Nitrogen and Phosphorus Removal from Urine by Sequential Struvite Formation and Recycling Process

Recovering nutrients from urine as solid minerals such as struvite can eliminate many hurdles related to the use of liquid urine as fertilizer in the current urine separation systems. The focus of this study has been to increase nitrogen and phosphorus removal efficiencies by developing a struvite formation and recycling process. Struvite crystallization was carried out in urine samples by addition of MgO where 92% of phosphorus as orthophosphate was recovered. In order to optimize the use of calcined struvite in the struvite recycling step, four calcination treatments were tested and calcination at 200°C for 3 h was chosen for further experiments. To remove the remaining ammonia present in urine a struvite recycling step was used subsequently. Through sequential struvite formation and struvite recycling process up to 90% of ammonium nitrogen was successfully removed.