This research aimed to assess the composition of total dissolved nitrogen (TDN) species, particularly dissolved organic nitrogen (DON), over the traditional wastewater treatment operations in three biological nutrient removal (BNR) wastewater treatment plants (WWTPs) in Jordan. It had been found that the DON percentage was up to 30% of TDN within the effluent plant;which restricted the plant's ability to eliminate nitrogen to minimal amounts. Effluent DON levels from the three plants varied from 11.7 to 34.8 mg N/L and would not fluctuate substantially, even if there seemed to be a substantial difference inside influent organic nitrogen levels. The main transforming of DON and biodegradable dissolved organic nitrogen (BDON( along the treatment train had been noticed in the aerobic method. More than 70% of effluent DON was consisting of hydrophilic materials, which promote algal growth. The research presented significant information for foreseeable future improving of WWTPs or the choice of DON elimination techniques to satisfy additional challenging nitrogen release limits.Keywords: total dissoloved nitrogen, dissolved organic nitrogen (DON), bioavailable/biodegradable dissolved organic nitrogen, wastewater treatment plants, Jordan.