The study aimed at solving the instability of shortcut nitrification-denitrification through real-time control strategies. The results showed that excess aeration (aeration was still on after nitrosation) had an adverse impact on the stabilization of shortcut nitrification-denitrification, with nitrosation ratio (NO(2)(-)-N/NO(x)(-)-N) decreasing from 96% to 29% after excess aeration for 13 cycles, indicating that excess aeration was prone to change nitrification modes from shortcut nitrification to full nitrification. By using real-time control, shortcut nitrification and full nitrification were clearly detected by characteristic points on ORP and pH curves. Thus, aeration was stopped once nitrosation was completed, and shortcut nitrification-denitrification was maintained with nitrosation ratio (NO(2)(-)-N/NO(x)(-)-N) higher than 96%. The study showed that real-time control strategy could prevent excess aeration and achieve stable shortcut nitrification-denitrification. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.