Nutrient Removal\nand Recovery from Urine Using Bio-Mineral\nFormation Processes

Harvesting nutrients from waste presents a promising\ninitiative\nto advance and deliver the circular economy in the water sector while\nmitigating local shortages of mineral fertilizers worldwide. Urine,\na small fraction of municipal wastewater, holds substantial amounts\nof nitrogen, orthophosphate (PO<sub>4</sub>–P), and chemical\noxygen demand (COD). Separating urine aids targeted nutrient recovery,\nemissions reduction, and releasing capacity in wastewater treatment\nplants and taps into overlooked vital nutrients like magnesium (Mg<sup>2+</sup>) and potassium (K<sup>+</sup>), essential for plant growth.\nThe ability of selected microorganisms (<i>Brevibacterium antiquum,\nBacillus pumilus, Halobacterium salinarum, Idiomarina loihiensis</i>, and <i>Myxococcus xanthus</i>) to remove and recover\nnutrients from fresh urine through bio-mineral formation of struvite\nwas investigated. The selected microorganisms outcompeted native microbes\nin open-culture fresh urine, and intact cell counts were 1.3 to 2.3\ntimes larger than in noninoculated controls. PO<sub>4</sub>–P\nremoval reached 50% after 4 days of incubation and 96% when urine\nwas supplemented with Mg<sup>2+</sup>. Additionally, soluble COD was\nreduced by 60%; urea hydrolysis was only < 3% in controls, but\nit reached 35% in inoculated urine after 10 days. The dominant morphology\nof recovered precipitates was euhedral and prismatic, identified using\nenergy dispersive spectroscopy and X-ray diffraction as struvite (i.e.,\nbio-struvite), but K<sup>+</sup> was also present at 5%. Up to 1 g\nbio-struvite/L urine was recovered. These results demonstrate the\nability of bio-mineral producing microorganisms to successfully grow\nin urine and recover nutrients such as bio-struvite, that could potentially\nbe used as sustainable fertilizers or chemicals.