Bioavailability of Effluent Organic Nitrogen (EON)

Assessing the bioavailability of EON along a freshwater to saltwater continuum

  • Funded by NSF: CBET. May 2008 to April 2010.
  • Bronk, Lead-PI Co-PI.  Bronk part $194,353.  Liz Canuel (Co-PI, VIMS), Margie Mulholland (Co-PI, ODU), Pat Hatcher (Co-PI, ODU), Nancy Love (Co-PI, UMichigan).

The National Coastal Condition Report II classified 79% of the estuaries assessed as threatened or impaired, with eutrophication listed as one of the main problems. Eutrophication is an especially pressing problem in Chesapeake Bay where continued water-quality problems led to the signing of the Chesapeake Bay 2000 agreement, which mandated a 48% reduction (from 1985 levels) in niotrogen (N) loads from point sources to the Bay and its tributaries. That agreement has resulted in increasingly stringent effluent discharge limits for total N by wastewater utilities that were projected in 2002 to cost between $1 and $8 billion.

Effluent from wastewater treatment plants includes inorganic and organic N. Currently, the organic N in effluent, which we term EON, is believed to be largely unavailable biologically and so it is not believed to be detrimental to the environment if released. As a result, some dischargers are applying to amend their nutrient discharge allowances to exclude recalcitrant N. The problem is that there are no quantitative data on EON bioavailability in both proximate and ultimate receiving waters and there is currently no standard method to accurately assess EON bioavailability to any system (STAC 2007). Any method that is developed to determine EON bioavailability must take into account uptake in the proximate receiving waters (typically freshwater) and well as the estuarine and saline waters downstream, and must be sensitive to changing microbial and environmental conditions along the estuarine gradient, including changes in photodegradation and salinity. We propose to use a combination of bioavailability, photochemical- and salinity-release assays, and chemical characterization to quantify the fraction and chemical character of EON, derived from a range of treatment technologies, that is bioavailable along an estuarine gradient.

This project has important societal and disciplinary relevance. The importance to society is two-fold. First, the data will suggest appropriate technological needs with respect to which EON fraction, if any, should be targeted for removal to best achieve our mutual goals of cost-effective and environmentally responsible wastewater management. If a sizable fraction of EON is determined to be non-bioavailable by the robust assessment methods proposed then the cost of N removal by utilities might be substantially reduced. Second, the study is an important first step to achieving our ultimate goal of developing a standard method to distinguish between bioavailable and recalcitrant EON.  Development of such a method is a prerequisite to a broader assessment of EON bioavailability across the full range of treatment technologies generating EON and the myriad aquatic and marine environments that will be affected by its release.

Scientific progress is often made at the boundaries of disciplines. Though we talk about the importance of interdisciplinary research, this project is the real deal, linking engineering, biogeochemistry, and aquatic microbial ecology. The proposed research will benefit all of these fields by expanding the frame of reference of the researchers and exposing them to previously unexplored tools, terminology, and literature. Additionally we will train graduate students who will be uniquely suited to straddle the disciplines relevant to the link between wastewater effluent and eutrophication—one of our nation's most pressing environmental problems.