Will dried sludge from fish farming become a contributor or competitor to the utilization of municipal sludge?

Rohold, L., Scanship, Norway



Production of Nordic Salmon has become an industry with continuous growth and the aim to exceed oil
and gas in terms of Norwegian export value in 2030.

This rapid growth in a traditional farm based production has required need for regulations and technical
solutions in order to handle both waste water treatment and sludge handling.

Scanship has successfully transferred technical solutions from waste handling at cruise ships to the
land based fish farming. The solution is dewatering and drying of sludge to a stable bi-product. This will
reduce transport cost and make it possible to store the product over longer periods in the remote fjord
areas of the Norwegian west coast.

As part of the solution Scanship has established collaboration with end users for the reuse of sludge as
a bi-product. The different areas where the bi-product has become a value are within fertilizer, biogas
and incineration.

The nutritious rich product with high energy content makes it a high-quality biproduct

Fish production in Norway has changed from being family owned production facilities to be larger and
more industrialized facilities. The industrialization has resulted in fish production controlled by larger
companies like Marine Harvest, Lerøy and Salmar etc. in addition to the individual producers. The first
part of the fish production starts in land based hatcheries where fish traditionally has been grown from
eggs to smolt at a size of 90-120 gram (Blytt et al 2011), before it goes to open sea cages. The challenge
with sea lice and expensive license for growing fish along the Norwegian coast has been some of the
drivers for larger size of fish that are produced in the fish hatcheries to 250 gram and even larger with
some plants aiming for fish at 1 kg (Hægh 2017) and (Ilaks. 2017a). The size of plants has changed
from production facilities of 1000-2000 ton biomass per year to 5000-10.000 ton biomass per year for
new plants which can be seen on the license for new facilities that has been granted the last 2 – 3 years.
It has been predicted that the Norwegian aquaculture production will increase 5 times from the level of
2010 to 2050 (DKNVS and NTVA. 2012), giving the challenge of growth for this industry.

The type of technology has changed from type of “Flow Through” plants where water simply runs
through the fish tanks, to plants including recycling of water with internal water treatment in order to reduce the water consumption, commonly known as RAS-technology (Recirculation Aquaculture Systems). The RAS plants typically consist of separation step for particles, biological treatment of soluble organic components, followed by nitrification step. After biological treatment the water is aerated for removal of CO2 and N2, before the water is oxygenized and returned to fish tanks. This treatment produces obviously a large amount of sludge that need to be handled outside of the plant.

The sludge treatment at fish farms has traditionally been considered as separation technology in order
to transport sludge to common facilities. But with increasing size of fish plants the need for logistic and
reuse of sludge has become more and more important. Drying of fish sludge is therefore considered as
a perfect solution for this type of sludge handling.

The increase in fish production the larger capacity of plants and the larger size of fishes produced on
land all contribute to the challenge of reducing the pollution from this growing industry. This has changed
the legislation and discharge permits for the industry and caught the attention from the consumers with
the question what happens with the valuable components in the by product from fish production.
The fish industry has become a sludge producer and handling sludge from fish industry has become an
interesting marked both in terms of technology and recycling of this sludge.

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