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Title of the thesis: Vivianite in wastewater treatment plants: Quantification and modelling of the iron – phosphorus interplay toward recovery

Thesis defender: Lobna Amin 
Opponents: Professor Damien Batstone, The University of Queensland, Australia and Scientific Project Manager Thomas Prot, Wetsus, European Centre of Excellence for Sustainable Water Technology, The Netherlands
Custos: Associate Professor Anna Mikola, Aalto University School of Engineering, Department of Built Environment

From phosphorus removal toward recovery in wastewater treatment

Phosphorus is an essential nutrient for food production, but global phosphorus resources are limited. Wastewater treatment plants contain large amounts of phosphorus, yet the main goal has traditionally been to remove it rather than recover it for reuse. This doctoral thesis investigates vivianite, an iron–phosphate mineral that can form spontaneously in wastewater sludge and offers potential for phosphorus recovery.

The study focused on understanding how iron and phosphorus interact in wastewater treatment plants and how these interactions influence vivianite formation. The work combined field sampling at full-scale wastewater treatment plants, laboratory experiments, advanced analytical methods, and modelling. Two large European wastewater treatment plants — Viikinmäki in Finland and Seine Aval in France — were investigated. Previous research has identified vivianite as a promising route for phosphorus recovery, but uncertainties remain regarding how and where it forms and how reliably it can be quantified. This thesis addressed these questions by studying iron transformations and mineral formation in real wastewater treatment systems.

The results showed that vivianite formation begins earlier in the sludge line than previously assumed, already before anaerobic digestion. The study also demonstrated the importance of iron-to-phosphorus ratios, iron-to-sulfur ratios, sludge retention time, and redox conditions in controlling vivianite formation. The research developed a multi-method analytical approach that improved the identification and quantification of vivianite in complex sludge samples. Additionally, a plant-wide model was calibrated to represent iron dynamics and vivianite precipitation. The findings can support wastewater utilities, researchers, and technology developers working on sustainable phosphorus management and circular economy solutions.

Overall, the work provides a foundation for transitioning wastewater treatment from phosphorus removal toward phosphorus recovery, supporting more sustainable and resource-efficient wastewater management in the future.

Key words: Vivianite, Phosphorus, Modelling, Recovery, Sludge, Iron

Thesis available for public display 7 days prior to the defence at . 

Contact information: lobna.amin@aalto.fi;