The synthetic wastewater was nitrogen-free and its composition is described in Table 2. The medium consisted also of 0.2 g/L MgSO4·7H2O, 0.0251 g/L CaCl2·2H2O, 5 g/L K2HPO4 and 3 g/LKH2PO4 and 1.0 mL/L of a trace elements solution, prepared as mentioned previously.