This purpose of this study was to investigate size fractionation of organic nitrogen (ON) along the mainstream of biological nutrient removal (BNR) wastewater treatment processes. Samples were collected from seven full scale BNR wastewater treatment plants (WWTPs). The results obtained
were analyzed to determine the fate of total nitrogen (TN), colloidal ON (CON) and dissolved ON (DON) through the plants. Influent ON from the seven plants ranged between less than 0.2 mg N/L to 6.5 mg N/L.CON was the dominant ON fraction in the influent ranging from less than 0.2 to 100 percent
of ON. CON in influent sample was as high as 3 mg N/L. The CON concentrations varied among each and within each plant on different sampling dates. It was found that conventional filtration with 0.45 μm pore-sized filter contains colloidal fraction and flocculation and filtration (FF) with
ZnSO4 was able to reveal the “true” DON concentration. The effects of operating conditions, influent wastewater characteristics, and treatment processes on effluent TN concentration were investigated. The wastewater treatment plants that utilized the same biological
technology but have different operating conditions had different TN concentration in final effluent. It was found that DON fraction was as high as 82 percent of TN in a low effluent TN plant. Lower DON fraction was observed in high effluent TN samples, however DON concentrations were within
the same ranges (0.3 – 1.7 mg N/L).
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