There- fore, the loading of KH2PO4, MgSO4·7H2O and (NH2)2CO were switched to 0.15 g/L, 0 g/L and 0.34 g/L (Nutrients II), respectively. At the steady state, the K+ concentration was still very high in the effluent because of its abundance in the feedstock. Although no Mg2+ was added, the Mg2+ concentration of 171 mg/L in the effluent demonstrated that its content in feedstock could meet the consumption during fermentation