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NERENBERG RESEARCH GROUP

 

NITROGEN REMOVAL FROM HEADWATER STREAMS USING ELEMENTAL SULFUR

 

Funding agency: CICEET

Project start: 6/2005

PI: Robert Nerenberg

Co-PI: Jennifer Tank (Biological Sciences)

Graduate researcher: Brenda Read

 

Publications and presentations:

 

B.L. Read, S.J. Green, and R. Nerenberg (2007).  Stimulating Denitrification in Agricultural Headwater Streams.  ASM General Conference, May 2007, Toronto.  (Poster)

 

 

Anthropogenic nutrient inputs, especially from agricultural activities, have significantly increased the nutrient loading into freshwater and coastal ecosystems (Townsend et al. 2003).  Nitrogen (N), a component of agricultural fertilizers, enters streams via groundwater input, tile drainage, or storm water flows.  N is exported downstream primarily in the form of nitrate (NO3-) (e.g., Conley 2000; Vitousek 1994), and elevated NO3- concentrations often result in eutrophication of receiving lakes, estuaries, and coastal waters (Turner and Rabalais 1994).  Innovative environmental strategies are needed to remove NO3- prior to downstream transport. 

 

Denitrification, defined as the microbial reduction of NO3- to gaseous nitrogen species, represents a long-term sink for NO3- in aquatic ecosystems.  Stream ecologists have found that high denitrification rates can occur in small headwater streams (Inwood et al. in press; Schaller et al. 2004; Peterson et al. 2001; Alexander et al. 2000).  Hedin et al. (1998) proposed that electron donors are the primary limiting factor for stream denitrification.  Therefore, the addition of an electron donor to headwater streams may stimulate denitrification and reduce N export. 

 

Two classes of electron donors can be used to drive microbial denitrification: heterotrophic (organic) donors and autotrophic donors (Rittmann and McCarty, 2001).  Heterotrophic donors include methanol, ethanol, acetate, and glucose.  Disadvantages of heterotrophic donors include:

 

·        Relatively high cost

·        High solubility and mobility

·        Need to be supplied continuously

 

Common autotrophic electron donors include hydrogen, elemental sulfur (So), and thiosulfate (Moon et al, 2003; Hasegawa et al, 2004).  While hydrogen is ideal for drinking water denitrification (Lee and Rittmann, 2002), it requires special infrastructure for its delivery and a high degree surveillance due to its explosive potential (Nerenberg et. al, 2002).  So may be the preferred donor for denitrification of natural waters.  Advantages include:

 

·        Low cost

·        Non-solubility in water

·        Persistance after a single application

·        Production of sulfate (SO42-), which is non-toxic and commonly present in fresh and saline waters. 

·        Low biomass yield (low production of bacteria per gram of NO3-)

·        “On demand” use by sulfur oxidizing bacteria

·        Widely available at agricultural supply stores

 

Our primary objective is to determine the feasibility of removing NO3- in headwater streams to below 1 mg/L NO3--N using sulfur-based denitrification.   Knowledge gained in these experiments will be used to guide further bench-scale research and to design an in-situ elemental sulfur addition to an agricultural stream in the future.  We are using microsensors and molecular techniques to characterize the sulfur-oxidizing, denitrifying communities.  

 

Oxygen Profile located in the Sulfur Bed