Recovery of ammonium and phosphate as struvite via integrated hydrolysis and incineration of sewage sludge

Abstract A sustainable struvite production pathway was proposed for the recovery of NH4+-N and PO43−-P from sewage sludge by two different pretreatments. Hydrolysis and incineration of sewage sludge yields NH4+-N rich solution (NH4+-N/PO43−-P of 2.66 in the supernatant) and phosphorus rich sewage sludge ash (SSA), respectively. From the sludge hydrolysate and the leachate of SSA, 88.0 % of NH4+-N and 94.1 % of PO43−-P were successfully recovered as struvite. Spectroscopic and chemical analyses showed that the recovered product had a composition of PO43−-P (12.5 %), NH4+-N (5.3 %), Mg2+ (9.3 %). It also had high struvite content (92.6 %), high P bioavailability (91.2 %), and a very low level of heavy metals to be used as an effective and environmentally friendly fertilizer.