Phosphorus is an essential nutrient for life of either animals or plants. Nowadays, phosphorus production relies on the mining of a non-renewable source, phosphate rock. Struvite (NH4MgPO4•6H20) crystallization might be an alternative in order to recover phosphorus from wastewaters, especially in streams with high phosphorous concentrations (P> 100 mg/L). Struvite may be used in agriculture as a slow release fertilizer, replacing industrial fertilisers. The formation of struvite is conditioned by thermodynamics and reaction kinetics that are influenced by several physico-chemical parameters such as pH, chemical composition of the wastewater, crystals seed, mixing energy and temperature. The pH range in which struvite may precipitate is in between 8 and 11. High purity struvite crystals may be obtained maintaining adequate operating conditions, even if complex liquid matrices are used as wastewater. Thus, struvite crystallization could offer an appropriate scenario to recover phosphorus in either urban or industrial WWTPs. However, magnesium and alkali requirements are the main factors that might affect the economy of struvite recovery, making the process unviable. The use of seawater or industrial grade magnesium oxide or hydroxide, is being assessed in our laboratory. Both are very cheap magnesium sources. Moreover industrial grade magnesium oxide/hydroxide may provide the alkalinity required to promote struvite precipitation. The impact of Ca ions from seawater on struvite precipitation was evaluated. The different industrial grade magnesium oxide/hydroxide products were evaluated in terms of reactivity or dosing requirements. Previous research allowed the development to our knowledge of the first Spanish industrial scale struvite crystallizer, located in a frozen fish factory.

Projects

Investigación sobre procesos de cristalización de estruvita. Recuperación de fósforo de efluentes residuales complejos para fertilizantes.
Espina & Delfín. (08MDS006E).