Struvite pellet crystallization in a high-strength nitrogen and phosphorus stream

Struvite crystallization is a reliable method to recover nutrients from wastewater. Laboratory-scale experiments were conducted to investigate nutrient recovery from synthetic wastewater with high-strength orthophosphate and ammonia-nitrogen by the formation of struvite pellets. Without adjusting pH, struvite crystal growth environment was achieved in ammonia-nitrogen and orthophosphate concentration ranges of 100–1,000 and 221–2,214 mg/L, respectively. The mean size of the harvested struvite pellets was in the range of 3–4 mm. pH is an important factor indicating the process supersaturation. A range of pH 6.2–9.0 was tested in order to enhance nutrient removal efficiency. The results showed although higher N, P and Mg removals were achieved at higher pH values, over 95% N, P and Mg removals were still achieved at pH of 7.6. Recycling ratio of the clarifier supernatant to influent had no significant promotion of N or P removal.