Anammox bacteria in sludge from an anoxic tank of a municipal wastewater treatment plant at Nongkhaem, Bangkok, Thailand were enriched in two sequencing batch reactors (SBRs; SBR-1 and SBR-2), under different conditions. SBR-1 was open to the atmosphere, while SBR-2 was closed and flushed with a mixture of 95% argon and 5% CO(2) during the fill period in order to provide strict anaerobic conditions. The specific nitrogen removal rates of SBR-1 and SBR-2 were 0.43 g N/g VSS-d and 2.59 g N/g VSS-d, respectively. Denaturing gradient gel electrophoresis (DGGE) analyses showed differences in band patterns among the Nongkhaem sludge and the two enrichment cultures. Based on fluorescent in situ hybridization (FISH), the anammox bacteria in both systems were either "Candidatus Brocadia anammoxidans" or "Candidatus Kuenenia stuttgartiensis". The results from this study demonstrate the potential of alternative anammox systems for nitrogen removal and provide information on the microbial communities of anammox cultures under different enrichment conditions.