Optimization of Reclaim Nitrogen and Phosphorus from Source-Separated Urine with Orthogonal Array Design

Urine source separation technology is a new concept for municipal wastewater management. With chemical precipitation theory to reclaim nitrogen and phosphorus from source-separated urine, MgCl₂·6H₂O and Na₂HPO₄·12H₂O were used as additives in the experiment to generate the magnesium ammonium phosphate (MAP) precipitation. The factors that affect MAP precipitation are choosed as following: pH, PO₄^3-:NH₄⁺, Mg²⁺:NH₄⁺ and reaction temperature. Under the experimental conditions of reaction temperature=15°C, mixing speed=100 r/min and reaction time=10 min, the effects of pH, phosphate amount and magnesium ion concentration on nitrogen and phosphorous removal were investigated respectively. The optimum reaction conditions were got by orthogonal array experiment such as pH=9.5, Mg²⁺:PO₄^3-:NH₄⁺ =1.3:1.0:1.0, and the experimental results demonstrated that NH₄⁺-N was effectively removed from initial 2850 mg/L down to about 125 mg/L, residual phosphate was about 7 mg/L. SEM and EDS figures indicate that the main precipitate are orthorhombic magnesium ammonium phosphate.