High phosphorus content in wastewater streams leads to eutrophication, therefore they must be treated to reduce environmental impacts. On the other hand, phosphate is a limited mineral on Earth thus an alternative or renewable source such as recovering phosphorus from wastewater should be considered. One potential approach is to recover phosphates by electrochemical precipitation of struvite. Struvite, also known as magnesium ammonium phosphate hexahydrate is considered a premium grade, slow-release fertilizer, which is a potentially marketable product for the fertilizer industry. The effect of pure-Mg versus AZ31 magnesium alloy as the only source of magnesium on anodically-driven struvite precipitation was investigated in a single-cell electrochemical batch reactor, in acidic environment with no pH adjustment. The results showed a crystalline struvite state with smooth sharp edges which indicates a high-quality pure struvite. The elongated needle-shaped pattern had a particle size of ca. 30 µm in length and ca. 6.5 µm in width. In a 6-hour batch experiment, the pure-Mg anode out-performed the AZ31 alloy by producing a 4.5-fold greater mass of struvite, next to a 2.8-fold higher current density. The measured magnesium dissolution rates were 1.2 mg cm-2 h-1 for the pure-Mg and 0.8 mg cm-2 h-1 for the AZ31 magnesium alloy anode, respectively. Overall, in this electrochemical reactor setup, the pure-Mg anode showed a better performance towards the electrochemical struvite precipitation.

Phosphate recovery by electrochemical precipitation of struvite in acidic environment: Pure magnesium vs. AZ31 alloy anode

2019 Fall National Meeting

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