Combination of struvite pyrolysate recycling with mixed-base technology for removing ammonium from fertilizer wastewater

Removal of ammonium from wastewater via struvite (MAP) pyrolysate recycling combined with a mixed-base NaOH/Mg(OH)2 technology was investigated, and the phosphate and magnesium concentration in the supernatant were measured. The optimal parameters for acidolysis were a pH of 1; temperature of 120 °C and time of 2 h. The presence of derivatives of amorphous magnesium hydrogen phosphate (MgHPO4), namely magnesium phosphate (Mg3(PO4)2) and magnesium pyrophosphate (Mg2P2O7) were verified by experiment. The ammonium removal ratio in this combined mixed-base technology was 96.8% in the first cycle, 80.6% in the second, and 81.0% after acidolysis. The phosphate and magnesium ions concentration in the supernatant were about 1 mg/L and 40 mg/L, respectively. The grain size of MAP was 1.52 nm without seeding and 1.79 nm with seeding, and the growth rate of MAP was 17.6%.