In Sweden, only about 25 per cent of our sewage sludge is presently being spread on arable land. In order to fulfil the requirements for the recycling of, most specifically, phosphorus from wastewater, sludge usage must increase significantly and without spreading contaminants.
Around the entire Baltic Sea, large quantities of seaweed and algae are cleared from beaches and ports every year. Despite its high nutrient content, most of the material cannot be used as fertiliser due to high levels of heavy metals.
When handling cereals and seeds within agriculture, nutrient-rich residues are produced in the form of, for example, seed crop residues. By reusing these, some of the nutrients that have been taken out of the arable land can be returned.
Each year, approximately 450,000 tonnes of park and garden waste are generated in Sweden’s municipalities. A significant proportion of this material cannot be recycled as it contains too high levels of various contaminants, including heavy metals.
Pyrolysis involves the organic residues being heated in an oxygen-free environment. The material is reduced to biochar while the energy is released at the same time. As part of the process, heavy metals and other contaminants contained in the residues are also separated out.
Cadmium is found in many different types of organic residues. Through the pyrolysis process, cadmium is separated out from the organic material, and as a result, the biochar contains significantly less cadmium than the original residue.
Biochar has a high nutrient and water-holding capacity and can improve both the establishment of plants and the growth in many drought-prone urban systems, which in the long term generates greener and healthier cities.
Modern agriculture has led to a significant general reduction in the humus content of the agricultural land. By adding biochar, which has a high water and nutrient-holding capacity, the fertility of the soils that are depleted is increased, while simultaneously allowing for carbon to be stored.
Biochar improves the water and nutrient-holding capacity of many different types of soil, which can lead to improved growth. Since biochar has a very slow degradation rate, it also acts as a carbon sink in the soil.
The addition of biochar in the sand filter of football pitches improves grass growth and increases the wear resistance of natural grass pitches, to the extent that they can compete with today’s less environmentally friendly artificial grass pitches.
Rest till Bäst is a Vinnova-funded project whose purpose is to develop solutions for managing society’s organic residues and create a much needed beneficial product, while at the same time minimising environmental and climate impact.