meet our customers challenges continues to grow.

This has been demonstrated only recently by the increase in demand for oxygen generation solutions for both freshwater and seawater applications, this technology has been adopted by Sterner through its association with Airsep corporation since the late 90,s with some of the original systems still offering critical life support for juvenile stocks.


At Sterner we can package any of our Standard Airsep oxygen generators with a multitude of
options to provide a turnkey solution for your oxygen needs.

We also have pre-configured containerised systems, which are designed to match the most common applications. Typical package systems consist of a Standard Airsep oxygen generator matched with a dedicted Kaeser air compressor. We also provide the option to integrate your containerised oxygen plant into an existing OxyGuard Commander Pacific system on site.

Through collaborations with valued customers this has expanded to seawater with turnkey oxygen generation and distribution systems delivering highly saturated O2 into sea pens for both life support and also improved production.

These systems vary in capacity and method of distribution dependent on site conditions and biomass and can be deployed as a containerised plug and play solution.

The current climate has also seen our containerised O2 systems deployed for back up to liquid supply for both traditional flow through and large RAS set ups to ensure continuity and peace of mind.

Sterner will undertake design, build and deployment for our oxygen generation packages all backed up with a service plan tailored to your individual needs



NEW OxyGuard Optical LDO Oxygen probe

OxyGuards new optical oxygen probe is developed in cooperation with world leading experts. Based on luminescence quenching of a sensor dye immobilized on a support foil it can be used for gas measurements as well as for dissolved oxygen (DO).

The presence of molecular oxygen quenches the luminescence, changing its intensity and lifetime fully reversibly. The measurement principle is very robust.  It shows virtually no interference to other gases and has very low drift. Bleaching is not an issue because low energy red light excites the sensor spot and emission is NIR.

Special features

  • High-accuracy measurements of oxygen in gas or water (DO)
  • Low drift
  • Long lifetime
  • Fast response
  • Digital output of all major oxygen units

Technical Data Sheet


Legionnaires’ Risks and Reopening Closed Businesses

Legionnaires’ Risks and Reopening Closed Businesses

Leaving the water systems in buildings unused for some time could be fatal if not properly treated upon return. It increases the risk of legionella bacterium, which can be life threatening.

If you are managing a premises with a water system, you have a legal responsibility to identify and manage any risk of legionnaires’. Read on to learn more about the bacteria and to find out what you should do if you are reopening your business after a period of closure.

Legal responsibilities and assessing the risks

If you are the employer or person in control of premises, you must organise a risk assessment from exposure to legionella. The revised Approved Code of Practice (ACOP) Legionnaires’ disease: Control of Legionella Bacteria in water systems (L8) issued by the Government’s Health and Safety Executive (HSE) significantly extends the scope of its guidance on control of legionella bacteria in water. The code applies to all hot and cold water systems in the workplace regardless of their capacity, i.e. the lower limit of 300 litres previously used to exclude domestic systems, no longer applies. Whilst domestic systems may represent a risk, the code only applies to a risk arising from a work activity. This means that all employers, who manage premises with hot/cold water systems and/or wet cooling systems, have a legal responsibility to identify any risk of contamination and to prevent or control it. These records have to be kept for a minimum of five years.

What is legionnaires’ disease?

Legionnaires’ disease is a potentially fatal form of pneumonia. The cause of the disease is a bacterium called legionella pneumophila.

How is it caught?

Legionnaires’ disease is caught by inhaling small droplets of water suspended in the air which contain the legionella bacterium, e.g. spray from showers and taps.

What are the sources of legionella bacterium?

The legionella bacterium is found mainly in stagnant water, e.g. ponds and rivers or buildings containing cooling tower, evaporation condensers, air conditioning and industrial cooling systems, humidifiers, spa baths and hot and cold water systems.

What areas are the most vulnerable?

A wide range of workplaces, but particularly residential accommodation managed privately or by organisations, e.g. local authorities, universities, hospitals, nursing and care homes, housing associations, charities, hostels, private landlords, managing agents, hoteliers and holiday accommodation providers, including guest houses.

Who is most at risk?

People most at risk are people over 45, smokers and heavy drinkers, diabetics and people who are already ill, particularly with chronic diseases or whose immune system is impaired.

How can using a thermometer help control legionella in water?

