Author: Brenda Ochola (SEI)
Nutrient run off into the Baltic Sea has had major ecosystem impacts, affecting fisheries and recreation. To tackle the problem, the BONUS RETURN project has been testing circular solutions to capture and reuse excess nutrients. Find out how below.
The Baltic Sea is one of the most nutrient-affected water bodies in the world. This is partly due to human activity – the Baltic Sea Region is home to 90 million people, along with industries and vast agricultural areas; and partly geography – the Baltic Sea is almost completely enclosed, meaning pollutants that enter it tend to accumulate. Despite significant reductions in the use of chemical fertilizer in recent decades, it is yet to reach a healthy ecological status.
Eutrophication – the excessive richness of nutrients in water bodies – is caused mainly by run-off of nitrogen and phosphorus from agriculture. The resulting seasonal algal blooms and oxygen depletion in the Baltic have had major ecosystem impacts, affecting fisheries and recreation.
Phosphorus is an essential fertilizer for ensuring food security. The current use of phosphate is predominantly linear – from phosphorous-rock mining, to fertilizer production, to agriculture, and finally to food consumption, with the excess phosphorous used in agriculture ending up in soil and run off. The negative impacts of eutrophication, and the limited global commercial phosphorous reserves together make a powerful case for creating a circular economy for phosphorous, especially in populated drainage basins like the Baltic Sea Region.
The BONUS RETURN project has been testing solutions to capture and reuse excess nutrients to promote recycling. Circular solutions can decrease both the dependency on mined phosphorus for food production and the total inputs of phosphorus, which would ultimately improve the ecological state of the Baltic Sea.
The BONUS RETURN project has also been working in three catchment areas in the Baltic Sea Region: Vantaanjoki in Finland, Slupia in Poland and Fyrisån in Sweden, exploring ecotechnologies to reduce, recycle and reuse biomaterials in wastewater and agriculture.
The River Vantaanjoki flows through Helsinki into the Gulf of Finland in the Baltic Sea. Phosphorous runoff from farms in southern Finland is the largest threat to water quality and living marine resources in this area of the Baltic. Decades of attempts to reduce this runoff through traditional farming methods have proven inadequate.
The Vantaanjoki case study shows that gypsum – a by-product of mined phosphorous fertilizer production in Finland – when added to fields offers a way to adsorb phosphorus before it ends up in run off.
Image: Igor Grochev/ Shutterstock
In the Slupia River basin, BONUS RETURN is testing how changes in land use and sludge management could affect the flow of nutrients to the river. Słupia is a mountain river in northern Poland, and a tributary of the southern Baltic drainage area.
The project is working with the Słupsk Wastewater Treatment Plant (WWTP), which has a 20-year track record of success in pollution reduction, sludge composting and reuse, and biogas energy production. In addition to the sludge being a potential source of energy, it contains nutrients and organic matter for agriculture. Because of this, farmers have been fertilizing their fields with sludge and the composted form “BIOTOP” for decades – an early example of a circular system.
Image: SEI
The question of how to make the best use of sewage sludge while preventing hazardous substances from reaching land and water bodies has been repeatedly discussed. In 1945, Uppsala was one of the first cities in Sweden to build a centralized sewage system, and since then, there have been various efforts to recover nutrient and carbon resources from sewage sludge.
In 2018 an inquiry was set up by the Swedish Government to explore a possible ban on the practice of spreading sewage sludge on croplands, and to set new requirements for recycling phosphorus from the sludge. The inquiry reported its findings in January 2020 and recommended two alternatives: 1) a complete ban on all agricultural and other reuse options, or 2) a limited ban on reuse, allowing sludge to be spread on farmland if it meets strict quality standards. It also recommended a 60% limit for recycling of phosphorus from wastewater treatment plants in cities with at least 20 000 inhabitants.
These recommendations would impose significant costs on Swedish municipalities, which are responsible for wastewater management.
