The Trelleborg Concep

By Fredrik Gröndahl and Mattias Müller

The Baltic Sea is a basin under a great environmental stress. Over time, the natural factors, that have rendered the sea sensitive to environmental alterations, in combination with the human activities have altered the sea conditions. During recent years the altered conditions have developed into severe environmental problems. At present, eutrophication against a background of climate change and organic pollution is the most serious environmental threat to the Baltic Sea.

The increased nutrient load stimulates the growth of filamentous macro algae such as the red algae Polysiphoniafucoids and the green algae Eneromorpha sp. and Cladophora rupestris. The algae form a large bio mass in shallow waters and also accumulate on beaches, especially in southern Sweden. The algae prevent the beaches being used for recreation and also release an unpleasant stench to the surroundings. The changes in the local ecosystem, with large important feeding and reproduction areas for fish and birds becoming non-functional are the other problems associated with macro algae. In the brackish Baltic Sea proper, noxious blooms of Cyanobacteria are a common phenomenon. High input rates of phosphorus (P) relative to nitrogen (N) favour the growth of nitrogen-fixing Cyanobacteria. Long-term monitoring data show the highest abundance of Cyanobacteria in the southern part of the Baltic Sea. The toxic Cyanobacteria Nodularia spumigena in particular has attracted its share of media attention. These bacteria form massive, poisonous blooms on the surface waters, polluting swimming and recreation areas along the coast.

The municipality of Trelleborg, which has Sweden's richest soils and thus very extensive farming, aims to serve as a model for sustainable development in the southern part of the Baltic Sea Region. Together with local farmers and landowners, Trelleborg will establish large-scale biogas production based on new wetlands established along the coastal zone of southern Sweden. Growth and harvesting of bio-energy (e.g. reed belts and submerged vegetation) will take place within these wetlands. Trelleborg will use the biogas for transportation fuel, heating of domestic houses in urban areas and local production of electric power.

The nutrients reaching the coastal waters of the southern Baltic from other sources, e.g. traffic or sewage treatment, and from other geographical areas will be removed with new technology for collecting macro algae from the sea. The biomass collected will be used for biogas production. The digestor residues from the biogas plant can contain heavy metals but there are existing techniques to remove these metals from the residues, which can then be used as fertiliser on arable land, resulting in nitrogen and phosphorus recycling.

During summers with extensive blooms of Cyanobacteria, surface accumulations of Nodularia spumigena will be harvested and used for biogas production. However, the residues will not be suitable as an agricultural fertiliser since they may contain toxic substances.

In addition to the establishment of wetlands in the coastal area and harvesting of algae, aquaculture of the blue mussel Mytilus edulis may be a way to indirectly remove nutrients from the Baltic Sea. Mytilus edulis is very efficient at filtering and removing micro algae from the water column. Several successful trials of this method have been conducted on the west coast of Sweden, but may also be useful in the Baltic Sea.

All these new means to remove nutrients from the highly eutrophied Baltic Sea in a low-intensity but steady process could bring about a much needed reversal in nutrient flow if they were to achieve widespread use among the member cities of the UBC. The Trelleborg Concept of transforming a problem into a resource by preventing eutrophication through biogas production has a number of benefits for the environment in the region, but also has a global perspective:

• Biogas means less CO2 and is thus an important  contributor to  decreasing climate change.
• The establishment of wetlands will stimulate biological  diversity in the region and will deal with the nutrient load from surrounding farm land.
• Harvesting of the reed belt will remove the nutrients from the wetland area.
• Harvesting of macro algae will remove nutrients and heavy metals from the Baltic Sea and improve local beaches for recreation purposes.
• The removal of Cyanobacteria will remove nutrients from the Baltic Sea, but perhaps the most important contribution is that it will improve recreational value in the region.
• When the shallow coastal waters are cleansed from  oxygen-depleting,  decaying accumulated macro algae, large areas will again become available to sustain the growth of juvenile fish.

The concept will also serve as a basic model for how environmental problems around the Baltic Sea can be solved. Partners from several Baltic Sea countries (e.g. Poland, Germany and Russia) are also associated with this new project concept.