Robustness of the anammox process at low temperatures and low dissolved oxygen for low C/N municipal wastewater treatment

•Excellent nitrogen removal was achieved at 30-15℃ and low DO (0.2-0.5 mg/L).•TINinf, TINeff, and NRE at 15℃ were 73.7 mg/L, 7.8 mg/L, and 89.4%, respectively.•Anammox offsets the low temperature effects on nitrification and denitrification.•Abundance, activity, and expression of the biofilm AnAOB were increased at 15°C.•Double nitrite supply guaranteed the stability of anammox at 15-30℃.