Incorrect water temperature is a key risk factor for legionella growth. The legionella bacteria multiply in water at temperatures between 20 to 45 °C. A typical method of control is to store hot water above 60 °C and distribute it at above 50 °C (care must be taken to prevent scalding). Cold water should be kept below 20 °C.

What action should be taken when reopening a business that has been closed for some time? 

The HSE guide to legionnaires’ disease states that:

‘Where a building, part of a building or a water system is taken out of use (sometimes referred to as mothballing), it should be managed so that microbial growth, including legionella in the water, is appropriately controlled.

All mothballing procedures are a compromise between adequate control of microbial growth, the use of water for flushing (while avoiding waste) and degradation of the system by any disinfectant added. Where disinfectants are used, these should leave the system fit for its intended purpose.

The systems should be recommissioned as though they were new (ie thoroughly flushed, cleaned and disinfected) before returned to use.’


RAS takes the heat off smolt producer

Changing over to a recirculating aquaculture system (RAS) brought a bonus for Norwegian salmon farmer Bremnes Seashore during the recent hot, dry weather.While some flow-through hatcheries were practically out of freshwater, the much smaller water requirements of a RAS meant the company never sweated over its supply in the sunshine.

Øyvind Haraldseid: “It feels good not to consume that much fresh water.”

“With the old plant with no RAS and 150 tonnes of production, we would have had to take drastic measures, otherwise there would have been little freshwater left,” said Øyvind Haraldseid, in charge of the plant at Trovåg, north of Bergen. “Instead, we now produce several times more biomass and use less water than ever.”

Freshwater basin

A survey of the freshwater basin used by the hatchery recently showed that the level had dropped by just one metre of a total of 2.6 metres available, despite an extremely dry summer.

“It feels good not to consume that much fresh water, water is a limited resource. RAS is the future of fish farming, it also has other benefits,” says Haraldseid.

The first of a planned four RAS halls has been in operation for two years. The second hall has been in operation for half a year, and the third and fourth halls are under construction.

“With the RAS, we can keep higher temperatures in the plant in winter. Salmon on land are also not bothered by parasites. We plan to keep the fish until they are half a kilo,” said Haraldseid.

3,500 tonnes of smolts 

Bremnes Seashore plans to gradually increase production to approximately 3,500 tonnes of biomass, which is expected to occur in about two to three years.

“On normal flow-through, it would be impossible to produce these quantities on land, at least here at Trovåg,” said Haraldseid. “The RAS consumes little water per kilo of fish;  we have already reduced it by 95% and it will go further down. In combination with the sea water we pump in from 75 metres deep we can let the salmon grow on. In the future I reckon the fish will spend one year at sea, and perhaps even less,” said Haraldseid.

In the long run, it is estimated the plant will produce eight generations per year.

By expanding its RAS and the size of its smolts, Bremnes Seashore will be able to increase production at its sea sites because fish that go in at 500 grams will reach harvest weight sooner. 

Bremnes Seashore is still building its RAS facility at Trovåg, north of Rogaland. The first RAS hall has been in operation for two years, and the second for six months. The third and fourth halls are now being constructed to the left of the existing buildings.

25 times more biomass

Until two years ago, the company had permission to produce 10 million smolts and 10 mill fry per year, limited to 2,850 tonnes, at Trovåg, but has since been given permission for 6,000 tonnes per year at the site if it wants to expand that much.

“In all we expect to increase the biomass on land by a factor of 25. This will use less than half of the water we now have available,” said Haraldseid.

The RAS plants are built as separate units. Hatchery and start feeding are also closed systems. All the equipment is supplied by Sterner, which has also delivered sludge treatment facilities, and has now developed a modular RAS after producing a steady supply of RAS for different customers.

A RAS in six months

“Customers see time as money, we now deliver a module in six months,” said Kim David Lid at Sterner. “If you already have a plant, we prefer to look at it before we get started, as a module is not always the best choice.” He said the firm’s customers also have preference, with some wanting to use ozone while others don’t.

“RAS is not rocket science, but never easy,” said Lid. “Some like to build it on their own. It may work if you have experience and expertise in hydraulics, water treatment and biocultures. Working with a fixed concept like the RAS modules has provided us new knowledge, and in a few weeks we’ll deliver our seventh RAS module. The modules are readily designed in different sizes.”

He said the most common mistake is incorrectly calculating the hydraulics, as large amounts of water and large-dimension pipes are needed.

“A Coke bottle looks nice on the table, but if you turn it upside down you will see that it is not designed for quick emptying. These are the things that must work in hydraulics,” said Lid.

