Effects of the presence of metal competitors on the formation of struvite recovered from nutrient-rich wastewater using air cathode electrocoagulation technology

This study examined the effect of metal competitors on the formation of struvite recovered from nutrient-rich wastewater. The metal ions studied in this research were Ca²⁺, Fe³⁺, and K⁺. The concentration of Ca²⁺ in wastewater varied based on the molar ratio of Ca: PO₄ ranging from 0 (without Ca metal), 0.5, 0.6, 0.8, and 1. Variations of Fe³⁺ were 5 ppm, 10 ppm, 30 ppm, and 50 ppm. Variations of K⁺ concentration were based on N: K molar ratios of 0.75, 1.8, 3.45, and 5. Variations containing all three types of metal simultaneously were also carried out in this study. The study was conducted by measuring the removal efficiency and removal rate of nutrients, and analysing characteristics of the precipitate using SEM-EDS and XRD. The results showed that the presence of Ca, Fe, and K in solutions reduced the efficiency of ammonium removal, inhibited struvite formation process, and reduced the amount and purity of struvite produced. The presence of Fe³⁺ had the greatest effect compared to the other two metals. The presence of Ca, Fe, and K simultaneously in solution caused extremely low ammonium removal efficiency. Metal competitors affected the precipitate produced by reacting with constituent ions, forming other types of minerals besides struvite, and were also incorporated into the struvite formed.