Abstract: At normal temperature of(19 ±1) ℃,without the addition of external carbon sources,simultaneous nitrification denitrification via nitrite(SND via nitrite) was studied in a lab-scale SBR treating domestic wastewater with low ratio of carbon to nitrogen.The results showed that under the long sludge retention time(SRT) of 50~66 d and limited aeration with the maximum ρ_DO below 2.0 mg/L and the average ρ_DO of 0.65 mg/ L,partial nitrification to nitrite was successfully achieved with ρ(NO₂^--N) /ρ(NO_x^--N) over 95%.Moreover,denitrification occurred during the above aerobic nitrification phase.The average ρTN removal efficiency by SND via nitrite maintained 52%,and the maximum was up to 63.1%.The low ρ_DO concentration under limited aeration is the key factor to achieving SND via nitrite.Under a long time operation with low ρ_DO concentrations,the altering of nitrifying communities,micro-environment for denitrifiers growth and biodegradation characteristics of ρ_COD and ρ(NH₄⁺-N) promoted the occurrence of SND via nitrite.