RAS-module as delivered by Sterner

Fish Sludge for Fertilizer

Picture: Osland Settefisk

Osland Settefisk invests NOK 12 million in drying facilities for fish sludge in connection with the expansion of the smolt plant. The end product will have high nutritional value and will be used in pelleted fertilizers.

Osland Settefisk at Sørebø in Sogn is one of the country’s oldest fish farming businesses. Established in 1963 and locally owned by the third generation Osland, it has clear ambitions for sustainable operations. In connection with the expansion of the setfish plant, full recovery of the cleaning sludge is planned. The end product, dried granules will go to fertilizer production.

RAS plant
The plant at Sørebø was early in the process of switching to reuse of water (RAS) and collection of effluent sludge. The sludge contains about 90 percent water, and has so far been transported to a sewage sludge treatment. Some have also been delivered to agriculture, after curing with lime.

In order to be able to supply a more robust smolt, the facility is now being further expanded, from an annual production of 250 tonnes to 1,000 tonnes, within a five million smolt license. This is done with RAS technology, where the investment come to NOK 120 million, with full production in the plant in two years.

– A larger smolt provides a better starting point for growth in the sea and less loss of fish, says Kjetil Rørtveit, operations manager at the plant.

More sludge
The expansion will lead to an increase in the amount of sludge, and after careful considerations it has been decided to invest in a plant for drying this sludge into granules.

– Instead of moving large amounts of thin sludge with about 90 percent water, we dry it to over 90 percent dry matter, and then deliver it for agricultural purposes. In line with a circular mindset, we thus treat the sludge as a resource, says Rørtveit.

The thin  sludge is collected during filtration of the waste water from the RAS plant, thickened and dried at low temperature. Thus, the nitrogen that would otherwise evaporate is not lost, and the granulate receives the greatest possible benefit as fertilizer. The fact that it is dry makes it easy to pellet for so-called “smart fertilizers”.

In total, it is estimated that approximately 100 tonnes of dried sludge will be produced annually when the plant is fully operational. Sterner will supply sludge treatment and drying plants, and the plant will be operational in February next year.

– Obviously it is a significant investment, but we choose to see this as part of the whole, we want to operate sustainably and environmentally friendly, then there is no other way to go. Instead of using large amounts of diesel to carry the gross sludge as waste, we choose to use some electrical energy, reduce the volume to a tenth and make it usable. The sludge has a high nutritional value, so we think that this is future-oriented, says Rørtveit.

Operating expenses
Sterner has ensured that the dried granules are retrieved free of charge for Osland Settefisk and that both transport and further use are in accordance with current requirements. Energy costs including cooling will amount to approximately NOK 300,000 per year. Sterner will be responsible for the costs of polymer, large bags and spare parts.

– We chose to go for the simplest solution in the market, where high ease of use and low energy costs have been crucial to the choice. With this solution, operating costs are kept as low as possible. We have good experiences with Sterner from the past, says Rørtveit.

The drying plant will be operational in the spring of 2020, and the investment in the plant will amount to approximately NOK 12 million. The granulate is scheduled to be delivered to Grønn Gjødsel at Rakkestad.

How to Choose an under-counter system

Basic protection

Reverse-osmosis membrane

Reverse-osmosis membrane

Any Aquaphor drinking water system will protect you from chlorine, sediment, lead and many organic compounds. So if you need final water polishing or basic purification any system will provide it. The choice between filtration systems lies beyond just the removal of bad taste and smell.

Dealing with hard water

Excess of minerals (also called hard water) is a concern for many people around the world. You know you have it by limescale build-ups, white stains on glassware and an oily film on the surface of hot drinks. Hard water weakens the joy of having a good coffee, tea or meal, as their taste are severely affected.
The uncompromising solution for dealing with hard water is a reverse osmosis system. It reduces the excess of minerals in water down to the level where it is perfect for cooking and brewing drinks. Aquaphor specialises in producing compact and water-efficient reverse osmosis units, able to cope with a very high water mineralization.

Fighting the invisible threats

Hollow fiber membrane

Hollow fiber membrane

Most dangers in drinking water are not easily spotted: heavy metals, pesticides, medicine or viruses cause harm even in the tiniest quantities and have no taste, smell or color. Here the reliability of the water purifier plays an immense role. All Aquaphor under-counter filters irreversibly trap lead, copper, mercury and other heavy metals.
The best way to protect from any other waterborne threat is a reverse osmosis system that reduces 99.9999% viruses, bacteria, cysts, hormones and antibiotics. The next most effective option is an ultrafiltration drinking water system with a hollow fiber membrane, which provides 99,9% bacteria and cyst reduction.

