Environmental legislation on waste management coupled with the potential for nutrients recovery are key factors encouraging the use of advanced treatment technologies to manage biosolids waste. In this context, phosphorus recovery from a sewage sludge treated by a wet oxidation process was carried out. High organic matter (up to 85% in COD) and Total Solids content (up to 75%) removal values were achieved at elevated temperature (up to 300 ºC) and pressure (up to 200 bar) conditions. The liquid and solid fractions found in oxidation process effluent contain amounts of phosphorus that can be recovered. This research aims to maximize its valorization in both liquid and solid fractions. In the liquid effluent, phosphorus was recovered (up to 90 mg P L-1) by chemical precipitation as struvite (MgNH4PO4∙6 H2O), a slow-release fertilizer. In this case, P recoveries greater than 95% were achieved. Also, the solid fraction, analyzed after filtration and drying (68 mg P gsolid-1), was treated by acid leaching, to achieve up to 60% phosphorus recovery. All phosphorus extracted was in orthophosphate form.

The impact of nutrients on the environment, particularly on water bodies, has led to extensive studies for nutrient control. Within this context, studies have been focused on source separation of human urine from domestic wastewater to recover nutrients. Potassium is one of the most important components of human urine. However, data on potassium removal or recovery are quite limited except for some indirect information through use of zeolites for mostly ammonia removal. Potassium struvite or K-struvite (MgKPO₄·6H₂O) is a sparingly soluble salt belonging to struvite and has the potential of being used as a means of potassium and phosphate recovery from segregated human urine. This study aimed to assess the potential of K-struvite precipitation for control and recovery of nutrients. Within this context, K-struvite precipitation experiments were performed on both synthetically prepared samples and synthetic human urine solution to determine effect of operation parameters i.e. pH, stoichiometry, and temperature on potassium recovery performance. Results indicated that process performance as well as type of solid phases co-precipitated with K-struvite were closely related to initial potassium concentration, pH and reaction stoichiometry. At pH 10, the potassium recovery efficiency was maximized up to 87% by application of 100% excess dose of Mg and P for both synthetic samples and synthetic human urine solution. On the other hand, application of excess dose of K did not provide any improvement in K recovery efficiency. The effect of temperature on solubility of K-struvite was insignificant at the temperature of 24-90°C. Solid phase analyses confirmed that K-struvite was co-precipitated with either Mg₃(PO₄)₂, MgNaPO₄·7H₂O, or MgHPO₄·7H₂O depending on pH and stoichiometry instead of a pure compound.

Materials based on Mg2+-containing phosphates are gaining great relevance in the field of bone tissue repair via regenerative medicine methods. Magnesium ions, together with condensed phosphate ions, play a significant role in the process of bone remodeling, affecting the early stage of bone regeneration through active participation in the process of osteosynthesis. Here we pro-vide a comprehensive overview of the usage of biomaterials based on magnesium phosphate and magnesium calcium phosphate in bone reconstruction. The role of magnesium ions in angiogene-sis, an important process associated with osteogenesis, is considered. Finally, the biological properties of magnesium phosphates for bone regeneration are summarized. They show promis-ing results in terms of use as bone replacement material.