New system will turn hatchery waste into fertiliser

Salmon farmer Bakkafrost Scotland has been granted a licence for a treatment system to turn fish waste into fertiliser.

The pyrolysis unit, which turns organic sludge into inert biochar, will be based at Bakkafrost’s hatchery at Applecross (pictured, photo: Euan Myles).

The company said it was an important step in establishing its “circular economy” credentials.

The licence for the pyroliser was granted by the Scottish Environment Protection Agency.

The surplus is a by-product of the wastewater treatment process in the hatchery’s recirculating aquaculture system (RAS) facility. It consists of organic and inorganic solids held in water. The process dries the sludge and turns it into inert biochar which is used as a fertiliser and soil improver, refining the structure and water retention in soils. This process also “locks away” carbon permanently.

In the first stage, hatchery sludge, roughly 97% water, is treated by going through a filter belt. The water content is reduced to about 80% and the dry matter content is increased to about 20%.

The next stage requires the license as it incorporates a pyrolysis unit which dries sludge at about 300°C, generating sludge pellets. These are then heated to 700°C without the presence of oxygen during a pyrolysis process. Heat is effectively absorbed and repurposed inside the system, increasing total energy efficiency. The end product is a biochar which is a material with a high stable carbon content.

Ian Laister, Managing Director, Bakkafrost Scotland, said: “In a RAS facility, substantial quantities of unused ‘waste’ materials are generated, which must be separated from the water circulating back to the fish.

“Traditionally, that material has been considered waste, but technological advancements have opened the door to a more sustainable management process and that must be good news for helping protect our environment.

“All of this is very much in line with Bakkafrost Scotland’s sustainability goals and supports building a circular economy from farm to fork.”

Bakkafrost Scotland’s ambition for its RAS facilities is to reduce waste by 90 per cent, to use 100 per cent sustainable power and to reduce the water used in the process by 90 per cent. Hydro, solar, recycled material, and heat recovery systems will be used to reduce impact on the environment.