CAREER: Unlocking Recalcitrant Carbon to Enhance Denitrification of Nonpoint Source Nitrogen in Woodchip Bioreactors

Nonpoint sources of nitrogen (N) such as nitrate from agricultural and stormwater runoff are among the most intractable drivers of pollution and water quality impairments in the United States, contributing to eutrophication, harmful algal blooms, and hypoxia, which adversely impact the ecological health, economic, and recreational values of the Nation’s surface water systems including lakes, rivers, and large estuaries such as the Chesapeake Bay and the Gulf of Mexico. Woodchip bioreactors (WBRs) have emerged as promising and scalable biofiltration systems for removing nitrate from agricultural and stormwater runoff.

Most WBRs consist of subsurface trenches filled with a carbon source (woodchip) designed to stimulate microbial denitrification (DN) to remove nitrate from a flowing runoff stream prior to its discharge into a receiving surface water system. The effectiveness of current WBRs is limited by the slow release of the bioavailable carbon (C) from the woodchip media required to support the growth and metabolism of DN bacteria.

The overarching goal of this CAREER project is to probe, elucidate, and leverage the redox biogeochemical reactions that control the release and mobilization of bioavailable C from woodchip media to stimulate DN in WBRs. To advance this goal, the Principal Investigator proposes to test the hypothesis that oxic-anoxic cycling during the operation of a woodchip bioreactor enhances denitrification by accelerating the decomposition of recalcitrant, lignocellulosic woodchip biomass into labile C during oxic periods to stimulate the growth and metabolic activity of DN microorganisms during subsequent anoxic periods.

The successful completion of this project will benefit society through the generation of new fundamental knowledge to support the development and deployment of more efficient and sustainable solutions to manage and mitigate nonpoint sources of nitrate pollution. Additional benefits to society will be achieved through student education and training including the mentoring of a graduate student at Cornell University.

Biogeochemical reactions of iron (Fe) and manganese (Mn) minerals at redox interfaces play an important role in the decomposition of lignocellulosic biomass (LB) in the environment, and mechanistic understanding of these organo-mineral interactions is rapidly evolving. This CAREER project will investigate and unravel the redox active biogeochemical reactions that control the release of labile carbon (C) from the degradation of woodchip media with the goal of leveraging this new knowledge to improve the performance of woodchip bioreactors (WBRs) that utilize LB as C source to stimulate the growth of denitrifying (DN) microorganisms to remove nitrate from agricultural and stormwater runoff.

The specific objectives of the research are to 1) probe and elucidate Mn- and Fe- driven redox reactions that control the release of dissolved organic carbon (DOC) from woodchip media in model WBRs using state-of-the-art characterization techniques including synchrotron-based spectroscopy and microscopy (e.g., micro-XANES and micro-XRF) and advanced mass spectrometry (e.g., FT-ICR MS); 2) assess and evaluate the effects of enzymatic vs. nonenzymatic transformations on the quantity and quality of DOC released from woodchip media in model WBRs; and 3) develop and validate process-based models to simulate the effects of redox fluctuations and cycling on the release of DOC and DN efficiency in flow-through WBRs. The successful completion of this project has the potential for transformative impact through the generation of new fundamental knowledge to advance the design and implementation of more efficient WBRs for the removal of nitrate from agricultural and stormwater runoff.

To implement the educational and outreach activities of this CAREER project, the Principal Investigator (PI) proposes to leverage existing programs and resources at Cornell University to develop and deliver new hands-on experiential learning opportunities in environmental engineering (EE) for students from underrepresented groups. The proposed activities will include i) an outreach program to high school students and teachers from rural areas of Central New York State and ii) a summer training and mentorship program for undergraduate and community college students.

In addition, the PI proposes to leverage the project resources and research findings to develop and integrate new course modules on sensing and control of water infrastructure systems for nitrogen pollution removal into the EE undergraduate curriculum at Cornell University.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.