Synergistic resource recoveries of phosphorus and usable water from sewage sludge incineration ash and concrete slurry wastewater

Abstract

The conventional wet process for P recovery from sewage sludge incineration ash (SSIA) demands substantial chemicals (e.g., acids and alkalis for subsequent P extraction and precipitation) and water, causing economic and environmental drawbacks. We minimized them by employing concrete slurry wastewater (CSWW) as alkali and water sources, achieving over 90 % P recovery at pH 7. The P product contained ∼ 12 % P and low metal contaminants, meeting the regulations for inorganic fertilizer. Powder X-ray diffraction and chemical equilibrium simulations revealed that the product comprised hydroxyapatite crystal (HAp) and amorphous CaHPO₄, forming at pH ∼ 4 and partially converting to HAp at higher pH. The supernatant was utilized in subsequent P extraction cycles to conserve water. By-products were assessed for hazard and recycled into cementitious materials, adhering to the zero waste principle. This study exemplifies the synergy between P recovery from SSIA and cementitious material production, transforming wastes into valuable resources.