Fate of Organic Nitrogen in Four BNR Plants

Last Modified: Dec 20, 2010


  • Chakkrid Sattayatewa and Krishna Pagilla - Illinois Institute of Technology
  • Robert Sharp, Ph. D. - Manhattan College
  • Paul Pitt, Ph.D., P.E. - Hazen and Sawyer

The fate of Dissolved Organic Nitrogen (DON) in four different BNR plants and the fraction of effluent DON that is biodegradable.

Potential sources of DON and summary of DON concentrations from 188 WWTPs in Virginia and Maryland.

Effluent organic nitrogen has become a key concern for wastewater treatment plants achieving very low total nitrogen levels (TN < 3mg N/L).

Most biological nutrient removal plants successfully remove inorganic nitrogen, but a significant fraction of organic nitrogen still remains in the effluent.

Although many plants report effluent organic nitrogen (EON) data from routine monitoring, the data have not provided a clear understanding about the fate of organic nitrogen through the treatment train of a WWTP.

Additionally, the EON data reported based on total Kjeldahl nitrogen (TKN) measurement and inorganic nitrogen species are not accurate enough to determine the organic nitrogen fraction at low levels. Therefore, this study was conducted to determine the EON fractions and also the fate of nitrogen species through the treatment trains of four BNR WWTPs in the United States.

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Read a related article starting on page 12 of the Summer 2010 Horizons.

Summary Findings

This study investigated the fate of nitrogen species, especially organic nitrogen, along the mainstream wastewater treatment processes in four biological nutrient removal (BNR) wastewater treatment plants (WWTPs). It was found that the dissolved organic nitrogen (DON) fraction was as high as 47% of the soluble nitrogen (SN) in the low-SN effluent plant, which limited the plant’s capability to remove nitrogen to very low levels. A lower DON fraction was observed in high-SN effluent plants.

Effluent DON concentrations from the four plants ranged from 0.5 to 2 mg N/L and did not vary significantly, even though there was a large variation in the influent organic nitrogen concentrations. Size fractation of organic nitrogen by serial filtration through 1.2-, 0.45-, and 0.22-um pore-sized membrane filters and the flocculation-and-filtration with zinc sulfate (ZnSO4) method was investigated. The maximum colloidal organic nitrogen (CON) fractions found were 68 and 45% int he primary effluent and the final effluent, respectively.

The experimental results showed that effluents after filtration through the 0.45-um pore-sized filter contain significant colloidal fractions; hence, the constituents, including organic nitrogen, are not truly dissolved. A high CON fraction was observed in wastewater influents and was less significant in effluents. The flocculation and filtration method removed the colloidal fraction; therefore, the true DON fraction can be determined.

The authors would like to acknowledge Christopher White and Theresa Bruton of Hazen and Sawyer for their assistance with field sampling during this research.

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