In this study, an alkali bacterial consortium was obtained by enrichment cultivation and was used to treat printing and dyeing wastewater (PDW, pH 11-12). The treatment effects and dynamic changes were evaluated in a biocontact oxidation reactor (BOR) and a sequencing batch reactor (SBR). During 3 months of continuous operation, the two bioreactors had similar treatment efficiencies (polyvinyl alcohol, PVA, 74.5-81.3%; COD, 73.5-77.4%; 2.15 pH decreases). Molecular biological analysis indicated that the microbial communities underwent dramatic changes during the operation, in which the SBR was superior to the BOR in retaining the alkali bacteria at the start-up stage, however, the BOR seemed to be more advantageous when the frequently changing influents were considered. The bacterial communities in BOR and SBR were diverse and included Bacteroidetes, Firmicutes, Proteobacteria, Actinobacteria and an unidentified cluster. Among these only Paracoccus sp. was successfully isolated and confirmed to have the ability to degrade PVA. (C) 2010 Elsevier Ltd. All rights reserved.