Alleviating Na+ effect on phosphate and potassium recovery from synthetic urine by K-struvite crystallization using different magnesium sources

• Published in: The Science of the total environment Vol. 655; pp. 211 - 219
• Main Authors: Huang, Haiming, Zhang, Dingding, Wang, Wenjun, Li, Bing, Zhao, Ning, Li, Jing, Dai, Jiankun
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.03.2019
• Subjects: K-struvite crystallization; Magnesium source; Phosphate; Potassium; Potassium; Phosphate; K-struvite crystallization; Magnesium source
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.11.259

Human urine is characterized by high concentrations of nitrogen (N), phosphorus (P) and potassium (K), of which the P and K can be recovered as K-struvite crystals. This study first investigated the formation of Na-struvite because of the high Na+ present in the urine. From the results, the optimal pH for the Na-struvite crystallization was observed to be 12, and the rise in the Na+ concentration distinctly favored the Na-struvite formation. As magnesium needed to be added to induce the K-struvite crystallization, several magnesium sources including MgCl2, Mg sacrificial electrode and Mg(OH)2 were applied to recover P and K from synthetic urine. The findings indicated that when MgCl2 was used as the magnesium source, the K removal could be slightly enhanced by prolonging the reaction time, which would correspondingly decrease the Na concentration in the precipitates; besides, the intermittent addition of MgCl2 could noticeably improve the removal efficiency of K by 6%, but simultaneously raise the Na content in the precipitates recovered. With respect to the use of the Mg sacrificial electrode, the recovery efficiencies of the P and K from synthetic urine were close to those with the use of MgCl2. However, when Mg(OH)2 was used as the magnesium source, the recovery efficiencies of P and K achieved only roughly 50%, which was much lower than those noted when MgCl2 and the Mg sacrificial electrode were employed. A comprehensive analysis revealed that the MgCl2 was the best magnesium source for the K-struvite crystallization, followed by the Mg sacrificial electrode and Mg(OH)2. [Display omitted] •Various Mg sources were applied for the K-struvite formation in synthetic urine.•The optimal pH for Na-struvite crystallization was 12.•Increasing reaction time could reduce the effect of Na+ on K-struvite formation.•Using soluble Mg source in K-struvite crystallization was the best.•Soluble Mg source was the most suitable for the recovery of K and P from urine.