Phosphorus Removal from Wastewater through Struvite Precipitation

Phosphorus is an essential nutrient to sustain life. With regards to limited Phosphorus resources, recovery and reuse of Phosphorus are necessary. Wastewater usually contains large amount of Phosphorus which could cause severe environmental problems such as eutrophication in water bodies. Thus, recovery of Phosphorus from wastewater removes the excess amount and prevents environmental pollution. The recovered Phosphorus could also be considered as a rich fertilizer and helps to sustainable use of Phosphorus resources. Struvite precipitation is a new method to remove and recover Phosphorus from wastewater. In this method, Magnesium, Ammonium and Phosphate are mixed in specific molar ratios and Phosphorus precipitates as struvite. Generally, struvite consists of 13% Phosphorus, 6% Nitrogen and 10% Magnesium. The precipitated struvite could be reused as slow release fertilizer. On the other hand, addition of chemicals like Iron and Aluminum in order to remove Phosphorus in wastewater treatment plants is costly and also affects adversely the plant availability of Phosphorus. Therefore, struvite crystallization as a no chemical method would increase the efficiency in Phosphorus removal and reuse capacity. In this study, the main goal was to achieve the highest Phosphorus removal from municipal wastewater by means of struvite precipitation. The obtained wastewater and reject water from HIAS wastewater treatment plant were enriched by 189 mg/l and 2220 mg/l PO43--P and NH4-N, respectively. MgCl2 was used as Magnesium source in three Mg: PO4 molar ratios of 0.6, 0.8 and 1.1. Also, two NH4:PO4 molar ratios of 5 and 10 were added into the wastewater. All the experiments were conducted during 20, 40 and 60 minute of stirring with magnet. pH of the solution was fixed at 8.3 by addition of NaOH 2 molar. The results demonstrate that Ortho-P removal from wastewater increased from 78.3% to 92.9% by increasing Mg: PO4 molar ratio from 0.6 to 1.1. Thus, the struvite mass has increased from 443 mg to 528 mg. The effect of different NH4 concentrations and mixing time was not significant regarding Phosphorus removal. Also, the produced struvite through this study consists of 10.5-16.5% Phosphorus and 6-10.8% Magnesium. Furthermore, the effect of different Mg and Ammonium concentrations along with different mixing time had no significant effect on heavy metals concentration except Zink.M-MIN