Simultaneous recovery of phosphorus and nitrogen from inorganic fertilizer wastewater

Abstract

Conventional method for removal of N and P from industrial wastewater by biological treatment requires a long hydraulic- retention- time (HRT) and strict conditions for protecting the microorganisms. This study focuses on N and P recovery by struvite (MgNH4PO4.6H2O) precipitation method which is a fast chemical process. In order to control the specs of the sample, a simulated wastewater solution was prepared according to the parameters of inorganic fertilizer wastewater. The influence of pH (7-9), Mg/P molar ratio (1-1.6), and N/P molar ratio (1.2-2) in struvite recovery efficiency were evaluated and the obtained struvite samples were characterized using X-ray diffraction (XRD), scanning electron micrograph (SEM). Response surface methodology (RSM) was utilized in Box-Behnken experimental design and data analysis to obtain mathematics for P and N recovery. The XRD and SEM results confirmed the formation of struvite structure with a particle size of about 7-50 micrometers. The obtained struvite contained nutrients N, P2O5, and MgO which can be used directly in fertilizer formulation. The mathematic models for P recovery and N recovery were obtained from analyzing experimental data with p-value <0.05. Basing on the proposed parameters (pH=9, Mg/P=1.4 and N/P=1.2) obtained from the mathematic model, 98% of phosphorous from an actual fertilizer wastewater sample (pH=8.3, N/P=1.2, P=2.98g L−1) can be recovered. The obtained mathematic model and the suggested technical conditions can be applied for simultaneous recovery of ammonium and phosphate from practical wastewater with high concentrations such as in the fertilizer industry.

Keywords

• fertilizer industry
• nitrogen recovery
• phosphorous recovery
• process optimization
• struvite