Assessment of Recovered Struvite as a Safe and Sustainable Phosphorous Fertilizer

Phosphorus (P) is an essential nutrient for crops. Modern agriculture is dependent on P derived from phosphate rock, which is a non-renewable resource that is becoming increasingly scarce and expensive. Therefore, it is necessary to identify alternative sources of P and develop novel technologies for its recovery. Such technologies are increasingly focused on the recovery of struvite (MgNH4PO4·6H2O) (STR) from urban wastewater. A reduction of P in effluents decreases the risk of eutrophication while allowing this mineral to be recovered and reused. Here we applied STR recovered from urban wastewater to three different soils and examined its slow-release properties. We performed a soil column leaching study and compared the results of soil treated with STR with those of soil amended with conventional phosphorous fertilizers, namely NPK, ammonium phosphate (MAP), and superphosphate (SSP). Phosphate leaching capacity followed the order MAP ~ NPK > SSP > STR in the three soils and was consistent with its rate of water solubility. Analysis of the soils after the leaching process showed differences in available P, the highest content being found in soils treated with STR. The results were consistent with those obtained in the leaching assay. STR behaves as a slow-release fertilizer and reduces the risk of eutrophication compared to the conventional P fertilizers tested.