In order to assess the impact of the inorganic carbon on the recovery and stability of SNAD process, excessive inorganic carbon was added to the SNAD reactor, which has collapsed due to the nitrate accumulation. The reactor was operated for 36 d under the conditions with a 370%-430% of theoretical inorganic carbon additive, and the effluent nitrate decreased from 12.1 mg/L to 3.47 mg/L under steady-state operation, simultaneously the feature ratio increased from 2.31 to 20.77. Then reduced the inorganic carbon additive to 260%-320% of the theoretical inorganic carbon concentration, the total nitrogen removal load increased from 0.176 g/(L·d) to 0.299 g/(L·d) after 42 d operation, the aerobic ammonia oxidation activity (AOR) and anaerobic ammonia oxidation activity (ANR) also increased from 0.061 4 g/(g·d) to 0.081 1 g/(g·d), and 0.040 6 g/(g·d) to 0.065 9 g/(g·d), respectively. Thus, sufficient inorganic carbon source not only released the problem of nitrate build-up, but also enhanced the activity of AOB and AnAOB.