Long-term operation of a pilot-scale reactor for phosphorus recovery as struvite from source-separated urine

BACKGROUND: The treatment of source separated urine allows for a more sustainable approach to nutrients recovery in actual wastewater treatment plants. Struvite precipitation from urine yields a slow-release fertilizer (struvite) with a high marketable value for agricultural use. Extensive research on struvite precipitation has been carried out at laboratory scale, but there is still a lack of specific knowledge about the operation and key parameters at larger scale and over the long term. The effectiveness of the struvite reactor was assessed, as well as the quality of the harvested struvite in terms of size and composition. RESULTS: The efficiency of recovery of P was maintained at 85-99% for 1 year of continuous operation. Phosphorus was recovered in the form of struvite with purity over 90%. Struvite was harvested as round pellets between 0.3 and 6 mm in diameter, with heavy metals concentration well below the legal limits for fertilizers in The Netherlands. The post-treatment of the reactor effluent yielded almost complete removal (>95%) of calcium and magnesium. A loss of 26±5% of the influent chemical oxygen demand and 16±1% of the NH₄ ⁺-N occurred during the magnesium ammonium phosphate (MAP) precipitation and the post-treatment. CONCLUSION: This work shows how the treatment of source-separated urine by struvite precipitation in a fluidized bed reactor allows for efficient recovery of phosphorus in the form of a potential fertilizer.