A very effective removal of nitrate in batch and continuous experiments was achieved by a newly biofilm-formative isolated bacterium, identified by 16S rRNA as Acinetobacter EMY. The anoxic denitrifying capabilities of Acinetobacter EMY, attached to plastic biocarriers in batch and continuous moving bed bioreactors, demonstrated up to 1.75 times higher nitrate removal compared with a bacterial suspension. The denitrification rates of nitrate (200 mg/l) in the continuous operation mode were 0.39, 0.65, 1.23, and 1.14 kg-N/m3/d, with hydraulic retention times (HRTs) of 12, 8, 4, and 2 h, respectively, whereas the batch reactor removal performance showed up to 1.49 kg-N/m3/d. To the best of our knowledge, these findings are the highest values obtained for nitrate removal in comparison to previous studies focused on the characterization of denitrifying isolates. In addition, this bacterium is able to consume all of the organic matter provided in solution together with the nitrate, without leaving any residuals of organic matter in the water. This is advantageous since nitrate removal treatments by heterotrophic bacteria usually require addition of organic matter to the system, leading to secondary pollution. The isolated bacterium therefore provides a good solution for biological treatment of nitrogen in water, particularly in treatment systems that integrate immobilized biomass in the treatment process.