Nutrient Removal and Recovery from Urine Using Bio-Mineral Formation Processes

Harvesting nutrients from waste presents a promising initiative to advance and deliver the circular economy in the water sector while mitigating local shortages of mineral fertilizers worldwide. Urine, a small fraction of municipal wastewater, holds substantial amounts of nitrogen, orthophosphate (PO₄-P), and chemical oxygen demand (COD). Separating urine aids targeted nutrient recovery, emissions reduction, and releasing capacity in wastewater treatment plants and taps into overlooked vital nutrients like magnesium (Mg²⁺) and potassium (K⁺), essential for plant growth. The ability of selected microorganisms (<i>Brevibacterium antiquum, Bacillus pumilus, Halobacterium salinarum, Idiomarina loihiensis</i>, and <i>Myxococcus xanthus</i>) to remove and recover nutrients from fresh urine through bio-mineral formation of struvite was investigated. The selected microorganisms outcompeted native microbes in open-culture fresh urine, and intact cell counts were 1.3 to 2.3 times larger than in noninoculated controls. PO₄-P removal reached 50% after 4 days of incubation and 96% when urine was supplemented with Mg²⁺. Additionally, soluble COD was reduced by 60%; urea hydrolysis was only < 3% in controls, but it reached 35% in inoculated urine after 10 days. The dominant morphology of recovered precipitates was euhedral and prismatic, identified using energy dispersive spectroscopy and X-ray diffraction as struvite (i.e., bio-struvite), but K⁺ was also present at 5%. Up to 1 g bio-struvite/L urine was recovered. These results demonstrate the ability of bio-mineral producing microorganisms to successfully grow in urine and recover nutrients such as bio-struvite, that could potentially be used as sustainable fertilizers or chemicals.