Combined carbon and nitrogen removal from acetonitrile using algal-bacterial bioreactors.

When compared with Chlorella vulgaris, Scenedesmus obliquus and Selenastrum capricornutum, C. sorokiniana presented the highest tolerance to acetonitrile and the highest O(2) production capacity. It also supported the fastest acetonitrile biodegradation when mixed with a suitable acetonitrile-degrading bacterial consortium. Consequently, this microalga was tested in symbiosis with the bacterial culture for the continuous biodegradation of acetonitrile at 2 g l(-1) in a stirred tank photobioreactor and in a column photobioreactor under continuous illumination (250 microE m(-2) s(-1)). Acetonitrile removal rates of up to 2.3 g l(-1) day(-1) and 1.9 g l(-1) day(-1) were achieved in the column photobioreactor and the stirred-tank photobioreactor, respectively, when operated at the shortest retention times tested (0.4 days, 0.6 days, respectively). In addition, when the stirred-tank photobioreactor was operated with a retention time of 3.5 days, the microbial culture was capable of assimilating up to 71% and nitrifying up to 12% of the NH(4) (+) theoretically released through the biodegradation of acetonitrile, thus reducing the need for subsequent nitrogen removal. This study suggests that complete removal of N-organics can be combined with a significant removal of nitrogen by using algal-bacterial systems and that further residual biomass digestion could pay-back part of the operation costs of the treatment plant.