PhD defence by Josephine Elisabeth Kooij
Phosphorus (P) speciation of sewage sludge biochars and their potential to improve P fertilization in agricultural systems
Recovering phosphorus (P) from sewage sludge through pyrolysis can decrease reliance on imported rock phosphate while potentially creating a less contaminated, carbon-rich P product. However, P dynamics of sewage sludge biochars upon addition to different soils, as well as their ability to provide consistent P fertilization to varying crops remains unclear. The aim of this PhD project was therefore to i) investigate the effects of pyrolysis of sewage sludges (treated with and without chemical phosphorus removal) on P speciation, ii) assess the resulting biochar’s P plant availability, iii) determine the resulting biochar’s P release, mobility and leaching upon addition to different soil types and iv) evaluate the possibility of integrating sewage sludge biochars in current cropping systems, specifically via investigating the strategies used by different cover crops to solubilize less labile P fractions in sewage sludge biochars.
The effects of pyrolysis on the P speciation of the materials, as well as their fertilizer value, was largely related to original treatment of the sewage at the wastewater treatment plants, whereas pyrolysis temperature didn’t have as large an effect. None of the biochars demonstrated significant mobility of labile phosphate in soils and did not pose a greater threat to leaching than unamended controls in the presence of growing ryegrass. Additionally, the extent to which different crops can solubilize and make use of P within sewage sludge biochars varies and is dependent on their adaptations to enhancing P mining. Overall, the findings throughout the PhD improve the collective understanding of the P speciation and P fertilizer value of sewage sludge biochars.
Assessment Committee
Professor Lars Stoumann Jensen, PLEN, University of Copenhagen, Denmark
Senior lecturer Helena Aronsson, Swedish University of Agricultural Scienes, Sweden
Professor Peter Sørensen, University of Aarhus, DK
Supervisors
Associate Professor Dorette Müller-Stöver, PLEN, University of Copenhagen, Denmark
Professor Sander Bruun, PLEN, University of Copenhagen, Denmark
Associate Professor Jakob Magid, PLEN, University of Copenhagen, Denmark
Time & venue
Thursday 10 April 2025 at 13:00
CPSC Auditorium, A2 11.01
Thorvaldsensvej 40, Frederiksberg
The defence is followed by a reception in meeting room R322/23 on 3rd floor
Everybody is welcome