Phosphorus Recovery from Sewage Sludge as Struvite

Abstract

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