Integrated fixed-film activated sludge (IFAS) is a modification of conventional activated sludge processes used for wastewater treatment consisting of biofilm attachment surfaces added to suspended-growth reactors, thereby creating hybrid suspended attached-growth systems. In this work, an IFAS system, with a total working volume of 560.7 L, was employed to investigate the performance of pollutants removal in industrial effluent. Microbial communities of suspended-growth and attached-growth biomass were investigated by a combination of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and fluorescence in situ hybridization (FISH). In the system, suspended-growth and attached-growth biomass worked together to maintain a stable COD, NH4+-N and TN removal efficiency of 74, 93 and 76%, respectively. PCR-DGGE results showed that Proteobacteria was the dominant genera of bacteria in both the suspended and attached growth sludge. Some of the bacterial species (Firmicutes and Pseudomonas) may play an important role in the organic degradation of this water. Denitrifying bacteria were found to be accumulated in the biofilms. FISH results showed that there were more nitrifying bacteria in the suspended-growth biomass than the attached-growth biomass but fewer denitrifying bacteria in the former biomass.

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