A pioneer in fish sludge treatment

(picture: Operation manager Morten Strøm (t.v) and technical manager Arne Skorstad. Picture: Flatanger Settefisk)

Today, wastewater is cleaned with a good margin in regard to public environmental requirements, and sludge from the effluent treatment goes to fertilizer in agriculture. But behind these achieved results lies a long story.

In 2010, Flatanger Settefisk received an extended license from 2.5 million smolt to 7.5 million smolt in annual production. What would be the start of something good, instead became a major problem for the smolt producer. With the new license came new requirements for the treatment of wastewater. A condition was laid down for the removal of at least 60 percent dissolved particles and a 20 percent reduction in the organic load to the environment, as well as a requirement for a fjord survey every three years.

"The challenge was that at that time there were no solutions for good processing of the sludge," says Arne Skorstad, Technical Manager at Flatanger Settefisk.


Previously, there was no requirement for particle cleansing, but requirements for safety against escape of fish. The new requirement was to reduce the organic load on level with public sewage treatment plants along the coast.

"It was possible to clean the effluent as the authorities demanded. But it would give us giant amounts of thin sludge with 98 percent water. This would require huge tank volumes, expensive transports and high delivery costs. We also had no good destination for the sludge. In our region at the coast there is only grass and dairy production in agriculture. Spreading it on pastures would end up in a watercourse, like new pollution, " explains Skorstad.

Hard times

Therefore, Flatanger Settefisk had to find a solution on its own, and started working on a diligent search for equipment and processes. There was contact with suppliers to the waste industry and travels both even abroad to look for solutions.

- Nor did SINTEF have experience with this or a solution to our needs. With stringent demands from the authorities over us, I have to say that the period from the expansion of the plant in 2010-2012 until the fall of 2014 was an uncomfortable period in the company's history, "explains Skorstad.

So Flatanger Settefisk decided to become  a pioneer in sludge solutions for fishfarming. Pilot operations were conducted in autumn 2010. A seminar was organized and SINTEF and Bioforsk were linked to the project. This ended in a report in the fall of 2011, but still there was no current technology that seemed good enough or could show success.

"Investing tens of millions og NOK in an insecure solution was not a good option, and we held back, even with a severe pressure from environmental authorities," says Skorstad.

The breakthrough

Just before the company were considering an emergency solution, equipment manufacturer Sterner appeared on the scene.

- Sterner had delivered equipment to us earlier. Now they had taken over the company BioTek, which had expertise in water purification and sludge treatment. We soon realized that they had a solution in the sleeve, and not long after we got a solution outlined. Hope increased, since we knew Sterner as a supplier who takes responsibility and does not give up until one's goal, "says Skorstad.

Three years later, Flatanger Settefisk has a complete solution for sewage treatment and sludge treatment in operation. The solution also allows the company to maintain a good margin for the emission requirements.

"We are pleased that we endured and did not choose something that would only buy us time. We today cooperate with forward-looking farmers and we can today supply nutritious, natural sludge that enriches their soil. After carrying out several tests, we see that our dried fish sludge is a good organic fertilizer that largely replaces the use of industrial fertilizers, says Skorstad.

Invested big sums

Today, 7.5 million smolt is produced at the plant. From a feed consumption of approx. 1000 tonnes you will be left with approx. 120 tons of dried sludge annually. The dried end product is storage stable and can be shipped in full loads when it suits the recipient. The company has delivered dried sludge to several, but today there is a creative grain peasant in Skogn that takes all the organics he can get.

The sludge is classified and approved according to public limit values.

"In the past, we had to pay to get rid of the sludge. Today it is delivered to the benefit of the farmer. There are costs involved in taking responsibility for the environment and we have invested large sums to get here. In the big picture, the price of the sludge actually has no economic significance. What matters is that we have a good solution and that we are well within the requirements for effluent, says Skorstad.

- The ring has ended

The plant was started three years ago and has been operating largely continuously since then. The sewage treatment scheme consists of a thickener, a press and a gentle drying process.

- We walked into this with open eyes and counted on some adjustments along the way. We soon saw that the drying capacity did not hold what it promised on this type of sludge, so we doubled a year ago the capacity of the dryer. It has been an exciting journey, and today we can say that we have a facility that works well, requires modest follow-up and consumes little energy during drying. Heat pump and heat recovery are involved, says Skorstad.

The sludge from Flatanger Settefisk has also been tried blended in organic fertilizer and has received very good feedback. You are experiencing agriculture in the region as interested and cooperative.

- It is rich in nitrogen and phosphorus. Because the sludge is dried slowly keeps the nutritional value. It is also energy efficient, since we use heat recovery, which is most efficient at low temperatures and provides low power billing, which is important in the long run. The content of zinc and cadmium is somewhat high, but not crucial. Plants need zinc. We are in between grades 1 and 2 by public scale and have placed ourselves in class 2 to have a margin. We see no practical limitations for the use of the sludge for agricultural purposes, so the ring has ended, says Skorstad.

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