Simultaneous recovery of phosphorus and nitrogen from sewage sludge ash and food wastewater as struvite by Mg-biochar

The drawback of biochar as a soil ameliorant is its low-nutrient content while the bottleneck of struvite production is its high chemical cost. This drew the idea of using designed biochar for nutrient recovery from nutrient-rich wastewater as struvite. Mg-biochar was used for simultaneous P and N recovery from sewage sludge ash (SSA) and food wastewater (FW) by using ground coffee bean (GCB) and palm tree trunk (PTT) waste. PTT Mg-biochar could recover 92.2% of PO43−-P and 54.8% of NH4+-N while GCB Mg-biochar could recover 79.5% of PO43−-P and 38.6% of NH4+-N. Adsorption, precipitation and cation-exchange mechanisms are involved in the Mg-biochar for the simultaneous recovery of PO43−-P and NH4+-N as struvite. Mg-biochars also showed higher struvite selectivity than the control samples. This method not only supports waste recycling and pollution mitigation but also highlights economical struvite production and the benefits of CO2 sequestration.