Electrochemical Precipitation of Struvite in Acidic Environment

Abstract

Phosphorus is a key element of fertilizers required for the food production chain worldwide. However, its global supply is limited to phosphate rocks, which is a non-renewable resource expected to last 50 to 300 years. Nutrients recovery from phosphorus-rich wastewater streams is a promising solution to conserve this valuable resource. It will also contribute to the sustainability of the commercial fertilizers’ production globally, by reducing the overall demand for new phosphorus sources. In this study, phosphorus from synthetic wastewater has been recovered electrochemically in the form of slow-release fertilizer known as struvite, magnesium ammonium phosphate hexahydrate (MgNH4PO4 .6H2O). The effect of two different types of sacrificial anodes (pure magnesium vs. AZ31 alloy) as the magnesium source on the electrochemical production of struvite were compared. Precipitates on the surface of the anode, cathode and the bulk solution were fully characterized in terms of elemental composition, structure, crystallinity, and morphology of the particles. The effect of temperature on open circuit potential was investigated with detailed characterization of anode surface. In addition, the ratio of faradaic vs non-faradaic precipitation of struvite was evaluated at different temperatures. The preliminary data on a single-compartment reactor containing 0.077 M dihydrogen ammonium phosphate resulted in a phosphorus and nitrogen removal of 38.8 ± 6.8 wt% and 16.0 ± 5.8 wt% respectively, for the experiments conducted with pure magnesium anode compared to that of 31.6 ±0.5 wt% and 7.7 ± 0.9 wt% in the case of AZ31 alloy. This study is the first of its kind to compare the production of struvite in an acidic environment without any pH adjustments.