Toxicologia Ambiental e Analítica

Separation of Struvite from Sewerage Water and its Evaluation as Phosphatic Fertilizer

Abstract

Sana-ur Rehman, Ghulam Jilani, Qaiser Hussain, Shahzada Sohail Ijaz, Ahmed Khan, Sajid Mehmood Jamali, Muhammad Irfan, Muhammad Ali Raza, Humair Ahmed Malik and Fayyaz Hussain

Magnesium ammonium phosphate hexahydrate (MgNH₄PO₄.6H₂O), commonly known as struvite is a crystalline mineral of low solubility. In wastewater treatment facilities, separating phosphorus by conversion to struvite could reduce its content in the wastewater. The experiment conducted for local wastewater sources to identify better source and recover struvite for phosphatic fertilizer evaluation. Chemical precipitation through pH elevation and (Mg²⁺:NH₄⁺-N:PO₄^3--P) molar ratio were used to recover NH₄⁺ and PO₄^3- as struvite from sewerage water of different sites. To recover (MAP) magnesium ammonium phosphate hexahydrate from the four different sources, chemicals including MgCl₂.6H₂O+Na₃PO₄ were applied at molar ratio (Mg²⁺:NH₄⁺-N:PO₄^3-P=1.2:1:1) and at different pH ranging from 8.0 to 11.0. Results indicated that maximum P removal was obtained as 87% at pH 10.5 from the source of I-9 sector containing high levels of P. For N results indicated that maximum N removal was obtained as 67% at pH 10.0 from the same source of P removal. In the experiment among various combinations, comprising of Mg:N:P ratio, pH levels and stirring speeds, the stirring speed of 250 rpm for 30 minutes was more desireable for struvite precipitation process. The MAP precipitation significantly reduced the contents of NH₄⁺ and PO₄^3- in sewerage water at different sites. So, it is necessary to develop the optimum conditions for small-scale and commercial production of struvite, because struvite recovery is technically feasible and economically beneficial. Therefore, this technology provides opportunities to recover phosphorus sustainably from sewerage water and preserve phosphorus reserves.