Cadmium (Cd) is toxic to nitrifying bacteria, but current studies on recovery process in Cd-inhibited activated sludge system are limited, especially on intensify-recovery processes with developing and optimizing nontoxic bio-accelerators. In this study, bioactivity recovery effects were demonstrated with respect to effluent NH4+-N, NO2-N, NO3-N concentrations, specific oxygen uptake rates and cadmium distribution in five parallel SBRs. Results indicated that bioactivity of nitrifying bacteria was mainly inhibited by surface-bound Cd. Dosing biotin, L-aspartic acid and cytokinin simultaneously was the most effective. Linear chain, together with amide (NH) and carboxyl (COOH) groups, may be important factors in fast nitrification recovery process. In terms of dosage and dosing mode, six-multiple dosage of optimal mixture with dosing at each cycle evenly was the most effective and bioactivities of nitrifying bacteria could 100% recovered within 7 days. The bio-accelerators and optimum usage can be potentially applied to cope with heavy metal shock-loading emergency situations. (C) 2015 Elsevier Ltd. All rights reserved.