Effect of storage on physicochemical characteristics of urine for phosphate and ammonium recovery as struvite

Abstract

Since human urine alone contributes to 90% of phosphorous (P) and 50–70% of nitrogen (N) load to municipal wastewater, retrieval of nutrients in the form of struvite (magnesium ammonium phosphate) from urine has gained much attention as it can act as an excellent slow-release fertilizer for plant growth. The present study aimed to comprehend the effect of urine storage on its physicochemical characteristics for the recovery of ammonium and phosphate in the form of struvite by adding magnesium chloride as an external source of magnesium (Mg). Various influencing factors such as pH, conductivity, salinity, total dissolved solids, and ion concentrations of phosphate, ammonium, calcium, nitrate, sodium and potassium were monitored over a period of 25 days to delineate its role on struvite recovery. The highest yield of 619.3 ± 54.41 mg L−1 of struvite was obtained on day 24. It was found that phosphate and ammonium recovery reached up to 90% with the storage of 25 days. Excessive addition of Mg increased both struvite yield and phosphate recovery (by 20%) but affects struvite purity undesirably due to the formation of struvite analogs. Statistical analysis with Spearman's coefficients revealed that total dissolved solids exhibited a strong positive correlation for struvite yield.