PhD defence by Clara Kopp

Recycling phosphorus (P) from waste materials through pyrolysis and incineration could reduce dependence on imports of rock phosphate and facilitate transport of P from regions with P surpluses. However, the P fertilizer effect of biochar and ash derived from these thermal treatments is limited due to a reduced P solubility. The objective of this PhD project was to assess the P availability from ashes and biochars derived from different P-rich wastes and to improve their P availability through different pre- treatment methods. Mainly chemical pre-treatments with sulfuric acid or sodium hydroxide were tested and the (pre-treated) materials were applied in growth experiments with different crops and soils. Differences in P fertilizer values between the materials and influence of factors such as soil pH were found and chemical pre-treatments that effectively increase the P fertilizer value of biochar and ash were identified, contributing to improved applicability and future use of biochar and ash as P fertilizers. 

Senior Scientist Kari Ylivainio, Natural Resources Institute Finland Professor Bettina Eichler-Löbermann, Universität Rostock, Germany Professor Sander Bruun (Chair), PLEN, University of Copen​hagen, Denmark 

Supervisors