Technical convenience

Ease of use, maintenance and replacing filters is another point to consider. Aquaphor’s know-how of connecting filters to the housing (“click and turn”) allows easy, simple and quick filter replacement without additional tools and prevents your contact with retained contaminants. All outer parts, including connecting pipes and fittings, are made of durable plastic which will easily resist possible pressure shocks in the water supply system.

The best solution to have exceptional quality drinking water at home is a reverse osmosis system. Note, technical conditions are required, including certain level of water pressure.

*Reduced contaminants may not be present in all users’ water.

Biogas from fish sludge to produce 500.000 kWh per annum

For the first time, sewage sludge from fish farming is used to make combustible biogas. The energy is used to heat the water to the fish. The residue can be mixed in organic fertilizer.

– Has taken time to build up biocultures

It is estimated that about 500,000 kWh per year is possible to extract from a production of nine million smolt. Cermaq uses the gas together with other energy to heat the water so that the fish grows better.

Robert Eliassen.

“It has taken time to build up the biocultures, but now gas is fully produced,” says Robert Eliassen, head of the sludge area at Sterner.

Wastewater from aquaculture is rich in energy, which is now extracted in the form of combustible gas. The biogas production follows sludge production, which in turn results from varying feed consumption during the growth phase of the fish.

– Uses only fish sludge as raw material

Cermaq’s purification plant collects around 260 tonnes of sludge annually, measured as pure dry matter. The sludge is a mixture of faeces and feed spills from 1,600 tonnes of feed annually. The sludge previously represented a challenge both for storage and disposal. Sludge from fish farming differs from other sludge types at a high nitrogen content, which requires a separate bioculture.
– There are many biogas plants in Norway. The unique thing about this plant is that it uses only fish sludge as raw material, says Arne Hjalmar Knap at Sterner, who has been responsible for the development of the technology.

The new plant at Forsan is grafted with a bioculture that is the result of a R&D project and pilot plant at Smøla Klekkeri and Settefiskanlegg. The biocultures have subsequently been cultivated by IMET (Institute of Marine and Environmental Engineering) at the University of Maryland. Enova has supported the development of the technology and the plant at Forsan.

10,000 tonnes of feed or more

The actaal biotechnology is based on a system for biogas production called Anaerobic Baffle Reactor (ABR), and the technology is further developed by Sterner for land-based farming.

Gas burner.

– The economic benefit of this type of sludge treatment will depend on the size of the farm, and plants can be built for 5,000, 10,000 tonnes or larger amounts of feed per year, says Robert Eliassen.

Economically and environmentally, the benefits of the energy in sludge being converted to methane, which can be used for the production of heat or a combination of electricity and heat. Recycling is therefore of great importance in the company’s climate accounts. Another advantage is that the dry matter (TS) in the sludge is reduced by up to 70 percent, so that what needs to be transported away after sludge treatment is considerably reduced.

Perfect Plant for Smolt

The closed concrete fleet retrieves water from 20 meters depth, has filters on the intake water and self-produced oxygen is added as needed. Thus, the smolt will have almost ideal conditions for growth. The goal is to take the fish up to half a kilo in three months.

Managing Director of Engesund Fiskoppdrett, Svein Eivind Gilje and Project Manager for Engesund-merden, Gisle Andre Enstad ahead of the 1000 kbm large pool where about 100,000 fish will be fed up to 0.5 kg in three months. All photos: Pål Mugaas Jensen / kyst.no

A new closed fish farm in the form of a concrete fleet is being transported from Stamneset in Bergen to the Ådnekvamme site in Masfjorden, north of Hordaland. In addition to modern equipment for water treatment, it has a 1000 cubic meter large pool for ingrowing of smolt. Here, the fish will meet ideal conditions for rapid growth without parasites and with stable water quality.
The goal of the company Engesund Fiskoppdrett is to take the fish from the smolt stage up to half a kilo in three months. Making use of large “postmolt” is an increasing practice and is something the company has experience with earlier. Already in 2012, they grew 70,000 fish of 400 grams.

