Phosphate Recovery from Incinerated Sewage Sludge Ash by Wet Chemical Extraction and Precipitation

Abstract

Incinerated sewage sludge ash contains significant quantities of phosphorus, making it a valuable secondary resource for nutrient recovery and sustainable waste management. This study investigates the recovery of phosphate from sewage sludge ash through wet chemical extraction followed by precipitation under controlled processing conditions. The research focuses on maximizing phosphate recovery efficiency while minimizing impurity dissolution and secondary waste generation. Experimental analyses were conducted to evaluate the influence of extraction reagent concentration, liquid-to-solid ratio, reaction temperature, extraction time, pH, and precipitation conditions on phosphorus solubilization and recovery performance. Results demonstrated that wet chemical extraction effectively dissolved phosphate compounds present in the ash matrix, enabling efficient separation and subsequent precipitation of recoverable phosphate products. Optimized operating conditions significantly enhanced phosphorus extraction efficiency and improved the purity of the precipitated phosphate material suitable for potential fertilizer applications. Kinetic and equilibrium evaluations revealed that extraction behavior is strongly influenced by ash composition, acid concentration, and reaction temperature. The precipitation process successfully converted dissolved phosphate into stable recoverable compounds while reducing the concentration of undesirable metallic impurities. Comparative assessment with conventional phosphorus disposal practices indicated that the proposed recovery approach offers environmental and economic advantages through nutrient recycling, reduced landfill dependence, and conservation of nonrenewable phosphate rock resources. Furthermore, the integrated extraction–precipitation process supports circular economy principles by transforming wastewater treatment residues into value-added products. The findings highlight the potential of wet chemical phosphate recovery as an efficient and sustainable strategy for resource recovery and nutrient management in wastewater and environmental engineering applications.