The primary purpose of this study is the investigation of a wastewater treatment plant in terms of nitrogen removal potential and possible operational problems that may be generated by possible inhibitors. To this end, the characterization of wastewater, biological treatability tests, the investigation of chemicals that can act as inhibitors in the activated sludge systems were examined. Possible inhibitory effects of aromatic hydrocarbons on the biodegradation of domestic wastewater were investigated by respirometric analysis. Naphthalene, n-butyl acetate, and xylene were used as the model PAH compounds.