Phosphorus Removal and Recovery from Human Urine with MAP Crystallization
MAP 结晶法回收和去除尿液中的磷

To realize the simultaneous removal and recovery of phosphate and partial nitrogen from stale human urine, a series of lab-scale jar tests, adopting MgCl2?6H2O as precipitator, were conducted to study the influence of the mole ratio of Mg/PO43--P, pH, mixing speed, reaction time and precipitation time on MAP precipitation. The experiment results showed that the mole ratio of Mg/PO43--P was found to be a very important operating parameter to affect phosphorus recovery efficiency. When the mole ratio of Mg/PO43--P was above 1.3:1, the phosphorus recovery efficiency was above 95% and the residual phosphorous was less than 10 mg/L in the solution. Increasing pH with 10 mol/L NaOH solution could not increase the recovery phosphorus efficiency obviously. Without pH control, the optimal parameters of reaction time, precipitation time and mixing speed could be set at 20 min, 2.0 h and 120 r/min, respectively. To reveal the chemical characteristics of MAP products from human urine, three MAP product samples, with no pH adjustment and under the above optimal operation condition, were obtained at different Mg/PO43--P mole ratios of 1:1, 1.3:1 and 1.5:1, respectively, and analyzed with SEM, XRD and ICP instrumentation. These precipitates were identified as nearly pure struvite (12.62% of P, 5.70% of N and 9.91% of Mg) with the presence of trace calcium, potassium and sodium. The contents of phosphorus, nitrogen and magnesium in the precipitates were 13.54%, 5.34% and 9.01% (Mg/PO43--P =1:1), 13.78%, 5.23% and 9.36% (Mg/PO43--P =1.3:1), as well as 13.34%, 5.12% and 9.15% (Mg/PO43--P =1.5:1), respectively.