Towards cost-effective and sustainable phosphorus recovery from sewage sludge ashes using a mining by-product as innovative precipitating agent

Phosphorus recovery from sewage sludge ashes (SSA) via wet chemical extraction followed by precipitation has garnered significant attention to alleviate pressure on natural reserves. This research focuses on the precipitation process at both lab- and small pilot-scale using conventional (NaOH, Ca(OH)2) and innovative (MgO by-product named PC8) precipitating agents with a focus on key process parameters. Laboratory experiments were conducted on leachates derived from mono-incineration bottom ash (BA) and fly ash (FA), employing various precipitation conditions in the pH range 4–10. Results from lab-scale experiments highlighted the role of leachate characteristics on a satisfactory P precipitation. Small pilot-scale experiments validated the efficacy of PC8 in increasing pH and nutrient content in solid precipitates, presenting a promising solution, although dosage optimization is to further investigate. XRD analyses identified cattiite (pH 9.5) and hydroxyapatite (pH 7) peaks in precipitates, suggesting the predominance of amorphous phosphorus. Some preliminary evaluations of the economic and environmental sustainability of the process to conventional ones highlighted the benefits of PC8 use. Overall, this study underscores the potential of innovative approaches for phosphorus recovery from SSA, contributing to sustainable nutrient management practices.