Simultaneous partial nitrification, anaerobic ammonium oxidation and denitrification (SNAD) system was applied to treat the opto-electronic industrial wastewater in a 2.5 L sequencing batch reactor. The characteristics of wastewater were low C/N ratio (similar to 0.2) with 100 mg-COD/L and 567 mgNH(4)(+)-N/L. The experiment was carried out over 8 months in six different stages, where nitrogen loading rate was gradually increased from 16 g-N/m(3) d in stage I to 230 g-N/m(3) d in stage VI. The COD and nitrogen removal rates by the SNAD system reached to 28 g COD/m(3) d and 197 g NH4+-N/m(3) d, respectively in stage VI. These results showed that the SNAD system is suitable to treat wastewater containing high nitrogen pollutants with low COD level. Presence of ammonium oxidizing bacteria and anammox bacteria were confirmed by polymerase chain reaction (PCR). PCR results also indicated that Candidatus Kuenenia stuttgartiensis may be one of the dominant species in the reactor. (C) 2011 Elsevier Ltd. All rights reserved.