Research at Karlstad University shows that sludge and ashes as paper mill residues can be used as effective fertiliser. This involves biochar, that is, carbon from organic material returned to the forest and thus closing the cycle.
"Biochar has many beneficial effects on the environment," says Maria Sandberg, senior lecturer in environment and energy systems and research leader for the project. "Our lab experiments show that by enriching biochar we can produce a very effective fertiliser for forest plants. If we bring biochar back to the forest, it will remain stable for a long time. In this way, carbon is bound up and there is less carbon dioxide in the atmosphere, which counteracts global warming."
When trees grow, they absorb carbon dioxide from the air and nutrients as well as base cations from the soil. When trees are felled for pulp and paper production, nutrients and base cations gather in sludge and ashes. A small segment of carbon accumulates in the waste from the purification plant, which purifies the process waste water. By transforming sludge into biochar and mixing it with ashes, among other things, a new type of soil conditioner improvement is produced which can be used in forest nurseries or directly in the forest. When the biochar is returned to the forest, both acidification and carbon dioxide emission can be reduced.
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