To validate the results of the orth

To validate the results of the orthogonal experiments,
two further tests with respective Mg:N:P(mol:mol:mol)
of 1.2:1:1 and 1.3:1:1 were conducted with all other
conditions fixed at those determined at optimum. The
residual NH4
+
-N and PO4
3−
-P concentrations were 251
and25mg/L(1.2:1:1), and 318 and 9.0 mg/L(1.3:1:1),
respectively. Hence, the MAP precipitation could recover
most NH4
+
-N and PO4
3−
-P from stale human urine, and
the NH4
+
-N and PO4
3−
-P recovery efficiency were above
95% and 85%, respectively. Moreover, the two precipitates
with the presence of trace calcium, potassium and sodium
collected revealed similar chemical structure to pure MAP
(Table 4). The XRD analysis also confirmed that the
precipitates were mostly pure MgNH4PO4·6H2O (Fig.4).
Since the NH4
+
-N concentration is higher than PO4
3−
-P
concentration in stale urine, the higher NH4
+
-N removal
rate could only be obtained at more chemical doses of
MgCl2·6H2OandNa2HPO4·12H2O with NaOH