ReLEAF paper on Struvite Crystals Obtained from Swine Wastewater and Urban Sewage Sludge Liquid Fraction as Fertilising Product 

ReLEAF partner Leitat valuated how to optimise crystal formation by evaluating different PO₄³⁻:Mg²⁺ ratios on this scienific paper under the umbrella of the project. This article is a summary of the paper with key takeaways. You can find the full paper on our website. 

hashtagvaluated how to optimise crystal formation by evaluating different PO₄³⁻:Mg²⁺ ratios.

Researchers have explored a way to turn two types of waste, liquid from pig farm wastewater and the liquid fraction of urban sewage sludge, into a fertiliser. They focused on producing struvite crystals, which contain phosphorus and ammonium as nutrients important for plant growth. By using these waste streams, the study aimed to increase sustainability in agriculture and reduce reliance on imported fertilisers.  

The study found that the ratio of nutrients used in the process matters a lot: for pig wastewater the best results came when the phosphate:magnesium ratio was about 1:2, while for sewage sludge the best ratio was about 1:1. Differences in other ions, especially calcium, affected how well the crystals formed. Some unwanted compounds formed when interfering ions were present.  

In practical terms, recovering struvite this way could significantly reduce Europe’s need to import phosphorus, a critical nutrient. The study estimates that up to around 6.5% of Europe’s phosphorus imports could be replaced through this process.  

Overall, the research shows promising potential for converting waste into valuable fertilisers, supporting circular economy goals, and helping agriculture become more sustainable. 

Key takeaways 

• • Turning Waste into Value: Scientists found that nutrient-rich waste from pig farms and urban sewage can be transformed into struvite, a natural fertiliser containing phosphorus and nitrogen — two essential nutrients for crops. 

• • Optimising the Process: The success of crystal formation depends on getting the right nutrient balance. Adjusting the ratio of phosphate and magnesium helps produce high-quality fertiliser while reducing unwanted residues. 

• • Reducing Fertiliser Imports: By recovering phosphorus from waste, Europe could replace up to 6.5% of its current phosphorus imports, making farming more sustainable and less dependent on non-renewable resources. 

You can find the original paper in the ‘scientific publications’ section of the website, or at this link.