Harnessing biofertilizer from human urine via chemogenic and biogenic routes: Synthesis, characterization and agronomic application

This study aimed at recovering nutrients from human urine as valorized products through chemical and biological mineralization, and assessing their fertilizer potential. Chemosynthesis of struvite (MgNH₄PO₄⋅6H₂O) was accomplished from fresh human urine through chemical mineralization using magnesia, whereas biogenic synthesis was achieved through microbial mineralization by employing a wastewater bacterium (Pseudomonas aeruginosa KUJM KY355382.1). Elemental analysis and other characterization results confirmed the synthesized products as struvite under both chemical and biological synthesis methods. The potential of the chemogenic and biogenic struvite products as slow release fertilizer was reflected in improved plant growth characteristics, including height, fresh weight, dry weight, pod length and seed yield, of cowpea (Vigna unguiculata) compared to the control set. Specially, the seeds obtained per plant were 137.71 and 125.14% higher after application of chemogenic and biogenic struvite, respectively, compared to a no-fertilizer control. When assessing aging effect on struvite's chemical structure by comparing a 15-year old struvite crystal with the recently synthesized biomineral, the weathered struvite was found to lose NH₄⁺ however, retain PO₄³⁻ and Mg²⁺, implying its phosphate supplying potential over a long period. Both the chemogenic and biogenic synthesis routes successfully converted human urine to fertilizer (‘waste into wealth’), but the struvite yield was higher in the case of chemogenic synthesis using magnesia (474 ± 9.64 mg L⁻¹) than biogenic synthesis employing Pseudomonas aeruginosa KUJM (345 ± 6.08 mg L⁻¹). Still, the biogenic synthesis is preferred over the chemogenic route because the process is more eco-friendly.