Exploring Nutrient Management via Quantification of Influent Non-Readily Biodegradable DON

Last Modified: Oct 03, 2018

Authors:

  • Mary Sadler, Ron Taylor, Stephanie Ishii - Hazen and Sawyer
  • Chandra Cox Farmer, Tim Broome - Johnston County

The Johnston County Regional Wastewater Treatment Facility (WWTF) discharges to the Neuse River basin and is subject to mass-based nitrogen limits set forth by Neuse River Basin Nutrient Sensitive Waters Management Strategy. The WWTF is currently permitted to discharge up to 71,477 pounds per year (lb/yr) of total nitrogen, which equals an effluent total nitrogen concentration of 1.74 milligrams per liter (mg/L) at a maximum month flow of 13.5 mgd. The County has observed a marked increase in effluent dissolved organic nitrogen (DON) over the last twelve years. In response, the County commissioned a study to quantify and characterize influent and effluent DON. This wastewater characterization study quantified the non-biodegradable (nbDON) fraction of DON from industrial inputs, combined WWTF influent, and combined WWTF effluent.

Quantification of nbDON involves the use of a bioassay to define the fraction of DON that is not readily biodegradable and therefore contributes to effluent nitrogen load. The nbDON technology-based bioassay was conducted by North Dakota State University (NDSU). The bioassay measures the fraction of DON that is not susceptible to biodegradation by a specific microbial community. A 20 day duration of each bioassay was conducted to provide a balance between sufficient time to observe degradation of DON and the avoidance of interferences from biological nitrogen and carbon cycling. The bioassay incubation period mimicked the WWTF solids retention time to represent biological transformations that occur in the activated sludge basins. Additionally, this study included sampling intermittent DON throughout the incubation period to define the biodegradation kinetics of DON in the influent and effluent samples. To explore the potential use of a surrogate water quality parameter, the nbDON results were correlated with corresponding BOD5, BOD20, COD, UV254, TN, and DON measurements.

This paper will present the results and conclusions of this study. The data has allowed the County to compare the relative influent nbDON loads to the WWTF to assess the viability of nbDON load management via the County’s Pretreatment Program. The County considers control of DON via pretreatment a potential option in the County’s holistic approach to nutrient management.

For more information, please contact the author at msadler@hazenandsawyer.com.

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