top of page

Seaweed and eelgrass

The problem

Seaweed and eelgrass washed up on the beach constitute both a marine environmental burden and financial challenge, both in Denmark and internationally.


Rotten seaweed is very smelly. When seaweed decomposes it excretes nitrogen that, when returned back into the sea, has a fertilizing and flourishing effect on algae that causes oxygen depletion and disruption of the natural marine fauna.


The smelly seaweed means that fine sandy beaches cannot be used for bathing and other recreational activities. This has a terribly negative impact on both local residents and tourism in the affected areas with economic decline as a result. Therefore, efforts are being made to reverse this trend.


Seaweed and eelgrass washed up on the beach can be removed manually, but this is both time-consuming and costly. Seaweed is often collected and removed by heavy construction machinery, which causes environmental impact to the beach, and also implies that sand is removed from the beach along with seaweed and eelgrass.

Rådden Tang Februar 2020.jpg
Skärmavbild 2021-05-21 kl. 13.56.52.png
From Problem to Resource

Rotten seaweed on the beach is an annoyance, and obviously it is both environmentally and economically attractive if seaweed and eelgrass can be processed industrially, instead of being a waste product expensive to remove.

Today, seaweed and eelgrass are only collected when it can be done from the coast, which means that the seaweed/eelgrass will be mixed with a lot of sand and seashells etc. when removed from the beach, just as the decay will often have begun. The sand must first be washed out with water and the seaweed/eelgrass dried before transport for further processing. Washing out the sand and drying the seaweed typically takes place in a field near the beach, and the process is both time and money consuming.

The collection process can be optimized by guiding the seaweed to suitable collection points and/or by collecting the seaweed at sea instead of waiting for the seaweed to hit the shore, where it mixes with sand and begins to rot.

You can read more about the challenges with seaweed and eelgrass in FLEX-FEB's White Paper, which can be downloaded by clicking here (currently in Danish only).

“Seaweed Guiding”

Seaweed guiding can be implemented for two different purposes. Either you can try to guide the seaweed to a preferred collection point ashore, or you can try to collect the seaweed at sea by guiding the seaweed/eelgrass to a Flexible Environment Barge.


Collection ashore

The collection process can be streamlined and the environmental impact from heavy construction machinery reduced if it is possible to guide the seaweed to selected collection points ashore. At the same time, it will be possible to keep the beaches free of seaweed and support the recreational use of the beach areas.


The seaweed can be guided to collection points with floating booms or with a fixed construction/barrier.



Collection at sea

Collecting seaweed at sea is a very environmentally friendly and attractive solution, as seaweed/eelgrass does not rot and decompose to nitrogen when collected at sea. Resources are saved on the removal of seaweed from the beaches, the impact of driving with heavy construction equipment is also avoided, and there is obviously no need to clean the seaweed from sand. In addition, when seaweed/eelgrass is collected at sea, it will be raw material of higher quality as, and thus better suited for further industrial production.


As far as we know there is currently no capacity developed and built to collect seaweed/eelgrass at sea. This is the reason why FLEX-FEB, in collaboration with Søby Værft (Søby Shipyard), has launched a project to develop, design and build a Flexible Environmental Protection Barge capable of solving this task, and at the same time constitute a functional capacity for collection of oil in the event of an oil spill at sea.


Read more about the project with development, design, and construction of the flexible environmental barge here (currently in Danish only).

bottom of page