A green method for the simultaneous recovery of phosphate and potassium from hydrolyzed urine as value-added fertilizer using wood waste

Nutrients recovery from source-separated urine offers a benefit of closing the nutrient loops as well as reduces the discharge of nutrients into aquatic environments. This study investigated a green approach by using magnesium-laden biochar (Mg-biochar), which was obtained from wood waste, to simultaneously recover phosphate and potassium from hydrolyzed urine. After recovery, the nutrient release of the nutrient-enriched Mg-biochar (NBC) as a fertilizer product was also evaluated. Langmuir maximum capacities of phosphate-P and potassium were 197 and 175 mg per g Mg-biochar, respectively. The P recovery was attributed to both adsorption and precipitation, whereas the K recovery was only through the precipitation of struvite-K. Consequently, solution pH and ion species were identified as the key to both P and K recovery. The result also showed that the obtained NBC can act as a slow-release P fertilizer other than a fast-release K fertilizer. Finally, the recovery efficiency of phosphate and potassium from ammonium-depleted hydrolyzed urine reached 90% and 37%, respectively, at a Mg-biochar dosage ratio of 0.8%. In general, Mg-biochar shows good potential for the simultaneous recovery of non-renewable resources from urine to value-added fertilizer.