The Baltic Sea has a large-scale oxygen problem, with a great deal of nutrients stored in the seabed, says Jonas Gustafsson, marine biologist at the Skane County Administrative Board, in a feature on Rapport on 29 January.
Yes, our beloved Baltic suffers from a eutrophication problem. Sweden has so far had two different strategies for meeting this challenge.
The first and perhaps most established is that we should simply choke off the supply of phosphorus and nitrogen running out into the Baltic. This can be done by limiting the number of animals such as horses and cattle, fertilising with less phosphorus and nitrogen, cleaner sewage handling and so on. A reduction in emissions can happen once the nine countries surrounding the Baltic arrive at a common strategy for how it is to be done. Once they have agreed and put the strategy into effect and emissions fall over time, one then waits for the Baltic itself to recover, hopefully, in the long run.
The second strategy is that the problem needs to be dealt with on site. Here there are ideas such as building many wind turbines that pump air down to the oxygen-free seabeds. Cultivated sea cucumbers that somehow convert the environment on the oxygen-free bottoms for the better. Another idea is to spread quantities of aluminium chloride to bind the phosphorus on the bottom. There are more ideas, but they all amount to costs for society and nothing else.
Our idea for the Baltic Sea is more realistic
Our model works by removing the oxygen-free “dead” sediment on a large scale. About 20,000 tonnes per day is entirely possible, and at the same time about 500,000 cubic metres of water can be circulated. That means the oxygen-free bottom water is exposed to air so that it is oxygenated before it is returned to the bottom it came from. Phosphorus, nitrogen, cyanobacteria, heavy metals and so on are removed, and what is left behind is a considerably cleaner seabed that gets the chance to be recolonised by biological life.
Our model works by removing the oxygen-free “dead” sediment on a large scale.
The risk that any important micro-organisms are removed is small, since the harvesting of sediment takes place in strips, so that any living organisms can easily find their way out into the harvested strips. This means a very large operation with large vessels, and an activity that can be likened to the offshore industry. We therefore call it a green offshore industry.
The survey vessel R/V Bothnia Surveyor
A green offshore industry naturally costs a great deal of money to run. This is where our industrial thinking comes into the picture. We have found outlets for the constituent parts of the sediment that will be able to give enough revenue to sustain the operation and give a good return:
- The cement and concrete industry is interested in the silt, since it allows them to lower the proportion of cement and other lime products that today carry a high carbon footprint.
- The organic mass can be digested and made into biogas, which can be further refined into hydrogen. Or a fossil-free carbon powder can be made in a heat process, and carbon atoms are of interest to both the steel and the chemical industries.
- The silicon can be used for manufacturing electronics such as semiconductors, but also for solar cells and much else. Part of the silicon consists of what is called amorphous silicon, and that silicon can be used both to manufacture more efficient solar cells and to be mixed into depleted or sandy soil to increase its ability to retain moisture. With only 3 percent amorphous silicon mixed into soil, the ability to retain moisture increases by almost 200 percent.
Before long we face a shortage of fossil-free carbon atoms. Raw materials such as trees for the production of fossil-free carbon are no future, since the trees have to remain standing to bind carbon dioxide. Kitchen waste gives perhaps 500,000 to 600,000 tonnes of digestible mass per year, but many municipalities today make biogas from it for their buses. The chemical industry in Sweden alone needs 8 million tonnes of carbon per year.
