o-Nitrobenzaldehyde manufacturing wastewater is characterized for being highly saline, with its TN content and dissolved organic concentrations giving rise to high COD loads. A sequencing batch reactor was established to investigate the effects of major processing variables, such as SRT and HRT, on system performance. The optimal COD (86%) and TN (40.9%) removal efficiencies were obtained at 16 d (SRI) and 12 h (HRT). Design equations were developed by applying experimental data. Changes in sludge flocs were studied using a combination of methods including: chemical analysis; fluorescence in situ hybridization (FISH); and denaturing gradient gel electrophoresis profile analysis of 16S rRNA genes. Dramatic changes occurred during adaptation and beta-Proteobacteria was found to be the most prevalent population. Besides, some species affiliated with alpha-subclasses of Proteobacteria and Cytophag Flavobacterium-Bacteroides (CFB) group were also enriched. This study may help with future research in providing a better understanding of the activated sludge biotreatment. (C) 2011 Elsevier Ltd. All rights reserved.