In this study, laboratory scale experiments were conducted by using Sequencing Batch Reactor (SBR) activated sludge process to treat wastewater stream from a pharmaceutical factory Biological nitrogen removal can be achieved via partial nitrification and denitrification and its efficiency was above 99% at 23 ℃±1 ℃ The experimental results indicated that the nitrite oxidizers were more sensitive than ammonia oxidizers to the free ammonia in wastewater The ammonia was oxidized at pH 7 and 7 5 respectively, which suggested a critical free ammonia concentration of 0 2 mg·L -1 at which the nitrite oxidizers were inhibited.
