Nitrogen and Phosphate Recovery from Source-Separated Urine by Dosing with Magnesite and Zeolite

There is increasing interest in source separation and treatment of urine so as to recover nitrogen and phosphate more efficiently than treating combined wastewater. Although previous studies primarily focused on struvite precipitation for the recovery of phosphorus, the composition of urine changes during storage. The present study compared the precipitation conditions for fresh urine and hydrolyzed urine. The optimal conditions for struvite crystallization were obtained from orthogonal experiment and single-factor optimization. The pH of fresh urine should be adjusted to around 9.5-10.0 to make the reaction thorough, while this was unnecessary for hydrolyzed urine. To reduce cost, magnesite was selected as an alternative for pure MgO, which presented similar efficiency for phosphate recovery. About 92.4% of phosphorus and 87.2% of ammonia-nitrogen were recovered from urine when adding 2.5 g/L of magnesite and 375 g/L of zeolite to get struvite crystals and nitrogen-rich zeolite as a slow-release fertilizer.