Gisle Andre Enstad has been Engesund’s project manager and takes position as production manager when the fleet will be in operation.

“It went great and we could start slaughtering already after 11 months. That is why this concrete pen is something we have dreamed for a long time, “Gilje told Kyst.no.

The fish from the new fleet will be scheduled every two years respectively in the locations of Duesund or Laberget. The fleet holds 1000 kbm, so with a density at the end of each production of around 50 kg / kbm, it indicates about 100 000 fish per cycle.
“We are excited about this. Experiences from others who have tried postmolt is that this is not always straightforward. This is a pioneering work. But we have good faith in our concept, he emphasizes.

Oxygen generator and storage tanks for oxygen
The concept of Engesundmerden is taken from Backe Bergen’s concrete fleets. Therefore, it is also built by the dry dock at Stamneset, now Backe Bergen is taken over by Bergen Group Sjøsterk. The fleet is funded by Innovation Norway and European Investment Found. The merd is built as a flow-through system.The water is collected from 20 meters, filtered for everything from jellyfish to lice larvae. The pump capacity is 1500 kbm / h. The water is added in one end and is collected in the other. Some of the water is oxygenated and reused, while the other is sent to 5 meters deep.

“We have no filter on the drain, but with the help of a washing robot that is cleaned daily, we get the most of the sludge. The robot will run automatically in the evening after the last feeding, says Enstad.

The merd will be supplied with land flow, but of course, have a unit on board for safety in case of a power failure. “We have counted on energy consumption. It will be about 1.35 kWh per kg of fish, which we believe is at the lower end of such production, he says.

Bernt Solheim shows the filter station for intake water.

To the project, Sterner supplies systems for pumping seawater, filtering of intake water, monitoring of water quality, oxygen production, and oxygen intake. Sterner also supplies automation and water quality control system as required, by pumping and oxygenation.

Calibrating your Handy Polaris

Now that you’ve chosen you Handy Polaris dissolved oxygen meter to help you take accurate DO readings in the water, it’s important to know how to maintain and service your instrument.

OxyGuard’s range of Handy Polaris dissolved oxygen meters (Polaris, Polaris 2, Polaris 2 TGP) are all easy to use and simple to maintain, but there are some basics to help you. Firstly always store your Handy in the storage pouch in a warm, dry room. If you’re using your unit for the first time in a while, it may need to be renovated. This is often seen by a build of white crystals on the tip of the probe.

To renovate your probe, we’ve got a handy view below, but it’s important to ensure you’ve got everything you need fist. To renovate your instrument you’ll need Type 1 Electrolyte and Handy Membranes.

If you’re any questions or queries, you can call our service department on 01463 250275. We also provide a professional and robust service centre for all OxyGuard instruments at our office in Inverness.

Point Four MBD Diiffusers

Oxygen and Air Diffusers

Oxygen and Air Diffusers for Hatcheries and Sea

With summer fast approaching, it’s all the more important to ensure you have sufficient aeration in your tanks or sea pens Having efficient and reliable oxygen and air diffusion is the key to manage your stock and your costs.

At Sterner we have a wide range of ceramic diffusers and our hugely popular RSB6 self weighted rigid diffuser, ideal for sea and loch pens.

Microbubble Diffusers

Pentair Point Four microbubble diffusers use a specially developed, ultra fine pore ceramic plate that produces a cloud of extremely fine bubbles of approximately 100–500 microns; far superior to airstones, porous hose or membrane type designs. The flat plate design ensures uniform bubbles across the entire surface and minimises bubble coalescence to achieve an absorption rate in excess of 80%, depending on depth and flow rate. Bubbling Pressure is 25 to 35 psi. (1.7 to 2.4 bar).

Sterner RSB6

The RSB6 diffuser has been specifically designed to introduce air into farm cages located in open water. It has been built to deliver optimum performance and withstand the harsh conditions of sea water with minimum maintenance. The RSB6 is constructed of a strong, woven polyester fibre material with an operating range of 1.2 – 3.6 cfm and comes complete with 3/8” stainless steel hose tail, making it extremely durable.

The bespoke self-weighted and rigid design of the RSB6 allows for optimum use of aeration in the cage. Compared to previous methods of aeration the RSB6 is extremely efficient at producing bubbles, which creates a curtain effect when the unit is installed horizontally. The deployment and removal of the RSB6 diffusers is straightforward with a bespoke, non-corrosive, fish friendly RSB lifting sling