Formation of struvite crystals in a simulated food waste aerobic composting process

Bench-scale treatments with three mixtures of Mg and P salts, including K3PO4+MgSO4, K2HPO4+MgSO4, and KH2PO4+MgSO4 as additives in a simulated food waste aerobic composting process, were conducted to test the magnesium ammonium phosphate(MAP) formation, and the compost products were analyzed by X-ray diffraction(XRD), Scanning electron microscopy(SEM), and Energy dispersive X-ray spectroscopy(EDS) analyses. The comparison results between XRD, SEM, and EDS analyses of MAPs in the dried compost and synthesized MAPs confirm the formation of MAP crystals in the simulated food waste aerobic composting process. The analysis of the compost also indicates that the addition of all the three mixtures of Mg and P salts in the aerobic composting process can increase nitrogen conservation and decrease nitrogen loss because of the formation of MAPs. The mechanism of MAP formation was verified as the reaction of ammonium(NH4 ⁺) with magnesium(Mg ²⁺) and phosphate[HnPO4 ^(3-n)-, n=0, 1, and 2).